High voltage switchgear is one of the few applications where the use of SF6 gas is still permitted under Greenhouse Gas Regulations. This is based on the premise there is no viable alternative. However, in the range 1-52kV there is a perfectly viable option in the form of vacuum switchgear with solid dielectric insulation. Vacuum switchgear is similar in size and technically equivalent, if not superior, to SF6 switchgear. It is being used increasingly by utilities in Europe for medium voltage (1-52kV) applications say W Porte and GC Schoonenberg from Eaton, in the second instalment of this two-part article 
*the first part of this article can be found at

Vacuum interruption is a proven technology, introduced more than 40 years ago. Arc interruption takes place in a vacuum ‘bottle'. Vacuum interrupters do not require costly leakage monitoring equipment. Electrical performance is comparable and, at times, better than SF6 switchgear. While capital cost is slightly higher, total life-cycle cost is lower due to the lower maintenance costs. All materials can be recycled at end of life.

Continuous development has seen the size of a 15kV vacuum interrupter bottle come down from180mm diameter in 1967 to 50mm today. Meanwhile modern sealing techniques ensure that units retain their vacuum for more than 25 years. On the rare occasions when leaks do occur, they normally manifest themselves early in life; so rigorous production testing helps identify such leaks before units reach the field. Any leaks are, of course, completely harmless to the environment.

Vacuum circuit-breakers are suitable for a wide range of medium voltage switching applications including transformer secondary protection, capacitor switching and motor switching. They are used by utilities for ring main units and MV switchboards in the range 3kV to 36kV.  They are suitable for current ratings from 100A to more than 4,000A and fault levels from 6kA to 63kA.

Apart from compact size, vacuum circuit-breakers offer excellent electrical performance. They will normally withstand a rated a.c. power frequency withstand voltage (an overvoltage due to power system switching operations) of 2-4 times normal operating voltage. Rated lightning impulse withstand is 4-12 times normal operating voltage. However, in normal service the breaker contacts are closed so lightning overvoltages are mostly seen by the line-to-earth or line-to-line insulation; in the rare event of a lightning impulse appearing across the open contacts of the vacuum interrupter, the current will be quickly broken. Under similar conditions an SF6 puffer-type circuit-breaker, air circuit-breaker or minimum oil circuit-breaker would probably explode.

An interesting characteristic of the vacuum circuit-breaker is self-conditioning of the contacts. Rough spots that can occur on the contact surfaces are smoothed out by the discharge when the contacts are opened on-load.

Vacuum interrupters offer exceptional performance under load switching conditions, far exceeding the mechanical life of any circuit-breakers and reclosers of which they form a part. Consequently they are used in railway switching applications where electrical and mechanical life in excess of 250,000 operations is required. They are also suited to motor switching duties in excess of one million operations, arc furnace switching and capacitor switching. Contact resistance remains low throughout life because contact erosion only occurs at the cathode and eroded material is deposited uniformly on the anode; the contacts act randomly as cathode and anode so the effect is evened out. In SF6 circuit-breakers, contact resistance increases during life.

Vacuum interrupters are constructed from materials that can be recovered and recycled at the end of life. They do not contain greenhouse gases; nor do they present potential health hazards due to the products of decomposition. No special precautions are necessary to protect the environment from the results of leaks or during disposal.

The compact size of modern vacuum insulator bottles means special measures are necessary to improve insulation levels. A 150mm ceramic length will only have a basic insulation level (BIL) of 125kV in air. For this reason insulators may be immersed in a dielectric medium such as oil or SF6 gas to raise the BIL to 170kV. Oil is being phased out because of the fire risk, so SF6 insulation is favoured by many manufacturers.

However, an alternative approach is to enclose the vacuum interrupter in a potting compound such as polyurethane or epoxy. In some cases an epoxy insulator with a contoured profile, similar to the ‘sheds' used on overhead line insulators, is used to increase creep distances. This is especially valuable when the equipment is used in industrial environments involving heavy atmospheric pollution or condensation. In some cases the entire interrupter and associated busbar are enclosed in solid insulation.

Modern vacuum switchgear with solid dielectric insulation is comparable in size to the SF6 gas insulated equivalent. The circuit-breaker assembly can operate in a normal enclosure with no special sealing or gas filling, and there is no need for costly monitoring equipment. Maintenance is negligible and life can be expected to be 30 years or more.

Total cost of ownership
While the unit cost for gas insulated switchgear is lower than for the solid insulated switchgear described above, total cost of ownership is much higher for the GIS equipment.  The specialist nature of the pressure checks needed by GIS equipment means that trained personnel with specialist equipment will have to carry out the work. One estimate has put the annual cost of this maintenance as 9% of the equipment value per year. This does not include any other safety and insurance costs.

Disposal costs for GIS equipment at end of life are difficult to quantify. Recycling of parts and by-products is not practicable and dismantling, transport and disposal costs will be high.  In contrast the solid-insulated equipment is fully compliant with ISO 14001, covering environmental management systems and standards. All parts are capable of being recycled.

There is no justification - environmentally, technically or financially - for using SF6 gas-insulated switchgear for circuit-breakers and ring main units up to 52kV. In fact vacuum interrupters up to 145kV are now in service. However, solid insulation has yet to catch up with this.

Remote circuit breaker racking from CBSArcSafe
On average in the US there are about 2,000 arc flash victims sent to burn centres every year. The goal is to reduce these injuries by protecting workers from electrical arc hazards in the workplace. While there are many different methods that can be used to accomplish this, increasing working distance is the best, safest, and in many cases, the most cost effective mitigation method available

What is an arc flash?
An arc flash is a voltage breakdown of the resistance of air, resulting in an arc which can  occur where there is sufficient voltage in an electrical system and a path to ground or lower voltage. An arc flash with 1000 amps or more can cause substantial damage, fire or injury. An arcing flash can release tremendous amounts of concentrated radiant energy at the point of the arcing in a small fraction of a second resulting in extremely high temperatures, a tremendous pressure blast, and shrapnel hurling at high velocity. (http://www.electricalreliability.com/ArcFlashFAQ.htm )

What is PPE?

Personal protective equipment (PPE) refers to protective clothing, goggles, or garment designed to protect the personnel's body from injury by impacts, electrical hazards, heat, and chemicals for job-related occupational safety and health purposes.

What is distance?

The distance from an arc flash source within which an unprotected person has a 50% chance of receiving a second degree burn is referred to as the "flash protection boundary". Remote operators or robots can be used to perform activities that are high risk for arc flash incidents like racking breakers on a live electrical bus.  (Homce, Gerald T. and James C. Cawley - Understanding and Quantifying Arc Flash Hazards in the Mining Industry. NIOSHTIC-2 No. 20032720. U.S. DHHS, CDC, NIOSH. Accessed October 27, 2008) By allowing more distance between the personnel and the switchgear you increase the personnel's safety. 

What is remote racking?

The CBS ArcSafe remote racking system enables service personnel to stand outside the arc flash protection boundary while racking low and medium voltage draw-out circuit breakers, in or out, while reducing the need for a full-body arc flash hazard suit. The remote racking system is new to the UK and Europe and has a design that has been in the US for many years helping companies with safety concerns. The CBS ArcSafe remote racking system is an advancement in operational safety for switchgear operations that allow personnel to be safer on the job. By permitting the automatic racking of the circuit breaker from a remote location, the CBS ArcSafe remote racking system replaces the manual racking operation and removes the operating personnel from manual contact with the circuit breaker. This remote racking system allows personnel to be six to 40 Metres away from the switchgear while racking the gear.  When moving the personnel outside of the arc flash hazard boundary you are removing the operator from potential burn and blast injuries if an arc flash occurs.

The unique universal fully adjustable design of the CBS ArcSafe remote racking system, with its specially manufactured drive shafts and couplings, enable the system to be used with all types of circuit breakers produced by the major switchgear manufacturers. It can be used with any drawout type of air, SF6, oil and vacuum circuit breakers that have either a horizontal or vertical racking operation.

To learn more about CBS ArcSafe remote racking solutions please visit us on the web at: http://www.cbsarcsafe.com/  


- Remote operation places operator outside the arc flash protection boundary

- Use with low and medium voltage circuit breakers produced by all the major switchgear manufacturers

- Use with horizontal and vertical types of air, SF6 & vacuum circuit breakers

- Height and angle of the drive is easily adjusted

- Quick release drive shafts & couplings simplify setup

- Over-racking protection is provided

- UL and CUL Listed

- Hand-truck design provides easy mobility

- Stair climber rails for ease of moving up and down stairs

- Wireless video camera, monitor and 24V LED light for ability to view breaker while racking at a safe distance

- Redundant AC/DC power to ensure reliability


Contact: This email address is being protected from spambots. You need JavaScript enabled to view it.   

T:07770 500577  

F:0871 989 2839  

W: www.CBSArcSafe.com

It is proven counting on human behaviour to effectively implement energy efficiency  action does not work in isolation. The only way to achieve sustainable energy savings is to put in place automated solutions, which help users to measure, drive, control and analyse usage of an installation. Here David Lewis from Schneider Electric discusses the options

When it comes to achieving greater energy efficiency within an organisation, the process to manage and improve energy usage can be broken into four simple steps; measure, fix the basics, automate, and monitor and improve. Firstly, by measuring energy usage through metering, energy audits and simple bill analysis, it is possible to examine the usage of the various installations, areas/rooms and different systems, such as heating and lighting, to identify where savings can be made.

