This paper is based on a study undertaken by ERA for the UK Health and Safety Executive (HSE) during 1992/93. The objectives of the study were: (i) to determine whether or not discharging activity which may occur in normally "nonsparking" rotating electrical machines, particularly induction motors, should be regarded as potentially ignition capable in explosive atmospheres; and (ii) to identify whether limits can be established below which the possibility of incendive sparking can be discounted, for example with respect to motor voltage and power ratings. The authors discuss the discharge mechanisms in HV machines, discharge detection and measurement, stator discharges, rotor discharges, tests on machines, relevant standards and codes of practice, and rotor design.
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