The HVDC Cross-Channel () is the high-voltage direct current (HVDC) interconnector that has operated since 1986 under the

English Channel The English Channel, also known as the Channel, is an arm of the Atlantic Ocean that separates Southern England from northern France. It links to the southern part of the North Sea by the Strait of Dover at its northeastern end. It is the busi ...

between the continental European grid at Bonningues-lès-Calais and the British electricity grid at Sellindge. The cable is also known as IFA, and should not be confused with the new IFA-2, another interconnect with France that is three times as long but only half as powerful. The current 2,000MW link is bi-directional and the countries can import or export depending upon market demands, mostly depending upon weather conditions and availability of renewable energy on the British Isles, and French surplus of nuclear generation or demand for electric heating. It was completed in 1986, and replaced the first cross-Channel link which was a 160MW link completed in 1961 and decommissioned in 1984. A fire in September 2021 caused the link to be removed from service. National Grid announced that half of its capacity would be restored on 20 October 2021, with full capacity being restored by October 2023.

160 MW system (1961)

The first HVDC Cross-Channel scheme was built by ASEA and went into service in 1961, between converter stations at Lydd in England (next to Dungeness Nuclear Power Station) and Echinghen, near Boulogne-sur-Mer, in France. This scheme was equipped with mercury-arc valves, each having four

anode An anode usually is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, which is usually an electrode of the device through which conventional current leaves the devic ...

s in parallel. In order to keep the disturbances of the magnetic compasses of passing ships as small as possible, a bipolar cable was used. The cable had a length of and was operated symmetrically at a voltage of ±100kV and a maximum current of 800amperes. The maximum transmission power of this cable was 160megawatts (MW). The cable was built by ABB. Given that the cable was laid on the surface of the seabed it was prone to being fouled by fishing nets, causing damage. Whilst repairs were undertaken there was considerable down time on the circuit resulting in a loss of trading. Indeed, by 1984 the circuit was disconnected from the Main Transmission System.

2,000 MW system (1986)

Because the first installation did not meet increasing requirements, it was replaced in 1975–1986 by a new HVDC system with a maximum transmission rating of 2,000MW between France and the United Kingdom, for which two new converter stations were built in Sellindge, between Ashford and

Folkestone Folkestone ( ) is a coastal town on the English Channel, in Kent, south-east England. The town lies on the southern edge of the North Downs at a valley between two cliffs. It was an important harbour, shipping port, and fashionable coastal res ...

Kent Kent is a Ceremonial counties of England, ceremonial county in South East England. It is bordered by Essex across the Thames Estuary to the north, the Strait of Dover to the south-east, East Sussex to the south-west, Surrey to the west, and Gr ...

, England and in Bonningues-lès-Calais (Les Mandarins station), near

Calais Calais ( , , traditionally , ) is a French port city in the Pas-de-Calais department, of which it is a subprefecture. Calais is the largest city in Pas-de-Calais. The population of the city proper is 67,544; that of the urban area is 144,6 ...

, France. Unlike most HVDC schemes, where the two converter stations are built by the same manufacturer, the two converter stations of the 2,000MW scheme were built by different manufacturers (although both have subsequently become part of the same parent company, Alstom). The Sellindge converter station was built by GEC and the Les Mandarins converter station was built by CGE Alstom. This HVDC-link is long in route, with between the two ends. The undersea section consists of eight long 270kV submarine cables, laid between Folkestone (UK) and

Sangatte Sangatte (; ) is a Communes of France, commune in the Pas-de-Calais Departments of France, department on the northern coast of France on the English Channel. The name is of Flemish origin, meaning hole or gap in the sand. Engineering Sangatte i ...

(France), arranged as two fully independent 1,000MW Bipoles, each operated at a DC voltage of ±270kV. Cables are laid in pairs in four trenches so that the magnetic fields generated by the two conductors are largely cancelled. The landside parts of the link consist of 8cables with lengths of in England, and in France. In common with the 1961 scheme, there is no provision to permit neutral current to flow through the sea. Although each station includes an earth electrode, this is used only to provide a neutral reference, and only one of the two electrodes is connected at a given time so that there can be no current flow between them. The system was built with solid-state semiconductor thyristor valves from the outset. Initially these were air-cooled and used analogue control systems, and in 2011 and 2012 respectively, the thyristor valves of Bipole 1 and Bipole 2 were replaced by modern water-cooled thyristor valves and digital control systems supplied by Alstom. This system remains the world's largest-capacity submarine cable HVDC system. In November 2016, during Storm Angus, a ship dragging an anchor cut four of the eight cable components, reducing capacity by 50%. Repairs were completed by the end of February 2017. The equipment occasionally faults, causing capacity to drop: in a bad year, this might happen several times. To maintain grid frequency and power, the National Grid has a variety of

frequency response In signal processing and electronics, the frequency response of a system is the quantitative measure of the magnitude and Phase (waves), phase of the output as a function of input frequency. The frequency response is widely used in the design and ...

assets, of which market batteries are the first to respond. In September 2021, a major fire at the Sellindge converter station led to the shutdown of the link. National Grid initially announced that half of the link capacity would be restored within a fortnight, with full capacity being restored in March 2022. The shutdown came at a time of high prices and supply shortage in the UK electricity market, caused by low wind speeds and high prices for natural gas. On 15 October 2021, National Grid announced that half of the link capacity would be restored within the next few days, that 75% capacity would be available between October 2022 and May 2023, and that they hoped to restore full capacity by October 2023.

Significance

Since the commissioning of the 2,000MW DC link in the 1980s, the bulk of power flow through the link has been from France to Britain. However, France imports energy as needed during the winter to meet demand, or when there is low availability of hydroelectric power. , imports of electricity from France have historically accounted for about 5% of electricity available in the UK. Imports through the interconnector have generally been around the highest possible level, given the capacity of the link. In 2006, 97.5% of the energy transfers were made from France to UK, supplying the equivalent of 3million English homes. Prior to the 2021 fire, the link availability was around 98%, which was among the best rates in the world. The continued size and duration of the flows are open to some doubt, given the growth in demand in continental Europe for clean electricity, and increasing electricity demand within France.

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