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Function principle and model recognition method of current transformer
Oct 26, 2017

Function principle and model recognition method of current transformer

Function and principle

The main purpose of the current transformer is to convert the large current in the AC circuit into a small proportion of the current (China's standard is 5 Andouble), for measurement and relay protection only use. We should know that in the process of power generation, substation, transmission and distribution, due to the different electrical equipment, the current often from tens to thousands of kilometers, and these circuits may also be accompanied by high voltage. Then, in order to monitor and measure the circuit of these circuits, and to solve the danger of high voltage and high current, the current transformer is needed. Some people may be seen with the electric clamp meter, which is a device used to measure AC current, it is the "clamp" is the core type current transformer.

The current transformer can be used to enlarge the range of AC ammeter.  When it is used, its original coil should be connected with the load line to be measured, and the secondary coil is connected with the ammeter to form a closed loop, as shown in the circuit diagram on the right.

The primary coil of a current transformer is made of rough wire, and its turns are only one turn or a few turns, so its impedance is very small. When the original coil is connected to the circuit to be tested, the voltage drop at both ends is very small. Although the number of turns of the auxiliary coil is many, the electromotive force E2 is not high, only about a few volts under normal conditions.

Because I1/I2=Ki (Ki is called the variable current ratio), so I1=KiI2

Thus, 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 is matched with a special current transformer, the scale of the ammeter can be marked according to the current value in the large current circuit. The maximum value of the secondary current of the current transformer is usually designed as the standard value 5A. The current transformers used in different current circuits are different, and their converter ratios are 10/5, 20/5, 30/5, 50/5, 75/5, 100/5 and so on.

For safety reasons, end of current transformer secondary windings and iron must be grounded.

Model recognition

The type of current transformer consists of 2~4 phonetic alphabets and numbers. Usually it can show the coil type, insulation type, conductor material and use place of the current transformer. The number behind the line represents the voltage level of the insulation structure (Class 4).

  

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