Black Start Diesel Generators for Power Stations and Substations

What a black start set does

The black start set energises the station’s essential auxiliaries from a dead state. In a gas turbine station it may power the starting system, lube oil pumps, fuel gas systems and controls so the first turbine can start. In an engine station it supplies pre-lubrication, cooling and fuel transfer. Once the first main unit is running, it takes over the auxiliary load and the black start set can stop.

In substations, standby diesels keep protection, control, communications and battery charging alive during a long outage so the network operator can restore supply in an orderly way.

Sizing for the starting sequence

Size the set for the largest step in the starting sequence, not just the total running load. Large motors such as lube oil pumps, cooling fans or a turbine starting motor draw high currents when they start. The set must accept those steps while keeping voltage and frequency within limits so drives and controls do not trip.

Write the starting sequence down with each load, its starting current and its timing, then check the set against it. A generator that carries the total load comfortably may still fail if two large motors start together. The kW, kVA and amps sizing chart helps convert ratings.

Independence from the failed system

A black start set must not depend on the grid or on the station it is restarting. It needs its own starting batteries or starting air, its own fuel supply, its own cooling and its own controls. Where the station has a central battery, consider whether the black start set should have a separate one.

Check common-mode risks: a fire, flood or cable fault that would disable both the main station and the black start set. Physical separation and separate cable routes reduce that risk.

Starting reliability

Black start sets often sit idle for weeks and are then asked to start first time in the worst conditions. Keep jacket water heaters and battery chargers on and monitored, use reliable starting systems and test them regularly. Our article on emergency diesel batteries covers the battery side in detail.

Some owners install two starting methods, for example batteries and air starters, or two smaller sets, so that a single failure does not stop the restart.

Fuel for a long outage

A wide-area blackout can last longer than planned. Hold enough fuel at the black start set to complete the restart and to keep substation and station essentials running if restoration is delayed. Rotate and test stored fuel so it is fit to use.

Plan resupply too. In a regional blackout, fuel deliveries may be disrupted. The fuel resupply planning guide explains how to set priorities with suppliers.

Controls and switching

The switching arrangement must let the black start set energise a dead auxiliary bus safely, without back-feeding the grid, and then hand over to the main unit. Interlocks, synchronising equipment and clear operating procedures prevent errors during a stressful event.

Write a step-by-step black start procedure for operators, with the switching order and checks at each stage. Keep it in the control room and train every shift on it.

Testing the real sequence

Running the set on a load bank proves the engine and alternator, but not the black start. At planned intervals, carry out a full test where the auxiliary bus is isolated from normal supply and the black start set starts and carries the real starting sequence. This is the only way to find coordination, voltage dip and interlock problems.

Grid codes and network operators may require periodic black start demonstrations from contracted stations. Agree the test method, frequency and reporting with them.

Black start and the wider restoration plan

A station’s black start capability is usually part of a wider grid restoration plan run by the network operator. The operator decides which stations restart first, which lines are energised and how islands are joined back together. Stations with black start contracts must be ready to follow those instructions, which means trained staff, tested communications and clear procedures on every shift.

Records and readiness

Keep records of every start, test, fault and maintenance action, along with fuel levels and battery tests. These records show the station’s readiness to the network operator and insurers, and help spot slow deterioration before it causes a failed start.

Review the black start arrangement whenever the station changes. New auxiliaries, larger motors or changed controls can push the set beyond its original sizing without anyone noticing.