What are Wire Wound Resistors?

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Ⅰ Structure of wire wound resistor

The insulating frame is made of materials such as ceramics, plastics, and metal coated with an insulating layer into various shapes such as tube and flat shapes. The resistance wire can be wound on the skeleton in one layer or multiple layers as needed, or the non-inductive winding method can be used. Wire wound resistors are mainly used for voltage division, voltage reduction, shunting, and load resistance in AC and DC circuits such as precision instruments, telecommunications instruments, and electronic equipment.

Wire wound resistor is one of the commonly used resistors, the structure is shown in the figure below. The resistor body of the wire wound resistor is a resistance wire. The resistance wire is wound on the ceramic frame, connected to the lead wire, and coated with a layer of glass glaze or insulating paint.

Wire wound resistor structure

Wire wound resistors are a type of fixed resistors. Its circuit symbol is the same as ordinary resistance. The internal and external structure of the wire wound resistor is shown in Figure. Its innermost layer is a glass fiber core column with resistance wires wound around the core column. The two end wires of the resistor are crimped together with the solder foot leads inside, and the outer layer is sealed with an insulating packaging filler.

The performance characteristics of wire wound resistors are extremely low noise, high-temperature resistance, high power, good stability, low-temperature coefficient, high precision, but poor high frequency. The resistance range of wire wound resistors is usually 0.1Ω～5MΩ, which is especially suitable for high temperature and high power occasions.

Ⅱ Types of wire wound resistor

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

wire wound resistors

Commonly used wire wound resistors are: RX20, RX21, RX22 glazed wire wound resistors, RX25 painted wire wound resistors, RX24 power wire wound resistors, RX10, RX12 precision wire wound resistors, RXG5 type wire-wound porcelain shell resistors, etc.

Because wire wound resistors have the characteristics of higher accuracy and better stability, they can be used in the circuits of instruments and meters, such as the voltage divider and shunt circuits of pointer multimeters, and can also be used in resistance box circuits. Because it can withstand greater power, it is also used as a current-limiting resistor in power circuits, but because of its greater inductance, it cannot be used in high-frequency circuits (which interferes with the circuit).

Ⅲ Production of wire wound resistor

The production idea is roughly like this: the wire wound resistor is to wind the resistance wire on an insulating rod or an insulating column in a certain direction, but this kind of single spiral wire-wound resistor will produce an inductance effect in the circuit and affect the accuracy. In order to eliminate this effect, a double-spiral reverse winding method is used to make the inductances generated by the two coils cancel each other out, and the entire winding resistor presents no inductance or slight inductance to the external circuit. This is a non-inductive winding resistor. The working principle is to make two coils with opposite magnetic fields cancel each other's inductance, and the external circuit presents the characteristics of non-inductance or slight inductance.

Ⅳ Working principle 

Wire-wound resistors are a type of resistors made by winding resistance wires on an insulating framework and then undergoing insulation packaging treatment. As shown in the figure, resistance wires are generally made of nickel-chromium, manganese-copper alloys with a certain resistivity. The skeleton generally adopts ceramic, plastic, or metal skeleton coated with an insulating layer. It has the characteristics of a small temperature coefficient and high accuracy. Among the wire-wound resistors, there is a high-power wire-wound resistor that uses ceramic as the skeleton, and the outer layer of the resistor is coated with glaze or other heat-resistant and good heat-dissipating insulating materials. The characteristic of the wire-wound resistor is high power dissipation which up to hundreds of watts. It is mainly used as a high-power load and can work in an environment of 150 ℃ ~ 300 ℃ temperature.

Among the wire wound resistors, there is also an adjustable wire wound resistor, which is equipped with a movable snap ring as a contact terminal on the outside of the wire wound, and a long and narrow window is left on the glaze (paint) layer to expose the wire Contact channel. The clasp can adjust the resistance by moving the contact on the contact channel, so it is a kind of variable resistor. There are two common types: glazed wire wound resistors and varnished wire wound resistors.

Ⅴ The role of wire wound resistors

Wire wound resistors are composed of resistance wires wound on an insulating frame and are generally made of a medium with a certain resistivity, such as nickel-chromium, manganese copper, and other alloys. Wire-wound resistors are mainly used to reduce voltage, shunt, load, feedback, transfer energy, and match in low-frequency AC circuits, or act as absorbers and voltage dividers in power circuits, and can also be used as oscillations attenuation adjustment in loops and transformers and shunts in pulse forming circuits. In addition, it can also be used for discharge and spark suppression of filter stage capacitors in rectifiers. At the same time, it can be widely used in household appliances, medical equipment, automobile industry, railway, aviation, military equipment, and other fields.

Ⅵ Application

Wire wound resistors and on-load voltage regulation both refer to the voltage regulation method of the transformer tap switch. The difference is that the non-excitation voltage regulation switch does not have the ability to switch gears with load, because this kind of tap switch is in the process of changing gears. There is a short-time disconnection process, and disconnecting the load current will cause arcing between the contacts to burn the tap changer or short circuit, so the transformer must be powered off when adjusting gears. Therefore, it is generally used for transformers that have less stringent voltage requirements and do not require frequent adjustments. On the other hand, the on-load tap-changer can switch gears with load, because the on-load tap-changer does not have a short-term disconnection process in the process of gear adjustment. It changes from one gear to another after a transition resistance. Therefore, there is no arcing process in which the load current is disconnected.

Wire wound resistors are generally used for transformers with strict voltage requirements and frequent adjustments. Most substations are outdoor air-insulated substations. In the substation, all primary equipment is arranged independently according to the connection requirements of the main connection. The control and protection devices are mostly arranged in the control room. Therefore, this kind of substation takes up a large area of land and has environmental effects.  Compared with outdoor air-insulated substations, gas-insulated metal-enclosed substations, namely GIS substations, have high reliability and long service life, but their primary investment costs are high. A new type of substation under research and development-modern compact substation combines the advantages of these two substations. The following will proceed from technical and economic optimization, discuss modern compact substations and their primary and secondary equipment integration technology based on the modern microcomputer, photoelectric, and communication technologies, and analyze the technical and economic benefits of such substations.

Ⅶ Detection method and replacement of wire wound resistor

The method and precautions for detecting wire wound resistance are exactly the same as those for detecting ordinary fixed resistance. Wire wound resistors generally work under high current conditions, so the damage rate is relatively high. When it is blown out and damaged, if there is no original matching type resistance replacement, according to the circuit requirements, the following methods can be used for emergency replacement:

(1) For the high-power low-resistance wire-wound resistor that has been disconnected, the surface insulation layer can be scraped off to expose the resistance wire and find the breakpoint. Retreat the resistance wire at the breakpoint by one turn and twist it tightly.

(2) Emergency replacement with resistance wire. The resistance wire surface J can be removed from the old wire wound potentiometer or wire wound resistor. Use a multimeter to measure a piece of resistance wire with the same resistance value as the original resistor, and wind it on the original resistor. After welding the two ends of the resistance wire to the two ends of the original resistor, install it into the circuit.

(3) When the resistance of the damaged wire wound resistor is large, an internally heated electric soldering iron core can be used instead. If the resistance does not meet the circuit requirements, the electric soldering iron cores can be connected in series and parallel to solve the problem. As long as the resistance values are similar, it will not affect the normal operation of the circuit.