Woodward highprotec MRI4, User Manual

Page: 495 / 727

Protective Elements
Commissioning: Thermal Replica
Object to be tested
Protective function ThR
Necessary means
Three-phase current source
Timer
Procedure
Calculate the tripping time for the current to be constantly impressed by using the formula for the thermal image.
The parameter of the temperature rise of the component »

w
« has to be known
to guarantee an optimal protection.
Legend:
Testing the threshold values
Apply the current you have based your mathematical calculation on.
Testing the trip delay
The thermal capacity should be zero before the test is started. See »Measuring
Values«.
For testing the trip delay, a timer is to be connected to the contact of the associated trip relay.
Apply the current you have based your mathematical calculation on. The timer is started as soon as the current is
applied and it is stopped when the relay trips.
Successful test result
The calculated tripping time and the fallback ratio comply with the measured values. For permissible
deviations/tolerances, please see Technical Data.
495 MRI4 DOK-HB-MRI4-2E
( )
t = τ-warm ln
I
2
- Ip
2
I
2
- (K*Ib)
2
.
t = Tripping delay
τ-cool = Cooling time constant
K = Overload Factor: The maximum thermal limit is defined as k *IB, the product of the overload factor and the base current .
I = measured current (x In)
Ip = Preload Current
Ib = Base current: Maximum permissible thermal continuous current.
τ-warm = Warming-up time constant