Cast Resin Transformers

The delivery programme for SGB Cast Resin Transformers comprises capacities up to 25 MVA und system voltages up to 36 kV just like with converter transformers, distribution transformers or special transformers.

With almost 30 years experience in the construction of cast resin transformers, SGB counts to the manufacturers with the most expertise worldwide and this is expressed in remarkably high quality coefficients such as MTBF of over 1,700 years.

Thanks to the special design, SGB Cast Resin Transformers offer a range of features which set them apart for one thing technically from other cast resin transformers and for another thing they become a very dependable and reliable solution.

1. SURE – Controlling high voltage safely
   
   Only SGB Cast Resin Transformers have moulded high voltage coils in vacuum in which the coil is effected in a double layer winding. That ensures safety in the control of impulse withstanding voltage

1. as the SGB double layer winding guarantees linear impulse impact for all coils and
   
   

2. regular coil winding of customary technology leads to greatly differing voltage stress, especially the input coil because 70% of the impulse impact do apply on the first 30% of the coils.

2. SURE – Making overload possible
   
   SGB Cast Resin Transformers not only have an advantage over oil transformers but also cast resin transformers of customary technology. These use regular coil winding where the conductor is comprised of an aluminium band and the coil/layer insulation is foil. Insulation simply has the insulation class F and also only in conjunction with the whole insulation system-without thermal reserves. It is quite different with SGB Cast Resin Transformers as SGB uses insulated profile wires for double layer winding where the primary insulation already exceeds insulation class H. Consequently the SGB Cast Resin Transformer has high thermal reserves.
   
   

3. SURE – Reliably overcoming temperature shocks
   
   Cast resin transformers are subject to great shocks and strains in their transport and in particular when operated. Therefore of great importance is the ability of the transformer to safely control steep temperature increases.
   
   A decisive factor in this feature is the construction of the cast resin composite material, the matrix into which the conductors are moulded. By doing this it depends especially upon the tensile stress and the thermal coefficients of expansion of the composite material in relation to the conductor material.
   
   
   
   With the customary cast resin transformers this composite material is comprised of epoxy resin which is filled over 70 % with a mineral bulking agent, mainly quartz flour. It is easily understandable that such a composite material can simply reach the tensile strength of the epoxy resin in the area of 50 N/mm². With the thermal coefficients of expansion the value of aluminium can roughly be reached with maximum mineral filling. However the reached valued is distinctly higher than with copper. This is the reason why cast resin transformers of customary technology were available for decades only with aluminium conductors. Recently there has been an improvement through an additional reinforcement by glass fibre.
   
   It is quite different with SGB. Here the composite system originally is comprised of a glass fibre concentrated epoxy resin with high tensile strength in the area of 120 N/mm² and a coefficient of expansion which equally are consistent with copper and aluminium. SGB Cast Resin Transformers are produced from the start both with copper and aluminium.
   
   The advantage of the chosen SGB composite system has frequently been recognised in tests. SGB Cast Resin Coils have safely passed the required temperature shock tests for climate class C2 based on an initial temperature of – 25 °C and even those based on an initial temperature of – 50°C.
   
   

4. SURE – Guaranteeing cooling
   
   Cast resin transformers must emit the heat resulting from the losses in the coils over the surface area of the coils to the cooling air without exceeding one of the temperatures rises inside the coil, allowed in accordance with the insulation class - neither the average coil temperature nor the Hot-Spot temperature. With a given heat transfer coefficient the parameters are for the heat quantity discharged with the defined ambient temperature, the surface temperature of the coil and the size of the surface area.
   
   
   
   With cast resin transformers of customary technology with regular coil winding only both inner and outer surface areas of the cylindrical coil are available for cooling. To reach the necessary surface areas, coils must be bigger from time to time than determined by electrical parameters.
   
   The chosen technolgy of SGB of double layer winding in comparison simply allows the introduction of additional cooling ducts inside the coil. In this way you achieve cooling surfaces and you can design the coils perfectly .
   
   The advantage of the SGB solution is obvious when you see that with transformers with regular coil winding with large capacities, despite considerable process relevant problems as well, cooling ducts are introduced as well. SGB Cast Resin Transformers always have that and guarantee a consistent distribution of temperature inside the coil with appropriate use of material.