## Distinguishing Group Harmonics versus Transient Analysis

Engineered systems are subjected to distortion, which is why there’s a matter of differentiating Group Harmonics from Transient Analysis to understand what goes on. Distortion refers to an out-of-the-ordinary occurrence that disturbs or alters the steady state of a system. It happens in many fields, namely electrical, mechanical, communications and more.

In electrical engineering, changes in the steady state of a system or equipment are cause for concern. It’s the reason scrutinizing the harmonic or transient response is essential in any design process. However, the application of both analyses begs the question of which specific tool should be used based on the situation.

In this article, we aim to explain what transient analysis and group harmonics are and how to determine which process is appropriate to apply.

## What is Group Harmonics?

By the definition of the Institute of Electrical and Electronics Engineers (IEEE), interharmonics refers to “the frequency component found in a periodic quantity that is not an integer multiple of the frequency at which the supply system is operating.”

Additionally, the International Electrotechnical Commission (IEC) defines group harmonics as further frequencies that are different from the fundamental and may appear as a wide-band spectrum or discrete frequencies.

Based on these explanations, interharmonics refers to a frequency signal that does not belong as an integer multiple of a fundamental frequency. In contrast to harmonics, which signifies the periodic fundamental component, interharmonics is non-periodic and is included in any non-periodic waveforms.

While a periodic waveform is represented by a Fourier series consisting of harmonics with different magnitudes, angles, and frequencies, nonperiodic components such as interharmonics are the measure of non-periodicity in the waveform of a power system, which also shows interharmonics distortion.

Interharmonics happen as a result of rapid and non-periodic changes to voltage and current in a power system caused by transient state loads. It may also take place when there is an amplitude modulation in current or voltage for control purposes.

Some of the sources of interharmonics include arching loads in welding machines and arc furnaces, saturation of magnetic circuits in induction motors, electronic frequency converters, voltage sourced converters, variable load dives, and power line communication.

## When to Apply Group Harmonics

Interharmonics can be measured using the basis of Fourier analysis, which is the definition of periodic waveforms through trigonometric functions. The IEC simplifies the process of measuring interharmonics and producing repeatable results by grouping (IEC 61000-4-7). The total interharmonics distortion can be determined using a set standard of calculations.

Harmonics analysis aims to understand the effects of interharmonics in a system. It could be related to similar harmonic effects, flicker, or changes in power line communication. Each phenomenon is assigned a limit to prevent issues in the power system.

Effects of interharmonics distortion that reduce the power quality, which is determined by the analysis results, could be mitigated through different actions such as reducing load sensitivity, lessening emission, or decreasing the coupling between sensitive loads and distortion-generating equipment.

## What is Transient Analysis?

The concept of transient state in electrical engineering refers to sudden changes in the equilibrium of a power system. It can be caused by changes in the system configuration or operating conditions. A transient phenomenon in power may refer to switching operations, faults, load variations, or lightning strokes.

Transients are abrupt and occur for very short intervals of time. It is also a distortion in a power system. Concerning DC analysis where current and voltage are observed in a steady state, a transient response may occur to the applied current or voltage, which then dies out over some time to reveal a new steady-state behavior.

A transient analysis is performed to determine how a circuit behaves under unstable conditions. It could be prompted by any change in peak input or a large peak load, which could cause the oscillation of the system.

The primary goal of a transient analysis is to simulate electromagnetic transients based on accurate representations of power components. It is most often used in the study of the maximum peak voltage of a system, which occurs on the first oscillation following a transient phenomenon.

## When to Apply Transient Analysis

It is necessary to accomplish transient analysis to determine a circuit’s integrity and stability. While the transient state is fleeting and can occur at a very short interval, it’s crucial to study the values at which a voltage or current drops or rises so that a circuit can sustain favorable conditions to operate efficiently.

A transient simulation is a critical test bench to verify circuits. It could show non-linearity, slew limiting, time issues, large signal bandwidth, and other matters that affect the power system if uncontrolled. Therefore, it’s crucial to identify the large-signal circuit performance and for full verification of circuit sustainability.

## Group Harmonics versus Transient Analysis

While both analyses are used to measure specific distortions in a power system, there are critical differences between group harmonics and transient analysis. A harmonics response analysis measures the response of any structure to an input load in correlation to sinusoidal time-history. It involves the periodicity of waveforms.

Transient analysis, on the other hand, is the study of transient distortions that occur for only a limited set of time. There are no assumptions of periodic frequency in transients, unlike that of harmonics. It computes the structure time-history to a load that has an amplitude-time history.

Analyzing transients involves using time-domain methods while analyzing group harmonics makes use of frequency-domain methods.

Distinguishing group harmonics versus transient analysis is purely on a situational basis. However, they ultimately reach a common goal, which is to ensure a functional power system that remains stable and operational despite unpredictable circumstances.

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