PCS-985 Generator Transformer Unit Protection Relay 87g Differential protection, Overcurrent protection, Definite-time overload protection, Inverse-time overload protection

The PCS-985 provides the complete main and backup protection of generator-transformer units which usually comprises generator, main transformer, auxiliary transformer and exciter or excitation transformer.It supports connections to conventional CTs/VTs and Electronic CTs/VTs, and is widely used in large capacity turbo-dynamo, gas-turbine generator and nuclear power generator with different connection modes.

For a vital generator-transformer unit, two sets of PCS-985 can be used to achieve duplicated protection configuration. Two PCS-985 use different CT groups, and main and backup protection in one PCS-985 share one CT group.

Generator protection

Differential protection. (87G)
DPFC differential protection. (87G)
High sensitive transverse differential protection. (87G)
Longitudinal zero-sequence overvoltage protection for interturn fault. (59N/60)
DPFC directional protection for inter-turn fault. (67)
Voltage controlled overcurrent protection. (50)
Phase-to-phase impedance protection. (21G)
Extreme current blocking function at generator terminal.
Fundamental zero-sequence voltage protection for stator earth fault . (64S)
Third harmonic overvoltage ratio protection for stator earth fault. (64S)
Third harmonic overvoltage differential protection for stator earth fault. (64S)
100% stator earth-fault protection with voltage injection. (64R)
Rotor one-point earth-fault protection. (64R1)
Rotor two-point earth-fault protection. (64R2)
Definite-time stator overload protection. (50S)
Inverse-time stator overload protection. (51S)
Definite-time negative-sequence overload protection. (50Q)
Inverse-time negative-sequence overload protection. (51Q)

Typical Applications
Loss-of-excitation protection. (40)
Out-of-step protection. (78)
Overvoltage protection. (59)
Definite-time over-excitation protection. (24)
Inverse-time over-excitation protection. (24)
Reverse-power protection. (32R)
Low-power protection. (37G)
Sequential tripping reverse-power protection. (32R)
 Underfrequency protection. (81U)
Overfrequency protection. (81O)
Startup/shutdown protection of differential current.
Startup/shutdown protection of zeros-equence voltage.
Low-freuquency overcurrent protection. (50)
Inadvertent energization protection. (50/27)
Breaker failure protection. (50BF)
Voltage balance function. (60)
VT circuit supervision. (VTS)
CT circuit supervision. (CTS)

Excitation Transformer/Excitor Protection

Differential protection. (87ET)
Overcurrent protection. (50)
Definite-time overload protection. (50)
Inverse-time overload protection. (51)

Main Transformer Protection
 Generator-transformer unit differential protection. (87GTU)
 Differential protection. (87T)
 DPFC differential protection. (87T)
 Restricted earth-fault protection. (64REF)
 Phase-to-phase impedance protection at HV side. (21P)
 Voltage controlled overcurrent protection at HV side. (50)
 Overload alarm. (49)
 Initiating cooling. (49)
 Directional zero-sequence overcurrent protection at HV side. (67G)
 Inverse-time zero-sequence overcurrent protection at HV side. (51G)
 Gap zero-sequence voltage protection at HV side.
 Gap zero-sequence current protection at HV side.
 Zero-sequence voltage alarm at LV side.
 Definite-time over-excitation protection. (24)
 Inverse-time over-excitation protection. (24)
 Pole discrepancy protection at HV side. (62PD)
 Breaker flashover protection.
 VT circuit supervision. (VTS)
 CT circuit supervision. (CTS)
 

Auxiliary Transformer
 Differential protection. (87T)
 Voltage controlled overcurrent protection at HV side. (50P)
 Voltage controlled overcurrent protection of branch 1 at LV side. (50P)
 Voltage controlled overcurrent protection of branch 2 at LV side. (50P)
 Zero-sequence overcurrent protection of branch 1 at LV side. (50G)
 Zero-sequence overcurrent protection of branch 2 at LV side. (50G)
 Overload alarm. (49)
 Initiating cooling. (49)
 Blocking on-load tap change. (OLTC)
 VT circuit supervision. (VTS)
 CT circuit supervision. (CTS)
 

Miscellaneous
 Mechanical protection.
 Voltage and current drift auto adjustment.
 Self diagnostic.
 GPS clock synchronization.
 Fault Recorder.