ABSTRACT
Figure11.1showsaschematicofapowersystemwithitsmaintransformers.Thesystemhasfour types of transformers: transmission, distribution, service, and circuit transformers.
1. Transmission transformers Figure 11.2a: These transformers are connected to both ends of the transmission line. At the generating power plants, the transformer steps up the voltage of the generators to very high levels (220 kV-1 MV) so that the current can be reduced substantially. At the other end of the transmission line, the transformer steps down the voltage to a lower level suitable for distribution to load centers. Since the transmission transformers carry the bulk power of the system, they are very large in size. The internal losses of the transformer, which are due to the high currents in the windings and core losses, can cause excessive heat inside the container of the transformer. Therefore, the transformer is immersed in cooling medium such as oil and the container is equipped with a system of pipes and fans to extract heat from the cooling medium much like the radiators in automobiles. The medium also increases the dielectric strength of the windings so that the transformer can withstand higher voltages.
