Power Quality Analysers for Testing Single and Three Phase Power Systems

Power quality problems are estimated to cost industry an estimated $xxxx per year. Varying loads are connected to modern electrical networks and these, along with power quality faults can have wide reaching effects on electrical systems. The whole purpose of the electrical system is to support the loads connected to it and when it fails to do that properly, devices can trip, cabling and infrastructure can overheat and cause major failures to the electrical network, due to the inability to support the load.

When this type of failure exists, then power quality is something that should be looked at as a potential underlying cause of the problem. Modern electrical systems carry a multitude of loads, and due to the critical operation of these networks, power quality analysis is becoming a big business, due to it’s overall importance in today’s industry and processes.

With so many different models of power quality analysers available, the problem for the end user is differentiating between the various functions and specifications. Like many instruments, there is a wide range of prices, all reflected in the functionality and capability of the power quality analyser. This in itself can be daunting enough to anyone who is not used to dealing with this type of equipment, and coupled with the fact that the analyser has to measure numerous power quality parameters, and then the user has to interpret the readings, it becomes a relatively difficult procedure, when compared to say taking a one off measurement with a clamp meter or a multimeter.

However, when all is said and done, power analysis requires some straightforward knowledge of power distribution systems, and some understanding of the effects of the power quality issues on the electrical system. It does not have to be a long, drawn out process as modern power quality analysers reduce the user’s involvement to setting up of the basic functions, (such as the recording period, type of electrical system etc.), installing the power quality analyser into a switchboard (or wherever the point of measurement is), connecting it and then finally after the recording is complete, downloading the data, analyzing it and presenting the findings to the appropriate person in the process.

Even the most basic power quality anlaysers are capable of monitoring a heap of power quality parameters. The vast majority of even the cheaper analysers can monitor and record voltage, current, power (active, reactive and apparent), energy consumption, power factor, phase angle, and at least some form of harmonics – most will be able to measure harmonics to 50^th order. The more expensive power quality analysers can offer more advanced features, such as true inrush current, flicker (short and long term) and can store various events and alarms, but that will get covered later on. For now, it is important to understand the difference between the different power quality analysers and meters, and to understand what each one is capable of before deciding on an investment.

In many cases, the end user can be confused by the different parameters which can be recorded in modern power systems and as a result, the whole process is transformed from what should be a relatively straightforward process, into a myriad of technical terms and processes, so hopefully, this article aims to shed some light on the whole thing and help to gain some understanding of the different features, and more to the point, the pertinent differences from one power analyser to the next. With the average cost of a professional level power quality meter ranging from under $3,000 up to over $10,000, and a wide range of products available, it’s easy to see why selection of a suitable product, and understanding it’s capabilities can be such a daunting task, when it really doesn’t need to be.

So, let’s take a look at the various functions and parameters that can be measured

A basic power quality analyser, would normally be able to measure voltage, current and power consumption, but in reality even the cheapest power meters can measure more than that, with power factor, energy consumption (which is not exactly the same as power consumption) and a few other things on top of that.

Voltage and Current are a pre-requisite to power measurements, in other words without measuring both of these, the power quality analyser can’t calculate any power functions. Once we measure voltage and current simultaneously, we now have a range of power information available.

Nearly all power quality analysers will record apparent power, active power and reactive power, but it is a poorly understood subject. When most end users think of power, they think of active power, which is what is measured in kW (kilowatts). Active power is the useful part of the equation, in other words, the power that is “used to do useful work”. It is this active power that is consumed by the load, and converted into another form, such as heat or light or movement. Reactive power on the other hand (kVAR) is power that exists in the circuit, oscillating between the source and the load. Reactive power cannot be converted into another form or consumed by the load, but it’s presence is still important in any power system, as it facilitates the transfer of real (active) power through transmission lines and equipment. In a nutshell, reactive power regulates the voltage in an electrical distribution system, and without it, you would have voltage collapse. Although the reactive element plays no direct part in useful work, it is necessary to assist in the transfer of real (active) power. I have heard comparison drawn to the beer glass as in the diagram to explain reactive power, which represents active power as the beer and reactive power as the head on top (in other words the wasted part), but I don’t like this analogy as reactive power has a very real part to play in transmission of power, so I prefer to use the buckets of water scenario as a better representation.

