The alarm response is based on the highest difference between any of the three phase-to-
phase voltage or phase-to-neutral true RMS values and the average voltage, as measured by
the controller. The phase-to-phase voltage is the default.
If phase-to-phase voltages are used, the controller calculates the average phase-to-phase
voltage. The controller then calculates the difference between each phase-to-phase voltage
and the average voltage. Finally, the controller divides the maximum difference by the average
voltage to get the voltage unbalance.
Controller types: This alarm is present in GENSET, EMERGENCY genset, and BUS TIE
breaker controllers.
Configure the parameters under Configure > Parameters > [Source] > Voltage protections > Voltage unbalance.
Table 3.31
Default parameters
Parameter Range Voltage unbalance
Set point 0 to 50 % 10 %
Delay 0.1 s to 1 h 10.00 s
Enable Not enabled, Enabled Enabled
Alarm action Warning
Table 3.32 Default inhibits
Controller type Inhibit(s)
GENSET ACM wire break
EMERGENCY genset EDG handling blackout
SHAFT generator ACM wire break
SHORE connection ACM wire break
BUS TIE breaker ACM wire break
Voltage unbalance example
A GENSET controller controls a genset with a nominal voltage of 230 V. The L1-L2 voltage is 235 V, the L2-L3 voltage is
225 V, and the L3-L1 voltage is 210 V.
The average voltage is 223.3 V. The difference between the phase-to-phase voltage and the average is 12.7 V for L1-L2,
2.7 V for L2-L3 and 13.3 V for L3-L1.
The voltage unbalance is 13.3 V/223.3 V = 0.06 = 6.0 %.
3.4.5 Negative sequence voltage (ANSI 47)
Protection
IEC symbol (IEC60617) ANSI (IEEE C37.2) IEC 61850 Operate time
Negative sequence voltage 47 PNSC < 200 ms*
*Note: This operate time includes the minimum user-defined delay of 100 ms.
DESIGNER'S HANDBOOK 4189340911K UK Page 64 of 521
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