Important Topic of Physcis: Harmonics

Important Topic of Physcis: Harmonics

A harmonic is defined as any member of the harmonic series. The term is used in a variety of fields, including music, physics, acoustics, electronic power transmission, radio technology, and others. It is typically applied to signals that repeat, such as sinusoidal waves. A harmonic is a wave with a frequency that is a positive integer multiple of the fundamental frequency of the original wave. The original wave is also known as the first harmonic, and the subsequent harmonics are known as higher harmonics. Because all harmonics are periodic at the fundamental frequency, the sum of harmonics is periodic as well.

Most acoustic instruments produce complicated tones with numerous individual partials (component simple tones or sinusoidal waves), but the untrained human ear does not recognize those partials as distinct events. Many acoustic oscillators, such as the human voice or a bowed violin string, produce complex tones that are more or less periodic and are thus composed of partials that are close matches to integer multiples of the fundamental frequency and thus resemble the ideal harmonics, and are thus referred to as “harmonic partials” or simply “harmonics” for convenience (although it is not strictly accurate to call a partial a harmonic, the first is the most accurate).

Non-linear loads that are highly inductive in nature, such as an iron-cored inductor, rectifiers, electronic ballasts in fluorescent lights, switching transformers, discharge lighting, saturated magnetic devices, and other such loads, produce harmonics. Harmonics can also be caused by the most powerful electronic switching circuits, such as a silicon-controlled rectifier (SCR), power transistors, power converters, and an electronics drive, such as a variable frequency drive (VFD) or variable voltage variable frequency drive (VFD). These switching circuits draw current only at the peak values of the alternating current supply, and because the switching current is non-linear, the load current is non-sinusoidal in nature and contains harmonics.

Harmonics are higher frequency waveforms that are superimposed on the fundamental frequency or frequency of the circuit and are enough to distort its wave shape. The amount of distortion applied to the fundamental wave is entirely determined by the type, quantity, and shape of the harmonics present.

Overview

Any member of the harmonic series, which is a divergent infinite series, is referred to as a harmonic. Its name is derived from the concept of overtones, or harmonics, in musical instruments: the wavelengths of the overtones of a vibrating string or a column of air (as with a tuba) are derived from the fundamental wavelength of the string (or air column). Every subsequent term in the series (i.e., the higher harmonics) is the “harmonic mean” of the neighbouring terms. Music is also responsible for the term “harmonic mean.”. Music, physics, acoustics, electronic power transmission, radio technology, and other fields all use the term. It is typically applied to signals that repeat, such as sinusoidal waves. A harmonic of such a wave has a frequency that is a positive integer multiple of the original wave’s frequency, known as the fundamental frequency. The original wave is also known as the first harmonic, and the subsequent harmonics are known as higher harmonics. Because all harmonics are periodic at the fundamental frequency, the sum of harmonics is periodic as well.

A harmonic is a signal or wave whose frequency is an integral (whole number) multiple of the reference signal or wave’s frequency. The term can also refer to the ratio of the frequency of such a signal or wave to the frequency of the reference signal or wave as part of the harmonic series. The first, or 1st, harmonic is the fundamental frequency or original wave. Higher harmonics are the following harmonics. The fundamental frequency of all harmonics is periodic, as is the total number of harmonics at that frequency.

Power quality issues are caused by harmonic frequencies in the power grid. Harmonics in power systems cause increased heating in equipment and conductors, as well as pulsing torque in motors. Because hysteresis loss is proportional to frequency and eddy current loss is proportional to the square of the frequency, harmonics cause increased operating temperature and iron losses (Hysteresis and Eddy current losses) in AC motors and transformers.

Active harmonic filter

Harmonics are caused by a non-linear load. Harmonic correction units, or active harmonic filters, are parallel devices that work as a noise cancellation system by injecting equal and opposite frequencies to eliminate harmonics. Additionally, the filters can provide additional current to correct the power factor. So all that’s left coming from the source and flowing back to the utility is a nice, clean, in-phase current. For example, if we run four 6-pulse variable frequency drives simultaneously, we get a harmonic spectrum with 5th, 7th, 11th, and 13th harmonics. In the total harmonic distortion, the waveform will show a significant amount of harmonic current. When the active harmonic filter is activated, it will inject equal and opposite harmonics to cancel out what is already present. The waveform is now clean and in phase. When we look at the harmonic spectrum, we can see that the current distortion is very low.

Adding active harmonic filters to power systems can be a suitable harmonic solution. Harmonic filters, albeit more expensive than other solutions, would be a dependable technique to collect any and all harmonics originating from the loads if you have several drives running all the time and numerous drives as backup. However, one key thing to remember from a system design aspect is that your drive should have either a DC choke or an AC line reactor to reduce harmonics. Active harmonic filters are typically available in 50, 60, 100, 200, and 300-ampere models that can be paralleled. Another advantage of using active harmonic filters is that they cannot be overloaded because once they have produced the maximum harmonic current and power factor correction that they are capable of producing, they stop producing at that level—whether it is 100 or 120 amperes, as the case may be. Active harmonic filters provide a system-level solution for internal and external harmonic protection on your power system.

Harmonic wave

A harmonic wave is a simple and useful example of a periodic wave. The physical separation between successive crests of a wave is defined as its wavelength. “A” denotes the maximum displacement of the wave, or its amplitude. The time between successive oscillations is referred to as the wave’s period. The wave frequency f, which is the reciprocal of the period, 1 is the number of oscillations per second.

Harmonic waves have well-defined velocities that are proportional to their frequency and wavelength. The wave frequency f is determined by focusing attention on a single point in space and counting the number of wave crests that pass that point per second. The distance traveled by anyone crest in one second past that point—the wave velocity v—is equal to the distance between crests multiplied by the frequency: v =λf.

The mathematical expression for displacement in both space and time illustrates the properties of harmonic waves. The spatial and time dependence of displacement for a harmonic wave traveling in the x-direction is (x,t)=Acos2x-2ft.

Harmonics in power system

A harmonic in an electric power system is a voltage or current that is a multiple of the system’s fundamental frequency. The shape or properties of a voltage or current waveform in relation to its fundamental frequency are known as harmonics. Harmonics are seen in waveforms that depart from a sinewave shape.

Harmonic frequencies in the power grid are a common source of power quality issues, causing increased heating in equipment and conductors, misfiring in variable speed drives, and torque pulsations in motors.

AC electrical loads are classified as linear or non-linear based on how they draw current from the power supply waveform. The relationship between the voltage and current waveforms is sinusoidal with a linear load, and the current at any time is proportional to the voltage; this is known as Ohm’s law.

The current drawn by a non-linear load is not proportional to the voltage and fluctuates based on alternating load impedance, implying that the current it draws does not have the same waveform as the supply voltage. Non-linear loads draw current in short bursts. These pulses distort current waveforms, resulting in harmonics that can cause power problems for both distribution system equipment and loads connected to it.

When harmonic distortion enters a power system, its ability to perform at peak levels is jeopardized. Because of the increased demand for power, harmonics cause inefficiencies in equipment operation. Increased overall current necessitates higher installation and utility costs, as well as overheating and decreased profitability.

Also read: Free, Forced and Damped Oscillations

Frequently Asked Questions

What is a harmonic series?

In music, a harmonic series is a diverging infinite sequence of overtones or harmonics. The overtone wavelengths of the vibrating string in this scenario are 12, 13, 14, etc., of the string's fundamental wavelength.

In an electrical context, what is harmonic?

The distortion of regular electrical current waveforms is referred to as harmonics. Non-linear loads are commonly used to transfer them.