4.8 Checking VT circuitsCheck 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)• Earthing check• Phase relationship• Insulation resistance checkThe primary injection test verifies the VT ratio and the wiring all the way from theprimary system to the IED. Injection must be performed for each phase-to-neutralcircuit.While testing VT secondary circuit and associated secondaryequipment, care shall be exercised to isolate the VT from the circuitbeing tested to avoid backcharging the VT from the secondary side.4.9 Using the RTXP test switchThe RTXP test switch is designed to provide the means of safe testing of the IED. Thisis 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 itshort circuits the CT secondary circuit and opens the VT secondary circuits makingthe IED available for secondary injection.When pulled out, the test handle is mechanically stopped in half withdrawn position.In this position, the current and voltage enter the protection, but the alarm and tripcircuits are still isolated and the IED is in test mode.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 restoredfor operation.Section 4 1MRK 511 360-UEN AStarting up50 Bay control REC670 2.1 IECCommissioning manual
