Checking The Need For Speed Switch; Cumulative Start-Up Time Counter - ABB REM 610 Technical Reference Manual

1MRS 755537
5.1.3.2.
5.1.4.
Motor protection Relay
Technical Reference Manual
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)
is 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.

Cumulative start-up time counter

The cumulative start-up time counter functions as backup to the thermal overload
protection and prevents too frequent motor start ups, i.e. ensures that the
recommendations from the manufacturer are followed.
There are two values to set: the restart disable value in seconds, 66, and the
countdown rate of the start-up time counter,
The restart disable value is calculated as follows:
66 = (n-1) x t + margin
where
n = allowed number of motor start ups
t = start-up time of the motor (in seconds)
margin = safety margin (~10... 20%)
The countdown rate is calculated as follows:
t
66 COOL =
t
reset
where
t = start-up time of the motor (in seconds)
t = time during which the maximum number of motor start ups stated by the
reset
manufacturer can be made (in hours)
If the motor manufacturer has recommended a maximum of three start ups in four
hours and a start-up time of 60 seconds/start up, the restart disable will be activated
when the third motor start up has been initiated, thus preventing a fourth motor start
up. Consequently, the restart disable value is to be set to 130 seconds.
2
x (48/14 TDLY) /(48/14) will be
2
x (48/14 TDLY) ,
∆
t.
66 COOL /
REM 610
2
x (48/
121