Overview - IEC TR 63021:2016 (Natural graphite brush for slip-ring)
IEC TR 63021:2016 is a technical report from the IEC on the use of natural graphite (NG) brushes for slip-rings in wound rotor-type induction motors. The report compiles technical characteristics, practical test results and application guidance obtained from field use of NG-brushes across heavy-duty installations (e.g., large water pumps, belt conveyors, lifts, winders, grinding mills, crushers, cranes, rolling mills, compressors and oil/gas boring motors). It compares NG‑brush performance with traditional copper brushes and summarizes operational benefits and constraints.
Key topics and technical requirements
- Performance characteristics
- Current density: NG‑brushes deliver comparable current density to copper brushes (typical NG range cited).
- Electrical resistivity and bulk density: NG-brush resistivity is higher (documented ranges: NG 5–15 µΩm vs copper 0.05–3 µΩm) and NG bulk density is lower (NG ≈ 1.35 g/cm3 vs copper 4.5–5.5 g/cm3), affecting heat and wear behavior.
- Operational issues addressed
- Fire-spark: reduced sparking between NG-brush and slip-ring versus metal brushes, lowering ring damage and ignition risk.
- Wear and life: brush wear, expected life of brush and slip-ring, and influence on maintenance intervals.
- Dust diffusion: lower particulate generation from NG wear, reducing contamination risk and insulation degradation.
- Noise and vibration: NG-brush porosity and friction characteristics contribute to vibration-absorbing ability and can reduce acoustic noise.
- Temperature and brush pressure: guidance on managing brush temperature and contact forces for stable operation.
- Testing and data
- References test methods such as IEC 60413 and IEC 60773; includes application data in Annex A for real installations.
Practical applications and users
- Where to apply: Slip-rings of wound rotor induction machines in mining, material handling, lifting, pumping, rolling and oil/gas drilling equipment - especially where sparking, dust or maintenance downtime are critical concerns.
- Who benefits:
- Electrical designers and rotating machinery engineers assessing brush material selection.
- Maintenance and reliability teams aiming to reduce unplanned outages and slip‑ring damage.
- Plant managers in heavy industries seeking improved safety (reduced fire-spark) and lower environmental contamination.
- Economic considerations: NG-brushes may offer reduced lifecycle costs through longer slip-ring life, lower wear debris and fewer fire-related incidents despite differences in initial unit price.
Related standards
- IEC 60413 - Test procedures for brush material physical properties
- IEC 60773 - Test methods and apparatus for operational characteristics of brushes
IEC TR 63021:2016 is a practical reference for engineers choosing brush materials and defining inspection, testing and maintenance strategies for slip-ring systems.