Automatic transfer and bus-tie coordination

Start with the source pair, calculated load, prospective short-circuit current and permitted interruption. PC-class ATK-CP transfers the load and requires coordinated upstream short-circuit protection. A CB-class arrangement incorporates circuit-breaker protection, whose settings must match the load duty. For motor and mixed loads, confirm the declared utilisation category for the exact frame and operating frequency. Rated current alone cannot establish making capacity, fault withstand or suitability for repeated transfer.

Define source-failure confirmation, standby-source availability, opening of the active source, the open interval and closure onto the standby source. Return requires stable normal-source conditions and its own delay; generator cooldown follows the project sequence. Motor residual voltage can require a longer open interval. Product contact-transfer time is only one part of total restoration time. Loads unable to tolerate that interval need a suitable UPS supply, coordinated with bypass and maintenance states.

For a two-incomer and bus-tie scheme, define permitted switch combinations before programming automatic transfer. An open-transition scheme must not inadvertently parallel the sources. Use both position feedback and the required electrical or mechanical interlocks; a command is not proof that a breaker moved. Before one source supplies both sections, check source, bus and feeder capacity and define any nonessential-load shedding. ATMT logic must also account for manual operation, maintenance isolation and a failed opening or closing action.

Check breaker Icu and Ics at the actual system voltage, then coordinate upstream delay with downstream clearing and the corresponding Icw duration. Do not transfer an unresolved downstream short circuit onto a healthy source. Choose pole configuration from the earthing and neutral arrangement, including generator and residual-current protection paths. Confirm that maintenance can isolate the required conductors and control supplies. Protection and interlock settings belong to one coordinated system design rather than independent device selections.

Use the single-line diagram and cause-and-effect matrix to test loss and recovery of each source, unavailable standby supply, transfer inhibition, manual mode and position-feedback failure. Record actual interruption at the load as well as controller and breaker events. Where one source carries both sections, verify load shedding and restoration order. Keep final settings, controller version, pole arrangement and test records together so later maintenance preserves the commissioned sequence.