What is Power Analysis and Electrical Power Measurement With Power Analyzer
By: Dewesoft Test
Tags: Electric Vehicles, Power, Energy, Power Analysis, Electricity

In this article, we will look into what is power analysis and the tools that are used to perform it. In this article you will:

See what is electrical power really is

what is electrical power really is Learn why we need power analysis and how it is calculated

why we need power analysis and how it is calculated Understand how power analysis is performed, and what is a power analyzer.

Are you ready to get started? Let’s go!

Jump to a section

What is Power Analysis?

What is a Power Analyzer?

What is Electrical Power

Quantifying Electrical Power

How Do We Calculate Electrical Power?

Understanding Power Measurement

Power vs. Energy — What’s the Difference?

Why Do We Measure Power?

What do Power Analyzers Do?

The Dewesoft Power Analyzers

Power Analyzer with Built-in FFT Analyzer

Multi-Phase Power Analyzers

Sensor Database Improves Current and Voltage Measurement Accuracy

The SIRIUS XHS — Next-generation Power Analyzer

Measuring Current with Dewesoft

SIRIUS XHS-PWR for Testing Hybrid and Electric Vehicles

Compatible Current Transformers

More Information

What is Power Analysis?

Power is the rate of doing work, i.e., the amount of energy consumed per unit of time. The power of an electrical system is the multiplication of the voltage with the current, integrated over and then divided through the periodic time. The periodic time (equals the frequency) must be known in order to calculate the power of an electrical system. “Power analysis” is simply the method by which power is tested and studied, typically using a power analyzer.

What is a Power Analyzer?

A power analyzer is an instrument that measures and quantifies the rate of power flow in electrical systems. Power flow is expressed in Joules/second (J/s) or kilowatt-hours (kW/h). Electrical power is the rate per unit of time that electrical energy is transferred in an electrical system between two points.

SIRIUS XHS Power Analyzer with 4x high-voltage and 3x low-voltage amplifiers for current transducer connection

Check out Dewesoft’s flexible and powerful precision Power Analyzer

What Is Electrical Power

You can look at an electric circuit, but you cannot see if the voltage is present or if a current is flowing. You must not reach out your hand to find out, because this is extremely dangerous and possibly even lethal. Therefore we must use the correct instrument to measure electricity.

So how can we visualize how electricity moves in a circuit? Well, we can see the water moving, so let’s use an analogy to explain how electrical circuits work. It is a well-known fact that if the water is to flow out of a pipe, the water needs to have a force or “pressure” pushing it, either from gravity or a mechanical pump.

Electrical Circuit Diagram Compared to a Water Pump

In our analogy:

Voltage is the pump that pushes the water through the pipe. This is measured in volts (V).

The current is the diameter of the pipe. Bigger diameter pipes allow more water to flow through, right?, This is measured in amperes (A).

Resistance is an obstruction inside the pipe that interferes with the flow of water. This is measured in ohms (R or Ω).

If the current is moving only in one direction, it is very much like water flowing through a pipe or hose. This is DC (direct current) in our analogy. However, if the current moves back and forth, then it is analogous to AC (alternating current).

AC power is what we use to send electricity long distances, from the power plant to our homes and businesses, for example. DC power is used for modern electronics as well as batteries.

The office computer you might be reading this on, for example, plugs into AC power, but it has a transformer inside that converts AC to DC power. If you’re using a notebook computer, that transformer is probably located in the external “brick” that connects between the AC outlet on the wall and the DC power system inside the notebook. If you’re reading this on a phone or tablet, it is also a DC device that uses an external AC/DC transformer to charge its internal battery.

Quantifying Electrical Power

In physics, electric power is the rate of doing work. It is equivalent to the amount of energy consumed per unit of time. The unit for power is Joule per second (J/s), also known as Watt (W).

What is Electrical Power

Electrical power is the rate per unit of time that electrical energy is transferred in an electrical system between two points. The first law of thermodynamics states that energy cannot be created or destroyed. It can merely change from one type of energy to another, or be transferred.

Since no electrical system can be ideal or perfect, there will always be some loss when there is a transfer of energy. The most common form of loss within an electrical system is heat. If a circuit is physically warm, that means that some of the energy that it is carrying is being transferred into heat, and therefore wasted.

