Voltage provided by Wind turbines must comply some requirements specified in the IEC 61400-21 standard. Here we are some power quality parameters that power energy from wind turbines must be under control:

**Rated Data**

- Rated Power (P
_{n}) (or Active Power): Maximum continuous electric output power for a wind turbine under operating conditions. - Rated Reactive Power (Q
_{n}): Reactive power under rated power, nominal voltage and frequency. - Rate Apparent Power (S
_{n}): Apparent power from the wind turbine while operating at rated power and nominal voltage and frequency. - Rated Current (I
_{n}): Current from the wind turbine while operating at rated power and nominal voltage a frequency.

**Maximum Permitted Power (P _{mc})**

It is the 10-minute average power from a wind turbine. Wind turbines with active control of output power (blade pitching and/or speed control) typically provide P_{mc} = P_{n}. Wind turbines with passive control of output power (fixed-speed or stall-controlled wind turbines) are fixed with P_{mc} some 20% higher than P_{n}.

**Maximum Measured Power (P _{60} and P_{0.2})**

Maximum measured power as a 60 and 0,2 seconds average value. They can be used as protection settings. For variable-speed wind turbines P_{0,2}=P_{60}=P_{n}. For fixed-speed wind turbines, stall or pitch controlled P_{0,2 }> P_{n}.

**Reactive Power (Q)**

It must be specified as a 10-minute average value as a function of 10%,…, 90%, 100% of P_{n}, P_{mc}, P_{60} and P_{0,2}. Wind turbines employing modern frequency converters can control the Reactive Power (Q) to zero (depending by the size of the converter.)

**Flicker Coefficient c(Ψ _{k}, ν_{a})**

Power fluctuations in wind turbines can have several consequences in the grid. Therefore, it is important to measure these fluctuations, “flickers”, with a flickermeter and to fulfill the IEC 61000-4-15 standard. Variable-speed wind turbines have usually low flicker coefficients, whereas fixed-speed wind turbines swing from average (stall-controlled) to high coefficients (pitch-controlled). The formula is;

Where;

- Ψk: Network impedance phase angle.
- νa: Annual average wind speed.
- Pst : Flicker emission from the wind turbine.
- Sn: Rated apparent power of the wind turbine.
- Sk: Short-circuit apparent power of the grid.

**Maximum Number of Wind Turbine Switching Operations (N _{10} and N_{120}).**

The following switch operations may cause voltage variations:

- Start-up at cut-in wind speed.
- Start-up at rated wind speed.
- Switching between generators (measurement of the worst case) in the case the wind turbine has more than one generator. So, N
_{10}is the maximum number of the switching operation within 10-minutes period and N_{120}within 2-hour period.

**Flicker Step Factor Kf(Ψk)**

It is the flicker emission due to a single switching operation of a wind turbine.

** **

- T
_{p}Duration of the voltage variation due to the switching operation.

Similar to the flicker coefficient, variable-speed wind turbines have low Flicker Step Factors, whereas values for fixed-speed wind turbines swing from average (pitch-controlled) to high (stall-controlled).

**Voltage Change Factor K _{u}(Ψk)**

It is the voltage change caused by a single switching operation of a wind turbine.

- U
_{max }and U_{min}: Maximum and minimum voltage (**Root Mena Square (RMS)**phase-to-neutral) due to the switching. - U
_{n}: Nominal phase-to-phase voltage.

Therefore, variable-speed wind turbines have low Voltage Change Factors, whereas values for fixed-speed wind turbines swing from average (pitch-controlled) to high (stall-controlled).** **

**Maximum Harmonic Currents (I _{h})**

It is the emission of harmonic currents of a wind turbine with an electronic converter. However, IEC 61400-21 does not require measurement of harmonic emissions from induction machines#mce_temp_url# with power electronic converters (Type A and B).

Tags: Asynchronous (Induction), Frequency Converter, Generators, Power, Requirements, Synchronous, Theory, Wind Turbines

## Leave a Reply