What You’ll Learn ⚡

Grasp power quality fundamentals: voltage/frequency deviations, waveform distortion, and grid stability standards (IEC 61000‑4‑30 Class A)
Measure and interpret harmonics, interharmonics, total harmonic distortion (THD), total demand distortion (TDD), and grouped frequency bands up to 150 kHz
Analyze symmetrical components (positive, negative, and zero sequence) to assess system balance
Perform flicker and flicker emission analysis (Pst, Plt) per IEC 61000‑4‑15/‑21 and identify rapid voltage changes (RVC)

Set up DewesoftX’s Power Quality module: select channels, configure calculations, and use data displays like numeric, recorder, FFT/harmonic FFT, and waterfall plots
Capture raw data to study fault events and transient behavior while applying sensor compensation (amplitude/phase correction)
Export and visualize data in real-time or later—via built-in displays or external tools—ensuring compliance with power quality standards

Course overview

The Power Quality Analysis course provides a detailed examination of electrical power integrity and grid compliance using Dewesoft’s comprehensive hardware and DewesoftX software. It starts by defining power quality—covering waveform purity, voltage and frequency stability, and the impact of non‑ideal conditions on equipment and operations.

You’ll then explore key disturbances: from harmonics that distort ideal sinusoidal waves—up to the 3000th order and grouped per IEC 61000‑4‑7—to symmetrical component analysis for detecting unbalance, along with flicker and rapid voltage changes per IEC 61000‑4‑15 guidelines . The course also covers Total Demand Distortion (TDD), interharmonics, and frequency‑dependent groupings that allow deep examination of power quality dynamics up to high-frequency bands.

In hands-on modules, you’ll configure DewesoftX’s Power Quality module: selecting analog channels, choosing FFT vs. time-based calculations, and enabling inline sensor compensation to ensure high accuracy . You’ll engage in real-time monitoring using numeric displays, recorders, harmonic FFTs, waterfalls, and scope views—then learn how to record raw waveforms during fault conditions for detailed post-analysis.

Finally, the course teaches effective data management: exporting recorded data, applying calibration corrections, and generating visual reports that comply with industry standards. By completion, you’ll be able to deliver compliant power quality tests, troubleshoot disturbances, and integrate power quality modules into broader electrical diagnostics (including motor efficiency, power analysis, and PQ solutions across renewable, industrial, and grid applications).

What are harmonics?

Harmonics are integer multiples of the fundamental frequency (e.g., 50 Hz for the grid in Europe) and cause distortion in the voltage and current waveforms. Harmonic voltages and currents, which result from non-sinusoidal loads, can affect the operation and lifespan of electrical equipment and devices. In motors and generators, harmonic frequencies can increase heating (iron and copper losses), affect torque (causing pulsations or reduction), create mechanical oscillations, and produce higher audible noise. They also accelerate the aging of shafts, insulation, and mechanical parts, ultimately reducing the overall efficiency of the motor.

Harmonic summation of sinusoidal waveforms

The image illustrates such a case. In the first recording, the fundamental frequency is shown together with the 3rd, 5th, and 7th harmonic orders overlapping. So, what is the problem? After all, they are all sinusoidal waveforms with different amplitudes, right? Well, no. In the second recording, only the fundamental frequency is shown. This perfect sinusoidal waveform is the preferred signal for all electrical equipment, as it is the ideal form to work with.

The problem with harmonic orders is that they add to the fundamental frequency, creating non-sinusoidal waveforms. The subsequent recordings show how the sinusoidal waveform changes as more harmonic orders are introduced. It is clear that the higher the order, the less sinusoidal the wave becomes. By the 25th harmonic order, the waveform begins to resemble a square wave. The more higher-order harmonics are added, the squarer the waveform becomes. With infinitely many harmonics, the waveform would transform into a perfect square wave.

Overview

Current harmonics in transformers increase copper and stray flux losses, while voltage harmonics increase iron losses. These losses are directly proportional to frequency; therefore, higher-frequency harmonic components are more critical than lower-frequency ones. Harmonics can also cause vibrations and increased noise. The effects on other electrical equipment and devices are similar and typically include reduced efficiency and lifespan, increased heating, malfunctions, or even unpredictable behavior.

