Generator sets play a crucial role in ensuring a stable power supply, especially during power outages. They are typically in standby mode during normal operation. However, their ability to start quickly and reliably during emergencies is vital for the power system's stability. Problems often arise when multiple generators operate in parallel, such as frequency and voltage differences, and unequal power distribution. If not addressed promptly, these issues can compromise the overall stability of the power system. This article discusses common technical problems with paralleled generator sets and offers solutions to better manage these challenges.
Reverse Power Issues in Paralleled Generators
When two or more generators run in parallel, differences in their performance, such as speed and load, can lead to frequency and voltage differences. These discrepancies can cause reverse power, where power flows in the opposite direction, negatively affecting the efficiency and safety of the generator sets.
1. Reverse Power Due to Frequency Differences
Problem: When two generators are connected in parallel but their frequencies differ, reverse power can occur. This results in abnormal readings on instruments like the ammeter and power meter. For instance, the generator with a higher frequency will show positive current and power, while the generator with a lower frequency will show negative current and power.
Solution: To eliminate reverse power, the speed (frequency) of one generator must be adjusted. By checking the power meter, adjust the generator's speed until the power meter reads zero. This will synchronize the frequencies of both generators.
2. Reverse Power Due to Voltage Differences
Problem: Reverse power may also occur when the voltages of two generators differ, even if their frequencies are the same. In this case, the power meter may show zero power, but the ammeter will still show current flowing, alternating between positive and negative currents.
Solution: To resolve this, adjust the generator voltage. Using the ammeter and power factor meter, adjust the voltage control knob on one generator until the ammeter shows zero. Then, based on the power factor meter, adjust the power factor to above 0.5, ideally around 0.8, for optimal performance.
Unequal Power Distribution in Paralleled Generators
Unequal power distribution is a common issue when multiple generators operate in parallel. This is especially problematic when load variations are significant. Some generators may become overloaded, while others may be lightly loaded. This imbalance reduces system efficiency and could lead to failures.
Consequences of Unequal Load Distribution
Overload: If the total load is high, one generator may become fully or over-loaded, while another may remain lightly loaded. This causes some generators to operate below their full capacity, reducing efficiency. Overloaded generators may trigger protective devices, disrupting the power station's operation.
Underload: If the load is too low, power circulation between generators can cause some to enter "generator mode," supplying power in reverse to the grid. This results in an imbalance of reactive power and could trigger reverse power protection to trip the system, causing a fault.
Solution: To prevent load imbalances, optimize load distribution with an automatic load distribution system. This ensures each generator operates within a reasonable load range. Regular checks and adjustments should be made to ensure each generator's output does not exceed its rated capacity, improving efficiency and preventing overload.
Problems Due to Imbalanced Reactive Power Load
Reactive power is essential for maintaining grid voltage stability and the magnetic field in motors. However, uneven distribution of reactive power in parallel operation can cause imbalances between generators, affecting performance and potentially damaging equipment.
Effects of Reactive Power Imbalance
Reactive Power Imbalance: When reactive power is unevenly distributed, circulating currents may develop between generators. This increases internal losses and can overload the generators, triggering protective devices. An imbalance in reactive currents may also coincide with an imbalance in excitation currents, leading to overloads in the excitation system and potentially damaging the generator's excitation equipment.
Consequences: Excessive reactive current increases internal losses within the generator, raising the risk of overload. In severe cases, it may damage the excitation system, such as burning the generator's rotor windings or damaging rectifier diodes.
Solution: Regular checks and adjustments to reactive power distribution are necessary to maintain balance. Installing reactive power compensation devices, such as synchronous capacitors, can help balance reactive loads and prevent faults caused by reactive current imbalances.
Comprehensive Solutions
To ensure that paralleled generator sets operate reliably during emergencies, consider the following.
Synchronized Starting and Adjustment: Before running generators in parallel, ensure that they have the same frequency and voltage. Adjust the generator speeds and voltages to synchronize their operation, reducing the chance of reverse power issues.
Load Balancing: Optimize load distribution to prevent overloading or underloading of generators. An automatic load distribution system can dynamically adjust each generator's load, ensuring that all generators work at optimal capacity.
Reactive Power Management: Regularly check and adjust reactive power to ensure balance between generators. This prevents damage caused by imbalances in reactive current.
Regular Maintenance and Monitoring: Regular inspections and maintenance are crucial to ensure all equipment is operating at peak performance. Strengthen the monitoring of protective devices to ensure they activate properly during abnormal situations, preventing accidents.
Conclusion
Common issues in paralleled generator sets, such as frequency and voltage differences, unequal power distribution, and reactive power imbalances, can negatively impact the stability and efficiency of generators. By carefully adjusting settings, balancing loads, managing reactive power, and performing regular maintenance, these problems can be effectively prevented. This ensures that generator sets will function reliably during emergencies. Power station operators should enhance equipment monitoring and maintenance to ensure that generators fulfill their emergency role when needed.
