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Solution: Current Transformer Mutual Ratio Test Simple Method - Electronic Chip Application Technology
Sep 12, 2017

Solution: current transformer mutual ratio test simple method - electronic chip application technology

The current transformer is a kind of special transformer specially used for changing current, under normal operating conditions, the current is substantially a current proportional to the connection and in the right direction, two current on a current phase difference is close to zero.

Principle of measuring voltage ratio of current transformer by 1 voltage method

The method of measuring current transformer ratio by voltage method is suitable for field test. The advantage of this method is that it has few equipment, simple circuit and easy operation.

The voltmeter V monitors the two voltage of the current transformer, and the voltmeter mV monitors the primary side voltage of the current transformer. This method is similar to the method of measuring the induction potential of the iron core.

From the phasor diagram: leakage impedance drop Us I = 0 (R + jX)

Two applied voltage: U2 = -E 2 + US

Induction potential: E 1 = 4.44fN1F M

E 2 = 4.44fN2F M

The ideal current transformer: K = N 2/N = 1 E 2/E 1, and the actual measured ratio: K = U2/U1 = E 2/U1, a type of visible, the error between the ideal current transformer ratio and the actual ratio, approximate that results U2 = E 2. In fact, as shown in Figure 2, since the angular difference is very small, you can assume that U 2 is equal in length to line OC. U2 = E + USsin 2 beta, so U2 and E have a difference between the 2: USsin 0 beta = I (R + jX) sin beta, due to the current transformer two winding resistance and leakage resistance are relatively small, as long as the excitation current of I 0 in a suitable range (mA grade), error difference between E 2 and U 2 have negligible voltage method to measure current transformer ratio, can get higher precision.

2 examples and measurement results

According to the above theoretical analysis, in order to verify the correctness and accuracy of the method, the variable ratio test of the current transformer with several different types and different ratio is done. The following are extracts of several sets of test results, the first set of 75/5A supported compound turn current transformers, second groups of 800/5 through wall current transformers, and third sets of 3000/5 bus type current transformers. The test results of the above three sets of current transformers are recorded in three groups. It can be seen from table 1, table 2 and table 3 that the method of measuring current transformer ratio by voltage is completely feasible and has certain accuracy. The ratio error is caused by the reading error of the measuring instrument. Voltage method to measure current transformer ratio has the following advantages:

It can measure any type of current transformer with any change ratio, and it can be widely used;

When the control is appropriate, the error is relatively small;

The test equipment is few and the operation is simple, which is more suitable for the construction site;

The current transformer is not dangerous for people and equipment even if it is opened for two times.

To sum up, it is a simple, practical and effective test method to measure current transformer ratio by voltage method. It is worth popularizing.


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