Ancillary services
System Management is responsible, under the Market Rules, for ensuring that the power system is operated in a safe, secure and reliable manner. In order to fulfill this obligation, System Management controls key technical characteristics of the power system such as frequency and voltage, through ancillary services.
Types of ancillary services
- Load Following: the primary mechanism in real-time to ensure that supply and demand are balanced. 'Load following' accounts for the difference between scheduled energy, actual load and intermittent generation. Load following resources must have the ramping capability to pick up the load ramp between scheduling steps as well as maintain the system frequency. Load following may be provided by units operating under Automatic Generation Control (AGC), or through manual control.
- Spinning Reserve: holds capacity in reserve to respond rapidly should another unit experience a forced outage. The capacity would include online generation capacity, dispatchable loads and interruptible loads (i.e. loads that respond automatically to frequency drops).
- Load Rejection Reserve: requires that generators be maintained in a state where they can rapidly decrease their output should a system fault result in the loss of load. This service is particularly important overnight when most generating units in the system are operating at minimum loading and have no capability to decrease their output in the time frame required.
- Dispatch Support:. ensures voltage levels around the power system are maintained, and includes other services required to support the security and reliability of the power system that are not covered by other ancillary services.
- System Restart: allows parts of the power system to be re-energised by black start equipped generation capacity following a system wide black out. Unlike other generators, black start equipped generators can be started up without requiring a supply of energy from the transmission network.
