Both the primary and the secondary sides must be disconnected from the line and the
IED when plotting the excitation characteristics.
If the CT secondary circuit ground connection is removed without the current transformer
primary being de-energized, dangerous voltages may result in the secondary CT circuits.
4.8 Checking VT circuits
M11724-2 v10
Check that the wiring is in strict accordance with the supplied connection diagram.
Correct possible errors before continuing to test the circuitry.
Test the circuitry.
• Polarity check when applicable; this test is often omitted for CVTs
• VT circuit voltage measurement (primary injection test)
• Grounding check
• Phase relationship
• Insulation resistance check
The primary injection test verifies the VT ratio and the wiring all the way from the primary system to the
IED. Injection must be performed for each phase-to-neutral circuit.
While testing VT secondary circuit and associated secondary equipment, care shall be
exercised to isolate the VT from the circuit being tested to avoid backcharging the VT
from the secondary side.
4.9 Using the RTXP test switch
GUID-F1E29C06-7FE8-44D8-AD5A-EE8990A2AA41 v6
The RTXP test switch is designed to provide the means of safe testing of the IED. This is achieved by the
electromechanical design of the test switch and test plug handle. When the test plug handle is inserted, it
first blocks the trip and alarm circuits then it short circuits the CT secondary circuit and opens the VT
secondary circuits making the IED available for secondary injection.
When pulled out, the test handle is mechanically stopped in half withdrawn position. In this position, the
current and voltage enter the protection, but the alarm and trip circuits are still isolated and the IED is in
test mode. Before removing the test handle, check the measured values in the IED.
Not until the test handle is completely removed, the trip and alarm circuits are restored for operation.
Verify that the contact sockets have been crimped correctly and that they are fully
inserted by tugging on the wires. Never do this with current circuits in service.
Current circuit
1MRK 504 165-UUS Rev. J Section 4
Starting up
Transformer protection RET670 53
Commissioning manual
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