Protecting Non-Rotating Objects; Earth-Fault Protection In An Isolated Or A Compensated Network; Earth-Fault Protection In A Solidly Earthed Network - ABB REM 610 Technical Reference Manual

1MRS 752263-MUM
5.2.4.
5.2.5.
5.2.6.
Motor protection Relay
Technical Reference Manual
The high-set overcurrent stage should be set out of operation to prevent the contactor
in a contactor controlled drive from operating at too high phase currents. In addition,
to avoid damaging the contactor, the earth-fault stage should be set to be inhibited
when one or several phase currents exceed the FLC of the motor sixfold
(SGF4/1 = 1, SGF4/2 = 0). During high phase current conditions the protection will
be based on the backup fuses.

Protecting non-rotating objects

In other than motor applications, start-up supervision is usually set to be based on
definite-time overcurrent protection (SGF3/6=1) or on thermal stress calculation
(start criterion I >I ). If start-up supervision is set to be based on thermal stress
L s
calculation (SGF3/6=0) and stage I
currents exceed the set start value (SGF3/7=1), the tripping of stage I
similar to that at the IDMT characteristic "extremely inverse".
If a core balance transformer is used for measuring the earth-fault current, refer to
section 5.1.7. Earth-fault protection.
When protecting objects without hot spot tendencies, weighting factor p is set to 100
per cent. When setting t
Usually, the time constant multiplier, K

Earth-fault protection in an isolated or a compensated network

Data of the motor stated by the manufacturer:
Network earth-fault current at fully
developed earth-fault
Required earth-fault sensitivity
Due to the high sensitivity required, a residual connection cannot be used, but
instead, a core balance transformer with a CT ratio of 100/1.
The start value of stage I
1A
× × ------------ -
20% 10A =
100A
Thus, I > = 2% and the 1A input is used.
0

Earth-fault protection in a solidly earthed network

Data of the motor stated by the manufacturer:
Rated current, I
nm
CT current ratio
Required earth-fault sensitivity
2
x t is set to start when one or several phase
s s
, the expression τ = 32.15 x t
6x
, is set to 1.
c
10 A isolated network
20% (=2A)
> is calculated as follows:
0
×
2% 1A
1650 A
2000/5 A (relay input = 5 A)
20% I
nm
REM 610
2
x t will be
s s
can be used.
6x
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