t/s
1000
100
500
200
50
10
20
5
1
2
3
4
30
40
300
400
2000
3000
4000
1
2
3
4
5
10
6
8
I/I
q
1.05
p
[%]
20
50
75
100
x
Cold
curve
Figure 185: The influence of Weighting factor p at prior load 1xFLC, timeconstant =
640 s, and Overload factor = 1.05
Setting the overload factor
The value of
Overload factor defines the highest permissible continuous load. The
recommended value is 1.05.
Setting the negative sequence factor
During the unbalance condition, the symmetry of the stator currents is disturbed
and a counter-rotating negative sequence component current is set up. An
increased stator current causes additional heating in the stator and the negative
sequence component current excessive heating in the rotor. Also mechanical
problems like rotor vibration can occur.
The most common cause of unbalance for three-phase motors is the loss of phase
resulting in an open fuse, connector or conductor. Often mechanical problems
1MRS757644 H
Protection functions
620 series
Technical Manual
371
