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What Tests Should Be Done Before The Current Transformer Error Test?
Jun 26, 2018

1. the measurement transformer is compared with the standard transformer accurately. The two current difference of the two transformer is 1. accuracy check: the transformer error test is generally compared with the standard transformer, and the two current difference of the two transformer is the measured transformer error. This method of testing is called comparative method. The requirement of standard transformer is two times higher than that of the measured transformer. The error of standard transformer is negligible. If the standard transformer is only one level higher than the measured transformer, the error of the test result should be considered with the standard transformer error. The two current difference between the measured transformer and the standard transformer is usually measured by mutual inductor calibrator. Read out the ratio difference FX (%) and the phase difference x (") directly from the instrument calibrator. Because the mutual inductance calibrator is measuring the ratio between the current difference between the measured transformer and the standard transformer and the ratio of the two current, the requirement for the instrument calibrator is not high. What level of transformer can be calibrating is determined by standard transformer.


2. demagnetization check: when the current transformer suddenly drops, the core of the mutual inductor may generate remanence. If the current transformer suddenly cuts off the power supply and the two winding suddenly opens in the case of large current. The core of the mutual inductor has residual magnetism, which reduces the permeability of the core and affects the performance of the transformer. After long term use, the transformer should be degaussing. Degaussing is also required before the transformer is tested. Demagnetization means altering the magnetic field by altering the exciting current by one or two windings. From 0, the alternating magnetic field (excitation current) is gradually increased to saturate the core and then slowly reduce the excitation current to zero to eliminate remanence. For the current transformer demagnetization, the first winding opens, the two winding passes the power frequency current, gradually increasing from zero to a certain current value (the current value is related to the upper limit of the design measurement of the transformer, generally it is about 20-50% of the rated current. " It can be judged that if the current suddenly becomes larger and larger, the iron core will enter the magnetic saturation stage. Then slow down the current to zero, so repeat 2-3 times. Before interrupting the power supply, the primary winding should be short circuited before disconnecting the power supply. The iron core is degaussing. This method is called open demagnetization. For some current transformers, the number of turns of the two windings is quite large. If the open circuit demagnetization method is adopted, the open circuit winding may generate high voltage. Therefore, a larger resistance can be connected to the two winding (10-20 times the rated impedance). The primary winding passes through the current and changes from zero to the maximum permissible current of the primary winding of the transformer and then changes to zero, so repeat 2-3 times. Because the loaded iron core may not be demagnetizing completely. Because the maximum current of the primary winding is limited, it may burn out the primary winding if it is too large. If the load generated by the two winding is not too high, the load resistance of the two winding can be increased. This can improve the demagnetization effect.

3. polarity check: the primary winding of current transformer is P1 and P2, and the two winding marks are S1 and S2. If P1 and S1 are of the same name, this sign is called polarity reduction. A current comes in from P1, and the two current is from S1. Polarity checking is very simple. Besides checking the transformer calibrator, DC inspection can also be used.


Add: No.38 South Taoyuan Road, Yaozhuang Town,Jiashan County, Jiaxing City, Zhejiang Province, China
Contact person: Elva Zhuang&Sunny Ni
Tel:+86-573-84775555
Fax:+86-573-84776699
Phone:+86-13732570078
E-mail:sales9@great-relay.com
       sunny.ni@great-relay.com