Features

When designing a power continuity plan for a data centre or any other type of critical operation, power quality should feature high on the tick list. Poor power quality can be as dangerous to critical loads as a partial or complete mains power supply failure and lead to intermittent data corruption and hardware failure explains Robin Koffler, general manager, Riello UPS

The actual quality of a mains power supply is measured in terms of its waveform, voltage and frequency and the presence or not of a variety of power problems including blackouts and momentary interruptions, sags, brownouts, surges, spikes and transients, electrical noise, frequency variations, and harmonics.


Of the eight most common types of power problem, harmonics is perhaps the least understood and planned for. Harmonics are voltage or current waveforms the frequencies of which are multiples of the fundamental. In Europe the fundamental frequency is 50Hz (50 cycles per second) and the multiples are ordered into a specific sequence. For example, the 2nd harmonic is 100Hz (2x50Hz), 3rd harmonic 150Hz (3x50Hz) and so on.


Often overlooked as a potential threat, harmonic pollution is a growing problem in the UK because its presence can be disruptive not only to a polluted site but also other customers of the utility provider. Most consumers are unaware that they are responsible, under the terms of their electricity supply contract, for the total harmonic values generated at the Point of Common Coupling (PCC) and building incomer when new installations are made. Acceptable levels are published within Engineering Recommendation G5/5-1, from The Energy Networks Association (www.energynetworks.org).  The critical point for new installations is that where the specified harmonic levels cannot be met, consumers must secure approval from their utility provider before connection or face penalties.


Within a new data centre, for example, the most prevalent loads will be high-end servers and associated data processing hardware, which are powered by Switch Mode Power Supplies (SMPS). It is the power supplies themselves which form the load on the electrical supply, and being non-linear draw their own power in regular modulated pulses of current, rather than as a continuous linear current. This action can lead to the generation of high levels of harmonics, especially where a large number are supplied from a three-phase mains power supply. Of the harmonics generated, it is the set known as Triple-Ns or Triplens whose harmonic orders are multiples of three and include 3rd, 9th and 15th. Other harmonic orders, not in phase with one another, simply cancel each other out and though still considered to degrade power quality, their impact is less severe.


When harmonics are present in a mains power supply they can lead to voltage distortion, overheating of building wiring circuits, neutral conductors, supply transformers and switchgear, and nuisance tripping of breakers. Harmonics can also cause disruption to equipment on the same supply and lead to random failures. Within a data centre environment their presence can therefore prove disastrous.


It is the 3rd order harmonics which potentially are the most serious within a three-phase mains supply (Fig. 1.11) due to the summing effects within its neutral conductor. As these harmonics are multiples of three, they are all in phase with one another and therefore their magnitudes are added together. Their effect is to greatly increase the current flowing within the neutral and this can lead to potential overload and affect associated switchgear.
Whilst, it is accepted practice to balance loads across the phases of a three phase mains power supply, even this will not counter-act the impact of Triplens. This is because Triplens can generate neutral currents up to 1.73 (?3) times the average currents present. This additional loading (and heat generation) can degrade upstream neutral conductors and/or wiring insulation leading to potential breakdown and a fire hazard if unmanaged.
Whilst SMPS may be the most common source of harmonics, others include: rectifiers, variable speed drives, discharge lamps, fluorescent lighting, mercury and sodium lamps. When designing a power continuity plan, it is therefore vital that all site loads are assessed for their impact and effect on overall power quality.

Mitigating Harmonic Pollution
Data centres are now one of the most concentrated users of SMPS in the racks of servers they deploy over relatively small footprints. Whilst most users apply a concerted effort to manage the resultant air conditioning demands, few realise the potential harm that can be done due to harmonic pollution.


Within such an environment it is common to select a centralised approach to power continuity and install an Uninterruptible Power Supply (UPS) and standby generator. Whilst the UPS will power critical loads, the generator will provide power to essential services such as air conditioning and security systems, as well as provide backup to the UPS should its battery set be discharged.


The UPS can therefore be considered to fit ‘in-line' between the loads and the mains power supply. In addition to providing power protection to the loads, it should also protect the mains power supply itself from any harmonics generated by the loads themselves.
However, it is again not commonly known that UPS themselves, by way of their design, also generate harmonic pollution. For any UPS this is typically stated as Total Harmonic Distortion (THDi). Care has to be taken when comparing different THDi values as these can differ when contrasting the two different types of on-line UPS (transformer-based and transformerless) and also with regard to the percentage of load applied for each measurement.
Within a UPS it is the rectifier that connects to the mains power supply and converts the mains alternating current (ac) into the levels of direct current (dc) required to power the inverter and charge the battery.


For transformer-based UPS, rectifiers are typically six or twelve-pulse, dependent upon the thyristor number and configuration. A six-pulse rectifier at full load will typically generate a THDi of around 29% and a 12-pulse around 8%. To reduce these values further a passive harmonic filter can be installed alongside the UPS. The obvious disadvantages of this approach being increased capital cost, wiring, installation, loss of efficiency and increased footprint. Harmonic filters can be added post-installation but further installation costs and downtime need to be planned for.


Transformerless UPS have a different type of front-end whose configuration is usually that of a rectifier-booster. THDi levels of less than 7% can be achieved and reduced to less than 4% when an active harmonic filter is installed. For some designs, the harmonic filter may be positioned inside the UPS cabinet reducing impact on overall footprint but still resulting in higher capital and operating costs.


Harmonics is just one research and development area for UPS manufacturers with the goal of producing zero-impact uninterruptible power supplies. The latest developments offer THDi levels of less than 3% using IGBT-based (Insulated Gate Bipolar Transistors) rectifiers and it is forecast that this approach will be adopted as a standard for UPS up to 200kVA or more over the next one to two years. Achieving a zero-impact also covers the areas of operating efficiency and input power factor. Such designs can now offer efficiencies of 96-98% and input power factors close to unity. Their cumulative effective offers high reliability systems that can achieve 35% energy savings and quicker capital payback than traditional UPS.
Harmonics is therefore a ‘hot-topic' when it comes to power continuity but one most people avoid. The subject can appear complex but requires thought at the planning stage of any new installation if the systems are to deliver the benefits intended and satisfy the requirements of the utility providers who in the end has the ultimate power.

