There is a polarity relationship between the primary and secondary sides of the power transformer coil. If there are several coils or power transformers combined, their polarity needs to be known in order to be used correctly. For a power transformer with two coils, if the electric potential induced within it at any moment has the same direction, it is called homopolarity or depolarization, otherwise it is called additive polarity. The connection group of power transformers is one of the important parameters of power transformers and an important condition for parallel operation of power transformers. In many cases, measurement is required.
1、Purpose and significance of polarity group and voltage ratio test for power transformers
Under the condition of no-load operation of a power transformer, the ratio of the voltage of the high-voltage winding to the voltage of the low-voltage winding is called the voltage ratio of the power transformer: K=U1/U2. The voltage ratio is generally calculated based on the line voltage, and it is an important performance indicator of the power transformer.
The purpose of measuring the transformation ratio of power transformers is to:
① Ensure that the voltage ratio of each tap in the winding is within the technically permissible range;
② Check the correctness of the winding turns;
③ Determine whether the leads and tap changer connections of each tap in the winding are correct.
2、 Test methods for polarity groups and voltage ratios of power transformers
① The DC method determines the polarity of power transformers, and there are two methods for measuring the polarity of power transformer windings: the DC method and the AC method.
DC method: connect a Dry cell to the high-voltage terminal of the power transformer, and connect a milliammeter or microammeter to the secondary side of the power transformer. During the experiment, observe the swing direction of the meter needle when the battery switch is closed to determine the polarity.
② Determine the group of power transformers using the DC method;
③ Use a fully automatic transformer ratio group tester to measure the transformer ratio.
3、 Notes and Consequence Analysis
① When using the direct current method to confirm polarity, the experimental process should be repeated several times to avoid the fallacy of the argument that the pointer swings quickly.
② When measuring the group, for transformers with high transformation ratio, higher voltage and small range DC millivoltmeter, microampere meter or multimeter should be selected; For those with a small transformation ratio, choose a lower voltage and less range millivoltmeter, microampere meter, or multimeter.
③ The transformation ratio of a transformer should be measured at each tap. When not only one degree coil has tap, the transformer DC resistance tester can take turns measuring at all tap positions of each coil, and its absolute tap coil should be connected to an additional tap.
④ For those with load voltage regulation devices, it is necessary to adopt electric operating devices to change the tapping.
⑤ Special attention should be paid to the alignment of transformers A and A during all measurement processes, otherwise high voltage will enter the bridge body.
⑥ When the test voltage is gradually increased, and the Voltmeter rapidly drops to the full degree, the lost power supply shall be turned off for review.
⑦ For the measured consequences, the voltage ratio of each corresponding tap should be opposite to the nameplate; The allowable deviation direction of the additional tap voltage ratio should be, while the deviation direction of other tap voltages should be within the impedance value of the transformer, but should not exceed.
The ZC-203AW fully automatic transformer ratio group tester is mainly used to supervise the quality of transformer products during delivery and use, to prevent inter turn short circuits, open circuits, connection errors, internal faults or contact faults of voltage regulating switches. The instrument is easy to operate, has complete functions, stable and reliable data, and has fast testing speed. It meets the needs of various large, medium, and small transformer ratio tests and is an ideal testing instrument for the power industry department.
Kvtester Electronics Technology Co.,Ltd. is a high-tech enterprise specializing in power testing, testing, research and development, production, and sales of testing equipment. It has been engaged in the electrical testing industry for many years, and its products are of high quality. We welcome customers to come and purchase.
