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19
19.1
19.1.1
19.1.2
19.1.3
Two step time delayed directional phase
overcurrent protection (TOC3)
Two step time delayed directional phase
overcurrent protection (TOC3)
Prepare the terminal for verification of settings as outlined in section "Preparing for
test" in this chapter.
Consider to apply an three-phase symmetrical voltage at rated value and ZΦ=0° if the
settings are directional. If distance protection (ZMn) not are included in the terminal test
of directional lines has to be carried out.
Ensure that the maximum continuos current of a terminal does not exceed four times its
rated value, if the measurement of 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
Measuring the operate and time limit for set values
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 TOC3-STNDLS appears.
3.
Compare the result of the measurement with the set value.
Measuring the definite time delay of the low set stage
1.
Set a current 1.5 times I>Low on the injection test equipment
and three-phase symmetrical voltage if directional.
2.
Switch the current on and compare the operation time on
TOC3-TRLS with the set value tLow.
The operate time shall be tRelay+tLow.
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
TOC3-TRLS when the current is less than I>Low.
Chapter 10
Verifying settings by secondary
injection
99
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