ABB REB670 Applications Manual page 244

Section 8
Voltage protection
238
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.
ResetTypeCrvn: This parameter for inverse time characteristic can be set: Instantaneous,
Frozen time, Linearly decreased. The default setting is Instantaneous.
tIResetn: Reset time for step n if inverse time delay is used, given in s. The default value
is 25 ms.
TDn: Time multiplier for inverse time characteristic. This parameter is used for co-
ordination between different inverse time delayed undervoltage protections.
ACrvn, BCrvn, CCrvn, DCrvn, PCrvn: Parameters to set to create programmable under
voltage inverse time characteristic. Description of this can be found in the technical
reference manual.
CrvSatn: When the denominator in the expression of the programmable curve is equal to
zero the time delay will be infinity. There will be an undesired discontinuity. Therefore a
tuning parameter CrvSatn is set to compensate for this phenomenon. In the voltage
interval Pickup> up to Pickup> · (1.0 + CrvSatn/100) the used voltage will be: Pickup> ·
(1.0 + CrvSatn/100). If the programmable curve is used, this parameter must be calculated
so that:
CrvSatn
× - >
B C 0
100
EQUATION1448 V1 EN
HystAbsn: Absolute hysteresis set in % of VBase. The setting of this parameter is highly
dependent of the application. If the function is used as control for automatic switching of
reactive compensation devices the hysteresis must be set smaller than the voltage change
after switching of the compensation device.
1MRK 505 337-UUS -
(Equation 77)
Application manual