ABB RELION REX640 Technical Manual page 584

Section 4
Protection functions
578
for the proper operation of the directional function, protection or measurement in
the protection relay.
• CT secondary loop resistance measurement to confirm that the current
transformer secondary loop DC resistance is within specification and that there
are no high resistance joints in the CT winding or wiring.
• CT excitation test to ensure that the correct core in the CT is connected to the
protection relay. Normally only a few points along the excitation curve are
checked to ensure that there are no wiring errors in the system, for example, due
to a mistake in connecting the CT's measurement core to the protection relay.
• CT excitation test to ensure that the CT is of the correct accuracy rating and that
there are no short circuited turns in the CT windings. Manufacturer's design
curves should be available for the CT to compare the actual results.
• Earthing check of the individual CT secondary circuits to verify that each three-
phase set of main CTs is properly connected to the station earth and only at one
electrical point.
• Insulation resistance check.
• Phase identification of CT shall be made.
CT and VT connectors are pre-coded, and the CT and VT connector
markings are different. For more information, see the installation
manual.
Both the primary and the secondary sides must be disconnected from
the line and the protection relay when plotting the excitation
characteristics.
If the CT secondary circuit is opened or its earth 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 unearthed.
Checking of the power supply
Check that the auxiliary supply voltage remains within the permissible input voltage
range under all operating conditions. Check that the polarity is correct before
powering the protection relay.
Checking binary I/O circuits
Always check the binary input circuits from the equipment to the protection relay
interface to make sure that all signals are connected correctly. If there is no need to test
a particular input, the corresponding wiring can be disconnected from the terminal of
the protection relay during testing. Check all the connected signals so that both input
voltage level and polarity are in accordance with the protection relay specifications.
However, attention must be paid to the electrical safety instructions.
1MRS759142 C
REX640
Technical Manual