The existence of high order harmonic, not only make the induction electric potential waveform becomes bad, and the harmonic voltage will cause additional loss of the generator
, the generator efficiency, higher temperature rise, while the higher harmonic of power lines, produced by the electromagnetic field on the nearby communications will also produces harmful interference.
Therefore, we should try to take some measures to eliminate the influence of high harmonics.
Improve generator voltage waveform of the method is: (
A short coil points in front of the known, trapezoidal wave can be decomposed into fundamental wave and higher harmonic.
In synchronous generator stator winding, the fundamental wave generated by the fundamental wave magnetic potential and harmonic magnetic field to produce three times three harmonic voltage, harmonic magnetic field to produce five times five times harmonic potential fundamental harmonic magnetic field, magnetic field and five diagram shows that if the polar moment of fundamental wave magnetic field for t, so, five harmonic magnetic moment t t = 1/5.
If a t y = 4/5 short coil on the fifth harmonic magnetic field, the short side of coil two effective exactly in the same polarity, in the short coil each edge effectively, the fifth harmonic potential are equal in size, but in the opposite direction, for the whole coil, both series offset each other, so the coil wire end five times between harmonic induced potential is zero.
Similarly, t y = 6/7, seven times can eliminate harmonic potential, therefore, choose the appropriate coil pitch, can eliminate or weaken the induced potential of higher harmonic.
Adopting distributed winding adopts the distributed winding, not only make full use of the circumference of the stator core, but also can improve the voltage waveform.
For distributed winding, in every moment of each coil induction electric potential is approximate trapezoidal wave, but each phase group after several winding components series, superposition after general induction voltage waveform is similar to sine wave.
Three harmonic elimination in synchronous generator stator winding induction potential of higher harmonic, harmonic potential numerical biggest three times.
But as a result of three harmonic voltage frequency is three times the base frequency of wave potential, therefore, three-phase winding each other three times in the harmonic voltage of phase 3 & times;
, that is, the same phase.
If the windings into a star, in the line voltage harmonic UAB3 = UA3 - three times
UB3 = 0 ubc3 = UB3 -
UA3 = 0 visible three-phase windings into star when they are in the line voltage is not three harmonic.
If the three-phase windings into triangle, triangle group close loop, the sum of total potential of three-phase electric potential.
For fundamental wave, due to the phase differences & 120 deg;
, so the EA1 + EB1 + EC1 = 0, won't produce fundamental wave in the triangle loop current.
But three harmonics in three phase winding, because the same phase, so the total potential as a phase three times that of the electric potential, this big three times harmonic potential, will produce very big three times in the triangle loop harmonic current and causes additional loss, so synchronous generator stator winding is generally used y connection.
In analysis shows that the three-phase stator windings into star, can eliminate the output voltage of three times and its multiples of every harmonic component and select appropriate winding pitch, can reduce or eliminate five times and seven times harmonic.
This makes potential waveform is similar to sine wave.
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