Key Precautions When Operating Multiple Diesel Generators in Parallel

Key Precautions When Operating Multiple Diesel Generators in Parallel

Parallel operation of multiple diesel generator sets is a widely adopted solution for ensuring flexible and scalable power supply. However, improper synchronization or configuration can lead to serious equipment damage, system failure, or even safety hazards. Below are the key prohibitions and critical precautions you must follow when operating diesel generators in parallel.

1. Do Not Parallel Without Voltage and Frequency Synchronization

Voltage Difference Limit:
Before connecting generators in parallel, ensure that the voltage difference between the units is within ±0.5%. A higher difference can cause circulating currents, which may overheat generator windings or trip circuit breakers.

Frequency Difference Limit:
The frequency deviation must be within ±0.2Hz. This can be adjusted using the speed governor. If the frequencies are not synchronized, it may result in power oscillation, and in severe cases, the generator may disconnect from the system.

2. Phase Sequence and Phase Angle Must Be Identical

Phase Synchronization:
Use a synchronoscope or automatic synchronizer to confirm that the phase angle difference is within ±10°. When performing manual synchronization, the breaker must close at the precise “synchronizing point.”

Phase Sequence Check:
Before the first parallel connection, use a phase sequence meter to verify correct phase order. An incorrect phase sequence can cause catastrophic equipment failure.

3. Avoid Unequal Load Distribution

Active Power Balance:
The load difference between generator sets should not exceed 10% of rated power. Unbalanced loads may lead to:

• Overloaded units: Higher temperatures, reduced efficiency, and shorter service life.

• Underloaded units: Incomplete fuel combustion, known as wet stacking, causing carbon build-up.

Reactive Power Balance:
Reactive power should be managed through each unit’s AVR (Automatic Voltage Regulator). Improper adjustment can lead to reactive power circulation, increasing the system’s instability.

4. Do Not Overlook Cooling and Ventilation Requirements

Ventilation Spacing:
When operating multiple sets, ensure at least 1.5 meters between units for proper airflow. Inadequate ventilation may trigger high-temperature alarms or automatic shutdown.

Exhaust Emission Handling:
When exhaust from multiple units is routed together, install mufflers and flow diverters to avoid back pressure, which can affect engine performance or damage turbochargers.

5. Do Not Operate Without a Proper Protection System

Essential Protection Features:

• Reverse Power Protection: Prevents power from feeding back into a stopped unit.

• Overcurrent and Short-Circuit Protection: Safeguards the generator and connected loads.

• Low Oil Pressure / High Coolant Temperature Shutdown: Ensures the engine shuts down before damage occurs.

Routine Testing:
Simulate faults monthly to test the response of protective devices and ensure all systems are functioning correctly.

Additional Recommendations

• First-Time Parallel Operation: Should be supervised by experienced engineers. Using automatic synchronizing controllers such as DEIF or ComAp can significantly reduce the risk of human error.

• Maintain Synchronization Accuracy: Regularly calibrate speed governors and AVRs. Units with over 5000 operating hours should undergo enhanced checks to maintain performance.

Conclusion

By strictly adhering to these guidelines and avoiding the critical pitfalls mentioned above, operators can maximize system stability, prolong generator lifespan, and ensure safe, efficient parallel operation of diesel generator sets. Always refer to the manufacturer’s technical manual and adapt settings according to specific site conditions.

At Hosem, we specialize in designing and supplying reliable diesel generator systems with parallel-ready configurations, including automatic control panels, AVRs, and synchronizers from trusted brands like DEIF and ComAp. And from the product from industrial generators, marine generators, light towers etc.