Drives, motors and controls

  • Mechanical and electrical framework invitation

    Mechanical and electrical framework invitation

    Gibbons Engineering Group has announced an invitation to join the Anglian Water mechanical and electrical (M&E) framework for the awarding of planned and emergency work at local AW sites.

    This means Gibbons is one of a number of companies to be allocated M&E projects for Anglian Water. Via an online interface, Gibbons’ quoting and invoicing of jobs now becomes much more streamlined.

  • Boulting Technology named Rockwell Automation Recognised System Integrator Partner

    Boulting Technology, a systems integrator and supplier of LV motor control centres, switchgear, control panels, telemetry and pumping system optimisation services announced it has now achieved the status of Rockwell Automation Recognized System Integrator for Process . 

    Boulting Technology became a Rockwell Automation Recognized System Integrator -Control in 2009. Now, Boulting Technology has attained the Process recognition, one of only a handful in the UK. This shows Boulting Technology’s proven application expertise and demonstrated success in delivering PlantPAX into process industries.

  • New keypad makes drives even easier to use

    ABB has launched a keypad with features that make programming and operating variable-speed drives more straightforward than ever. 

  • Drives can be installed in any location

    At this year’s Drives & Controls exhibition (8-10 April – NEC), Vacon (stand G60, Gambica Pavilion)

  • PEMD 2014 -The 7th IET international conference on Power Electronics, Machines and Drives

    Join over 400 power electronics, machines and drives specialists at one of the world's most important conferences in this field. The last conference, held in 2012, attracted attendees from 40 countries, making PEMD an essential forum for international knowledge-sharing.

    Take part in detailed technical sessions on

    • FACTS & HVDC

    • Design & Modelling

    • WBG device applications

  • The drive for productivity – variable-speed drives in process improvement

    Variable-speed drives have long been known for their abilities to improve the control of industrial processes. Today’s drives offer sophisticated functions that make them an ever more vital element in the drive for efficient processes. John Guthrie looks at these functions and how they are helping companies transform their production

  • The 7th IET international conference on Power Electronics, Machines and Drives


    The 7th IET international conference on Power Electronics, Machines and Drives

    8 - 10 April 2014

    Midland Hotel, Manchester, UK

    Call for Papers deadline: 16 September 2013

  • Variable frequency drives are user-friendly, efficient and robust

    Diversified industrial manufacturer Eaton Corporation has launched its new PowerXL variable frequency drives with a rating up to 250 kW at this year's SPS/IPC/Drives in Nuremberg.

    With this launch the company is expanding its lean strategy in the machine building and panel building sectors.

  • Drives have major role in RSC automation

    The four-year, £112m transformation of the Royal Shakespeare Theatre in Stratford-upon-Avon has included a major project to automate the movements of back-drops and scenery as well as the complex system of lighting arrays.

    At the heart of the project, designed and installed by Dutch theatre automation company Trekwerk, are around 100 AC drives and servo motors from Control Techniques. The contract was awarded by Trekwerk to Control Techniques’ Rotterdam Drive Centre.

  • Energy and safety debates top of the agenda at Drives & Controls

    With only weeks to go, the NEC is set to become the focus of the largest manufacturing  and engineering event of 2012. The Drives and Controls Exhibition – co-located  with the International Fluid Power Exhibition (IFPEX), Air-Tech, and The Plant  and Asset Management Exhibition – taking place between 17-19 April  2012, at the NEC Birmingham will form part of the manufacturing and engineering  series of shows alongside MACH.

  • Drives save €1,000 a week for county council

    An ABB low voltage AC drive has cut pump maintenance costs for a local authority by €1,000 a week.

    The water services department of Laois County Council in the Republic of Ireland had problems with the sewage pump at its Connolly Street Pumping Station in Mountmellick, a town of around 5,000 residents. The foul sewer submersible pump is housed in a building at a road junction in the town and is six metres below the surface level. The location is the second largest of eight pumping stations in the area.

  • Lifecycle services lead the way for variable-speed drives future

    ABB recently appointed Neil Ritchie to head up its AC drives sales business in the UK. Neil replaces Steve Ruddell, who after 10 years in the role, has moved into a global position within ABB. For a similar duration, Neil has been managing ABB’s service activities for drives and motors. His appointment, therefore, is a timely reminder of the emphasis that manufacturers place on service to retain customer loyalty. Electrical Review caught up with Neil to see how he views the business

    Drives today are very reliable. What role does service play?

