Reverse Power Protection
1- Protection against overspend 32G (# 1).
In case of Turbine Failure, the Turbine is tripped and then the Generator is tripped by operation of reverse power relay to prevent overspending of the Turbine generator unit.
2- Protection against generator motoring 32G (#2).
Generator motoring protection is designed for the prime mover or the system, rather than for the generator.
With steam turbines, Turbines will overheat on low steam flow, motoring results from a low input To the Ac Generator,
When This I/P can’t meet all the losses, the deficiency is supplied by absorbing real power from the system.
since field excitation should remain the same , the same reactive power would flow as before motoring , thus, on motoring the real power will be into the generator, while the reactive power may be either flowing out or into the generator
Setting of Reverse Power Relays
Data for setting calculations
-Rated Capacity of Generator -------- 440,000 KVA
-No Load Loss of Generator --------- 1,785 KW
-No Load Loss of Turbine ---------- 1,350 KW
-No Load Loss of TG unit ---------- 3,135 KW
-Permissible Motoring Time ------- 60 Sec.
-Relay Constant ------------------- 1 P.U. = Generator KVA
Setting Of Reveres Power Relay 32G ( #1 )
1- Reverse Power Trip Level
Trip Level < No load loss of TG unit * 0.3
= 3,135 * 0.3
= 940.5 KW
Pick up = Trip level / relay constant
= 941 / 440,000
= 0.0021 P.U.
Setting = - 0.002 P.U. ( 880KW )
2- Reverse Power Trip Delay
Trip Delay < Perm. Motoring time (60 Sec.)
Setting = 50 Cycles (1 Sec.)
Setting Of Reveres Power Relay 32G ( #2 )
1- Reverse Power Trip Level
Trip Level < No load loss of TG unit * 0.5
= 3,135 * 0.5
= 1,568 KW
Pick up = Trip level / relay constant
= 1,568 / 440,000
= 0.004 P.U.
Setting = - 0.004 P.U. ( 1,760KW )
2- Reverse Power Trip Delay
Trip Delay < Perm. Motoring time (60 Sec.)
Setting = 750 Cycles (15 Sec.)