What Is a Wirewound Resistor?

Wire-wound resistors are a type of resistor wound from a constantan, manganese-copper, or nickel-alloyed alloy wire on a ceramic skeleton, with a protective paint or glass glaze on the surface. Advantages: low noise, no current noise and non-linearity. The temperature coefficient is small, the stability is good, and the accuracy can reach 0.5% ~ 0.05%. Disadvantages: Poor high-frequency characteristics.

Wire wound resistor is one of the more commonly used resistors, and its structure is shown in the figure below. The resistor of a wire wound resistor is a resistance wire. The resistor wire is wound on a ceramic skeleton, the leads are connected, and a surface is coated with a glass glaze or insulating paint to make a wire wound resistor. ^[1]

There are many types of wire-wound resistors, which can generally be divided into fixed and adjustable types.

Commonly used wire-wound resistors are: RX20, RX21, RX22 enamel wire-wound resistors, RX25 paint-coated wire-wound resistors, RX24 power wire-wound resistors, RX10, RX12 precision wire-wound resistors , RXG5 wire-wound ceramic shell resistors, etc.

Because the wire-wound resistor has the characteristics of higher accuracy and better stability, it can be used in the circuit of instrumentation, such as the voltage divider and shunt circuit of the pointer multimeter, and it can also be used in the resistance box circuit. Because it can withstand larger power, it is also used as a current limiting resistor in power circuits, but because it has a large inductance, it cannot be used in high-frequency circuits (interference to the circuit). ^[2]

Wire-wound resistors are a type of resistors made by winding a resistance wire around an insulating skeleton and then subjecting it to insulation packaging. As shown in the figure, the resistance wire is generally made of a certain resistivity nickel-chromium, manganese-copper and other alloys for insulation. The skeleton is generally made of ceramic, plastic, or metal with an insulating layer. It has the characteristics of small temperature coefficient and high accuracy. Among wire-wound resistors, there is a high-power wire-wound resistor with ceramic as the skeleton, and the outer layer of the resistor is coated with glaze or other heat-resistant and good heat-dissipating insulating material. Wire-wound resistors are characterized by high power dissipation It can reach hundreds of watts. It is mainly used as a high-power load and can work in the environment of 150 ~ 300 .

Among wire-wound resistors, there is also an adjustable wire-wound resistor. It is equipped with a movable snap ring as a contact terminal on the outside of the wire-wound. A narrow window is left on the glaze (lacquer) layer to expose the wire. Contact channel, the snap ring can adjust the resistance value by moving the contact on the contact channel, so it is a variable resistor. There are two types of enamel wire-wound resistors and lacquered wire-wound resistors.

Wire-wound resistors and on-load voltage regulators refer to the voltage regulation method of transformer tap-changers.The difference is that non-excitation voltage-regulating switches do not have the ability to change the gear with a load, because this tap-changer is in the process of changing gears There is a short-time disconnection process. Disconnecting the load current will cause the arc between the contacts to burn the tap-changer or short-circuit. Therefore, the transformer must be powered off when the gear is adjusted. Therefore, it is generally used for transformers whose voltage requirements are not very strict and do not require frequent shifting. The on-load tap-changer can switch gears under load, because the on-load tap-changer does not have a short-time disconnection process during the gear shifting process. After a transition resistance transition, it switches from one gear to another. Therefore, there is no arc-drawing process when the load current is disconnected.

Generally used for transformers with strict voltage requirements and frequent shifting. Most substations are outdoor air-insulated substations. Within the substation, all primary equipment is independently and independently arranged in accordance with the connection requirements of the main line. Poor, low reliability, high operating and maintenance costs. Compared with outdoor air-insulated substations, gas-insulated metal-enclosed substations, that is, GIS substations, have high reliability and long service life, but their one-time investment costs are high. A new type of substation, a modern compact substation, which is being researched and developed, combines the advantages of these two types of substations. In the following, starting from the technical and economic optimization, the modern compact substation and its primary and secondary equipment integration technology based on modern microcomputers, optoelectronics, and communication technologies are discussed, and the technical and economic benefits of this substation are analyzed.