Multifunction Protection and Switchgear Control unit REF542plus
Manual: Motor Protection with ATEX-Certification
4.5.1 Setting parameters
For operation purposes, the parameters need to be set as shown below:
Figure 9: Tripping characteristic for thermal protection at τ = 146sec or t
6IB
= 5sec
Where:
Is Current starting value, related to the rated current of the current
transformer or current sensor
K Temperature rise constant for the item of equipment to be pro-
tected
Reset time Time up until complete clearing of the thermal memory contents
Discharge rate Reduction of the reset time in percentages
4.5.1.1 Setting the current starting value
The unbalanced load protection is activated only after the unbalanced load current
has exceeded the preset current starting value Is. Normally, the motor or generator
manufacturer can provide information on this setting. During operation, an unbal-
anced load of 10% of the rated current does not cause an impermissible temperature
rise in the motor or generator. So, it is possible to set the current starting value to 0.1
of the rated current of the motor or the generator. The unbalanced load protection is
activated and started if the unbalanced load is larger than the starting value.
4.5.1.2 Setting the tripping time
For the unbalanced load protection function, the tripping time is not set directly. The
size of the temperature rise constant K and the size of the unbalanced load finally de-
termines the tripping time in accordance with the equation given above. The tempera-
ture rise constant K should be provided by the manufacturer of the motor or the gen-
erator.
The following example demonstrates how to calculate the tripping time constant. In
this context, the following data are assumed:
1VTA100114-Rev. 04 en PTMV, 19.01.05 Motorprotection 28 / 66
Valid from Version V4D02
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