Checking Ct Circuits - ABB RELION 630 Series Comissioning Manual

1MRS756801 E
2.7
630 series
Commissioning Manual
Be sure to set the correct technical key in both the IED and PCM600
to prevent writing an application configuration to a wrong IED.
See the engineering manual for information on how to create or
modify an application configuration and how to write to the IED.

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 L1, L2, L3.)
• 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.
• 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.
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.
Section 2
Starting up
15