Secondly, the building's occupants and operators should know how to reduce electrical consumption by switching off devices when they're not in use and utilising components such as energy efficient lighting and power factor correction. However, part of this element relies on behavioural changes, which can lead to inconsistencies and under-performance in improving energy efficiency. So the solution lies in automation, which is the third step in the energy saving cycle. Devices range from timers, impulse relays and presence detection to variable speed drives (VSDs) and management systems, which will help limit energy consumption.

When integrating automation technologies to reduce a building's energy usage, lighting should be the first area of focus as it can account for up to 40% of total electricity consumption. There are three ways to improve the energy efficiency of lighting. The first option is to have control command components, which offer direct control of a group or individual lamps. The final choice is to have an integrated system, which provides full control of the building environment at the touch of a button via automated programming. The second is to use voltage regulation technology, which reduces the voltage supply to the lamp.

As with the first option, devices such as Schneider Electric's Lubio work by lowering the operating voltage to the light fitting. The component allows the operating voltage of the lighting to be adjusted so the optimum light level is provided, at the same time as achieving maximum energy efficiency. Reducing the levels of electricity also results in the longer life of consumables, such as lamps, and this can save significant amounts of money on the maintenance of commercial properties.

With control command products, achieving the most energy efficient lighting solution means optimising lighting based on the three main parameters of time, light level and occupancy. This means taking into account the time of day the space is occupied and the frequency or amount of time people spend in an area.

For commercial buildings with standard working hours, it is worth utilising pre-set timing for switching lights on and off. Time delay switches can be used in less frequented areas or those where entry and exit are at different points. While this type of technology has been around for years, gone are the days of pneumatic timers, which slowly released before cutting the power to the light. Today's solutions are electronic and fully programmable to whatever time setting is required, for as little as 100 mille-seconds or as much as one hundred hours.

The second option is occupancy sensing, which will detect the presence or absence of people within the parameters of the sensor and will turn lights on and off accordingly. This solution is most suited to areas of a building where occupancy is unpredictable, such as meeting rooms and private offices. The use of these sensors, commonly known as presence detectors, in a private office, could save around 45% of its yearly energy usage. For spaces where use is much more regulated and predictable, scheduled lighting controls can be used to turn lights on and off at set times.

Going beyond just switching lights on and off, a daylight harvesting control, reduces power to the lights or turns them off completely, depending on the level of natural light. Photosensors linked to control devices will vary the lighting output and provide an ideal solution for premises that have numerous offices and meeting rooms with many windows, or even a modern, glass fronted building where the space isn't always being used and the quality of natural light varies. This will allow the user to control their own environment depending on the daylight conditions and light level sensors will only turn lights on when natural brightness drops below a certain level and needs to be supplemented. This ensures lighting is not used unnecessarily, consequently saving energy and therefore money.
Organisations also need to think long term when it comes to automated solutions. By being aware of the ever emerging technologies, businesses can maintain and improve their lighting efficiency through integrated energy efficient design. Schneider Electric's Clipsal C-Bus control system, for example, can accommodate multiple lighting controls and offers the flexibility to reprogramme lighting groups to accommodate any future changes to the building. This could include new office structures, partitions, or new open plan desk configurations or even a change of use.

As well as lighting, it is highly likely businesses will also have other processes that demand greater power than other areas, so it is important for companies to look at the technologies they utilise - perhaps they are out-dated and inefficient. For example, variable speed drives offer more efficient management of energy intensive applications such as compressed air, pumping and ventilation installations.

In most variable torque pump and fan applications, VSDs can be used to regulate the speed of the AC (alternating current) electric motor according to the requirement. By controlling the rotational speed of the drive, process demand and machine output can be matched. Rather than using a constant throttle valve, which can overload the motor and increase energy consumption, VSDs can be regulated depending on the demand of the process - only using the energy required. According to the Carbon Trust, by reducing the speed of a motor by 20%, energy usage can be slashed by up to 50%, meaning that the initial investment will soon be recouped in energy savings.

With Schneider Electric's new range of drives, the drive also uses its in-built ‘motor flux optimisation' function to maximise the potential savings available, typically between five and 10% additional savings in some applications, helping to reduce the payback period even more.

Automation goes beyond just lighting and VSDs, and it is important to recognise the benefits of command control components in other areas. These controls can also be used to manage heating, ventilation and air conditioning, leading to a complete building management programme. Centralised monitoring and control is a must for any energy-conscious organisation. Control systems enable a building manager to control the entire premises remotely, and dynamic graphic displays make it easy for them to respond to service requests, locate potential trouble spots and take corrective action - often before problems become evident to occupants. Remote access to the system via dial-in or the internet lets them check status and diagnose problems remotely when the building is closed. Through a building management system, users can increase system efficiency, occupancy comfort and staff productivity, while reducing energy consumption.

When it comes to delivering results, it is essential those responsible for implementing processes and deploying technologies, such as the operations, buildings or plant manager, have access to the right equipment that will enable them to control the plant more effectively. Poor implementation of an energy efficiency scheme could significantly reduce the potential for savings, so check the business has the resources to manage the procurement and installation of equipment and ensure the project stays on track.

Following the automation of systems, it is then possible to complete the final stage of the energy management cycle, which involves continuously monitoring and recording usage to help make further improvements. Automating areas, systems and processes that have a significant energy usage, will make this part of the process easier and more efficient, as organisations will be provided with an accurate account of their energy consumption. This will supplement any behavioural changes that are achieved among staff, making sure every dimension of good energy management practice is covered.

How can lighting designers use intelligent controls to improve building energy  management? Philips Dynalite energy management segment manager, Brett Annesley, explains how an environmentally sustainable development (ESD) strategy can deliver energy efficiency while addressing indoor environmental quality (IEQ) and changing occupancy requirements

It is widely accepted artificial lighting contributes approximately 30% of electricity consumption in a commercial building, and buildings collectively account for 40% of total world energy use. In view of this, energy management approaches to lighting control and design may provide the key to reducing energy consumption within the commercial sector. However, the drive to improve energy efficiency in commercial lighting is only one part of the ‘environmentally sustainable development' (ESD) equation. Considerations of equal importance include the sustainable life-cycle assessment (LCA) of material used, and ensuring indoor environmental quality (IEQ) standards meet occupant comfort demands. Together, these can be considered the three global ‘green drivers' within the built environment.

The aim of the first of these green drivers - LCA - is to minimise demand on resources and energy consumption over the lifetime of a building. This will necessarily impact the manufacturing, procurement and delivery processes of the various constituent components. Lighting designers can help reduce the ultimate carbon footprint of a building by taking LCA into account during specification of the system. With an LCA baseline established, the lighting design itself can then play an equally significant role in ESD over the life of a building. Lighting installations can be rendered more energy efficient and a building's lighting design made more ‘future-proof' by the implementation of these LCA principles. Future-proofing can be enhanced by the selection of products that will give an extended service life, the adoption of modular installation practices, and the use of systems providing a high-resolution of control. Such high-resolution-or ‘granular'-lighting control systems allow the lighting to be changed as required during the evolution of a building.

Changes to a building's fabric and occupancy are often referred to as ‘churn'. The flexibility of a lighting system to accommodate churn can be best achieved by enabling lighting grid changes and luminaire group re-zoning, without the expense and disruption associated with rewiring a facility. User-friendly configuration software is an important component of these flexible installations, but is also dependent on the control technologies in place-such as digital addressable lighting interface (DALI) and structured wiring. DALI is a dedicated lighting control protocol, where each light unit has its own individual digital address, allowing re-zoning of luminaires easily across a network using an appropriate software interface. Structured wiring, by contrast, comprises combined power and data cabling that can be quickly connected and disconnected from a lighting installation, thereby facilitating physical reconfiguration of lighting systems. While LCA is an important consideration in environmentally sustainable lighting design, the energy consumption of a lighting installation will impact the energy efficiency on a day to day basis. Specific strategies to reduce energy consumption include the increased use of daylight in preference-or as a bolster-to artificial lighting, and the use of sensors to automatically adjust lighting levels in accordance with natural lighting levels and area occupancy. ‘Smart sensors' have developed from simple on/off control, into a ‘front-line' energy-management technology, capable of adapting dynamically to changing occupancy, environment and daylight requirements.

The use of daylight harvesting technologies needs to address both energy management and occupant comfort issues. Daylight harvesting involves the strategic substitution of artificial fluorescent light with natural light - slowly dimming lights to balance daylight entry - and this can achieve considerable energy savings. Window treatments - such as curtains, blinds, and glass-transmission factors - become an important factor, as these have a direct impact on how much natural light enters the office environment.

The correct selection of blinds and sensors becomes critical to both energy-efficiency and occupant comfort. Moreover, sensor positioning can be as essential as sensor selection. Positioning a photoelectric (PE) sensor within a direct pathway of reflected light from shading louvers, for example, can lead to incorrect lux levels being applied by the PE sensor.

