98
Time delayed overcurrent protection
(TOC)
Chapter 11
Verifying settings by secondary
injection
15
Time delayed overcurrent protection (TOC)
Prepare the terminal for verification of settings as outlined in section “Preparing for
test” in this chapter.
To verify the settings the following fault type should be tested:
•
One for a phase-to-earth fault
Ensure that the maximum continuous current of the terminal does not exceed four times
its rated value.
15.1
Measuring the operate limit of set values
15.1.1
Time delayed phase overcurrent
Procedure
1.
Inject a phase current in the terminal with start below the set-
ting value.
2.
Increase the injected current (measured current) in the L
n
phase until the starting signal TOC--STL
n
(
n
=1-3) appears.
3.
Switch off the fault current.
Observe the maximum permitted overloading of the current cir-
cuits in the terminal.
4.
Compare the measured operating current with the set value
IP>.
5.
Set the fault current to about 1.5 times the measured operat-
ing current.
6.
Switch on the fault current and measure the operating time of
the TOC protection. Use the TOC--TRP signal.
7.
Compare the measured time with the set value tP.
15.1.2
Time delayed residual overcurrent (non-dir.)
Procedure
1.
Inject a phase current in the terminal with start below the set-
ting value.
2.
Increase the injected residual current (measured current) in
the L
n
phase until the starting signal TOC--STN appears.
