ABB REB670 - Page 255

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-US (Equation 69)
and operation for phase-to-phase voltage over:
Vpickup (%) VBase(kV)> ×
EQUATION1992-ANSI V1 EN-US (Equation 70)
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. 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-ground faults 1 out of
3 can be chosen, because the voltage will normally rise in the non-faulted phases at
single phase-to-ground faults. In subtransmission and transmission networks the UV
function is mainly a system supervision function and 3 out of 3 is selected.
Pickupn: Set pickup overvoltage operation value for step n, given as % of VBase. 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.
tResetn: Reset time for step n if definite time delay is used, given in s. The default
value is 25 ms.
tnMin: Minimum operation time for inverse time characteristic for step n, given in s.
For very high voltages the overvoltage function, using inverse time characteristic, can
give very short operation time. This might lead to unselective trip. By setting t1Min
longer than the operation time for other protections such unselective tripping can be
avoided.
1MRK 505 370-UUS A Section 8
Voltage protection
Busbar protection REB670 2.2 ANSI 249
Application manual