Design engineers face many challenges with the layout of electrical and electronics enclosures, and one frequently asked question addresses the location of thermal management products. The goal is to position the equipment so as to provide adequate protection from temperature extremes as well as preventing the formation of condensation. Phil Herbert of Stego (UK) explains

Heating and cooling devices in enclosures are designed to protect electrical and electronic components primarily from condensation and also from low and high temperatures. However, even with the appropriate equipment and controls, problems may arise due to incorrect positioning within the enclosure.

Heating
As the requirement of heaters for the prevention of condensation formation becomes more widely acknowledged, engineers and design teams must consider the equipment placement in an enclosure along with the devices they are intended to protect. It is not uncommon to find systems added after the fact, fitted into whatever space remained. While this may be the only solution available, it could potentially be the cause of other problems such as creating ‘hot spots' or ‘heat nests' near temperature sensitive electronics.

Ideally, most heaters will perform optimally when mounted near the bottom of an enclosure and used in conjunction with a separate controller such as a thermostat and/or hygrostat. With the controller located in an area of the cabinet that is representative of the average temperature or humidity requirement, the heater should then be placed in a position near the bottom but not directly beneath the controller. This placement will ensure that the controller is not influenced by direct heat from the heater.

For smaller areas, heaters will generally provide adequate heating power to maintain temperature and humidity control. For example, a 900 x 600x 600 wall mounted, insulated stainless steel enclosure with a desired interior temperature of 10°C with an ambient temperature of 0°C will require a 100W heater:
Power (W)  = (enclosure surf. area) x (delta T) x (heat transmission coefficient)
= (1.014 m2) x (10 K) x (4.5W/ m2K)
= 91W
In the case of Fig. 2, with all other parameters remaining the same, the height and width have been increased to 800 and 600mm thereby increasing both the air volume and the surface area. Accordingly, the required heating power has also increased:
Power (W)    = (encl. surf. area) x (delta T) x (heat transmission coefficient)
= (1.428m2) x (10 K) x (4.5W/m2K)
=   129W
For larger enclosures with greater heating power requirements, standard heaters are not a practical solution. As Fig. 2 shows, the most effective heat distribution is accomplished by a fan-assisted heater with greater air circulation to ensure rapid and efficient control of the temperature and/or humidity.

However, as mentioned previously, space for a tall heater is not always available. Packing densities have increased as more equipment is designed into smaller spaces. In the case of an example enclosure, only 100W of heating power is required, but the high packing density limits the available space for a convection heater.

The alternative is a compact fan-assisted heater positioned to provide adequate heat distribution throughout the cabinet. The position of the controller can vary depending on the air flow and temperature gradient, providing that it is not impacted by direct heat.
In any circumstance where a heater is required, the location of all other equipment relative to a heater should be carefully considered. Most heater manufacturers recommend a minimum distance of 50 mm from components inside an enclosure. However, the temperature sensitivity of each component should be assessed along with the heater temperature profile to ensure no damage will occur. (Calculations are available online at  http://www.stego.co.uk/)

Cooling
Enclosure cooling solutions range from filter fans to heat exchangers and high performance air conditioning systems. In all cases, the intent is to remove excess heat from the cabinet interior. Whether naturally or mechanically achieved, the basic principle of heat rising is utilized.

One common and simple method is by using forced air ventilation, which is most effectively achieved with filter fans. Since outside air is introduced into a clean sealed environment, high efficiency filters are required to maintain that integrity.

This arrangement with the filter fan (air intake) at the bottom and the exhaust filter near the top is highly effective by using cooler ambient air to displace the warmer air inside the enclosure. The exhaust filter is typically mounted as close to the top of the cabinet as possible to take advantage of natural convection forces, and should also be located as far as possible from any heat producing components. If designed properly, the air path created by the filter fan system will pass through critical areas that are to be cooled, allowing for maximum cooling efficiency. Ideally, a control thermostat should be located in one of the critical areas where it will turn the fan on and off when temperature set points are reached.
Many other arrangements are possible, even so far as letting ventilation occur naturally. One such system would allow for passive cooling by letting the warmer air escape through a roof-mounted vent. Again, the key is that cooler air is used for displacement, so an intake filter would be required near the bottom of the cabinet.

Conclusion
Designing the layout of cabinets and enclosures that house sensitive electronic components is a challenging task. While it may seem a less important consideration than many other aspects of proper control system design, the suitable placement of heating and/or cooling components can have a major impact on system operations. Following these simple guidelines will help ensure system functionality and long service life.

The introduction of BS EN 62305: Protection Against Lightning on 1 September 2008 is already having a profound impact on the industry and its customers says Colin McElhone, managing director at Omega Red Group

Having spent the past two years preparing for the introduction of the new standard, it shouldn't really be a surprise now it's here.

But like many in the lightning protection industry I have spent my entire working life working under its predecessor and knew it inside out. Doubtless we had all become comfortable with the old standard.

BS EN 62305 has given us new ways to apply concepts outlined within the standard to tackle problems with a logical, systematic approach. In BS 6651 basic surge protection was mentioned under Annex C. BS EN 62305-4 Electrical and Electronic systems within structures is a complete document dedicated to the problems, and solutions, encountered due to lightning current and induced surges. Mike Forsey, technical manager at DEHN (UK) explains

The new standard calls for a risk assessment calculation to be carried out, part of the assessment determines if surge protection is necessary and if so what type of surge protection device, or devices, needs to be installed.

