As well as providing peaking energy to the National Electricity Market, Snowy Hydro Limited provides a number of ancillary services to the National Electricity Grid.  Ancillary services are some of the key technical characteristics of the power system that assist the Australian Energy Market Operator (AEMO) to operate the system in a safe, secure and reliable manner.

The Ancillary Services Market was established to competitively trade the provision of these services.  Snowy Hydro Limited is a major player in this market providing the essential ancillary services of voltage and frequency control, contingency reserve and emergency start capability in the event of a widespread system failure.

There are three categories of ancillary services:

• Frequency Control Ancillary Services (FCAS) - used to maintain the frequency on the electrical system
• Network Control Ancillary Services (NCAS) - used to control the voltage at different points of the electrical network and to control the power flow on network elements.

An example of ancillary service activity is frequency control. When the balance between demand and supply in the power system is disrupted, the power system frequency deviates from its designated value. Variations in frequency or voltage can cause damage to generation equipment and industrial, commercial and domestic machinery and create safety concerns. Ancillary services are used to maintain this balance and to correct disturbances quickly.