The Draft Network Code Requirements for Grid Connection Applicable to all Generators (NC RfG) being the first EU action on addressing how generators should be equipped in the Internal Electricity Market contains 53 requirements of which 44 are of mandatory nature.
It is a regulatory issue whether the costs of meeting these requirements should be allocated to ancillary services and collected via grid tariffs or internalised in market prices for electricity.
The ENTSO-E document “Network Code “Requirements for Generators” in view of the future European electricity system and the Third Package network codes” recalls the self-evident nowadays thesis that the transmission system is “the cornerstone and key facilitator for the low-carbon energy future of Europe.”
The above document defines the position of the NC RfG in the entire set of the network codes currently being developed stating that ”The NC RfG is only one code in a suite identified in the EC/ACER/ENTSO-E 3-year plan in accordance to the Third Package legislation that will establish the Internal Electricity Market, contribute to security of supply and facilitate the integration of RES in achieving the EU’s 2020 targets and 2050 aspirations. The other codes cover both system and market design and operation in addition to system design and are being developed to different timelines by different drafting teams but clearly interact.”
Moreover, the NC RfG needs be “the starting and not the blocking point for all codes”.
The current status of the work on the NC RfG is ENTSO-E assessing, in collaboration with stakeholder associations, how ACER’s recent comments on NC RfG can be best addressed.
ENTSO-E refers to the fact that today approximately 80% of the installed capacity in Europe consists of large scale generators connected at EHV level falling into the so-called type D category of the NC RfG and provides the majority of the necessary ancillary services required for secure system operation, but the transmission system operators gathered in this organisation consider that forward-looking EU act must anticipate future developments in energy market (i.e. high penetration of RES) as well as the extensive timelines for running through with the potential amendments to the EU legislation.
Types of Power Generating Modules pursuant to the NC RfG:
Type A requirements are the basic level requirements, necessary to ensure capability of generation over operational ranges with limited automated response and minimal system operator control of generation. For new installations, there is normally little or no additional cost in complying with these requirements once introduced as part of the standard product.
Type B requirements provide a wider level of automated dynamic response with higher resilience to more specific operational events to ensure use of this higher dynamic response and a higher level system operator control and information to utilise these capabilities.
Type C requirements provide refined, stable and highly controllable (real time) dynamic response to provide principle balancing services to ensure security of supply. These requirements cover all operational network states with consequential detailed specification of interactions of requirements, functions, control and information to utilise these capabilities. They provide sufficient generation functionality to respond to both intact and system disturbed situations, and the need for information and control necessary to utilise this generation over this diversity of situations.
Type D requirements cover a wide area of control and range of operation They ensure specific needs for higher voltage (equal to or greater than 110kV) networks and their operation and stability over wide areas, allowing the use of balancing services from generation Europe wide.
The said document “Network Code “Requirements for Generators” in view of the future European electricity system and the Third Package network codes” summarises the following key issues, arising from the increasing levels of non-synchronous RES generation being connected to the European power system(s) that are addressed in the NC RfG:
Fault Ride Through (FRT) - Small levels of RES generation (geographically dispersed) are unlikely to significantly impact the secure operation of the system should they shut down simultaneously. However, as the levels of RES increase it is of increasing importance that a single system event should not result in the large scale shut down generation. RES generation needs to be resilient to system faults staying connected (and generating) during the initial voltage transients (as conventional generation does today). Since a cost efficient FRT functionality is embedded deeply in the power electronics of generation units, with a long development period, that capability has to be identified today to meet future operational requirements
Frequency Stability - is significantly impacted by the rapid increase of RES generation both through the variability of generation patterns (driven by wind speed and solar irradiation) and reduced system inertia as large conventional synchronous generation is replaced by non-synchronous convertor based RES generators. To compensate new response and reserve strategies are required with generation having to be resilient to wider frequency ranges and provided new capabilities (e.g. fast frequency response and system inertia) if system security is not to be compromised.
Voltage stability - would be compromised if the increasing levels of generation connected at distribution voltages are unable to provide the necessary reactive power support. There are also economic benefits in providing voltage support at a distribution level (close to the demand) rather than from centralized sources connected to the transmission system. Since reactive compensation capability is embedded in the complete design of a generation unit or generation unit technology the requirements of the future need to be identified today if the long lead times for development are to be met economically.
Remote Control of distributed generation units - is a highly relevant requirement in the modern electrical network. In this sense, there already exists a very successful experience in Europe with the Spanish CECRE. The control capability is foreseen to include active as well as reactive power regulation in order to support grid stability as well as online reconfiguration. Functionality like on the fly reconfiguration is foreseen to be essential for implementation of Smart Grid solutions in the near future, an added enabler for further RES integration.
Requirements of the NC RfG have been also divided into the two useful categories having regard to the regulatory approach:
1) Category-1-requirements (exhaustively described by NC RfG) include:
- Frequency ranges, including limited frequency sensitive mode,
- Voltage ranges,
2) Category-2-requirements (not exhaustively described by NC RfG) include among others:
- Reactive Power,
The said document mentions that the 9 non-mandatory NC RfG requirements, such as the provision of synthetic inertia for power park modules or black start capabilities are those for which, at this point, a European harmonisation is not sought, however their importance to system security is such (especially for smaller, RES dominated synchronous areas when considering for example synthetic inertia or black start capability) that they are defined at European level and the possibility for coordinated action in national grid codes is highlighted.
An important distinction has also been underlined as regards the ancillary services, namely the NC RfG does not dictate how these services are to be procured or remunerated, instead, it defines what generators should be capable of delivering.
According to ENTSO-E the delivery of these services will be done generally in a market based context as, for example, in the forthcoming Balancing Network Code.