Electrical Power Measurement and Analysis with Dewesoft

Course Overview

The Power Analysis online course provides a comprehensive learning journey into the measurement and analysis of electrical power using Dewesoft’s DAQ hardware and DewesoftX software. Beginning with the theory, you’ll explore the definitions of active, reactive, and apparent power, and learn to compute instantaneous and average power by integrating voltage and current over time.

Progressing into practical setups, the course guides you through DewesoftX Power Module configuration—covering wiring diagrams, channel setup, sampling, triggering, and averaging techniques. You’ll perform DC measurements, and single- to multi-phase AC tests in star, delta, V, Aron, and configurable inverter environments.

The training highlights Dewesoft’s FFT-based periodic time detection method, which ensures high precision even with distorted waveforms, a key differentiator from conventional zero-crossing analyzers  . You’ll also dive into detailed analysis of harmonics and interharmonics, learn how to calibrate sensors (amplitude and phase), and understand power quality analytics. Finally, the course equips you with skills to visualize, export, and optimize power measurement performance—ensuring reliable results across complex electrical systems.

Our Power Brochure provides a clear overview of all power applications as well as the full range of products offered. Please click the link to be directed to the download page.

For additional information, be sure to visit the Power Analyzer section of our website.

What is power?

In physics, power is the rate of doing work. It represents the amount of energy consumed per unit of time. The unit for power is the joule per second (J/s), also known as the watt (W). The integral of power over time defines energy (performed work).

What is power analysis? 

Power is the rate of doing work, i.e., the amount of energy consumed per unit of time. In an electrical system, power is calculated as the product of voltage and current, integrated over a period and then divided by the period duration. The period (which is the reciprocal of frequency) must be known to calculate the power of an electrical system. Power analysis is the process of testing and studying power, typically using a power analyzer.

How do we calculate power?

The power of an electrical system is calculated by multiplying the voltage by the current.

But is it really that simple? What about measuring a 7-phase system or frequency inverters? Power calculation can be straightforward, for example when measuring DC systems, but it becomes more complex when dealing with inverters with multiple phases.

In this Pro Training, the correct methods for measuring electrical power in different systems will be explained, along with applications such as grid systems, motors, and inverters, among others. First, the theoretical part will be covered, providing background on power calculations. Next, we will discuss the calculation of basic power parameters, explain how to configure the power module, and show how to visualize power parameters on the measurement screen of the Dewesoft software. Finally, the practical section will demonstrate step-by-step how to measure DC power, single-phase, two-phase, and three-phase AC power (in star, delta, Aron, and V-connections). It will also cover key considerations when measuring inverters and provide an example of how to calculate the power of a six-phase motor.

Electrical power is the rate at which electric energy is transferred by an electric circuit. The SI unit of power is the watt (W). The following formula describes the calculation of electric power for AC or DC systems in general.

• P is power in Watt [W]

• u is voltage in Volt [V]

• i is current in Ampere [A]

• T is the periodic time in seconds [s] 

So, power is not just voltage multiplied by current as initially stated. Instead, it is the integration of this product over the periodic time, divided by the period. This means that it is necessary to know the period of time (frequency) to calculate the power of an electrical system.

Measuring DC power is not as complicated, since voltage and current are constant and there is no frequency, as shown in the image below. In this case, the time interval for integration simply defines the averaging interval of the power calculation.

To measure AC systems, the periodic time must be known. This cannot be done by simply taking the normal grid frequency (e.g., 50 Hz) as a constant. The grid frequency is constantly changing depending on the balance between energy supply and electrical load at any given moment. With variable drives—where the frequency continuously changes across a wide range (from 1 Hz up to 2000 Hz)—the calculation of power becomes even more difficult. Therefore, the exact period time must be determined. This is particularly challenging when measuring inverters, where the voltage is no longer a sinusoidal waveform but instead a series of pulse packets.

Frequency determination

This is where the Dewesoft Power Analysis tool sets itself apart from conventional power analyzers. Conventional analyzers use zero-crossing detection to determine the periodic time. In other words, they measure when the voltage or current crosses the x-axis and use that information to calculate the period. While this method works well in many cases, it can lead to significant errors when measuring strongly distorted signals.

