Numerical relay settings calculation for the generator at HPP Prancevici
Abstract
The paper deals in detail with the calculation and selection of settings for the numerical relay device type 7UM6225 from Siemens for the relay protection of the synchronous generator and its associated block transformer at the Prancevici SHPP. The following protection functions of the numerical relay device were activated and set: (1) differential protection of the generator and block transformer, (2) overcurrent protection with undervoltage hold, (3) underimpedance protection, (4) overvoltage protection, (5) undervoltage protection, (6) instantaneous overcurrent protection, (7) 90% stator earth fault protection in two variants: (a) overvoltage earth fault protection connected to the open delta of the voltage measuring transformer winding at the generator terminals and (b) overcurrent earth fault protection connected to the current transformer on the secondary of the earthing transformer, (8) 100% stator earth fault protection (overvoltage protection with third harmonic measurement), (9) rotor earth fault protection, (10) protection against unsymmetrical load, (11) thermal protection, (12) reverse power protection, (13) protection against loss of excitation, (14) protection against excessive magnetic induction, (15) frequency protection (overfrequency and underfrequency), (16) protection of the stationary generator and (17) protection against circuit breaker failure. When calculating the settings of the protection functions, care was taken to optimally satisfy the following basic criteria: the fastest possible fault tripping, selective action, the highest possible sensitivity and reserve protection to the greatest extent possible.