Dewesoft measures harmonics for voltage, current, and both active and reactive power up to the 3000th order. All calculations are implemented in accordance with IEC 61000-4-7 and can be selected in the power module, as shown in the following image. To calculate higher harmonics, the sampling rate must be adjusted accordingly. For example, at a sampling rate of 500 kS/sec or higher, DewesoftX can calculate up to the 3000th order.

Harmonic measurement options in the power module

Harmonics

Up to 500 harmonics can be calculated. In addition, there is an option to select all harmonics or only even or odd ones. If current channels are used in the power module, it is also possible to calculate phase angles, P, Q, and impedance.

Harmonic measurement calculation options in the power module

Number of Sidebands

The basic idea of sidebands is that a certain frequency range is treated as one harmonic.

Example: One full sideband (±5 Hz) at a frequency of 50 Hz means that the range from 45 Hz to 55 Hz is considered the first harmonic. The same principle applies to all other harmonics. If two sidebands are selected, the first harmonic will cover the frequency range from 40 Hz to 60 Hz.

Number of Halfbands

According to IEC 61000-4-7 (page 22), the grouping of harmonic sidebands requires that only the square root of the quadratic half be added. This applies to the lowest and highest lines and is defined as halfbands in Dewesoft.

Example I: One sideband and one halfband at a frequency of 50 Hz means that the frequency range from 45 Hz to 55 Hz is considered the first harmonic. Additionally, the square root of the quadratic half of the 40 Hz and 60 Hz lines is included.

Example II: Two sidebands and one halfband at a frequency of 50 Hz means that the lines from 40 Hz to 60 Hz are taken with full amplitude, while the lines at 35 Hz and 65 Hz are included only with the square root of the quadratic half.

Interharmonics

Interharmonics include all frequency components that are not integer multiples of the fundamental frequency and are therefore not classified as harmonics.

Please refer to page 26 of IEC 61000-4-7

Group FFT Lines

The higher-frequency components can be grouped into 200 Hz or 2 kHz bands, up to 150 kHz.

Depending on the measurement requirements, Dewesoft provides the option to select one or both of these harmonic groupings.

Please be aware that according to page 29 of IEC 61000-4-7 these groups start at -95 Hz to +100 Hz around the middle frequency.

For 2.1 kHz, lines from 2005 Hz to 2200 Hz are considered to be one group.

Harmonic grouping according to the IEC 61000-4-7 standard

Full FFT

This option calculates a full FFT, which can then be exported to the database and displayed as a 2D graph.

Harmonics Smoothing Filter

This option enables the low-pass filter required by the IEC 61000-4-7 standard (page 23).

Background Harmonics

With this option, it is possible to subtract an existing and known harmonic pattern (magnitude and phase) from the measured values. This is typically applied during the commissioning of a high-power converter to determine the noise contribution of the converter.

This function is available for both voltage and current and can be selected from the Background Harmonics Editor in DewesoftX.

For this calculation, only the magnitude and phase angle of the harmonic pattern need to be entered, as illustrated in the input mask image below.

Example

The following images show a specific harmonic pattern measured using Dewesoft DAQ devices. A harmonic filter was then applied to the same measurement in DewesoftX, resulting in an adjusted harmonic pattern by subtracting the background harmonics.

Measurement screen without a harmonic filter applied

Measurement screen with a harmonic filter applied

How to perform a measurement with DewesoftX?

DewesoftX offers a range of display options for measurements such as voltage, current, active and reactive power, phase angle, impedance, interharmonics, and higher frequencies. These values can be shown as numeric displays, on recorders, or as 2D graphs, as illustrated in the following image. Users are free to configure the display as needed.

Display options for the measurement screen in the power module

There are two options for displaying harmonics in DewesoftX: the Harmonic FFT and the 2D graph. The following image shows the icons used for these options—on the left is the Harmonic 2D graph, and on the right is the Harmonic FFT.

