ABB Relion 670 Series Applications Manual page 228

Section 8
Voltage protection
decreasing the voltage. The function has a high measuring accuracy and hysteresis setting to allow
applications to control reactive load.
OV2PTOV (59) is used to disconnect apparatuses, like electric motors, which will be damaged when
subject to service under high voltage conditions. It deals with high voltage conditions at power system
frequency, which can be caused by:
1. Different kinds of faults, where a too high voltage appears in a certain power system, like metallic
connection to a higher voltage level (broken conductor 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. Ground-faults in high impedance grounded systems causes, beside the high voltage in the neutral,
high voltages in the two non-faulted phases, (unsymmetrical voltage increase).
OV2PTOV (59) 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.
8.2.3 Setting guidelines
The parameters for Two step overvoltage protection (OV2PTOV ,59) are set via the local HMI or
PCM600.
All the voltage conditions in the system where OV2PTOV (59) performs its functions should be
considered. The same also applies to the associated equipment, its voltage and time characteristic.
There are wide applications where general overvoltage functions are used. All voltage related settings
are made as a percentage of a settable base primary voltage, which is normally 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 (59) 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:
The hysteresis is for overvoltage functions very important to prevent that a transient voltage over set
level is not "sealed-in" due to a high hysteresis. Typical values should be ≤ 0.5%.
8.2.3.1 Equipment protection, such as for motors, generators, reactors and
transformers
High voltage will cause overexcitation of the core and deteriorate the winding insulation. The setting has
to be well above the highest occurring "normal" voltage and well below the highest acceptable voltage for
the equipment.
8.2.3.2 Equipment protection, capacitors
High voltage will deteriorate the dielectricum and the insulation. The setting has to be well above the
highest occurring "normal" voltage and well below the highest acceptable voltage for the capacitor.
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1MRK 505 370-UUS Rev. K
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Busbar protection REB670
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