With the increase of electrical and electronic systems being used within both business and private environments the continuing reliance, functioning and uninterrupted use of these systems is becoming essential. Equipment ranging from the basic power supply and distribution systems to specialist equipment for computer, networks, building management (BMS), telecommunications, control and security, etc now play an essential role in our lives. Damage caused by lightning and switching related events has not only a direct repair cost but also an indirect consequential cost due to down time, data re-instatement, etc.

Using the protection principles outlined in BS EN 62305-4 the protection of such systems against surges is based on the principle of lightning protection zones (LPZs), in which the building or structure being protected is divided subject to the location of the equipment within the structure. Using this approach, suitable zones can be defined according to the number, type, immunity and sensitivity of the electrical and electronic devices or systems present within the structure. Sizes ranging from small local zones to large integral zones that can encompass the whole building can be established. At the boundary of each internal zone, equipotential bonding must be carried out for all metal components and utility lines entering the building or structure. For mains power, data, telecomm, etc this is carried out with the use of suitable surge protection devices.

As can be seen from the diagram below a lightning current arrester, SPD Type 1,  (Waveform 10/350) is required at the interface of zones LPZ0/1 for any cable entering from a zone LPZ0A. At the boundaries of LPZ1/2 and higher a surge arrester, SPD Type 2 (Waveform 8/20) would be used.

The same principle is used for all conductive cables entering the structure be they mains power, telecomm, data, networks or CCTV.

Spatial shielding within the structure also forms part of the protective measures. By correct design and placing of suitable shielding the magnetic fields within the structure can be attenuated.

Protection management
For new buildings and structures, optimum protection of electrical and electronic systems within the structure can be best achieved cost-effectively if these systems are designed together with the building and are taken into account before its construction. For existing buildings and structures, the cost of this protection is usually higher than for new buildings and structures. If however, the LPZs are chosen appropriately and existing installations are used or upgraded, the costs can be reduced. If the risk analysis as specified in the new BS EN 62305 -2 shows that surge protection is required, this is best achieved if:
- The measures are designed by a lightning
protection specialist having knowledge of
electromagnetic compatibility;
- There is close co-ordination on all aspects of
the work between the building experts (e.g.
civil and electrical engineers) and the surge
protection experts;
- An appropriate management plan is
adhered to.

The rising cost of energy and the focus on "green issues" has put great responsibility on every commercial building manager and owner. The pressure is on to make continuous energy savings and this must be achieved through effective building management. Systems that track the energy performance of a building in real time can identify all areas where there is need for improvement, allowing the owner or occupier to take steps to further improve energy efficiency. Finding the best building management system and the most effective long-term solution to controlling energy usage is the challenge

The KNX Standard is the world's only open standard for building control and automation. The KNX standard is approved as: 
- European Standard (Cenelec EN 50090 and CEN EN 13321-1)
- International Standard (ISO/IEC 14543-3)
- Chinese Standard (GB/Z 20965) 
- US Standard ( ANSI/ASHRAE 135)

The standard has been adopted by many international manufacturers, who together provide a vast array of KNX certified products for a range of building control applications. The installation of KNX products can make major energy savings of up to 60%, significantly reducing the carbon footprint of a building. This is truly green sustainable technology that can be applied to small and large buildings alike.

An ever growing number of building owners are accepting KNX as a technology to achieve maximum energy efficiency. It has a number of advantages over alternative solutions including the ability for it to be integrated with any type of BMS thanks to its open protocol OPC Gateway. Once this integration has been achieved, KNX brings local and zonal control to every area of a building.

The over-riding advantage of KNX is it provides a holistic approach to efficient energy usage and is not limited to individual control of lighting/ HVAC/ intruder alarms/ audio visual systems/ household appliances/ blinds/solar control and automatic window control, façade management/ metering and monitoring applications. The KNX platform has been adopted by many and highly respected major manufacturers with their vast choice of products covering all these product lines. This is important to building owners in the longer term, as any installation is future proofed. Contractors, consultants, specifiers and end users looking for an open solution for building control applications are increasingly heralding KNX and recognising the drawbacks of proprietary solutions or various hardware-based controls. Were they to choose a proprietary protocol from a single manufacturer or integrator, then they would be beholden to that company and its technology. This could be problematic during the life cycle of a development. With KNX, in the event of a certain product no longer being available, there will be an alternative to replace it.

As KNX covers such a diversity of applications using one standard, it means cabling networks can be much simpler. A single twisted pair cable can often suffice, with multiple elements all operating together on a single network. KNX controlled devices are generally based around the standard green KNX bus cable (i.e. twisted pair) but can be run across radio bus (wireless), ethernet (structured cabling), fibre optic and occasionally power line.

A number of manufacturers have also developed ‘gateways' to other control protocols, such as DALI (digital addressable lighting intelligence). These simple devices are used to expand the capability of KNX control systems to provide the complete solution for a building. KNX has also worked closely with management-level protocols such as BACnet to enable a close co-operation between these two standards when the project requires additional integration.
What also helps to maintain KNX's superiority is that every KNX-compliant piece of equipment has been fully tested and certified to this highly stringent standard by an independent regulatory body. It is only at this point that it can carry the KNX logo, as controlled by the international KNX Association of Brussels. Therefore there is total confidence in reliability and interoperability, whatever KNX devices are chosen.

Another advantage of KNX is the ability to seamlessly add functions that work away in the background and go largely unnoticed. What is more, KNX is distributed technology so in the event of failure of one element of building services, the rest carries on regardless.
With the pressure on energy management, it is vitally important to make the most effective use of energy. For instance, a lighting control system can be simply configured to only put the lights on when someone is present in the room, and can monitor natural daylight levels to dim or turn the lights off when enough ambient light is present. A drive through any town centre or industrial estate at night will reveal there is much energy for lighting being wasted and this could be preserved by employing simple measures. Effective use of lighting control alone can result in highly significant energy savings and when integrated with shutter and blind controls, solar panels, façade management and effective monitoring, there are potentially massive savings.