    You are right, today’s drives are clearly ultra-reliable – they have fewer components, use well proven and tested technology and have the best engineering support infrastructure. Yet, just like motor vehicles, there is a need to look after the drive and regularly service it. Like any electronic device there are components within a drive that by their nature will degrade, such as electrolytic capacitors, power semiconductors and fans. When components degrade unchecked then this has a direct impact on the drive’s ability to save energy.

  • Drives & controls - Get the facts on energy sustainability

    Cutting electrical energy use in motor-driven applications through the use of variable- speed drives (VSDs) is a well-proven method, but not everyone is getting the message. ABB takes a systematic approach to energy sustainability that provides proof of just how much can be saved

    A major part of sustainable manufacturing is using energy wisely. As energy prices continue to rise, it is becoming increasingly important to make the most efficient use of energy, both as responsible companies that care about the impact on the environment and for the future profitability of the company.

    Yet, many companies do not know where their biggest energy use is and have misguided ideas about how best to cut it. A survey of UK manufacturing managers revealed the most common method of reducing the electricity bill was to switch suppliers, yet as all suppliers are increasing their prices, this can only provide a minimal saving. Other managers cited increased compressor efficiency or improved factory heating. The real answer lies in looking objectively at where electricity is used most and assessing how it can be reduced cost- effectively.

    The elephant in the room is electric motors when you consider 65% of the total electricity at industrial sites is consumed by electric motors driving pumps, fans and compressors to name but a few.

  • Make savings with long distance drives

    Make savings with long distance drives

    The networking of drives and controllers is an accepted practice these days. Numerous network protocols are routinely employed in industrial environments across the world. Among these, Ethernet TCP/IP, perhaps by virtue of its being more synonymous with office applications, is less familiar on the factory floor than might be expected, explains Mark Daniels of Rockwell Automation.

    Unlike decidedly blue-collar protocols like DeviceNet, ControlNet and ProfiBus, Ethernet TCP/IP was not conceived primarily as an industrial protocol. But while its apparent lack of industrial street-credibility might make the ubiquitous Ethernet seem a little too much of a ‘one-size-fits-all’ solution for industrial control applications, EtherNet/IP – the industrial ‘flavour’ of Ethernet – offers enough advantages over the native industrial protocols to make it a serious candidate worthy of consideration in industrial applications.
    Ethernet as a network has been around for a long time and over that time has evolved to become a very efficient way of making information widely and easily accessible across a variety of platforms. It is, after all, the technology that forms the bedrock of the internet. Its long history and broad usage has made it a cost-effective and reliable networking solution that is readily understood by non-specialist engineering support personnel. Ethernet’s ability to move information around networks and across network boundaries also makes it a powerful tool in the industrial environment.
    It’s 2am: are your drives still running? If they’re networked using EtherNet/IP, you could know the answer in seconds, no matter where you are. Production line problems invariably happen when it’s most inconvenient. The strength of EtherNet/IP networking is that it can effectively deliver drive information and control when and where it is required. What it lacks in robustness compared to ControlNet or scalability compared to DeviceNet, EtherNet/IP more than makes up for in connectivity. But connecting drives is just the start: Because of Ethernet’s plug-and-play connectivity with the wider network infrastructure, drives connected over an Ethernet IP network are able to deliver diagnostic information via a standard web browser, just like any website. If a drive triggered an alarm or became faulty, text messages to pagers or mobile phones can be delivered via the same medium.
    The ability for information – be it diagnostic data or commands – to flow effortlessly internally and externally across network boundaries is a great strength of Ethernet connectivity. But that’s not all. In purely practical terms, there is a significant labour and material cost saving from not having racks of I/O modules and wires running everywhere just to communicate with drives.
    Drives wired using discrete or point-to-point wiring require multiple discrete and analogue I/O modules, along with the associated wires snaking through panels and panel interconnects. Users also have to take the time to buzz out wiring during installation, or again if there are problems with I/O operations later on. All of this results in increased labour time that can be avoided with EtherNet/IP networking.
    With Ethernet, a single cable removes the need to run a multitude of wires through conduit and trunking. Dozens of drives can be networked over just one cable and, once the Ethernet connection is made, functionality testing is simply a matter of ‘pinging’ the required device from any Windows PC.
    Using readily available software tools, EtherNet/IP allows facility managers to have a virtual ‘window’ into the drive, providing complete access to metering data, diagnostic values, configuration parameters and fault information. Viewing this information gives staff time to correct production issues before they can impact the rest of the process. In addition, if a drive faults, the maintenance staff will have a significant amount of information available to enable them to troubleshoot the problem.
    In a situation where a drive or motor is beginning to operate outside of established parameters, users will know because the drive or controller software can be set to inform them directly. Drive configuration options are available that can e-mail or page someone with an alarm before a problem occurs, after a problem or faults occur and after an alarm or fault has been cleared. A hyperlink included in the e-mail message can be used to launch a web browser connected directly with the drive that sent out the message.
    Additional software tools can be launched from the browser to allow complete access to the drive’s information. Not only is this a very useful facility for front-line support, but EtherNet/IP also delivers a very cost effective way for OEM’s to troubleshoot when offering support contracts. Cost savings from being able to troubleshoot online are significant because often an engineer does not need to be dispatched over long distances to repair or adjust a system.
    Readily available wireless Ethernet technology makes life even easier by allowing maintenance personnel to roam freely to wherever a problem occurs. A wireless Ethernet card in a laptop or hand-held device and wireless access points on the factory floor are all that’s required to keep ‘connected’ to the network. The laptop becomes both the means of alerting that a problem has occurred and the tool to fix it. That makes it a very powerful tool indeed.

