ABB REM 610 - Protecting a Motor at an Ambient Temperature Other than 40°C

If the pickup value of element 50P is set to be doubled during motor start up (SGF3/
8=1), the pickup value should be set below the start-up current of the motor, i.e to
75...90% x the start-up current of the motor: 50P = 0.75 x 6.2 ≈ 4.65.
6.3. Protecting a motor at an ambient temperature other than 40°C
Data of the squirrel cage motor stated by the manufacturer:
Rated power, P
nm
4500 kW
Rated voltage, U
nm
3300 V
Rated current, I
nm
930 A
Start-up current of the motor 6.2 x FLA
Start-up time of the motor 11 s
Safe stall time 19 s
Ambient temperature 20...70°C
CT current ratio 1000/5 A (relay input = 5 A)
Setting calculations
The protected unit scaling factor is calculated as follows:
1000
930
5
5
1 075 1 08
A
A
A
A
×= ≈..
(15)
For a direct-on-line started motor, p = 50%.
At an ambient temperature of 40°C the internal FLA is 1.0 x FLA of the motor.
Thus, the start-up current of the motor is 6.2 x the internal FLA. A safe stall time of
30 seconds is selected as in the previous application example.
If the ambient temperature is lower than 40°C, the motor can be run at a slight
overload in relation to the specified maximum load at 40°C. If the ambient
temperature is higher than 40°C, the continuous load must be lower than the
specified maximum load at 40°C.
At an ambient temperature of 20°C the internal FLA is 1.09 x FLA of the motor.
Thus, the start-up current of the motor is 6.2/1.09 = 5.69 x the internal FLA. If a safe
stall time setting of 30 seconds is selected, the relay will allow two hot starts instead
of one. If this is unacceptable, however, and only one hot start is to be allowed, a
safe stall time setting of 23 seconds is to be selected instead.
At an ambient temperature of 65°C the internal FLA is 0.75 x the FLA of the motor.
Thus, the start-up current of the motor is 6.2/0.75 = 8.27 x the internal FLA. If a safe
stall time setting of 30 seconds and a prior load of 0.75 x the FLA of the motor are
selected, the relay will not allow a hot start until the motor has been at standstill for
several minutes. However, if a hot start is to be allowed, a safe stall time setting of
approximately 50 seconds is to be selected instead.
All other settings are as in the previous application example.
140
REM 610REM 610
Motor Protection Relay
Technical Reference Manual - ANSI Version
1MRS755537