A simplified configuration of wind turbines equipped with American-style box-type transformers

Wind power generation, as a renewable and clean energy source, has relatively mature technology and has witnessed rapid development in China in recent years. It is estimated that by 2010, the total installed capacity will reach 1.8×10⁴ MW. Wind power generation is characterized by a short construction period, quick results, and the most cost - effective advantages. Typically, it takes only about one year to build a 50 - MW wind farm. After completion, the operation cost is low, and the operation and maintenance workload is relatively small.

Overview of Step - up Transformers Selected for Wind Farms

Each wind turbine unit is equipped with a step - up transformer, which is used to step up the generated voltage (0.69 kV) and connect it to the internal collector lines of the wind farm. The unit connection mode of "one machine - one transformer" is adopted for the wiring. The collector lines are connected to the power grid through the step - up substation of the wind farm. Currently, the selected transformers mainly include three types: ordinary oil - immersed transformers (less commonly used), European - style pre - fabricated substations, and American - style pre - fabricated substations (referred to as American - style box - type substations). Among them, American - style box - type substations are currently used more frequently.

Compared with European - style pre - fabricated substations, American - style box - type substations have the advantages of compact structure, full - sealing, small volume, use of elbow - type cable plugs, absence of gas protection, and convenient operation and maintenance. American - style box - type substations are mainly used in urban distribution networks, such as residential areas, industrial parks, commercial centers, and other power - supply places. In recent years, they have been widely used as step - up transformers supporting wind turbines. Their typical electrical wiring scheme (basically the same as that applied in the distribution network) is shown in Figure 1. In accordance with the requirements of the distribution network, American - style box - type substations are equipped with the following corresponding protections:

• Oil - immersed plug - in fuses, which blow when a short - circuit fault occurs on the low - voltage side of the transformer;
• Oil - immersed current - limiting fuses, which blow quickly to cut off the transformer when a short - circuit fault occurs on the high - voltage side inside the transformer, preventing the accident from expanding.
• A three - phase interlocked load switch, immersed in oil, which can complete the closing operation of the transformer with load;
• An intelligent circuit breaker (or fuse disconnect switch), mainly used to protect the load side.

Simplification of the Protection Configuration of American - style Box - type Substations

Simplification Principles

An American - style transformer refers to a transformer that retains the basic features of an American - style box - type substation, such as its structure, corrugated radiators, absence of gas protection, pressure - relief valves, and current - limiting fuses. However, it simplifies the protection devices. Based on the summary of wind power operation experience, some components of its grid protection are removed, making it a transformer specifically used for wind power.

Simplified Protection Configuration

It is technically feasible to remove the grid protection components from American - style box - type substations applied in wind power. The collector lines are equipped with reliable protection devices (installed in the step - up substation). The collector lines need to be connected to the step - up substation, and after stepping up the voltage, they are connected to the system. The step - up station sets up line protection for each collector line respectively. The protection range not only covers the collector lines but also extends to the box - type substation and the wind turbines. Once a short - circuit or other faults occur on a certain line, the line protection will act and disconnect that line. The wind turbines are equipped with a complete set of grid protection devices (installed in the ground control cabinet). Once a grid fault or abnormality occurs, the wind turbine protection will act and cut off the wind turbine (here, the grid refers to the collector line and box - type substation system). Table 1 shows the grid protection set by the wind turbine manufacturer.

Some of the protection configurations of box - type substations are relatively simple. Their protection functions are far inferior to those of the collector line protection and wind turbine protection, and they form redundant cross - protection. Therefore, the grid protection configured in box - type substations is unnecessary and can be removed. The protection scope and functions of intelligent circuit breakers can be completely replaced by the grid protection of wind turbines. Meanwhile, eliminating some unnecessary components, such as load switches and plug - in fuses, helps reduce potential accident points and improve the operational reliability of the equipment.

Protection Settings of Simplified American - style Box - type Substations

To ensure that the simplified American - style box - type substations can meet the operational requirements of wind farms, the Electric Power Research Institute of Jilin Electric Power Co., Ltd. organized 18 experts from Jilin Electric Power Co., Ltd., Beijing Sifang Micro - Electronic Co., Ltd., Datang Jilin Company, and other units to carefully demonstrate and review the configuration of simplified American - style box - type substations. It was recognized that the simplified American - style box - type substation is a dedicated transformer for wind power, developed based on the digestion of American - style box - type substation technology. Technologically, it fully meets the requirements for the safe and reliable operation of wind turbine units, has good economic benefits, and can be widely promoted and used in wind farms. The configuration of the simplified American - style box - type substation is shown in Figure 2.