  • Drives & controls - Industry vulnerable to hidden power costs

    Drives & controls - Industry vulnerable to hidden power costs

    Power quality is an unfamiliar issue for many in UK industry, but it is likely to become very well known in the near future. Power quality covers a vast range of issues from voltage excursions, frequency variations, supply imbalance and harmonic distortion. Uncorrected power quality issues can bring a host of problems from unnecessary power losses which can disrupt production through to catastrophic equipment failure. Steve Barker, energy and power quality manager at Siemens Automation & Drives, outlines the extent of the power quality problem in the UK and offers some solutions for business...

    British industry of all sizes tends to take its electricity supply for granted. A simple flick of a switch and a plant or production facility has access to the supply network which will give a business as much electricity as it requires at any time of the day, no questions asked. A whole range of equipment from machinery and computers through to lighting and electric motors rely on the mains supply network with little thought given thereafter, other than paying the bill.
    However, the use of increasing levels of electronic equipment by business is causing a phenomenon called “harmonic distortion” on the UK electricity supply network. Harmonic distortion is caused by non-linear loads on the electricity supply system, such as personal computers, lighting systems, switch mode power supplies and variable speed drives.
    Regulation ER G5/4-1, published by the energy networks association (ENA) is the UK’s instrument to control this distortion and to assist compliance by business with the harmonised network standards such as the European EN50160 (it is important to note however that the UK measures are more severe than in the rest of Europe).
    ER G5/4-1 which was first published in 2001 and subsequently updated in November 2005, is the UK’s attempt to control harmonic distortion back onto the supply network and is the updated version of the earlier ER G5/3 which was originally published in 1976. Ironically, many of those businesses affected by power quality issues remain unaware of the original regulations let alone the updated version which are far more stringent.
    The updated regulation is far more onerous than previous regulations and specifies voltage and current limitation to which all industrial sites in the UK must comply in a three stage approach which takes into account different sizes of installation. Stage 1 applies mainly to small commercial installations supplied from the public low voltage network. Most industrial sites are typically assessed under Stage 2. Industrial sites of large users may fall under Stage 3 which applies for incoming supplies taken at 33kV and above.
    Excess harmonic distortion on a site can lead to two types of problem. Firstly, ER G5/4-1 compliance issues which can ultimately result in disconnection if remedial measures are not taken. More often than not, electricity users are not familiar with compliance issues and attempts by a company to achieve compliance with ER G5/4-1 can consume huge resources of time and money. I have personal experience of a number of installations where compliance issues have been tackled badly and the remedial measures have been more costly than early preventative considerations. One example involved a company foregoing a £50k investment in preventative measures that could have saved a small food and beverage company in the North of England around £1m – a figure which was later spent on mandatory remedial issues to correct the problem.
    Secondly there are a number of practical issues for end users involving power frequency harmonic distortion that can cause often hidden problems which can include:

  • Drives - Successful motor and drive combinations

    Drives - Successful motor and drive combinations

    Variable speed drives bring great advantages in controlling motors but care needs to be taken to match the characteristics of the drive to the motor to ensure the combination is a winning one. Geoff Brown, drive applications consultant for ABB investigates

