Rolling blackout
A rolling blackout, also referred to as rotational load shedding or feeder rotation, is an intentionally engineered electrical power shutdown where electricity delivery is stopped for non-overlapping periods of time over different parts of the distribution region. Rolling blackouts are a last-resort measure used by an electric utility company to avoid a total blackout of the power system. They are a type of demand response for a situation where the demand for electricity exceeds the power supply capability of the network. Rolling blackouts may be localised to a specific part of the electricity network or may be more widespread and affect entire countries and continents. Rolling blackouts generally result from two causes: insufficient generation capacity or inadequate transmission infrastructure to deliver sufficient power to the area where it is needed.
Rolling blackouts are a common or even a normal daily event in many developing countries where electricity generation capacity is underfunded or infrastructure is poorly managed. In well managed under-capacity systems, blackouts are scheduled in advance and advertised to allow people to work around them, but in most cases they happen without warning, typically whenever the transmission frequency falls below the 'safe' limit. Rolling blackouts are also used as a response strategy to cope with reduced output beyond reserve capacity from power stations taken offline unexpectedly such as through an extreme weather event.
Rolling blackouts in developed countries sometimes occur due to economic forces at the expense of system reliability (such as in the California electricity crisis of 2000-2001).