To assure selectivity between different protections, in the radial network, there has to
be a minimum time difference Dt between the time delays of two protections. T
o
determine the shortest possible time difference, the operation time of protections,
breaker opening time and protection resetting time must be known. These time delays
can vary significantly between different protective equipment. The following time
delays can be estimated:
Protection trip time: 15-60 ms
Protection resetting time: 15-60 ms
Breaker opening time: 20-120 ms
The different characteristics are described in the technical reference manual.
tx: Definite time delay for step x. The definite time tx is added to the inverse time when
inverse time characteristic is selected. Note that the value set is the time between
activation of the start and the trip outputs.
Pickup"x": Operate residual current level for step x given in % of IB.
INx>Max and INx>Min should only be changed if remote setting of operation current
level, INx>, is used. The limits are used for decreasing the used range of the INx>
setting. If INx> is set outside INx>Max and INx>Min, the closest of the limits to INx>
is used by the function. If INx>Max is smaller than INx>Min, the limits are swapped.
kx: T
ime multiplier for the dependent (inverse) characteristic for step x.
IMinx
: Minimum pickup current for step x in % of IB. Set IMinx below Pickupx for
every step to achieve ANSI reset characteristic according to standard. If IMinx is set
above for any step, signal will reset at current equals to zero.
txMin: Minimum operating time for inverse time characteristics. At high currents, the
inverse time characteristic might give a very short operation time. By setting this
parameter, the operation time of the step can never be shorter than the setting.
Section 8 1MRK 511 401-UUS A
Current protection
176 Bay control REC670 2.2 ANSI
Application manual
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