Comprehensive monitoring of field winding short circuits for salient pole synchronous motors

An interturn insulation failure in the field winding of synchronous motors is a common problem that can lead to degradation in performance and accelerated wear of motor components. Existing offline tests for detecting this fault are known to be unreliable and inconvenient to perform, as they require motor disassembly. Online monitoring based on airgap flux monitoring has been proven to be successful, but could lack sensitivity for cases where the number of turns per pole is large. In addition, field winding turn shorts can be intermittent depending on the centrifugal force and could be unobservable at standstill or under an steady state operation. Therefore, monitoring of the turn faults under standstill and starting conditions with high sensitivity and without motor disassembly is desirable. In this paper, the detection of field winding short circuits for salient pole synchronous motors based on an airgap search coil under the starting transient, and new methods for standstill testing without motor disassembly are proposed. Two-dimensional finite element analysis and experimental testing on a 30-kW motor are given to verify the claims made. It is shown that the proposed set of tests can provide sensitive and reliable detection of field winding short circuits under standstill and starting conditions.