Multifunction Protection and Switchgear Control unit REF542plus
Manual: Motor Protection with ATEX-Certification
4.1 Supervision of a blocking rotor
When the rotor is blocked, the current in the motor increases and is determined by
the starting current which magnitude is a multiple of the rated motor current. In order
to prevent a thermal overload, a fast tripping must be generated. The blocking rotor is
supervised by a special, overcurrent definite time protection function which generates
a tripping signal with settable delay as soon as an adjustable current threshold is ex-
ceeded.
4.1.1 Setting parameters
For operation, the parameters need to be set as shown below:
Figure 1: Parameter settings for monitoring the rotor blocking
Where:
IMn Nominal motor current, related to the nominal current In of the cur-
rent transformer or current sensor
Start value Threshold value, related to the nominal motor current IMn
Time Tripping time in ms.
As soon as the start value for the current during the starting process is exceeded, the
time for generating the trip is started. The start value is specified in the manufacturer's
data sheet for the current in case of blocked rotor. The time for the tripping can be set
to approximately to the permissible blocking time. If a sensor for detecting the rotor
movement is available, the signal can be used for blocking this protection function.
4.1.2 Functional check
For checking the blocking rotor monitoring functions, it is recommended to use single-
or three-phase testing equipment. By varying the test current it is possible to observe
the generation of the start signal and, after the preset time has expired, the tripping
signal.
1VTA100114-Rev. 04 en PTMV, 19.01.05 Motorprotection 11 / 66
Valid from Version V4D02
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