Spinning Reserve

Minute Lectures

Electricity cannot be stored in an economic way (in large quantities)

Therefore, at each moment the electrical power consumed should equal the electrical power generated.

Companies that sell electricity estimate the amount of energy their clients will consume. They buy this “Scheduled Power” from generation companies, who put it on the transmission grid.

Balancing the net

Spinning Reserve

Minute Lectures

But what if the clients (or power stations) consume (or produce) more, or less, than scheduled?

The Load Diagram

24 hour loaddiagram for a power system

Spinning Reserve

Minute Lectures

The difference between the scheduled consumption and the real load is counteracted by the transmission system operator, who is responsible for keeping the network balanced

The difference between the scheduled production and the actual production should be also taken into account

An imbalance results in a frequency that is lower or higher than the target frequency (generally 50Hz)

The system operator maintains the balance by making use of the “spinning reserve”

The Transmission System Operator

Spinning Reserve

Minute Lectures

Spinning reserve = the unused capacity which can be activated on decision of the system operator

Spinning reserve is provided by devices that are synchronized to the network and able to affect its active power

Negative spinning reserve = capacity that can be switched off quickly to compensate a dip in energy demand.

Definition

Spinning Reserve

Minute Lectures

Who provides it? (1/2)

The system operator pays a generation company to provide spinning reserve

This makes the system operator a client of generation companies

Though less common, a consumer can provide spinning reserve as well, if he agrees to reduce its load upon request of the system operator

Spinning Reserve

Minute Lectures

Who provides it? (2/2)

• Thermal power plants at less than full output

• (Large) consumers

• Pumped storage stations

Spinning Reserve

Minute Lectures

Secondary frequency control

A centralized automatic control that delivers reserve power on short notice in order to bring the frequency back to the target value.

Spinning Reserve

Minute Lectures

Tertiary frequency control

A manual change in the dispatching in order torestore the secondary reserve and provide a more

permanent solution if the imbalance between consumed power and scheduled power persists

react if the secondary reserve does not sufficemanage congestions (which the secondary control

does not do)

Spinning Reserve

Minute Lectures

The complete picture (1/2)

Schematically, frequency regulation can be represented as follows:

A tie-line is a circuit (e.g. a transmission line) connecting two or more control areas or systems of an electric system

A transmission system operator (TSO) is a company that is responsible for operating, maintaining and developing the transmission system for a control area and its interconnections

[UCTE Handbook]

Spinning Reserve

Minute Lectures

Spinning reserve and frequency control

Link between the spinning reserve and the frequency control reserves

The spinning reserve consists of the secondary frequency control reserve the synchronized tertiary frequency control reserve

The primary frequency control is not part of the spinning reserve, because it is not controlled by the Transmission System Operator.

Spinning Reserve

Minute Lectures

The complete picture (2/2)

Allocation of the capacity of a generation unit

(in this example spinning is reserve is positive, but it can also be negative)

Spinning Reserve

Minute Lectures

What about the primary control?

Just like the secondary control, the primary frequency control automatically delivers reserve power to counteract frequency changes although it also helps balance consumption and production

However, the primary frequency control is not part of the spinning reserve, but a local control with network stability as its primary focus (although it can also help balance consumption and production).

Spinning Reserve

Minute Lectures

Round-up

The spinning reserve is a synchronised unused capacity that can be activated quickly by the TSO to offset the differences between the scheduled load/production and the real load/production. It controls the frequency on the net.

The spinning reserve is the responsibility of the transmission system operator, who will “rent” the required capacity from generation companies.

Spinning Reserve

Minute Lectures

Further information

• Y Rebours & D Kirschen (University of Manchester)What is Spinning Reserve?

A survey of Definitions and Specifications of Reserve Services

• UCTE Operations Handbookview