Such demands on sensor functionality have led to the rise of multifunction sensor devices that incorporate PE detection for changing light levels, and passive infra-red (PIR) and ultrasonic for motion detection. While these sensors are commonly used in a single mode, they can also have the intelligence to be used in ‘multi-mode' to provide logic control. For example, if the sensor detects that lux levels have fallen below a specified value, then artificial lighting levels can be increased, but only when motion is detected. In this way lighting levels will be maintained for occupied areas only.

Motion-detection functionality can be further configured to perform different routines according to the time of day. During the standard working day, for instance, a sensor may be tasked to dim lights over a workstation by 25% when all occupants have been gone for 10 minutes. After hours, the same sensor might action a gradual fade-out before eventually switching off. However well-intentioned or effective the energy management strategies within a building, they should not be implemented at the expense of IEQ - another important driver for ESD of commercial buildings. A lighting design can be flexible and save energy, but if occupants do not feel comfortable, the design can be considered to have failed.

The use of natural light not only saves energy, but also has an important bearing on the well-being of occupants. Studies have shown people need to feel connected to the world outside, and exposure to daylight-when correctly managed-can measurably improve worker productivity. Fade time is critical to occupant comfort when using sensors to manage lighting levels. Typically, an extremely slow fade-time during the process of daylight linking will result in minimal disruption and a greater acceptance rate by occupants.

‘After hours' worker comfort further provides a challenge in order to balance the associated increased energy demands with the ongoing target of energy savings. Instead of the traditional solution of illuminating an entire floor-plate after core working hours, the control system can be tasked to provide a worker with more specific illumination-such as their immediate surrounding areas and an egress path-using motion detection sensors. Gradual closure after all movement has ceased will ensure energy is not wasted after the departure of the last worker.

The implementation of control-management software further enables the individual user to control task lighting requirements from their own workstation, aiding individual worker comfort. Energy savings can also be realised by minimising lux levels for overhead lighting in preference for individual task lighting over the desk area. This solution is becoming increasingly practical with the development of LEDs, and such a strategy may well serve to avoid conflict between individual and general lighting requirements. In a similar manner, where daylight harvesting is employed, zoning blinds will enable occupants to control their specific shading requirements.

Commissioning guidelines are provided by CIBSE Code L and M for the Australian Green Star and by Ashrae under the LEED tool in the US. It is becoming an increasing requirement to implement commissioning guidelines such as CIBSE or Ashrae as the nominated standard to safeguard against substandard installation and commissioning practices. Poor commissioning practices have historically resulted in owner/occupiers failing to achieve their energy efficiency targets. Project-specific applications can be audited and approved by independent commissioning authorities, however, to optimise the installed systems and ensure the design criteria are met.

Just as new buildings can fall short of their design criteria, so too do older buildings differ widely in their energy efficiency performance. The lighting installations of existing occupied buildings can be professionally audited, however, to assess their efficiency. Comprising data-logging of local distribution boards and monitoring lighting-usage through lux meters, these audits will monitor when the lights are on/off and the amount of energy used during different periods. The results can prove a valuable tool in highlighting where corrective building tuning is needed - both from a facilities-management and an occupant-activity perspective. Within the holistic approach to ESD, such building tuning will help ensure that the efforts made through the three green drivers of LCA, energy efficiency and IEQ are not wasted in the pursuit of a reduced building carbon footprint. When the right balance is achieved, the result is a building that will remain energy efficient throughout its life, and which will continue to bring unprecedented levels of comfort to its occupants long into the future.

Traditionally on-site power systems depended on analogue control systems to provide reliable service to a facility's electrical loads. Today, reliable, flexible and user-friendly digital control technology is available for every on-site power system. For traditional standby power systems, that power only emergency lighting for a small building, analogue controls may still be adequate. However with larger on-site and standby power systems, critical 24/7 power needs, more complex power distribution systems, and a mix of linear and non-linear loads digital controls provide greater performance capabilities. Jim Iverson, senior applications engineer at Cummins Power Generation explains

Analogue devices in power system control are discrete components (resistors, switches, capacitors, coils and relays) that coordinate input and output signals, and perform rudimentary logic for specific control functions. Adjustments to the system usually involve a physical adjustment such as increasing or decreasing the resistance of a variable resistor or substituting modules. Analogue control hardware communicates system status and fault conditions with indicator lights, analogue meters or alarms.

In modern generating systems, there may be more than 200 typical alarm conditions having to do with the load, the utility, other paralleled generators, the engine or the alternator. As the number of potential status or alarm conditions has grown, analogue control systems have not been able to communicate this information to operators effectively. A digital control system uses a microprocessor to control input, output and logic functions. System status can be graphically displayed on a computer, and operational adjustments are made through inputs on a keyboard or touch-screen. Changes can be made on the computer screen attached to the power system's master control, or even on a remote computer connected via a local area network or the Internet. Digital systems allow a high degree of control function integration, so one digital control can do the job of several analogue controls.

Many power system end-users have learned to depend on their analogue control systems, feeling that they understand exactly how they work and how to fix them when they fail to work. If users don't have experience with digital generator sets, transfer switches, or paralleling controls, they may be reluctant to make the change from analogue.

This attitude is ironic, since the decision to stay with analogue controls actually makes the system less reliable and burdens a facility with controls that are, for all practical purposes, obsolete when they are installed.

Digital generator controls are demonstrably more reliable. For example, digital controls used in the PowerCommand master control systems for generator sets from Cummins Power Generation, have demonstrated a reliability of 300,000+ hours MTBF (mean time between failures). Few discrete components in an analogue control system can approach that kind of reliability. What's more, in an analogue system, all system components need to function properly for the system to operate at all. In contrast, digital systems have built-in redundancy that significantly improves reliability by allowing the system to function properly even with a component failure in one portion of the control circuit. Reliability is also enhanced because the physical electrical interconnections between logic functions have been eliminated with solid-state digital components.

On a more practical level, the number-one reason standby generators fail to start is due to dead starting batteries. Over 80% of all starting failures are from this cause. This shouldn't surprise anyone, because the same thing happens in our own cars. In order to test a battery, whether it is in your car, or on a generator set, a service technician needs to test the battery using a load bank. Basically, the load is applied, and output voltage is observed at the same time. If the voltage drops too low, too fast, the battery should be replaced. Digital power system controls have a function which detects a weak battery. With this function, battery voltage is monitored under load while the engine is cranking. If the battery voltage drops too far for too long, a weak battery alarm is sounded.

System integration
One of the primary advantages of digital controls is their seamless integration of the functional components of power systems. For example, the status of all components and values in a complex power system can be viewed and controlled from a central or remote computer screen. In addition, electro-mechanical equipment (modern gas and diesel engines, alternators, transfer switches) can also be monitored and integrated into the control strategy.

This ability of digital systems to integrate diverse functions is especially important in modern emissions-controlled diesel engines. Integrating engine control functions (fuel rate and injection timing) with fluctuations in generator load is critical for minimizing exhaust emissions from diesel engines. In fully integrated digital systems, these functions are combined in the digital master controller and not isolated in a separate engine governor. The result is better engine performance under varying loads, reduced exhaust emissions, and more stable output frequency and voltage.

The ability of a digital control system to perform logic functions is also crucial in reducing exhaust emissions while starting the generator set. In most generator sets, the engine speed control system does not "know" that the generator set is in a starting mode. Consequently, the control has a tendency to over-fuel the engine during startup, resulting in a cloud of black smoke from the exhaust. This occurs because as power is applied to the governor control, it senses that the engine is a long way from proper speed, so it applies the highest possible fuel rate in order to quickly get the engine to proper speed.

With a digitally based system, the control ‘knows' that the engine is in a starting mode, so it does not immediately try to accelerate the engine to rated speed. Instead, when the engine starts cranking, it checks for engine rotation, and then provides enough fuel to accelerate the engine gradually to rated speed. This practically eliminates black smoke upon starting. Finally, since a digital control ‘knows' what the engine temperature is, it can adjust the governor settings based on temperature, making the engine more stable on starting and more responsive as it warms up.

Reduced space requirements
The move to solid-state electronics and digital technology is not only more effective from a performance and reliability point of view, it is highly beneficial from a space-saving point of view. Depending on the application, digital power system controls can save from 25% to 40% in valuable mechanical room floor space. Digital controls are also more environmentally rugged than analogue, allowing many control systems to be located with the generator set rather than being isolated in a separate dust- and vibration-free room. The result is that digital systems occupy less floor space and require less environmental protection. These factors also help simplify installation, commissioning, and reduce maintenance and repair.

Digital systems provide superior protection
Analogue devices, such as circuit breakers, provide protection for simple power systems by sensing overloads and opening to protect wiring and, in general, the generator set. However, analogue circuit breakers do not do a good job of protecting the alternator as required by electrical codes. Excessive current in the alternator (due to even brief overloads) creates heat, which shortens insulation life and can lead to alternator failure. Molded case circuit breakers (MCCB) offer little protection against alternator overloads and heat buildup.

