How to use a multimeter to determine ct polarity
Current transformer, CT is: current transformer Electromagnetic current transformer (hereinafter referred to as current transformer) is widely used in power system, and its working principle is similar to that of transformer.
The characteristics of the current transformer are: (1) The primary coil is connected in series in the circuit, and the number of turns is very small. Therefore, the current in the primary coil depends entirely on the load current of the circuit under test. It has nothing to do with the secondary current; (2) The current coil impedance of the instrument and relay connected to the secondary coil of the current transformer is very small, so under normal circumstances, the current transformer operates in a state close to a short circuit.
The ratio of the primary and secondary rated currents of the current transformer is called the rated mutual inductance ratio of the current transformer: kn=I1n/I2n
Because the rated current I1n of the primary coil has been standardized, the rated current I2n of the secondary coil is uniformly 5 (1 or 0.5) ampere, so 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 coils of the transformer, that is, kn≈kN=N1/N2 where N1 and N2 are the turns of the primary and secondary coils.
The role of the current transformer is to measure relatively large currents.
In layman's terms, if you want to measure a 400A current, what should you do if you don't have a 400A watt-hour meter, so you need to use a current transformer to convert a large current through the transformer into a small current and input it to the watt-hour meter. The transformer has a transformation ratio. For example, 200/5 is 40 times that of the watt-hour meter. That is to say, your watt-hour meter has a kilowatt-hour of electricity. In fact, you have used 40 kilowatt-hours of electricity. There are many grades of transformers. There are 15/5's..30/5,,50/5,,75/5,,,etc,,,,,
For the field, the best way to determine the polarity of the transformer is to use a dry battery or a pointer multimeter MF47, plus a wire, the most direct and easy to see, the accuracy can reach more than 90%, the method is very simple Transformer The primary side has P1 P2 standard type, the secondary side is mostly S1S2 K1K2, etc. Connect the positive pole to the secondary side of P1, connect the positive pole to S1, connect the negative pole to the other section, connect the secondary side directly, and then use the battery to directly short-circuit the supply. Apply DC current to the primary side of the transformer. At this time, you will see that if the pointer of the multimeter swings clockwise, it is positive, and counterclockwise is negative, indicating that the internal winding is wrong. At this time, it is necessary to observe in detail, because the swing of the pointer Big, in the same way, it is recommended to use 2 1# batteries, because too many batteries are too dangerous, and the test should be stopped for half an hour or replace the battery after about 10 tests, because the battery is very hot during the test, and it is recommended not to be lazy to use it again The 12V 6V that the alternating current turns into thinks that you save the battery, but the error increases and the safety decreases.
