Current transformer is an important secondary equipment in power system. It is widely used in measurement, measurement, relay protection and other secondary circuits. In the case of high current or high voltage, we can not directly measure the current of the circuit with a galvanometer, only through the secondary side of the current transformer to measure, so that it will be safe. For the parameters of current transformer, 0.5, 1.0 levels. And what do 10P20 and 5P20 mean? How do we choose to use it? The following will be explained carefully for you:
I. Principle of Current Transformer
Current transformer, like transformer, is an instrument that converts the large current of primary side into small current of secondary side to measure according to the principle of electromagnetic induction. Current transformer is composed of closed core and winding. Its primary winding turns are very few, and it is strung in the line of current to be measured. The number of secondary winding turns is relatively large, which is connected in series with the measuring instrument and the protection circuit. When the current transformer works, its secondary circuit is always closed. Therefore, the impedance of the series coil of the measuring instrument and the protection circuit is very small, and the working state of the current transformer is close to the short circuit.
II. Types of Current Transformers
According to its use, it can be divided into:
Current Transformer for Measurement: Settlement of Electricity Expenses
Measuring current transformer: Measuring current, calculating electric power, etc. The accuracy is generally lower than that of dual-purpose transformer, not used for settlement.
Current transformer for protection: current speed protection, overcurrent protection, overload protection, etc.
III. Accuracy of Current Transformers
1. Accuracy of current transformer for calibration: 0.1S level. The error is 0.1%. It is often used to check the accuracy of the current transformer.
2. Measurement current transformer accuracy: 0.2S 0.5 level. Errors of 0.2% and 0.5% are used for the basis of electricity billing, and 0.5 grade is also used in some occasions.
3. Measuring level current transformers: 0.5, 1.0, 2.0, etc., commonly used in ammeters.
4. Precision of protective current transformer: 10P10, 10P20, 5P10, 5P20, etc. Meaning of precision: Take 10P10 as an example, that is, when the current flowing through the current transformer is less than 10 times its rated current, the error of inductor is less than (+10%)
5. In some special occasions, there are more precise current transformers, such as 0.005 level, 0.05 level, which are less used.
IV. Type and Selection of Current Transformers
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