Parallel Operation of Generators: Real and Reactive Load Sharing
Parallel operation of generators is a critical aspect of power systems, particularly for ensuring load sharing between generators to maintain system stability and efficiency. This process requires precise control of both real power (kW) and reactive power (kVar), ensuring that the load is shared proportionally to each generator’s rating.
In this post, we will discuss the principles of real and reactive load sharing, the importance of proper installation, and precautions to take during parallel operation of generators.
Understanding Real and Reactive Load Sharing
1. Real Power (kW)
Real power is the actual electrical power output of a generator and is controlled by the torque applied to its shaft.
- Torque Control: The prime mover (diesel engine, steam turbine, etc.) adjusts torque to regulate the generator’s real power contribution.
- Proportional Sharing: Generators in parallel must share real power according to their respective ratings to prevent overloading.
2. Reactive Power (kVar)
Reactive power maintains voltage stability and is controlled by the generator’s excitation system.
- Excitation System: Adjusting the field excitation changes the reactive power output.
- Voltage Droop Control: Voltage droop ensures proportional reactive power sharing between generators.
- Under-Excitation Risks: Generators operating under-excited can destabilize the system if not balanced properly.
Key Components for Reactive Load Sharing
Three-Phase Sensing Regulator
A three-phase sensing regulator helps manage reactive load sharing by sensing voltage across a reactor that carries current proportional to one phase. This ensures balanced reactive power distribution.
Installation Requirements for Parallel Operation
1. Current Transformer (CT) and Burden Resistor
- CT Placement: Installed in the generator terminal box to sense current in one phase (commonly the “W” phase).
- Burden Resistor: A 40-ohm resistor with a variable tap is used to adjust the desired voltage droop under reactive load conditions.
2. Connection Details
- The “W” phase conductor passes through the CT for correct polarity and current flow direction.
- CT terminal connections:
- L Terminal: Connected to the generator terminal.
- M Terminal: Connected closer to the load.
- AVR Integration:
- Remove the direct link between the AVR and the generator’s “V” phase.
- Connect the L terminal of the CT to the AVR terminal “VR” or “R.”
- Connect the M terminal to the generator’s “V” phase.
Precautions During Parallel Operation
1. Avoiding Confusion Between Windings and Cables
- Paralleled Windings: Ensure all cables associated with a winding pass through the CT.
- Paralleled Cables: Multiple cables for one winding must also pass through the CT for accurate measurement.
2. Correct Placement of Current Transformers
- The CT should encompass all phase conductors linked to a specific winding. Improper placement can cause inaccurate reactive power sharing and instability.
3. Proper AVR Configuration
- Follow the manufacturer’s guidelines for configuring the Automatic Voltage Regulator (AVR). Verify connections and adjust settings to maintain correct voltage droop.
Benefits of Proper Parallel Operation
- Enhanced Stability: Balanced load sharing prevents overloading and phase imbalances.
- Improved Efficiency: Generators operate closer to their optimal performance points.
- Extended Equipment Lifespan: Reduced mechanical and electrical stress minimizes maintenance requirements.
- Scalability: Easily add or remove generators based on fluctuating load demands.
How Real and Reactive Power Are Shared
| Aspect | Real Power (kW) | Reactive Power (kVar) |
|---|---|---|
| Control Mechanism | Torque adjustment through the prime mover. | Excitation system adjustments. |
| Stability Factor | Maintains load distribution. | Ensures voltage stability across the system. |
| Measurement | Proportional to generator capacity. | Monitored through voltage droop. |
| Risks | Overloading if not shared proportionally. | System instability with improper excitation. |
Steps for Efficient Generator Parallel Operation
- Assess System Requirements:
- Calculate total load and divide it proportionally among the generators.
- Ensure generator ratings are compatible for parallel operation.
- Install Critical Components:
- Use properly rated CTs and burden resistors.
- Configure AVRs to ensure voltage droop control.
- Conduct Testing:
- Perform load tests to verify real and reactive power sharing.
- Monitor system parameters for any anomalies.
- Monitor and Adjust:
- Continuously monitor load sharing.
- Adjust settings as necessary to maintain balance and stability.
Common Issues and Troubleshooting
| Issue | Cause | Solution |
|---|---|---|
| Imbalanced Load Sharing | Incorrect CT placement or connection. | Re-check CT positioning and connections. |
| Reactive Power Instability | Improper AVR configuration or under-excitation. | Adjust AVR settings and excitation levels. |
| Overloaded Generators | Unequal distribution of real power. | Verify torque adjustments for each generator. |
Conclusion
Parallel operation of generators is essential for maintaining stable and efficient power systems. By ensuring proper real and reactive load sharing, you can enhance system reliability, reduce operational costs, and improve scalability. Follow installation guidelines, configure AVRs correctly, and monitor load distribution to achieve optimal results.
For complex systems, consult generator manufacturers or experienced professionals to tailor solutions for your specific operational needs. Proper planning and execution are key to leveraging the full benefits of parallel generator operation.
very good job… keep it up:)