What Is The Difference Between The Ratio On The Current Transformer And The Ratio On The Watt-Hour Meter？
The transformation ratio should be based on the primary load calculation current IC to select the transformation ratio of the current transformer. There are various specifications such as the rated current standard ratio of the primary side of the current transformer (such as 20, 30, 40, 50, 75, 100, 150, 2×a/C).
The proportional side current rating on the watt-hour meter is usually 1A or 5A. Among them, 2×a/C means that the same product has two current ratios, which can be realized by changing the connection method of the product. When connected in series, the current ratio is a/c, and when connected in parallel, the current ratio is 2×a/C.
In general, the selection of the transformation ratio of the current transformer for metering should make the primary rated current I1n not less than the load current in the line (that is, calculating IC).
If the calculated current of the load in the line is 350A, the transformation ratio of the current transformer should be selected as 400/5. In order to ensure the accuracy of the current transformer used for protection, the transformation ratio can be selected to be larger.
The wiring of the current transformer should follow the series principle. That is to say, the primary winding should be connected in series with the circuit under test, and the secondary winding should be connected with all instrument load current transformers to select an appropriate transformation ratio according to the measured current, otherwise, the error will increase. At the same time, one end of the secondary side must be grounded to prevent the high voltage on the primary side from entering the secondary low voltage side once the insulation is damaged, causing personal and equipment accidents.
The secondary side is absolutely not allowed to open the circuit, because once the circuit is opened, the primary side current I1 will all become magnetizing current, causing φm and E2 to increase sharply, resulting in excessive saturation magnetization of the iron core, serious heat generation and even burning of the coil.
