How to Choose the Right Emergency Diesel Generator?

In modern society, the stability of power supply is critically important. Whether in hospitals, data centers, communication stations, or large commercial buildings, a power outage can result in severe consequences. This is precisely where emergency diesel generators (EDGs) play a vital role. This article provides a detailed guide on how to select the appropriate emergency diesel generator to ensure rapid power restoration during emergencies, thereby maintaining the normal operation of the emergency diesel generator.

Emergency diesel generators are primarily used in critical locations where the loss of power could have significant consequences. In the event of a power outage or other emergency situation, these generators can quickly restore electricity and maintain supply for a period of time. The types of loads that they serve are commonly referred to as priority loads. These typically include communication equipment, instrumentation, and computer systems, all of which have strict requirements regarding downtime.

For such critical equipment, it is not sufficient to rely solely on a diesel generator. Additional backup power systems, such as batteries or Uninterruptible Power Supplies (UPS), are often installed to ensure that power can be restored in the shortest possible time. This combination of systems ensures the reliability of critical operations, particularly in locations where human life, sensitive data, or high-value equipment is at stake.

Emergency diesel generators have two primary operational characteristics that distinguish them from standard or continuous-duty generators:

Emergency Use: Emergency generators are primarily intended for use in emergency situations. Their continuous operational time is typically short, generally lasting only a few hours and usually not exceeding twelve hours. Unlike generators used for continuous or prime power applications, emergency generators are designed to start quickly and carry priority loads during outages, but they are not intended for long-term continuous operation.

Standby Status: Under normal operating conditions, emergency diesel generators remain idle, in a standby mode. They automatically start only when the main power supply fails. Once the main power is restored, the generators automatically shut down. This standby arrangement ensures that the generator is immediately available when needed while reducing unnecessary wear and fuel consumption during normal conditions.

Selecting an emergency diesel generator begins with determining the correct capacity. Several key factors must be considered to ensure that the generator can meet emergency power requirements.

The rated capacity of an emergency diesel generator is typically given as a 12-hour rated capacity, which is adjusted for environmental factors such as altitude, ambient temperature, and humidity. These environmental conditions can have a significant impact on the generator's actual output power.

For instance, at higher altitudes, the air density decreases, which reduces the amount of air entering the engine. This in turn lowers the generator’s output power. Therefore, generators installed in high-altitude regions must undergo a power correction calculation to ensure that they can meet the required load under actual operating conditions. Similarly, extreme ambient temperatures or high humidity can also affect performance and should be considered during generator selection.

The generator capacity must be sufficient to supply the total emergency load. This involves performing a detailed calculation of all equipment that requires power during a blackout, including lighting systems, communication devices, computer networks, medical equipment, and other critical loads.

Special attention should be paid to equipment startup characteristics, especially for electric motors. Electric motors typically require a large inrush current at startup, which is much higher than their running current. Therefore, the generator must be sized to handle the startup of the largest motor among the priority loads. Failing to account for motor startup requirements can result in generator overload or failure during emergencies.

Emergency diesel generators are generally equipped with three-phase AC synchronous generators, with a rated output voltage of 400V. These generators provide stable output voltage and high reliability, making them suitable for emergency power applications. Synchronous generators are preferred for their ability to maintain voltage and frequency stability under fluctuating load conditions, which is critical for sensitive electronic equipment and medical devices.

Determining the number of generators required involves several considerations to ensure reliability, redundancy, and operational efficiency.

If multiple generators are available as potential backups, typically only one emergency diesel generator is needed. However, for increased reliability, two generators can be installed to operate in parallel. Parallel operation provides redundancy, allowing one generator to immediately take over in the event of a failure in the other unit.

It is generally recommended that the number of emergency generators not exceed three. Installing too many generators increases cost, complexity, and potential operational challenges, which can paradoxically reduce the system’s overall reliability. Therefore, careful planning is required to balance redundancy, cost, and operational simplicity.