Dewesoft, however, was not satisfied with “works well most of the time.” Therefore, a special FFT (Fast Fourier Transform) algorithm—called Software PPL—was developed to determine the periodic time (frequency). The algorithm calculates the periodic time of the signal using an FFT-based approach with a sampling window of multiple periods (typically 10, adjustable in the power module). The calculated frequency is highly accurate (to the millihertz level) and works for every application, including motors, inverters, and grids.

How a low-cost Watt-meter calculates the power of an AC system

A low-cost watt-meter calculates the power of an AC system using the peak values of voltage and current, according to the following formula:

To calculate power, they simply multiply the RMS values of voltage and current. This method works well when both current and voltage waveforms are ideal sinusoids (as produced by generators in power plants). However, in modern systems, the waveforms of both voltage and current are rarely ideal due to non-linear loads and non-linear generation units. As a result, this method of calculating power is outdated—especially when measuring inverters—since it often produces completely incorrect results.

How a conventional power analyzer calculates the power of an AC system?

Conventional power analyzers calculate the RMS values of voltage and current directly from sampled data points. The RMS value is obtained by taking the square root of the average of the squared sample points of the waveform.

How Dewesoft power analyzer calculates the power of an AC system?

As mentioned earlier, conventional power analyzers calculate power in the time domain, while Dewesoft calculates power in the frequency domain. Using the predetermined period time, an FFT analysis of voltage and current is performed for a definable number of periods (typically 10 in electrical applications) and at a definable sampling rate.

The FFT provides the amplitude of voltage, current, and the cosine of the phase angle (cos φ) for each harmonic. One major benefit of this FFT-based method is that the behavior of amplifiers and current or voltage transducers—both in amplitude and phase—can be corrected across the entire frequency range using the Sensor XML. This approach yields the highest possible accuracy for power analysis. Another advantage is that harmonic and other power quality analyses can be performed fully synchronized to the fundamental frequency.

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

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

Some of the benefits of the Dewesoft power calculation method, compared to conventional methods, are:

• Raw data storage simultaneous with power analysis

• Additional sensor calibration for amplifiers and sensors in both amplitude and phase across the full frequency spectrum

• Simplified power quality analysis (harmonics, interharmonics, higher frequencies)

• Resampling capability

• Period values available for power, voltage, current, and symmetrical components

AC power can be classified into three types: active power, reactive power, and apparent power.

Power triangle

The power triangle illustrates the relationship between active, reactive, and apparent power.

In the diagram, P represents active power, Q represents reactive power (positive in this case), S is the complex power, and the length of S corresponds to apparent power. Reactive power does not perform any work and is therefore shown on the imaginary axis of the vector diagram. Active power, on the other hand, performs work and is represented on the real axis.

Active power - P

Active power is measured in watts (W) and refers to the energy transferred from an electric generator to a load. It is the portion of power that can be used by electrical loads to perform useful work.

Reactive power - Q

Reactive power is measured in volt-ampere reactive (VAr). It does not represent usable energy but is essential for the operation of most types of magnetic equipment, such as motors and transformers. Reactive power is supplied by generators, synchronous condensers, or electrostatic equipment like capacitors. It directly affects the voltage of the electrical system and the capacity of the power transmission line.

Apparent power - S

Apparent power is measured in volt-amperes (VA) and is calculated as the voltage in an AC system multiplied by the total current flowing through it. It represents the vector sum of active and reactive power.

Power factor

The ratio between active power and apparent power in a circuit is called the power factor. For two systems transmitting the same amount of active power, the system with the lower power factor will have higher circulating currents due to the energy returned to the source from storage elements in the load. These higher currents cause increased losses and reduce overall transmission efficiency. A circuit with a lower power factor therefore has higher apparent power and greater losses for the same amount of active power. The equation is often multiplied by 100 to express the power factor as a percentage.

Cos Phi

Cos φ (cos phi) is the angle between the phase voltage and the current. The difference between cos φ and the power factor is that cos φ is calculated for each individual harmonic, starting with the fundamental frequency, while the power factor includes the entire spectrum (all harmonics).

Power triangle analogy to beer 

The power triangle can be more easily understood using a beer analogy. Reactive power is like the foam (head) on top of the beer, while active power is the actual liquid in the glass. The foam takes up space and reduces the volume of beer available to drink. Although foam is a natural part of pouring beer, we try to minimize it to maximize the usable liquid in the glass. Similarly, reactive power is always present in transmission lines and reduces the capacity available for real (active) power, but it is minimized whenever possible. Only active power can perform useful work.

