GE Industrial Solutions Entellisys System User Manual - Manual (Page 67)

Single Point Relay protection 67
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• Dropout Over Frequency – Over frequency relay has dropped out of pickup.
• Voltage Below Over Frequency Blocking Voltage – The voltage has dropped below the over
frequency blocking voltage threshold.
• Voltage Above Over Frequency Blocking Voltage – The voltage has exceeded the over
frequency blocking voltage threshold.
To view these events, click Sequence of Events on the Main Menu.
5.2.4 Under Frequency Relay
The Entellisys System executes the Under Frequency Relay function by comparing the
fundamental frequency of the phase A voltage to the programmed pickup set point.
The relay can be in three states:
• Pickup – If the frequency of the phase A voltage is less than the pickup set point, the relay
goes into pickup, and is said to enter Pickup state
• Operate – If the relay stays in pickup state for a specified pick up delay time, the system
trips the appropriate circuit breaker or activates an alarm, and the relay is said to be in
Operate state
• Drop out – The relay drops out of pickup when the frequency exceeds 103% of the
programmed threshold. The relay is said to be in Drop out state.
The system trips the appropriate circuit breaker or activates an alarm if the frequency is less
than the pickup set point for the specified time delay.
5.2.4.1 Accuracy
Pickup accuracy is less than ± 0.1 Hz. Trip time accuracy is ± 0.1 seconds.
Blocking voltage option: A 'blocking voltage' user-defined input option is provided. The under
frequency relay function is not performed if the blocking voltage option is enabled and the
voltage is less than the blocking voltage. If the Under Frequency Relay goes into pickup, and the
voltages subsequently drop below the blocking voltage, the relay goes out of pickup and the
delay is reset.
The accuracy of the blocking voltage depends on the frequency deviation and is listed in
Table 5-7.
Table 5-7 Blocking voltage accuracy
Frequency Deviation Blocking Voltage Accuracy
0 Hz ±2%
2 Hz ±5%
4 Hz ±7%
6 Hz ±10%
8 Hz ±13%
10 Hz ±15%