Excerpt from paper “Review of Some Motor Field Problems and Recommendations”
Induction Motor, 12.5 kV, BUS EMCs (80 pF sensors)
Cable Arcing Exposed by High PD Activity in Motor
PD measurement is a good monitoring tool for looking into the health of stator winding. However, attention needs to be made that PD was not coming from sources other than stator insulation. This particular user uses PDTrac for their online PD monitoring purpose, but reported erratic & high PD readings over an extended period of time, as shown in Fig 1.
Figure 1 – Erratic & High PD
An on-site inspection during their scheduled downtime did not find problem on the stator winding. Instead, we uncovered that those main lead cables had inadequate spacing that caused arching (as shown in Fig 2) when the motor was installed by their contractor (this motor was shipped out from the factory with main box separated). A temporary fixed was implemented on site so they could have the motor back to service as scheduled. PD readings measured using TGA-B the next day showed significant reduction in PD magnitude. A permanent fix (with special-designed lead separator) was subsequently installed during their next scheduled outage. The latest information received from this user was that their readings have been stable & low. Because of this incidence, we have since attached a warning tag on lead cables for every motor shipped out from our factories so end-users and the installation contractors would pay more attention to that.
Figure 2 – Evidence of Arching