Power Transformers. Your partner in energy solutions

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1 Power Transformers Your partner in energy solutions

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3 Contents CG Power Systems. Smart Solutions, Strong Relationships 5 Transformer design 6 Quality Assurance 8 Core construction 9 Windings 10 Insulation 12 Core and coil assembly 13 Tanks 14 Processing of core and coil assembly 15 Oil preservation system and fault protection 16 Tap changing 17 Cooling 18 Testing 19 Shipping and Installation

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5 CG Power Systems. Smart Solutions, Strong Relationships The CG Power Systems Group ranks as one of the world s top manufacturers of threephase transformers. A certified full-line supplier, the Group has production plants on three continents, an annual productive capacity of 40,000 MVA, and a worldwide network of sales offices and specialized agents serving customers in over 135 countries. More than 500,000 CG Power Systems transformers are currently in use throughout the world. A consolidated annual turnover of more than US$500 million, reflects the international efforts of the companies more than 2,300 employees. From its base in Mechelen, Belgium, CG Holding Systems acts as the overall holding company, defining the Group s corporate strategy. The Group s full range of transformers consists of: > > Liquid-filled distribution transformers for the distribution of electricity to consumers (15 kva to 10,000 kva / 36 kv) > > Cast resin transformers (up to 10,000 kva / 36 kv) as an alternative to liquid-filled distribution transformers, with the emphasis on reduced environmental impact and increased fire safety > > Power transformers (up to 750 MVA / 500 kv) for the transmission of electrical energy > > Auto-transformers (up to 400 MVA / 500 kv) > > Transformers for HVDC stations (up to 315 MVA / 500 kv DC) > > Specialty transformers like zig-zag transformers and phase angle transformers > > Multiwinding transformers for dedicated solar power generation Our new power transformer plant in Washington, MO is a new addition to the multiple production facilities already existing in the world, and underlines the high quality and edge technology that our group represents. Being the amongst the most advanced manufacturing facility with enhanced clean production areas, robotics and a computer supported test facility, it will take a long time before this plant will find its equal in the current market.. With a production capacity of 200 units per year at an average of 25 MVA, this plant is built around the efficient delivery of small and medium power transformers, to be able to meet the stringent delivery and quality requirements of our customers in a very competitive environment as is North America. < View of active part assembly hall (CG PT Mechelen) - 5 -

6 13/ /17 16/17 13/ /19 18/ / /19 1 LS KADER 13/ (10) 7(8) 24 U V W 5(6) 24 11(K) 1(2) 3(4) Transformer design Our designers are familiar with all international and national standards such as ANSI, NEMA, CSA, IEC, BS, since we supply our transformers throughout the world. Every transformer is individually designed to its specific requirements and applications. The following specially-developed computer programs are used to further ensure the reliability of the product: > > optimization of design in relation to labor and material costs, loss evaluation and sound level, > > distribution of voltage stresses under lightning impulse and switching surge conditions, > > behavior during short-circuit conditions, > > analysis of those areas where high electrical stresses can occur, > > calculation of stray losses and thermal effects. Should seismic withstand be required, CG Power Systems can provide either a static or a dynamic design analysis to prove that the transformer can withstand the specified conditions. Many CG Power Systems transformers have been subjected to short circuit tests since more than 40 years, and such test data supports the innovative and exceptional know-how developed within the group s core engineering team. Design Team Before being issued to the plant, new designs are reviewed by a team consisting of representatives from Engineering, Quality Assurance, Manufacturing, Testing, and Research and Development. Each design remains the responsibility of the individual project engineer, who carefully follows and checks progress throughout the manufacturing process. Together with a dedicated order administration team, this approach ensures the one thing that CG Power Systems stands for: we build our teams to serve our customers. Mechanical designers use 3D design software < U 1V 1 W Experience CG Power Systems expertise is extensive in the design and manufacture of standard and special transformers, and includes production of EHV units. The first EHV 500kV unit was shipped in 1970, and many have been shipped since then within and outside North America. The production plant built in Washington, MO, USA, is a beautiful spin off of the known technology and experience of our plants in Belgium, Indonesia and Canada. Technological exchange within the group, and regular meetings between engineers of these plants ensure that we employ the best practices in all of our plants for the benefit of our customers. These efforts are translated in the lowest failure rate worldwide for power transformers U 1V 1 W Design of the leads - 6 -

7 Design transformed into reality - 7 -

8 Quality focused operations CG Power Systems goal is to build products which perform safely and reliably, meeting the requirements specified by its customers and providing excellent life cycle value. The establishment of measurement standards and inspection procedures is only one step towards this goal. The major step is the complete commitment of all employees towards the entire concept of quality. All CG Power Systems plants are ISO 9001 certified. Certification was achieved through recognized institutes such as AIB Vincotte, Kema or the Canadian General Standards Board. Shortly after the start of production in our new power transformers facility in Washington, MO, we were promptly awarded with an ISO 9001 award, becoming this way the plant with the shortest ISO certification turnaround time in the whole group. ISO 9001 includes the greatest number and scope of quality system elements available in the 9000 series, including elements such as delivery and service. The ISO standards describe elements of quality systems which are designed to ensure that products and services meet all requirements before they are delivered to the customer. In order to achieve registration, facilities have to document every process they follow, and successfully undergo an audit by an independent third party. Qualified employees inspect, check and sign the progressive control record book system at their particular stage of manufacture. The quality inspectors audit the system by checking various aspects of the work to ensure that the system is working correctly. They direct any corrective actions which may be required. In addition, inspectors perform incoming and final inspections to ensure that materials meet the required quality level. The progressive control record system ensures that a complete, permanent record is kept for each stage of the manufacturing process. The method of using qualified employees to perform inspections in their own area requires that they are well-trained in the procedures and purpose of the work they carry out. All employees continue to receive in-depth training in all aspects of their jobs

9 Core construction CG Power Systems transformers are of the Core Form design. All cores are stacked, using high-quality grain-oriented silicon steel laminations, purchased slit-to-width and coated with carlite to increase the interlamination resistance and to reduce eddy current losses. Where loss evaluations justify its use, laser or mechanically scribed or plasma treated silicon steel will be used. All cores utilize the step lap principle in the corner joints to reduce losses, magnetizing current and sound level. The cores are fully-mitered on all joints in order to improve the flux distribution. Ultra modern computerized core shears supply fully-mitered, high-efficiency cores. These machines are able to shear the maximum width of core steel needed for the size and voltages to be produced in our facility. The E-core cutting and stacking machines in our plant in the USA automatically stack the legs and yokes to minimize steel handling and mechanical stresses, helping to guarantee the designed loss and sound level. Smart technology ensures that any misalignment is immediately reported to the operator. to the implemented SMART technology, the core stacker will ensure the perfect round shape of the core even with variable silicon sheet thicknesses. The exposed edges of all finished cores are bonded with low viscosity, high-strength epoxy resin on the legs and bottom yoke to help lower the sound level and prevent corrosion of the slit edges. The temperature rise of the core is designed to be low and is controlled, if necessary, by careful placement of vertical oil ducts within the core packets. The core is clamped using structural steel clamps which provide high strength under both static (lifting and clamping) and dynamic (short-circuit) mechanical loads. The clamps are very lightweight for their strength and provide a smooth surface facing the winding ends, eliminating regions of high local electrical stress. Depending on the customer s needs, we can construct these clamps with either tie rod and flitch plate designs. The laminations are stacked in steps, resulting in a circular core shape which gives the windings optimum radial support, especially during short-circuit conditions. Due - 9 -

10 Making a regulating winding with twin copper conductor

11 Windings Windings are of circular design, with concentric coil placement. This arrangement provides the highest short-circuit strength while providing good cooling of conductor surfaces. Generally, only copper conductor is used in medium and large MVA designs. Conductors are either paper-covered magnet wire or continuously transposed cable. High tensile-strength conductor is supplied if required to meet anticipated shortcircuit forces. Conductor cross sections are chosen to be as large as possible to minimize short-circuit stress, while ensuring that eddy losses in the conductors are kept under control. Winding types are selected by the design engineer, depending upon the specific application. Strip, barrel, layer, helical, disc and counter shielded disc types are all available to the designer, depending on the voltage and current requirements of the design. Control of electrical stresses is achieved by placement of custom-designed stress rings on the ends of high voltage windings and anywhere else they are required. Where needed, dovetailed key spacers are employed to give the windings extra strength and ensure proper cooling. Oil flow through the windings is directed in a zigzag pattern to ensure cooling of all conductor surfaces and to limit the hot spot temperature. Careful attention is paid to ensure an even distribution of oil to all sections of all windings. Continuously transposed cable can be supplied with epoxy bonding, greatly increasing its short-circuit strength. Modern winding machines utilize fully adjustable steel mandrels to ensure tight tolerances and more efficient winding operations. The winding machines areequipped with hydraulic braking devices which ensure that the proper tension is maintained on the winding. Turn counters and a HMI interface on each machine ensures that the correct winding configuration is maintained

12 Insulation All major insulation is manufactured from the highest quality pressboard insulation material, fully oil impregnable to eliminate internal partial discharges from voids. Winding keyspacers are manufactured from precom-pressed pressboard to provide high mechanical and short-circuit strength. Care is taken in the manufacture of the insulation components to ensure that all critical surfaces have an adequate supply of oil during impregnation and service in order to limit partial discharge problems. Following completion of the windings, all coils are dried in a hot air oven and hydraulically pressed to size to obtain the design height and to guarantee full short-circuit resistance. This allows an accurate determination to be made of their final size and provides a dimensionally-stable assembly. The windings are then ready to be mated with the core, leadwork and other internal accessories. Insulation is checked during design with finite elements calculations

13 Core and coil assembly First, the prefabricated coil-to-clamp insulation is placed on the bottom clamps. The major insulation is usually of rigid form and is prefabricated in a special area, isolated from other departments to provide carefully-controlled clean and dry manufacturing and storage facilities. Coil assemblies are carefully lowered over the core legs and packed solidly to the core to eliminate any possible movement. The top coil-to-clamp insulation is then placed in position, followed by the top clamps. Windings are clamped using a system of either internal flitch plates or external tie rods. The flitch plates are heat-treated and stress-relieved and are located between the outer packet core insulation and the innermost winding cylinder. Slots are made in the plates to reduce the eddy currents and thus losses by stray inductance. Tie rods are used on small units with low insulation levels. They are located outside the core and coils and care is taken to avoid circulating currents. The core clamping is designed so that coils cannot shift during shipment and can withstand the maximum forces that may develop under short-circuit conditions. Careful control of temperature rise due to the eddy currents generated by leakage flux is taken into account in the design of the clamping structure. The top yoke steel is then carefully interleaved with the legs, and the complete assembly is clamped. Lead assemblies are then added to the transformer and all of the winding and tap connections are made. Leads and busbars are rigidly supported by transformer wood structures to withstand shocks during shipping and handling, as well as those developed during short circuits. Potential high-stress areas due to metallic supports on the clamps or tanks are reduced or eliminated during the design stage. Other special internal accessories, such as potential transformers and current transformers mounted on leads, are added at this time. Coil assembly of a 60 MVA 230/27.5/27.5 kv trackside transformer >

14 Tanks Our tank design is fully automated and made with 3D software. The software determines the optimum size and the number and location of required tank supports. Tanks are built with high strength continuous welds. T-welds ensure a proper weld quality and high strength. Occasionally a proprietary stress relief bracing is used in the corners. In some designs the corners of the tank may be rounded off to further reduce the transformer weight without sacrificing quality and reliability. Careful design choices are made with the objective to reduce the tank size and weight as much as possible, which facilitates easier handling, assembly and installation by the customer. Tanks are designed to withstand full vacuum as required by specification and are manufactured from high-quality steel plate. Facilities for lifting, jacking and pulling are provided on each transformer tank. Openings in the covers and side walls are formed by raised flanges so that bolts do not extend through the wall or cover and that water entry into the tank during inspection is avoided. Handholes and manholes are placed for easy access to interior components such as deenergized tap switches. Tank bases are either flat or have structural members which allow skidding of the transformer in two directions, as required by the specification. The tank design either uses a welded cover system, or a bolted cover. Large covers are typically domed to avoid standing water. All tanks are grit-blast cleaned to remove weld splatter, mill scale and oxides, providing an excellent surface for the adherence of the primer and paint. The inside of the tank will be painted with a white oil-resistant paint to create good visibility during internal inspection

15 Processing of core and coil assembly The completed core and coil assembly is thoroughly dried to pre-determined dew point values by the vapor phase drying process (all units above 5 MVA), providing the fastest, most efficient and most effective drying of the transformer insulation available. The vapor phase process uses the standard kerosene cycle method. In this system, kerosene is vaporized and drawn by vacuum into a heated autoclave where the transformer has been placed. Condensation of the vapor on the core and coil assembly rapidly causes the temperature to rise and allows moisture to be drawn out of the insulation by the vacuum. High temperature up to 125ºC can be used within the autoclave, due to the high vacuum (lack of oxygen) and, due to the resulting short cycle time of the process, the insulation undergoes minimal aging. When the measured core/coil temperatures, dew point measurements and the removal rate of moisture have reached the required levels, the flow of kerosene vapor is stopped and a high vacuum is used to boil off the remaining moisture and kerosene. Because so much water is removed in this process, the insulation physically shrinks in size. Following removal from the autoclave, the transformer is repacked as required and then undergoes its final hydraulic clamping to ensure maximum short-circuit strength in the finished product. Tanking of the dried core and coil will typically happen within one shift of the removal from the oven. A deep vacuum is pulled and maintained for at least 24 hours before the unit is filled with oil of extremely low gas and moisture levels, which enables immediate testing after settling of the oil

16 Oil preservation system and fault protection CG Power Systems will use a sealed tank or conservator oil preservation system depending on the size and requirement of the customer. The conservator oil preservation system Although generally specified for smaller transformers, many publications have stated the technical advantages of a conservator system over both sealed tank and automatic positive pressure oil preservation systems for larger units, these being: 1. high dielectric integrity, 2. positive static pressure on unit at all times, 3. reduced maintenance. The conservator oil preservation system uses an expansion tank to and from which the transformer oil may flow freely as it expands or contracts due to thermal cycling. This system always provides a head of oil above the main tank and keeps it completely filled. An oil level gauge is mounted on the conservator tank and indicates the change in liquid level. A silica gel breather is always installed to absorb any moisture from the outside air. Before the air comes in contact with the silica gel it passes through an oil filled trap which removes all airborne dust particles. As an option, the conservator tank can be equipped with an expandable nitrile membrane which eliminates contact between the oil and the outside air. Every CG Power Systems transformer with conservator oil preservation system is equipped with a gas collection relay (Buchholz relay). In the unlikely event of an internal fault, combustible gases will be generated in the oil which try to escape at the highest point of the transformer. The Buchholz relay is mounted between the main tank and the conservator and collects the escaping gases. If a sufficient amount of gas has been collected, a float will be activated to give an alarm signal. In case of a severe fault, e.g. a short circuit, the Buchholz relay acts as a sudden pressure relay. A large volume of gas or oil will be generated and immediately activates a second float which trips the transformer breaker. The fault pressure function of the Buchholz relay eliminates the need for a separate sudden pressure relay. the sealed tank oil preservation system With a nitrogen system, a nitrogen storage system together with pressure regulating valves will keep the pressure in the gas space constant. Varying temperatures may cause the pressure to increase above or decrease below allowable levels, at which time the system will intervene with injecting or bleeding gas. A large storage tank for Nitrogen ensures a low maintenance interval. In case of an automatic nitrogen generation system, the nitrogen is continuously extracted from the surrounding air, reducing even further the need for maintenance. CG Power Systems will supply either sealed tank (max. B.I.L. 650 kv) or conservator designs as required to meet customer needs. Sealed tank designs are available in nitrogen cushion designs, with active gas bottle make-up systems or with automatic nitrogen generation systems

17 Tap changing If required, CG Power Systems transformers can be equipped with either a deenergized tap changer, a load tap changer or with both. Should load tap changing be required, CG Power Systems can provide either a resistive bridging type or reactor type L.T.C. Both types offer a virtually maintenance free operation during the lifetime of the transformer. The L.T.C. can be installed inside the transformer tank with the diverter switch in its own oil compartment, so that no contamination of the transformer oil can occur due to arcing during switching, or can be installed in a separate compartment external to the main tank. If a resistive bridging L.T.C. is installed in the low voltage winding, it may be necessary to use a series transformer to decrease the current through the L.T.C. contacts. This configuration may even be used to further prolong the life of the switch. In case of a reactor bridging LTC, the interruptions occur in vacuum bottles. The contact life is largely increased and maintenance is avoided. Oil contamination due to arcing is avoided and biodegradable oil can be used in some cases. Detail of the selector of an in-tank load tap changer Bottom view of a mounted M III 500 Y 72.5/B 10193W load tap changer from Reinhausen A 400 MVA phase shifter before tanking. View of the six load tap changers

18 Cooling All transformers are equipped with detachable panel radiators, connected to top and bottom headers, in order to provide the necessary cooling surface (ONAN). If factors such as expected future load growth or exposure to prolonged high ambient temperatures have to be taken into account, several auxiliary cooling methods are available to increase the self cooled rating of the transformer. Most commonly, forced air cooling (ONAF) is used to increase the cooling capacity. Cooling fans are activated in one or more stages by the relay contacts of the top oil temperature sensor. Other cooling methods such as forced oil and forced air (OFAF), directed forced oil flow through the windings and forced air (ODAF) or water cooling with forced oil flow directed through the windings (ODFW) are available if required by local circumstances or the specifications. Thermal image of the cooling bank of a 750 MVA autotransformer at ONAN cooling stage

19 Testing Prior to shipment, all transformers manufactured by CG Power Systems are tested in accordance with the latest applicable standards and according to customer specifications. Most industry standard and optional tests with the exception of short-circuit tests, can be performed in-house by trained personnel using accurate and modern test equipment. Our plant in the USA is equipped with a state of the art automated measuring system. The following major test equipment is available in this facility: Impulse Testing A state-of-the-art digital impulse recording system, the Haefely HIAS system, provides the most accurate analysis of impulse results available today. Electronic recording of the impulse current and voltage waveforms allows quick mathematical comparisons to be made, including the difference between the two waveforms under scrutiny. This difference is digitally magnified and displayed, allowing small perturbations in a test to be quickly identified. In addition, the transfer function of the winding is calculated using the fast Fourier transform technique, allowing better identification and faster correction of any problems which are discovered. Accurate printed and plotted final results are quickly available. If required, printouts from the impulse waveforms can be supplied. The construction of the test area incorporates a complete copper mesh ground mat system, with extensive grounding points provided. This eliminates high impedance grounds and provides exceptionally clean test records. For precise triggering, this generator is equipped with a pressurized polytrigatron gap in each stage. For chopped wave tests, a Haefely controlled multiple chopping gap is used. Our plant is fully capable of performing lightning impulse, switching impulse and front-of-wave tests as required. Induced Testing The voltage and frequency controls are mastered through a power electronic source. The power electronic source is able to vary the frequency from 20 Hz to 1000 Hz, and through a step up transformer, its output can be varied to practically any test voltage. During the induced test, partial discharge measurements both in pc and/or µv are taken and equipment is available to locate internal partial discharges by the triangulation method. Loss Measurement The power is provided by the electronic power supplies, and the voltage is stepped up to the desired power. A capacitor bank with capacity up to 40 MVAR is switched automatically, based upon the transformer specifics to ensure a perfect reactive power compensation. Losses are measured by an automated system using high precision zero flux Current Transformers and resistive voltage dividers. This system has a fully automated digital readout and printer

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21 Testing AC Testing A test supply with an output voltage infinitely adjustable from 3-300kV is available for high voltage AC testing. To measure the applied voltage level, a digital peakresponding RMS calibrated voltmeter is used. Short-circuit testing CG Power Systems high profile on the international transformer market is amply backed up by many years of short-circuit testing at the independent test laboratories of KEMA in The Netherlands and IREQ in Canada. Such continuous successful testing underlines the know how that is used in all of our transformers worldwide, and provides you with the most reliable power transformers available in the industry. The following transformers have successfully been subjected to short-circuit tests: SHORT-CIRCUIT TESTS OF CG POWER SYSTEMS POWER TRANSFORMERS MVA HV/LV Impedance Lab Year / Kema / Kema /36 115/ Kema / Kema * 150/2x Kema * 55/ Kema /120/40 220/63/ Kema * Kema / Kema / Kema / / Kema /(63/31.5) 12.0 Kema , / HydroQuebec / /63/ Kema * 400/ Kema /40 60/10.5/ Kema /16.05/10 11 Kema /16.05/10 11 Kema /64 12 Kema * 230/ Kema 2009 * Single Phase

22 Shipping and installation Depending on transportation considerations, CG Power Systems transformers may be shipped either with or without bushings, radiators, fans, conservator and oil. CG Power Systems experience in delivering power transformers to over 135 countries throughout the world guarantees fast and reliable transportation. Installation of the transformer can either be done by the customer or by an experienced CG Power Systems Field Service Crew

23 Shipping of a complete mobile substation

24 CG Power Systems worldwide CG Power Systems USA Inc One Pauwels Drive, Washington Missouri 63090, USA T F usa@cgglobal.com -