Detailed Explanation of the Functions and Roles of Diesel Generators

A diesel generator serves as a crucial emergency backup power source. Its core function is to supply emergency electricity to safeguard the safety of substations, prevent equipment damage, and avoid the escalation of power grid accidents when both the normal operating power supply and backup power supply at the station are lost.

2. Main Roles

2.1 Ensuring the Operation of the Main Transformer Cooling System

• Issue: A main transformer generates a large amount of heat during operation. If the entire station loses power, its forced oil circulation air cooling or water cooling system will shut down. However, residual heat inside the transformer will still accumulate, causing the transformer oil temperature and winding temperature to rise sharply. This can lead to permanent and catastrophic damage to the transformer insulation within a short period (possibly as little as tens of minutes).
• Role: After the diesel generator starts, it prioritizes restoring power supply to the main transformer cooling system, restarting the oil pumps and fans for forced cooling. This protects the main transformer—valued at tens of millions or even hundreds of millions of yuan—from damage.

2.2 Providing Charging Power for DC Systems and UPS

• Issue: The control, protection, signaling, and automatic devices of a substation all rely on the DC power system. When the entire station loses power, the battery bank starts discharging. Although the battery has a certain capacity, it can only maintain power for a limited time (usually 1–2 hours). If the battery is drained, all protection and control equipment will “malfunction”, triggering an “avalanche effect” that prevents faults from being isolated and cleared.
• Role: After the diesel generator starts, it supplies power to the charging device. The charging device then performs floating charging or equalizing charging for the battery, ensuring stable voltage in the DC system. This guarantees the continuous operation of critical functions such as relay protection, emergency lighting, and circuit breaker switching.

2.3 Ensuring the Ability to Handle Accidents and Restore Power Supply

• Issue: When the entire station loses power, lighting goes out and monitoring systems shut down, leaving operators unable to perform normal operations or identify faults.
• Role:
  • It supplies power to emergency lighting, ensuring sufficient illumination in the control room and key production areas to facilitate operator operations and accident handling.
  • It provides power to monitoring systems (SCADA) and communication systems (via UPS), ensuring smooth information exchange between the station and the dispatch center. This allows operators to clearly understand the status of on-site equipment and perform remote control/regulation operations, creating conditions for rapid power restoration.

2.4 Supporting “Black Start” Plans

• Issue: In extreme cases where the entire regional power grid collapses (known as a “blackout”), power supply must be restored gradually starting from a “launch point” in the grid.
• Role: Power plants or large-scale substations with black start capability can use their diesel generators as the initial power source to drive auxiliary equipment, start small-scale units, and then gradually transmit power outward. Like a “spark”, this eventually restores the operation of the entire power grid. In such cases, the diesel generator in the step-up substation serves as this critical “spark”.

2.5 Safeguarding Other Important Auxiliary Equipment

3. Operating Scenarios and Startup Logic

1. Detection of AC power loss: When the automatic control system of the diesel generator detects that the voltage of both incoming lines (main and backup) of the station transformer is below the set value for a certain period, it issues a startup command.
2. Automatic startup and closing: The diesel generator starts successfully within tens of seconds, establishes voltage and frequency, and then automatically closes its emergency power output switch to supply power to the pre-configured “emergency bus”.
3. Priority-based load connection: Loads on the emergency bus (such as main transformer cooling, DC charging, and emergency lighting) are connected automatically or manually in a pre-set priority order to avoid excessive impact on the generator.
4. Automatic shutdown: When the system detects the restoration of the normal station power supply (stable voltage and frequency), it automatically switches power sources, transfers the load back to the normal power supply, and then the diesel generator runs at no load for a period to cool down before shutting down automatically.

Conclusion

• Preventing damage to key equipment (especially main transformers) and avoiding huge economic losses.
• Maintaining the operation of control systems and preventing further escalation of accidents.
• Creating necessary conditions for the rapid restoration of the power grid.