How To Measure Ct Polarity With Multimeter

How to measure ct polarity with multimeter

How to measure ct polarity with multimeter

Current transformer, CT: Electromagnetic current transformer is widely used in power system, and its working principle is similar to that of transformer.

The characteristics of current transformer are as follows: (1) The primary coil is connected in series in the circuit with few turns, so the current in the primary coil depends entirely on the load current of the circuit to be tested, but has nothing to do with the secondary current; (2) The impedance of the current coil of the instrument and relay connected to the secondary coil of the current transformer is very small, so under normal circumstances, the current transformer runs in a near short-circuit state.

The ratio of primary and secondary rated current of current transformer is called the rated mutual inductance ratio of current transformer: kn=I1n/I2n.

Because the rated current I1n of the primary coil has been standardized and the rated current I2n of the secondary coil is unified to 5(1 or 0.5) A, the rated mutual inductance ratio of the current transformer has also been standardized. Kn can also be approximately expressed as the turns ratio of the primary and secondary windings of the transformer, that is, where kn≈kN=N1/N2 is the number of turns of the primary and secondary windings.

The function of current transformer is to measure relatively large current.

Generally speaking, if you want to measure the current of 400A, what should you do without a 400A watt-hour meter? Therefore, you should use a current transformer to change a large current into a small current and input it into the watt-hour meter. The transformer has a variable ratio, for example, 200/5 is 40 times that of the watt-hour meter, which means that your watt-hour meter has been charged once. In fact, you have used 40 degrees of electricity, and there are many levels of transformers, with 15/5.

For the field, the best way to determine the polarity of the transformer is to use a dry battery and a piece of pointer multimeter MF47. With wires, it is the most direct and easy to see, and the accuracy can reach more than 90%. The method is very simple. The standard secondary transformer with P1 P2 on the primary side is S1S2 K1K2, etc. Connect the positive electrode on the secondary side of P1 to the negative electrode of S1, and the secondary side is directly connected. Then directly short-circuit the DC current to the primary side of the transformer with the battery. At this time, you will see that if the pointer swing of the multimeter is extremely positive clockwise, it is negative counterclockwise, indicating that the internal winding is wrong. At this time, you should observe it in detail. Because the pointer swing is not large, it is advisable to use two 1# batteries in the same way, because it is too dangerous to have too many batteries, and stop for half an hour or replace the batteries after about 10 tests. Because the battery was very hot during the test, it is suggested that you should not be lazy to use the 126V converted from alternating current because you saved the battery, but the error increased and the safety decreased.