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

REM 610
5.2.4.
5.2.5.
5.2.6.
128
Motor Protection Relay
Technical Reference Manual
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
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 5.1.7. Ground-fault protection.
When protecting objects without hot spot tendencies, weighting factor p is set to 100
per cent. When setting t
6x
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:
1A
× ×
20% 10A ------------ -
=
100A
Thus, 51N = 2% and the 1A input is used.

Ground-fault protection in a solidly grounded network

Data of the motor stated by the manufacturer:
Rated current, I
nm
CT current ratio
Required ground-fault sensitivity
). If start-up supervision is set to be based on
, the expression τ = 32.15 x t
, is set to 1.
c
10 A isolated network
20% (=2A)
×
2% 1A
1650 A
2000/5 A (relay input = 5 A)
20% x I
nm
1MRS 755537
2
x (48/14
2
x (48/14 TDLY) will
can be used.
6x