Checking Ct Circuits - ABB REQ650 Commissioning Manual

1MRK 505 385-UEN A
4.7
Breaker protection REQ650 2.2 IEC
Commissioning manual
When the configuration is written and completed, the IED is automatically set into
normal mode. For further instructions please refer to the users manuals for
PCM600.

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 circuit diagram provided with
the IED, both with regards to phases and polarity. The following tests shall be
performed on every primary CT connected to the IED:
• Primary injection test to verify the current ratio of the CT, the correct wiring
up to the protection IED and correct phase sequence connection (that is L1,
L2, L3.)
• Polarity check to prove that the predicted direction of secondary current flow
is correct for a given direction of primary current flow. This is an essential test
for the proper operation of the differential function and directional protection
functions.
• CT secondary loop resistance measurement to confirm that the current
transformer secondary loop DC resistance is within the specification for the
connected protection functions. When the measured loop resistance is near the
calculated value for maximum DC resistance, perform a complete burden test.
• CT excitation test in order to confirm that the current transformer is of the
correct accuracy rating and that there are no shorted turns in the current
transformer windings. Manufacturer's design curves must be available for the
current transformer 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.
While the CT primary is energized, the secondary circuit shall
never be open circuited because extremely dangerous high voltages
may arise.
Both the primary and the secondary sides must be disconnected
from the line and the IED when plotting the excitation
characteristics.
Section 4
Starting up
M12182-2 v15
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