Calculation of power values (P, Q, S) for each harmonic

To better understand how the power of each harmonic component is calculated, refer to the image below, which illustrates the calculation of several harmonic active power values. The same principle applies when calculating both apparent and reactive power, using their respective equations.

The new power triangle

The traditional power triangle illustrated earlier is no longer sufficient because additional parameters, such as distortion and harmonic reactive power, must now be considered. This need arises primarily due to the increasing presence of non-linear loads (e.g., inverters, electronic ballast units) and new types of power generation (e.g., wind, photovoltaic systems).

As a result, the modern power triangle has evolved into a new form, with an additional dimension:

Harmonic reactive power - QH

Harmonic reactive power is the sum of all harmonic reactive components. It occurs due to the phase shift between voltages and currents of the same frequency.

Distortion reactive power - DH

The combination of voltages and currents at different frequencies produces distortion power.

Name in DewesoftX (e.g. for L1)– distortion power of all harmonic components’ reactive powers where voltage (u) and current (i) have different harmonic orders.

Distortion - D

Distortion power accounts for everything except the fundamental (first) harmonic..

Name in DewesoftX (e.g. for L1): – distortion power of all harmonic components’ reactive powers (where u and i have the same harmonic order but not equal to 1, or have different orders).

These are part of the Power Quality (PQ) parameters. All other PQ parameters calculated in DewesoftX (such as harmonics, THD, rapid voltage changes, symmetrical components, etc.) can be found in the Power Quality chapter.

Calculation of power values (P, Q, S) for each harmonic for the new power triangle

Energy calculation

The DewesoftX software can automatically calculate a system’s energy using the power module. It is possible to calculate the total energy consumption, or to separate it into positive energy (consumption) and negative energy (delivery). This is especially useful when measuring electric vehicles with recuperation (energy recovery) or when analyzing the load profile of households or industries that include a power generation unit (e.g., photovoltaic systems).

The energy calculation is a simple integration of all power values:

• To obtain positive energy, only positive power values are integrated.

• To obtain negative energy, only negative power values are integrated.

• A selection can be made to calculate positive, negative, or both.

P = Power in watts [W][W][W]

E = Energy in watt-hours [Wh][Wh][Wh]

In the following images, the settings for the energy calculation in the power module are shown.

In addition to the basic power calculations, it is also possible to start or reset the energy calculation at trigger events. Otherwise, the energy will be calculated as soon as you switch to Measure mode. You can also reset values at the start of acquisition or via a channel.

Efficiency calculation

The efficiency of electrical devices can be easily calculated using the Dewesoft Math library and the Formula Editor. Efficiency can be calculated for power or energy values, even during measurement.

Where η is the efficiency in [%]

There are applications where energy is measured at multiple points—for example, in electric vehicles that use energy recuperation. The following Sankey diagram illustrates the energy flow typically measured in a recuperating electric vehicle.

The Power Module is one of the most complex mathematical modules in DewesoftX. It enables measurements of power grids at different frequencies, in various configurations, and even with variable frequency sources. This section will demonstrate how to use it.

After configuring the voltage inputs (see the Voltage Pro Training) and current inputs (see the Current Pro Training), you can add a new power module by clicking the “+” button in the Channel Setup. Then, click on the “Power Analysis” button. Once selected, the Power icon will appear and be available for use.

The following image provides an overview of the Power Module setup screen.

Power module configuration and wiring

In the Power Module, several wiring schematic configurations are available. The most common are single-phase, three-phase star, and three-phase delta connections. A two-phase configuration is used with certain special motors and in some grid applications. The Aron and V configurations are essentially star or delta setups, but they measure only two currents instead of three (see Three-phase measurement). Special configurations, such as 6-, 7-, 9-, or 12-phase motor measurements, can be performed using multiple single-phase systems and summing the power values in the Math library.

The wiring schematics will be covered in a later chapter, while this chapter focuses on configuring the Power Module.

 Line frequency

The line frequency must be set first. In public grids, the frequencies are 50 Hz in Europe and 60 Hz in the USA (make sure the correct frequency is set for the region where the measurement will take place). Other line frequencies are also available (16.7 Hz, 25 Hz, 400 Hz, 800 Hz) for special applications. For inverter measurements, “Variable Frequency” must be selected. This setting automatically detects the fundamental frequency in the signal using an FFT algorithm (highest peak).

