Generator Load Sharing

Synchronisation Connects the Generators.

Load Sharing Determines What Each Generator Carries.

Once multiple generators operate on a common bus, the system must distribute electrical demand appropriately.

Engineering intent

Generator Load Sharing 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

Synchronisation requires interlocks to prevent unsafe operating states. Actual protection must follow the equipment, SLD and engineering study. Reverse power can occur when a generator operates as a motor instead of exporting power. It can be related to engine power, breaker state, load sharing, governor behaviour or protection. A synchronising or parallel system should consider reverse-power protection where applicable. Do not diagnose reverse power from one symptom alone. Real power sharing is strongly associated with engine mechanical output and governor/load controls. Total bus load alone may hide individual generator stress. Reactive power sharing is strongly associated with alternator excitation and voltage control.

Selection and design considerations

Insert this under “After Paralleling: The Question Changes”: After generators are synchronised, active power sharing is primarily governed by engine governor and fuel-input behaviour, while reactive power sharing is primarily governed by excitation and AVR behaviour. Poor load sharing can create generator overload, reverse power, unequal heating, poor power factor, circulating reactive current, instability and nuisance trips. Correct synchronisation is only the beginning; stable parallel operation requires coordinated governor, AVR and load-sharing control.

BESS / Micro Grid	Hybrid Power & BESS Guide, future integrated energy pages

Integration and protection considerations

Poor kVAr sharing may not be obvious from kW alone. The AVR controls excitation and therefore generator voltage behaviour. A system can share kW correctly while sharing kVAr poorly. Therefore load-sharing review must include both real and reactive power. while one generator is overloaded and another is lightly loaded. The plant should be evaluated generator-by-generator, not only bus-by-bus. A paralleled generator plant is not automatically superior to a single generator. It becomes superior only when the control system manages the plant correctly. If all three generators are required to support normal demand, losing one generator may still overload the remaining system.

Testing, commissioning and verification

The relative electrical angle must be appropriate for breaker closure. The controls should understand whether the bus and breakers are in the expected condition. The exact synchronisation limits depend on the actual: Once the incoming generator closes onto the common bus, successful synchronisation has only completed the joining event. Real power is associated primarily with engine mechanical output. When multiple generators run together, appropriate controls influence how the real-power load is divided. The system needs appropriate coordination to avoid poor reactive load distribution. A rental plant can appear acceptable if total kW is correct while individual generators are carrying unequal electrical stress.

Operating and lifecycle considerations

The power-management system therefore has a continuous engineering objective: MATCH AVAILABLE GENERATION TO REQUIRED LOAD—WHILE PRESERVING STABILITY, RESERVE, MACHINE LIMITS AND LOAD PRIORITY. LOAD → ONLINE CAPACITY → RESERVE → GENERATOR DISPATCH → kW SHARING → kVAr SHARING → LARGE-LOAD PERMISSIVES → START/STOP SEQUENCING → LOAD SHEDDING → RESTORATION → FAILURE RECOVERY → MONITORING → OPTIMISATION Once two or more generators are paralleled, the common bus fixes their electrical operating relationship. The generators must then share the connected load according to an engineered control strategy. Load sharing has at least two distinct components: They must not be treated as the same control problem. Real power is principally associated with mechanical input from the prime mover. Increasing mechanical torque tends to increase that generator’s share of real power when operating on a common islanded bus under the appropriate control architecture.

Decision and application considerations

If two paralleled generators have mismatched excitation/voltage-control references, reactive-power circulation or unequal kVAr sharing can occur. Some systems use appropriate cross-current/reactive-droop/load-sharing methods. Generator kVAr / Power-Factor Sharing Guide should remain technology-neutral and avoid assuming one implementation. Modern generator controllers can coordinate kVAr/PF through digital communications/load-sharing functions. Generators may remain paralleled while reactive sharing degrades depending on their control architecture. the machines can effectively exchange reactive power while the net load requires much less. Generator kVAr / Power-Factor Sharing Guide should detect opposing-sign generator kVAr values and flag: It should not diagnose the exact cause automatically. CT/VT ratio/polarity/scaling errors can create misleading results.

Direct answer

Synchronisation Connects the Generators. Load Sharing Determines What Each Generator Carries.

The practical decision for Generator Load Sharing 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.

Related photographs and videos