Oil leak causes and prevention in large electric motors

Oil leaks are a common maintenance problem in large electric motors that can cause down time and even complete failure. The oil can migrate either to the inside of the machine or to the outside environment. This oil migration can be contributed to many factors, but one major cause is due to the differential pressure between the oil sump cavity and the outside environment. A conventional electric motor design does not allow for positive sealing due to the fact that the stationary seal does not contact the rotor shaft. The design intent is to protect the shaft from wear which can be very costly. However, this leaves an open path between the oil cavity and the inboard and outboard environments of the motor. The seals should be designed to provide resistance to any pressure differential in that open space, but often the design robustness is limited by available space and economics. There are valuable rules and procedures to maintain the integrity of the oil seal and its performance. Proper installation and maintenance is critical to prevent leaks even with the most robust designs. This paper will discuss the issues relating to oil leak problems and their prevention.