Black start generator protection considerations

A black start is the process of restoring a power station to operation without relying on external power sources. Normally, the electric power used within the plant is provided from the station generators. The high-voltage grid provides station service power through the transmission lines if all the main generators are shut down. This off-site power source is not available during a wide-area outage. Therefore, a black start is required in the absence of grid power. Generating plants using steam turbines require station service power up to ten percent of their total load capacity (to bring on-line: boiler-feed water pumps, boiler-forced draft combustion air blowers, and fuel preparation equipment, for example). It is uneconomical to provide such a large standby capacity at each station, so black start power is only provided over the electrical transmission network from specific stations. Often hydroelectric power plants are designated as the black start sources to restore network interconnections since these stations need very little initial power to start and can put a large block of power online very quickly to allow start-up of fossil fuel and nuclear stations.