An evolotionary tale

Part of a grid operator's job is to safeguard both the safety and quality of its electricity supply. Grid codes (main story) contain the ground rules for connection of all forms of power plant to electricity networks and are similar for low and high voltage networks, but with slightly different demands as voltage increases.

For safety reasons, electricity plant must generally be incapable of generation if a circuit becomes unserviceable and not attempt to restart without permission -- network "islands" must not reconnect to the "mainland" without an order to do so. Wind turbines have had no difficulty complying with safety rules. To meet quality standards, network operators must deliver electricity as near as possible to a pure sine wave -- and within specified tolerances for voltage and frequency. With the improved electrical characteristics of wind turbines over the past 20 years, problems with "flicker" have been overcome: wind turbines these days are not often blamed for injecting disturbing "harmonics" into the network.

Rules for harmonics and for "islanding" exist in grid codes at both the distribution and transmission levels. Complying with them has been part and parcel of wind plant design and operation for some time, particularly at the level of the distribution network. With wind power's increasing maturity, however, comes greater responsibility. Today, wind plant are expected to play their part in providing services to the grid to ensure its smooth operation, also in times of trouble. As a full member of the power generation club, wind must contribute to meeting the club's purpose -- safe and secure supplies of electricity at least cost to all.

That said, wind may merit some dispensation from certain demands of a grid code. There are precedents. The inflexibility of nuclear plant has long been recognised and specifically acknowledged in the British code. Indeed, amendments for wind power are being included in the grid codes relevant in wind's major markets.

The evolution of grid codes specific to wind power has followed a familiar pattern. First, the transmission system operator (TSO) specifies stringent requirements that all wind plant should meet. Next, the wind industry responds by pointing out that many of the requirements are not really necessary, some may be costly to deliver, and others may be left to the market to provide. After a period of negotiation, most TSOs modify their initial proposals and a compromise is settled on. In liberalised markets such as the United States, the process is overseen by the electricity regulatory authority to ensure fair play between the all powerful TSO and the weaker independent generator.

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