ELECTRICAL FUNDAMENTALS A Presentation on “ ELECTRICAL FUNDAMENTAL” By RAJNEESH

BUDANIA (B.Tech Electrical

Engineering, a 3rd year student in jaipur national university,india)

RIPPLE FUNDAMENTALS

The most common meaning of ripple in electrical science is the small unwanted residual periodic variation of the direct current (dc) output of a power supply which has been derived from an alternating current (ac) source. This ripple is due to incomplete suppression of the alternating waveform within the power supply.

As well as this time-varying phenomenon, there is a frequency domain ripple that arises in some classes of filter and other signal processing networks. In this case the periodic variation is a variation in the insertion loss of the network against increasing frequency. The variation may not be strictly linearly periodic.

In this meaning also, ripple is usually to be considered an unwanted effect, its existence being a compromise between the amount of ripple and other design parameters.

TIME DOMAIN RIPPLE

Ripple factor (γ) may be defined as the ratio of the root mean square (rms) value of the ripple voltage to the absolute value of the dc component of the output voltage, usually expressed as a percentage. However, ripple voltage is also commonly expressed as the peak-to-peak value. This is largely because peak-to-peak is both easier to measure on an oscilloscope and is simpler to calculate theoretically.

Filter circuits intended for the reduction of ripple are usually called smoothing circuits.

Full-wave rectifier circuit with a reservoir capacitor on the output for the purpose of smoothing ripple is shown above.

The simplest scenario in ac to dc conversion is a rectifier without any smoothing circuitry at all. The ripple voltage is very large in this situation; the peak-to-peak ripple voltage is equal to the peak ac voltage. A more common arrangement is to allow the rectifier to work into a large smoothing capacitor which acts as a reservoir.

After a peak in output voltage the capacitor (C) supplies the current to the load (R) and continues to do so until the capacitor voltage has fallen to the value of the now rising next half-cycle of rectified voltage. At that point the rectifiers turn on again and deliver current to the reservoir until peak voltage is again reached.

If the time constant, CR, is large in comparison to the period of the ac waveform, then a reasonably accurate approximation can be made by assuming that the capacitor voltage falls linearly. A further useful assumption can be made if the ripple is small compared to the dc voltage. In this case the phase angle through which the rectifiers conduct will be small and it can be assumed that the capacitor is discharging all the way from one peak to the next with little loss of accuracy.

Ripple voltage from a full-wave rectifier, before and after the application of a smoothing capacitor is shown below

For a full-wave rectifier:

For a half-wave rectification:

Where, Vpp is the peak-to-peak ripple voltage I is the current in the circuit f is the frequency of the ac power C is the capacitance

For the rms value of the ripple voltage, the calculation is more involved as the shape of the ripple waveform has a bearing on the result. Assuming a sawtooth waveform is a similar assumption to the ones above and yields the result:

Where, γ is the ripple factor R is the resistance of the load

EFFECTS OF RIPPLE

Ripple is undesirable in many electronic applications for a variety of reasons:

(1)The ripple frequency and its harmonics are within the audio band and will therefore be audible on equipment such as radio receivers, equipment for playing recordings and professional studio equipment.

(2)The ripple frequency is within television video bandwidth. Analogue TV receivers will exhibit a pattern of moving wavy lines if too much ripple is present.

(3) The presence of ripple can reduce the resolution of electronic test and measurement instruments. On an oscilloscope it will manifest itself as a visible pattern on screen.

(4) Within digital circuits, it reduces the threshold, as does any form of supply rail noise, at which logic circuits give incorrect outputs and data is corrupted.

(5) High-amplitude ripple currents shorten the life of electrolytic capacitors.

HARMONIC FUNDAMENTALS

A distortion is the alteration of the original shape (or other characteristic) of an object, image, sound, waveform or other form of information or representation. Distortion is usually unwanted, and often many methods are employed to minimize it in practice. In some fields, however, distortion may be desirable; such is the case with electric guitar distortion.

