Load-sharing controls should distribute demand according to the approved operating philosophy and available generating units. Identify the supported configurations and relevant operating modes. Equal sharing, proportional sharing or another strategy must be specified in relation to the equipment and application.
Review real and reactive control interfaces
Governor and excitation functions play different roles in the sharing arrangement. Their interfaces and settings need to be assessed together with the control system. A communications connection alone does not demonstrate satisfactory sharing behaviour.
Application details
Once generators are connected to a common bus, controls may need to coordinate:
Proportional sharing
Generators of different ratings may share load according to their relative capacity rather than equal numerical kW.
Problems from poor sharing
- one engine overloaded
- another lightly loaded
- reverse power
- reactive circulating current
- poor PF distribution
- unstable plant behaviour
Communication
The purpose of load sharing is not to make generators show the same number.
Verify changes in plant configuration
The assessment should address the relevant conditions when units connect, disconnect or become unavailable. Record the test loads, configurations and results. Keep accepted settings controlled so that later equipment or software changes can be evaluated against the established operating basis.
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Related guidance
Engineering intent
Load-Sharing Controls should be evaluated as part of the complete power system rather than as an isolated catalogue item. Operating duty, connected load, interfaces, protection, controls, installation conditions, testing requirements and lifecycle consequences determine whether the arrangement is appropriate.
Control-system requirement
The control architecture must connect sensing, source readiness, permissives, breaker or transfer commands, feedback, alarms, communications and fallback modes. An individual component test does not prove the complete operating sequence.
Engineering considerations
kW SHARING AND kVAr SHARING ARE DIFFERENT CONTROL PROBLEMS Or voltage may look acceptable while one engine carries excessive real power. Operators should therefore not assess parallel performance from one number. Equal numerical kW allocation may not represent equal percentage loading. Where mixed capacities are designed to operate together, load allocation may need to reflect the appropriate rated capacity and control strategy. The system should be evaluated using the actual equipment and approved operating philosophy. Before assuming two generators can be paralleled effectively, verify relevant system interfaces. A project may theoretically involve generators from different manufacturers or generations of control equipment. Compatibility should therefore be verified before making a commercial commitment.
Selection and design considerations
One generator can carry acceptable kW but excessive reactive load. Total plant kW alone cannot prove correct sharing. Poor voltage/excitation matching can create reactive-current circulation between paralleled generators. This can increase alternator current without producing useful additional real power. High current with normal kW can be a reactive-sharing problem. Some parallel-generation architectures use governor droop characteristics to support stable load sharing. Conceptually, machine speed/frequency reference changes with load according to the configured characteristic. Actual droop values and implementation are controller/OEM-specific. Multi-generator systems can also use coordinated isochronous load-sharing controls to maintain system frequency while distributing real load among machines. Do not configure multiple independent isochronous governors on a common islanded bus without the required load-sharing strategy.
Integration and protection considerations
But the real operating question begins after paralleling: In a parallel generator plant, the total load is not enough. Load sharing is therefore not simply a controller feature. It is the operating discipline of a multi-generator power system. Do Not Just Parallel Generators. Make Them Share the Work Correctly. Load-sharing controls are the control, measurement and protection functions that manage how multiple generators divide electrical load after they are connected in parallel. The goal is not merely to keep generators running together. The goal is to keep the complete plant stable, protected and efficient. Can this generator safely connect to the bus? How should the connected generators divide the work?
Testing, commissioning and verification
Supplying loads independently when the grid is unavailable. A strategy that works in grid-connected mode may not automatically work in island mode. Reverse power occurs when a generator connected to another source absorbs active power instead of exporting it. Reverse-power protection protects the machine from sustained motoring. Do not treat reverse power as a simple alarm. It can indicate a serious prime-mover or load-sharing problem. Reverse reactive power or abnormal kVAr flow can indicate excitation or reactive-sharing problems. Poor reactive sharing can heat alternators even when kW sharing looks acceptable.
Operating and lifecycle considerations
TWO GENERATORS CAN BE PERFECTLY SYNCHRONISED—AND STILL SHARE LOAD BADLY. Yet DG-1 is fully loaded while DG-2 retains substantial unused capacity. A relatively small additional load step can overload DG-1 even though the plant as a whole appears to have adequate installed capacity. COMMON BUS → GOVERNOR CONTROL → REAL-POWER SETPOINT / LOAD-SHARE SIGNAL → ENGINE TORQUE → GENERATOR kW → SHARING FEEDBACK → LIMIT SUPERVISION → PMS COORDINATION kW load sharing determines how the total real-power demand is distributed among generators operating in parallel.
Decision and application considerations
Intentional droop can be an engineered control strategy. Do not classify it as a fault simply because frequency reference changes with load according to the control philosophy. Modern generator controllers can coordinate multiple generators while maintaining system frequency according to their load-sharing architecture. Steady-state proportional sharing does not guarantee identical transient sharing. A large load step should not be assumed to divide equally among the three machines. The control and dynamic models determine transient sharing.
Direct answer
Load-sharing controls should distribute demand according to the approved operating philosophy and available generating units. Identify the supported configurations and relevant operating modes.
The practical decision for Load-Sharing Controls should be based on verified load, equipment, interface and site information. Where equipment-specific data, regulatory applicability or a project study is required, this guidance does not replace that verification.