Display options for harmonics in the power module

Harmonic FFT

In the Harmonic FFT, the harmonics of voltage, current, power, and reactive power can be displayed. The following image shows the voltage harmonics of a three-phase system.

2D Graph

With the 2D graph, voltages and currents of different phases can be displayed in a single graph. In addition, a wide range of display options is available, which the user can configure as needed for the specific application. The following figure shows the harmonics for the phase voltage of L1. On the right-hand side are the available display options for 2D graphs. Here, the graph type can be selected—either line or histogram—as well as the graph scale, which can be set to linear or logarithmic. The scaling of the graph axes can also be adjusted independently.

Persistence

There is also an option to display the persistence of the harmonics in the 2D graph. This means that when the harmonics change during a measurement, the variations appear blurred, as illustrated in the following figure.

Higher frequencies

Example: Higher frequencies from 2 Hz to 20 kHz displayed in a 2D graph as a histogram (application: HVDC converter station).

Interharmonics

Example: Interharmonics displayed in a 2D graph as a histogram. A peak appears at 900 Hz, which corresponds to the switching frequency of an HVDC converter operating in the public grid.

Interharmonic measurement screen in a 2D graph and a FFT graph

What are the symmetrical components?

Fundamental symmetrical components

Normally, an electric power system operates in a balanced three-phase sinusoidal steady-state mode. Disturbances, such as faults or short circuits, can lead to an unbalanced condition. As shown in the following image, the left-hand side depicts a balanced system with a symmetrical phase shift and equal vector distances, while the right-hand side illustrates an unbalanced system with an asymmetrical phase shift and uneven vector lengths.

Balanced system and an unbalanced system

By using the method of symmetrical components, any unbalanced three-phase system can be transformed into three separate sets of balanced components: positive, negative, and zero sequence.

Unbalanced system to balanced system transformation

The advantage of using a symmetrical balanced system is that calculations are simplified. If a fault occurs or a short circuit develops in the system, the unbalanced system can be transformed into a balanced system using symmetrical components. In this form, system calculations can be carried out with the standard formulas used for balanced systems. The calculated values are then transformed back into the unsymmetrical (real-world) phase voltages and currents. In general, a three-phase system can be represented and mathematically described as follows:

A balanced three-phase system, as shown in the image below, has the same RMS value for all line voltages and currents, with a 120° phase shift between each of them.

To explain the basic idea of symmetrical components, the first step is to define the operator as a unit vector with a phase angle of 120° (or 2π/32\pi/32π/3).

a=e\frac{j2 \pi}{e^3}

The voltages can be expressed mathematically in several ways, as shown in the table below:

Symmetrical components complex and angle calculations

Calculation of zero-sequence system

In a symmetrical system, the following equation is valid:

U_{L1}+U_{L2}+U_{L3}=0

In a real system, the sum will not be zero. A voltage difference will occur, as shown in the following equation:

U_{L1}+U_{L2}+U_{L3}= \underline{\Delta} u

This voltage difference, divided by three, represents the so-called zero-sequence system:

U_0 =\frac{1}{3} \cdot \underline{\Delta}u =u_{10}= u_{20}= u_{30}

The zero-sequence systems for the three phases (u10,u20,u30u_{10}, u_{20}, u_{30}u10,u20,u30) all have the same amplitude and phase. Therefore, only the value of the zero-sequence system U0U_0U0 is shown.

The calculation of the zero-sequence current is analogous to that of the voltage equation.

When the currents of the zero-sequence system are multiplied by three (=I_0 * 3) it will yield he current that is flowing in the neutral line U_N.

Calculation of positive-sequence system

The positive-sequence system has the same rotation direction as the original system (right). This means it will match the rotation direction of an electrical machine connected to the grid.

\underline{v_{1m}} = \frac{1}{3} (\underline{v_1} + \underline{av_2} + \underline{a^2v_3})

\underline{v_{2m}} = \underline{a^2v_{1m }} = \frac{1}{3} (\underline{v_1} + \underline{av_2} + \underline{a^2v_3}) \cdot \underline{a^2}

\underline{v_{3m}} = \underline{av_{1m }} = \frac{1}{3} (\underline{v_1} + \underline{av_2} + \underline{a^2v_3}) \cdot \underline{a}

Since the values of the positive-sequence system for all three phases have the same amplitude (being symmetrical) and a phase shift of exactly 120°, it is sufficient to display only one value. In DewesoftX, this value is denoted as U1U_1U1.

