What Are the Functions of Current Transformer?

A current transformer is an instrument that converts a large current into a small current according to a certain transformation ratio. Current transformers are generally used to measure large currents. In modern technology, it is difficult to produce an AC instrument that can directly measure large currents, and even if they are manufactured, they will be brought to us when we use them. It's very dangerous. For this reason, clever technical engineers have manufactured current transformers based on the principles of transformers. In practical applications, current transformers also play many important roles. The following article will talk about the role of current transformers.

• The structure and working principle of current transformers:

1. The structure
   The structure of the current transformer is composed of iron core, primary winding, secondary winding, terminal and insulating support. The primary winding of the current transformer has a small number of turns. It is connected in series in the line that needs to measure the current, and a larger current flows through it. The secondary winding has a large number of turns, which is connected in series to the measurement surface or the relay maintenance circuit in.
2. The working principle
   The working principle and equivalent circuit of the current transformer are the same as those of the general transformer, except that the primary winding is connected in series in the circuit under test, and the number of turns is small; the secondary winding is connected to a low impedance load such as an ammeter and a relay current coil, which is approximately a short circuit. The primary side current and the secondary side current depend on the load of the circuit under test and have nothing to do with the secondary side load of the current transformer. When the current transformer is running, the secondary side is not allowed to open circuit. In this case, the primary side current becomes the excitation current, which will cause the magnetic flux and the secondary side voltage to greatly exceed the normal value and endanger the safety of people and equipment. Therefore, it is not allowed to connect a fuse in the secondary circuit of the current transformer, and it is also not allowed to disassemble the ammeter and relays without bypassing during operation.

• The function of current transformers:

1. Expand the range of AC instruments
   The current transformer is made according to the principle of the transformer, it has a certain current ratio, as our electricity users, we must choose according to the amount of electricity consumption. If it is a large electricity user, such as factories and mines and enterprises, they need 100A current. The single-phase and three-phase watt-hour meters we use now cannot enter such a large current. Therefore, a current transformer must be selected to change the large current proportionally. To small current, and then measure with a low-range meter, which is equivalent to expanding the range of the AC meter.
2. Isolate large currents and improve the safety of users
   We use a current transformer to turn a large current into a small current. We can see from the structure of the current transformer that there is no direct electrical connection between the primary side and the secondary side. They are only the coupling of the magnetic circuit. When the current is large, the primary side of the current transformer has a direct electrical connection with the measuring circuit, while the secondary side is connected with the AC instrument. It has no direct relationship with the measured circuit, so that the measured AC instrument and the operator are connected with The high voltage voltage is separated, thereby protecting the personal safety and the safety of the instrument.
3. Rreduce production costs and standardize the production of instruments
   We know that the current on the secondary side of the current transformer is uniformly made into a standard 5A, so the manufacturer only needs to produce an AC ammeter with a range of 5A, and then equip different current transformers according to different current levels. Up. In this way, it has not only reduced production costs, but also standardized the instruments, achieving two goals with one stone.