While today's power grid is actually more reliable than it has ever been, the cost to end-users of a power failure has steadily increased, making any power failure of any duration unacceptable. If the reliability of the standby power system is compromised because of obsolete analogue technology, then the financial risk of a power outage goes up. However, digitally controlled power systems reduce an end-users' financial risk by improving reliability.

Easy access to information
Just as digital computers have exponentially increased our access to information, digital control systems have increased our access to real-time and historical power system operating information. Once information is inserted into a microprocessor-based control system, there are numerous options for making that information available in many parts of the facility-or even remotely. Building automation systems, communication systems, security, and safety systems can all make use of the information from the power system's digital control system. The availability of information makes it easier to manage a facility efficiently and economically.

Unlike analogue systems, digital control systems provide real-time status of all major components within the system. Engine oil and coolant levels and temperatures; battery charge status; fuel levels; and the status of every transfer switch in the power distribution system-are all available on a computer screen on the digital master control in the control room, or even on a secure remote terminal connected via the Internet. With analogue systems, for example, the status of transfer switches can only be known by individual physical inspection of each switch - an antiquated approach that involves more labor and time and increases costs.

Digital controls for power systems offer significant advantages over traditional analogue control systems. These advantages include higher system reliability, lower system life-cycle costs, smaller size, greater operational flexibility, longer equipment life, real-time and historical operating information, easier maintenance, easy system changes through software, remote monitoring and control, and better emissions control.

High voltage switchgear is one of the few applications where the use of SF6 gas is still  permitted under Greenhouse Gas Regulations. This is based on the premise that there is no viable alternative. However, in the range 1-52kV there is a perfectly viable option in the form of vacuum switchgear with solid dielectric insulation. Vacuum switchgear is similar in size and technically equivalent, if not superior, to SF6 switchgear. It is being used increasingly by utilities in Europe for medium voltage (1-52kV) applications explain W Porte and GC Schoonenberg from Eaton, in the first instalment of this two-part article

The notion there is no viable alternative to SF6 switchgear for high voltage applications, which is exploited by the producers of SF6 and manufacturers of SF6 switchgear, can be attributed in part to the different methods of classifying voltage levels. IEC terminology identifies two voltage bands - low voltage for applications up to 1,000V a.c. and high voltage for anything greater than 1,000V. However the term medium voltage is widely used for distribution voltages in the range 1kV-52kV. Thus it is perceived by some that SF6 is the only option for systems greater than 1kV when, in reality, vacuum switchgear is a ‘green' option up to 52kV.

F-gas Regulations
The Fluorinated Greenhouse Gas Regulations 2009, which came into force in March, impose strict legal requirements upon personnel and companies in five industry sectors which use fluorinated greenhouse gases (F gases).  These gases include the fluorocarbons (CFCs and HFCs) as well as sulphur hexafluoride (SF6).   High voltage switchgear is one of the five industry sectors along with refrigeration and air conditioning, fire protection systems and certain types of solvent.

The Regulations and steps that can be taken to train personnel in the recovery of SF6 gas, or mixtures of the gas, during maintenance or at end of life were described by Gary Eastwood in the August issue of Electrical Review.

Concerned utilities are turning increasingly to vacuum technology for medium voltage applications. Northern Ireland Electricity became the first United Kingdom utility to order Eaton's Xiria vacuum ring main units in 2007, as part of its framework contract for secondary power distribution, and last year EDF Energy placed a three-year framework contract with Eaton to supply 11kV double-busbar switchgear incorporating its Innovac vacuum circuit-breakers. The first 60 units were supplied to EDF Energy for a major substation in Stratford, East London.

In the Netherlands, the government is supporting a Green Switching initiative involving  four utilities, the SenterNovem (a Dutch agency of the Ministry of Economic Affairs for the promotion of sustainability and innovation)  and Eaton. This group is working to increase awareness of the issues surrounding non-carbon greenhouse gases and to promote the development of alternative technologies. It believes that there should be tighter controls over the use of SF6 with a ban on its use up to 52kV. A position paper and other documentation are available on www.greenswitching.com.

In the USA, the Environmental Protection Agency (EPA) is promoting a voluntary SF6 emission reduction programme in which 80 utilities are participating. Between 2000 and 2006, emissions by these utilities fell from 15.1% to 6.5%.    Meanwhile, the Leadership in Energy and Environmental Design (LEED) system for rating green buildings, developed by the US Green Building Council, is being adopted in many parts of the world as a way to quantify and compare sustainability. Use of vacuum switchgear with solid dielectric will help achieve the objectives of the LEED standards.

SF6 switchgear
Approximately 8,000 tonnes of SF6 are produced annually, of which 80% is used in electrical switchgear. It is used for two functions - circuit interruption and insulation.

For circuit interruption SF6 offers excellent arc quenching and heat transfer properties. It has a high chemical stability and a fast dielectric recovery time with self-healing properties under electrical discharge conditions. Under normal operating conditions it is non-flammable and non-explosive, making it an excellent alternative to oil-filled switchgear, which has largely disappeared as a technology over the last thirty years.

As an insulating medium, SF6 has an electrical breakdown strength approximately three times that of air at atmospheric pressure. This means by filling a circuit-breaker enclosure with SF6 gas the line-to-line and line-to-earth distances can be reduced, making for compact equipment. This is the principal reason why SF6 gas has been used so extensively as an insulation medium in gas insulated switchgear (GIS) even where vacuum technology is used for circuit interruption.

However, SF6 is one the of six most potent greenhouse gases identified by the Intergovernmental Panel on Climate Change (IPCC) and consequently included in the Kyoto list of substances whose use and emission should be minimised. Although far less common than carbon dioxide, it has a global warming potential (GWP) listed as 23,900. This means one tonne of SF6 has the same greenhouse effect as 23,900 tonnes of CO2. At present its contribution to global warming is only 0.01% but, unlike other greenhouse gases, it is largely immune to chemical and photolytic degradation so its effects are cumulative. Annual rate of increase in the atmosphere is said to be 8% and lifetime in the atmosphere is estimated as 3,200 years (CO2 is 50-200 years).

Under the F-gas Regulations of 2006, the use of SF6 was prohibited for most applications including sports shoes, tennis balls, car tyres and double glazing. However, its continued use for HV switchgear is permitted on the basis that there is no viable alternative. Nevertheless, the Regulations imposed strict requirements for the manufacture, use, maintenance and disposal of SF6 switchgear, including special requirements for the training and certification of personnel. These requirements were strengthened by the 2009 Regulations.

The extent of leakage of SF6 into the atmosphere is not known, but emissions of 6-13% per annum have been estimated. Under the F-gas Regulations all larger systems containing SF6 should be inspected regularly and emissions should be prevented as far as possible during maintenance. Some authorities insist on continuous monitoring of all gas-filled enclosures to detect leaks.

SF6 also poses a number of health risks. For example, although it is non-toxic and chemically and thermally stable under normal conditions, it can break down into highly toxic substances such as HF, SOF2, SF4 and S2F10 when exposed to arcing, partial discharges or incineration. Under normal operating conditions these are generally recombined after a discharge is cleared but some toxic residue may remain in the housing. If there is a catastrophic failure, these products could be released into the atmosphere, exposing the public to risk. Consequently, SF6 switchgear should not be used in residential areas, commercial buildings, shopping malls, railway stations, hospitals, educational campuses or underground installations.

Asphyxiation is another risk. SF6 is a colourless, odourless gas which is about five times the density of air. Consequently locations should be well-ventilated and gas analysing equipment may be needed to alert staff to any risk from leakage.

End-of-life disposal is an important consideration. Measures must be in place to recover the SF6 gas and personnel need to be protected against risks from harmful by-products. The presence of these by-products restricts the ability of the materials to be recycled.

It should also be borne in mind while these products are manufactured under controlled conditions in industrialised countries, they are being sold worldwide, including countries where controls embodied in the F-Gas Regulations and similar legislation are not enforced. End-of-life disposal becomes even more uncertain in these countries. The risks are exacerbated when used equipment containing SF6 gas is exported as waste to third-world countries where it may be dismantled by unqualified personnel.

The second part of this feature will appear in the November issue of Electrical Review

Public sector spend on building projects, in particular educational and health facilities, has been one of the few glimmers of hope for the construction industry this year - even after the government put a squeeze on some of the funding available. This special feature from Chris Scott at Marshall Tufflex looks at the effect this has had on the cable management sector

Contracting companies and building product manufacturers less familiar with public sector work have been quick to throw their hats into the ring in an attempt to secure a slice of the much-needed business - a good example of this scramble to win work was the 50 or so contractors who applied to be part of the academies framework in England. The framework, part of the Building Schools for the Future (BSF) initiative, has £4 billion to spend on the design and build of academies.

Those working on public sector contracts - especially education related - will know that they are awash with acronyms, ranging from the well-accepted PFI (Private Finance Initiative) to BSF, PCP (Primary Capital Programme), PFS (Partnerships for Schools) and LEP (Local Education Partnership). Given the huge sums of money being invested and the manner in which the money is allocated and spent, we feel that knowledge of public procurement processes is vital in assisting clients with achieving the most desired outcome.

