82
Instantaneous overcurrent protection
(IOC)
Chapter 10
Verifying settings by secondary
injection
10 Instantaneous overcurrent protection (IOC)
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.
10.1 Measuring the operate limit of set values
10.1.1 Phase overcurrent protection
Procedure
1. Inject a phase current in the terminal with start below the set-
ting value.
2. Increase the injected current in the L
n
phase until the
IOC--TRL
n
(
n
=1-3) signal 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.
10.1.2 Residual overcurrent protection (non-dir.)
Procedure
1. Inject a phase current in the terminal with start below the set-
ting value.
2. Increase the injected current in the L
n
phase until the
IOC--TRN signal 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.
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