The following points shall be checked during and after commissioning:. No abnormality in the system after energization.
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Voltage measurement shall be done for all points and found normal. Phase sequence check for correct rotation. Phasing check before paralleling two circuits by either hot stick or VT secondary side. Battle for lordaeron bug.
If the circuit is loaded, CT secondary current of all cores and phases shall be measured with angle with respect to any one of the phase voltages. Directional test shall be done for directional protection, like directional O/C, E/F, and distance protection. This test has been explained later. Stability test shall be done for. If applicable, on load test for automatic voltage controller shall be done for transformer. Check for correct readings on indicating meters.
Live test for auto-changer over scheme, auto-reclosing scheme shall be done. Phasing checks:Before making two live feeders parallel, the phasing must be checked though the source is same.
This could be done in two methods. One method is hot phasings, most reliable method, since the check is done on the primary. The voltage difference between feeders shall be monitored by connecting hot stick (Voltage detector equipment, rated for system voltage, that will indicate presence of voltage) between Rph-Rph, Yph-Yph, Bph-Bph of two feeders respectively.Another method is phasing between VT secondaries, and a caution be taken for this method, that there is no mistake on secondary wiring.To ensure correct connection of primary and secondary, energise both the VTs by any one supply and do phasing between secondaries.
For correct connection no voltage difference shall be observed during phasing. Now the VTs could be energised with respective feeder’s supply and repeat the phasing between VT secondaries. If there is no considerable between the feeders voltage, they are ready to parallel. Synchronising Check:Before making to different source of same voltage level, in addition to phasing check, synchronisation must be done. The following steps shall be followed. Adopt proper setting for synchro-check relay. Check the secondary grounding for all VTs are at same point (star point or Y phase).
Energise both the VTs with same source. Do phasing between VT secondaries, check synchro-check relay picks up continuously and synchroscope is staying at 12’o clock position. This ensures that the primary and secondary connections of VTs are correct.
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Now energise the VTs with respective sources. Check the synchroscope the pointer continues to rotate.
3.5 OnLoad Stability TestThis is the test to confirm the stability of a differential protection for through fault with load current. The following precautions shall be taken during test. Protection shall be put out of service, i.e. All out put contacts are isolated.
Never open circuit CT circuit. At the end of the test all the connections shall be restored back.3.5.1 Transformer Differential protection:The current inputs to the relay from all the windings of the transformer shall be measured with angle WRT any phase voltage of VT. The differential current also is measured externally or internally by relay. There should be no differential current (practically not zero) during this test. If sufficient load is not available on the transformer, this test could be done by making two transformers parallel and keeping at different taps (A circulating current will be flowing between them). 3.5.2 Pilot wire differential protection:The CT currents at both the ends shall be measured with phase angle.
The pilot current shall be measured between the relays at normal load condition. The following steps are followed. Isolate trip and alarm. Enable the pilot wire relay with O/C check input energised (if applicable). Measure the relay CT input current at both ends in all phases. Measure the pilot current with normal pilot connection.
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Connect only ‘R’ phase CT to the relay and other phase’s CT short and isolate at both the ends fig 4.1. Now check the pilot current and observe the relay is stable. Reverse the pilot connection and measure the pilot current.
Should pilot current reduce and relay operates for correct function. It shall be repeated for ‘Y’,’B’,’RY’,’YB’,’BR’,”RYB’ combinations.3.5.3 Busbar differential protection:The entire feeder’s current shall be measured with phase angle. The differential current at main relay and voltage across CT bus shall be measured. At normal load condition there should be no differential current and voltage. Fig 1 – Pilot wire protection on load test.
Electrical Commissioning Start-up TestingElectrical commissioning is essential to the start up of any electrical system for the first time, regardless of size or industry. Once equipment is installed, Electrical Testing Solutions will perform visual, mechanical, and electrical tests to help ensure trouble-free energizing of the equipment.