Parallel Operation Power Distribution of Diesel Generator Set

In today's power supply systems, diesel generator sets play an important role in many fields due to their unique advantages, especially in remote areas, emergency backup power, and marine power systems. However, when multiple diesel generator sets operate in parallel, the even distribution of power becomes a critical issue. This article will explore in depth the importance, influencing factors, and adjustment methods of power distribution during the parallel operation of diesel generator sets, helping readers better understand and apply relevant knowledge to ensure efficient and stable operation of the diesel generator sets.

However, when multiple diesel generator sets operate in parallel, an often overlooked but extremely important issue emerges, power distribution. Whether the power is evenly distributed directly affects the operating efficiency, economic performance, and overall reliability of the power system.

Active power is the actual power output of the generator set and is used to drive various equipment and loads. During the parallel operation of diesel generator sets, even distribution of active power is crucial. If the distribution is uneven, some serious problems may arise. For example, when the total load power is large, if one generator is fully loaded or overloaded while another remains lightly loaded, the capacity of the generator sets cannot be fully utilized, and damage may occur to the overloaded unit. The diesel engine or generator may fail due to prolonged overload operation, or protective devices may be triggered, affecting the normal operation of the entire station.

Conversely, when the total load power is small, imbalance in active power may cause active circulating currents between generator sets, sending some units into a motoring state. This is unacceptable for diesel engines since they are designed for power generation rather than motoring. If the generator set is equipped with reverse power protection, reverse power will trigger reverse power tripping and cause a fault. This issue is particularly prominent in diesel-electric stations of marine propulsion systems. When ships are sailing at full speed, total load power is high, and uneven distribution of active power often causes one generator to overload and trip. When ships are docked, total load is small, and lightly loaded generators may enter reverse power conditions, also causing tripping and seriously affecting the reliability of the station and the entire vessel.

Although reactive power does not directly drive equipment, it also plays an important role in the power system. The power rating of a generator is determined based on its apparent power, which is the vector sum of reactive and active power. Therefore, imbalance in reactive power will lead to imbalance in apparent power, limiting the capacity utilization of the generator sets. Particularly for power stations with low power factors, the load capacity of the units is not determined by the rated power of the diesel engine but by the rated current of the generator. Imbalanced reactive load can be considered a circulating current between two generators, which may exceed the generator's load current, causing additional internal losses and even overloading the generator. Reactive overload current may also cause the generator's main switch to trip, leading to faults.

In addition, the magnitude of the generator's reactive current corresponds to its excitation current. Imbalance in reactive current often corresponds to imbalance in excitation current, causing the excitation system to overload or fail. For example, the generator rotor winding may burn out, or the rectifier diodes of the compound excitation device may be damaged, these consequences are extremely serious. Therefore, even distribution of reactive power is as important as that of active power.

China has clear requirements for the power distribution of diesel generator sets operating in parallel. When the load varies between 20% and 100% of the total rated power, the generator sets should operate stably. Specifically, power distribution errors must meet the following requirements:

When the generators have the same rated power, the difference between the actual active power borne by each generator and the calculated value based on rated power proportion must not exceed ±10% of the generator's rated active power.

When the generators have different rated powers, the difference between the actual active power borne by each generator and the calculated proportional value must not exceed +10% of the largest generator's rated active power and ±20% of the smallest generator's rated active power.

The difference between the actual reactive power borne by each generator and the calculated proportional value must not exceed ±10% of the generator's maximum rated reactive power.

These standards and requirements ensure that generator sets can operate stably and efficiently under various load conditions and help avoid issues caused by uneven power distribution.

During the parallel operation of diesel generator sets, even power distribution is key to ensuring efficient and stable system operation. However, in actual operation, multiple factors influence power distribution, including generator characteristics, load characteristics, control system performance, and line impedance.

Differences in Generator Set Characteristics: Different models or manufacturers may produce generator sets with characteristic differences, for example, diesel engine speed characteristics or generator excitation characteristics. These differences affect power distribution during parallel operation. If two generator sets are not well matched, uneven power distribution may result.

Load Variation Characteristics: Load variation characteristics also affect power distribution. If the load changes frequently or significantly, generator sets must constantly adjust outputs to adapt. If adjustments are untimely or inaccurate, uneven power distribution easily occurs. For example, in marine power systems, sailing states and equipment operations change load frequently, requiring rapid, accurate power adjustment from generator sets.

Control System Performance: Control systems play a critical role in generator parallel operation. The accuracy, response time, and stability of the control system all affect power distribution. If the control system has errors or responds slowly, imbalanced distribution may occur. When load changes, if the system cannot adjust output in time, deviations arise.

Influence of Line Impedance: Line impedance also affects distribution during parallel operation. Impedance causes voltage drops and uneven current distribution. If line impedance is high, accuracy of power distribution decreases. Therefore, line impedance should be minimized during system design and installation.

Next, we outline the key methods for adjusting power distribution to ensure efficient and stable generator operation.

Adjusting Generator Characteristics: Power distribution can be balanced by adjusting generator characteristics, for example, tuning diesel engine governor characteristics to align speed characteristics among sets, and adjusting generator excitation characteristics to stabilize voltage and reactive power outputs. These adjustments help reduce characteristic differences.

Optimizing Control System Performance: Since the control system is crucial, advanced control algorithms can be used to improve precision and response time. Sensors and monitoring devices can be added to provide accurate real-time data for adjustments. Through these improvements, precise power control can be achieved.

Using Proper Line Design: To reduce the impact of line impedance, conductors with larger cross-sectional area may be used, resistance minimized, and line layout optimized to shorten distances. Compensation devices such as capacitors or reactors can also be applied to improve distribution uniformity.

Real-Time Monitoring and Adjustment: Real-time monitoring is essential. By monitoring active and reactive power outputs of each generator set, deviations can be corrected immediately through adjustments such as throttle control (for active power) and excitation current adjustment (for reactive power). This ensures stable operation.

To better understand the effectiveness of these adjustment methods, this section analyzes practical applications in different scenarios.

Parallel operation is common in maritime power systems. Because load varies frequently and significantly, accurate power distribution is required. At full sailing speed, imbalance can overload one generator. When docked, reactive power imbalance may cause reverse power faults. Advanced control systems and monitoring are essential to avoid these issues.

Diesel generator sets serve as backup power in data centers. Upon utility failure, they must start quickly and share all load evenly. Through high-precision control systems, optimized line design, and real-time monitoring, stable power supply during outages can be ensured.

Even power distribution during the parallel operation of diesel generator sets is complex yet essential. Balanced active and reactive power not only affects efficiency and economics but also directly determines power supply reliability. China's standards provide clear guidelines to ensure stable operation. Factors such as generator characteristics, load variations, control system performance, and line impedance all affect power distribution. Through characteristic adjustment, control optimization, proper line design, and real-time monitoring, even distribution can be achieved. In practical applications such as marine systems and data centers, advanced technologies and methods effectively solve distribution issues and ensure stable, efficient generator operation.