In distribution substations, the bus protection is often provided by overcurrent relays, phase and neutral, located on either the low-voltage or high-voltage side of the transformer. Fuse protection has the merits of being economical and requiring little maintenance. Fuses require no circuit-interrupting devices. ABB's transformer protection relays are used for protection, control, measurement and supervision of power transformers, unit and step-up transformers, including power generator-transformer blocks in utility and industry power distribution networks. Effective relay protection depends on. Generator protection covers: phase-to-phase short circuits in stator windings, stator ground faults, inter-turn short circuits in stator windings, external short circuits, symmetrical overload, stator overvoltage, single- and double-point grounding in the excitation circuit, and loss of excitation. All equipment installed in a power electrical system have standardized ratings for short-time withstand current and short duration power frequency.
[PDF Version]