When selecting multiple generators, it is recommended to choose units that are of the same model, capacity, and have similar voltage and speed regulation characteristics. This ensures compatibility between units, facilitates operation and maintenance, and allows for sharing of spare parts. Additionally, fuel type should be consistent across units to avoid performance differences caused by varying fuel properties.

In configurations with two generators, the automatic start system should ensure that both units can serve as backups for each other. After a mains failure is detected for a specified period, a self-start command is issued. If the first generator fails to start after three consecutive attempts, an alarm is triggered and the second generator automatically starts. This mutual backup mechanism significantly improves system reliability and ensures rapid power restoration during emergencies.

When selecting an emergency diesel generator, it is essential to consider both performance parameters and brand reputation. Key performance factors include:

Emergency diesel generators are generally recommended to use high-speed, turbocharged engines that are low in fuel consumption and highly reliable. High-speed turbocharged engines can provide higher single-unit capacity while occupying less space, which is important in locations with limited room. Low fuel consumption reduces operational costs, and high reliability ensures stable performance during emergency operations.

Generators equipped with electronic or hydraulic speed regulation devices are preferred. These devices allow the generator to quickly adjust engine speed in response to load changes, maintaining stable output voltage and frequency. This is particularly important for sensitive electronic equipment and medical devices that require consistent and stable power.

Brushless excitation synchronous generators are recommended for emergency applications. These generators have higher reliability, lower failure rates, and are easier to maintain compared to traditional generators with brushes and slip rings. Brushless excitation systems eliminate potential faults caused by poor brush or slip ring contact, enhancing overall system stability and reliability.

Choosing generators from reputable brands ensures quality and reliable after-sales service. For example, emergency diesel generators from leading manufacturers may feature diesel engines from well-known domestic and international brands, including Yuchai, Shangchai, Weichai, Volvo (Sweden), and Cummins (USA). These engines have a strong market reputation and are widely applied in critical environments. All products undergo strict quality control and testing to provide safe, stable, and reliable power.

To better understand the selection and application of emergency diesel generators, consider a practical example: A large hospital required emergency diesel generators to maintain power in operating rooms, intensive care units, and other critical areas during outages. The hospital’s total emergency load was 500 kW, including multiple large medical devices and lighting systems.

Capacity Selection: After detailed load calculations and adjustments for environmental factors, the hospital selected two emergency diesel generators, each with a rated power of 300 kW. These units operate in parallel, providing sufficient redundancy so that if one generator fails, the other can immediately assume the load.

Performance Parameters: The hospital chose high-speed turbocharged diesel engines equipped with electronic speed regulation and brushless excitation synchronous generators. These high-performance components ensure rapid startup and stable operation under emergency conditions.

Control System: The generators are equipped with an advanced automatic control system capable of detecting a mains failure and initiating startup within 3–5 seconds. Generators remain in a pre-lubrication and warm-up state to ensure immediate responsiveness during emergencies.

Installation and Maintenance: The generators are installed in a dedicated engine room equipped with silencers and vibration dampers to minimize noise and vibration impact. The hospital has implemented a regular maintenance schedule to ensure that generators remain in optimal operating condition at all times.

This case clearly demonstrates that proper selection and configuration of emergency diesel generators can effectively secure power supply in critical environments, minimizing the potential losses caused by outages.

Selecting the appropriate emergency diesel generator is a complex but essential process. It requires a comprehensive evaluation of multiple factors, including generator capacity, the number of units, performance parameters, brand reputation, control systems, installation, and maintenance considerations.

Through detailed load calculations, environmental factor adjustments, careful selection of performance parameters, and deployment of reliable control systems, emergency generators can start quickly and operate stably, providing dependable power to critical equipment.

It is strongly recommended to work with professional suppliers who can provide technical expertise and after-sales support, ensuring the selection of the most suitable generator units and guaranteeing long-term stable operation. Remember, emergency diesel generators are not merely backup power; they are a vital safeguard for life, safety, and property protection.