This algorithm calculates the frequency with very high accuracy (in the millihertz range), but it is also very CPU-intensive. For optimal performance, it is recommended to set a range (start and end frequency) for the fundamental frequency using the “Exact frequency settings” option. For example, when measuring an inverter-driven motor, if it is known that the fundamental frequency will not exceed 200 Hz, the end frequency should be set slightly higher—e.g., 250 Hz.

Output limits

When measuring high power, it can be useful to change the output unit to a larger unit. The available options are Watt (W), Kilowatt (kW), and Megawatt (MW).

Frequency source

A special functionality in the Power Module is the ability to select the frequency source. As a source, you can choose the voltage, current, an external signal, or an arbitrary channel.

An arbitrary channel uses filters for more accurate and stable frequency determination. For all types of frequency sources, it is possible to select the channel that should be used for frequency calculation.

If there is more than one power module, the modules can be synchronized using arbitrary channels (e.g., by selecting one phase from another power module).

As shown in the following image of an inverter measurement, the voltage waveform (green) is no longer sinusoidal—it has become a packet of pulses. In this case, if voltage is selected as the frequency source, the determination may be inaccurate. On the other hand, the current waveform (orange) has a clean and stable sinusoidal form and should be selected as the frequency source, as this will yield much better results. The oscilloscope function in the DewesoftX software is extremely useful for analyzing signals to determine the best frequency source.

Number of cycles

The number of cycles used for power calculation can be set, as shown in the image below on the left-hand side. By default, this value is 10 periods for 50 Hz measurements and 12 periods for 60 Hz applications (as required by the 61000-4-30 standard).

In the dropdown list, only 10 and 12 cycles are selectable, but any arbitrary number up to 999 can be entered manually. The minimum number of periods is 5.

For applications that require faster updates, the “period values” functionality can be used. Ensure that this function is enabled by clicking the checkbox—when active, a tick will appear in the box as shown in the image on the right-hand side.

Nominal voltage

The entry of the nominal voltage is important when calculating Flicker values. For other measurements, the voltage should be set to at least the approximate voltage of the measurement. If this value is set too high (e.g., measuring an inverter with a 20 V output but setting the nominal voltage to 400 V), frequency determination may fail.

Examples:

• 230 V – line-to-earth voltage for star configuration

• 400 V – line-to-line voltage for delta configuration

In the drop-down list, 120 V and 230 V are available, but it is also possible to manually enter any required voltage for the measurement in the nominal voltage field.

Calculation sample rate

The calculation sampling rate in the power module acts as a sample rate divider for power calculations. At high sampling rates (>100 kHz), reducing the calculation rate is often necessary due to performance limitations (CPU load). Nevertheless, the required calculation rate should always be selected based on the measurement.

If all data is stored at the full sampling rate (always “fast”), it is also possible to perform calculations in the power module at the full rate later in the post-processing function.

Typical calculation rates:

• Grid measurement – 10 to 20 kHz

• Wind/renewable sources – 50 kHz

• Inverter measurement – 100 kHz or higher

After all the configurations have been completed, the channel list will display which parameters are calculated by the DewesoftX software.

The power module calculates a wide range of parameters. However, in most applications, not all of them are required. In these situations, unnecessary parameters can be deselected, which reduces the size of the data files. The degree of reduction depends not only on the number of parameters deselected but also on their computational intensity, which can vary.

Multiple power modules

In the DewesoftX software, multiple power modules can be created. This allows power to be measured at multiple points in complete synchrony. Within the math library, the power modules can be further refined; for example, efficiency can be calculated automatically (see efficiency calculation). This feature is especially useful when measuring multi-phase motors (6–12 phases). To add another module, simply click the + next to the already active power modules.

Period values

Period values are required to perform detailed analyses of electrical equipment (e.g., analyzing behavior during faults or switching processes) and for fault recording (as a trigger argument). These values are calculated for voltages, currents, active power, reactive power, apparent power, power factor, as well as other parameters.

They can be calculated with a definable overlap (up to 99%) and for a definable number of periods (up to 4). For example, using a 99% overlap at a 50 Hz measurement allows power values to be calculated every 0.2 ms. This is a unique feature of Dewesoft X.

