The DCC can be considered as the sister code to the NC RFG. It contains requirements for the demand side (users who take power from the grid). The requirements are similar to those in RfG for reasons of non-discrimination.

A section of the NC RfG deals with requirements that are specific to AC connected offshore generation (mostly wind, sometimes also tidal or wave energy). These AC connections are commonly used for connections close to the shore. More and more offshore wind parks (especially at longer distances from shore) are being connected with HVDC links.

These HVDC connected generators are not in the scope of the NC RfG but are being covered in a dedicated Network Code on HVDC Connections and DC Connected Power Park Modules (NC HVDC).

These significant overlaps between NC RFG and NC HVDC are being carefully managed.

Recording the large volume of comments received during consultation was done using a specific template, which allowed comments on a particular code article to be considered and then validated and discussed by the various drafting teams.

ENTSO-E involved stakeholders at each stage of the NC RfG drafting process. In 2009, ENTSO-E and ERGEG (ACER’s predecessor) began work on the pilot NC RfG and the corresponding framework guidelines. During the pilot phase, ENTSO-E organised two public workshops, conducted a dozen bilateral stakeholder meetings and organised a written consultation on the draft RfG code, which received almost 1500 comments.

Since formal development of the code commenced in 2011/2012, stakeholders have been engaged at every step of the code development process through bilateral meetings, five user group meetings in which 13 European associations contributed, Brussels-based and regional public workshops and a formal written consultation.

The Network Code on Requirements for Generators (NC RfG) has identified four classes of generators to which the code will apply (type A, B, C, D).  These are categorised by size, with type A covering the smallest generating units (anything above 800W) and including technologies such as solar panels installed on the roof of a house or a small wind turbine. Requirements increase as size increases, with type D applying to the largest plants connecting to electricity transmission systems. These thresholds vary by synchronous area (regional groupings) in the European power system.

Type A generators have to meet the most basic set of requirements, focused on frequency stability. The requirements increase progressively; for example, some type D generators will have to meet most of the requirements met by a type A, B and C generators in addition to other specific requirements.

Taken in isolation, a single domestic solar (PV) panel has no impact on the operation of the transmission grid. However, if all domestic PV installations have the same reaction to a system event (a disruption of some nature on the transmission system), then without rules, their combined impact could have a potentially destabilising effect on the system.

For example, Germany has an installed capacity of over 25GW of photovoltaic generation – equivalent to the output of about 15 nuclear power plants.

If we assume that a transmission system event occurred (for example if a large generator unexpectedly stopped working), the system frequency could deviate slightly from the 50Hz value at which it normally operates. If all PV units were set to trip at 50.2Hz (which was common practice across Europe in the past decade), the trip of 1.000.000 units of 5kW (which is a common size for a domestic plant) would mean a combined loss of 5GW.

The continental European system is currently designed to cope with the loss of 3GW. Therefore, there could be a significant risk of a transmission system blackout. For this reason, it is important that the cumulative impact of small generators is considered and planned for.

The requirements set out in the NC RfG will apply to new generators.  The code will not apply to existing generators unless a national TSO and corresponding regulatory authority request it. For this to happen, a clear process must be followed including extensive analysis and approval by regulatory authorities. This is at the discretion of the Member States.

If there is a valid case for retrofitting existing generators, the NC RfG provides a transparent process to be followed. This involves a number of steps including; a quantified cost benefit analysis, public consultation and final decision by the national regulatory authorities.

Sections of the Network Code on Requirements for Generators (NC RfG) contain specific requirements for AC connected offshore generation (mostly wind but also tidal generators). These AC connections are commonly used for connections close to the shore. Increasingly, offshore wind parks at longer distances from shore are connected with HVDC links.

These HVDC connected generators are outside the scope of the NC RfG, but are being covered in a dedicated Network Code on HVDC Connections and DC Connected Power Park Modules (NC HVDC) to take full benefit of synergies in the design of both HVDC links and offshore wind parks.

Some combined heat and power (CHP) generators may be exempt from the requirements set out in NC RfG.

• A first case is that of industrial CHP generators (that meet a detailed set of technical requirements) which primarily use their facilities to produce heat for production purposes. These will be exempted from a small number of requirements in the NC RfG (though will need to comply with the majority of the network code).

• A second case is that of micro-generation for which some technologies have a low market penetration at present, but show significant potential in supporting Europe’s energy goals. The NC RfG provides a dedicated transitional process for emerging technologies, which gives manufacturers a window of opportunity to adapt their products and make them compliant with the NC RfG.

The connection criteria contained within the NC RfG are essential to ensuring that electricity transmission grids can accommodate increasing amounts of electricity from renewable energy sources.  Not including renewable electricity generators, who will continue to play an ever-increasing role in the electricity mix, would jeopardise the long-term security and stability of Europe’s electricity transmission network. It would be akin to building a car but forgetting to include the wheels.

