Electricity + Control January 2015

CABLES + ACCESSORIES DRIVES, MOTORS + WITCHGEAR

• Check that oil rings are free and in place - if these are fitted • Insulation resistance stator • If bearings are insulated, check bearing insulation • Motor earth connection • Cable connections - including earthing; and if surge protection is fitted, check connections and earthing of surge arrestors • Temperature sensor connections and test winding and bearings • Space heaters - if fitted • If themotor is designed and suppliedwith pedestal bearings align- ment and clearance are critical and must be checked. The air gap

Henry du Preez is an independent consultant with extensive experience in ac and dc electrical machines and transform- ers. He consults in mining and industry, locally and globally. He offers specialised training courses in association with ‘Specialized Knowledge’ and ABB (Transformers). Enquiries: Email henry@hdupreez.co.za

between the rotor and stator must be checked as bolting the motor frame down could alter the air gap which could cause vibration and other problems. The air gap should always be checked in pedestal machine and large motor where provision has been made to do so after installation • Run the motor uncoupled and check the cur- rent, vibration, bearing oil rings and lubrica- tion system • Couple the motor and run checking current and starting time • Check and measure vibration • Check and record operating current, voltage and motor conditions (temperatures and vibration) • Set protection to the correct operating condi- tions and motor specifications Conclusion It is important to install the motor with care and monitor the operation conditions if the motor is to operate for the expected service life. References [1] Du Preez, H. 2014. Is Partial Discharge an Is- sue? Electricity+Control, July 2014.12.09 [2] IEC 60034-18-41. 2014. Rotating electrical machines - Part 18-41: Partial discharge free electrical insulation systems (Type I) used in rotating electrical machines fed from voltage converters - Qualification and quality control tests. [3] Nailen RL. Managing Motors. PE Barks Pub- lications Inc. These values must be checked against the re- pairer or manufacturers test report.

MARTHINUSEN AND COUTTS - LEADERS IN ELECTRIC MOTOR AND POWER GENERATION REPAIR, MAINTENANCE AND SPECIALISED MANUFACTURE.

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