    Of the approximately 10m motors installed in UK industry, only some 3% are controlled by variable speed drives. Despite the huge energy savings to be gained, often in excess of 50%, many companies are still not making use of variable speed drives to run their motors.
    Yet, process operators cannot simply connect a drive to any old motor and expect huge energy savings overnight or even a successful motor and drive match.
    To minimize the risk of selected motor failing, users need to understand the required operating and environmental characteristics of the application. Motors have to cope with all sorts of environments, from high ambient temperatures, to being immersed in sewage, to operating in dust or gas hazards.
    Special designs exist for all of these cases and the user must ensure he follows the motor manufacturer’s instructions. Getting all the help you can from motor and drive manufacturers is also a good idea in general; their experience with motors and drives will help find the most compatible motor and drive combination. Many will have local service representatives who can assist with setting up the drive. Users installing their own drives need to read up about the issues that exist when connecting AC motors and drives.
    Drives and their effects on motors
    Variable speed drives come in standard voltage ratings, which must be chosen to match your line voltage. In general, the lower the voltage, the easier it is on the motor.
    The high switching rates of inverter power devices can place a rain of high switching voltage pulses at the motor terminals, which will cause an electrical stress on the windings, which is partly dependent on the length of the cable connecting the inverter to the motor. The drive manufacturer will usually advise on the maximum practical cable lengths between 15m and 300m depending on the power rating. In some cases long cable runs may also require additional drive components such as du/dt filters. Long cable runs can also lead to EMC issues.
    Because a higher carrier frequency means more frequent pulses, a useful feature of the drive is an adjustable carrier frequency. Lower carrier frequencies place lower stress on the motor insulation system and reduce the incidence of damage due to bearing currents. However, higher carrier frequencies have a positive effect on reducing motor noise levels. Some switching strategies such as direct torque control have no fixed carrier frequency, which can also help, while ensuring a low noise spectrum.
    Frequency converters with non-sinusoidal current can also cause additional losses in the motor and an increase in motor losses of up to 15% was not uncommon in early PWM inverter designs, which translates into an overall reduction in motor efficiency of up to 1%.
    Modern inverter designs still increase motor losses, beyond those of a true sinusoidal supply, but in practice the effect is less than that caused by connecting to the supply network.
    Major factors causing an apparent reduction in output with modern drives is the fact that the output voltage is lower than the input voltage, due mainly to the presence of chokes and other components used to limit harmonics, and the improved switching patterns in the inverter. The reduction in voltage can often be compensated by using a low harmonic “active rectifier” drive solution.
    Choosing a motor for
    drive operation
    Given these points, how do you go about choosing a suitable drive for a motor? Firstly, always choose a good quality motor. High quality materials will extend the life of a motor, as well as improve efficiency. Look for thinner core plates giving lower iron losses, good slot fill giving improved stator performance, good bearings reducing rolling resistance. Reduced losses make for smaller fans, cutting noise and windage losses.
    Another important quality factor is the level of insulation of the windings. Voltage stress acting on microscopic air bubbles in the winding varnish can cause ionization flash-over, known as a partial discharge, breaking down the insulation. Different insulation materials can withstand different levels known as the partial discharge inception voltage (PDIV), so you need to make sure the insulation level is adequate. Standard motors commonly have a PDIV in the region of 1350 to 1600V. A higher withstand voltage is better in variable speed drive applications. Unfortunately as yet there is no common visible classification on a motor nameplate, the use of Class B, or F or H materials does not in itself confer a specific PDIV withstand level.
