ABB REQ650 - Page 166

High impedance earthed systems
In high impedance earthed systems, earth-faults cause a voltage increase in the non-
faulty phases. OV2PTOV can be 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.
The following settings can be done for Two step overvoltage protection
GlobalBaseSel: Selects the global base value group used by the function to define
(IBase), (UBase) and (SBase).
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 .
OV2PTOV measures the phase-to-earth voltages, or phase-to-phase voltages as
selected. The function will operate if the voltage gets higher than the set percentage of
the global set base voltage UBase. This means operation for phase-to-earth voltage
over:
( )
(%)
3
UBase kV
U > ×
IEC09000054 V1 EN (Equation 69)
and operation for phase-to-phase voltage over:
U (%) UBase(kV)> ×
EQUATION1993 V1 EN (Equation 70)
Characteristic1: 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. 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 for step n (n=step 1 and 2). The setting
can be 1 out of 3, 2 out of 3 or 3 out of 3. In 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 3 out of 3 can be chosen, because the voltage will normally rise
in the non-faulted phases at single phase-to-earth faults.
Un>: Set overvoltage operating value for step n (n=step 1 and 2), given as % of the
global parameter 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 for step n (n=step 1 and 2), given in s. The setting is highly dependent
of the protection application. In many applications the protection function has the task
Section 7 1MRK 505 291-UEN A
Voltage protection
160
Application manual