Overvoltage Elimination: Resolving Capacitor Bank Switching Issues in a 150 kW Industrial Bakery

A leading bakery production facility in Ontario, operating a 150 kW electrical system, contacted Smart Power Solutions after experiencing repeated voltage surges up to 650 V on its 600 V distribution bus. These overvoltage events caused sensitive control systems to trip, disrupted production, and raised serious concerns about long-term equipment reliability and safety.

I. Problem Definition

The facility was supplied by a dedicated 480 V/600 V, 100 kVA transformer. During production peaks, random and unexplained voltage swells were observed, sometimes exceeding +8.3% above nominal voltage. These events occurred without significant load changes and were frequent enough to cause operational downtime.

• Impact: Nuisance tripping of protective devices, premature equipment wear, and reduced process reliability.
• Risk: Long-term exposure to overvoltage significantly shortens the lifespan of motors, PLCs, and power electronics.

II. Diagnostic Methodology

Our engineering team conducted a comprehensive power quality investigation using IEC 61000-4-30 Class A compliant instrumentation to capture, analyze, and correlate overvoltage events with system behavior under real load conditions.

• Fluke 1777 Power Quality Analyzer: Continuous three-phase RMS and transient recording, harmonic analysis up to the 63rd order (per IEC 61000-4-7).
• Fluke 1587 FC Insulation Multimeter: Verification of insulation integrity to rule out dielectric faults as a contributing factor.
• Fluke Ti480+ Thermal Imager: Non-contact inspection of capacitor stages, contactors, and distribution panels under operational load.

III. Root Cause Analysis

The recorded data revealed a clear correlation: every voltage swell event coincided with automatic capacitor bank switching. The inrush current generated by newly engaged capacitor stages caused a short-duration rise in bus voltage, while parallel resonance between the capacitor bank and system impedance amplified harmonic voltage components.

• Voltage Swells: Peaks of up to 650 V lasting 100–200 ms immediately after capacitor switching.
• Resonance Indicators: Elevated 5th and 7th harmonic voltages exceeding IEEE 519 recommended limits.
• Exclusions: Primary supply voltage remained stable, ruling out utility-side fluctuations or transformer regulation issues.

IV. Implemented Solution

Smart Power Solutions implemented a multi-layered corrective plan to eliminate overvoltage events and stabilize the facility’s distribution network.

• Detuned Reactors: Installed on each capacitor stage to shift the resonance frequency below the 5th harmonic.
• Staged Switching Logic: Reprogrammed the automatic control system for gradual capacitor engagement, reducing inrush current magnitude.
• Transformer Tap Adjustment: Calibrated secondary voltage to remain within ±3% of nominal under varying load conditions.
• Continuous PQ Monitoring: Installed permanent power quality monitoring for real-time system performance tracking.

Conclusion

Following corrective actions, the maximum bus voltage was reduced to 612 V (within IEC tolerance), all transient events were eliminated, and the facility achieved 99.9% uptime. This case demonstrates how precise diagnostic methods, advanced measurement tools, and harmonic mitigation strategies can resolve complex power quality issues, extend equipment life, and ensure uninterrupted production.