System Service Contract
Context
System Services help to maintain "the balance of electricity flows on the power grid, as well as grid reliability, safety and efficiency, at all times": this is the basic task assigned to the transmission system operator by the Law of 10 February 2000. To perform that task, RTE must guarantee the stability of two fundamental parameters: current frequency and voltage at various points on the power network.
Current frequency
Frequency is the "tempo" of oscillations in alternating current. It is directly linked to the generation-demand balance: the loss of a generating unit or a sudden increase in demand caused by a change in temperature, leads to an abrupt variation in frequency, with significant implications for all devices and systems connected to the power network (equipment can be damaged or generating units disconnected), which are optimized for a value of 50 Hz. Frequency therefore needs to be maintained - under contracts - within a range of 50 Hz ? 0.5 Hz..
Voltage
Voltage, meanwhile, allows devices connected to the power network to operate correctly (equipment, industrial processes and generating units). Proper voltage control also helps to reduce network losses, allows available transmission capacity to be used efficiently and avoids the risk of voltage dips. The voltage level is directly dependent on the circulation of reactive power.
Role of RTE
"System Services" encompass the various measures or resources that system players - and mainly generators - make available to RTE to ensure it is able to comply with contractual commitments to maintain frequency and voltage.
Frequency and voltage control is mainly done via les the generating units, which are able to modulate their active (frequency control) or reactive (voltage control) power levels very quickly. Frequency and voltage are controlled automatically, by systems installed on units' alternators: the machines work the same way as a car, whose engine speed adapts depending on the amount of effort required.
RTE is responsible for system reliability, and as such is tasked with the real time implementation of these "services", which are provided by generators based on contracts stipulating the reserve volume and its purchase price.
System Services participation contract
The Contract for Participation in System Services is signed by programming managers responsible for generating units connected to the Public Transmission System (PTS) and which have sufficient technical capacities to enable them to contribute to System Services. For new generating units, these characteristics are described in the applicable government decrees and technical decisions, in particular those relating to the general technical prescriptions for design and operation, with which electricity generation facilities are required to comply in order to be connected to the PTS (Decree n° 2008-386 of 23 April 2008 and Decision of 23 April 2008). These characteristics are specified and detailed in RTE's Reference Technical Document (Articles 4.1 and 4.2).
The Contract for Participation in System Services sets out the technical, legal and financial terms under which RTE acquires the contributions from generating units required to control frequency and voltage.
In particular, it sets out:
- the suitability conditions required for generating units;
- the procedure for remunerating control services; this is determined by RTE and is non-negotiable. The fixed prices of the various remuneration components are defined here:
- for frequency control: payment of control capacities prescribed for primary and secondary reserves, remuneration of the energy generated or saved through secondary control;
- for voltage control: payment of a fixed component for units situated in network zones deemed to be sensitive in terms of voltage control, and a variable component proportional to the operating time of the unit on the PTS
The current version of the contract is detailed in RTE's Reference Technical Document (Articles 8.10)
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