28.07.2023
In this article, we will look at what "power analysis" is and the tools used to implement it. In this article, you will:
See what electrical power really is
Find out why we need to analyze the capacity and how to calculate it
Understand how power analysis is measured with a power analyzer
Ready to get started? Let's go!
What is Power Analysis?
Power is the rate of doing work, i.e., the 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 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-per-hour (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 amplifier and 3x low voltage amplifier for connecting current converter
What is electricity?
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 electricity moving through a circuit? Well, we can see the water moving, so let’s use it as 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.
Diagram of an electrical circuit compared to a water pump
In our analogy:
Voltage is the pressure that forces the water through the pipe. The higher the pressure the faster the water will flow. This is measured in volts (V).
The current is the available volume for the water to flow in. The larger the volume the more water can flow. This is measured in amperes (A).
Resistance is volume reduction inside the pipe that restricts 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).
The office computer you might be reading this on, for example, plugs into AC power, but it has a type transformer inside known as a switched-mode power supply (SMPS) that converts AC to DC power and converts the DC voltage to the desired level. If you’re using a notebook computer, the SMPS is likely located in the external “brick” that connects 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 SMPS to charge its internal battery.
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).
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 be converted from one type of energy to another, or be transferred.
Since no ideal electrical system exists, there will always be some losses 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 converted into heat, and therefore cannot be used to do useful work.
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 conversion to heat. Electrical power is just an extension of the basic physics of power in general.
Conventionally electric power is expressed in kilowatts (kW).
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 applied power, reactive power, and apparent power, including phi angle and power factor, also known as cosine phi (cos phi)
Let's dig deeper into these terms and what they actually mean:
Active power (P) also known as “real power” or “active power” is the useful power that is used within the AC circuit.
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.
Apparent power (S) is the vector sum of active and reactive power in an AC power system.
The power factor (PF) is the ratio between active and apparent 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 factor by which the useful 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.
The Power factor is often denoted as “cos phi,” “cosine phi” or “cos 𝜑.”
Reactive power can be positive or negative, indicated by the positive or negative sign of the 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 very close to 1. This means that voltage and current are in phase, so there is very little reactive power present 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°.
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 analyses 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
Measuring power at the highest possible level of accuracy is important for several reasons:
For R&D to increase the performance of products and services
To increase energy efficiency
Reduce costs and consumption time
Compliance with national and international standards
Ensure product and operator safety
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 was shown previously only holds true for ohmic loads, but currently, there are more and more non-linear loads as well as non-linear production units connected to the grid. This has introduced a new dimension into the power triangle namely distortion and harmonic reactive power.
In the example below, the AC power line voltage feeds into the system and the switching rectifier converts it to the DC power required by the LEDs. Let's look at the schematic diagram of the measurement setup:
LED test power measurement setup diagram with both AC and DC voltage and current waveform measured by 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 generation). 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 Energy Analyzer
The Dewesoft Power Analyzers are not only the smallest power analyzers in the world, but it’s also the most powerful ones. The flexible hardware platform combined with powerful software features gives unique testing possibilities for any kind of electrical measurement. The Dewesoft power analyzer 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 devices and functions in a single device – power analyzer, FFT analyzer, RAW data recorder, oscilloscope, harmonic analyzer, temperature recorder, vibration recorder, etc.
The Dewesoft R8 power analyzer can be equipped with up to 64 high-speed analog inputs (up to 1 MS/s @ 16-bit bandwidth and 2 MHz per channel) to measure voltage and current in a single box.
The Dewesoft R8DB power analyzer can be configured with 64 channels, selectable to suit the measurement application for all-in-one metrology equipment
The inputs are completely isolated on both the sensor side (grounding channel), as well as the excitation between channels and even the isolation sensor. True electrical isolation means less interference, avoidance of grounding loops, and superior signal quality.
The high voltage can be measured directly by our high voltage input with protection of 1600 V DC/CAT II 1000 V/CAT III 600 V. The current can be measured by high-precision current sensors, such as Zero-flux current sensors, AC/DC current clamp, Rogowsky coil and Shunt resistor.
Dewesoft offers a wide range of current sensors and current sensors for any current measurement range and accuracy
And although it is primarily a power analyzer, it can also measure various types of additional signals, including accelerometers, strain gauges, force and load sensors, thermocouples, RTDs, counters and encoders, GPS, CAN BUS, XCP, FlexRay and even videos. All channels are synchronized with each other.
Typical 3-phase delta measurement monitor from Dewesoft power analysis software
Power analyzer with built-in FFT analyzer
Conventional power analyzers use zero point detection to determine periodic timing. This means that they evaluate when a voltage or current passes through that x-axis and use that value to calculate periodic timing.
On the other hand, Dewesoft uses a special FFT (Fast Fourier Transform) algorithm to determine the periodic time (frequency).
Based on this predetermined time period, it is possible to perform an FFT analysis of voltage and current over a number of identifiable intervals (
The Dewesoft power module has a built-in FFT analyzer in addition to other types of visualizations
Due to the modular design of Dewesoft measuring devices, users are never limited to measuring only power values. Dewesoft DAQ systems can connect to almost any sensor in the world, which means engineers can also measure temperature, force, vibration, audio, GPS, video, speed, RPM, torque, etc.
Engineers performing tests on electric or hybrid vehicles may also want to measure the car's speed, battery temperature, CAN bus data and GPS location, and even plot its exact location on the 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 measurement.
Data is completely synchronized down to a single sample.
All the data can be viewed on one screen and written into one data file.
Configuring and using only one DAQ system and software saves a lot of test preparation time.