If the CT secondary circuit earth connection is removed without thecurrent transformer primary being de-energized, dangerous voltagesmay result in the secondary CT circuits.4.8 Checking VT circuits M11724-2 v10Check 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 switch GUID-F1E29C06-7FE8-44D8-AD5A-EE8990A2AA41 v5The 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 plughandle. When the test plug handle is inserted, it first blocks the trip and alarmcircuits then it short circuits the CT secondary circuit and opens the VT secondarycircuits making the IED available for secondary injection.When pulled out, the test handle is mechanically stopped in half withdrawnposition. In this position, the current and voltage enter the protection, but the alarmand trip circuits are still isolated and the IED is in test mode. Before removing thetest handle, check the measured values in the IED.Section 4 1MRK 506 383-UEN AStarting up42 Line distance protection REL650 2.2 IECCommissioning manual
