Safe Stall Time For Hot Starts - ABB REM 610 Technical Reference Manual

1MRS 752263-MUM
5.1.2.2.
Motor protection Relay
Technical Reference Manual

Safe stall time for hot starts

The safe stall time setting, t
motor. The safe stall time can easily be determined from the trip curves at prior load
1 x FLC.
Normally, the safe stall time setting is selected to allow one hot or two cold starts.
The appropriate trip curve is selected by means of the start-up current and start-up
time (and margin) of the motor. If multiple hot starts are allowed, the total start-up
time instead of a single start-up time is to be used.
The safe stall time setting can be calculated as follows:
------------------------------------------------------------------------------------------------------------
t =
6x





× ----------------------------------------------------------------------- -
32.15 ln




where
t = required operate time (i.e the number of hot starts x start-up time of the motor
and margin)
ln = natural logarithm
I = start-up current of the motor
start
FLC = internal FLC (equals the FLC of the motor at an ambient temperature of
int
40°C)
p = weighting factor
I = prior load current (normally equal to the FLC of the motor).
prior
Note!
Cooling between starts is not considered in the formula above.
The operate time with the selected safe stall time setting can be calculated as
follows:
operate time = 32.15 t
, is determined according to the start-up time of the
6x
t
I I
2
p
 
start prior
---------------- - -------- - ---------------- -
×
–
 
FLC 100 FLC
int
I
2
 
start
---------------- -
– 1.1025
 
FLC
int

I

start

---------------- -

 FLC
× × ----------------------------------------------------------------------- -
ln

6x





REM 610

2




int




2 I
p
 
prior
-------- - × ---------------- -
–
 
100 FLC
int int
I 2

start
---------------- -
– 1.1025

FLC
int

2








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