Wind Distortions Essay

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Harmonics:
Harmonic distortions are injected at the generation as well as the consumer end. At the consumer end, harmonics are caused by nonlinear loads such as PCs, CFLs, electronic devices, etc. The harmonics distortion caused by non-linear load such as electric arc furnaces, large concentrations of arc discharge lamps, variable speed motors, saturation of magnetization of transformer and a distorted line current. The current generated by such loads will interact with power system impedance and increases harmonics. Harmonics can lead to degradation of power quality at the consumer’s end, increase of power losses, and malfunction in communication system. The harmonics voltage and current should be limited to acceptable level at the point
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Also, with fluctuation of active and reactive power of turbine (yaw error), wind turbulence, switching operations, flicker is caused. Flicker is an important PQ aspect in wind turbine generating system. It is defined as fluctuation of voltage in a frequency 10-35 Hz. Flicker is considered as a serious drawback and limits the maximum amount of wind power generation that can be connected to the power grid. Many factors affect flicker emission of grid connected wind turbines during continuous operation. Variable-speed wind turbines show better performance related to flicker emission in compared to fixed-speed wind turbines. The flicker study is necessary and important as the wind power penetration level is increasing quickly. Due to the smoothing effect, large wind turbine produce lower flicker than small wind turbines.
The flicker level depends on the shape, amplitude & repetition frequency of the fluctuated voltage waveform. IEC 61400-4-15 specifies flicker meter which can be used to measure flicker directly. Flicker coefficient gives dimensionless, normalized measure of flicker which doesn’t depend on short circuit apparent power of grid and situation of network. It gives a ratio of short circuit power and generated rated apparent power necessary to achieve long term flicker lever
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Mechanically switched fixed shunt capacitors enhance the voltage stability limit of system, but are rather insensitive to sudden voltage changes. Also, voltage regulated by the wind generators equipped with only fixed capacitors can become higher than the voltage limit of 1.05 pu. Hence, a fixed capacitor cannot serve as the only source of reactive power compensation.
In a STATCOM, the maximum compensating current is independent of system voltage, so it operates at full capacity even at low voltages. A STATCOM’s advantages include flexible voltage control for power quality improvement, fast response, and applicability for use with high fluctuating loads.
One of the most important advantages of using STATCOM over a thyristor based SVC is that it’s compensating current is not dependent on the voltage level at the connection point which means that the compensating current is not lowered as the voltage drops. The output of the wind power plants and the total load varies throughout the day. Also, reactive power imbalances, which can seriously affect the power system, can be minimized by reactive power compensation devices such as the STATCOM. It can contribute to the low voltage ride through requirement since it can operate at full capacity even at lower voltages. Fig. 4 shows installations of STATCOM by various utilities with their voltage lever across

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