ABB Relion 670 series - High Impedance Grounded Systems

10.2.3.4 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.
10.2.3.5 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 (given in GlobalBaseSel): 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-ground over voltage is automatically divided by sqrt3. This means
operation for phase-to-ground voltage over:
(%) ( ) / 3V VBase kV> ×
EQUATION1713 V2 EN
(Equation 510)
and operation for phase-to-phase voltage over:
Vpickup (%) VBase(kV)
> ×
EQUATION1992-ANSI V1 EN (Equation 511)
The below described setting parameters are identical for the two steps (n = 1 or 2).
Therefore the setting parameters are described only once.
Characteristicn: This parameter gives the type of time delay to be used. The setting can be
Definite time, Inverse Curve A, Inverse Curve B, Inverse Curve C or I/Prog. inv. curve.
The choice is highly dependent of the protection application.
OpModen: This parameter describes how many of the three measured voltages that should
be above the set level to give operation. The setting can be 1 out of 3, 2 out of 3, 3 out of 3.
1MRK 506 369-UUS - Section 10
Voltage protection
Line distance protection REL670 2.2 ANSI 573
Application manual