Table of Contents
Advertisement
14.7.3.3 Motor Start Protection
A motor start can be critical if the load duration or the current increases. The motor start behaviour
depends on the switching torque of the specific machine load. In general, these overloads are
more critical for the rotor (rotor-critical motor) than the stator. The manufacturer assigns an allowable
current-time start integral I
information on the maximum allowable start current and the maximum allowable start time.
Fig. 72
Nominal Motor Current (IMn):
Start Value (Is):
Time (ts):
Motor Start (IMs):
Parameter
Nominal Motor Current (IMn)
Start Value (Is)
Time (ts)
Motor Start Threshold (IMs)
End of Start Threshold (Ieos)
a 0,95 p.u. di IMs
The threshold setting range is expressed in primary current Ampere [A]. IMn is the motor nominal
current, by default equal to In, the feeder Nominal Primary Current value entered in the General
Settings.
2
t for motors. As an alternative, the motor manufacturer can provide
Nominal Motor current for operational condition detection
Motor start current for Trip condition detection (start energy integral
2
I
t).
Time for Trip condition detection.
Current threshold for motor start condition detection.
Values
Default
0.80 – 1.20 p.u. di In
100
1.00 – 20.00 p.u. di IMn 100
50 .. 300000
50
0.5 – 0.8 p.u. di Is
50
da 0.45 di Is
45
Step Unit
Explanation
1
A
Motor nominal current.
1
A
Trip condition detection
2
(integral I
t).
10
ms
Time for integral Trip
condition.
1
A
Current threshold for
Start condition.
1
A
Current threshold for
Start/ exit condition.
81
Advertisement
Table of Contents
