Transmission congestion

Electricity transmission congestion is a condition of the electrical grid that prevents the accepted or forecasted load schedules from being implemented due to the grid configuration and equipment performance limitations. In simple terms, congestion occurs when overloaded transmission lines are unable to carry additional electricity flow due to the risk of overheating and the transmission system operator (TSO) has to direct the providers to adjust their dispatch levels to accommodate the constraint or in an electricity market a power plant can produce electricity at a competitive price but cannot transmit the power to a willing buyer. Congestion increases the electricity prices for some customers. There is no universally accepted definition of the transmission congestion. Congestion is not an event, so it is frequently not possible to pinpoint its place and time (in this respect it is similar to traffic congestion). Regulators define congestion as a condition that prevents market transactions from being completed, while a transmission system operator sees it as inability to maintain the security of the power system operation with the power flow scheduled for the grid. A congestion is a symptom of a constraint or a combination of constraints in a transmission system, usually the limits on physical electricity flow are used to prevent the overheating, unacceptable voltage levels, and loss of system stability. Congestion can be permanent, an effect of the system configuration, or temporary, due to a fault in the transmission equipment. Avoiding the congestion is essential for a competitive electricity market and is "one of the toughest problems" of its design. The goal is ensure that a power flow as defined by the wholesale market result does not violate the constraints during the normal operation of the grid and in the case of failure of any one particular component (so called n-1 criterion). The existing markets use a range of approaches to solve the problem.