Indeed, climate control is a critical area within office buildings and a KNX system will know when the blinds are closed as an inherent feature. At the same time, heating and ventilation can be regulated separately in each room via temperature sensors. During the winter, when warmth and light make an even greater contribution to the comfort that a building provides, KNX technology regulates climate and lighting for each room in accordance with the outdoor temperature and prevailing daylight levels. Investment return on each KNX device is highly geared as each product on the bus, such as a movement detector, can not only switch lighting as in conventional installations, but can also set back heating when a room is empty.
Another growth area is building security. In any property at night, for example, the KNX system can act as an "electronic watchdog" deterring crime. Motion detectors, glass break sensors and electronic shutter control can be connected to an alarm system or emergency call circuit. If there are suspicious noises, a panic button can be pressed and the lights go on and the shutters open. Should any alarm conditions occur, they can be conveyed by email or SMS and to a mobile phone.

Thus a KNX based intelligent building system offers benefits in terms of energy savings, comfort, lifestyle and security - as well as some more unexpected advantages. A growing application is in the area of assisted living where KNX can help in the execution of daily household tasks which otherwise may not be accomplished.

With the continued development of new KNX products from various manufacturers, the ability to record energy consumption data and to process this data for accounting and billing software products is now readily available.

Connection of the metering devices to the KNX bus system and coupling to IP allows the display and processing of the data on a touch panel. The visualisation can display the recorded and current data of every metering point. The conversion of the data with export functionality to Excel can be achieved with the push of a button and allows post-processing for the various accounting and billing software products currently available.

KNX metering products can record data such as heat consumption using heat meters; power consumption (different energy meters, flexible with IR interface); water consumption (water meter with KNX connection); fill level meter for tank content (oil, water, liquids).
The development of a worldwide standardised system to meter electronically the consumption of different commodities and to convert data for external post processing offers a number of advantages.  For example, customers can get an overview of the current consumption data at a push of a button and can identify irregularities faster and therefore save time, money and energy. A number of KNX manufacturers are involved in on-going development of meters.

There is a growing network of integrators who have joined KNX UK to share their experiences, to help to promote the KNX standard and assist consultants as well as building owners in achieving the optimum solution for their building. They can get involved at the drawing stage of any project, liaise with the client and install a KNX infrastructure that can be developed as the building itself develops or its use and occupants change.

 

Lightning can cause significant damage to sensitive, mission-critical systems within a building if lightning protection measures are not adequate. Paul Considine of Wieland Electric explains how the risk can be aligned to the cost of protection

With the increasing use of, and dependence on, technology in just about every business, protecting sensitive equipment is becoming ever more important. In a manufacturing or logistic operation, for example, disruption to processing or handling systems can have a catastrophic effect on productivity. Similarly, in the financial sector, server rooms are mission-critical and any failure can lead to losses of millions of pounds every hour.

Poor power quality is responsible for many different electrical problems. In addition to the obvious accidental causes like power cables being damaged by digging work, or bird strikes on overhead lines, every load on the electrical grid will have some impact on the power that is delivered. Some power quality problems are very complex, but there are also many common causes says John Outram, managing director of Outram Research

A purely resistive load, for example an oven, will tend to pull down the local voltage due to the current flowing in the power lines that have a finite impedance; capacitive and inductive loads can cause the current to lead or lag the voltage, degrading the power factor; motors and pumps have large inrush currents, potentially superimposing transients onto the voltage; and modern compact fluorescent lighting may only draw current at the peak of the voltage waveform, causing harmonic distortion of the supply voltage.

In most cases the impact of loads on the power supply is not problematic, but in extreme cases the effect on other devices on the grid may be serious. The mechanisms by which the utility companies try to accommodate all of these influences may themselves add transients and momentary variations, further complicating the situation. The effect of poor power quality can range from unnecessarily lost power in transmission lines caused by low power factor (out-of-phase current and voltage), to flickering lights, and power wasted in motors and transformers due to the presence of harmonics.

Taking motors as an example, when power is wasted it will generally be dissipated as heat, increasing wear and shortening life. Harmonics may also cause vibrations in motors which can increase noise as well as be a potential source of mechanical failure.

Some causes of power quality problems are almost impossible to control; vulnerability to accidental causes such as those mentioned above is a function of our infrastructure and they should be expected occasionally. However, with the right equipment and approach, power quality issues can be identified and resolved, and although complex situations may require experienced power quality professionals, engineers can identify straightforward issues by following six simple steps.

Step 1 - Gather Information
If you don't measure it, you can't manage it! However, before any measurement survey is made, think about the best approach. How is the problem presenting itself? Are complaints widespread? Are there any common threads? What about the infrastructure or the installation itself? Is it old; is there any corrosion, leaking oil? If so, could the distribution impedance have been compromised?

Most problems are local or self-inflicted. One of the best sources of information is the operator of equipment affected. Asking the operator when the problem happens, whether other things go on at that time and what he/she thinks is causing it, can provide excellent clues to the cause of the problem.

This stage should also be used to prepare for the survey. What are the local loads? How many points need to be monitored? The more information available, the better the monitoring can be targeted.

Step 2 - Produce a Harmonic Profile
Harmonics on the line tend to lead to long-term problems - motors and transformers overheating or other failures that do not happen instantaneously, although they can also cause rapid equipment failure. Typically these measurements would be taken over a period of at least a week, as most power quality issues have either daily or weekly periodicity (for example, happening the same time every day, or happening during the week but not at weekends). Understanding the periodicity can give important clues as to the cause of the problem; for example a car breaker's yard is unlikely to be causing problems that happen during the night!

