Protecting A Motor At An Ambient Temperature Other Than 40°C - ABB REM 610 Technical Reference Manual

REM 610
5.2.2.
126
Motor Protection Relay
Technical Reference Manual
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
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
Rated voltage, U
nm
Rated current, I
nm
Start-up current of the motor
Start-up time of the motor
Safe stall time
Ambient temperature
CT current ratio
Setting calculations
The FLA secondary scaling factor is calculated as follows:
1000A 5A
× 1.075 1.08
--------------- - ------ -
=
930A 5A
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.
4500 kW
3300 V
930 A
6.2 x FLA
11 s
19 s
20...70°C
1000/5 A (relay input = 5 A)
≈
1MRS 755537
≈
4.65.