Synchronising controls must correspond to the sources, bus and switching equipment in the installation. Identify the permitted connection paths and operating modes. The control philosophy should define the conditions for connection and how the system confirms the relevant equipment states.
Review sensing and protection interfaces
The controller depends on appropriate measurement and switching information. Errors in these interfaces can undermine the intended sequence even where the controller has suitable features. Use the applicable equipment requirements and competent design review to establish the arrangement.
Control objective
Bring the incoming source into acceptable alignment with the live bus and permit breaker closure under the approved conditions.
Generator-to-generator vs generator-to-grid
- protection
- operating
- regulatory
- requirements
Treat example settings as examples
Published protection guides illustrate synchronism checking with specific equipment and example tolerances. Commissioning values must instead come from the approved study and the installed controller and breaker data.
Retain settings and sequence evidence
Testing should demonstrate the agreed connection and disconnection behaviours under defined conditions. Record the configuration and results, including any outstanding limitations. Settings used in another installation should not be adopted without confirming their suitability for the actual plant.
Review Technical Guidance • Request Engineering Review
Review Technical Guidance • Request Engineering Review. Share the application, location and information available so the next discussion can address your actual requirement.
Related guidance
Engineering intent
Synchronising 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
Permissive logic protects the system from unsafe breaker closure. In some systems, the first generator may close onto a dead bus. That is different from synchronising to a live bus. Do not confuse dead-bus closing with live-bus synchronisation. When synchronising to a live bus, the incoming generator must match the live electrical conditions before breaker closure. Is the incoming source electrically compatible with the live bus at this moment? A synchronising controller may supervise the measurement and close-command logic. But the controller is not the whole system. A synchronising alarm should not automatically be blamed on the controller alone. If sensing is wrong, the control decision can be wrong. Measurement error can create a control problem that looks like a generator problem.
Selection and design considerations
If sensing is lost or incorrect, synchronisation should not proceed. If generators synchronise but share load poorly, the issue may involve: If a generator trips after breaker closure, record: The event sequence can reveal where the chain failed. A reset can erase the most valuable evidence. The commissioning plan must define what is included. A synchronising test should state whether it verified: Synchronising settings can affect whether and when breaker closure is permitted. They must follow equipment, system design and commissioning requirements. Changing synchronising settings can change the behaviour of the power plant. Actively adjusts speed/voltage and closes when conditions are met. Actual capability depends on controller, governor, AVR, wiring and system design.
Integration and protection considerations
Any automatic reattempt should follow the approved control/OEM philosophy. A previous synchronising window cannot simply be reused after the breaker fails to close. If acceptable synchronising conditions cannot be achieved within the approved interval: A sync-check function can supervise whether the electrical conditions permit breaker closure. This is distinct from the synchroniser’s active matching process. For high-consequence paralleling, the architecture can include an appropriately independent synchronism-check layer where required. Automatic Synchronising Control Architecture ensures that generator can be safely connected to the live bus. AVR control changes from pre-parallel voltage matching into parallel reactive-power behaviour. This is one of the most important control transitions in a parallel generator plant. Where required, the transition between synchronising and load-sharing modes should avoid undesirable control discontinuity.
Testing, commissioning and verification
THE MOST DANGEROUS “DEAD BUS” CAN BE A LIVE BUS THAT THE CONTROL SYSTEM BELIEVES IS DEAD. But suppose the voltage measurement is zero because: The physical bus is actually energised from another source. If DG-1 closes out of synchronism, the result can impose severe electrical and mechanical stress. MEASUREMENT HEALTH → SOURCE STATUS → BREAKER TOPOLOGY → BUS VOLTAGE → DEAD/LIVE CLASSIFICATION → SYNCHRONISING REQUIREMENT → SYNC-CHECK → CLOSE PERMISSIVE → BREAKER COMMAND → FEEDBACK → STATE UPDATE Before connecting an incoming source, the controller must choose between two fundamentally different paths: Selecting the wrong path can defeat the entire paralleling philosophy. How do we synchronise an incoming source to an energised bus? How do we determine whether synchronising is required and whether closure is permitted?
Operating and lifecycle considerations
Do not infer neutral behaviour from a four-pole label alone. phase sequence • voltage matching • frequency matching • phase-angle measurement • breaker closing time • synchronism-check permissive. The commissioning program should demonstrate that unacceptable synchronising conditions do not permit breaker closure according to the approved test method. This negative test is as important as proving a valid close. Measurement-circuit failure should not be confused with dead bus. Do not accept “all breakers closed” as successful synchronising-panel commissioning. lead/lag • next-generator start • unloading • stop sequence • failed-to-start handling. PMS logic should behave correctly as plant demand changes. A simulated generator-loss/capacity-deficit condition should produce the intended: The system should not reconnect every large motor simultaneously unless explicitly engineered to do so.
Decision and application considerations
Frequency mismatch can cause mechanical and electrical stress at synchronising. The controller must not close the breaker based on unstable or incorrect frequency information. Even if voltage and frequency appear correct, the phase relationship must also be acceptable. Synchronising logic must determine when the incoming generator is in the correct relationship with the live source or bus. Breaker closure at the wrong angle can create severe torque, current and mechanical stress. Do not treat phase angle as a minor detail. The generator breaker is a critical part of synchronisation. A synchronising controller command does not prove the breaker actually closed. Permissives are the conditions that must be satisfied before breaker closure.
Direct answer
Synchronising controls must correspond to the sources, bus and switching equipment in the installation. Identify the permitted connection paths and operating modes.
The practical decision for Synchronising 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.