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

Abstract

The damper (or amortisseur) winding of synchronous motors (SMs) is a critical component required for starting the motor. Several cases of the forced outage of industrial processes due to the starting failure of salient-pole SMs caused by damper bar failure have recently been reported. The detection of broken damper bars is difficult since they are active only during rotor acceleration, and offline visual inspection is the only means of testing available in the field. It was recently shown that the broken damper bars can be detected from the airgap flux, but this requires the installation of airgap flux sensors inside the motor. In this article, a method based on the 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. Finite-element analysis (1 MW) and experimental testing (30 kW) performed on salient-pole SMs with emulated broken damper bars show that the proposed methods can provide the sensitive and reliable detection of damper bar failures.