Power resistors are used in power generation and distribution, high-voltage applications, control systems, and other power system applications. They include load banks, grounding resistors, and dynamic braking resistors. Load banks develop an electrical load, apply the dummy load to an electrical power source, and then convert or dissipate the resulting power output. Load banks are used to test generators, uninterruptible power supplies (UPS), and other backup generation systems. Grounding resistors or neutral earthing resistors provide resistance grounding in industrial power systems. They allow fault current to flow to protective relays, but limit the value to prevent damage to power generation or distribution equipment. Dynamic braking resistors are designed for high-heat, high-power applications where space is limited. These power resistors are often used in material handling and fabrication equipment, elevators, escalators, cranes, power inverters, and industrial drives.
Specifications for power resistors include mounting style, lead type, and resistor material. Power resistors can be bolted, chassis mounted, surface mounted, or through-hole mounted. Chassis-mounted resistors attach to a metal surface for maximum heat dissipation. Surface mount technology (SMT) and through-hole technology (THT) are other common mounting styles. Lead types include: axial leads, gull-wing leads, J-leads, radial leads, screw terminals and tab terminals. Power resistors without leads are also available. Choices for power resistor material include: carbon film, ceramic, metal alloy, metal film, metal oxide, thick film, thin film, and wire wound. Carbon power resistors are made of a mixture of finely-ground carbon and insulating material held together by a resin binder. Ceramic power resistors are made of solid, high-temperature, ceramic, resistive materials with bonded metal contacts. Metal alloy power resistors contain two or more metallic elements. Wire wound power resistors are made by winding thin wire onto a ceramic rod.
Power resistors differ in term of packing method. Some passive electronic components are packed in tape reel assemblies that include a carrier tape with embossed cavities for storing individual components. Others are packed in trays (rails) are made of carbon-powder or fiber materials and molded into rectangular outlines that contain matrices of uniformly spaced pockets. These containers protect components during shipping and provide proper component location and orientation for use with industry-standard, pick-and-place board assembly equipment. Power resistors that are packed in shipping tubes, stick magazines, or bulk packs are also available.
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