Multifunction Protection and Switchgear Control unit REF542plus
Manual: Motor Protection with ATEX-Certification
Figure 2: Setting parameters for motor start protection
Where:
IMn nominal motor current
Start value Is start current value, related to the nominal motor current, as a
measure for the permissible temperature rise
Time permissible time for determination of the current/time starting
integral
Motor start (IMs) the setting for detecting a starting process, related to the
start value Is
In the following example, it is assumed that the blocking current of the motor corre-
sponds to a 6-fold nominal motor current and that the permissible blocking time is 5
sec. Generally, the blocking current can be assumed to be identical with the starting
current under heavy load condition. In this case, the starting value is set to 6 IMn
(nominal motor current) and the time is set to 5000 ms. The startup is supervised
based on the setting for motor startup, e.g. 0.8 as shown in figure 2. As soon as a
starting current is detected, the protection function for motor startup monitoring is
started and the current/time starting integral is calculated. The tripping time depends
on the magnitude of the actual starting current.
If, in the example above, a starting current of a 0.8 starting value Is is assumed, the
starting current will be 0.8 x 6 = 4,8 of the rated motor current IMn. A tripping signal is
generated after a time of
s 7.81s
8.4
56
2
2
==t
1VTA100114-Rev. 04 en PTMV, 19.01.05 Motorprotection 13 / 66
Valid from Version V4D02
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