    Inverters also have common mode voltages in their outputs, which can give rise to induced voltages in the rotor, and if the path is not blocked can give rise to circulating currents, which can destroy bearings. This problem is solved by breaking the circuit by using insulated bearings.
    Choose the right combination for the environment
    A particular concern is the use of variable speed drives to power motors in hazardous areas. The main sources of risk are high surface temperature and sparks in either the winding or the bearings. This can result in increased temperature rises and higher voltage stresses on the motor insulation. These increase when self-cooled motors are used, as the speed of the cooling fan is reduced along with the motor speed.
    These factors can combine to create a source powerful enough to ignite an explosion. The best way to reduce this risk is to choose a combined Atex package, which gives end users the assurance that the motor and drive combination is optimised for their application.
    Note that the application of a drive with an existing, pre Atex motor is at the owners risk, and possible only in a Zone 2 area. In any case the product certification is the responsibility of the motor manufacturer.
    This practice of supplying matched drive and motor pairs is a growing trend and one that progressive vendors have adopted to help cut users’ workload to a minimum.
    Choose high efficiency
    The efficiency of the motor is always a major factor in the choice. Although a VSD will bring system efficiency gains, it will not compensate for a poor or inefficient motor. Always use the highest efficiency motor possible. Ideally, the motor should have a good efficiency across the load range.
    Motor power plays a major part because AC motors work at their peak efficiency over a limited range of their power output. Modern EFF1 electric motors usually produce peak efficiency at around 75 per cent of rated load. By contrast, older designs often have peak efficiency in a very narrow band around full load.
    This is important in energy saving installations because the object of a drive is to vary the speed of the load, especially with centrifugal fans or pumps. The time spent running at full load will therefore normally be limited to emergency situations, such as extracting smoke in the event of a fire.
    A new high efficiency EFF1 motor rated at 90kW with 95.2% efficiency, will cost around £5,900 and will use electricity costing around £37,250 per year, but will save nearly £9,000 compared to a standard efficiency EFF3 motor with 93% efficiency, over a 10-year service life. For companies operating large industrial complexes with many motor driven machines, such savings can mean tens of thousands of pounds, and tonnes of CO2 emissions annually.
    Although an existing motor already in place can usually be used with a drive, it may not be known how well the motor has been treated and higher efficiency may be gained by using a new motor.
    Choose the right speed profile
    It is important when designing a system to consider the motor as a source of torque. Torque equates both power and speed, and with variable speed it is the torque profile which is of importance.
    The two most common profiles are variable torque and constant torque. The first is used for centrifugal fans and pumps while the second is used for conveyors, extruders, positive displacement pumps, and similar loads.
    Variable torque loads are the easiest applications for motors and drives because load power is governed by the cube of the shaft rpm for centrifugal loads acting with little static head.
    It is also worth considering most load machinery is designed for sale in both 50 Hz locations such as Europe, and 60 Hz locations such as the US. Due to this the best efficiency is often between 50 Hz and 60 Hz nominal speeds, i.e. between 1500 and 1800 r/min. A variable speed drive allows this to be exploited. The freedom to select the output shaft speed can also be used to advantage to eliminate inefficiencies in belt drives.
    Constant torque can pose problems because in order to maintain a constant torque at low speeds, the motor needs to be supplied with a relatively constant current throughout its speed range. This mode of operation will continually produce more heat, which will need to be dissipated at low speeds.
    The current ratings of the inverter must also match the motor’s current requirements both at full load and during acceleration. The drive’s current rating and its suitability for the motor needs to be checked with the motor manufacturer, especially on motors operating below 30Hz and whenever acceleration torque is critical.