Available options:

• Overlap: 25%, 50%, 75%, 90%, 95%, 99%

• Periods: 1/2, 1, 2, 4

The period values are not corrected in amplitude and phase, unlike the other power calculations in the power module.

When considering period values for symmetrical components (for more details, please see the Power Quality Pro training), more than 50 parameters are available.

The following section provides more detail on the possible measurement setups available in DewesoftX. It explains how to connect both voltage and current in various configurations and includes instructions for setting up the measurements in the software. Several screenshots also illustrate what the measurements may look like once the setups are complete.

DC power measurement

Hardware configuration

For a simple DC measurement, connect the voltage and current inputs to the Sirius device as shown in the image below.

Analog setup

In the next step, the analog setup must be configured in DewesoftX for both voltage and current. (Please refer to the Pro Training on Current and Voltage as references.) The image below shows what a typical DC setup looks like.

Power module setup

In the power module, the wiring must be set to DC measurement, as illustrated in the red square in the image below. After that, the configuration for the selected application must be completed.

On the wiring schematic page, two different calculation modes can be selected, as shown in the blue square in the image. You can either specify the required calculation rate manually or synchronize the measurement to another channel. The synchronized channel can also come from another power module, for example, a 3-phase power module. Additionally, an energy calculation can be added, as illustrated in the yellow square in the image.

DC Math power calculation (only required in Dewesoft X2)

In Dewesoft X2, a simple math formula needs to be created: by multiplying the DC voltage with the DC current, the DC power is calculated.

Measurement screen

On the measurement screen, the voltage, current, and power can be visualized. In the image below, the battery power of an electric vehicle is displayed. The voltage (magenta) remains relatively constant, while the current (green) appears only when power is applied (acceleration – blue).

1-Phase Measurement

Hardware configuration

For a single-phase AC measurement, connect the voltage and current inputs to the Sirius device, as shown in the following image.

Analog setup

In the next step, the analog setup must be configured in DewesoftX for both voltage and current. (Please refer to the Pro Training on Current and Voltage as references.) The image below shows what a typical 1-Phase setup looks like.

Power module setup

In the power module, the wiring must be set to single phase, and the configurations for the specific application must be completed.

For example, when measuring a load connected to the public grid:

• The line frequency is set to 50 Hz (60 Hz in North America, parts of South America, Japan, etc.).

• The output unit should be set to watts.

• The frequency source is voltage.

• The number of cycles is 10 (12 in the case of 60 Hz).

• The nominal voltage (line to earth) is 230 volts in Europe (this varies from country to country).

In the dropdown list, 120 V and 230 V can be selected, but in the input mask, it is also possible to manually enter the value that corresponds to the measurement.

Measurement screen

After switching to measurement mode, the screen layout can be customized according to the user’s requirements. The image below shows a measurement screen with the most common graphs and values used in a single-phase measurement.

2-Phase measurement

Two-phase measurements are rarely required, but some motors (e.g., stepper motors) operate with two phases, where one phase is shifted by 90° relative to the other.

Hardware Setup
For a two-phase AC measurement, connect the voltage and current inputs to the Sirius device, as shown in the following image.

Analog Setup

The next step is to configure the analog setup for the voltage and current inputs. (Please refer to the Pro Training on Voltage and Current for more information.)

Power module setup

In the power module, the wiring must be set to 2-phase, and the configuration for the specific application must be completed.

Measurement screen

After switching to measurement mode, the screen layout can be customized to meet the user’s requirements. In this example, the scope and vector scope of a 2-phase stepper motor are shown, along with the single-phase voltage and current of the grid.

3-Phase star measurement

The star connection is mainly used for measuring 3-phase systems, especially when a neutral line from the grid or the star point of a motor is available. The three-phase voltages are connected to the Sirius HV modules on the high-voltage side. The low-voltage side of the three inputs is at the potential of the neutral line or the motor star point. If neither is available, an artificial star point can be created by short-circuiting the low sides of the amplifiers.

Hardware Configuration

The following image shows the connection for a 3-phase star measurement, including three zero-flux transducers for current measurement. In this setup, zero-flux transducers are used; therefore, a Sirius MCTS slice must also be connected. This is necessary because zero-flux transducers require more power than the Sirius 4xHV 4xLV can supply. The Sirius MCTS is designed to deliver up to 20 W per channel.  

Analog setup

The next step is to configure the analog setup for the voltage and current inputs. (Please refer to the Pro Training on Voltage and Current for more information.)

