What Are ? Harmonics In Synchronous Machines
Harmonics: When the uniformly sinusoidally distributed air gap flux is cut by either the stationary or rotating armature sinusoidal emf is induced in the alternator. Hence the nature of the waveform of induced emf and current is sinusoidal. But when the alternator is loaded waveform will not continue to be sinusoidal or becomes non-sinusoidal. Such non-sinusoidal wave form is called complex wave form.
1. Distribution of stator winding.
2. Short Chording
3. Fractional slot winding
5. Larger air gap length.
Effect of Harmonics on induced emf:The harmonics will affect both pitch factor and distribution factor and hence the induced emf. In a well designed alternator the air gap flux density distribution will be symmetrical and hence can be represented in Fourier series as follows.
The RMS value of the resultant voltage induced can be given as
Eph2 = [(E1)2+ ....+ …………… (En)2]
**(A)2 Means A Square
Effect of Harmonics of pitch and distribution Factor:The pitch factor is given by Kp = cos /2, where is the chording angle.
For any harmonic say nth harmonic the pitch factor is given by Kpn = cos n α/2
The distribution factor is given by Kd = (sin mβ /2) / (m sin β/2)
For any harmonic say nth harmonic the distribution factor is given by
Kdn = (sin mn β/2)/(m sin nβ/2)
This is the detailed info about Harmonics In Synchronous Machines,Minimization Methods of Harmonics.Effect of Harmonics on induced emf.