Harmonics are evaluated continuously and averaged over a period of time. Measuring the harmonics does not require as high a sample rate as transients because the lower harmonics will tend to contain the most energy. Of particular interest in 3 phase systems are the 3rd, 6th and 9th harmonics, as these will not generate balanced current flow but reinforce each other, and therefore can cause high currents to flow in the neutral.
The harmonic direction - the phase angle of the current with respect to the voltage waveform of the harmonics, can also be a helpful clue to the cause of the problem. In this case however, it is important to make sure the analyser records harmonic direction correctly from typical data, rather than inferring it from a non-typical waveform capture, which may only be captured due to a momentary transient, notch, or ring.

Step 3 - Look for transients
Short-term transients such as spikes, dips and sags can cause immediate failures - for example blown light bulbs, PLCs resetting or computers dropping internet connections and worse, when they lead to partial process failures, where part of a production line is affected causing back-up, overflow, perhaps spillage and general loss of control. They can also be responsible for less catastrophic though highly irritating problems such as flickering of light bulbs.

Although some transients can be slow, others can be very fast. Monitoring such sub-cycle transients requires high-speed waveform capture, and power quality analysers such as the Outram Research PM7000, offer sampling speeds in excess of 1MSPS.

However, with high sampling rates it is not possible to record all the data, and so some way needs to be found of identifying the waveforms to be retained. Most power quality meters offer a threshold approach, which may mean an iterative process of setting different thresholds until the right amount of data is captured. The best systems offer a data management technology, which retains the ‘worst' waveforms over whatever is the monitoring period chosen. This avoids the need to set thresholds, simplifies setup, and significantly improves the likelihood of capturing useful data first time.

Step 4 - Compare the current and the voltage
Having monitored transients and harmonics, the engineer will have a good idea of what the problem is electrically, but may still have no idea of the cause. By monitoring the current and voltage together with good time resolution the cause of the problem can often be identified quickly. If the current and voltage rise or fall together, the problem is likely to be outside of the system being monitored, whereas if they move in opposite directions, the problem is likely to be inside.

Consider monitoring the supply at the point of entering a building - if the current spikes up and the voltage spikes downward at the same time, it will probably be because a load within the building has drawn more current, pulling down the voltage due to impedance in the transmission lines, whereas if they both move together, the fall in voltage is likely to be caused by an external load, and the local current falls in sympathy. The situation is not always simple because some modern electronic equipment, particularly those using switch-mode power supplies, can display negative resistance. Investigating the cause of a positive or negative link between current or voltage movement should add to the understanding. 
Many power quality analysers offer a fixed interval for current and voltage measurements, an approach that might cause critical information to be lost. Figure 1 shows how variable sampling intervals - in this case Outram's adaptive store technology - can identify rapid changes whilst still making effective use of the analyser's memory.

Step 5 - Undertake some detective work
At this stage we should know whether the problem is within our building or not. If we are causing the problem, then all that is required is a step by step approach to identify the culprit. This can be done by moving the power quality analyser on to monitor different loads within the building or simply by turning things off while monitoring until the cause is identified.  Sometimes problems can be revealed by their physical effects; hot spots on connections or excessive humming of transformers are typical examples.

If the problem is external, a little more detective work is required and you may need to involve the Utility Company. Some frequent causes include pumping stations, compressors, car breakers yards and welding shops, although causes can range from fixed installations or steelworks and other heavy industry to mobile equipment such as cranes.

If the source of the problem is still not obvious, then it is useful to measure the power quality at the substation to isolate the cause. Sometimes the premises next door to the cause may suffer serious power quality issues, but the impedance in the line will mean that nothing is visible at the substation.

Most power quality issues will require the engineer to repeat these steps in an iterative process - for example repeating the steps at different points in the electrical supply network to try to identify the cause geographically.

Step 6 - Confirm the diagnosis
Once the engineer has identified what he/she thinks is the cause of the problem, it is useful to see if there is any other corroborating evidence or even any contra-indications - particularly if the remedial action is likely to be expensive or unpopular!
Usually measurements will also be taken after the problem has been resolved to ensure that no lingering effects exist.

Quality of power is becoming an increasingly important issue. Utilities are penalising companies for poor power factor as the power wasted can be considerable and costly to the Power Company. Modern loads, such as electronic power supplies and compact fluorescent lights, are more and more introducing significant harmonic distortion that not only causes power to be wasted, but can ultimately shorten the life of motors, transformers and other valuable equipment.

By following a systematic step-by-step process and using the right equipment, an engineer can troubleshoot his plant for simple power quality problems. Complex issues may require more specialised expertise using instruments capable of distinguishing and recording unpredictable events, enabling unexpected or previously unencountered power quality issues to be identified.

The consequences of poor power quality include increased electricity consumption and equipment and process failure. With the ever-increasing focus on efficient operations, reducing energy costs and cutting carbon dioxide emissions, power quality issues must not be ignored.

The long awaited launch of the new low voltage switchgear and controlgear assemblies standard, happened in January of this year. Unusually for such an important document, it was issued as a technical revision, meaning it immediately supersedes the 60439 version. Craig Mckee of 3 Phase Design looks at some of the training needs created by the new standard's arrival

This new standard is a significant change from the previous one, one of the most surprising changes for some will be the removal of the terms ‘type tested assembly' and ‘partially type tested assembly', these have been replaced by ‘design verification'. With the well known seven type tests increasing to 13 design verification characteristics

A further change is that Part 1 is now ‘general rules' with Part 2 now also required to be used for all power switchgear and controlgear assemblies. Part 6 (which is yet to be published) is to cover busbar trunking as previously covered by Part 2 of the IEC60439 series.

