Total harmonic distortion

Table 23.2 Premissible individual and total harmonic voltage distortions - as in G5/3, UK engineering recommendations...

A term used in PFC is total harmonic distortion. This is defined as... 

The results of the Fourier analysis show that the magnitude of the sine wave at 1 kHz is 7.463 V, and the magnitude of the sine wave at 2 kHz is 1.393. These results are similar to the results obtained using Probe. This method also gives us the magnitude of the frequency components too small to see on the Probe graph, the phase of each frequency component, and the total harmonic distortion. From the data above, an equation for the output voltage is ... 

Total harmonic distortion is approximately 0.0001 %. Compare this distortion to the distortion of the push-pull amplifiers on page 369. 

Distortion factor — Ratio of the RMS of the harmonic content of a periodic wave to the RMS of the fundamental content of the wave, expressed as a percent. This is also known as the total harmonic distortion (THD) further explanation can be found in Chapter 4. 

Total harmonic distortion (THD) is a term used to describe the net deviation of a nonlinear waveform from ideal sine waveform characteristics. Total harmonic distortion is the ratio between the RMS value of the harmonics and the RMS value of the fundamental. For example, if a nonlinear current has a fundamental component of /, and harmonic components of /2, /3, /4, /5, /6, /7,. .., then the RMS value of the harmonics is ... 

Example Find the total harmonic distortion of a voltage waveform with the following harmonic frequency make up ... 

The individual harmonic distortion indicates the contribution of each harmonic frequency to the distorted waveform, and the total harmonic distortion describes the net deviation due to all the harmonics. These are both important parameters. In order to solve harmonic problems, we require information on the composition of the individual distortions so that any treatment may be tailored to suit the problem. The total harmonic distortion, while conveying no information on the harmonic makeup, is used to describe the degree of pollution of the power system as far as harmonics are concerned. Defining the individual and total harmonic distortions will be helpful as we look at some typical nonlinear waveforms and their harmonic frequency characteristics. 

Note Isc = maximum short-circuit current at PCC IL = maximum fundamental frequency demand load current at PCC (average current of the maximum demand for the preceding 12 months) h = individual harmonic order THD = total harmonic distortion, based on the maximum demand load current. The table applies to odd harmonics even harmonics are limited to 25% of the odd harmonic limits shown above. 

Note PCC = point of common coupling THD = total harmonic distortion. 

We can deduce that, when using 12-pulse-power conversion equipment, harmonics below the 11th harmonic can be made insignificant. The total harmonic distortion is also considerably reduced. Twelve-pulse-power conversion equipment costs more than six-pulse-power equipment. Where harmonic currents are the primary concern, 24-pulse-power conversion equipment may be considered. 

A second IEEE report, which does explain its mnemonics, and which competes for mention here, is by Tolbert etal. (2002), which predicts the arrangement of the electrical equipment for heavy hybrid electric vehicles capable of operating in fuel-cell-only mode, engine-only mode and with both power sources. To achieve minimum THD (Total Harmonic Distortion) use is made of cascade multilevel voltage inverters allied to batteries... 

Switchgear rated voltage (volts) Total harmonic voltage distortion (%) Individual harmonic voltage distortion (%) ... 

All but the smaller ratings of inverters used in the oil industry require a sinusoidal ouqtut waveform. The quality of the waveform is typically defiued as, being that no greater than 5% total harmonic distortion should be present. In order to achieve a sinusoidal output it is uecessary to include a filter iu the output circuit. The output of the inverter usually has a double wouud transformer so that the required line voltage is obtained. The filter is placed on the load side of the transformer, its leakage reactance of the transformer contributes to the filteriug process. 

Total Harmonic Distortion - The measure of closeness in shape between a waveform and it s fundamental component. 

Figure 1 shows the Xbar-S control chart for the Total Harmonic Distortion of Voltage (THDV) of the LI phase of Sample B, with rational subgroups grouped together by days and by weeks. In the figure it can be seen that in both cases the process is stable and is under statistical control, since there are no outliers, or any violations of additional rules for the detection of small standard shift variations, or unusual patterns (in the weekly control chart the control limits are variables because the sizes of the sample are different). In this situation, it can be concluded that the analyzed process is solely subject to natural variability and is therefore under statistical control. Consequently, it can... 

Total harmonic distortion (THD) level in a power network is directly related to the characteristics of the network itself. In the case of a mine under construction, these characteristics do change as equipment installation progresses. Someday, a network modification will shift a natural resonance on or within vicinity of a higher level drive harmonic. Normally unnoticed, this particular harmonic will resonate, pushing the THD beyond acceptable limits. 

Current Harmonic Distortion is usually described by THI index (Total Harmonic Current Distortion). Up to this point, only harmonic currents have been considered these are related to power converter topologies and are somehow independent of network characteristics. 

Voltage Harmonic Distortion is usually described by THD index (Total Harmonic Distortion). 

Most regulations include a limit on the total harmonic distortion voltage. The purpose of these limits is to safeguard the performance of electrical supply systems. Human safety issues are discussed in Section 8.5.1.2. Since measured AC voltages are root-mean-square values, the total harmonic voltage is the square root of the sum of the squares of the individual harmonics ... 

PE logic solvers may require electrical power with lower total harmonic distortion than electrical or electronic logic solvers. 

Both instrumentation and operational amplifiers are available as single-package devices. These incorporate laser-trimmed resistors that are critically matched for optimum performance. Fixed and adjustable gain units are offered with gains up to 1000 (60 dB), equivalent input noise of —128 dB, and total harmonic distortion (THD) of 0.0001% at 20 kHz. 

Distortion measurements are a way of quantifying the amount of unwanted components added to a signal by a piece of equipment. The most common technique is total harmonic distortion (THD), but others are often used. Distortion measurements express the amount of unwanted signal components relative to the desired signal, usually as a percentage or decibel value. This is another example of multiple level measurements that are combined to give a new measurement figure. 

FIGURE 20.7 Illustration of total harmonic distortion (THD) measurement of an amplifier transfer characteristic. 

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