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The principle, type, accuracy and type selection of current transformer

Views:1     Author:Site Editor     Publish Time: 2020-12-22      Origin:Site

Current transformer is an important secondary device in the power system. It is widely used in secondary circuits such as metering, measurement, and relay protection. In large current or high voltage occasions, we cannot directly use an ammeter to measure the current of the circuit. It can be measured through the secondary side of the current transformer, so that it is safe. So what does the 0.5, 1.0, 10P20, 5P20 mean for the current transformer parameters? How do we choose to use it? The following will explain it carefully for everyone:


1. The principle of current transformer

Current transformers, like transformers, are instruments that convert a large current on the primary side into a small current on the secondary side based on the principle of electromagnetic induction. The current transformer is composed of a closed core and windings. Its primary winding has a few turns and is stringed in the line of the current to be measured. The secondary winding has a large number of turns and is connected in series in the measuring instrument and the protection circuit. When the current transformer is working, its secondary circuit is always closed. Therefore, the impedance of the series coil of the measuring instrument and the protection circuit is very small. The working condition of the current transformer is close to short circuit.

Types of current transformers

It can be divided into:Current transformer for metering: settlement of electricity costsCurrent transformer for measurement: measuring current, calculating electrical power, etc. The accuracy is generally lower than that of dual-purpose transformers and not used for settlement.Current transformer for protection: current speed protection, overcurrent protection, overload protection, etc.;

Transformer accuracy1. The accuracy of the current transformer for calibration: 0.1S level. The error is 0.1%, which is often used to verify the accuracy of metrological current transformers.2. Accuracy of current transformer for measurement: 0.2S 0.5 level. The error of 0.2% and 0.5% is used as the basis for electricity bill settlement, and 0.5 level is also used in some occasions3. Measuring current transformer: 0.5, 1.0, 2.0, etc., generally used for ammeters.4. The accuracy of the current transformer for protection: 10P10, 10P20, 5P10, 5P20, etc. The meaning of the accuracy: Take 10P10 as an example, that is, when the current flowing through the current transformer is within 10 times of its rated current, the The error is within ±10%.5. In some special occasions, there are more precise current transformers, such as 0.005 class, 0.05 class, etc., which are used in fewer occasions.

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