Calculation of negative-sequence system

The negative-sequence system has the opposite rotation direction of the original system (left). This means it will rotate in the opposite direction of an electrical machine connected to the grid.

\underline{v_{1g}} = \frac{1}{3} (\underline{v_1} + \underline{a^2v_2} + \underline{av_3})

\underline{v_{2g}} = \underline{av_{1g }} = \frac{1}{3} (\underline{v_1} + \underline{v_2} + \underline{a^2v_3})

\underline{v_{3g}} = \underline{a^2v_{1g }} = \frac{1}{3} (\underline{a^2v_1} + \underline{av_2} + \underline{v_3})

Since the values of the negative-sequence system for all three phases have the same amplitude (being symmetrical) and a phase shift of exactly 120°, it is sufficient to display only one value. In DewesoftX, this value is denoted as U2U_2U2.

Matrix of zero, positive and negative-sequence system

According to the following equations, the phase voltages and currents are transformed into symmetrical components. The result is three balanced three-phase systems: positive (U1,I1U_1, I_1U1,I1), negative (U2,I2U_2, I_2U2,I2), and zero-sequence (U0,I0U_0, I_0U0,I0).

Matrices of the zero-,positive-, and negative sequence system

The basic values of symmetrical components (U_0, U_1 U_2, I_0, I_1, I_2) are calculated for each harmonic and addd up geometrically.

As illustrated in the following images, an unbalanced system can be represented using the positive, negative, and zero symmetrical components. The image below shows an unsymmetrical system in a screenshot taken from DewesoftX.

Unbalanced system vectorscope in Dewesoft X This screen was provided by Kurt STRANNER (KNG Netz GmbH)

The following image shows a screenshot of the three systems—positive, negative, and zero—of the symmetrical components in DewesoftX:

nbalanced system to balanced system transformation in Dewesoft X This screen was provided by Kurt STRANNER (KNG Netz GmbH)

From the parameters of the symmetrical components (positive-, negative-, and zero-sequence), the original system can be easily reconstructed, e.g.:

U_{L1}=U_0 + U_1 + U_2

The following variables are calculated in DewesoftX and represent the components of the zero- and negative-sequence systems in comparison to the positive-sequence system (for both the total and the fundamental harmonic).

Zero-,positive-, and negative sequence system calculations in the power module

Extended positive sequence parameters (according to IEC 614000)

The following calculations are based on Annex C of IEC 61400-21.

From the measured phase voltages and currents, the Fourier coefficients of the fundamental are calculated over one fundamental cycle TTT as the first step.

u_a cos= \frac{2}{T}\int_{t-T} ^{t} u_a (t) cos (2 \pi f_1 t) dt

u_a sin= \frac{2}{T}\int_{t-T} ^{t} u_a (t) sin (2 \pi f_1 t) dt

It is important to note that the index a refers to the line voltage L1L_1L1. The coefficients for L2L_2L2 (ubu_bub) and L3L_3L3 (ucu_cuc), as well as the coefficients for the currents (ia,ib,ici_a, i_b, i_cia,ib,ic), are calculated in the same way. Furthermore, f1f_1f1 is the frequency of the fundamental. The RMS value of the fundamental line voltage is:

U_ {a1}= \sqrt{\frac{u^2_{a,cos}+u^2_{a,sin}}{2}}

Extended positive sequence calculations in the power module

Extended negative sequence parameters (according to IEC 614000)

Extended negative sequence calculations in the power module

Extended zero sequence parameters (according to IEC 614000)

Extended zero sequence calculations in the power module

What is a flicker?

Flicker refers to fluctuations (repetitive variations) in voltage. Flashing light bulbs are a clear indicator of high flicker exposure. Flicker is particularly common in grids with low short-circuit resistance and is caused by the frequent connection and disconnection of loads (e.g., heat pumps, rolling mills) that affect the voltage. A high level of flicker is perceived as psychologically disturbing and can be harmful to humans.

