IEEE C57.116-1989 pdf free

04-29-2021 comment

IEEE C57.116-1989 pdf free.IEEE Guide for Transformers Directly Connected to Generators.
IEEE C57.116 generating system came into usage as generator size and generator bus fault current levels beganto exceed the capability of breakers that were available to isolate the generator from the power system.Generally, thegenerator auxiliaries load is fed from a transformer that is connected directly to the generator bus.An alternate sourceof power is normally supplied from the transmission system by a second transformer during unit startup, shutdown.and other contingencies. Such a system is shown in Fig 1. Typically, an isolated phase bus is used for connectionbetween the generator and its UT and UAT; thus, the system is unit connected.
Studies indicate that through faults for the UT are normally not severe in terms of either thermal or mechanical duty.However, the stresses in the UAT can be severe under certain conditions, such as low-side faults, paralleling out ofphase with the SST, and generator load rejection.
On units without generator breakers, faults at location (3) in Fig 1 will be fed predominantly by two sources, namely,through the UT from the system and from the generator. Normally the differential relay protection system, which willdetect faults at location (3), will initiate a unit trip that will disconnect the unit from the system and remove thegenerator excitation.The loss of load may result in a higher voltage on the generator that will continue to feed the faul.This higher voltage due to load rejection will increase the generator ‘s current contribution to a level higher than beforeload rejection.However, the system contribution will be absent. The generator’s contribution will continue at a leveland for a period that depends on the generator’s fault-current decrement characteristics. The fault-current decrementcharacteristics are a function of the generator short-circuit parameters and its excitation system.As a result of thegenerator’s fault-current decrement characteristics,faults at location (3) in Fig 1 may exceed the thermal andmechanical capabilities of the UAT if it is designed solely in accordance with ANSIIEEE C57.12.00-1987[8].
Abnormal operating conditions, such as generator load rejection, may result in high-generator bus voltages that mayalso cause overexcitation of the transformers connected to the generator bus. Should a fault occur at location (3) inFig 1 during this period of overexcitation, both the thermal and mechanical capability of the UAT may be exceeded.
Out-of-phase paralleling of the UAT with the SST can produce high currents that may exceed the mechanicalcapability of these transformers.Frequency mismatch between the generator and system voltages also can causesevere mechanical stresses on the transformers.IEEE C57.116 pdf download.

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