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%.
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.
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.
Power supply quality
The setting has to be well above the highest occurring "normal" voltage and below the
highest acceptable voltage, due to regulation, good practice or other agreements.
High impedance grounded systems
In high impedance grounded systems, ground-faults cause a voltage increase in the non-
faulty phases. Two step overvoltage protection (OV2PTOV, 59) is used to detect such
faults. The setting must be above the highest occurring "normal" voltage and below the
lowest occurring voltage during faults. A metallic single-phase ground-fault causes the
non-faulted phase voltages to increase a factor of √3.
The following settings can be done for the two step overvoltage protection
ConnType: Sets whether the measurement shall be phase-to-ground fundamental value,
phase-to-phase fundamental value, phase-to-ground RMS value or phase-to-phase
RMS value.
Operation: Disabled/Enabled.
VBase: Base voltage phase to phase in primary kV. This voltage is used as reference
for voltage setting. OV2PTOV (59) measures selectively phase-to-ground voltages, or
phase-to-phase voltage chosen by the setting ConnType. The function will operate if
the voltage gets lower than the set percentage of VBase. When ConnType is set to PhN
DFT or PhN RMS then the IED automatically divides set value for VBase by √3. When
ConnType is set to PhPh DFT or PhPh RMS then set value for VBase is used.
Therefore, always set VBase as rated primary phase-to-phase ground voltage of the
protected object. If phase to neutral (PhN) measurement is selected as setting, the
operation of phase-to-earth over voltage is automatically divided by sqrt3. This means
operation for phase-to-ground voltage over:
1MRK504116-UUS C Section 3
IED application
517
Application manual
To Next Page
Loading...
