In short. A site is black-start ready only if every element needed to start the first source, close its breaker and energise the next steps can operate with no external power. Assess each dependency, find those that need power to make power, and fix or provide a manual alternative.
Readiness questions
| Area | Question | Typical gap |
|---|---|---|
| First source | Can it start with no grid and no other source? | Weak or flat starting batteries |
| Fuel | Does fuel reach the engine without electric pumps? | Electric transfer pump on a dead bus |
| Cooling and ventilation | Do fans and pumps run from the first source? | Cooling on a non-generator circuit |
| Control power | Do controllers, relays and PLCs have battery backup? | Control batteries exhausted |
| Breakers | Can breakers close and trip with no AC? | Spring charging needs AC |
| Communications | Do networks and HMIs stay up? | Switches without UPS |
| Protection | Do relays work and settings suit the first source? | Relays disabled or wrong group |
| Loads on the bus | Are loads open before energising? | Auto-closing loads |
| Transformers | Is inrush limited? | Several energised together |
| People and access | Can staff get in, see and operate in the dark? | Doors, lighting, keys |
How to run the assessment
- Draw the dependency tree from the first source: each element it needs, and what those need.
- Mark any element that needs AC or a source that is not yet running.
- Check the age and test status of every battery in the chain.
- Walk the restart sequence on paper, step by step.
- Rank gaps and define fixes.
Scoring (illustrative)
- Ready: every dependency has an independent source and has been tested in a real dead-start.
- Conditional: works but relies on manual steps or an untested element.
- Not ready: at least one dependency would block restart.
Typical fixes
- Battery-backed or generator-first supply for fuel pumps, or gravity feed.
- Battery-backed controls and a monitored DC system.
- Manual breaker closing and charging procedures.
- A documented, practised restart procedure.
- A rental connection point as a last resort.
See black-start architecture and black-start automation.
Testing
A paper review finds gaps, but only a real dead-start test proves readiness. Plan it carefully, with rollback, at a low-risk time, and measure how long each step takes.
Worked illustration
A site’s assessment finds three gaps: the day-tank pump is on a non-generator circuit, the breaker spring-charge motors need AC, and the control batteries are five years old. The fixes: move the pump to the generator bus with a manual hand-pump alternative, add a hand-charge procedure, and replace the batteries. The generator was never the problem. A real dead-start test confirms the fixes.
Dependency assessment
Black-start readiness means the plant can restart from total darkness without the utility. List every dependency of the first generator and check whether it works without power.
| Dependency | Question | Readiness evidence |
|---|---|---|
| Starting energy | Batteries or air for several attempts? | Battery load test, receiver pressure |
| Control power | DC supply independent of the grid? | Autonomy calculation |
| Fuel | Gravity feed, DC pump or manual pump? | Pump test without AC |
| Cooling | Engine-driven or independently powered? | Design review |
| Ventilation and louvres | Open without mains? | Test with power off |
| Breaker operation | Spring-charged by hand or DC? | Operation test |
| Logic | Dead-bus closing rules working? | Simulation |
| People | Trained operators, procedures, torches | Drill record |
Scoring
Mark each line green (proven by test), amber (designed but untested) or red (dependent on mains or unknown). Fix reds first.
Test
A planned black-start drill, with all precautions, is the only real proof. Record time to first source on bus and time to full load.
See black-start architecture and black-start state machine.
Common mistakes
- Testing starts with grid supply present.
- Not testing control batteries under load.
- No written restart procedure.
What to send us
Send the single-line diagram, auxiliary supply list and restart procedure. Send your application details. See also black start and spinning reserve.
Questions engineers ask
What is the most common black-start failure?
A hidden dependency, such as fuel pumps, control power or breaker closing that needs AC.
Do I need to test a real blackout?
For critical sites, yes, in a controlled way. It is the only full proof.
Can a BESS provide black start?
A grid-forming BESS can, if its own controls and auxiliaries start from a dead state.
How often should readiness be reviewed?
After changes, and periodically, including battery replacement cycles.
This guide gives general principles. A site-specific assessment is needed.