Design Verification;
The 13 design verification characteristics are split down into two main areas, that of ‘construction' and ‘performance'. The construction tests cover such areas as:
-?Strength of materials and parts - which looks at the suitability of plastics and metals to prove the long term capabilities of the equipment.
-?Degree of protection of enclosures - referencing the same standard as before. 
- Incorporation of switching devices and components - this requires the panel builder to ensure that devices are installed in line with manufacturer's instructions.
- Terminals for external conductors -?again putting the onus onto the panel builder to ensure that the contractor will be able to terminate his cables onto the switchboard.
The performance areas cover, among others;
- Temperature Rise -?one of the biggest areas of change in the standard revolves around this area. No longer can you fit a device into a compartment and rate it at a level it would not be capable of carrying without exceeding the limits set by the standard. The standard now requires that the maximum current a circuit is capable of carrying, within the temperature limitations, is noted as its rating, irrespective of what the device manufacturers claims for the device alone.
-?Short circuit withstand strength - this is principally the same set of tests as per the previous version of the standard, with a few amendments.
-?Mechanical operation - this ensures the components of the system are mounted in such a way that through normal use, they will not fail or change the capabilities of the switchboard. In this case the test value is set at 200 operations.

After successfully completing all 13 design verification characteristics, the benchmark will be set for future adaptations of the design, since IEC61439 now accepts both verification by design rules and verification with a reference design, when carried out in line with the standard, are equal and equivalent to verification by test. This is another area of change that can be misinterpreted and needs full clarification by reading and understanding what options are open to users for each clause of design verification, since not all are acceptable under each clause.

Upon completion of the above, and moving into production, the standard requires routine verification be carried out by the switchboard manufacturer to ensure continued compliance to the design verified solution is met. These routine verifications must be carried out on each and every board that is manufactured and is principally a simplified subset of the 13 design verification characteristics, but this cannot be seen just as a job for the final QC department, since important areas such a device ratings, terminal sizes, swapping of components etc. needs to be fully investigated prior to any work being started.

The above has concentrated on the panel builder. However consultants must also be aware of the changes that IEC61439 will bring, with some being slightly more subtle than other, but nevertheless important to what can be supplied. An excellent example of this is the slightly flawed thought we currently hold of a Form 4 assembly. Currently, most people would expect this to mean a multi compartmentalised assembly with each device being housed in its own ‘zone'. IEC60439 did not give a clear account of what an acceptable segregation method was. However clarifications within IEC61439 now confirm the outer case of a device ie an MCCB is acceptable to create a Form 4 assembly, without any further segregation. If the end user and consultants require a multi compartment assembly, their specifications will need to be updated to take account of this, or they could end up with a switchboard being supplied in line with the standard, but not what they actually wanted.

With these changes, the daunting thought of reading through the IEC61439 standard with no one to give guidance, and the inevitable costs in this current economic climate, it is easy to think it will be pushed into the sidelines or lie at the bottom of the ‘to-do' list until it is too late.  Using a good quality training provider with in-depth experience in the subject matter is essential to gain the most efficient use of both time and money. With this in mind, 3 Phase design has created a training programme that explains the standard in a relevant and interesting waymaking it easier to understand -?with the added benefit of being able to give completely independent advice on any area within IEC61439, including specification checking and switchboard testing support.
www.3phasedesign.com

In a dangerous situation, emergency alarm systems (fire alarm systems or burglar alarm systems) should signal ‘actively', and remain ‘passive' in safe situations according to DEHN UK. Malfunctions of these systems (no response in case of danger, or alarm signal in case of no danger) are undesirable and expensive. False alarms sent by emergency alarm systems result in expenses, which, in the industrial countries, amount to several hundred million Euros per year. Another aspect of malfunctions is the possible direct or indirect danger to human lives. In this context, we may remember the malfunction of the fire alarm system in the tower of the Frankfurt Rhein-Main airport in 1992, where a false activation of the fire extinguishing system occurred because of a lightning strike. Within a few minutes, the air traffic controllers had to leave the control room. In this critical situation, approaching airplanes had to be redirected to other airports. Considerable delays occurred in the air traffic. False alarms of emergency alarm systems are also disturbing in another respect:
- When false alarms accumulate, the operator can no longer rely on the system and questions the significance of the system (investment) as such.
- The guard starts ignoring alarm messages.
- Neighbours will be disturbed by acoustic alarms.
- Fire-fighting forces (e. g. fire brigade) will be bound unnecessarily.
- The activation of the fire extinguishing system causes interruptions of operations.
- Damage is caused by not signaling existing dangers.

All these factors cause unnecessary expenses. They can be avoided, when possible causes for false alarms are already recognised in the design stage and are eliminated by suitable preventive measures. For this purpose, the German Insurance Association (Gesamtverband der Deutschen Versicherungswirtschaft e. V. - GDV) published VdS guidelines (VdS 2095; VdS 2311; VdS 2833). One of the measures also requested in the VdS guidelines is lightning and surge protection.

A coordinated lightning and surge protection prevents a false alarm caused by atmospheric discharges and improves the availability of the early detection of dangers and alarms. When installing comparable alarm transmission systems, for which, out of financial reasons, a VdS approval is not used (in residential building for example), the guidelines may also be used for project design and for the construction as well as for agreeing individual measures between constructors and operators. Indeed,  fire alarm systems installed nowadays have an increased surge immunity in accordance with IEC 61000-4-5 for primary and secondary wires as well as for the mains inputs. However, a comprehensive protection against damage by lightning discharge and surges can only be achieved by external and internal lightning protection measures.

Monitoring principles
Different monitoring principles are applied for emergency alarm systems:

Impulse line technology
The information from the triggering alarm device is transferred in digital form. This allows recognition of the alarm device and the exact localisation of the trouble spot (Fig. 9.9.1).

DC line technology
Each alarm line is permanently monitored according to the closedcircuit principle. If an alarm device is activated in the line, this line is interrupted and an alarm is triggered in the control and indication equipment. Hereby, however, only the alarm line can be identified but not the individual detector.

Regardless of the used monitoring principle, the lines of the emergency alarm system must be integrated into the lightning and surge protection of the complete system.