  • Drives - Energy management with Intelligent motor control solutions

    Drives - Energy management with Intelligent motor control solutions

    Rising energy prices are motivating industry to explore new methods – such as energy-efficient motor control solutions – for lowering operating costs. Engineers and consultants are tasked with selecting the most reliable motor control solution with the lowest total cost of ownership, which must take into consideration lifetime costs such as installation, operating efficiency, maintenance and energy use, explains Jonathan Smith, field business leader for power control at Rockwell Automation

    - Since over 80% of pump and fan applications require control methods to reduce flow to meet demand, those applications are crucial to savings. Process engineers commonly use fixed-speed controllers and throttling devices such as dampers and valves, but these are not very energy efficient.
    Variable-frequency drives (also known as adjustable speed drives) offer an alternative that will both vary the motor speed and greatly reduce energy losses. Advancements in drive topology, careful selection of the hardware and power system configuration and intelligent motor control strategies will produce better overall operating performance, control capability and energy savings.
    Things to consider when choosing a motor control solution include peak-demand charges, operating at optimised efficiency, power factor, isolation transformer cost and losses, regeneration capabilities, synchronous transfer options and specialised intelligent motor control energy-saving features.

    Beat peak-demand charges
    It’s important to be aware utility companies charge higher peak-demand electricity prices when companies exceed a preset limit or base load of electricity. Peak demand charges often occur when industrial motors draw large peaks of current when started across-the-line. Variable frequency drives (VFDs) help reduce the peaks by supplying the power needed by the specific application, and gradually ramping the motor up to speed to reduce the current drawn. The VFD also automatically controls the motor frequency (speed), enabling it to run at full horsepower only when necessary. Running at lower speeds and power levels during peak times contributes to a reduction in energy costs and increased operating efficiency.
    Kraftwerke Zervreila, a hydroelectric power generation plant in Switzerland, was causing a 20 percent under-voltage condition and line flicker on the electrical grid every time it started its 3.5 MW synchronous water pump motors that drew 1,600A in full-voltage starting conditions. In 2000, Zervreila retrofitted its 40-year-old motors with Allen-Bradley PowerFlex 7000 medium-voltage drives, which limited their starting current to 200A, greatly reducing its peak energy demand.

    Optimise power usage
    In addition to starting the motor, also consider how energy-efficiently the pump or motor operates. In applications where motors are unloaded or lightly loaded, VFDs can deliver additional energy savings and performance capabilities. Centrifugal loads, such as pumps and fans, offer the greatest potential for energy savings when applications require less than 100 percent flow or pressure. For example, significant energy savings can be gained by using VFDs to lower speed or flow by just 20%. If this reduction doesn’t impact the process, it can reduce energy use by up to 50%, which in many operations, can equate to substantial energy savings.
    Energy consumption in centrifugal fan and pump applications follows the affinity laws, which means flow is proportional to speed, pressure is proportional to the square of speed, and horsepower is proportional to the cube of speed. That means if an application only needs 80 percent flow, the fan or pump will typically run at 80 percent of rated speed. But at 80% speed, the application only requires 50% of rated power. In other words, reducing speed by 20% requires only 50% of the power needed at full speed. It’s this cubed relationship between flow and power that makes VFDs energy savers.
    Energy savings can also be realised by managing input power based on system demand. Vattenfall Europe Mining AG, in Germany, modernised the overburden conveyor systems of its open pit coal mine with 6.6kV Allen-Bradley PowerFlex 7000 medium voltage VFDs. The drive’s inherent regenerating capability allows fast, coordinated deceleration without the need of braking components and without wasting energy. The optimised conveyor loading (OCL) ensures system efficiency by using a material tracking system across an array of conveyors to continuously adjust speeds so that the conveyor belts are fully and uniformly loaded. A partly loaded conveyor wastes energy and causes unnecessary wear.
    Vattenfall’s biggest benefit is the reduced amount of installed drive power. Before modernisation, the conveyor required six fixed-speed controllers at 1.5MW each, totalling 9MW to start the motor. The conveyor with a variable speed solution now uses installed power of only three units at 2MW each, for a total of 6MW to generate a smooth start.

    Power factor makes a difference
    Power factor and how it affects displacement and harmonic distortion is an important consideration in drive selection. Drives that are near-unity true power factor translate to reduced energy use. Leading drives produce a 0.95 power factor or greater throughout a wide operating speed range. An example of the effect of power factor on energy cost compares two 4,000hp drives, one with a true power factor of .95 and one with a true power factor of .98. The annual operating cost for 8,760 hours of use at

  • China drives electric

    China drives electric

    The 2004 Michelin Challenge for sustainable mobility was held last week in Shanghai. More than 150 vehicles took part with 70 of them electric-driven, of which 46 were built in China.

    The high number of battery electric, hybrid-electric and fuel cell-electric cars showed the access to advanced technology enjoyed by Chinese carmakers and academic institutions.

    North American, Japanese and European electric-drive entrants included Audi, Volkswagen, Peugeot, Ford, Toyota, Volvo, GM, DaimlerChrysler, Hyundai, and Nissan. Michelin, which founded and sponsors the annual event, entered its own EV’s, built in cooperation with Swiss-based PSI.

  • New benchmark for large drives

    Silverteam will be using the Drives & Controls show to launch the high power versions, 160kW to 400kW, of the Hitachi SJ700 variable speed drive - small and medium sized version having been introduced in 2007.

    The SJ700 is a radical development of drives technology, it being the first off-the-shelf unit with integral easy sequence programmable functionality (EzSQ) as standard.

    Perhaps the first notable thing about the SJ700 is its compact size, an increasingly important issue as users and systems buiders seek to reduce control panel size. It also incorporates a patented power switching technology to reduce dVdT, with the IGBT (insulated gate bipolar transistor) stack at the heart of the drive. High dVdT is associated to motor insulation breakdown by the increased terminal voltage of motors when used with AC drives.

    The smaller drives caused a stir in the market when launched last year, and the new large drives are expected to be even better received.

