Key ancillary services include:

1. Frequency Regulation Service (FRS): Ensures that the supply and demand balance is maintained on a moment-by-moment basis to keep the system frequency within acceptable limits.
2. Responsive Reserve Service (RRS): Provides backup power that can be quickly dispatched in the event of a significant frequency deviation or a large contingency, such as the loss of a generator.
3. Non-Spin Reserve Service (NSRS): Involves resources that can be brought online within thirty minutes to provide additional capacity if needed.
4. Voltage Support Service (VSS): Maintains the voltage levels within the transmission system to ensure efficient and reliable power delivery.