Harmonic Injection Research Paper

Harmonic Injection
Authors – Nanda kishor Panda, H.Bharadwaj
Registration numbers – 15BEE0117,15BEE0170 Abstract –The paper basically deals with harmonic injection. The paper concentrates on understanding what harmonics are in general and in electric circuits particularly. The paper gives a detailed overview about the main sources of harmonics, their disadvantages and the steps to curb it specifically in the electric circuits.
I. INTRODUCTION - Harmonics
A harmonic refers to a sine wave which has a frequency as a whole number multiple of a wave/signal’s fundamental frequency. A series of all harmonics of a particular frequency is called it’s harmonic series. Harmonics are seen in musical instruments, in electric circuits and signal processing,

Harmonics in electrical circuits
Electrical AC power generation only produces voltage waveform of a single frequency which is the wave’s fundamental frequency. Linear loads like purely resistive loads which obey ohm’s law do not induce harmonics into a system. But non-linear loads draw currents which are not sinusoidal in nature thus injecting odd-harmonics in the wave (current/voltage). The main sources of harmonic current are rectifiers, inverters, ballasts in fluorescent lights and transformers. This results in an “impure” waveform instead of the “pure” sinusoidal input given to these equipments.
IV. Disadvantages of harmonic injection
Presence of harmonics in a network lowers the quality of power due to the following factors
• Excessive neutral current – 3 phase connections use the fact that addition of the 3 phases produces a neutral to decrease the wiring. But the presence of the 3rd harmonic in the wave causes a net neutral current (as the 3rd harmonic adds up in phase) which causes the neutral wire to be overheated. Fig. 2. 3rd harmonic in 3 phase circuits
• Incorrect readings- Harmonics are a cause of incorrect readings in induction watt meters and averaging type current

The net effect of these 2 factor show the loss in power due to the presence of harmonics.
A vital factor which helps in quantifying harmonic injection is Total Harmonic Distortion (THD). It is a measure of the harmonic distortion and is found by normalizing the currents or voltages at all frequencies. Fig. 4. Total Harmonic Distortion Fig. 5. Individual harmonics in a signal
VI. Circuit simulation
In this paper we are simulating a Bridge type full wave rectifier.. We have used Simulink and done Fast-Fourier Transform (FFT) of the output waveforms. We have measured the input and output voltages and currents and shown the analysis as follows.

Fig..6. Simulink circuit of a bridge rectifier with a filter

Fig 6 is the circuit of the bridge rectifier used for analysis. The load is connected in parallel with a capacitor whose value is initially set to 0 (i.e. analysing the circuit without a filter), produces the following output voltage and current