Current practice indicates that all generator technologies, including nuclear, can achieve the NC RfG requirements. Some countries already request nuclear facilities to provide load following flexibility, which is becoming more important in a system with more volatile RES. A general exemption for nuclear power plants is therefore not justified. However, generators of all types, including nuclear, are entitled to apply for a derogation from certain requirements via the derogation procedure.

A key principle of the NC RfG is that it is generation technology-neutral. All requirements are driven by electricity system needs, irrespective of whether they are based on gas, nuclear, wind or any other form of generation.  Of relevance is how the generator interacts with the grid.

Two large categories of generation exist, rotating machine generation and power electronic interfaces. For each category, specific requirements are set out in the NC RfG. Specific considerations for a given technology can be dealt with at the national implementation level.

The NC RfG sets capabilities for new connecting users. It states what they should be able to do but does not prescribe how they should operate, how they can be controlled, or how they would be remunerated for this.

Operational rules or market mechanisms could evolve quickly if needed, whereas changing the capability of a generator may require costly retrofits, which this code aims to avoid. The capabilities of this code ensure that operational rules and can evolve over time in an efficient manner.

Electricity transmission infrastructure has developed differently in many European countries. This is based on a number of national factors including; scale, topography, economy etc. Furthermore, levels of interconnection between countries vary greatly.

The Network Code on Requirements for Generators (NC RfG) recognises these national and regional variations and it is for this reason that many of the requirements in the NC RfG require a national specification. However, the code provides guidance on the way these requirements will be set and, in many cases, sets ranges within which values must be chosen.

The requirements contained within the NC RfG are based on existing national rules that have proven to be best practice. However, as rules vary from country to country and the purpose of the network codes is to put in place a single coherent set of rules, it is possible that for some countries the requirements of the code will differ from those already in place.

Standards are driven by voluntary harmonisation to remove trade barriers and cut compliance costs and are developed based on consensus. The network codes on connection rules are largely driven by the need to ensure security of supply for Europe’s electricity transmission system, which is undergoing vast changes due to changing generation and user patterns.

The relationship between standards and network codes was acknowledged in a Memorandum of Understanding, signed by ENTSO-E and CENELEC signed in September 2013. This underlines the legal basis of network codes and the benefit of standards, which give further specifications and are based on the network codes. For the NC RfG, this would be specifically useful for type testing of small generators.

When the electricity system experiences an event, such as a large generator breaking down (tripping), it tends to lead to an imbalance between generation and demand. This imbalance causes the system frequency to move away from its usual value of 50 hertz.

Generators are designed to automatically disconnect from the transmission system if a particular frequency value is reached, to prevent generator damage or because of local distribution islanding protection. If this happens at a small frequency deviation, the situation will worsen, as a potentially large volume of generation will disconnect at the same time. This will in turn increase the imbalance and aggravate the situation.

There is consequently a need for generation to be able to remain connected within uniform ranges per synchronous area. The frequency range requirements in the NC RfG are in line with various national grid codes, as well as the international IEC 60034 standard for electrical rotating machines.

The aim of this requirement is to ensure that generators can still operate at times when the transmission system is experiencing a disturbance, or is being restored after a partial blackout. This does not mean that TSOs will operate the power system according to these ranges – indeed the Network Code on Load Frequency Control and Reserves (LFCR) describes target frequency quality parameters for all TSOs – but ensures extreme events can be managed safely.

The transmission system across Europe is designed in such a way that when a fault occurs (e.g. a tree hits the line during a thunderstorm), the fault is quickly and securely isolated. In most situations, the end consumer will not notice the disturbance and remain continuously supplied with electrical power from the grid.

During this action however, the grid voltage will be strongly perturbed for a very short time. A fault-ride-through requirement aims at keeping the generator connected during that very short time before it would be allowed to disconnect. If this were not explicitly requested, a large number of generators in the close geographical area of the fault would trip (at transmission as well as distribution levels). These simultaneous disconnections can result in a significant imbalance between generation and demand, which in turn results in a frequency disturbance that is seen across the synchronous area.

There is consequently a need for generation (transmission as well as distribution connected) to be able to ‘ride through the fault’. The need for this capability has been widely acknowledged in academic research, many TSO studies and is a feature of the ongoing work by CENELEC to standardise requirements (TS50549).

The NC RfG makes this requirement mandatory for all units as of type B. Specific details of how this requirement can be tested or simulated are driven by local system conditions.

The requirement is non-mandatory, but may be needed from power park modules in systems with a lot of non-synchronous generation.

A very fast injection of reactive power may be crucial to ensure protection schemes operate as quickly and reliably as possible. The response time after the fault in which 2/3 of the reactive current is to be delivered does not require an accurate measurement, but can use similar techniques as in fault detection (which often recognises a fault as fast as 5ms).

A slower component is (e.g. after 40 to 60ms) but with a high accuracy can be equally important to ensure voltage stability.

It is acknowledged that this requirement may be easier to accomplish for those technologies (e.g. DFIGs with a rotating mass and natural fault current injection) and is strongly related to the specifications made in the other fault-ride-through requirements.

