<![CDATA[Reliability of 6 kV auxiliary motors is critical to combustion stability in coal-fired steam power plants, yet the quantified effectiveness of overhaul interventions on such motors is seldom reported. This study evaluates a 6 kV Primary Air Fan (PA Fan) induction motor through multi-parameter diagnostics performed during a scheduled overhaul, covering insulation resistance, winding-resistance unbalance, bearing vibration, and mechanical clearance, referenced to IEEE Std 43-2013, ISO 20816-3, IEC 60034-1, NEMA MG 1, and the manufacturer design tolerances. Vibration under load decreased by 49.1% in the vertical direction at the non-drive-end (NDE) bearing, and the mean of the six load-condition readings fell by 20.5% (2.13 to 1.69 mm/s), correlating with the equalization of the NDE bearing top clearance (0.19/0.32 to 0.23/0.22 mm), which indicates that the dominant benefit of the overhaul for this motor was mechanical. Winding-resistance unbalance was 0.279%, far below the 2% acceptance limit. The post-cleaning drop in absolute insulation resistance is consistent with measurement on a warm winding after the running test; as winding temperature was not recorded, insulation integrity is confirmed by the ratio-based Dielectric Absorption Ratio (DAR, 1.62) and Polarization Index (PI, 2.39) rather than by absolute comparison. All measured parameters comply with their applicable acceptance criteria, and the motor is deemed fit for continued operation. The study quantifies overhaul effectiveness and illustrates, on a field case, the consequence of omitting the temperature normalization required by IEEE Std 43-2013: a legitimate maintenance action can be misread as dielectric degradation.]]>
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