Protection recommendations
For protection of alarm lines with dc line technology, Blitzductor CT BCT MOD BE. is recommended. It is chosen according to the voltage of the alarm lines, which is normally 12 or 24 V. Blitzductor CT BCT MOD BE is recommended to avoid having to change the loop resistance of the alarm lines too much.

Regardless of the line topology, the outputs of the control and indication equipment, for acoustic and visual signalisation for example, should be protected by Blitzductor CT. Care should be taken to ensure the nominal current of the protective devices is not exceeded. In case of nominal currents > 1A, the company suggests a DEHNrail DR 24 FML protective device be used. (see Table 9.9.1). The control and indication unit is normally connected to an exchange line of a fixed-network operator by means of a telephone dial unit. For this application, the SPD type Blitzductor CT, BCT MOD BP 110 would be suitable. The surge protection of the power supply is important, too. For alarm systems, which are certified by the German Insurance Association, (systems recognised by VdS), the manufacturer of the alarm system should be contacted. The installations as well as the lightning and surge protection equipment have to be set up in accordance with VdS 2095, VdS 2311 or VdS 2833.

Conclusion
A distinct increase in the operational reliability of these systems can be reached with specific lightning and surge protection of alarm systems, including the prevention of false alarms when no danger exists, and the prevention of costs arising from this. This allows effective damage limitation by informing the auxiliary personnel reliably., counteracting potentially catastrophic conditions including danger to human lives and pollution of the environment.
In the event of injuries to persons or environmental damage, the operator of a plant is liable first. This comprehensive responsibility for security can normally be expected from managers or executives of a company. However, in the legal sense, an operator of a plant is a technical layman, who is not able to assess the potential risk involved in a technical solution. Therefore, skilled persons as suppliers of technical solutions must ensure in each individual case, the solutions offered correspond to the actual requirements.

Regardless of the fact, whether fire alarm systems are VdS-approved systems or not, they should be furnished with a surge protection.

The introduction of the new and more complex standard BS EN 62305:2006 Protection against Lightning has led to many new questions and the resurfacing of several ‘old chestnuts'. We look at a few of the most frequently asked questions fielded by Furse engineers

My building has stood for 100 years, and has never been hit.  So there is no chance of it being struck now!

Not being hit by lightning in the past has no bearing on being struck in the future. The probability of a strike and whether protection should be fitted will be shown by carrying out a risk assessment. York Minster was around 600 years old when it was ‘eventually' struck by lightning in 1984, causing extensive irreplaceable damage. Remember a direct strike to the structure is not even necessary for lightning to cause damage through fire, electric shock or electronic systems failure.

I have an air finial on the tallest part of the building and a down conductor, so that should be adequate?

This is unlikely to give adequate protection in accordance with BS EN 62305 which calls for a full Faraday Cage, comprising a number of conductors on and around the building.

My building has reinforced concrete columns. Can I use these columns as down conductors?

Yes, provided you ensure the electrical continuity of one or more reinforcing bars in each column. Where sections of reinforcing bar overlap, they should be welded or clamped together, or overlapped by at least 20 times their diameter and securely bound for the entire length of the overlap.

How do I know if my building needs lightning protection and, if so, what level of lightning protection system (LPS) is required?

There's no intuitive way of doing this - you need to carry out a risk assessment in accordance with BS EN 62305:2006 Part 2. The risk assessment in BS EN 62305-2 is much more detailed and has many more parameters than the assessment contained in BS 6651. There are software packages available that can help. Furse's bespoke risk assessment software package is called StrikeRisk. It has just been updated to version 5, and a free trial version is available to download from its website - www.furse.com

I have looked at the number of parameters required to carry out a risk assessment, but cannot find all the information. What should I do?

The risk assessment carries default values, which can be used where accurate information is not available. However, these values are conservative, so you should try and obtain as much accurate information as possible.

Why is there now so much emphasis on protection of sensitive electronic systems? This wasn't a requirement of BS 6651.

The protection of electronic systems was covered in Appendix C of BS 6651, and although this was an informative annex, the philosophy is broadly similar to that of the new standard. Our increasing reliance on electronic systems means that damage or downtime can have serious financial and operational consequences and hence their protection is reflected in the single risk assessment of the new standard..

I have a lightning conductor system on my building, so will this protect my electronics within the building?

No, this will protect the structure itself but not the electronics within it. You therefore need specialist surge protection to prevent equipment damage from LEMP (lightning electro-magnetic impulse). BS EN 62305 focuses on coordinated SPDs (surge protection devices), where the locations and LEMP handling attributes of a series of SPDs are coordinated to nullify the conducted LEMP effects - thereby protecting equipment within their environment.

Is it adequate to put surge protection on the main electrical incomer only?

Although protection of the main incomer is certainly recommended, other services should be considered for protection against transient overvoltages (surges). For example, a lightning strike up to 1km from a building can transfer huge voltages onto overhead or underground cables - like data or telephone lines - through inductive or resistive coupling. Once transferred to the cable, transients will flow along it, seeking a path to earth and damaging any electronic components they encounter.

I am fitting an LPS to a building, which contains no sensitive electronics systems. Do I still need to fit Type 1 (equipotential bonding) SPDs?

Yes. Type 1 SPDs (for mains power supplies) and Category D SPDs (for data/telecom lines) form an integral part of the equipotential bonding requirements for an LPS. They are needed to prevent partial lightning currents from causing dangerous sparking and the possibility of a fire or electric shock hazards. Type 1 SPDs are not designed to protect equipment, but form the first part of a coordinated SPD set further consisting of Type 2 and 3 SPDs.