These provisions are strongly related to the other fault-ride-through specifications (voltage-time curve and fast reactive current injection) and are therefore best left to be specified at the national level, in a coordinated and consistent manner with other fault-ride-through requirements. In some systems more importance may be put on reactive current injections (to preserve voltage stability), while in others the active power component is more crucial (to preserve power balance and frequency stability).

The European electricity system is changing. In the past large monopoly, companies controlled both electricity generation and the wires that transmitted and distributed the electricity nationally.

Greater liberalisation of electricity markets and greater interconnection between national electricity transmission systems means that generators are now supplying more electricity across borders. In addition, the nature of how electricity is generated is changing. Renewable generation such as wind and solar is forming a much larger percentage of the energy mix and electricity is being generated at ever-smaller scales. In some cases, consumers are now generating their own electricity.

Transmission system operators (TSOs) and distribution system operators (DSOs) facilitate the operation of the electricity market. They own and operate the networks though which electricity is transported from generators to customers, and provide open access to this grid. The electricity system cannot operate reliably without the support of those connected to it, which produce or consume. The Network Code on Requirements for Generators sets out the rules that new generators must adhere to in order to connect to the transmission system.

The NC RfG sets out the technical requirements that all new electricity generators will adhere to. The requirements depend on the size of the generator – with the smallest only facing a minimum set of requirements, and the obligations building up gradually as plant size increases.

The code clearly sets out the tasks and responsibilities for generation owners and network operators. The NC RfG determines procedures to ensure that all generators, regardless of where they are located, are subject to clear and fair rules. This is done by harmonising some rules at a European level and, in other areas, by setting out ranges of values, which can be chosen. These ranges are based on detailed studies of the needs of the electricity transmission system in the future.  Individual countries are then provided with the final decision on which value to choose.

Creating an integrated European electricity market, building stronger connections between national grids and maintaining a high level of security of supply requires rules for the grid to develop in an efficient and safe manner. The Network Code on Requirements for Generators (NC RfG) sets out transparent and proportionate processes for all generators wishing to connect to the transmission system.

Europe is committed to decarbonising its energy sector and national and European policies are stimulating the development of large volumes of renewable energy sources (RES). Certain types of RES generation, such as wind and solar, are intermittent by nature – the amount they produce depends on weather conditions – making them less easy to predict and control.

These RES technologies also have different technical characteristics to conventional generation and are often smaller in size. For them to contribute to system security in a similar way to traditional plants (which is vital as more renewable generation is added to the energy mix and as older plant closes), they need to be designed to provide these services. The NC RfG will facilitate this process and allow more RES to be connected to the system while ensuring that electricity transmissions grids remain stable.

The Network Code on Requirements for Generators (NC RfG) will enter into force 20 days after it is published in the Official Journal of the EU.  However, because it requires various provisions to be developed over a period of time, the different requirements will apply from different points in time.  Due to the need for regulatory approvals, it is impossible to say with absolute certainty when varying elements of the code will apply.  ENTSO-E understands that the Commission will finalise the adoption procedure in early 2014.

Because the NC RfG sets out a clear set of requirements which every generator will need to meet in future, it enables the long-term development of the electricity transmission network to be planned in a more efficient way.  Transmission infrastructure is costly and has a lifespan of up to 40 years or more. 

Therefore building it in the right place at the right time is crucial. In simple terms, if you know what capabilities generators can provide, it is much easier to work out which investments transmission system operators (TSOs) and distribution system operators (DSOs) need (and don’t need) to undertake to maintain system security.  It is also easier to operate the system.

Unfortunately, things will occasionally go wrong when managing a transmission network.  It is absolutely critical that TSOs are certain about the way that generators will react when this happens and are sure that they have the right tools available to contain the problem, stop it spreading and solve it.  By creating a clear pan-European framework of capabilities which generators will provide, the TSOs have much greater certainty that the future transmission grid can be operated safely.

Europe is committed to decarbonising its energy sector and national and European policies are stimulating the development of large volumes of renewable energy sources (RES). Certain types of RES generation, such as wind and solar, are intermittent by nature – the amount they produce depends on weather conditions – making more difficult to predict and control.  Nevertheless, they can produce carbon free electricity at a very low cost.

These RES technologies have different technical characteristics to the generators that have traditionally connected to transmission grids and are often smaller in size. For them to contribute to system security in a similar way to traditional plants (which is vital as more renewable generation is added to the energy mix and as older plant closes), they need to be designed to provide these services.

The requirements in the Network Code on Requirements for Generators (NC RfG) will allow this to happen. Without these requirements it would not be possible to integrate very large amounts of renewable energy into electricity grids (countries like Ireland and Denmark produce 50% of electricity from renewables at some times).  Hence, the NC RfG is critical to continue to connect large volumes of renewable energy in future.

The NC RfG is also needed to assist in the creation of an efficient pan-European (and global) market in generator technology. Manufacturers of the electricity generation equipment will have greater certainty about the rules that will apply, and will not need to deal with a bespoke network of national procedures.  This should help make it easier to do business and bring down costs.