In short. Islanding is feasible only if there is enough generation to match the load, a source that can set frequency and voltage, protection that works at low fault levels, controls that manage the transition, and approval from the utility. Assess each of these before committing to a design.
Readiness questions
| Area | Questions |
|---|---|
| Generation | Is there enough capacity for the island load, with redundancy? Is there a source able to form the grid? |
| Load | Are loads classified? Can non-essential load be shed? What is the largest step or motor start? |
| Storage | Is there fast reserve to cover steps and transitions? |
| Interface | Is there a breaker at the point of common coupling with loss-of-mains detection and sync-check? |
| Control | Is there a controller that manages mode changes, dispatch and shedding, with a safe fallback? |
| Protection | Does it work at island fault levels? Is earthing correct in the island? |
| Communications | Is there redundant, secure communication? |
| Fuel and energy | Is there enough fuel or stored energy for the island duration? |
| Approvals | Does the utility allow it? Do grid codes apply? |
| Operations | Are procedures and training in place? |
A simple scoring approach
Score each area as ready, partly ready or not ready. Any critical area not ready blocks islanding, such as no source able to form the grid. Partly ready items need a plan with cost and time.
Key technical checks
- Capacity balance: island load with allowances must fit within available generation after derating and N+1 as needed.
- Frequency and voltage control: a unit in isochronous or grid-forming mode, with others sharing.
- Step response: the system must hold during the largest step. See load-step screening.
- Fault level: compute the minimum fault level in the island and check protection sensitivity.
- Transition: whether a brief interruption is acceptable or storage must bridge.
See islanded operation and microgrid architecture.
Likely gaps
- No source in a frequency-setting mode.
- Relay settings that assume grid fault levels.
- No fast reserve for a large motor start.
- Controllers that depend on a single communication link.
- No utility agreement.
Worked illustration
A campus wants islanding capability. The assessment finds 3 MW of generators for a 2.4 MW island load (acceptable), but no source forming frequency during the transition, relays set for grid fault levels, and no agreement with the utility. The plan: add a grid-forming BESS or configure one generator for isochronous operation with a controller, re-study protection for island fault levels and apply for utility approval. The readiness score tells the team the priority order.
Island readiness checklist
| Area | Check |
|---|---|
| Capacity | Island generation covers load, with N+1 where required |
| Forming source | Identified, with backup |
| Disconnect | Point-of-common-coupling breaker, with fast detection |
| Protection | Settings valid at low fault current |
| Frequency and voltage control | Droop or isochronous plan |
| Load shedding | Defined and tested |
| Reserve | Spinning reserve and battery energy |
| Fuel | Autonomy for planned island duration |
| Resynchronisation | Sync-check and return procedure |
| Utility approval | Agreement in place if required |
Readiness score (illustrative)
Count the items met out of ten. Below seven, island operation is not ready; the missing items become the work list.
Frequent gaps
- No analysis of protection at island fault levels.
- Solar counted as firm capacity.
- No plan for reconnecting when the utility returns.
- Untested transition under load.
See islanded operation and microgrid controller.
Common mistakes
- Assuming that having generators means the site can island.
- Ignoring protection at low fault levels.
- Skipping utility approval.
What to send us
Send the single-line diagram, sources and loads. Send your application details. See also islandable microgrids.
Questions engineers ask
Can any generator site become an island?
Not automatically. It needs the capabilities in this assessment.
What is the biggest technical risk?
Stability and protection at low fault levels, plus step response.
Do I need storage?
Often yes, for fast reserve and seamless transitions, but not always.
Who must approve?
Typically the utility, and sometimes the regulator. Check local rules.
This guide gives general principles. Feasibility needs studies and approvals.