Power module setup

In the power module, the wiring must be set to 3-phase star, and the configuration for the specific application must be completed.

Measurement screen

After switching to measurement mode, the screen layout can be customized to the user’s requirements. In this example, the load of a household is shown.

• At the top left of the screen, digital meters display the RMS voltage and current values.

• In the center, the current power consumed from the grid is shown.

• At the top right, the current power values of the three phases are displayed.

• The left scope in the middle of the screen shows the voltage waveform, while the right scope displays the current waveform (which is noticeably distorted).

• At the bottom, the load profile is shown in a recorder.

3-Phase delta measurement

The delta connection is used when a neutral line or motor star point is not available. The three-phase voltages are connected to the Sirius HV modules on the high-voltage side at the live terminals (red). The neutral terminals of the HV amplifier must then be connected to the next live terminal: neutral terminal L1 to live terminal L2, neutral terminal L2 to live terminal L3, and neutral terminal L3 to live terminal L1.

Hardware Configuration

The following image shows the connection for a 3-phase delta measurement, including three zero-flux transducers for current measurement. In this setup, zero-flux transducers are used; therefore, a Sirius MCTS slice must also be connected. This is necessary because zero-flux transducers require more power than the Sirius 4xHV 4xLV can supply. The Sirius MCTS is designed to deliver up to 20 W per channel.

Analog setup

The next step is to configure the analog setup for the voltage and current inputs. (Please refer to the Pro Training on Voltage and Current for more information.)

Power module setup

In the power module, the wiring must be set to 3-phase delta, and the configuration for the specific application must be completed.

Measurement screen

After switching to measurement mode, the screen layout can be customized to the user’s requirements. In this example, the measurement of a PV inverter in delta configuration is shown. The vectorscope in the top right indicates that power is being fed into the grid; therefore, the current vectors have a 180° phase shift relative to the voltage vectors, compared to where they would be if the system were consuming power. The scopes also display the waveforms of both voltage and current as nearly perfect sinusoids. 

For comparison, the next image depicts a single-phase PV inverter with unfavorable waveforms for both voltage and current. The voltage has a rectangular waveform, and electrical devices like this place significant stress on the grid. This is mainly due to harmonics present in the signals, which distort the voltage and current waveforms, causing them to deviate from their ideal sinusoidal shape. Please refer to the Power Quality Pro Training for more information.

Star - Delta calculation

A special feature in the DewesoftX power module is the star-delta calculation.

This feature allows the calculation of all delta connection values from a star connection (waveforms, RMS values) and vice versa. This means that regardless of the hardware connection used, both connection types can be measured. For example, to view the analog voltage signal of a delta connection when a star connection is being used, simply select the option “Calculate waveforms” (highlighted in blue in the figure). The next option, “Calculate line voltages” (highlighted in red), allows RMS voltages and harmonics to be displayed.

The following table shows the calculations used in DewesoftX for star–delta and delta–star conversions.

Aron, V-connection and 3-phase 2-meters

In some applications, only two currents and/or voltages are measured instead of three in a three-phase arrangement. The main reason for this approach is cost reduction.

This method is used when it is certain that the load is perfectly synchronous. In such cases, the third current can be calculated from the two measured currents. This approach is often applied in grid measurements, where current transducers are expensive and the load is assumed to be symmetrical.

Aron connection

Hardware configuration

The most common way of measuring active power with symmetrical or asymmetrical loads without a neutral (N) connection is the two-power-meter circuit, also known as the Aron circuit. Compared to the three-power-meter circuit, it has the advantage of saving one measuring device. Additionally, with a symmetrical load, cos φ and reactive power determination are also possible. The Aron connection is essentially a star connection where only two currents are measured.

Power module setup

In the power module, the wiring must be set to 3-phase Aron, and the configuration for the specific application must be completed.

V-connection

Hardware configuration

The V-connection is a delta connection where only two currents are measured, but it fundamentally operates on the same principle as the Aron connection.

Power Module setup

In the power module, the wiring must be set to 3-phase V, and the configuration for the specific application must be completed.

3-Phase 2-meters connection

Hardware configuration 

The 3-phase 2-meter connection is a delta configuration in which only two voltages and two currents are measured.

Power module setup

In the power module, the wiring must be set to 3-phase 2-meter, and the configuration for the specific application must be completed.

