Ancillary services

Ancillary services are the services necessary to support the transmission of electric power from generators to consumers given the obligations of control areas and transmission utilities within those control areas to maintain reliable operations of the interconnected transmission system.

"Ancillary services are all services required by the transmission or distribution system operator to enable them to maintain the integrity and stability of the transmission or distribution system as well as the power quality".

Ancillary services are specialty services and functions provided by actors within the electric grid that facilitate and support the continuous flow of electricity, so that the demand for electrical energy is met in real time. The term ancillary services is used to refer to a variety of operations beyond generation and transmission that are required to maintain grid stability and security. These services generally include active power control or frequency control and reactive power control or voltage control, on various timescales. Traditionally, ancillary services have been provided by large production units such as synchronous generators. With the integration of more intermittent generation and the development of smart grid technologies, the provision of ancillary services is extended to smaller distributed generation and consumption units.

There are two broad categories of ancillary services:

Other types of ancillary services provision include:

Electricity frequency is directly connected to the balance of consumption and generation of active power (${\displaystyle \Delta P=P_{generation}-P_{consume}}$) and the total rotating energy (${\displaystyle W_{tot,kin}}$) of the synchronous power system. During a sudden change of ${\displaystyle \Delta P}$ the frequency will initially (before any remedial actions) change according to the following equation:

${\displaystyle {\frac {df}{dt}}={\frac {\Delta P\cdot f}{2\cdot W_{kin}}}}$

The equation can be rewritten using the normalized inertial constant ${\displaystyle H}$: