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<p>TRANSFORMING YOUR NEEDS INTO SOLUTIONS</p> <p>DISTRIBUTION</p> <p>TRANSFORMERS</p> <p>Presentation of the Pauwels Group Construction of a distribution transformerthe ferromagnetic core the windings the active part the tank finishing operations and testing 6 10 12 14 18</p> <p>5 6</p> <p>A comprehensive product range Economic choice of transformers Transformers and the environmentlow-noise transformers leakproof tanks and environmentally sound coolants recyclable materials radical exclusion of PCBs electromagnetic compatibility optimized use of raw materials lower consumption of primary energy sources, due to the use of transformers with low losses 27 25 26 26 27 27 27</p> <p>20 22 24</p> <p>Design, specifications and standards Logistics Quality assurance Sales and customer service After-sales service Protection equipment</p> <p>28 29 30 32 33 34 35</p> <p>CONTENTS4</p> <p>Contacts</p> <p>3</p> <p>The Pauwels Group is one of the worlds leading transformer manufacturers. Group companies operate manufacturing plants and sales offices in three continents, with a worldwide network of sales agents and customers in over 135 countries.</p> <p>From its base in Mechelen, Belgium, Pauwels International N.V. acts as the overall holding company, defining the Groups corporate strategy and coordinating the marketing of its entire product range. The Pauwels Group is a full-line supplier, offering a wide range of transformers consisting of: liquid-filled distribution transformers (15 kVA to 10,000 kVA/36 kV) cast resin transformers (up to 10,000 kVA/36 kV) power transformers (up to 575 MVA/500 kV) auto-transformers (up to 400 MVA/500 kV) HVDC station transformers (up to 315 MVA/500 kV DC)This brochure provides information about Pauwels liquid-filled distribution transformers. Our distribution transformers are usually filled with mineral oil. As an alternative, silicone liquid or synthetic organic esters may be used as insulating medium and coolant.</p> <p>PRESENTATIONThe Pauwels Groups six manufacturing plants are located in Belgium (Mechelen and Gent) Ireland (Cavan) the United States of America (Washington, Missouri) Canada (Winnipeg, Manitoba) Indonesia (Bogor, Java) In Saudi Arabia, distribution transformers and compact substations are built under license from Pauwels. Pauwels International N.V. and its subsidiary companies employ a total of over 2,300 people, producing some 30,000 transformers each year with a total output of more than 35,000 MVA. Pauwels International has a consolidated annual turnover of some 350 million euros, over half of which represents exports from Europe. More than 500,000 Pauwels transformers have been produced since the companys formation in 1947. Pauwels Trafo Service S.A. (Charleroi, Belgium) provides transformer installation, repair and maintenance services.</p> <p>of the Pauwels Group</p> <p>Main factory and headquarters of the Pauwels Group in Mechelen, Belgium (49,500 m2)</p> <p>Pauwels Contracting N.V. (Mechelen, Belgium) specializes in building conventional, mobile and modular substations, and its core activities also include transmission line projects. Distribution transformers are manufactured in Mechelen, Belgium (100 kVA to 10,000 kVA/36 kV) Cavan, Ireland (15 kVA to 630 kVA/36 kV) Washington, USA (45 kVA to 10,000 kVA/69 kV)</p> <p>Winding area in Pauwels Trafo Ireland</p> <p>5</p> <p>The construction of a transformer comprises two active components: the ferromagnetic core and the windings. Within the transformer industry, the core and windings together are normally referred to as the active part. The passive part of a transformer is the cooling system, consisting of the tank and the cooling liquid (mineral oil, silicone liquid or synthetic organic esters).</p> <p>The reactive power dissipation can be lowered by limiting flux disturbances and minimizing air gaps in the joints between the core legs and the yokes. This is achieved by overlapping the core sheets while stacking them (see page 9 under Cutting and stacking of the core sheets).</p> <p>CONSTRUCTIONThe heart of the matter: the ferromagnetic coreThe cut of the core sheets and the material of the ferromagnetic core are optimized according to the desired no-load characteristics and the specified noise level. Extensive rationalization of the shape and the clamping devices enables us to produce a core with minimum losses and dimensions. This methodology optimizes the consumption of both materials and energy, bringing benefits to the user, the environment and the manufacturer. The core has to be constructed in such a way as to limit the energy losses caused by eddy currents and hysteresis to a minimum. This is achieved by the use of silicon steel, a special soft steel with a 3.5% silicon content, which is characterized by low hysteresis losses and high resistivity. The core consists of a series of laminations made from very thin sheets of steel insulated on both sides by an oxide layer (see opposite under Material).</p> <p>The ferromagnetic coreof a distribution transformer</p> <p>Evolution of the quality of magnetic steel</p> <p>MaterialThe core is constructed using thin sheets of cold-rolled grain-oriented magnetic silicon steel insulated on both sides. Conventional grainoriented steel (CGO steel) is used for transformers with normal no-load loss characteristics, while transformers with reduced no-load losses are built using higher-quality HiB steel (usually laser treated). These steel sheets are 0.30 mm, 0.27 mm or 0.23 mm thick. Extremely low no-load losses can be achieved only by using wound cores made of amorphous metal. This has highly specific properties (very thin sheets just 0.025 mm thick are used) and therefore it requires a specially adapted design.</p> <p>6</p> <p>7</p> <p>Cutting and stacking of the core sheetsMinimum magnetic flux distortion in the transition areas between yokes and core legs is achieved by optimizing the cut of the core sheets and the stacking pattern. First of all, the core sheets are cut at an angle of 45, thus allowing maximum flow of magnetic flux in the rolling direction. This is extremely important because losses in grain-</p> <p>The core: main characteristics:The 45 cut of the core sheets guarantees optimum flow of magnetic flux. The oval shape allows optimization of the core section. Low sound levels can be achieved using the step-lap stacking pattern. The type of magnetic steel is chosen according to the desired loss level. The simple supporting structures and clamping devices of the core contribute to the compactness of the design.</p> <p>oriented magnetic steel are smallest in the direction of rolling. Then the sheets are stacked in an overlap pattern of either single or multiple overlaps. The multiple overlap or step-lap method offers additional benefits in terms of lower no-load losses and noise levels. Because they involve a rather more complicated production technology, step-lap cores are preferably made on fully automatic cutting and stacking machines. Once the sheets are stacked, the core is compressed and glued to form a firmly-bonded whole. This also helps to reduce noise levels.</p> <p>CONSTRUCTIONShape of core sectionThe vast majority of the distribution transformers built by Pauwels have an oval-shaped core section, formed by combining the traditional stepped and fully filled round shape with a square mid-section. This gives great flexibility in the height to which the steel sheets can be stacked,Typical oval-shaped core cross section</p> <p>The ferromagnetic coreof a distribution transformer</p> <p>thus allowing the ideal core section to be made for any design, while maintaining the use of standard materials and dimensions. Using this method combines the benefits of a rectangular core section (simplicity of production) with those of a round core section (excellent short-circuit withstand capability of the windings).</p> <p>Clamping devicesBy using simple profiled-steel yoke clamping systems and a number of metal tensioning bands, Pauwels has eliminated the need for either clamping bolts in the yokes (which would distort the magnetic flux) or tie rods between the upper and lower yokes (which would require the tank to be larger).</p> <p>Fully automatic cutting and stacking machine</p> <p>9</p> <p>CONSTRUCTIONLOW HIGHLow voltage windingsLow voltage windings are usually made of copper or aluminium sheet conductor (foil). The benefit of this is that any high voltage ampere-turn asymmetry which might occur is compensated automatically by an appropriate internal current distribution in the low voltage foil. This reduces the axial stresses produced by short-circuits to a minimum (down to 10% of those for conventional windings), thus enabling the axial support construction to be greatly simplified. The sheets and connectors welded onto them are made of electrolytically pure copper or aluminium with a rigorously guaranteed conductivity. Designs are adapted to the thermal, electrical and chemical characteristics of each type of conductor, thus ensuring that both versions are of equivalent quality, whether made of copper or aluminium. The special diamond pattern of epoxy adhesive coated onto the kraft The maximum voltage between each turn is only a few tens of volts. This allows the insulation needed between the turns (foils) to be limited to 1 or 2 sheets of fine kraft paper only a few hundredths of a millimetre thick. The high voltage winding is wound directly onto the low voltage winding, According to the design specification, this insulation may be coated with a thermo-hardening epoxy adhesive which cures and bonds during the drying process. over the structures forming the main gap, giving maximum mechanical strength, rigidity and compactness. This mechanical strength is of the utmost importance since, in the event of Foil windings may be wound either on a winding mandrel or, preferably, directly onto the core leg. This ensures minimum play between core and winding, for optimum rigidity. The structures forming the main gap, i.e. the insulating space separating the low and high voltage windings, are fitted directly