Inverter measurement

When measuring inverters, or at the output of inverters, care must be taken to ensure that all relevant factors are considered in order to achieve correct results with the highest possible accuracy.

High-speed amplifiers

Always use high-speed (HS-HV and HS-LV) amplifiers when measuring inverters. Since the voltage is modulated (in amplitude or phase) with switching frequencies of up to several hundred kilohertz, it is essential to use high-speed amplifiers to obtain accurate results.

Current sensors

Measurements of inverters, or at the output of inverters, contain many high-frequency components as well as some DC components. Therefore, always use current sensors with high-bandwidth capabilities that can measure both DC and AC currents. The recommended current transducers are Dewesoft zero-flux transducers, fluxgate current clamps, or Hall-compensated AC current clamps. (Please note that fluxgate and zero-flux current sensors require a PWR-MCTS for power.)

Frequency source

It is important to set the current as the frequency source for this measurement because the voltage output of an inverter no longer has a sinusoidal waveform. The inverter modulates the signal using pulse-width or amplitude modulation, resulting in a packet of pulses. In the following image, an inverter-modulated voltage (green) is shown. The current (orange), however, has a sinusoidal waveform and should therefore be used as the frequency source.

Measurement configuration

The choice between using a star or delta connection for measuring after inverters is open and can be freely selected by the user. However, an Aron or V-connection should never be used for this type of measurement. For basic power analysis, a delta connection is a suitable choice, especially if no star point is available. Use caution, though: since the measurement is made between voltages, this connection is not always appropriate for detailed inverter analysis (e.g., analysis of switching pulses).

When measuring with a star-point connection, a star-point adapter should always be used. An artificial star point via the modules does not conform due to impedance differences. While the active power analysis is not affected, the displayed analog signals will be incorrect. The apparent power and power factor values obtained from such a setup will also be inaccurate. By contrast, using a star connection with a star-point adapter yields very accurate power values and true analog signals, which can then be used for detailed power analysis.

The most reliable way to measure an inverter is with a star connection and a star-point adapter. If this is not possible, the delta configuration is the preferred alternative.

Motor cable shielded or unshielded

A frequently asked question when measuring an inverter is: Is there a difference between using a shielded and an unshielded motor cable?

The answer is yes—there can be a difference. Due to the high switching frequencies of the inverter, leakage currents may flow through the cable shield. This leakage current can affect results in the following ways:

• Phase shift – A phase shift may occur. Comparative measurements with and without shielded motor cables have shown that the shift can exceed 15°.

• Bandwidth damping – With shielded motor cables, the signal is likely to be damped, especially at higher frequencies.

• Higher DC current – Measurements with shielded motor cables may indicate the occurrence of higher DC currents.

This capacitive leakage can introduce low-pass characteristics (phase shift and loss of higher frequencies), which in turn affects measurement accuracy.

Measurement screen

After configuring the power module, the measurement screens can be set up in measurement mode. As discussed earlier, different visualization modes can be added by switching to design mode. The available visualization options are located at the top of the window. On the right side of the window is the channel list, and on the left side are the properties of the selected visualizations.

The most relevant visualizations for power analysis are:

• Digital meters – display the instantaneous values calculated by the power module.

• Recorder – shows charts of power values over time.

• Scope – depicts the waveforms of voltages and currents.

• Vector scope – illustrates the relationship between voltages and currents.

• Harmonic FFT – displays the harmonics of voltage, current, power, and reactive power, synchronized to the fundamental frequency of the signal.

Channel list

In the channel list, you can now find all the parameters that are automatically calculated by the power module. These are categorized to make it easier to locate the desired values.

In the next section, the vector scope and the harmonic FFT will be described in more detail, as these two visualizations were specifically implemented for power module calculations.

Vector Scope

The vector scope shows not only the absolute values of current and voltage but also the phase relationship between them. This is essential because only the portion of current that is in phase with the voltage can be used to produce useful work.

In the vector scope, both the absolute values and the phase angle, known as phi (φ), are measured. From phi, the value of cos φ can also be calculated. (In principle, this is simply the cosine of the angle phi, which is important because it represents the direct ratio of useful work performed compared to the total consumed current.) The vector scope displays the voltage vector (hollow arrow) and the current vector (solid arrow) for each harmonic.

