Alert no. 400 | 03 November 2021 | Version 1

Electric motor terminal cover catastrophic failure

What happened?

A 400kW electric pump motor has suffered a rapid pressurisation in the motor body resulting in the motor terminal cover catastrophic failing. It was ejected from the terminal box propelling metal fragments approximately 15 metres. A similar incident occurred in August 2000 (refer significant incident report no. 29).

How did it happen?

A drive-end bearing has over heated due to a lack of lubrication and possible variable speed drive circulating  currents. The temperature rise has resulted in an ignition of the bearing grease. This caused a significant pressure rise in the motor which has then resulted in the terminal cover fasteners failing and the cover being ejected with significant force. There were no electrical faults and the motor continued to run after the event.

Key issues

1. The bearing had not been receiving adequate lubrication.
2. The shaft earthing brush was not contacting the shaft.

Recommendations

1. Mines should review their Safety and Health Management System (SHMS) to ensure maintenance schemes adequately provide for electric motor lubrication and its effectiveness.
2. Mines should review their SHMS for effective condition monitoring of electrical motors.

References and further information

• OEM technical specifications
• Significant Incident Report No.29
• Similar overpressure events occurred at another site in 2020 although these did not result in the failure of the motor terminal covers but did cause other damage