102
Two step time delayed phase overcurrent
protection (TOC2)
Chapter 10
Verifying settings by secondary
injection
20
Two step time delayed phase overcurrent
protection (TOC2)
Prepare the terminal for test as outlined in section “Preparing for test” in this chapter.
Ensure that the maximum continuos current of a terminal does not exceed four times its
rated value, if the measurement od the operating characteristics runs under constant
voltage conditions.
To verify the settings the following fault type should be tested:
•
One for a phase-to-earth fault
20.1
Measuring the operate and time limit for set values
20.1.1
Measuring the operate limit of the low step overcurrent protection
Procedure
1.
Inject a phase current slightly smaller than the functional val-
ue I>Low.
2.
Increase the current slowly and check the function value by
observing when the signal TOC2-STLS appears.
3.
Compare the result of the measurement with the set value.
20.1.2
Measuring the definite time delay of the low set stage
1.
Set a current 1.5 times I>Low on the injection test equipment.
2.
Switch the current on and compare the operation time on
TOC2-TRLS with the set value tLow.
The operate time shall be tLow.
20.1.3
Measuring the inverse time delay of the low set stage
1.
Set temporarily tLow = 0.000 s.
If I>Low is set higher than I>Inv, check that there is no trip signal
TOC2-TRLS when the current is less than I>Low.
2.
Check the time delay at two points of the inverse time curve.
Check with the current I>Low or 2·I>Inv (the highest value of
these two) and the current that according to the inverse time curve
corresponds to tMin.
