Test method for measuring no-load loss and no-load current of transformers

Transformer routine test when measuring no-load loss and no-load current.

All the excitation characteristics of the transformer are determined by no-load test, the purpose of no-load test is to measure the no-load loss and no-load current of the transformer, verify the design and calculation of the transformer core, and whether the process manufacturing meets the requirements of standards and technical conditions; Check whether the transformer core has defects, such as poor local insulation. No-load loss is mainly the hysteresis loss of electrical silicon steel sheet, and the additional loss of normal transformers can be ignored.

The transformer no-load test generally applies a waveform from a low voltage winding (such as a low voltage winding) that is sine wave, rated voltage at rated frequency, and the other winding is open.

If the winding to which the voltage is applied is tap-connected, the tap-changer should be in the main tap-connected position. If there is an open triangular connection winding in the test, it should be closed. The wiring and the tank housing at ground potential in operation should be reliably grounded.

Test wiring should pay special attention to the polarity of the voltage transformer and current transformer, and the three-phase power should be the algebraic sum of two watts. The accuracy of the voltage and current transformer used in no-load test is preferably not less than 0.1 level, and the accuracy of the instrument used is not less than 0.5 level. The wattmeter with power factor COSφ less than 0.2 should be used for measuring power.

Field test generally adopts two-watt-meter method, using two voltage transformers and two current transformers.

When the three-phase unbalance symmetry of the test transformer is less than 2%, the average value of the three line voltages or the line voltage between a-c can be applied to measure the no-load data. If the asymmetry of the three-phase voltage is greater than 2%, but less than 5%, the voltage can be applied in a-b, b-c, c-a respectively. When the voltage waveform is distorted, even if the mean value is different from the reading of the effective voltmeter, the mean voltmeter time voltage U should be used to measure no-load loss Pm, no-load current I and effective voltage U.

Three-phase transformer no-load test adopts single-phase test method. The location of the fault is determined by the test.

When the loss of the same type of transformer is large, the single-phase no-load test of the transformer should also be carried out when there is a problem with the magnetic circuit. The current and loss of single-phase no-load test of transformer core structure with three columns can be converted to the three-phase test results, and the single-phase test results of transformer core structure with five columns can not be converted to the three-phase test results, and can only be compared with the test results of the same model with the same capacity and structure. The low voltage no-load measurement of transformer also adopts the method of single-phase measurement.
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