Overview
ISO 20958:2013 - Condition monitoring and diagnostics of machine systems - provides authoritative guidance for online electrical signature analysis (ESA) of three‑phase induction motors. Published by ISO, the standard describes accepted techniques for extracting diagnostic information from electrical measurements at motor terminals or via fitted transducers. It is applicable to both squirrel‑cage and wound‑rotor induction motors and is intended to provide early warning of motor or driven‑equipment faults.
Key topics
- Stator current analysis (Current Signature Analysis, CSA)
- Measurement and spectral analysis of supply currents to detect rotor cage defects (broken bars, cracked end rings), eccentricity, bearing defects, misalignment, and stator winding problems.
- Sideband components appear close to the mains frequency and can be 0.3–3 Hz away and typically 100–1 000 times smaller than the fundamental - requiring high dynamic range and frequency resolution.
- Guidance on interpreting results and differentiating motor faults from driven‑equipment effects (e.g., gearbox sidebands) and on testing at different loads.
- Voltage, power and multi‑phase analysis
- Techniques that analyse all three phases and the relation between current and voltage for enhanced diagnostics.
- Magnetic flux and rotor current analysis
- Use of flux and rotor‑side information to complement stator current analysis.
- Partial discharge (PD) analysis
- Online PD detection methods for stator insulation assessment; recommendations include locking converter frequency/voltage when testing inverter‑fed motors.
- Electromagnetic interference (EMI) testing and shaft voltage analysis
- Methods to detect EMI issues and shaft voltage conditions that can lead to bearing damage.
- Analytical approaches
- Mention of Park’s vector approach (informative annex) and spectral/processing considerations for robust fault detection.
Practical applications
- Online condition monitoring programs for industrial plants (pulp & paper, mining, petrochemical, manufacturing).
- Predictive maintenance and asset management to reduce unplanned downtime and extend motor life.
- Root‑cause analysis when vibration or mechanical diagnostics indicate anomalies - CSA can confirm rotor, winding, or drive‑train issues.
- Commissioning and acceptance testing of motors and motor drives, especially when assessing insulation health or converter‑related spectral components.
Who should use this standard
- Condition monitoring engineers, reliability teams, maintenance planners, electrical test technicians, and motor manufacturers or OEMs integrating ESA into predictive maintenance workflows.
Related standards
- ISO 13372 - Condition monitoring and diagnostics of machines: vocabulary (normative reference cited by ISO 20958:2013).
Keywords: ISO 20958:2013, electrical signature analysis, condition monitoring, three‑phase induction motors, current signature analysis, rotor bar detection, partial discharge, Park’s vector.
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