the circuit is not provided with a continuous trip-circuit supervision, it is possibleto check that circuit is really closed when the test-plug handle has been removed byusing a high-ohmic voltmeter and measuring between the plus and the trip outputon the panel. The measurement is then done through the trip coil of the circuitbreaker and therefore the complete trip circuit is checked.Note that the breaker must be closed.Please observe that the test system does not provide built-insecurity during this test. If the instrument should be set on Ampinstead of Volts, the circuit breaker naturally is tripped, therefore,great care is necessary.Trip circuit from trip IEDs to circuit breaker is often supervised by trip-circuitsupervision. It can then be checked that a circuit is healthy by opening trippingoutput terminals in the cubicle. When the terminal is opened, an alarm shall beachieved on the signal system after a delay of some seconds.Remember to close the circuit directly after the test and tighten theterminal carefully.12.2.2.7 Measurement of service currents SEMOD56528-30 v4After a maintenance test it is recommended to measure the service currents andservice voltages recorded by the protection IED. The service values are checked onthe local HMI or in PCM600. Ensure that the correct values and angles betweenvoltages and currents are recorded. Also check the direction of directionalfunctions such as Distance and directional overcurrent functions.For transformer differential protection, the achieved differential current value isdependent on the tap changer position and can vary between less than 1% up toperhaps 10% of rated current. For line differential functions, the capacitivecharging currents can normally be recorded as a differential current.The zero-sequence current to earth-fault protection IEDs should be measured. Thecurrent amounts normally very small but normally it is possible to see if the currentcircuit is "alive".The neutral-point voltage to an earth-fault protection IED is checked. The voltageis normally 0.1 to 1V secondary. However, voltage can be considerably higher dueto harmonics. Normally a CVT secondary can have around 2.5 - 3% third-harmonicvoltage.Section 12 1MRK 505 372-UEN ACommissioning and maintenance of the fault clearing system168 Busbar protection REB670 2.2 IECCommissioning manual
