Help needed on an Entergy Arkansas Large General Service account in Jonesboro. Client replaced their main 200 HP motor last month and now they're getting hit with a $1,850 PF penalty that never existed before. The new motor is supposedly more efficient but the power factor dropped from 0.91 to 0.82. Plant manager swears the motor specs show 0.93 PF at full load. I'm thinking the motor isn't running at rated capacity or there's a wiring issue. Anyone seen efficiency upgrades cause PF problems like this?
Entergy Arkansas - Massive PF penalty after motor replacement
Kenneth, this is pretty common with modern high-efficiency motors. The PF rating is only valid at full load, but most motors run at 70-80% capacity in real applications. A 200 HP motor running at 150 HP load might only achieve 0.85 PF instead of the rated 0.93. Also check if the new motor has a different frame size or electrical characteristics. The plant might need to adjust their capacitor bank to match the new motor's reactive power profile.
Lucille is spot on about the load factor impact. I see this all the time here in Oklahoma with OG&E accounts. Premium efficiency motors have different magnetizing current requirements. The old motor probably had higher losses but better partial-load power factor characteristics. You might need to add 15-20 kVAR of correction specifically for the new motor. Get a detailed power analysis during normal operating conditions.
Thanks Susan, that makes sense. The plant only runs the motor at about 75% capacity most of the time. I'll recommend they have an electrical contractor check the existing cap bank sizing. The motor replacement contractor should have considered this but obviously didn't. The $1,850 monthly penalty will pay for correction equipment in about 8 months.
Kenneth, also verify that Entergy is measuring PF correctly for penalty calculation. Down here in Texas, some utilities changed their measurement methods when smart meters were installed. They might be using different averaging periods or measurement points than before. Request a detailed explanation of how they calculate the monthly PF value used for penalties.
Vivian raises a good point about measurement changes. Also consider that the motor replacement might have coincided with other facility changes that affect power factor. New lighting, HVAC modifications, or even different production schedules can impact the overall facility PF. The motor upgrade might just be coincidental timing with other power quality issues.