Most school and many hospital projects are delivered via PFI. We find that this makes each job very different and calls for closer contact with site - more time is spent there than working off-site with an architect or consultant as would be normal on a ‘private' project. There are also decision makers up and down the chain of command and it pays to remain in close contact through the specification, installation and hand-over.

However, it is possible to push aside the jargon and buzz words in order to understand what's required of new-build and refurbished educational and health facilities. Quite simply they must provide an ultra-modern environment for today and be capable of adapting to the needs of future decades.

Applying this mantra to cable management, our specific area of interest, is easy. All new and refurbished schools, colleges, hospitals and other healthcare infrastructure require the very best in ICT (information and communication technology) provision. For example, classrooms no longer have blackboards - teachers and pupils use interactive electronic whiteboards, along with laptops and other internet-enabled devices. This creates a need for effective and safe delivery/management of power and data cables.

As a cable management systems supplier we are obviously only involved later on in the build schedule. And, as specifications and fit-out requirements have become more hi-tech, so the demands on trunking systems have changed and our range of solutions has evolved over the 25 or so years we've worked with the education and health sectors.

A good example of this is modular wiring systems, such as Marshall-Tufflex's MT32 sytem. Prefabrication has been a buzzword for a number of years and modular wiring systems deliver just this for specifiers and installers. They are not a trunking solution but work in conjunction with trunking to deliver a super fast installation that can be reconfigured at a later date.  These factory-tested ‘plug-and-play' power connection solutions are a quick and easy way of taking power from source and delivering it to final outlets via plug-in connectors. Modular wiring delivers tool-free, fast-track installation of complete cabling runs. There is no on-site wiring required, allowing installers to simply click together, circuit test and sign-off. Installation times can be reduced by up to 80%, with overall cost savings of up to 50% possible. The best systems are plug and play - keyed connectors do not allow it to be installed incorrectly, increasing the safety factor for both contractors and clients. What's more the systems can be reconfigured (for example during office moves), stripped out (during refurbishments) and re-used.

Modular wiring is therefore perfect for future-proofing projects - install it in an ICT suite today to feed power to, for example, 15 computers and when 15 become 25 computers, simply unclip the front cover of the trunking, ‘plug-in' extra lengths of MT32 in order to add new sockets, circuit test and sign off. Not only does this negate the need for a major re-wiring exercise, MT32 can reduce installation times, achieving double the workload with the same resource.

Purr-fect choice
Future-proofing data installations can also be achieved through the correct specification of cable containment. Historically local area networks were designed with a Category 3 circuit for voice transmission and a Category 5 or 5e circuit for data. This configuration eventually failed to cope with rapidly increasing data rates/networked devices and was replaced with Cat 5e throughout. Now the industry is looking to Cat 6 and above to deliver performance required now or in the future.

However, as data wiring develops to handle larger amounts of information and networked devices, it becomes dimensionally larger, creating problems for designers and installers, particularly when cabling needs feeding around corners. To give an example, Cat 6 cabling is approximately 5-6mm in diameter, with ‘data bends' of up to 25mm - 50mm (depending on cable specification) required within cable containment systems to channel it around corners. Cat 7 cabling is about 10mm in diameter requiring a bend radius of 40mm minimum and poses real issues when it comes to cable containment. Sounds innocuous enough, but if more space is not allowed for these ‘data bends' and the cable is fed through a standard radius bend in a cable containment system problems may arise - subjecting Cat 6 or higher cabling to standard bends can ‘pinch' or compress the copper data cables, resulting in a drop in performance - data may be lost in transmission or streaming quality affected.

Marshall-Tufflex has invested heavily in developing cable management systems appropriate for use with Cat 6 cabling. Design engineers looking for bend radius of 25mm or 50mm can consider its Sterling range or its tamper-proof, all-curved profile, Odyssey system.

Future-proofing installations by installing Cat 6 compliant trunking is a major consideration where networks will be required to handle large volumes of devices and information. But what other factors should design and build specialist be considering when considering cable management solutions for schools?

Function or form
How about both? The latest generation of trunking can offer great performance coupled with architect-pleasing curves, so there is no need to compromise on design. Curved profile trunking also offers another huge advantage - it simply cannot be used as a shelf. Not only does this keep classrooms, corridors etc clear of clutter and litter, it also aids cleaning since the PVC-U can be easily wiped clean, a major benefit when specified in sensitive environments such as schools. The curved profiles are also completely in keeping with the design of many new schools, with architects utilising softer lines to make learning environments more appealing.

And curves don't just apply to the trunking profile - Marshall-Tufflex offers a special service to adapt its systems or pre-fabricate specialised and bespoke solutions. This means trunking can be curved off-site in order to fit snugly against a curved wall.

Material choice
Trunking is usually steel, aluminium or PVC-U, a proven material that it is easier and quicker to install than metal systems. Not only does it reduce time on site for contractors and maintenance staff, it also reduces facility down time during refurbishments. In addition, PVC-U systems can be supplied with EMC screening - a copper spray is applied to the inside of the trunking, creating a Faraday Cage to exclude electrostatic interference, delivering the required screening without compromising trunking capacity. PVC-U is also tough and hard-wearing, making it a good choice for areas where hard knocks are inevitable. When specifying PVC-U trunking check that it complies with British Standards BS4678 & BS EN 50086 which govern impact strength.

Cable containment manufactured from PVC-U can be impregnated with an antimicrobial agent to help prevent the spread of infections such as MRSA, E-Coli, Salmonella and a range of everyday bugs. Antimicrobial trunking systems come in two variants:
* The silver-based formulation is added to the PVC-U during manufacture, ensuring that it is evenly distributed throughout the product. Should the trunking get scratched, the active agent continues to do its job. This is the system used by Marshall-Tufflex.
* The silver-based formulation is applied to the surface of the cable containment. However, once this coating is scratched, germs can penetrate the surface layer of these products and breed unchecked.

Specifiers should give priority consideration to trunking with the antimicrobial agent integral to the product to ensures maximum performance throughout the lifetime of the trunking. Those thinking of using an antimicrobial system should confirm that it is registered with the Environmental Protection Agency and compliant with the European Biocidal Products Directive.

Correctly specified cable management systems have the ability to neatly and efficiently deliver power and data with the minimum fuss and little to no maintenance, particularly when manufactured and supplied by a specialist producer with in-depth experience of the PFI sector. As demonstrated, there are a number of important factors to be considered when specification decisions are being made - get those decision right and the client will have a power and data delivery system that delivers now and many years into the future.

The August and September issues of Electrical Review carried a two-part article on arc flash, by Mike Frain and Jim Phillips, which attracted a number of emails from readers. Below are a selection of those emails along with a response from Mike Frain:

I read with interest the articles on Arc Flash in the August edition of the Electrical Review.

The views expressed are not the only views on this topic, I (as do many others) hold absolutely different views than those of the authors - that after some 25 years as an HSE Principal Electrical Inspector and 30 years in industry dealing with these issues. People are trying to mitigate the consequences of accidents rather than preventing them occuring in the first place.

Would you allow me to have a "rant", I am an equally grumpy old git, angry at commercial interests selling services on the back of American experiences rather than to resolve the issues in the UK by British and European experiences which are diametrically opposed to those in America.

There is a seminar being held at EA Technology in December 8th 2009 at Capenhurst on the UK position on Arc Flash hazards, we are looking at the seminar structure just now, perhaps you could discuss with EA Technology to see if you could report on the seminar.


Windsor Coles



The statistics for electrical accidents in the articles seem to be many times the figures reported to HSE. The net result for me was the whole approach was inconvincing. Arc flash protection has a place in a safe system of work but let us be sensible and place it in perspective. The improvements in fabrics and other materials have made it much more attractive than it was a few years ago but it is not a substitute for good equipment, appropriate maintenance nor good training - it is a useful supplement.


Bernard Quigg



I have never worked at MV or HV - although I have seen the results of arc flash at these levels - but it should not be forgotten that very nasty effects can be produced at much lower voltages. It was spectacularly unpleasant when someone dropped a spanner across the terminals of a large 12v battery, the spanner substantially vapourising. Fortunately for me, I was the other side of the room - others were not so lucky. My own worst burn occurred when one of my stretchy metal armbands (having a large chest size and short arms) shorted between the -50v and 0v busbars when I reached into a control cabinet. Instant electric single bar fire - I was wearing a synthetic material shirt which melted into the flesh, the burn took months to heal and I still have the scar.

For the record, the lowest voltage that is known to have killed a large mammal was 6v. The unfortunate donkey was down a Cornish tin mine and it's ears bridged the bus bars running along the tunnel roof. Fortunately, most engineers are not so excessively equipped!

Thank you for some interesting articles.

Michael Rowe (Eur Ing ..........C.Eng MIET)



I am no longer in the lighting industry but I am the former chief engineer of Thorn Lighting, the former technical and marketing director of Siemens and I have a degree in Illuminating Engineering. I say this so that you will know that my comments are well-informed and that I am disinterested in the subject except as a user.

