How Does Load Sharing Work in Parallel Diesel Generators?

Introduction

Large data centers, mining operations, industrial plants, and independent power stations often use multiple diesel generators operating in parallel.

However, connecting generators to a common busbar is only the first step.

An important question remains:

How much power should each generator supply?

Without proper generator load sharing, one unit may become overloaded while another operates at a relatively light load.

This can reduce system stability and increase operating risks.

Automatic generator load sharing helps distribute electrical demand among connected generators according to their capacities and operating requirements.

What Is Generator Load Sharing?

Generator load sharing is the process of controlling how multiple parallel generators divide the electrical load.

For example, consider two identical 1000 kW generators supplying a total load of 1200 kW.

With equal load sharing:

An unbalanced condition might instead produce 1000 kW from one generator and only 200 kW from the other.

Although total output remains 1200 kW, this arrangement places significantly different demands on the two engines.

A properly configured load-sharing system adjusts their contributions to maintain the required distribution.

Two Types of Generator Load Sharing

Parallel AC generator systems must manage two different types of power:

• Active power sharing (kW)

• Reactive power sharing (kVAr)

Both are necessary for stable parallel operation.

How Does kW Load Sharing Work?

Active power, measured in kilowatts, represents the real electrical power delivered to the load.

In parallel diesel generators, active power sharing is primarily controlled through the engine governor or electronic engine control system.

The basic process is:

Load Measurement → Controller Calculation → Governor Adjustment → Active Power Redistribution

Consider two generators supplying 1200 kW.

Initially:

• Generator 1: 800 kW

• Generator 2: 400 kW

If the target is equal sharing, the control system adjusts engine power commands until both generators approach 600 kW.

With different generator capacities, sharing is normally based on configured ratings or operating requirements rather than equal absolute kW.

How Does kVAr Load Sharing Work?

Reactive power, measured in kVAr, is important for maintaining voltage and supporting inductive electrical loads.

Examples include large motors, pumps, compressors, and industrial ventilation equipment.

Reactive power sharing is primarily managed through alternator excitation and Automatic Voltage Regulator (AVR) control.

By coordinating excitation, the system distributes reactive power among generators and reduces unwanted circulating currents.

kW sharing primarily involves engine power control, while kVAr sharing primarily involves alternator excitation control.

Main Components of a Load-Sharing System

A typical automatic generator load-sharing solution includes:

The exact architecture depends on the selected controllers, generator models, and paralleling strategy.

How Does Automatic Load Sharing Operate?

A typical parallel generator sequence includes:

• Starting the required generators.

• Matching voltage, frequency, phase sequence, and phase angle.

• Closing the appropriate generator breakers.

• Measuring total and individual generator loads.

• Adjusting engine power and alternator excitation.

• Maintaining the required kW and kVAr distribution.

The system continues making adjustments as electrical demand changes.

Some installations also include load-dependent starting and stopping to operate a suitable number of generators.

What Happens When Load Sharing Is Incorrect?

Poor load-sharing configuration can create several problems.

Uneven active power: One generator may approach overload while other units remain lightly loaded.

Reactive power imbalance: Unequal excitation can cause excessive reactive currents and unnecessary alternator heating.

Power instability: Improper control settings may cause power oscillations, unstable voltage, or frequency deviations.

Reverse power risk: Under certain conditions, a generator may absorb active power instead of supplying it. Proper reverse-power protection is essential.

Correct load sharing does not replace protection systems, synchronization checks, or proper generator sizing.

Voltgent Generator Load-Sharing Solutions

Voltgent provides customized multi-generator paralleling solutions for data centers, mining, industrial facilities, oil and gas projects, and independent power plants.

Depending on project requirements, our solutions can include automatic synchronization, kW and kVAr load sharing, paralleling control panels, electrical distribution, and containerized power generation systems.

Our engineering team evaluates generator ratings, operating loads, engine controls, alternator excitation, and system integration requirements.

The objective is to achieve stable power distribution, flexible operation, and reliable generator performance.

Frequently Asked Questions

Is load sharing included in every paralleling panel?

Not necessarily. It depends on the controller, operating mode, and system configuration.

Do parallel generators always share equal power?

No. Identical units commonly share equally, while different-sized generators may share proportionally to their ratings.

What controls kW load sharing?

The engine governor or ECU, coordinated by the paralleling control system.

What controls reactive power sharing?

Alternator excitation and AVR control are central to reactive power sharing.

Can incorrect load sharing cause generator damage?

Yes. Severe imbalance can contribute to overload, excessive currents, unstable operation, or protective trips.

Conclusion

Automatic load sharing allows multiple diesel generators to operate as a coordinated power system.

Effective parallel operation requires proper management of both active and reactive power.