Time Constant Dial, Kc; Start-Up Supervision; Start-Up Supervision Based On Thermal Stress Calculation; Checking The Need For Speed Switch - ABB REM 610 Technical Reference Manual

REM 610 REM 610
6.1.2.7.
6.1.3.
6.1.3.1.
6.1.3.2.
134
Motor Protection Relay
Technical Reference Manual - ANSI Version
Generally, the prior alarm level is set to 80...90 per cent of the trip level.
Time constant dial, K
The time constant dial, K
the heating time constant:
τ
cooling
=
K
τ
c
heating
Generally, the time constant dial of the motor is set to 4...6. However, when
protecting non-rotating objects, e.g. feeder cables or transformers, for instance, the
time constant dial is generally set to one.

Start-up supervision

Start-up supervision is based on thermal stress calculation by default but can also be
set to be based on definite-time overcurrent protection, especially in other than
motor applications.

Start-up supervision based on thermal stress calculation

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.
For instance, if the start-up current of the motor is 6.2 x FLA and the start-up time
11 seconds, 48/14 PICKUP = 6.2 and 48/14 TDLY = 11 s x 1.1 = 12 s.

Checking the need for speed switch

When protecting motors of ExE-type, for instance, the safe stall time may be shorter
than the start-up time of the motor, which is why a speed switch on the motor shaft
is required to give information on whether the motor is accelerating during motor
start up. In this case, the start-up time is set to slightly below the safe stall time.
The speed switch should be open at standstill and closed during acceleration. When
the input is activated, element (48/14 PICKUP)
blocked. If the motor does not start to accelerate, element (48/14 PICKUP)
14 TDLY) will trip when the reference value, (48/14 PICKUP)
exceeded. If start-up supervision is based on overcurrent protection, element 48/14
will trip on expiration of the set operate time
However, if the safe stall time is longer than the start-up time of the motor when no
prior load, a speed switch will not be required.
c
, is the ratio of the cooling time (at motor standstill) and
c
2
1MRS755537
(10)
x (48/14 TDLY)/(48/14) will be
2
x (48/14 TDLY), is
2
x (48/