For these examples:
•
The system is running with the bus tie breaker closed.
•
There are no recent load share changes, and so the "Delay after load share changes" timers are not relevant.
•
Gensets A, B and C are connected, and have equal load sharing.
Genset A governor set point failure example
The
GOV increase
relay that regulates Genset A is stuck in a closed position. This drives up the load on Genset A, while
the other gensets have less load. The busbar section frequency starts to increase.
One of the following ABP protections trips the BTB:
•
P load sharing failure (high frequency) on a DG
•
Overload on a DG
•
Over-current on a DG
Genset A continues to draw load from Genset B. This ABP protection can trip the Genset A generator breaker:
•
P load sharing failure (high frequency) on DG
Alternatively, one of the following AC protections can trip the Genset A generator breaker:
•
Overload
•
Over-current
•
Directional over-current
•
Fast over-current
•
Inverse time over-current
The system now runs with a split busbar, and the generator with the faulty governor (Genset A) disconnected.
Genset C AVR excitation failure example
Genset C's AVR fails, and does not excite the generator as needed. Genset C takes less of the reactive load. The busbar
section voltage starts to decrease.
One of the following protections trips the BTB:
•
Q load sharing failure (low voltage) on DG
•
Reactive power import on a DG
Genset C tries to supply the required reactive load for the busbar section, but cannot, and the voltage is low. The
Busbar
under-voltage
alarm trips the generator breaker, and activates a precautionary genset start of Genset D.
The generator breaker trip causes a blackout on the busbar section. When Genset D is started, the power management
system connects Genset D in order to recover from the blackout.
4.10.2 Calculating the load sharing error
For active power, the load sharing error is based on the difference between the measured power and the internal controller set point,
as a percentage of the genset nominal power.
Load sharing error = (Measured power - Internal set point power) / (Nominal power)
Load sharing error example
Two gensets are connected to the busbar. Genset A has a nominal power of 1000 kW, while Genset B has a nominal
power of 500 kW. The gensets are configured to each take an equal percentage (based on the genset nominal power) of
the load.
DESIGNER'S HANDBOOK 4189340911K UK
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