Measure the polarity of the CT with a multimeter
Current Transformer (CT), also known as Electromagnetic Current Transformer, is widely used in power systems. Its working principle is similar to that of a transformer.
The characteristics of a current transformer are: (1) The primary coil is connected in series in the circuit with very few turns, so the current in the primary coil depends entirely on the load current of the measured circuit and is independent of 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 operates in a near short-circuit state.
The ratio of the primary and secondary rated currents of a 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, and the rated current I2n of the secondary coil is uniformly 5 (1 or 0.5) amps, the rated mutual inductance ratio of the current transformer has also been standardized. Kn can also be approximated as the ratio of turns between the primary and secondary coils of a transformer, i.e. kn ≈ kN=N1/N2, where N1 and N2 are the turns of the primary and secondary coils.
The function of a current transformer is to measure relatively large currents.
Simply put, if you want to measure a current of 400A, what should you do if you don't have a 400A electricity meter? Therefore, you need to use a current transformer to convert the large current into a small current for input into the electricity meter. Transformers have a conversion ratio, for example, 200/5 is 40 times that of the electricity meter. In other words, if you have used one kilowatt hour on your electricity meter, you have already used 40 kilowatt hours. There are many levels of transformers, including 15/5 30/5, 50/5, 75/5, etc,,,,,
The best method for determining the polarity of a transformer on site is to use a dry battery or a pointer type multimeter MF47. With wires, it is the most direct and easy to see, and the accuracy can reach over 90%. The method is simple. The primary side of the transformer has P1 P2 standard secondary, such as S1S2 K1K2. Connect the positive pole on the P1 secondary side to the positive pole on the S1 secondary side and the negative pole on the S1 secondary side to another section. Connect the secondary side directly, and then use a battery to short-circuit and apply direct current to the primary side of the transformer. At this time, you will see that the pointer of the multimeter swings. If it is clockwise, the polarity is positive, and counterclockwise, the polarity is negative, it indicates that the internal winding is incorrect. At this time, it is necessary to observe in detail because The pointer movement is not significant, and it is recommended to use two 1 # batteries for the same method, as having too many batteries is too dangerous, And after about 10 tests, stop for half an hour or replace the battery, because the battery heats up severely during the test. It is recommended not to slack off and use the 12V 6V converted from AC power to save the battery, but the error increases and the safety decreases,