onto the low voltage foil winding, thus forming a part of it. These processes all enhance the transformers short-circuit withstand capability. short-circuit, the windings have to sustain very high radial repellent forces. The mechanical effect of these forces is minimal in round windings, since these windings inherently have the ideal form to withstand radial stresses. The mechanical effect is much greater in rectangular windings. In order to combine the advantages of a rectangular core section (simplicity of production) with the benefits of round windings (excellent short-circuit withstand capability), Pauwels has developed the unique concept of oval-shaped cores and windings (see drawing above). paper cures during the drying process, bonding the windings into a single structure.HV LV CORE</p> <p>Windings</p> <p>of a distribution transformer</p> <p>RADIAL REPELLENT FORCES ACTING ON HV AND LV WINDINGS</p> <p>High voltage windingsRECTANGULAR ROUND OVAL</p> <p>High voltage windings are almost exclusively of layered construction. The copper or aluminium conductors are made of one or more round or square wires, either with an insulating enamel coating or wrapped in insulating paper. Each design is drawn up in accordance with the specific characteristics of the conductor material to be used. The insulation between the layers consists of pre-coated kraft paper, applied either in sheet form or wound in a continuous narrow strip, a technique which allows optimum adjustment of the insulation thickness to the electrical gradient at each layer position.</p> <p>The main benefits of layered windings are:They form a simple winding, which allows continuous or semi-automatic winding. The impulse voltage distribution throughout the winding is predictable and controlled. Axial cooling ducts are simple to build and fit. Any taps required can be brought out anywhere in the winding through the layers.</p> <p>Supplementary benefits of foil windings are:Greater simplicity in fitting cooling ducts. More even heat distribution through the windings. Semi-automatic winding techniques can be used.</p> <p>10</p> <p>11</p> <p>Assembling cores and windings to build an active partAssembly of cores and windings to build an active part may be carried out in either of the following two ways:</p> <p>Bushings are mounted on the cover, which is then fixed onto the assembled active part. The next step consists of connecting the windings to the bushings. The connection methods are durable and selected so as to ensure a solid, low-resistance connection between the linked conducting materials, including junctions between aluminium and copper components. Transformers are often fitted with an off-circuit tap changer. This switch allows the increase or decrease of</p> <p>If the windings have been wound on a mandrel, the E-shaped cores and the windings are transported from their various construction locations to the assembly area. The windings are pushed over the core legs and wedged up to fill the spaces between the core and winding as much as possible. The magnetic circuit is then completed by interleaving the laminations of the upper yoke with the laminations of the core legs.</p> <p>a certain number of turns while the transformer is disconnected from the circuit. Small variations in the nominal supply voltage can be accomodated by adjusting the tap changer to keep the output voltage at the required value. The off-circuit tap changer is always fitted on the high voltage side of the transformer, since this is where the current is smallest. A second tap change switch is incorporated in transformers with dual high voltages in order to change the high voltage. Tap changers and tap switches are controlled either by cable or by a drive shaft. The voltage ratio of the active part is then tested, and the assembly is dried for a specified time in a forced-air oven to remove the moisture from the insulating materials. This time depends on the quantity of insulating materials, which in turn depends on the transformers rating and voltages.</p> <p>If the windings have been wound directly onto the core legs, the three core legs are positioned on a tilting table. The upper and lower yokes are then fitted highly accurately in the same way as described above.</p> <p>CONSTRUCTION</p> <p>Active part</p> <p>of a distribution transformer</p> <p>13</p> <p>Functions of the transformer tank:It forms a container for the cooling liquid. It acts as a heat exchange surface for the dissipation of heat losses. It is a protective, earthed safety shell. It provides shielding against electromagnetic field leakage caused by current-carrying conductors.</p> <p>Hermetically sealed transformers offer indisputable advantages compared with transformers fitted with a conservator, including:The insulating liquid cannot come into contact with the air, thus guaranteeing preservation of its dielectric integrity. Reduced maintenance, e.g. no checking required of the air dryer, no need to monitor the liquid for water ingress, etc. They are cheaper to buy. They occupy a smaller space,...</p>