Electrical Monitoring of Damper Bar Condition in Salient Pole Synchronous Motors without Motor Disassembly

The damper (or amortisseur) winding of synchronous motors (SM) is a critical component required for starting the motor. Several cases of forced outage of industrial processes due to starting failure of salient pole SMs caused by damper bar damage have recently been reported. Detection of damper bar failure is difficult since they are active only during motor starting, and testing in the field currently relies on off-line visual inspection. It was recently shown that broken damper bars can be detected from the airgap flux, but this requires installation of airgap flux sensors inside the motor. In this paper, a method based on analysis of the stator starting current is proposed for detecting broken damper bars. In addition, an electrical detection method based on signal injection from the motor terminals is proposed. The new methods have been devised to provide remote testing from the motor control center without motor disassembly required in existing tests. Experimental testing performed on a 30 kW salient pole SM prototype with emulated broken bars shows that the proposed methods can provide sensitive and reliable detection of damper bar failures.