How to Solve Power Quality Issues in Power System Transformers

Transformers and Power Quality Monitoring

The transformer is a core component of the power system. Power quality monitoring is fundamental to ensuring transformer safety, improving system efficiency, and reducing operation and maintenance costs—directly impacting the reliability and performance of the entire power network.

Why Perform Power Quality Testing on Transformers?

• Ensure Safe Transformer Operation
  Power quality issues—such as harmonics, voltage fluctuations, and load imbalance—can cause overheating, insulation aging, reduced efficiency, and even premature failure.

• Identify Harmonic Pollution and Prevent Overloading
  Modern power systems widely use nonlinear loads (e.g., UPS systems, power electronics, inverters), which generate harmonic currents. These increase iron and copper losses in transformers. When Total Harmonic Distortion (THD) exceeds 5%, transformers face a significant risk of overload.

• Prevent Equipment Malfunction Due to Voltage Fluctuations
  Frequent voltage fluctuations or flicker can destabilize the transformer and downstream equipment, leading to operational errors.

• Control Load Imbalance to Avoid Localized Overheating
  Three-phase load imbalance causes excessive neutral current, resulting in localized overheating, reduced efficiency, and potential transformer damage.

• Ensure Grounding System Safety and Prevent N-G Voltage Issues
  Improper grounding design can lead to neutral point drift, causing abnormal Neutral-to-Ground (N-G) voltage, which disrupts transformer operation and protective device functionality.

How to Conduct Systematic Power Quality Monitoring on Transformers

Harmonic Control and K-Factor Application

• Use K-Factor Transformers: Select appropriate K-rating (e.g., K-4, K-13, K-20) based on load harmonic characteristics to enhance the transformer’s ability to withstand harmonic currents.

• Limit THD (Total Harmonic Distortion): Maintain THD below 5%, in compliance with IEEE 519 standards.

• Install Filtering Equipment: Deploy active or passive filters near harmonic sources to reduce harmonic injection into the system.

Voltage Distortion and Fluctuation Suppression

• Use Voltage Stabilization Equipment: Employ Automatic Voltage Regulators (AVR) or Static Var Generators (SVG) to stabilize voltage.

• Optimize Load Scheduling: Avoid simultaneous startup of high-power equipment to minimize voltage sags.

• Implement Monitoring and Alarming: Deploy power quality monitoring systems to detect and alert on voltage anomalies in real time.

Load Imbalance Mitigation

• Optimize Load Distribution: Maintain balanced three-phase currents.

• Use Load Balancers: Automatically balance loads in applications where manual adjustment is impractical.

• Regular Inspection and Adjustment: Use power quality analyzers to monitor and correct imbalance levels periodically.

Transformer Grounding Practices

• Proper Grounding System Design and Maintenance

• Neutral Grounding: In Separately Derived Systems (SDS), the neutral point must be properly grounded per standards such as NEC 250 to prevent "floating ground."

• Control N-G Voltage: Stabilize the neutral potential through proper grounding to minimize Neutral-to-Ground voltage.

• Compliant Grounding Resistance: Ensure grounding resistance meets code requirements (e.g., ≤4Ω).

• Avoid Grounding Mixing: Keep signal ground and power ground separate to reduce interference.

• Regular Testing: Use a ground resistance tester to periodically verify system integrity.

Capacity Sizing with Distortion Factor Correction

• Account for Crest Factor (CF) and Harmonic Derating Factor (HDF): Adjust transformer capacity based on actual load characteristics.

• Follow ANSI/IEEE C57.110: Apply the standard’s derating factors for accurate capacity selection.

• Provide Capacity Margin: Reserve 10–20% extra capacity during design to accommodate future loads and harmonic effects.