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Voltage Unbalance:
The Hidden Motor Killer in Your Distribution System
Small imbalances create big problems — long before anyone sees a fault.
This white paper breaks down why even a few percentage points of voltage unbalance can cripple polyphase induction motors, slash equipment life, trigger nuisance trips, and degrade power quality across your system. Pulling from ANSI C84, NEMA MG-1, and symmetrical components theory, it shows exactly how unbalance forms, how it impacts motor behavior, and how utilities can detect and mitigate it early using modern PQ tools.
Whether your team is troubleshooting industrial complaints, fielding motor-failure claims, or navigating DER-driven phase skew, this paper provides the foundation you need to understand the root cause — and stop repeat failures before they start.
Key topics covered:
- What voltage unbalance is and how it develops
- Methods for calculating unbalance (ANSI C84 and symmetrical components)
- Impacts of voltage unbalance on motor torque, speed, current, and temperature
- Motor derating requirements under NEMA MG-1
- How to detect and monitor unbalance using PQ recorders
Why utilities should care:
Voltage unbalance is one of the most common — and most expensive — hidden drivers of motor failures, VFD issues, and customer power-quality complaints. Even a 3% voltage unbalance can create up to a 40% current unbalance, cause overheating, and cut motor life by 25%, all while appearing “within normal limits” on a quick check. For utilities balancing workforce limits, rising DER penetration, aging infrastructure, and increasing regulatory scrutiny, understanding unbalance isn’t optional — it directly improves reliability, reduces outage-adjacent equipment failures, and strengthens customer relationships. This paper gives teams the tools to identify unbalance correctly, quantify its impact, and prevent equipment degradation before it becomes downtime, damage, or claims.
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