Load Sharing between Generators: Typical Issues and Solutions

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Load Sharing between Generators is a critical process in industrial facilities and power plants where multiple generators operate in parallel. When load sharing is not properly managed, it can result in uneven load distribution, equipment stress, and reduced generator lifespan. One common question engineers face is: Why is one generator taking more load than the others when running in parallel?

Addressing such challenges requires a combination of technical knowledge, precise settings, and reliable equipment. Advanced Synchronization Solutions can help ensure generators operate smoothly in parallel, providing balanced load sharing, improving efficiency, and minimizing the risk of mechanical or electrical faults.

In this article, we will explore typical load sharing issues, their causes, and practical solutions to achieve optimal generator performance.

1. What are the typical issues and solutions for Load Sharing between Generators? 

Load Sharing between Generators is critical for maintaining efficiency and stability in power plants or industrial facilities. Typical issues include uneven active load distribution, reactive load imbalance, load hogging, and circulating currents.

  • Uneven Active Load Distribution: This occurs when one generator carries more of the total kW than others, often due to mismatched droop settings or governor differences.

  • Reactive Load Imbalance: Uneven kVAR sharing can destabilize voltage levels and reduce power quality.

  • Load Hogging: A single generator dominates the load, forcing others to operate below optimal levels.

  • Circulating Currents: Small voltage or phase differences between generators can cause current to circulate, creating unnecessary losses and heating.

Solutions:

  • Calibrate droop settings accurately for proportional load sharing.

  • Adjust AVR to stabilize reactive power distribution.

  • Use advanced load sharing controllers to automate balancing.

  • Monitor generator performance continuously and conduct preventive maintenance to detect issues early.

2. Why is one generator taking more load than the others when running in parallel?

Unequal load distribution is one of the most common problems engineers encounter. It can be caused by:

  • Droop Mismatch: If droop settings are inconsistent between generators, some units may take more load than others.

  • Governor Differences: Generators with slower governor response may lag in adjusting to load changes, while faster units pick up more load.

  • Mechanical or Electrical Differences: Variations in generator efficiency, transformer impedance, or cable routing can affect load distribution.

Practical Steps:

  • Measure the active power output of each generator.

  • Adjust droop and governor settings to achieve proportional sharing.

  • Inspect transformers and cables to ensure consistent impedance.

  • Repeat tests after adjustments to confirm balance.

3. How do I adjust the droop settings to balance active power sharing (including generators of different ratings)?

Droop settings determine how a generator shares load in proportion to its capacity. Proper calibration is essential for parallel operation, especially when generators have different ratings.

Procedure:

  1. Identify Generator Ratings: Note kW ratings for each generator.

  2. Set Droop Percentage: Larger units typically have lower droop percentages to share more load.

  3. Synchronize Governors: Ensure governor response curves are consistent with droop settings.

  4. Test with Incremental Load Changes: Observe load sharing and adjust settings iteratively.

  5. Document Settings: Maintain records for future troubleshooting or maintenance.

Correct droop adjustment ensures proportional load distribution and prevents overload on any single generator.

4. What causes circulating currents between generators?

Circulating currents occur when small voltage or phase differences exist between generators connected in parallel. This leads to unwanted current flowing between units rather than supplying the load.

Causes:

  • Minor phase angle differences.

  • Voltage mismatches due to AVR differences.

  • Impedance differences in cables or transformers.

Consequences:

  • Increased losses and heating.

  • Potential damage to generator windings.

  • Reduced efficiency and stability.

Solutions:

  • Check phase alignment and voltage levels before synchronization.

  • Use digital synchronoscopes for accurate monitoring.

  • Correct AVR settings and ensure cable/transformer impedance is balanced.

5. Why is reactive load sharing (kVAR) uneven even if active load is balanced, and how does AVR mismatch affect it?

Reactive load imbalance occurs when generators do not share kVAR proportionally, even if active kW load is balanced. The primary cause is AVR mismatch, which affects terminal voltage.

Effects:

  • Voltage fluctuations across the bus.

  • Increased losses and reduced power quality.

  • Uneven heating of generator windings.

Solutions:

  • Calibrate AVR on all generators to maintain consistent terminal voltage.

