If the CT secondary circuit is opened or its ground connection is missing
or removed without the CT primary being de-energized first, dangerous
voltages may be produced. This can be lethal and cause damage to the
insulation. The re-energizing of the CT primary should be prohibited as
long as the CT secondary is open or ungrounded.
8.2.3
Checking VT circuits
Check that the wiring is in strict accordance with the supplied connection diagram.
Correct possible errors before continuing to test the circuitry.
Test the circuitry.
•
Polarity check
•
VT circuit voltage measurement (primary injection test)
•
Grounding check
•
Phase relationship
•
Insulation resistance check
The polarity check verifies the integrity of circuits and the phase relationships. The
polarity must be measured as close to the protection relay as possible to ensure that most
of the wiring is also checked.
The primary injection test verifies the VT ratio and the wiring all the way from the primary
system to the protection relay. Injection must be performed for each phase-to-neutral
circuit and each phase-to-phase pair. In each case, voltages in all phases and neutral are
measured.
8.2.4
Checking binary input and output circuits
8.2.4.1
Checking binary input circuits
•
Preferably, disconnect the binary input connector from the binary input cards.
•
Check all the connected signals so that both the input level and the polarity are in
accordance with the protection relay specifications.
1MAC456939-IB D
Section 8
Commissioning
620 series ANSI
113
Operation Manual