DewesoftX includes a special feature that allows the orientation of the vector scope to be changed. The scope can be displayed either clockwise or counterclockwise, and in some special applications, its orientation can also be shifted to the right. This setting can be adjusted under “Settings” → “Extension” → “Power Grid Analysis.”

By default, the vector scope displays the first harmonic. However, through the “Shown Harmonic” input field in the visualization properties, each individual harmonic can be selected.

Furthermore, the scaling for voltage and current can be defined either manually or automatically. The option “Show Measured Values” adds digital values of basic power parameters for each phase on both the right and left sides of the vector scope. The option “Tick Count” defines the number of circles to be displayed.

• Upper, CW – zero at the top, positive phase angle to the right

• Right, CW – zero at the right, positive phase angle to the right

• Upper, CCW – zero at the top, positive phase angle to the left

• Right, CCW – zero at the right, positive phase angle to the left

Harmonic FFT

In the power module, harmonics can be calculated for apparent power, active power, and reactive power for each individual harmonic. But is it really necessary to calculate the harmonics?

In theory, voltage and current follow a perfect 50 Hz (or 60 Hz) sine wave. This is the case when only linear loads (Ohmic) are connected to the grid (e.g., incandescent light bulbs). However, as more non-linear loads are connected (e.g., ballast units, inverters), and with certain generation units such as wind and PV systems also being non-linear, the voltage waveform is no longer an ideal sine wave.

The images below illustrate this difference:

• Left: The voltage and current of an incandescent light bulb, where the current waveform (blue) is sinusoidal.

• Right: The voltage and current of an LED, where the current waveform (red) appears as pulses with a high crest factor.

The following Harmonic FFTs illustrate the significant differences between the two loads (current harmonics):

In an AC motor, the first harmonic (line frequency) drives the motor. The remaining harmonics produce vibrations and noise. In practice, some harmonics are more harmful than others:

• 2nd, 5th, 8th… harmonics – especially harmful, as they brake the motor.

• 3rd, 6th, 9th… harmonics – can either drive or brake the motor.

• 4th, 7th, 10th… harmonics – drive the motor but also generate significant noise and vibrations.

In the Harmonic FFT, the following parameters can be visualized, each fully synchronized to the fundamental frequency:

• Voltage

• Current

• Active power

• Reactive power

• Line voltage

• Show Data Panel – Displays the power values of each harmonic in the top-right corner of the FFT. Individual harmonic values can be viewed by clicking on the order number.

• Y-Axis – Harmonics can be displayed on a linear or logarithmic scale, and values can be shown either in absolute terms or as percentages relative to the fundamental frequency.

• Draw Full FFT – Shows all frequencies, not only multiples of the fundamental frequency (as seen in the Line Voltage FFT image).

More details about harmonics and full FFT analysis are covered in the Power Quality Pro Training.

All common configuration setups are available in the DewesoftX power module. However, in E-Mobility applications, configurations for 6-, 7-, 9-, or even 12-phase motors are sometimes required. The reasons for this include lowering the voltage level or reducing stress on components.

With conventional power analyzers, performing a comprehensive analysis of such motors is not possible. In contrast, with Dewesoft’s modular hardware systems combined with its powerful software, these applications can be handled without difficulty.

For example, a 6-phase motor can be measured by using six single-phase power modules and calculating the total power in the power module.

This application demonstrates the power and flexibility of the Dewesoft Power Analyzer.

If the computer used for measurements does not have sufficient computing power to calculate all available parameters, the following tips can help optimize performance:

• Acquisition Rate – The acquisition rate should be set to match the respective application. In many cases, lowering the acquisition rate does not affect measurement results. For inverter measurements, the sampling rate should be 10–20 times the switching frequency.

• Calculation Rate in the Power Module – Lowering the calculation rate often does not affect power calculation accuracy. The advantage of this, compared to lowering the acquisition rate, is that the analog signal remains available. If the data is stored with the “Always Fast” option, the power module can be recalculated after the measurement using the full sampling rate.

• Post-Processing – In Offline Mode, the power module is already present, or when recording raw data, additional power modules can be added and calculated later in Analyze Mode.

• Downsizing – Deselect options and channels (analog, math, power) that are not needed for the measurement. Some options in the power module are very performance-intensive, especially: Harmonic Smoothing Filter, Flicker, and Period Values. In the Math module, Filters, Statistics, FFT, and formulas with cosine and sine calculations also require significant CPU power.