Abstract
A special three-phase stator winding consisting of a parallel combination of delta and star is proposed for wind-driven, self–excited induction generators (SEIGs), increasingly used for supplying isolated loads. This winding configuration enables the SEIG to be operated over a wide range of wind speeds, in three stages. The winding is set at parallel delta-star connection at higher wind speeds and then changed to conventional series delta and series star connections at medium and low wind speeds, respectively. An equivalent circuit has been developed for SEIG with this unconventional winding, and the expressions for the evaluation of its performance characteristics have been derived. A method of determining a suitable value of excitation capacitor bank has also been formulated using genetic algorithm. Taking an example of a 2.2 kW, three-phase SEIG, its predetermined characteristics and the corresponding experimental results have been presented. Taking the wind data from an actual wind farm, the annual energy output obtainable from this generator is also estimated. The proposed switching scheme is thus shown to be optimum for covering a wide range of wind speeds. A cluster of several such generators can lead to the establishment of battery charging stations and formation of micro-grids.
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Abbreviations
- \(a\) :
-
Per unit (p.u) frequency
- \(b\) :
-
P.u speed
- C :
-
Excitation capacitance per phase, µF
- \(E_{{\text{d}}}, E_{{\text{s}}}\) :
-
Transformer emf in the delta and star components, respectively, V
- \(E_{{\text{ds}}} , E_{{\text{sd}}}\) :
-
Speed emf in the delta and star components, respectively, V
- \(I_{2}\) :
-
Rotor phase current, A
- \(I_{{\text{d}}} ,{\text{I}}_{{\text{s}}}\) :
-
Stator phase current of delta and star components, respectively, A
- \(I_{{\text{CL}}}\) :
-
Capacitor bank line current, A
- \(I_{{\text{CP}}}\) :
-
Capacitor bank phase current, A
- \(I_{{\text{LL}}}\) :
-
Load line current, A
- \(I_{{\text{LP}}}\) :
-
Load phase current, A
- \(I_{{\text{GL}}}\) :
-
Generator line current, A
- \(I_{{\text{GP}}}\) :
-
Generator phase current in the combined equivalent circuit of the delta and star components of the generator, A
- \(P_{{\text{o}}}\) :
-
Output power of the generator, W
- \(P_{{\text{m}}}\) :
-
Mechanical input power to the generator, W
- \(R_{1} ,R_{2}\) :
-
Per phase stator and rotor (referred to stator) resistance, respectively, Ω
- \(R,X\) :
-
Per phase load resistance and reactance, respectively, Ω
- \(T_{{\text{ph}}}\) :
-
Effective turns in series per phase in the winding, between phase terminal and neutral (or equivalent neutral in Δ)
- V GL :
-
Generator line voltage, V
- \(X_{1} ,X_{2}\) :
-
Per phase stator and rotor (referred to stator) reactance, respectively, Ω
- \(X_{{\text{m}}}\) :
-
Magnetising reactance per phase, Ω
- \(X_{{\text{c}}}\) :
-
Capacitive reactance per phase of the excitation capacitance, Ω
- \(Z_{{\text{loop}}}\) :
-
Loop impedance of the equivalent circuit per phase, Ω
- \(Z_{{\text{L}}}\) :
-
Load impedance per phase, Ω
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Acknowledgement
The authors wish to thank Dr. M. Subbiah, Emeritus Professor, Department of Electrical and Electronics Engineering, Rajalakshmi Engineering College, Chennai, for his valuable suggestions in the preparation of this paper.
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Appendix
Appendix
1.1 Magnetisation characteristics of series delta, series star and parallel star connections
For series delta connection
For series star connection
For parallel star connection
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Essaki Raj, R., Kamalakannan, C. & Karthigaivel, R. An optimum three-stage stator winding connections for wind-driven stand-alone self-excited induction generators for enhanced annual energy output. Electr Eng 103, 865–880 (2021). https://doi.org/10.1007/s00202-020-01125-0
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DOI: https://doi.org/10.1007/s00202-020-01125-0