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Wirewound resistor basics

View: 13808/29/2019  

What is a wirewound resistor


Wirewound resistors are a type of fixed resistor. The wirewound resistor is formed by winding a resistance wire around the insulating bobbin. The resistance wire is generally made of an alloy such as nickel chrome or manganese copper having a certain electrical resistivity. The insulating skeleton is made of a ceramic, a plastic, a metal coated with an insulating layer, or the like, and is formed into various shapes such as a tube shape and a flat shape. The electric resistance wire can be wound on the skeleton as needed, or can be wound into a plurality of layers, or a non-inductive winding method can be used. Wirewound resistors are mainly used for voltage division, buck, shunt and load resistance in AC and DC circuits such as precision instruments, telecommunication instruments, and electronic equipment.


The wirewound resistor is made of nickel-chromium wire or manganese-copper wire and a constantan wire wound on a porcelain tube. It is divided into two types: fixed type and debuggable. The wirewound resistor is characterized by extremely high resistance value, low noise during operation, stable and reliable, can withstand high temperatures, and can still work normally at an ambient temperature of 170 °C. However, it is bulky and has a low resistance value, mostly below 100 kΩ. In addition, due to structural reasons, its distributed capacitance and inductance are relatively large and cannot be used in high frequency circuits.


The wirewound resistor is formed by winding a resistance wire around the insulating bobbin. The resistance wire is generally made of an alloy such as nickel chrome or manganese copper having a certain electrical resistivity. The insulating skeleton is made of a ceramic, a plastic, a metal coated with an insulating layer, or the like, and is formed into various shapes such as a tube shape and a flat shape. The electric resistance wire can be wound on the skeleton as needed, or can be wound into a plurality of layers, or a non-inductive winding method can be used.


Wirewound resistors are a type of fixed resistor. Its circuit symbol is the same as a normal resistor. The internal and external structure of the wirewound resistor is shown in the figure. Its innermost layer is a glass fiber stem with a resistance wire wound around the stem. The two end wires of the resistor are crimped together internally with the solderet leads, and the outer layer is sealed with an insulating package filler.




Type of wirewound resistor


There are many types of wirewound resistors, which can be generally classified into fixed type and adjustable type.


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


Because the wirewound resistor has the characteristics of high precision and good stability, it can be used in the circuit of instrumentation, such as the voltage divider and shunt circuit of the pointer multimeter, and can also be used in the resistance box circuit. Because it can withstand large power, it is also used as a current limiting resistor in the power circuit, but because it has a large inductance, it cannot be used in high frequency circuits (interference to the circuit).


Wirewound resistor works


The wirewound resistor is a type of resistor which is wound on the insulating bobbin and then insulated and packaged. As shown in the figure, the resistance wire is generally made of alloy of nickel-chromium, manganese-copper or the like with a certain resistivity. The skeleton is generally made of ceramic, plastic, and a metal skeleton coated with an insulating layer. It has the characteristics of small temperature coefficient and high precision. In the wire wound resistor, there is a high-power wirewound resistor that uses ceramic as a skeleton, glaze on the outer layer of the resistor or other heat-resistant and heat-dissipating insulating material. The wirewound resistor is characterized by large power dissipation. It can reach hundreds of watts and is mainly used as a high-power load. It can work in an environment with a temperature of 150 ° C ~ 300 ° C.


In the wire wound resistor, there is also an adjustable wirewound resistor which is provided with a movable snap ring on the outside of the wire as a contact lead end, and a long and narrow window is left on the glaze (paint) layer to expose the winding. The contact path, the snap ring can be adjusted by the movement of the contact on the contact track, so it is a variable resistor. Commonly used are glazed wire wound resistors and painted wirewound resistors.


Winding resistance


The wirewound resistor is formed by winding a resistance wire around the insulating skeleton, and is generally made of a medium having a certain resistivity, such as a nickel-chromium or manganese-copper alloy. Wirewound resistors are mainly used to reduce voltage, shunt, load, feedback, energy transfer, matching, etc. 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 the loop and transformer and shunt in the pulse forming circuit. 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 home appliances, medical equipment, automotive industry, railway, aviation, military equipment and other fields.


Winding resistor manufacturing process


The manufacturing idea is generally as follows: the wire-wound resistor is wound on the insulating rod or the insulating column in a certain direction, but the single-spiral winding resistance is connected to the circuit to generate an inductance effect, which affects the accuracy. In order to eliminate this effect, the double-spiral reverse winding method is adopted to make the inductances generated by the two coils cancel each other, and the entire winding resistance exhibits no feeling or slight feeling to the external circuit, which is a non-inductive winding resistance. The working principle is that the coils with opposite directions of the two magnetic fields cancel each other's inductance, and the external circuit exhibits the characteristics of no feeling or slight feeling.


How to look at the resistance and power of the winding resistance


The resistor and the sliding varistor are connected in series in the same circuit, and the current I passing through the resistor is measured by an ammeter, and the voltage U across the resistor is measured by a voltmeter, and the resistance value is calculated by R=U/I, by P= The UI can calculate the power.


Wirewound resistor application field


Wirewound resistors and on-load tapping are all transformer tap changer voltage regulation methods. The difference is that the non-excited voltage regulator switch does not have the ability to load shift gears because the tap changer is in the process of shifting gears. There is a short-time disconnection process. Disconnecting the load current will cause the arc between the contacts to burn out the tap changer or short circuit. Therefore, the transformer must be powered off during the shift. Therefore, it is generally used for transformers that do not require strict voltage requirements and do not require frequent shifting. The on-load tap-changer can be used to switch the gear position, because the on-load tap-changer does not have a short-time disconnection process during the shifting process, and transitions from one gear to another after a transitional resistance transition. Therefore, there is no arcing process in which the load current is disconnected.


It is generally used for transformers that require strict voltage regulation for voltage requirements. Most of the substations are outdoor air-insulated substations. In the substation, all primary equipment are independently opened and arranged according to the connection requirements of the main wiring. Most of the control and protection devices are arranged in the control room. Therefore, this substation occupies a large land area and has poor environmental effects. Low reliability, high operating and maintenance costs. Compared with outdoor air-insulated substations, gas-insulated metal-enclosed substations, ie GIS substations, have high reliability and long service life, but their investment cost is high. A new type of substation, a modern compact substation, being researched and developed combines the advantages of these two substations. The following will discuss the modern compact substation and its primary and secondary equipment integration technologies based on modern microcomputer, optoelectronics and communication technology, and analyze the technical and economic benefits generated by this substation.


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