This decreases the efficiency of the overall electrical system. It is not a coincidence that mechanical systems also generate heat — don’t put your hand on a lit incandescent bulb, or you will directly experience the energy lost to heat conversion. Electrical power is just an extension of the basic physics of power in general.

Electric power is expressed in kilowatts (kW).

How Do We Calculate Electrical Power?

The amount of power in a circuit is calculated by multiplying the Voltage (V) with the Current (A) which yields Watt (W), using the following equation:

P(t)=V(t) I(t)

This basic equation can be transformed using ohm’s law, which states that the current flowing through a linear resistance is directly proportional to the voltage and inversely proportional to the resistance of an electrical circuit at a constant temperature. Ohm’s law can be written in several ways:

V=IR

P=VI

P=I2R

P =V2/R

But ohm’s law is only true for direct current (DC), where the flow of voltage and current is constant.

But with alternating current (AC), the ohm’s law equations will yield the power at only one instant in time. So we need a different method of measuring AC.

We need an equation that accurately describes electrical power if we want to analyze its characteristics. Luckily, there is such an equation:

Where:

P is power in Watt (W)

is power in Watt (W) i is current in Ampere (A)

is current in Ampere (A) u is the voltage in Volt (V)

is the voltage in Volt (V) T is the periodic time in seconds (s)

Let’s visualize this equation on a graph:

Power calculation equation visualized on a cartesian plane showing the voltage and current, and the resulting power curve after integration.

Looking at the curvature of the waveforms in the visualization we can see that the power in an AC system is not just voltage multiplied with current as in a DC system. It is defined by the time average of the instantaneous power over one cycle. This means that we must know the frequency in order to calculate the power of an electrical system.

Understanding Power Measurement

Principally there are three types of power in alternating current (AC) electrical systems to be measured. These are:

Active power (P) Reactive power (Q) Apparent power (S)

To illustrate the relationship between them there is a handy tool that we can use, known as the power triangle, based on the Pythagorean Theorem:

Power triangle, illustrating the relationship between active, reactive, and apparent power, including the angle phi and the power factor, also known as cosine phi (cos phi)

Let’s look deeper into these terms and what they really mean:

What is Active power (P)

Active power (P) also known as “real power,” is the useful power that is used within the AC circuit.

What Is Reactive power (Q)

Reactive power (Q) is not used but is transported between the source such as a power station and the load, it is mainly used to transport the active power through the electrical system.

What is Apparent power (S)

Apparent power (S) is the vector sum of active and reactive power in an AC power system.

What is the power factor (PF)

Power factor (PF) is the ratio between active and reactive power and can take on values between 1 and -1.

The power factor is an indication of the amount of active power that is present in the transmission line compared to the apparent power that combines both the active and reactive power. In other words, it is the amount by which the power in the transmission line is less than the maximum power theoretically possible. Reductions in the theoretically ideal power factor are caused by the voltage and current being out of phase.

Power factor is often written as “cos phi,” “cosine phi” or “cos 𝜑.”

Reactive power can also be positive or negative, as indicated by the positive or negative sign of angle phi (𝜑). This tells us if the current is leading the voltage, or if it is lagging behind the voltage in the transmission line.

When the reactive power value is positive it is lagging, indicating an inductive load that is consuming reactive power.

When the reactive power value is negative it is leading, indicating a capacitive load that is delivering reactive power.

Pure ohmic loads, like traditional incandescent light bulbs, have a power factor of very close to 1. This means that voltage and current are in phase, so there is very little reactive power in the transmission line.

With positive power factors, the closer they get to zero, the larger the phase difference between voltage and current, and the more reactive power is present in the transmission line. This is similar to the negative power factor, just in the opposite direction: at PF = -1 the phase difference between voltage and current is 180°.

Power vs. Energy — What’s the Difference?

The terms “electric energy” and “electric power” are not interchangeable, because they are not the same thing. Using our water analogy, it’s easy to illustrate this difference:

Power means capacity while energy represents delivery over time.

Power is essentially the flow rate of water in the hose, based on its pressure and diameter. Electric power is measured in watts (W), kilowatts, and megawatts (MW).

Energy is the amount of water that comes through the hose over a period of time. That’s why your electric bill will be given in kilowatt-hours (kWh).

Check out Dewesoft Power and Energy Measurement Solutions

Why Do We Measure Power?