As an example, purely in layman’s terms, imagine that electricity can be represented by buckets of water. At the source, someone picks up two buckets full of water and carries them to the load, and empties the buckets before walking back to the source to refill them and repeating the process continuously. Active power is the water, which is used to perform useful work, the buckets represent reactive power, as they have no direct benefit in performing any work, but they are necessary to transfer the power to the load. The sum of this, is what is called apparent power (measured in VA or KVA) and is the total power. The ratio of the active power to the apparent power (in simplistic terms), or in other words the ratio of the real power used to do work, against total supplied power is what we call power factor. A great deal of emphasis is placed on power factor, as a higher figure is more desirable because the conversion of electricity by the load is more efficient.

Most, but not all power quality analysers are capable of monitoring harmonics. Harmonics are caused by non-linear loads in power systems and are a frequent cause of power quality problems. These harmonics can cause over heating in cables and equipment, as well as problems in variable speed drives and motors. In electrical power systems, harmonics are multiples of fundamental wavelength, so therefore the first order harmonic is that at 50Hz in Australia, second order 100Hz, 3 order is 150Hz and so on. The third order harmonic in particular is responsible for overheating of cables and distribution equipment. Power and utilities companies place a large emphasis on third order neutral harmonics because three phase power, in theory has a phase angle of 120 degrees between the phases, which has advantages such as electromotive torque. In this sort of balanced three phase system, the phases should cancel each other out, and all three phases should be perfectly balanced, however in reality this is seldom, if ever true and so the purpose of the neutral conductor is to carry the unbalance current. Harmonics when present add to the amount of current that the neutral has to carry, and as these harmonics increase, the current required to be carried by the neutral increases, which requires larger conductors due to overheating caused by the extra current. Economically, the neutral conductor is more expensive to install if it is required to be larger, and so power distribution companies pay attention to this quite extensively. Many customers call us and are not interested in recording harmonics, but it plays a big part in power quality issues, and is therefore important to have some understanding of this. Recently one client sent a power quality recording to our office for further advice, because the neutral current on the site they were recording was high – more or less higher than any of the three phases. However, they felt that harmonics was not a particularly important issue and failed to record them. As it turned out, the harmonics were responsible as the recording was done during an event with lots of non-linear loads, such as compressors and motors connected to the network.

The cheaper power quality analysers are, on the whole capable of harmonics recordings, with the exception being the Kyoritsu 6305, which is a power quality meter, designed for simple recording of power, but without advanced analysis. This would be an ideal meter for someone who just wants to record energy consumption and basic power information, such as current, voltage, active power, reactive power, power factor, but without the addition of analyzing harmonics.

Flicker and Inrush tend to be available on most of the mid-range to high end power quality analysers, and again, they are not terms which are particularly well understood. Inrush current is better understood of the two. Basically, start up a motor, or a lighting circuit, and when the start-up, there is a momentary surge of current being drawn by the load. This “spike” of current is known as inrush current and normally will be from several to many times larger than the device’s full load current. Although this inrush current usually exists for just a few cycles, it still has to be taken into account when selecting over current devices and protective devices, as they need to be able to react quickly in the event of a short circuit or overload, but they must not react to the initial inrush current flowing in the circuit, which is generally considered both normal and harmless. Flicker on the other hand is caused by voltage fluctuations, the cause of which are very often related to changing loads in the electrical network. This voltage fluctuation is responsible for high speed flickering of lights, computer monitors and can affect sensitive people in various ways. Additionally, flicker can also affect industrial processes which rely on a constant electricity supply. The likelihood of flicker increases with relation to the size of the load change and the amount of prospective short circuit current available (at the common connection points of the loads). Nevertheless, it is still a very real power quality issue, and is either measured over long term or short term. Long term flicker (Plt) is generally observed over a 2 hour interval, with short term flicker (Pst) observed over a 10 minute interval. The algorithmic scaling differs for each type of flicker, but it would be outside the scope of this article to write a full explanation.

