Checking The Installation; Checking Of The Power Supply; Checking Ct Circuits - ABB RELION 620 Series Operation Manual

Section 8
Commissioning
8.2
8.2.1
8.2.2
112

Checking the installation

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 CT circuits

Check that the wiring is in strict accordance with the supplied connection
diagram.
The CTs must be connected in accordance with the terminal diagram provided with the
protection relay, both with regards to phases and polarity. The following tests are
recommended for every primary CT or CT core connected to the protection relay.
• 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.
1MAC456939-IB D
620 series ANSI
Operation Manual