Characteristx: Selection of time characteristic for step x. Definite time delay and
different types of inverse time characteristics are available.
Inverse time characteristic enables fast fault clearance of high current faults at the
same time as selectivity to other inverse time phase overcurrent protections can be
assured. This is mainly used in radial fed networks but can also be used in meshed
networks. In meshed networks, the settings must be based on network fault
calculations.
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. To
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 operate 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.
INx>: 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: Time multiplier for the dependent (inverse) characteristic for step x.
IMinx: Minimum operate current for step x in % of IB. Set IMinx below INx> for every
step to achieve ANSI reset characteristic according to standard. If IMinx is set above
INx> 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.
1MRK 502 071-UEN - Section 9
Current protection
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 345
Application manual
To Next Page
Loading...