For more than three decades, the design and testing of switchgear and controlgear  assemblies has been governed by IEC 60439-1. In 1999, the IEC started a thorough overhaul and full restructuring of this series of standards within the SC17D/MT11 committee. In January this year, parts 1 and 2 of IEC 61439 were published. certification body Kema looks at the new standards' progress

Kema's project manager for industrial components, Henk Kormelink, explains: "The first thing to note is, although the new IEC standards already apply in many parts of the world, they are still awaiting European ratification. Furthermore, in the current transitional period, the choice whether to apply the old or new versions rests with switchgear customers. Eventually, of course, the new standard will prevail".

Kema is thoroughly familiar with the requirements of the new standard. Kormelink is a member of the IEC SC 17D MT11 committee, which is responsible for restructuring the IEC 60439 series. In this way the company contributes to the improvement of the standard by bringing in its experience as a test and certification body and its familiarity with the operations of equipment manufacturers. In fact, he is one of the few representatives of test and certification bodies on the committee and is thoroughly familiar with the requirements of switchgear manufacturers.

The old standard, IEC 60439-1 (Low-voltage switchgear and controlgear assemblies - Part 1: Type-tested (TTA) and partially type-tested (PTTA) assemblies), covered the design and testing of a wide range of equipment. This standard put the emphasis on testing of TTA assemblies, which led to difficulties when revising designs or substituting components. How should a PTTA assembly be verified? This resulted in a situation in which many PTTA systems in the market did not fully comply with the standard. The old situation made it particularly difficult to apply the standard to variants of type-tested assemblies. To prove compliance with the old standard for partially type-tested assemblies was difficult, or at least not very clear.

The new standard provides clear rules for dealing with design variants and component substitutions and can therefore provide end-users with greater certainty that their equipment meets the requirements. Kema is working with a number of large customers to recertify existing products to the new standard and to adopt it in new projects.

Wider scope
The new IEC 61439 standard has a different structure, in that Part 1 includes the general requirements, while Parts 2 - 6 address specific types of equipment. Now this structure is aligned with the IEC 60947 series of standards. Under the new standard, the TTA and PTTA definitions have been removed and now tests can be combined with calculations or design rules to demonstrate that equipment meets the requirements. This is the most important change in the new standard. As a result, the standard now specifies how some changes can be made to equipment without requiring new type tests. This can clearly save a great deal of time and money and is particularly relevant to modular switchgear. More assemblies now meet the requirements and the old partially type-tested assemblies in particular are now covered much more effectively.
The two new standards published so far are:
- IEC 61439-1, General rules (Part 1)
- IEC 61439-2, Power switchgear and controlgear assemblies (Part 2).
The following parts will be published in 2010 to 2011: 
- IEC 61439-3, Distribution boards 
- IEC 61439-4, Assemblies for construction sites 
- IEC 61439-5, Assemblies for power distribution 
- IEC 61439-6, Busbar trunking systems

Until these other parts have been published, the older standard, IEC 60439 will remain in force for the design of such assemblies.

Moving from the old to the new standard
Manufacturers should consider how best to implement the new standards in their design and test workflow. In consultation with the test and certification body they use, it may be possible to re-use test data obtained for the old standard for verification of designs under the new standard. This will reduce the costs of introducing the new standard.

However, this is more difficult with respect to the temperature rise requirements where re-using old data can lead to lower product ratings. To solve this issue, it may be advantageous to carry out some temperature rise tests in accordance with the new standard. This is an aspect panel builders will need to carefully address and discuss with their test and certification bodies.

The standard is detailed and complex, so getting advice from experts in the field is recommended. In recent months Kema has discussed the consequences of the new standard with our large customers and helped them get started with this process.

Testing reference systems
Under the new regime there is much greater scope for testing a reference system and then using calculations and design rules to prove that systems derived from this reference design also meet the requirements.

Working with a reference system as a basis for other designs is particularly attractive when dealing with many variants of the same systems as it can save significant time and costs. The new standard ensures that the performance of all assemblies can now be more thoroughly verified than before. This can be done by testing, by calculation/measurement or by satisfying design rules. Verification covers parameters such as the circuit rating, impulse rating, short-circuit rating, diversity and temperature rise

Special requirements in the Middle East
The speed with which the new standards are adopted will to some extent depend on the demand from the market. In Kema's experience, customers in the Middle East are already requesting that their products be certified to the new standard. The company is particularly familiar with this market and its requirements. In fact, they can carry out tests at non-standard temperatures such as 50°C, which is a requirement of some customers in this region.

Comprehensive service
Kema's positioning is that it can cover the whole range from low voltage to high voltage testing and has extensive in-house test facilities. Any low-voltage tests that are carried out in external laboratories are always witnessed by one of its experts. Depending on the desired degree of risk reduction manufacturers require, they can choose appropriate measures that correspond to an acceptable safety level. This approach can be applied from a simple IP test right up to comprehensive panel certification schemes such as Kema-Keur for panels and the Kema World Panel Program. All these factors combined put the company in a strong position to offer a comprehensive service to manufacturers planning to adopt IEC 61439.

Your move
Panel builders must address the issue as to when their customers want to see the new standards applied. They will then have to review their design, test and manufacturing processes and identify the changes that need to be made. Any additional testing will have to be designed, together with the test and certification body.

Furthermore, panel builders will need to update their design process to incorporate the new arrangements for verification based on the new calculations and design rules, and decide how to optimise their business processes to benefit from the new options. Clearly, any type testing should support this new approach effectively. In this way panel builders can continue to offer their customers the best product at the most attractive price, supplied in the shortest possible time.

A big step forward
In essence the publication of the IEC 61439 series is a great step forward, as the standards now fit in better with the demands of both manufacturers and their customers. The new approach means that compliance with the requirements of the standard can be verified more easily for a range of equipment, without requiring excessive testing or leading to inflexibility. Implementing the standards effectively will, of course, require extensive consultation between a manufacturer and its customers, and with the test house and certification body used by the manufacturer.

Click on the PDF below for a breakdown of the Kema Risk Reduction Building

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