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.
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:
Section 10 1MRK 506 369-UUS -
Voltage protection
574 Line distance protection REL670 2.2 ANSI
Application manual
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