In the words of the world-renowned management consultant Peter Drucker: “If you can’t measure it you can’t manage it”.

Measuring voltage and current is only the initial step to analyzing an electrical system, and can easily be done with any power analyzer or power meter on the market.

But in order to manage something successfully, one needs as much information as possible. This is exactly what a power analyzer is designed to do. Power analyzers make it easy for the user to perform complex analysis of any electrical system with only a few operations.

As electricity and power become more and more important, it is critical that it can be measured and managed to the highest standards possible to ensure that the supply continues and that the equipment that operates using it is reliable, safe, and efficient. From energy production itself to the transmission phase that brings it to our homes and businesses, power analyzers are critical to making accurate and comprehensive measurements.

Measuring power to the highest possible level of precision is important for various reasons:

For R&D to increase the performance of products and services

To increase energy efficiency

Reducing cost and time consumption

Compliance with national and international standards

Ensuring the safety of products and operators

What do Power Analyzers Do?

Power analyzers conduct a wide range of tests and measurements on electrical components, circuits, and systems. Some of the most common analyses that are done include:

Load Flow Analysis is used to establish the components of a power system which include voltage magnitude, current magnitude, the phase angle phi of the system, active power, reactive power, apparent power, and the power factor in a steady-state operation.

Additionally, for non-linear loads, distortion reactive power as well as harmonic reactive power need to be measured and analyzed. In theory, voltage and current have a perfect 50 Hz sine wave in Europe (and 60 Hz mostly in North and South America). This is the case if there are only pure ohmic linear loads connected to the grid (e.g. incandescent light bulbs, electrical heaters, AC electromotors, etc.).

The power triangle that is shown previously is true for ohmic loads, but currently, there are more and more non-linear loads as well as production connected to the grid. This has introduced a new dimension into the power triangle namely distortion and harmonic reactive power. These phenomena are covered in the separate What is power quality article.

Let’s take a look at the new power triangle:

The new power triangle illustrates the relationship between active, reactive, and apparent power, including the new dimension of distortion and harmonic reactive power

In the example below, the line voltage feeds AC power into the system, and the switching rectifier converts it to the DC power that the LED requires. Take a look at the schematic diagram of the measurement set-up:

Schematic diagram of a LED testing power measurement set-up with both the AC and the DC voltage and current waveforms measured with the power module from Dewesoft

Currently, there are more and more nonlinear loads (ballast units, rectifiers, inverters, personal computers, etc.) connected to the grid, as well as nonlinear generation units (wind, solar, and other forms of energy). Therefore, the waveforms of voltage and current are distorted and not ideal sinusoidal waveforms. Therefore, harmonic analysis is necessary to determine the effects that these nonlinear loads have on the current and voltage in an electrical system.

Short circuit analysis is done to provide information on all the possible operating scenarios of the electrical system and to ascertain the capacity of individual components in the system to interfere with or withstand the magnitude of the current in the circuit.

Coordination analysis is used to support the development of overcurrent protection. It takes into consideration the characteristics of the protection device, including its sizing and settings, in order to establish the ideal operating range.

Dewesoft Power Analyzers

Dewesoft Power Analyzers are not only the smallest power analyzers in the world, but they’re also the most powerful ones. The flexible hardware platform combined with powerful software features gives unique testing possibilities for any kind of electrical measurement. Dewesoft power analyzers can calculate more than 100 power parameters, such as P, Q, S, PF, cos phi, and many others.

It also offers several features of other instruments:

Raw data recording capabilities

Oscilloscope

FFT analysis

Harmonics

etc.

All these calculations can be done online in real-time, in post-processing, or both.

The Dewesoft Power analyzer combines multiple instruments and functionalities in a single device — power analyzer, FFT analyzer, RAW data recorder, oscilloscope, harmonics analyzer, temperature recorder, vibration recorder, and many more.

The Dewesoft power analyzer can be equipped with up to 64 high-speed analog inputs (up to 15 MS/s @ 16-bit and 5 MHz bandwidth per channel) for voltage and current measurement in a single box.

The Dewesoft R8DB power analyzer is capable of 32 high voltage and 32 current channel in a single box with RAW data storing and real-time power analysis

The inputs are fully isolated both on the sensor side (channel to the ground), as well as channel-to-channel, and even isolated sensor excitation. Real galvanic isolation means less noise, ground loop avoidance, and superior signal quality.

