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Section 8
Voltage protection
( )
>
U
%
IECEQUATION2290 V1 EN-US
The setting depends on the required sensitivity of the protection and the type of system
earthing. In non-effectively earthed systems, the residual voltage cannot be higher than three
times the rated phase-to-earth voltage, which should correspond to 100%.
In effectively earthed systems, this value depends on the ratio Z0/Z1. The required setting to
detect high resistive earth faults must be based on network calculations.
tn : time delay of step n , given in s. The setting is highly dependent on the protection
application. In many applications, the protection function has the task to prevent damage to
the protected object. The speed might be important, for example, in the case of the protection
of a 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
time for other protections such unselective tripping can be avoided.
ResetTypeCrvn : Set reset type curve for step n . This parameter 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.
kn : 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 for step n , to set to create programmable
undervoltage inverse time characteristic. Description of this can be found in the technical
reference manual.
CrvSatn : Set tuning parameter for step n . When the denominator in the expression of the
programmable curve is equal to zero, the time delay will be infinite. There will be an undesired
discontinuity. Therefore, a tuning parameter
phenomenon. In the voltage interval
U> · (1.0 + CrvSatn /100). If the programmable curve is used this parameter must be calculated
so that:
CrvSatn
×
B
100
EQUATION1448 V1 EN-US
HystAbsn: Absolute hysteresis for step n , set in % of UBase . The setting of this parameter is
highly dependent of the application. The hysteresis is used to avoid oscillations of the START
output signal. This signal resets when the measured voltage drops below the setting level and
leaves the hysteresis area. Make sure that the set value for parameter
smaller than the set pickup value. Otherwise there is a risk that step n will not reset properly.
216
(
)
×
UBase kV
3
-
>
C
0
CrvSatn is set to compensate for this
U> up to U> · (1.0 + CrvSatn /100) the used voltage will be:
1MRK 505 370-UEN D
(Equation 74)
t1Min longer than the operation
(Equation 75)
HystABSn is somewhat
Busbar protection REB670
Application manual
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