ABB Relion REC670 - Page 183

(%) ( )
3
U UBase kV< ×
EQUATION1447 V1 EN-US (Equation 91)
and operation for phase-to-phase voltage under:
U (%) UBase(kV)< ×
EQUATION1990 V1 EN-US (Equation 92)
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 , Prog. inv. curve . The selection is dependent on
the protection application.
OpModen : This parameter describes how many of the three measured voltages that should be
below the set level to give operation for step n. 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 low to give operation. If
UV2PTUV shall be insensitive for single phase-to-earth faults,
2 out of 3 can be chosen. In
subtransmission and transmission networks the undervoltage function is mainly a system
supervision function and 3 out of 3 is selected.
Un< : Set operate undervoltage operation value for step n , given as % of the parameter UBase .
The setting is highly dependent of the protection application. It is essential to consider the
minimum voltage at non-faulted situations. Normally this voltage is larger than 90% of
nominal voltage.
tn : time delay of step n , given in s. This setting is dependent of the protection application. In
many applications the protection function shall not directly trip when there is a short circuit or
earth faults in the system. The time delay must be coordinated to the short circuit protections.
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. When
using inverse time characteristic for the undervoltage function during very low voltages can
give a 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 to 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.
kn : Time multiplier for inverse time characteristic. This parameter is used for coordination
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 Un<
down to
Un< · (1.0 - CrvSatn /100) the used voltage will be: Un< · (1.0 - CrvSatn /100). If the
programmable curve is used this parameter must be calculated so that:
1MRK 511 358-UEN A Section 8
Voltage protection
177
Application manual