8.10 Summary
In this chapter we have developed the protection concepts for single- and three-phase transformers.
We began with overcurrent protection, and after examining the effects of nonlinearities in the magnetic circuits, arrived at the harmonic restraint percentage differential relay as the protection
system of choice for large power transformers.We considered the effect of the wye–delta connection
of the power transformer on the protection system. We have also studied the protection problem
of a transformer when it is a part of a complex power system, with different bus and breaker
configurations.
Many of these concepts are further illustrated by the problems at the end of the chapter.