Which procedures are needed during the verification process
GB1208-1997 "Current Transformer" GB8170-87 "Data Rounding Rules" JJG313-94 "Measurement Procedures for Measuring Current Transformers" DL408-91 "Electricity Safety Work Regulations (Electrical Part)" Q/CSG 10004-2004 Electrical work ticket technical specifications (transformation part)
Key terms in the testing process
Secondary load secondary loop impedance, expressed in ohms and power factor. Current error (ratio difference) The error that occurs when a transformer measures current. This is due to the fact that the actual current ratio is not equal to the rated current ratio. The percentage value of the current error is expressed by the following equation: Current error = [100 (KnIs - Ip) / Ip] % In the formula: Kn - rated current ratio Ip - actual primary current Is - secondary current through Ip under measurement conditions The phase difference between the phase difference primary current and the secondary current phasor, the phasor direction is determined by the phase difference in the ideal transformer being zero. If the secondary current phasor leads the current phasor, the phase difference is positive. Usually expressed in minutes ('). When the excitation potential saturation point volt-ampere characteristic test, the voltage applied to the secondary winding of the current transformer increases by 10%, the current increases by 50%, and the corresponding voltage value.
Safety measures during testing
1. The current transformer on-site calibration must be powered off and the first type of work ticket should be filled in. The test personnel must be no less than two people; before the on-site work begins, the work permit should be performed with the duty officer, and the safety must be checked carefully. Whether the measures and technical measures meet the requirements, recognize the name of the equipment, and guard against the wrong position. 2. The test site should be equipped with a fence or fence. Safety helmets should be worn at the test site. Seat belts must be used for climbing operations. Objects must not be thrown up and down. When handling ladders on site, they should be transported by two people and maintain a sufficient safety distance from the live parts. 3. The test power supply must be connected to the power supply cabinet, test power cabinet or other power supply that can be used for this test. It is strictly forbidden to take power directly from the running equipment. The power switch of the test device should use a bipolar knife with obvious disconnection. The gate and the knife gate shall be provided with an insulating cover. There should be two series switches in the low-voltage circuit of the test device, and an overload automatic trip device should be installed. 4. The tester should concentrate on the insulation pad for operation. When changing the connection line or at the end of the test, the test power should be disconnected. 5. Before the on-site calibration, the relevant protection circuit should be exited, and all secondary windings of the transformer should be disconnected from the secondary circuit and marked for recovery after the test. This work is carried out in accordance with the “Second Equipment and Circuit Work Safety Technical Measures Sheetâ€. A current transformer with multiple secondary windings. When testing one winding, the other ends of the secondary winding must be short-circuited. 6. At the end of the test, the self-installed grounding wire, short-circuit wire, etc. should be removed, the site should be inspected and cleaned, and the test equipment and test tools should be inspected. 7. There are live running equipment at the test site. In order to prevent damage to the equipment and personnel caused by high-voltage induction, the grounding point of the equipment must be grounded reliably. When replacing the high-voltage side wiring, the high-voltage side of the transformer should be short-circuited to ground. 8. Prevent the overhead transmission line from being inductive or inductively struck after the power failure. During the test, ensure that the transformer under test is disconnected from the overhead transmission line and the grounding wire is hung.
Means to prevent electric shock during testing
1. Insulate protection when connecting the test power supply. When it is not sure whether it is energized, the equipment should be regarded as live equipment. 2. When replacing the secondary wiring or at the end of the test, the power should be disconnected. 3. When replacing the high-voltage side wiring, the high-voltage side of the transformer should be short-circuited to ground. 4. When transporting long objects such as ladders, they must be transported by two people and pay attention to the safety distance. 5. Current transformers with multiple secondary windings. When testing one winding, the other ends of the secondary winding must be short-circuited.
How is the test cycle specified?
1. The current transformer after new installation or overhaul must be verified on site. 2. For the current transformer for measurement, at least one on-site calibration should be performed every 10 years. 3. The current transformer for protection shall be verified with the overhaul period of the equipment. The test items shall include: insulation resistance measurement, polarity inspection, ratio measurement, and volt-ampere characteristic test.
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