High voltage inputs are measured directly with 1600 V DC/CAT II 1000 V/CAT III 600 V protection. Current can be measured with high-accuracy current sensors, like zero-flux current transducers, AC/DC current clamps, Rogowsky coils, and shunts.

Dewesoft provides a broad range of current transducers and currents sensors for any current measurement range and accuracy

And while it is mainly a power analyzer, it can also measure additional and different signal types, including accelerometers, strain gage, force and load sensors, thermocouples, RTDs, counters and encoders, GPS, CAN BUS, XCP, FlexRay, and even video. All channels are synchronized with each other.

Typical phase delta measurement screen from DewesoftX power analysis software

The SIRIUS XHS — Next-generation Power Analyzer

The SIRIUS XHS power analyzer is the latest version of the SIRIUS line. It is a high-speed data acquisition system capable of recording each of its eight analog inputs up to 15 MS/s/ch with up to 5 MHz bandwidth.

The SIRIUS XHS shown with four HV amplifiers and four LV amplifiers

It features an all-new HybridADC technology that is capable of high-bandwidth transient recording and very high-dynamic, alias-free data acquisition. Alias-free filtering allows the acquisition of signals with up to 160 dB dynamic range. High channel-to-channel and channel-to-ground isolation prevents damage to the systems from excessive voltage and avoids ground loops.

In most power applications, the SIRIUS XHS is configured with four each of the high voltage (HV) and low-voltage (LV) amplifiers:

SIRIUS XHS HV : Highly isolated CAT II 1000V high voltage input. This amplifier can measure ranges from 20 V to 2000 V peak directly, with 5 MHz bandwidth and an accuracy of 0.03%. This amplifier is ideal for the direct connection of high voltage signals. The connectors of this amplifier are always insulated safety banana jacks (red/black).

: Highly isolated CAT II 1000V input. This amplifier can measure ranges from 20 V to 2000 V peak directly, with 5 MHz bandwidth and an accuracy of 0.03%. This amplifier is ideal for the direct connection of high voltage signals. The connectors of this amplifier are always insulated safety banana jacks (red/black). SIRIUS XHS LV: Highly isolated low voltage input. This amplifier can measure ranges from 0.05 V to 100 V, with a 5 MHz bandwidth, an accuracy of 0.03%, and excitation for selected sensors (requires DSUB9 connector for sensor excitation). This amplifier is ideal for the direct connection of low voltage signals and current transducers. The connectors of this amplifier are available in several types: Insulated safety banana jacks (blue/black), DSUB9, or BNC. Note that the DSUB9 connector also offers sensor excitation as well as TEDS for smart sensor setup.

When the DSUB9 connector is used, this amplifier also accepts DSI series smart interface adapters, allowing other kinds of sensors to be connected to each LV channel. These include:

DSI-ACC for IEPE accelerometers and microphones

DSI-CHG for charge type accelerometers

DSI-RTD for RTD temperature sensors

DSI-TH for thermocouples (J, K, T, etc.)

DSI-LVDT for LVDT displacement/distance sensors

When any DSI model is connected to an LV channel, Dewesoft X data acquisition software automatically detects it (using TEDS sensor standard), and configures that channel for it, setting the input type, gain, range, and scaling to be appropriate. The user can make further settings, and save them into the on-board sensor database.

Noise floor, common-mode rejection, gain and offset drifts of both amplifiers at lower bandwidth are comparable to the standard DualCoreADC SIRIUS line of instruments.

These amplifiers are perfect for e-mobility measurements, where the highest precision such as power analysis is an absolute necessity.

Learn more about Dewesoft and how to use TEDS sensor technology:

Dewesoft Online PRO Training: Voltage measurement

Voltage Measurement in Data Acquisition Applications

Power Analyzer with Built-in FFT Analyzer

Conventional power analyzers use zero-point detection to determine the periodic time. This means that they evaluate when the voltage or current crosses that x-axis and use that value to calculate the periodic time.

Based on this predetermined period time, an FFT analysis of voltage and current can be done for a definable number of periods (typically 10, if the system’s base frequency is 50 Hz), and at a selectable sample rate. The FFT analysis yields an amplitude for the voltage, current, and the cos phi for each harmonic.

