Views:1 Author:Site Editor Publish Time: 2020-12-03 Origin:Site
The current transformer has the function of current conversion and electrical isolation. It is a sensor for secondary equipment such as measuring instruments and relay protection in the power system to obtain current information of the electrical primary circuit. The structure of a current transformer is composed of a primary winding, a secondary winding, an iron core, a frame, a housing, and a terminal that are insulated from each other. Its working principle is basically the same as that of a transformer. The primary winding has fewer turns N1. It is directly connected in series with the power supply line. When the primary load current passes through the primary winding, the alternating magnetic flux generated induces a proportionally reduced secondary current; 2. The secondary winding has a large number of turns N2, which forms a closed loop in series with the secondary load of the current coil such as meters and relays.
At present, the current domestic current transformer is mainly oil-immersed vertical type, which is the most traditional form in my country. Its primary wire is a traditional U-shaped structure, and its main insulation is transformer oil and cable paper insulation structure. The main insulation is mainly composed of cables. Wrapped with paper, in order to make the internal electric field more uniform, a main screen and an end screen are arranged inside the insulating layer. Since the current transformer has a U-shaped structure, the outer insulating sleeve is generally a tower structure.
The inverted oil-immersed current transformer is produced in China through the introduction of technology. The product is an oil-immersed cable paper insulated current transformer. The secondary coil is wrapped by a metal shield and placed on the top of the product. A piece of metal inside the secondary coil The tube is led into the low-voltage side, the secondary coil and the lead metal tube are not covered with cable paper and crepe paper insulation. The primary wire is generally a straight copper tube or aluminum tube
Dry-type current transformer is a new product. Its primary wire adopts U-shaped copper wire or aluminum wire. The insulating layer is wrapped with polyester film tape. The gap between the polyester film is filled with silicone grease during the wrapping process to improve the insulation performance. The silicone rubber umbrella is glued outside the insulating layer to form the external insulation of the current transformer; the secondary coils are respectively sleeved on both sides and closed with a metal shell. Since the product is filled with semi-liquid medium inside the insulating layer, there will be no oil leakage.
With the rapid development of optoelectronic technology, many technologically developed countries have turned their attention to using optical sensing technology and electronic methods to develop new electronic current transformers, referred to as photoelectric current transformers. Electronic current transformers refer to current transformers that output low-voltage analog signals or digital signals. In addition to photoelectric current transformers, they also include other current sensors that use electronic testing principles. Electronic current transformers are divided into two categories: active and passive.
The advantages of electronic current transformers are that there is no iron core, simple and reliable insulation structure, small size, small quality, good linearity, good electromagnetic interference resistance, no magnetic saturation, high measurement accuracy, and the output signal can be directly input to the microcomputer Metering and protection equipment interface.
The disadvantage is that the sensor head is more sensitive to temperature and vibration. In order to improve the accuracy and stability, the circuit of the electronic signal processing part will be more complicated. For active electronic current transformers, the stability of the power supply must be ensured.