Utility companies use an Energy Management System (EMS) to monitor and control their electrical equipment. Typically, an EMS will be installed in a centrally located control center. The EMS consists of both hardware and software. The Supervisory Control And Data Acquisition (SCADA) component of the EMS is responsible for monitoring the telemetry received from the electrical equipment in the field. This data is presented in graphical format to the operators of the control center. The operators have a wide variety of software tools to assist in the analyzation of the data and control of the power system. Once decisions are made about how the power system should be controlled, commands are issued back out to the field through the Supervisory Control portion of SCADA.
One tool at the disposal of the operators is the Automatic Generation and Control (AGC) system. This system monitors the generation levels of all of the power plants owned by the utility as well as power being transported across transmission lines. It is the responsibility of the Automatic Generation and Control system to ensure that the total generation of the power plants is sufficient to meet the total load from the utility's customers. This must be done continuously on a real-time basis. In other words, when the sun beats down on a city and hundreds of thousands of air conditioners turn on at about the same time, the system has to increase the generation of the power plants to meet the load.
Since utility companies are in the business of making money, they will naturally want to produce the electricity efficiently. Some power plants may cost more to operate. Others may take longer to warm up before they can supply power. Maintenance schedules for power plant equipment also need to be taken into account. The possibility of catastrophes such as the loss of a transmission line during a storm need to be factored in. All of this and the requirement that the generation distribution needs to be recalculated every 2 to 4 seconds can pose some interesting challenges for the AGC system.