Low energy light bulbs (compact fluorescent lamps - CFLs) are a good product but they have different characteristics that limit their use:

• CFLs are in theory about 5 times more efficient for a similar result.
• CFLs can, under ideal conditions and if designed and manufactured correctly last 5 to 10 times longer. Most do not.
• CFLs do not provide their full light output when switched on. Depending upon the design, they can takes a few minutes for the mercury vapour pressure to stabilise and the light output to reach a maxium.
• CFLs rely upon emissive coatings on the electrodes to provide electrons without excessive energy loss. Every time the lamp is switched on some of this coating is lost. This reduces light output and efficiency. More importantly, when the emitter is gone the lamp fails. So every switching reduces the life of the lamp.
• The light source of a CFL is a large area not a high luminance small filament. This makes it difficult to design light fittings that achieve efficient optical control of the light and means that the overall efficiency is reduced. If you get it right, the light fitting is usually a lot bigger.
• It depends upon the light fitting, but even when compact fluorescent lamps provide the same luminous flux (light output) as an incandescent lamp, people think that they provide less light. This is caused by a combination of the slow warm up and the lower brightness of the lamp.
• In many domestic lighting fittings you cannot physically fit a CFL that has the same light output.
• The output of a CFL is temperature sensitive.
• CFLs do not start at low temperature and cannot withstand high temperatures.
• CFLs cannot be dimmed except for special versions.

All this means one thing. That there are applications where a CFL is ideal and others where a GLS lamp is ideal.

Banning GLS lamps, even if legal, is stupid. Yes the public should be encouraged to buy CFLs. The prices and benefits should speak for themselves.


Bob Bell

I spent 35 years as an electrical engineer in the oil industry and only once experienced an arc flashover incident. This turned out to be result of a stupid mistake by an electrician with insufficient knowledge to carry out his task. It resulted in the HSE electrical inspector almost camping on the site for about a week! The injury was minimal though the man was taken to hospital and was off work for a couple of days.

If these incidents are occurring with the frequency suggested in US then it is time they examined their work practices. If they occurred here we may not have enough inspectors to carry out all the safety investigations!

In my installations we had all voltages up to switching at 33kV and never remember any occasion when an electrician or engineer was required to work on live conductors. All work was covered by a 'permit-to-Work' system, where the safety implications were studied before the permit was issued. This method meant that live working was eliminated as much too dangerous and some other safe method of work devised.

I consequently cannot follow the suggestion by the authors of the article that this is a common problem today.The protection systems devised over the years have served the British Electrical industry well in the past and I would hate to think that gloves were now required as a line of defence.

Michael Rowe in his letter does however raise an important situation often overlooked regarding work with high capacity low voltage batteries where personnel may not appreciate the arc flash danger.

Please report on the seminar as suggested by Mr Windsor Coles.

GM Mcllwrick FITE




I would like to reply to the letter from Windsor Coles regarding the arc flash article Jim Phillips and I wrote in the August and September editions of the Electrical Review. I have a great deal of respect for Windsor and for his 25 years of public service but he has jumped to a conclusion that we are merely mitigating the consequences of arc flash without the benefit of reading the full text.

Windsor will know from my last presentation at EA Technology that I believe that the vast expansion in knowledge about nature of electrical arcs through the empirical research in the US allows UK Engineers to apply a new understanding to our risk assessment processes. The main spin off from this research is that there are now recognised methods of predicting the level of harm to electrical workers and others who may be affected by electrical flashover.

Can you ignore the research? Well, no you can't. Let me quote from Phil Hughes and Ed Ferrett, the authors of the prime text book for NEBOSH students, about the meaning of adapting to technical progress and information as expressed by Principles of Prevention in the Management of Health and Safety at Work Regulations.

"It is important to take advantage of technological and technical progress which often gives designers and employers the chance to improve both safety and working methods. With the internet and other information sources available a very wide knowledge, going beyond what is happening in the UK or Europe, will be expected by the enforcing authorities and the courts." Introduction to Health & Safety at Work - Hughes & Ferret, published by Elsevier.

I have argued that the IEEE 1584 calculations, produced by the largest learned electrical engineering body in the world, are a sound basis for the evaluation of the severity of arcing faults. There are some flaws that I will not go into here but the formulae are used by professional engineers the world over. I also believe that the defence due to lack of knowledge about the nature of the danger from arcing faults, as expressed in the Memorandum of Guidance on the Electricity at Work Regulations, will diminish in time as the understanding from ongoing research improves.

It has been stated the calculation methods require a maths degree which is nonsense. Jim Phillips and I held a seminar in Watford recently and some 100 delegates actually used manual calculations to determine arcing current, incident energy and flash protection boundaries from worksheets. (The only new thing to them was pressing the LOG button on their calculators which hadn't been touched for the past 20 years.)

One of the speakers was a current HSE specialist inspector and I received lots of positive correspondence from senior electrical and HSE engineers after the event. I remember when the first adiabatic equations were introduced through the IEE Wiring Regulations in the 1980s. Some of the older guys in the office felt like falling on their slide rules at the time. Today, even 5 ampere lighting circuits are sized in accordance with these formulae without a problem.

It has also been said that arc flash studies need masses of data but actually over 90% of the data required is for a single line diagram, fault level study and protection coordination studies all of which are implicitly required under UK Law anyway. Where these records are not available you should prepare them "as a matter of urgency" according to HSE guidance.

To suggest that our articles were designed for a PPE first approach is simply not true. In the UK I have good record of discovering very dangerous levels of arc energy through calculation and then engineering the problem out. To quote from our articles:- "A fundamental safety principle of UK legislation is to design out, eliminate, or remove the electrical hazard at its source."
"It must be emphasised that PPE does not prevent the accident happening in the first place."
"There is no substitute for safe working practices and the goal should be to work only on de-energised equipment"

Hopefully, Windsor will have sight of the second article and has reviewed part 1 by now and will agree Jim and I are not advocating that we merely mitigate the consequences of accidents rather than preventing them occurring in the first place.

I have been asked by the Institute of Engineering and Technology to deliver a couple of talks on the subject of 'a risk assessment approach to electrical flashover' this month; one at Hull on the 20 October and the other at High Wycombe on the 27 October. If you email me at This email address is being protected from spambots. You need JavaScript enabled to view it. I'll let you have full details.

Mike Frain

Mike Frain and Jim Phillips explained the arc flash hazard and how it can be predicted in last month's Electrical Review. In this month's article the authors speak about the various measures that can be adopted to protect organisations against the sometimes catastrophic effects of an electrical flashover, and also to prevent injuries to workers

There are many ways in which the hazards associated with arc flash can be reduced and in some cases eliminated. A risk assessment must be performed where there could be danger which may include performing an arc flash calculation study to define the severity of the hazard. It is a fact many workers are put to work on very high incident energy equipment without a thought for the consequences which results in a huge risk to the company and the individual. There is a great deal of helpful information on the HSE website about risk assessment starting with the five step guide referenced at the end of this article. There is a need to evaluate the arc flash risk as a part of the process and also the methods for controlling that risk. The amount of energy that could be released in an electrical flashover is the starting point in that evaluation process. Once that is known then risk control measures can be explored to determine the test of reasonableness in working live and suitable precautions as laid out in the Electricity at Work Regulations 1989.

Hierarchy of risk control measures
The need for risk assessment is embodied in European Law through directive 89/391 and is transposed into UK Law through Management of Health and Safety at Work Regulations. Most people are familiar with the general principles of prevention as laid down in these documents and in other UK regulations. They say that "Where an employer implements any preventative measures, he shall do so on the basis of the principles of prevention" shown below. The authors' thoughts are shown in italics on how these principles can be interpreted when it comes to arc flash prevention.

1. Avoiding the risk - which means dead working. Not energised = no danger
2. Evaluation the risks which cannot be avoided - by arc flash assessment
3. Combating the risks at source - by designing out the problem
4. Adapting to the individual - the avoidance of monotonous work
5. Adapting to technical progress/information - take advantage of technological and technical progress to improve both safety and working methods. The evaluation of the hazard has progressed as have mitigation and protection techniques in respect of arc flash.
6. Replacing the dangerous by the non dangerous -
replace vulnerable legacy switchgear and control panels preferably with arc protected equipment.
7. Developing a coherent overall prevention policy - specific to structure environment, workforce & equipment issues.
8. Giving collective protective measures priority over individual protective measures - by screening live parts, by good design, create a safe place approach.
9. Giving appropriate instruction to employees - create a safe person approach.

The general principles of prevention given previously should be considered against a hierarchy of risk controls with priority as given below. The top of the list should always take priority with PPE as a last resort.

1. Elimination of the arc flash hazard
2. Reduction
3. Information and training
4. Control the risk
5. PPE

All these measures should be properly monitored and reviewed and this is particularly important when considering the lower order risk controls. Each of these risk controls are expanded in the context of arc flash as follows.

1. Elimination of the arc flash hazard
The best way to prevent injuries from occurring is to de-energize equipment before beginning work and as pointed out last month, a fundamental safety principle, which is embodied in U.K. legislation, is to design out, eliminate or remove the electrical hazard at its source. Designers of electrical systems should consider the need to eliminate live work as part of the overall system design. Some of the elimination measures include the segregation of power and control circuits, safe control voltages and currents, finger safe shrouding of terminals and built in test points. Even then, the condition of the electrical equipment must be verified before work commences. It is not uncommon to have accidents occur on equipment that has been rendered dangerous, because electrical workers have not reinstated vital safety components such as door interlocks and insulating shielding after completion of work.

