Parallel generating sets need to share the required real and reactive demand within the intended operating arrangement. These are related but distinct aspects of control. Assess the relevant governor and excitation interfaces using the equipment configuration and approved operating philosophy.
Keep the calculation assumptions explicit
The power triangle shown on this page describes the stated sinusoidal relationship. It should not be applied without qualification to every non-linear load condition. Measurements and calculations need consistent boundaries and units so that the result represents the operating state being discussed.
Unequal machines
If generators differ in capacity, proportional sharing may be more appropriate than equal numerical kW sharing.
Poor sharing can create
Synchronisation joins the machines. Load sharing determines whether they work together correctly.
The sinusoidal power triangle
For the stated sinusoidal relationship, kVA² = kW² + kVAr². Real power, reactive power and apparent power must refer to the same operating condition and consistent units. This simplified triangle should not be treated as a complete description of every non-linear load. Real- and reactive-power sharing also require the actual control and equipment arrangement to be assessed.
Assess sharing across the operating range
A system should be reviewed for the configurations and load conditions it is expected to encounter. Changes in the number of online units or control mode may affect the assessment. Record the accepted settings and test evidence rather than assuming that equal nameplate ratings ensure satisfactory sharing.
Start Engineering Review
Start Engineering Review. Share the application, location and information available so the next discussion can address your actual requirement.
Related guidance
Engineering intent
kW/kVAr 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
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
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.
Integration and protection considerations
TWO GENERATORS CAN SHARE kW PERFECTLY AND STILL FIGHT EACH OTHER FOR kVAr. Consider two identical generators supplying a common bus. Generator 1 is supplying three times the reactive power of Generator 2 even though their real-power contributions are identical. 800 kW + 600 kVAr = 1000 kVA at PF 0.8 lagging. Generator kVAr / Power-Factor Sharing Guide must independently arrive at the same apparent-power result. under the simplified system balance and defined sign convention. Generator kW Load-Sharing Guide and Generator kVAr / Power-Factor Sharing Guide must therefore interoperate without becoming one confused calculator.
Testing, commissioning and verification
Capacitor banks can supply reactive power and therefore change generator kVAr demand. under the defined sign convention and operating condition. Do not recommend capacitor size from Generator kVAr / Power-Factor Sharing Guide without considering the relevant system conditions. But its P/Q capability is constrained by converter current/MVA and actual operating limits. But actual PCS capability/control limits require OEM verification. So poor reactive sharing can overload one alternator even when kW sharing looks correct. kW SHARING CAN BE PERFECT WHILE ONE ALTERNATOR IS OVERLOADED. of 625 kVA on the basic apparent-power screen. It does not prove the physical AVR/excitation/load-sharing system will reach and maintain it. But exact control depends on the generator and paralleling architecture.
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.
Direct answer
Parallel generating sets need to share the required real and reactive demand within the intended operating arrangement. These are related but distinct aspects of control.
The practical decision for kW/kVAr 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.