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

REM 610 REM 610
6.5.
6.6.
142
Motor Protection Relay
Technical Reference Manual - ANSI Version
As one motor start-up uses 9 s/20 s ≈ 45% of the thermal capacity of the motor, the
restart disable level, 49 REDIS, should be set to below 55 per cent, e.g. to 50 per
cent.
The prior alarm level, 49 ALARM, is set to 80...90 per cent of the trip level.
The time constant multiplier, K
The high-set overcurrent element 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 ground-fault element should be set
to be disabled when one or several phase currents exceed the FLA 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
(pickup criterion I >48/14 PICKUP). If start-up supervision is set to be based on
p
thermal stress calculation (SGF3/6=0) and element (48/14 PICKUP)
TDLY) is set to pickup when one or several phase currents exceed the set pickup
value (SGF3/7=1), the tripping of element (48/14 PICKUP)
be similar to that at the IDMT characteristic "extremely inverse".
If a core balance transformer is used for measuring the ground-fault current, refer to
Section 6.1.7. Ground-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

Ground-fault protection in an isolated or a compensated network

Data of the motor stated by the manufacturer:
Network ground-fault current at fully
developed ground-fault
Required ground-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 pickup value of element 51N is calculated as follows:
1 A
× ×
20 % 10 A
100 A
Thus, 51N = 2% and the 1A input is used.
, is set to 4...6.
c
, the expression τ = 32.15 x t
6x
, is set to 1.
c
= ×
2 % 1 A
1MRS755537
2
x (48/14
2
x (48/14 TDLY) will
can be used.
6x
10 A isolated network
20% (=2A)
(17)