Types of Ancillary Services
The following ancillary services are defined in the Market Rules:
- Load Following. Load following is the primary mechanism in real-time to ensure that supply and demand are balanced. Load following accounts for the difference between scheduled energy and 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. This service holds capacity in reserve to respond rapidly should another unit experience a forced outage. The capacity would include on-line generation capacity, dispatchable loads and interruptible loads (i.e. loads that respond automatically to frequency drops).
- Load Rejection Reserve. This service requires that generators be maintained in a state in which 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. This service 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. This service 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.