Wide area synchronous grid

A wide area synchronous grid, (also called an "interconnection" in North America), is an electrical grid at a regional scale or greater that operates at a synchronized frequency and is electrically tied together during normal system conditions. These are also known as synchronous zones, the largest of which is the synchronous grid of Continental Europe (ENTSO-E) with 667 gigawatts (GW) of generation, and the widest region served being that of the IPS/UPS system serving countries of the former Soviet Union. Synchronous grids with ample capacity facilitate electricity market trading across wide areas. In the ENTSO-E in 2008, over 350,000 megawatt hours were sold per day on the European Energy Exchange (EEX).

All of the interconnects in North America are synchronized at a nominal 60 Hz, while those of Europe run at 50 Hz. Interconnections can be tied to each other via high-voltage direct current power transmission lines (DC ties), or with variable-frequency transformers (VFTs), which permit a controlled flow of energy while also functionally isolating the independent AC frequencies of each side.

The benefits of synchronous zones include pooling of generation, resulting in lower generation costs; pooling of load, resulting in significant equalizing effects; common provisioning of reserves, resulting in cheaper primary and secondary reserve power costs; opening of the market, resulting in possibility of long term contracts and short term power exchanges; and mutual assistance in the event of disturbances.

Wide area synchronous networks improve reliability and permit the pooling of resources, they can level out the load, which reduces the required generating capacity, allow more environmentally friendly power to be employed, can permit more diverse power generation schemes, and can permit economies of scale.

Wide area synchronous networks cannot be formed if the two networks to be linked are running at different frequencies or have significantly different standards. For example in Japan, for historical reasons, the northern part of the country operates on 50 Hz, whereas the southern part uses 60 Hz. This makes it impossible to form a single synchronous network, and this was problematic when the Fukushima Daiichi plant melted down.

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