The transfer function of an ideal amplifier, with perfect gain and delay, is only an approximation. The true behavior of the system is usually different. Nonlinearities in the transfer function of an active device (such as vacuum tubes, transistor, and op-amp) are a common source of non-linear distortion; in passive components (such as a coaxial cable or optical fiber), linear distortion can be caused by inhomogeneities, reflections, and so on in the propagation path.

Amplitude Distortion Harmonic Distortion Frequecy response Distortion Phase Distortion Group delay Distortion Audio Distortion

Amplitude Distortion

Amplitude distortion is distortion occurring in a system, subsystem, or device when the output amplitude is not a linear function of the input amplitude under specified conditions.

Harmonic Distortion

Harmonic distortion adds overtones that are whole number multiples of a sound wave's frequencies.Nonlinearities that give rise to amplitude distortion in audio systems are most often measured in terms of the harmonics (overtones) added to a pure sinewave fed to the system. Harmonic distortion may be expressed in terms of the relative strength of individual components, in decibels, or the Root Mean Square of all harmonic components: Total harmonic distortion (THD), as a percentage.

Frequecy response Distortion Non-flat frequency response is a form

of distortion that occurs when different frequencies are amplified by different amounts, caused by filters. For example, the non-uniform frequency response curve of AC-coupled cascade amplifier is an example of frequency distortion. In the audio case, this is mainly caused by room acoustics, poor loudspeakers and microphones, long loudspeaker cables in combination with frequency dependent loudspeaker impedance, etc.

Phase Distortion

This form of distortion mostly occurs due to the reactive component, such as capacitive reactance or inductive reactance. Here, all the components of the input signal are not amplified with the same phase shift, hence causing some parts of the output signal to be out of phase with the rest of the output.

Group delay Distortion

It can be found only in dispersive media. In a waveguide, propagation velocity varies with frequency. In a filter, group delay tends to peak near the cut-off frequency, resulting in pulse distortion. When analog long distance trunks were commonplace, for example in 12 channel carrier, group delay distortion had to be corrected in repeaters.

Audio Distortion

In this context, distortion refers to any kind of deformation of a waveform, compared to an input, usually Clipping, harmonic distortion and intermodulation distortion (mixing phenomena) caused by non-linear behavior of electronic components and power supply limitations. Terms for specific types of nonlinear audio distortion include: crossover distortion, slew-Induced Distortion (SID) and transient intermodulation (TIM).

HARMONIC FUNDAMENTALS

Harmonics are electric voltages and currents that appear on the electric power system as a result of certain kinds of electric loads. Harmonic frequencies in the power grid are a frequent cause of power quality problems.

Causes of Harmonics

When a non-linear load, such as a rectifier, is connected to the system, it draws a current that is not necessarily sinusoidal. The current waveform can become quite complex, depending on the type of load and its interaction with other components of the system. Regardless of how complex the current waveform becomes, as described through Fourier series analysis, it is possible to decompose it into a series of simple sinusoids, which start at the power system fundamental frequency and occur at integer multiples of the fundamental frequency.

Effects of Harmonics

One of the major effects of power system harmonics is to increase the current in the system. This is particularly the case for the third harmonic, which causes a sharp increase in the zero sequence current, and therefore increases the current in the neutral conductor. This effect can require special consideration in the design of an electric system to serve non-linear loads.

Effects of Harmonics on electric motor

Electric motors experience hysteresis loss caused by eddy currents set up in the iron core of the motor. These are proportional to the frequency of the current. Since the harmonics are at higher frequencies, they produce more core loss in a motor than the power frequency would. This results in increased heating of the motor core, which (if excessive) can shorten the life of the motor. The 5th harmonic causes a CEMF (counter electromotive force) in large motors which acts in the opposite direction of rotation. The CEMF is not large enough to counteract the rotation, however it does play a small role in the resulting rotating speed of the motor.

Effects of Harmonics on Telephone lines

In the U.S., common telephone lines are designed to transmit frequencies between 180 and 3200 Hz. Since electric power in U.S. is distributed at 60 Hz, it normally does not interfere with telephone communications because its frequency is too low. However, since the third harmonic of the power has a frequency of 180 Hz, its higher-order harmonics are high enough to interfere with telephone service if they became induced in the line.