2. Reduction of the arc flash hazard
Since incident energy is a function of short circuit current and the protective device clearing time, a reduction of the arc flash hazard may be achievable by evaluating the protective device sizes, settings and time current curves. Many times where the incident energy is at dangerous levels, it is because the upstream protective device's instantaneous adjustment is set too high and the device is operating in the long time delay region. Lowering the instantaneous setting may allow it to trip faster resulting lower overall incident energy.

Caution should be exercised however, because lowering a device's trip setting can create a reliability issue by compromising selective coordination with other devices. This could cause multiple devices to trip during a short circuit and lead to a more widespread outage. The problem can be solved by changing the device settings only when live work is going to be performed. After the work is completed, the original settings can be restored to maintain existing selective coordination. These types of temporary setting changes are often referred to as ‘maintenance settings'.

Protection arrangements should be explored at design stage to minimise the effects of electrical flashover through the use of fast acting and/or current limiting devices. Other solutions may include retrofitting circuit breakers with instantaneous trip units. Another protection method that has been developed uses an optical sensor that detects the ultraviolet light emitted from an arc flash and causes the protective device to instantaneously trip. Equipment manufacturers are continually developing better methods to reduce or eliminate the arc flash hazard.

Incident energy levels are roughly proportional to the inverse square of the distance. This means a small increase in distance between the live part to be worked upon and the torso of the worker can result in a significant decrease in incident energy. This is therefore, a valid reason to keep workers as far away as possible when undertaking work including inspections on or near to energised circuits. Enclosed switchgear which has a front cover removed and facing the worker acts to magnify the effects of the arc flash and will direct the energy outwards.

3. Information and training
Many times electrical workers and even management do not fully understand the nature of the arc flash hazard and the seriousness of the injuries that can be sustained. Experienced personnel are frequently involved in these types of accidents. Competent electrical workers should be trained in the decision making process necessary to determine the degree and extent of the hazard and the PPE and job planning necessary to perform the task safely.

A review of electrical procedures and safe systems of work can raise the profile and understanding of the hazard and associated control measures. Periodic awareness and refresher training, toolbox talks and specific training in the policy, rules and procedures.

Warning notices were mentioned in last month's article, and arc flash studies will give information about the incident energy level, PPE and various approach boundaries. The Health and Safety (Safety signs and signals) Regulations 1996 is the relevant legislation on the provision and use of safety signs at work the purpose of which is to encourage the standardisation of safety signs throughout the member states of the European Union so safety signs, wherever they are seen, have the same meaning. If you are designing labels you ought to consider the requirements of this legislation as warning and prohibition signs will need to be in accordance with this directive. Warning signs for instance must be yellow (or amber), they must be triangular and the yellow must take up at least 50% of the sign.

4. Control the risk
Safety rules and procedures with clear responsibilities are essential parts of a safe system of work. They should deal with properly assessing and authorising only competent people with systems for risk assessment. Where live working cannot be avoided, then the safe working systems should stipulate the use of the correct equipment and instruments. Electrical flashover accidents are very often caused by the operator dropping un-insulated tools or metal parts or by using incorrectly specified instruments. There should be a rule that no live work will be allowed on equipment that is damaged even for the reasons of proving dead. There have been many incidents involving damaged cables where an approach has been made to prove dead when the damaged cable was in fact still live.

The main objective of an electrical maintenance program is to keep electrical equipment in good working condition so that it can reliably and safely operate within its design criteria. This includes testing and maintenance of circuit breakers, protective relaying and associated equipment on a regular basis. Improper maintenance of equipment can contribute to the severity of an arc flash. When a protective device such as a circuit breaker or relay is not properly maintained, the likelihood of it operating slower (or not at all) increases, which would also increase the duration of exposure to the arc flash. Although not technically part of an arc flash calculation study, a proper equipment maintenance program is vital in making sure the protective devices will operate correctly.

5. PPE
The final risk control measure in the hierarchy of controls is PPE. You will notice PPE is not mentioned in the principles of prevention given above and PPE alone will not prevent the accident. It is seen as a last line of defence but where used properly has prevented injury to individuals and reports among utility companies have confirmed this. There has been research that shows that the hands, arms and face are the most commonly affected parts of the body in an arc flash incident so face and hand protection should also be considered.

Flame resistant PPE is surprisingly comfortable nowadays and can be worn as everyday workwear. Non flame resistant clothing may ignite or melt at low incident energy values and once ignited will continue to burn after the electrical arc has been extinguished. Three seconds of burning material next to the flesh can result in serious full thickness burns. This actually means that ordinary clothing could actually become a hazard and for this reason it is well worth considering a policy of comfortable FR clothing.

Web Exclusive Safety continues to loom high on everyone's agendas it seems and for once I have to say  I'm in full agreement with the various concerned sentiments expressed by those corresponding both with myself and with Electrical Review about arc flash.

I have to confess to being one of those who generally decries the concept of nanny statesmanship. I don't believe that people who water roadside floral arrangements should be compelled to wear visibility jackets, goggles, ear defenders and hard hats. Risk assessment, after all, should take a balanced view on the actual chances of injury or death rather than a theoretical possibility. If we are not careful the one in 20 billion chance of death by tea cosy could spell the end of traditional tea making as we know it!

I mention the above only to establish that I am not prone to over reaction in safety matters - indeed, at times I am maverick (see below in this article). But, it is very real risks that concern all of us in the electrical field. 

Chris Ross, managing director of J&K Ross wrote to me about the simplest of precautions relating to arc flash - that of personal protective clothing. Mr Ross does have a vested interest if you'll pardon the pun, in that his company supplies PPE products. However, he rightly explained that it remains commonplace for engineers in "at risk areas" to be seen wearing polyester cotton garments that not only melt and burn in contact with high heat, but which exacerbate injury in what might otherwise be a relatively minor burn. One look at the damaged gloves in September's issue of Electrical Review should help emphasise Mr Ross' point.

Safety can never be taken lightly and the response to Electrical Review's various articles and the two part feature on arc flash is laudable. Let's hope increasing numbers of switchgear users take heed and perhaps review the safety of their own installations.

On which note, I have a sobering little personal tale relating to safety and how taking a rebel approach to safety is neither big nor clever. Regular readers may have noted my absence for a couple of months during summer. I was in France refurbishing a house in Brittany. One of the things I had to do was to change some light fittings, but the room I was trying to work in was very dark even with bright sunshine outside. Foregoing the hassle of buying an inspection lamp (mine was ‘safely' back in the UK) I decided to work ‘live' so that I could leave other lights on in the room by which to see. Yes, I know it is stupid, but it gets worse.

The French lighting was all two-wire, so I was very careful. Now, when I came to install the next fitting, there was plenty of natural light, so I very conscientiously went to the consumer unit to isolate the circuit. Only when I went to flick the switch did I notice that the lighting circuit I had been working on was hanging on a 17A breaker!

This brings home the final safety point of this column, if you're going to do something extremely dim-witted like working live, then at least check exactly how brainless you're being! That is very real risk assessment.

I stand corrected on energy

A while back I had a rant about energy consumption. Mr Andrew Warren, Director of the Association for the Conservation of Energy, very kindly wrote to challenge some of the figures about energy consumption I had used.

One of the problems when discussing energy consumption is that many - including me - fall into a trap of considering energy within confines or specific parameters. In my case I tend to think primarily about the built environment and to a lesser extent energy in manufacturing. What Mr Warren has explained is that electricity actually makes up a much smaller percentage of energy consumed than electrically biased bods like me consider.

In fact, the latest issue of DUKES (Digest of UK Energy Statistics), states that out of a total inland consumption figure for 2006 of 164,599 ktoe, just 29,402 ktoe is ascribed to electricity use. This equates to just 19% of all energy consumed and not 60% as I had suggested. Oil and natural gas continue to be the dominant energy sources. Like many, I do tend to get carried away in regarding electricity as the primary energy resource to be conserved.

For greater authority on energy consumption in the UK visit the Association's website at www.ukace.org

Fully matched generator sets and UPS systems are the only true ‘no-break' solution  for long-term power protection, explains Alan Luscombe from  Uninterruptible Power Supplies Ltd (UPSL)

Changing business priorities, the risk and consequence of power cuts, and a dependency on technology have heightened the need for secure and integrated power protection.
Providing continuous power to critical processing and communication applications such as data centres, online banking and emergency services is essential, and often nothing less than 24/7 availability can be tolerated.

Consequently, the recognised solution for continuous power is the combination of a standby generator and an uninterruptible power supply (UPS).  While a UPS alone will protect against short term utility power loss and supply quality problems, the UPS will eventually shutdown when its batteries reach the end of their discharge period. Increasing the size or number of batteries will of course extend the autonomy time but this is becoming more expensive as the rising cost of lead directly affects battery pricing. Irrespective of this, the exposure to a possible ‘blackout' period when exceeding the UPS battery autonomy will always remain a reality.

