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Energy Industry Challenges > Renewable Energy Sources > Description of technology > Wind power > Grid connection - wind power

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• ENERGY INDUSTRY CHALLENGES
• RENEWABLE ENERGY SOURCES
• DESCRIPTION OF TECHNOLOGY
• Wind power
• Description of technology - wind power
• Grid connection - wind power
• Offshore wind farms
• Solar power
• Wave and tidal power
• Hydro power
• Bio power
• ECONOMIC ASPECTS
• ENVIRONMENT AND PUBLIC AWARENESS
• LEGISLATION
• FINAL COMPARISON
• REFERENCES

GRID CONNECTION

Connected wind power plant, as all of devices connected to the grid, has larger or lesser affect on power quality. Moreover the wind farms are located in well wind condition territory, where grid is weak develop. Nevertheless wind farms are required to connect in one of a few ways, such as e.g.: [5], [7]

• Single wind turbine connected to the low voltage (LV) line (transmittable power – up to 300kW). This method is for small consumers like household.[5], [6], [7]
• Wind farm connected to the exist medium voltage line (MV) which feeds surrounding demands (transmittable power – from 2 to 5 MW). In this method distance between farm and connection point is short (not longer than 20km). This method is relatively inexpensive.[5], [6], [7]
• If MV line is too weak for wind farm, it could be connected to the MV busbar in the nearest HV/MV substation by own line (transmittable power – from 10 to 40 MW). This method is more expansive than the first one but farm has lesser influence on local power quality. Distance also should be not longer than 20km. [5], [6], [7]
• Wind farm connected to the HV busbar in the nearest HV/MV substation by own line with own HV/MV transformer (transmittable power – up to 100 MW). This method is required for large wind farms (power higher than a few MW). It is the most expansive solution. [5], [6], [7]
• Wind farm connected with grid by the DC cable line (submarine cable in off shore wind farms case) with DC/AC converter (transmittable power – more than 0,5 GW). This method already is common for large off shore wind farms and less for on shore (in this case only for the largest farms). This technology allows for long distance transmission to 50km or even more. Wind turbines produce AC MV voltage, which is transform on HV (or extra high voltage - EHV) in own MV/HV transformer (EHV transformer) or in common transformer with the nearest wind farms. After then the AC voltage is converted on DC voltage in rectifier substation (own one for one farm or common for a few nearest). The DC line transmits current to the nearest HV substation (EHV substation) with power inverter. Investment cost is high but allow constructing large power farms in long distance from coast.[5], [6], [7]

Regardless of a connection method wind farm puts into the grid more or less power variations. Unfortunately the most common solution poses MV connection, which spawns the most of interferences. The most dangerous and undesirable are: voltage amplitude fluctuation, voltage deeps, frequency variations, flicker, voltage and current harmonics, increased short-circuit currents, local and global system destabilization, increased (or decreased, dependent on a grid configuration) active power wastages. Main reason of these problems is irregular wind speed but also winds farm construction and installed devices like rectifiers and power inverters. Active power on the generators taps is in cubic relation with wind speed thus provide to frequency variations even from 1 to 10Hz (also more), voltage amplitude fluctuation in 10% of nominal value( in blast case to 20%). The rest of interferences are provide from construction reasons such as e.g.: shadow effect (time while the blade comes through the tower), turbulence in blade swept area, tower oscillation, switching operations and soft starting. Nevertheless wind farms have some advantages related with active and reactive power regulation during normal system operation and in case of failure. Usefulness depends from type of installed generators. An asynchronous generator does not allow to considerable regulation of reactive power (by voltage regulation) in contradistinction to double-fed generator and synchronous generator. Regulation does not as easy as in case of conventional power plant generator and depends from wind condition in that moment however wind farm can temporary regulate high amount value of voltage. An active power regulation does in similar situation. [1], [3], [5], [6], [7], [11]

• RELATIONS
• Grid connection - solar power
• Grid connection - wave & tidal power
• Grid connection - hydro power
• Grid connection - bio power

Description of technology| Economic aspects| Environment and public awareness| Legislation| Final comparison| References