Checking The Set Safe Stall Time For Cold Starts - ABB REM 610 Technical Reference Manual

REM 610
5.1.2.3.
118
Motor Protection Relay
Technical Reference Manual
t/s
50
40
30
20
10
5
4
3
2
1.05
1
2 3
1
Fig. 5.1.2.2.-3 Selected safe stall time=60 s

Checking the set safe stall time for cold starts

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. The total start-up time should permit as many
cold starts as stated by the motor manufacturer.
In applications where, for instance, three cold vs two hot starts are allowed, the total
start-up time of the motor may allow too many cold starts. In this case, the thermal
protection can be supplemented by using the cumulative start-up time counter for
limiting the number of cold starts. Alternatively, setting the weighting factor to 40
per cent, instead of to 50 per cent, has at times proved useful.
The operate time when no prior load with the selected safe stall time setting can also
be calculated as follows:
operate time = 32.15
t
6x
[s]
120
60
30
20
15
10
5
2.5
I/I
n
4 5 6 8 10

I


---------------- -

 FLC
× × ----------------------------------------------- -
t ln

6x
I


start
---------------- -


FLC
 int
1MRS 752263-MUM

2

start



int

2


– 1.1025


