Multifunction Protection and Switchgear Control unit REF542plus
Manual: Motor Protection with ATEX-Certification
motor current IB, a tripping is effected by the motor startup monitoring function. In the
range above 6.3 IB, a tripping is effected by the rotor monitoring function. The higher
the temperature rise or the thermal memory contents, the shorter the tripping time of
the thermal protection function. The illustration below shows how the tripping time
changes in comparison with the one applicable to the cold condition.
Tripping Characteristic Warm und Cold
1
10
100
1000
10000
0,5
1,0
1,5
2,0
2,5
3,0
3,5
4,0
4,5
5,0
5,5
6,0
6,5
7,0
7,5
8,0
8,5
9,0
9,5
10,0
I/IB
Time in s
TC 1112s; Warm
TC 1112s; Cold
Start up
Rotor
Figure 13: Reducing the tripping time at a 100% preloading
5.6 Behavior after recovering of the auxiliary voltage
When the auxiliary voltage of the REF542plus fails, the motor to be protected must
also be switched off. The duration of the failure of the auxiliary voltage can be super-
vised by the internal real time clock. The clock is able to operate in the next 2 hours
with the required accuracy. As soon as the auxiliary voltage recovers again, the
cooled down motor temperature is calculated according to equation 14. The result of
the calculated temperature is now used as initial temperature to continue the thermal
overload protection of the motor.
In this example the following are assumed:
td = 10 Min = 600 s
Tfail = 130°C
Tenviro = 20°C
Zk off = 1026 s
1VTA100114-Rev. 04 en PTMV, 19.01.05 Motorprotection 36 / 66
Valid from Version V4D02
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