ABB REM 610 - Ground-Fault Protection in a Solidly Grounded Network

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6.7. Ground-fault protection in a solidly grounded network
Data of the motor stated by the manufacturer:
Rated current, I
nm
1650 A
CT current ratio 2000/5 A (relay input = 5 A)
Required ground-fault sensitivity 20% I
nm
The pickup value of element 51N is calculated as follows:
20 1650
5
2000
16 5%%×× =×A
A
A
A
(18)
Thus, 51N = 16% and the 5A input is used.
The operate time of the ground-fault element is set to 50 ms when the network is
solidly grounded.
If the drive is contactor controlled, refer to Section 6.4. Protecting a contactor
controlled motor.
Motor Protection Relay
Technical Reference Manual - ANSI Version
REM 610REM 610
1MRS755537