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Principle of Action of Current Transformer
May 03, 2017

The current transformer is a simple device that can measure the AC current according to the principle of electromagnetic induction.

The main purpose of the current transformer is to convert the high current in the AC circuit to a certain percentage of the small current (5 times the national standard) for measurement and relay protection only use. We should know that in the power generation, substation, transmission, power distribution process due to different electrical equipment, the current is often from a few tens of security to tens of thousands of security are, and these circuits may also be accompanied by high pressure. So in order to be able to monitor the circuit of these lines, measurement, but also to solve the high-pressure, high current risk, then you need to use the current transformer. Some people may have seen the electrical clamp table, which is a device used to measure the AC current, it is the "clamp" is through the heart of the current transformer.

The structure of the current transformer is shown in the figure on the right, and it can be used to enlarge the range of the AC ammeter. In use, its original coil should be measured with the current load line in series, the secondary coil is connected with the ammeter into a closed loop, as shown in the right side of the circuit shown in the figure.

current transformer.jpg

The original coil of the current transformer is wound with a thick wire, the number of turns is only one turn or a few turns, so its resistance is minimal. When the original coil is connected in series to the circuit under test, the voltage drop across it is extremely small. The number of turns of the secondary coil is much, but in normal circumstances, its electromotive force E2 is not high, only about a few volts

Since I1 / I2 = Ki (Ki is called the current ratio), I1 = KiI2

It can be seen that the current through the load is equal to the product of the current measured by the secondary coil and the current ratio Ki. If the ammeter with a dedicated current transformer supporting the use of the ammeter scale can be marked by the current value of the current circuit. Current transformer secondary current maximum, usually designed for the standard value of 5A. Different current circuits are equipped with current transformers are different, the flow ratio is 10 / 5,20 / 5,30 / 5,50 / 5,75 / 5,100 / 5 and so on.

For safety reasons, the end of the secondary coil of the current transformer and the iron must be grounded


Contact Us

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