falling down to a crossing overhead line, transformer flash over fault from the
high voltage winding to the low voltage winding and so on).
2. Malfunctioning of a voltage regulator or wrong settings under manual control
(symmetrical voltage decrease).
3. Low load compared to the reactive power generation (symmetrical voltage
decrease).
4. Earth-faults in high impedance earthed systems causes, beside the high voltage in
the neutral, high voltages in the two non-faulted phases, (unsymmetrical voltage
increase).
OV2PTOV prevents sensitive equipment from running under conditions that could
cause their overheating or stress of insulation material, and, thus, shorten their life
time expectancy. In many cases, it is a useful function in circuits for local or remote
automation processes in the power system.
7.2.3
Setting guidelines
The parameters for Two step overvoltage protection (OV2PTOV) are set via the local
HMI or PCM600.
All the voltage conditions in the system where OV2PTOV performs its functions
should be considered. The same also applies to the associated equipment, its voltage
and time characteristic.
There is a very wide application area where general overvoltage functions are used.
All voltage related settings are made as a percentage of a settable base primary
voltage, which normally is set to the nominal voltage level (phase-to-phase) of the
power system or the high voltage equipment under consideration.
The time delay for the OV2PTOV can sometimes be critical and related to the size of
the overvoltage - a power system or a high voltage component can withstand smaller
overvoltages for some time, but in case of large overvoltages the related equipment
should be disconnected more rapidly.
Some applications and related setting guidelines for the voltage level are given below:
Equipment protection, such as for motors, generators, reactors and
transformers
High voltage can cause overexcitation of the core and deteriorate the winding
insulation. The setting must be above the highest occurring "normal" voltage and
below the highest acceptable voltage for the equipment.
Equipment protection, capacitors
High voltage can deteriorate the dielectricum and the insulation. The setting must be
above the highest occurring "normal" voltage and below the highest acceptable
voltage for the capacitor.
1MRK 505 291-UEN A
Section 7
Voltage protection
159
Application manual
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