High Impedance Earthed Systems; The Following Settings Can Be Done For The Two Step Overvoltage Protection - ABB Relion REC670 Applications Manual

Section 8
Voltage protection
8.2.3.4

High impedance earthed systems

In high impedance earthed systems, earth-faults cause a voltage increase in the non-faulty
phases. Two step overvoltage protection (OV2PTOV) 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 earth-fault causes the non-faulted phase voltages to
increase a factor of √3.
8.2.3.5 The following settings can be done for the two step overvoltage
protection
ConnType : Sets whether the measurement shall be phase-to-earth fundamental value, phase-
to-phase fundamental value, phase-to-earth RMS value or phase-to-phase RMS value.
Operation : Off / On .
UBase (given in GlobalBaseSel ): Base voltage phase to phase in primary kV. This voltage is used
as reference for voltage setting. OV2PTOV measures selectively phase-to-earth voltages, or
phase-to-phase voltage chosen by the setting
voltage gets lower than the set percentage of
RMS then the IED automatically divides set value for UBase by √3. When ConnType is set to
PhPh DFT or PhPh RMS then set value for UBase is used. Therefore, always set UBase as rated
primary phase-to-phase 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-earth voltage over:
>
U (%)
and operation for phase-to-phase voltage over:
>
U (%) UBase(kV)
EQUATION1993 V1 EN-US
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
most applications it is sufficient that one phase voltage is high to give operation. If the
function shall be insensitive for single phase-to-earth faults
the voltage will normally rise in the non-faulted phases at single phase-to-earth faults. In
subtransmission and transmission networks the UV function is mainly a system supervision
function and 3 out of 3 is selected.
Un> : Set operate overvoltage operation value for step n , given as % of UBase . The setting is
highly dependent of the protection application. Here it is essential to consider the maximum
voltage at non-faulted situations. Normally this voltage is less than 110% of nominal voltage.
tn : time delay of step n , given in s. The setting is highly dependent of the protection
application. In many applications the protection function is used to prevent damages to the
protected object. The speed might be important for example in case of protection of
transformer that might be overexcited. The time delay must be co-ordinated with other
automated actions in the system.
180
×
UBase kV ( ) / 3
×
ConnType . The function will operate if the
UBase . When ConnType is set to PhN DFT or PhN
1 out of 3 , 2 out of 3 , 3 out of 3 . In
1 out of 3 can be chosen, because
1MRK 511 358-UEN A
M13852-19 v5
M13852-22 v8
(Equation 95)
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