2 Functions
106
7UM61 Manual
C53000-G1176-C127-3
2.16 Overvoltage Protection (ANSI 59)
Overvoltage protection serves to protect the electrical machine and connected electri-
cal plant components from the effects of inadmissible voltage increases. Overvoltages
can be caused by incorrect manual operation of the excitation system, faulty operation
of the automatic voltage regulator, (full) load shedding of a generator, separation of the
generator from the system or during island operation.
2.16.1 Functional Description
Mode of Operation By means of the overvoltage protection feature, the user can select if he wants to
monitor the phase-to-phase voltages or the phase-earth-voltages. In case of a high ov-
ervoltage, the switchoff is performed with a short-time delay, whereas in case of lower
overvoltages, the switchoff is performed with a longer time delay to allow the voltage
regulator to take the voltage back into the nominal range. The user can specify the
voltage limit values and the time delays individually for both stages.
Each stage can be blocked individually and/or for both stages can be blocked, via
binary input(s).
The following figure shows the logic diagram for the overvoltage protection function.
Figure 2-32 Logic Diagram of the Overvoltage Protection
2.16.2 Setting Notes
General Overvoltage protection is only effective and available if this function was set during
protective function configuration (Section 2.2, address 141, OVERVOLTAGE is set to
Enabled. If the function is not required Disabled is set. Address 4101
OVERVOLTAGE serves to switch the function ON or OFF or to block only the trip
command (Block relay).
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