The Dewesoft power module has a built-in FFT analyzer in addition to the other display types

Multi-Phase Power Analyzers

In the Dewesoft X power module, there are several predefined system configurations available for you to choose from. The most common ones are:

direct current,

1-phase

2-phase — is used, e.g. with special types of motors

3-phase star

3-phase delta

Aron and V configuration is basically star and delta configurations but measuring only two currents instead of three. This is normally done as a space-saving or cost reduction measure.

Special configurations such as 6-, 7-, 9- or 12 phase motor measurement can be done with multiple single-phase or 3-phase systems and adding up the power values in the Math library. This means that power can be measured at multiple points completely synchronous.

In the math library, the power modules can be further refined, for example, the efficiency can be calculated automatically. This is also very helpful when measuring multi-phase motors (6 to 12 phases).

The Dewesoft power module can be configured for 1, 2, and 3-phase systems. These can be combined to create 6, 7. 9 or even 12-phase systems

Engineers can simply select one or more of the systems that they are measuring from this list:

1-Phase

2-Phase

3-Phase star

3-Phase delta

3-phase Aron

3-phase V

3-phase 2-meters

In addition, a wide range of other choices is available, including the line frequency, output units, frequency source (the channel to be evaluated to determine the exact frequency), phase, and more.

Due to the modular design of Dewesoft measurement devices, the user is never limited to only measuring power values. Dewesoft DAQ systems can connect to virtually every sensor in the world, which means that the engineer can also measure temperature, force, vibration, sound, GPS location, video, speed, RPM, torque, etc.

The Dewesoft power analyzer wiring schematic for testing inverter and electric motors

Engineers performing tests on electric or hybrid vehicles may also want to measure the speed of the car, the battery temperature, CAN bus data, GPS position, and even plot its exact location on a test track.

Instead of using two, three, or even more different measuring instruments, Dewesoft offers all measurements to be recorded simultaneously within a single instrument. This brings several key advantages:

No need to merge the data together manually after the test.

Data is completely synchronized down to a single sample.

All the data can be viewed on one screen and written to one data file.

Configuring and using only one DAQ system and software spares a lot of test preparation time.

Dewesoft Power Analyzer Explained Live at the Battery Show Expo

Sensor Database Improves Current and Voltage Measurement Accuracy

It should be noted that every amplifier, current, and voltage transducer has some kind of inaccuracy or non-linearity. However, in Dewesoft power analyzers, these errors can be measured ahead of time and entered into an XML sensor database. Dewesoft X software applies correction factors in real-time, resulting in more accurate readings and results.

The Dewesoft analog sensor database

The built-in sensor database also eliminates errors caused by manual data entry mistakes. Selecting a transducer from the list rather than entering the parameters manually not only saves time, but it prevents typographical errors which can lead to wrong scaling or gain selections.

Inside the sensor database, scaling can be set up using y=mx+b formulas, look-up tables, polynomials, and even transfer curves. This only has to be done one time for most sensors. Engineers can add, edit and delete sensors, and update their calibration information at any time, including CAL due dates, etc.

The sensor database’s units are based on and derived from the seven international SI unit “defining constants”:

Length — meter (m)

Time — second (s)

Amount of substance — mole (mole)

Electric current — ampere (A)

Temperature — kelvin (K)

Luminous intensity — candela (cd)

Mass — kilogram (kg)

So while they are metric at their core, such as m/s2, for example, the user is free to select G or g, in this case. Therefore the output engineering units can be comfortable for all users worldwide.

Dewesoft software also includes sensor databases for counter/encoder/RPM sensors.

Learn more about Dewesoft and how to use TEDS sensor technology:

Dewesoft X Sensor Database Manual

Analog and Digital Counter Sensor Database Online PRO Training

Measuring Current with Dewesoft

Current measurement is usually divided into two major groups:

Direct

Indirect

“Direct” — is when the conductor must be disconnected and a sensor is connected in series with the circuit. This method works without any additional circuits.

The most common direct current measurement device is a shunt resistor, which is then connected in series with the circuit. A shunt resistor has a very low resistance which has been very accurately determined by the manufacturer. A shunt resistor works on the principle that when the current flows through this resistor, there will be a very small voltage drop that we can measure and convert to current using ohm’s law.