    "Large drives tend to be installed and used for many years so can look very dated by the time they are replaced," explains Stuart Harvey of Silverteam, Hitachi's Drives and Automation Company in the UK. "The SJ700 resets the benchmark for small and medium sized drives, offering multipoint positioning and near servo performance from a standard induction motor. The 160kW-400kW SJ700 makes similar performance available right through the power range.

    The SJ700 is a sensorless vector drive, with 150% torque at zero speed and near total immunity to motor constants problems. It sets new levels of responsiveness and accuracy and includes enhanced autotuning for increased ease of set up. An optional feedback card can be used to close the vector loop for even finer control.

    "The built-in EzSQ functionality provides a very powerful controller that negates the need for an external unit such as a PLC in even the most demanding of applications," says Harvey. "Its communication with both the external system and the drive's internal circuitry is naturally very fast and very secure. This enhances operational performance all round."

    The large SJ700s should set new performance standards in water pumps, fans, hoists, lifts and many other applications. "With lifts, for example, we can offer very smooth floor transitions with adjustable S ramps and brake release confirmation signals, while the superior torque and speed control make it particularly suited in hoist applications like cranes or theatre flying systems."

    The SJ700 also offers notable benefits for applications where high performance is not critical. "There are savings because you don't have to buy a separate PLC, panel space savings, installation and commissioning time savings and an increase in reliability."

    Hitachi has designed the SJ700 for a working life of at least 10 years. As Harvey puts it: "Every detail has been looked at to design out possible failure modes. The patented switching is just one example of this.

    "We tested all the leading drives with many different makes of motor. Voltage spikes leading to insulation breakdown was always a potential problem particularly with cable runs over 50m, so we gave the designers the targets of reducing problems to negligible levels and for the drives to be usable with cables over 100m long without line reactors. To achieve this they could not refine existing techniques, so they had to develop next generation technologies."

    Other features of the SJ700 include brake transistors on sizes up to 22kW , integral EMI/RFI filters across the whole range, a full range of comms options, customisable display panel, intelligent energy saving, active frequency matching for restarting and flying load catching, regenerative braking under E-stop conditions and full RoHS compliance.

    Silverteam Limited

    Tel: +44 (0)1493 669879

    Fax: +44 (0)1493 669647

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

  • Drives & Controls - Saving energy through drive system efficiency

    Many pump and fan systems are designed with safety margins which can make them grossly oversized. This in turn leads to inefficient use of energy, but the efficiency can be vastly improved with the use of variable speed drives

    Of all the resources used in modern manufacturing, energy is arguably the most fundamental. This resource has long been taken for granted, but rising energy prices and concerns over greenhouse gas emissions are increasingly leading users to critically assess their energy usage.

    In many technology areas, significant energy savings are difficult to achieve and gains of a couple of percent are then celebrated as breakthroughs.
    There are technologies, however, that can deliver very significant reductions in energy use. Foremost among these is the variable speed drive. It doesn't make much noise or develop extreme temperatures or go through complex motions. In fact it sits in a cabinet and usually doesn't even get a mention when the overall process is explained. However, it can deliver great cuts in energy consumption, frequently nearly halving the consumption, and if applied in all relevant plants worldwide, it can deliver energy savings that equate to the electrical consumption of a country such as Spain.

    The principle is simple: In the past, the motors that powered pumps were usually run at full power all the time, with the output controlled with valves. A drive regulates flow through direct control of the electrical power fed to the motor, so eliminating friction-based controls and the associated losses.

    The lack of system standards
    However, a lack of system standards for energy efficiency may result in up to 90 percent of pump installations being incorrectly sized, leading to energy waste.
    "We have standards for everything," you may argue. However, in the area of energy efficiency there are still important gaps. While there are standards for pump designs and many for the hydraulic data such as developed head, efficiency and net positive suction head, a search for standards providing guidance in system design is less likely to produce a result.

    To use an analogy, if somebody were to buy a three-ton truck for use on shopping trips, it would do the job, but would not be a demonstration of energy efficiency - even if the truck selected boasted the best efficiency figures for three-ton trucks. 

    When planning a system, there is a degree of uncertainty as to the shape of the system curves (friction, pipe cross section changes and the number of bends in the final pipe layout all take their toll). These factors all add to the risk that the expected operating conditions will not be met. There are three basic ways to address the changed operating conditions: 
    - If the changed condition is permanent, then the pump or fan size should be changed to match the load. 
    - This adds to the installation cost
    - The pump or the fan speed can be changed, or the impeller can be modified. 
    - A throttling device (such as a valve, damper or guide vane) can be added. 
    - Both of these options can waste energy. 