The Dewesoft Power Analyzer can measure all flicker parameters in accordance with the IEC 61000-4-15 standard. Flicker emission calculations are implemented according to the IEC 61400-21 standard and allow for the evaluation of flicker emissions fed into the grid by wind power plants and other power generation units.

The flicker-meter architecture is shown as a block diagram in the next image. It is divided into two parts: the simulation of the response of the lamp–eye–brain chain, and the online statistical analysis of the flicker signal, which produces the defined parameters. The blocks within the diagram will be discussed briefly.

Block 1

The first block contains a voltage-adapting circuit that scales the input mains voltage to an internal reference level. This method allows flicker measurements to be performed independently of the actual input voltage level and may be expressed as a percentage ratio.

Block 2

The second block recovers the voltage fluctuations by squaring the input voltage scaled to the reference level, thereby simulating the behavior of a lamp.

Block 3

The third block consists of a cascade of two filters, which may either precede or follow the selective filter circuit. The first low-pass filter removes the double mains frequency ripple components of the demodulated output.

The high-pass filter is then used to eliminate any DC voltage component. The second filter is a weighting filter that simulates the frequency response of the human visual system to sinusoidal voltage fluctuations of a coiled-filament, gas-filled lamp (60 W/230 V and/or 60 W/120 V).

Block 4

The fourth block consists of a squaring multiplier and a first-order low-pass filter. Human flicker perception—through the combined response of the eye and brain to voltage fluctuations applied to the reference lamp—is simulated by the nonlinear interaction of blocks 2, 3, and 4.

Block 5

The last block in the chain performs an online analysis of the flicker level, allowing direct calculation of key evaluation parameters.

The following image shows an example of a rectangular voltage flicker.

How the channel list is defined in DewesoftX?

Dewesoft has developed a special FFT algorithm (software PLL) to determine the periodic time (frequency). The algorithm calculates the periodic time of the signal using this FFT method over a sampling window of multiple periods (typically 10 periods, configurable in the power module). The calculated frequency is highly accurate (in the millihertz range) and works reliably for all applications, including motors, inverters, and grids.

How Dewesoft X calculates the power of an AC system

While other power analyzers calculate power in the time domain, DewesoftX performs the calculation in the frequency domain. Using the predetermined period time, an FFT analysis of voltage and current is performed over a user-defined number of periods (typically 10 for electrical applications) and a configurable sampling rate. The FFT provides the amplitude of the voltage, current, and the cosine phi for each harmonic.

One major advantage of this FFT-based transformation is that the behavior of amplifiers and current or voltage transducers—in both amplitude and phase across the entire frequency range (using the Sensor XML)—can be corrected. This method of power analysis delivers the highest possible accuracy. Another advantage is that harmonic analysis and other power quality assessments can be carried out fully synchronized with the fundamental frequency.

With the FFT-corrected values, the RMS voltages and currents are calculated from the RMS values of each harmonic.

U_{rms_{total}}=\sqrt{U^2_0 + U^2_1 +U^2_2 + ...+U^2_n}

I_{rms_{total}}=\sqrt{I^2_0 + I^2_1 +I^2_2 + ...+I^2_n}

The rectified mean is the average of a rectified signal. For an AC signal, it represents the average of the absolute values of voltage or current.

U_{RECT}= \frac{1}{T}\int_{t=0} ^{T} \left\vert u \right\vert (t)dt

I_{RECT}= \frac{1}{T}\int_{t=0} ^{T} \left\vert i \right\vert (t)dt

The rectified mean is used, for example, in transformer testing, as it is proportional to the magnetic flux.

The power values for each harmonic, as well as the total values, are calculated using the following formulas:

There are two definitions for reactive power included, because there is up to date no official definition that has been standardized. The formula of Q1_L1 loses sign, while QH_L1 does not. If there is a need to calculate the reactive power form only the harmonics (no fundamental included) the following simple math formula can be used: ‘QH_L1’ – ‘Q_L1_H1’