ABB REM 610, Technical Reference Manual

Page: 139 / 158

139
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 40°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
× = ≈
. .
(14)
For a direct-on-line started motor, p = 50%.
At an ambient temperature of 40°C the internal FLA equals the FLA of the motor.
Thus the start-up current of the motor is 6.2 x the internal FLA.
The safe stall time setting, t
6x
, is calculated or selected from the trip curves at prior
load 1 x FLA. A safe stall time setting of 30 seconds is selected, permitting a start-
up time slightly longer than the one stated by the motor manufacturer.
By selecting the correct trip curve from the trip curves at no prior load according to
the previously selected or calculated safe stall time setting, the total start-up time of
the motor can be read from the curve. In this case, the thermal protection element
will trip in approximately 28 seconds, which will allow two cold starts.
However, as the operate time when no prior load is longer than the safe stall time of
nineteen seconds, single motor start ups should instead be protected by the start-up
supervision. The start-up current, 48/14 PICKUP, is set to equal the start-up current
of the motor and the start-up time, 48/14 TDLY, to approximately ten per cent above
the start-up time of the motor in order to leave a safety margin for operation. Thus
48/14 TDLY is set to 1 s x 1.1
≈
12 s.
As the safe stall time is longer than the start-up time of the motor, no speed switch
will be required.
As one motor start up uses 11 s/28 s
≈
39% of the thermal capacity of the motor, the
restart disable level, 49 RESTDIS, should be set to below 61 per cent, e.g. to 55 per
cent.
The prior alarm level, 49 ALARM, is set to 80...90 per cent of the trip level.
The time constant multiplier, K
c
, is set to 4.
Motor Protection Relay
Technical Reference Manual - ANSI Version
REM 610 REM 610
1MRS755537