10.3.3 Setting guidelines
All the voltage conditions in the system where ROV2PTOV (59N) performs its functions
should be considered. The same also applies to the associated equipment, its voltage
withstand capability and time characteristic.
All voltage-related settings are made as a percentage of a settable base voltage, which
shall be set to the primary nominal voltage (phase-phase) level of the power system or the
high-voltage equipment under consideration.
The time delay for ROV2PTOV (59N) is seldom critical, since residual voltage is related
to ground faults in a high-impedance grounded system, and enough time must normally be
given for the primary protection to clear the fault. In some more specific situations, where
the residual overvoltage protection is used to protect some specific equipment, the time
delay is shorter.
Some applications and related setting guidelines for the residual voltage level are given
below.
10.3.3.1 Equipment protection, such as for motors, generators, reactors and
transformersEquipment protection for transformers
High residual voltage indicates ground fault in the system, perhaps in the component to
which two step residual overvoltage protection (ROV2PTOV, 59N) is connected. For
selectivity reasons to the primary protection for the faulted device, ROV2PTOV (59N)
must trip the component with some time delay. The setting must be above the highest
occurring "normal" residual voltage and below the highest acceptable residual voltage for
the equipment.
10.3.3.2 Equipment protection, capacitors
High voltage will deteriorate the dielectric and the insulation. Two step residual
overvoltage protection (ROV2PTOV, 59N) has to be connected to a neutral or open delta
winding. The setting must be above the highest occurring "normal" residual voltage and
below the highest acceptable residual voltage for the capacitor.
10.3.3.3 Power supply quality
The setting must be above the highest occurring "normal" residual voltage and below the
highest acceptable residual voltage, due to regulation, good practice or other agreements.
Section 10 1MRK 506 369-UUS -
Voltage protection
576 Line distance protection REL670 2.2 ANSI
Application manual
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