Generator ATS, AMF and Paralleling: ISO 8528 and IEC 60947-6-1

How to coordinate automatic transfer, generator start, synchronizing, load sharing, bypass and closed-transition operation for standby and prime power systems.

1. Treat Transfer Equipment as a Rated System

ISO 8528-5:2025 specifies design and performance criteria for a reciprocating engine and AC generator operating as a unit, including units that run in parallel with the grid or without it. IEC 60947-6-1:2026 covers transfer switching equipment up to 1,000 V AC or 1,500 V DC, including manually operated, remotely operated, automatic, bypass/isolation and closed-transition equipment.

The ATS, generator breaker, bypass, neutral arrangement, protective devices and controller must be ordered as a tested and coordinated system.

2. Transfer Sequence

StageData to define
Failure detectionSource voltage/frequency limits, phase loss, delay and nuisance-trip immunity
Generator startCrank attempts, start permissive, warm-up, breaker readiness and fuel autonomy
TransferOpen transition, closed transition, in-phase transfer, overlap time and neutral switching
ReturnUtility stability timer, retransfer, cooldown, unload and fail-to-return behaviour
BypassManual bypass, isolation, maintenance source and interlock against unsafe paralleling

3. Paralleling and Load Sharing

For multiple sets or a grid-parallel application, specify synchronizing window, voltage and frequency matching, kW/kvar sharing, reverse power, under/over-frequency, loss of mains, island mode, load shedding and black-start authority.

A generator’s nameplate kVA does not prove that the alternator, governor, AVR, breaker and controller can accept the site’s largest load step or motor starting event. Validate the transient response with the actual load sequence.

4. Test and Handover

  • Test source failure, start, transfer, interlocks, phase rotation, neutral, bypass and emergency stop.
  • Verify breaker Icu/Ics/Icw, busbar duty, generator fault contribution and downstream selectivity.
  • Run step-load, load-bank, retransfer and communication-loss tests; record time stamps from a common reference.
  • Keep the AMF/ATS logic, generator settings, load-shed matrix and final single-line under revision control.

*Reference: ISO 8528-5:2025; ISO 8528-1:2018; IEC 60947-6-1:2026; IEC 61439-2:2020.*