ABB 615 series Technical Manual page 491

1MAC059074-MB A
615 series ANSI
Technical Manual
• Primary injection test to verify the current ratio of the CT, the correct wiring up to the
protection relay and correct phase sequence connection (that is A, B, C.)
• Polarity check to prove that the predicted direction of the secondary current flow is
correct for a given direction of the primary current flow. This is an essential test 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.
• Grounding check of the individual CT secondary circuits to verify that each three-
phase set of main CTs is properly connected to the station ground and only at one
electrical point.
• Insulation resistance check.
• Phase identification of CT shall be made.
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 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.
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
Section 4
Protection functions
485