  • Adjust reactive load sharing settings if using advanced load sharing controllers.

  • Monitor reactive power in real time using SCADA systems.

6. Why do generators hunt or oscillate when connected in parallel, and how do differences in governor response affect this?

Generator hunting or oscillation is a cyclical fluctuation in speed and load, often caused by mismatched governors or inappropriate droop settings.

Causes:

  • Differences in governor response times.

  • Droop settings too low or too high.

  • Load changes not being absorbed proportionally.

Solutions:

  • Fine-tune governor response curves.

  • Adjust droop settings for stability.

  • Test load changes incrementally to observe and damp oscillations.

7. How to detect and fix load hogging by one generator?

Load hogging occurs when a single generator takes more than its fair share of load.

Detection:

  • Monitor active and reactive power output.

  • Compare actual load sharing with expected proportional values.

Fix:

  • Adjust droop settings.

  • Check governor response.

  • Ensure other generators are capable of sharing load (not limited by capacity or faults).

8. What’s the effect of cable or transformer impedance on load distribution?

Impedance differences affect voltage drop and, consequently, load sharing. High or unbalanced impedance can cause some generators to carry more load than intended.

Solutions:

  • Measure impedance of cables and transformers.

  • Ensure matched impedance paths for all generators.

  • Adjust settings or reroute cables if necessary.

9. How to troubleshoot synchronization issues that affect load sharing?

Synchronization issues directly impact load sharing.

Steps:

  • Verify voltage, frequency, and phase alignment.

  • Use digital synchronoscopes or multimeters.

  • Correct AVR and governor settings.

  • Gradually connect generators under controlled load to confirm balance.

10. Can environmental factors (temperature, altitude) affect load sharing accuracy?

Yes, environmental factors like high temperatures or high altitude can affect generator efficiency, voltage output, and governor response.

Mitigation:

  • Apply derating as per manufacturer guidelines.

  • Monitor real-time performance and adjust droop/AVR as needed.

11. How to prevent overload on one generator during load changes, and why does one generator trip when others are sharing load?

Sudden load changes or misconfigured settings can overload a generator, causing protective trips.

Solutions:

  • Set appropriate droop and governor limits.

  • Use automated load sharing controllers.

  • Monitor active and reactive loads continuously.

  • Ensure protective relays are properly coordinated.

12. How to test load sharing performance in real-time without stopping the plant?

Methods:

  • Use SCADA or HMI systems to observe load distribution.

  • Apply small incremental load changes and monitor responses.

  • Compare measured load sharing with expected proportional values.

13. Best practices for commissioning multiple generators for stable load sharing

  • Pre-commissioning checks: droop, AVR, governor calibration.

  • Incremental load connection for each generator.

  • Real-time monitoring of active/reactive power.

  • Document all settings for future reference.

14. How to integrate load sharing with SCADA monitoring systems?

  • Connect generator controllers to SCADA via standard protocols.

  • Monitor active/reactive power, voltage, frequency, and alarms.

  • Configure alerts for imbalance or overload conditions.

15. What are the risks of poor reactive load sharing on power quality?

  • Voltage instability and flicker.

  • Increased harmonic distortion.

  • Generator overheating.

  • Possible trip events or equipment damage.

16. How to identify faulty sensors or transducers affecting load distribution?

  • Compare sensor readings with reference instruments.

  • Inspect signal wiring and calibration.

  • Replace defective sensors to restore accurate load measurement.

17. How often should load sharing settings be checked and recalibrated?

  • Recommended: quarterly or after major maintenance.

  • Always check after adding or removing generators.

  • Record adjustments for maintenance history.

Conclusion

Proper management of Load Sharing between Generators is essential for safe, efficient, and reliable operation in industrial and power plant environments. By understanding common issues such as uneven active or reactive load, load hogging, circulating currents, and generator oscillations and applying practical solutions like droop calibration, AVR adjustments, and real-time monitoring, engineers can maintain balanced load distribution and prevent costly equipment failures.

Preventive maintenance, careful commissioning, and integration with SCADA monitoring systems further enhance stability and power quality. Implementing these best practices ensures generators operate harmoniously, reduces the risk of trips or overloads, and extends the lifespan of your equipment.

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