    The cost of energy is the all-dominating part of the lifecycle cost of a pump or a fan. Energy consumption is the best place for optimization to start.

    How systems get over-dimensioned
    Systems get oversized throughout the design process, but variable speed drives can be used to conserve energy.

    Despite careful analysis and design, many systems do not operate optimally. One reason is that many systems are simply sized too large to start with, resulting in higher operating and investment cost. To illustrate this, the case is considered of a system with a fan in a process plant.

    In this example, it is assumed that the ‘true' nominal condition for the application is 100 units of flow, requiring 4000 units of pressure. 
    In order to be on the safe side concerning the maximum flow, the figure for the fan communicated to the engineer is 110 units of flow. With the assumed system curve, this would require a fan with a higher capacity that can deliver 110 flow units and 5000 units of pressure. 

    When establishing the fan capacity, the engineer estimates the overall pressure drop that these 110 flow units will cause. The pressure drop value that is calculated is increased by a 10 % margin because is difficult to foresee whether the assumed number of bends in the duct will conform to that estimated (possibly the installation contractor will have to add bends to avoid other equipment). Also, the cross-section of the duct may be uncertain. A smaller cross section would lead to a higher pressure drop. This therefore means that a 10 percent margin is not unreasonable. 

    So what data are finally sent out in the requests for tender? Flow: 110 units at a pressure of 5500 units. Even if the original assumptions were correct, the fan is now grossly oversized. At 100 units flow the necessary additional pressure drops over the damper must be about 2800 units. This corresponds to 70% of the assumed correct total pressure. However, it is rare that 100% of the design flow will be needed other than for very short bursts. Assuming that most of the time, 80% of the flow rate will be required; the additional throttling needed across the damper will be about 6000 units. This corresponds to 150% of the assumed correct total pressure.

    The steps illustrated in this example are more common than they may seem. An additional factor is that, when it comes to the selection of a fan, this choice must be made from a standard range of fixed sizes. The next larger one will usually be chosen, with a motor sized to suit.

    The correctly sized fan for this example at point ‘g' should be 100 × 4000 = 400,000 power units, and the normal running at point "l" will require 80 x 2500 = 200,000. The case above produces a requirement for a fan of at least 110 x 5500 = 605,000 power units (150% of the optimum). Correcting this with damper control leads to high levels of wasted energy. The additional losses at the 80% flow point amount to 80 x (8100 - 2500) = 448,000 power units (120% of the full power of a correctly sized fan). These figures will in practice become worse, because the fan will not be working at its optimum efficiency throughout the operating range. With a speed controlled fan instead of damper control, nearly all of this energy can be saved.

    Old pumps given energy boost
    The Corus site at Port Talbot in Wales is one of the biggest steelmaking plants in the UK with an annual output of 5 million tonnes. Energy is Corus' second highest cost after raw materials. The costs and revenues of the business are fairly fixed, so high productivity is crucial to stay competitive.

    As part of a plant-wide energy saving programme, 24 ABB industrial drives, ranging from 140 to 400 kW, are being installed to control pumps on the hot strip and cold mills, plus three fans on the coke ovens. The pumps recirculate cooling water in the mills, while the fans are used for dust extraction at the coke ovens. The cost of the drives about £1m; the whole project including pumps, cabling etc. is around £2.5m.

    "The pump and fan motors were clearly oversized and running longer hours than necessary," says Guy Simms, leader of the energy optimisation team. "Much of the equipment on the site was installed during the sixties, seventies and early eighties. At the time, it was common practice to oversize the equipment by as much as 50%, to make sure it was sufficiently robust. In many ways this was a successful policy - after all, it has lasted all these years. But with the ABB drives we are now installing, we can fine-tune the applications to a degree that just wasn't possible in those days."

    The applications have varying demand but until now, the pumps and fans have been running continuously at full speed. Running to demand will not only reduce energy costs, a million pounds in annual energy savings is expected, but also save water and improve control, particularly of the cold mill, which could potentially result in better product quality.
    In any process where a restriction is used to control flow, energy can be saved, and in any process where volume can vary, energy can be saved.

    Picture top right: 24 ABB drives, controlling pumps on the hot strip and cold mills, plus fans on the coke ovens, will be saving a million pounds in energy annually at Corus Strip Products in Port Talbot

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