Typical shunt current measurement hook-up

We can measure this drop and apply Ohm’s law to calculate the current.

Graphical representation of Ohm’s Law

In addition, the accuracy of the resistor is an important factor, since this directly affects the accuracy of the measurement itself.

Dewesoft DSIi-10A Current Shunt

Dewesoft offers several compact size current shunts, each designed with a different resistor inside, intended to measure different current ranges. These shunts have been engineered to have the least possible effect on the circuit itself.

DSI adapters can be plugged into virtually all Dewesoft data acquisition devices. The isolated analog inputs of Dewesoft amplifiers is an important factor in ensuring accurate measurements, since the shunt is connected directly to the circuit being measured, and isolation between the circuit and the measuring system is always important. Isolated inputs mean that you can place your shunt on the low-side or high-side of the circuit, and not worry about a ground loop or common-mode measuring errors.

Considering Ohm’s law again and the interlocking nature of voltage, current, and resistance, it is absolutely clear that a DAQ system must be able to make a very accurate voltage measurement and resistance measurement in order to make an accurate current measurement.

“Indirect” — is when the current sensor does not make contact with the circuit directly. Instead, it measures the magnetic field that is induced when current flows through a conductor and then converts it to a current reading (Electric charges produce electric fields).

The advantage of indirect current measurement is galvanic isolation of the sensor from the conductor and the fact that the circuit itself does not have to be disturbed or disconnected. It also allows very high currents to be measured.

Dewesoft supports nearly all of the current transducers available on the market today. Some of the current transducers can be powered directly from the measurement device and some current transducers require an external power supply, as the amount of excitation power that they need cannot be delivered by the measurement device.

Dewesoft has a solution for this: SIRIUS PWR-MCTS2 is a power supply unit for powering these current transducers directly from Dewesoft instruments without any external power supply. SIRIUS PWR-MCTS2 can be built as compatible SIRIUS or SIRIUS XHS modular chassis or directly into a SIRIUS-based rack chassis such as R1DB, R2DB, R3, R4, or R8 data acquisition system.

SIRIUS models with integrated MCTS2 current transducer power supply

Learn more about Dewesoft and how to use TEDS sensor technology:

Dewesoft Online PRO Training: Current measurement

How To Measure Current Using Current Sensors

SIRIUS XHS-PWR for Testing Hybrid and Electric Vehicles

Another innovation is the SIRIUS XHS-PWR, a new version of the classic SIRIUS DAQ system dedicated to testing hybrid and electric vehicles. It features a patented DC-CT current transducer technology that allows very precise current measurements, even in the most demanding applications, such as very high current peaks as well as leakage current testing.

The SIRIUS XHS-PWR with integrated DC-CT current transducer

This new instrument is perfect for e-mobility measurements, where the highest precision such as power analysis is an absolute necessity. The current transducer uses patented DC-CT® technology based on the Platiše Flux Sensor. It offers ranges of 100A, 500A, and 1000A, packed into a very small chassis, 1 MHz bandwidth, immunity to external magnetic fields, low offsets, and excellent linearity.

Typical in-vehicle power test, showing additional inputs like CAN bus, video camera, and real-time GPS position superimposed over a map

The amplifiers can also measure voltage 2000V peak (CAT II 1000V) with up to 5 MHz bandwidth

The SIRIUS XHS-PWR

This instrument has two inputs:

1xHV (high voltage) and

and 1xHA (high current) with DC-CT current transducer.

These inputs connect directly to the power line of the vehicle, for the ultimate in e-mobility testing convenience, bandwidth, and accuracy. It offers an IP65 degree of protection which allows the usage in harsh environments and during rough drives.

Comparison table of DC-CT current transducer versus other current sensor types:

Compatible Current Transformers

Below is a table that gives a short overview of the current transducers that are available and which characteristics these transducers possess, as well as for which applications they are best suited.

Overview of current transducers and their application areas

Dewesoft designs and produces world-renowned measurement and data acquisition equipment for a wide range of industries and applications. A focus since the early 2000s has been power analysis and power quality analysis.

Little did we know back then that automobiles would be turning electric at such a rapid pace as they are today. And that’s just one application where portable, high-performance power analyzers and power quality analyzer measuring instruments are essential.

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