The National Grid is under pressure to meet growing demand with an aging infrastructure and uncertainty about future energy sources. Growing dependence on power for business critical systems adds impetus to the need for robust protection - and standby generation capacity - to cope with deteriorating supply, more frequent interruptions, and longer term power cuts. This firmly places integrated UPS and generators at the frontline of business continuity.

Tandem back-up
Using a standby generator alone will serve as an alternative source of power but will not provide a no-break solution in the event of a loss of mains power. However, a generator with a secure fuel supply can provide a source of power, far exceeding the duration of a long term mains blackout and the back-up capability of a static UPS system.  It is therefore clear that the respective limitations of utilising a UPS or a standby generator alone are fully overcome by operating these two different sources of back-up power in tandem. 

During normal operation the utility mains feeds the critical load via the UPS, whilst the UPS battery is also float charged. The UPS will protect against breaks and disturbances in the mains supply and after a pre-set time, typically from 2 to 10 seconds, the automatic mains failure (AMF) panel sends a signal to the generator to start-up.

The UPS battery serves as an alternative source of supply to support the critical load while the generator starts. Once the generator has stabilised, the UPS accepts the generator as a mains replacement, continuing to supply the critical load and recharges the battery for the duration of the mains failure. When the AMF senses that the mains supply is restored and stable it shuts-down from the generator, with the UPS battery once again covering the power interruption caused by the changeover. This sequence ensures uninterrupted clean power to the load and demands no user intervention.

However, a standby generator and UPS do not have natural plug and play compatibility; they must be carefully matched with one another to ensure reliable co-operation. Although reliability is of course a critical consideration, it is not the only one. There are significant cost implications in ensuring that the generator is optimally sized for the UPS, as well as many physical and environmental factors to consider.

UPS considerations
Constant voltage and frequency are directly proportional to the size and type of generator. The generators used by the power generation companies produce consistent power because they are extremely large. A standby generator, by comparison, is quite small and cannot supply such consistent power. Any increase in electrical load requires an instantaneous increase in mechanical power to supply it and whereas in a large generator many of these variations are ‘absorbed' by the inertia of the rotating parts, a small generator set with less inertia will actually slow down until the engine governor compensates. The resultant instability in generator voltage and frequency must be accommodated by a correctly selected UPS system.

UPS Compatibility
There can sometimes be compatibility problems between generators and UPS systems. The generator output voltage may be acceptable to the UPS, but often the generator's frequency range is wider than the UPS is designed to accept. In the worst case the frequency variations of the generator will be such that the UPS cannot synchronise with it, either because the frequency is outside limits or it is varying too quickly for the UPS to follow (slew rate) causing, in some cases, the UPS to revert to battery supply and putting the integrity of its output supply in jeopardy.

This problem can be overcome by ensuring the generator is properly matched to the UPS and fitted with an electronic governor that allows the generator to operate within tight frequency tolerances.

The type of load presented to the generator by the input stage of the UPS can also cause problems. Typically a UPS utilises a phase controlled rectifier which imposes notches on the power feed, interfering severely with some types of generator control systems. Phase controlled rectifiers also draw a non-sinusoidal input current, creating harmonics, measured as total harmonic distortion (THDi). These can cause excessive heating in the generator alternator, especially as some UPS systems on the market generate up to 30% input THDi.
Some UPS manufacturers introduce a capacitor and inductor filter at the input to the UPS to attenuate the level of input current harmonic distortion. However, this is often a passive filter tuned to optimum load conditions, which can create a leading power factor if the UPS is subsequently lightly loaded. When a leading power factor is presented to the generator the alternator over-excites and the output voltage rises. To compensate, the voltage regulator reduces exciter power to reduce the strength of the magnetic field. Under such circumstances the magnetic field can fail causing the generator to shutdown or even result in catastrophic alternator damage.

Generator sizing guidelines
In practice, it is usually necessary to size the generator to handle more than just the UPS. The generator may also be required to power emergency lighting, air conditioning, building alarm systems etc. As a very general ‘rule of thumb', when assessing the rating of a generator the  multipliers (above) should be applied.

Step Loading
Most generators cannot accept 100% of their load rating in one single step. For example, an Auto Mains Fail (AMF) panel cannot present a 100kVA load to a 100kVA generator in one single ‘hit'. A generator's ability to take large load steps is a function of its design and turbo charged generators can, typically, take larger load steps than standard generators. It is good practice to not introduce the entire load to the generator when this load is greater than 60% of the generator's standby rating. This can be achieved by either over-sizing the generator, which is a potentially expensive option, or by ensuring that load equipment such as the UPS and air conditioning has a ‘soft start' facility or by the use of time delay contactors on the essential services distribution board.

Location and installation
A key decision involves whether to site the generator within the user's building or outdoors. There are pros and cons to both choices. Indoors, a generator requires significant environmental management; for example, exhaust ducting, adequate airflow for cooling, noise attenuation, space etc. Outdoors, these requirements can be easier to handle, but the generator itself must be environmentally protected. Smaller generators of up to 750 kVA usually have a combined weatherproof and acoustic canopy, while larger generators are typically installed into a container for out of building operation. 

The fuel storage tank must be double skinned or bunded, or have a drip tray to contain oil spillage in accordance with environment contamination regulations. Most standby generators have a base tank, often referred to as a ‘day tank' fitted as standard. For longer autonomies a separate bulk fuel storage tank is required which adds to the cost, space and complexities of the installation. Whether the generator is installed indoors or outdoors the local authority and fire officer should be advised.

As a minimum, a power cable rated to carry full generator power and a signal cable to carry generator start/stop signals must be run between the generator and the AMF panel and/or the essential services board. If the cable from the generator is long then it may be necessary to increase the cable cross sectional area to reduce the ‘volt drop' along it. This increases the electrical installation costs of the generator, therefore the generator should be located as close as practically possible to the AMF panel and/or the essential services board.

Uptime in a downturn
Turnkey supply and installation of the UPS and generator delivers valuable integration benefits, ensuring seamless interaction between systems. This avoids the problem of demarcation between different suppliers and eliminates potential points of failure. Individually sourced units can compromise system autonomy and present a risk of mis-sizing, causing installation and commissioning problems.

With a packaged solution, the complexities of matching a UPS and generator are taken care of, removing the responsibility from the consultant and contractor and alleviating any concerns for the end user. Significant cost savings and operating efficiency can also be gained.

Power failures can be catastrophic, particularly in a recession when businesses can least afford productivity and revenue losses through system downtime. Fully matched UPS and standby generators - correctly configured and installed - ensure a true ‘no-break' solution in the event of an extended power failure, maximising the protection of critical loads and assuring uptime.

Environmental legislation, especially laws compelling businesses and Local Authorities to engage in more recycling, has been growing since the first pieces of producer responsibility legislation in the 1990s. Tough targets have been set for businesses to recover and recycle packaging and waste electrical items and electronics, but these targets have been met with little or few problems. This is about to change as UK producers and retailers of portable batteries, the  definition of which includes those sold with equipment such as laptops, phones, tools and toys, will soon have to take responsibility for a step change in UK recycling

The Waste Batteries and Accumulators Regulations 2009 became law on 5 May 2009 and introduce the tried and tested concept of ‘producer responsibility'. The rules apply to all battery types, although automotive and industrial battery producers should not face too much difficulty due to the current high recovery rates of these items.  Portable battery producers and retailers on the other hand will have to comply with stretching new obligations.

All retailers selling over 32kg of portable batteries per year (the equivalent of about 16 AA cells per week) will have to offer free consumer collection points in store as of February next year. This might seem straight-forward but batteries require special treatment. Collection points may have to register under the Hazardous Waste Regulations, and batteries must be transported as ‘Class 9 dangerous goods' (the most dangerous) under the relevant transport regulations.

For those classed as producers (most of the businesses affected by the 2007 WEEE Regulations are expected to fall into this bracket) there are also potential issues. The targets for portable battery collection and recycling rates in 2010, to be funded by producers, is 10% - more than three times the UK's current rate of approximately 3%. In addition, this figure rises steadily until 2012 when a rate of 25% must be achieved. Producers have until October this year to register with a compliance scheme but Valpak advises producers to start planning and budgeting as soon as possible.

The costs to be met by producers under the new rules from January 2010 are currently difficult to estimate.  Some operators are offering fixed (but very high) prices based on a ‘per battery placed on the market' system and the only publicly available costs (from WRAP) are calculated from short term trial data and are therefore not representative.  However, Valpak is currently offering budget estimates for its members and we are confident we can, as with other producer responsibility regimes, match or beat any competition.

Valpak is the UK's leading compliance scheme specialising in producer responsibility laws like this one. We're also a member owned ‘not for distribution' company with a sound track record of reliable compliance for our members for over 10 years. We are currently offering full ‘compliance' information services for all businesses who think they may be affected by the Batteries Regulations, which include simple explanations and expert interpretations of the law, free member seminars and the most up-to-date information. We can also provide both information and solutions to retailers affected by the new laws.


Tel: 08450 682572