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Brake Resistor Technologies: Lessons from the Field
B
raking resistors are critical components within Power Drive Systems, (PDS) converting excess regenerative energy into heat to prevent overvoltage and protect sensitive
demand for braking solutions capable of withstanding harsh environments, vibration, and rapid duty cycles. This article examines three key construction methods—tubular, frame (register or
grid), and aluminium clad—exploring their strengths, limitations, and lessons learned from recent real-world applications, especially in the industrial and transport sectors. These have provided valuable insights into how resistor construction affects long-term reliability, safety, and performance.
Tubular Resistors Tubular resistors, remain one of the simplest resistor constructions. Built around a ceramic core with resistance wire wound along its length, the assembly is often cement-coated for insulation and rigidity. This design is low cost but has some limitations, e.g. Working voltage is restricted because windings are closely spaced, increasing the risk of arcing under transient or surge conditions and with limited ingress protection—typically IP00 to IP20—tubular resistors are also vulnerable to contamination and moisture, and can exhibit audible noise in some applications. Exposure to vibration and humidity can cause insulation breakdown, winding displacement, or failure of surface coatings. While adequate in clean, temperature- controlled settings, they are increasingly viewed as unsuitable for demanding industrial or outdoor environments.
Frame (Register/Grid Type) Resistors elements—often stainless steel or nickel-chromium alloy —mounted on insulating supports to form a grid. Spacing between windings improves voltage withstand and Frame resistors are still limited by their open construction and in vibration-
intensive settings, such as cranes or rail vehicles, mechanical stresses can lead to failures. As they are often force-cooled to reduce size, cooling-system maintenance can become a limiting factor.
Aluminium Clad (Encapsulated) Resistors Aluminium-clad, encapsulated resistors, Figure 1, have become the benchmark for reliability and safety in demanding drive and traction applications. In these designs, mechanically robust assembly with ingress protection typically from IP20 up to IP66 or even IP67.
Aluminium-clad resistors also integrate additional safety features such as an The encapsulation dampens acoustic noise, which is especially useful in Building Technology applications and isolates the windings from external contamination, making these units particularly suitable for outdoor drives, rail traction, and renewable energy applications.
electricalengineeringmagazine.co.uk
Comparison and Outlook Tubular, frame, and aluminium-clad resistor designs illustrate a clear technological progression. Tubular resistors, though economical, offer limited resilience and are best suited to low-cost, indoor applications. Frame resistors provide improved electrical performance and modularity but remain vulnerable to environmental stress. Encapsulated resistors, while more expensive, especially at high power ranges, offer superior performance, ingress protection, and long-term reliability.
REO (UK) Ltd • +44 (0)1588 673411 •
marketing@reo.co.uk •
www.reo.co.uk
ELECTRICAL ENGINEERING • NOVEMBER 2025 11
EMC Considerations and Shielding Under EN 61800-3, braking resistors form part of the PDS — the combined drive, motor, cabling, and associated components must meet EMC emission and immunity resistor designs and their cabling can act as unintentional antennas, coupling high- frequency noise into surrounding equipment, cabling and metallic structures. Aluminium-clad, encapsulated resistors provide an EMC advantage, the metal housing provides a grounded, conductive barrier that functions as a Faraday cage, installed using screened or armoured cable, and the cable braid is bonded directly Proper shielding and bonding of the brake resistor can simplify overall compliance, by reducing the improve RFI noise emissions of the system as a whole.
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