The AEMC PEL-103 is probably the most popular power quality analyser we stock, and outsells all other power quality analysers, mainly because of it’s low price an number of features, which would most likely give it the best performance to cost ratio of any of our power quality analysers. You get a full kit, in a bag, which includes the PEL-103, three flexible current probes, four voltage leads, Dataview software, an SD card and card reader, as well as a power lead to keep the PEL-103 powered up and the back up battery fully charged. The PEL-103 can measure voltage, current, harmonics to 50^th order (7^th order on a high frequency 400Hz network), total harmonic distortion in %, active power, apparent power, reactive power, active, apparent and reactive energy consumption, power factor, crest factor, and a number of other power parameters. AEMC have kept the PEL-103 simple with an easy to read LCD display and thee unit itself is compact, being only 35mm or so thick, and the ruggedised housing also has four strong magnets embedded into it, allowing for fast and easy positioning in metal switchboard cabinets. You can either choose to configure recordings from the Dataview software by just connecting the PEL-103 to a Windows PC or you can set up most functions on the PEL-103 itself. It’s possible to either just start it recording as soon as the button on the front panel of the instrument is pressed, or you can even set the PEL-103 to schedule the start and end of a power quality recording. AEMC provide a number of connection interfaces, including the familiar USB, Bluetooth and even Ethernet. The PEL-103 can be plugged into a LAN, or even a GSM point and monitored remotely from anywhere with a connection. AEMC have also recently made an Android app, known simply as PEL, which allows the PEL-103 to be set up and configured, over it’s Bluetooth connection. It is also possible to connect to the power analyser and view the data in real time, or even download it. The supplied Dataview software allows data to be downloaded from thee PEL-103 and customized reports can be created with graphs and tabulated data for professional presentation of results. The PEL-103 also has a sort of “little brother” in the form of the AEMC PEL-102. It’s physically the same size, but lacks the LCD screen, making set up and configuration possible only from the Dataview software or the Android App. For the sake of only $300-400 or so, the PEL-103 is by far the more popular power meter. There are also some downsides of the PEL series. For instance because of it’s compact size, it only has around 30 minutes of battery back up should the power supply fail. AEMC have added an optional adapter, which can be plugged into the PEL-102 or PEL-103 and allows them to be powered from the switchboard voltage connections.

Going on from there, AEMC recently released the PEL-105 power quality analyser, which is sort of a much enhanced PEL-103. The screen is similar with the same LCD style of display, but it’s housed in a weatherproof case, which is rated to IP68 and also is pole mountable. Additionally, the PEL-105 also has a fourth current sensor, so it is capable of directly measuring neutral current, unlike the PEL-103 which calculates the neutral current, based on the loading, power and harmonics in each of the three phases. Direct measurement of the current and voltage in the neutral will, of course give more accurate results, particularly where harmonics (3rd order neutral harmonics) are concerned. As well as the fourth current sensor, the PEL-105 also has an additional voltage input, so both line to earth and line to neutral voltage can be measured, as well as the phase to phase voltage in a three phase electrical circuit.

The AEMC Dataview software has also received an upgrade for the PEL-105 and offers the user a number of enhanced features, such as the ability to view phasor (or vector) diagrams on the software, and the ability to set up most functions of the PEL-105. Just like the PEL-102 and PEL-103, the PEL-105 can be configured either through the DataView software, through the Android app (via the Bluetooth connection) or via the front panel.

The AEMC PEL-105 is fully phase powered, meaning that although there is a power charger included with it, most of the time this is not used, other than on occasions where you may want to plug it into mains power in the office or when phase power is not available. Whenever the PEL-105 is recording or monitoring in a switchboard, up a pole or somewhere else, then mains power is always going to be available, so all that needs to be done is the current sensors fastened on (these are flexible ones so can just be unclipped and fastened on) and the voltage leads connected. The V1 and N connections will supply the PEL-105 with mains power in order to keep it running and recording, and also the backup battery will be kept charged by these connections.

One thing that the PEL-105 has which is not a feature shared with the PEL-102 and PEL-103 is WiFi, which allows for wireless connection to a mobile device, or even wireless connection to a LAN. With the DataView software, it is even possible to connect multiple PEL units to a building and then monitor them via this link.

Most of the connections are on the front panel, but when the lid is closed on the PEL-105, these connections are not accessible (mains charger input, USB port, Ethernet port, SD card slot). The inputs for the voltage and current sensors are all; in one place at the end of the unit. If the PEL-105 is pole mounted, then these connections will be at the bottom, and once connected and with the lid closed and fastened, the PEL-105 boasts a very high IP68 rating, making it waterproof and dustproof, which is essential for using outdoors, or in harsh environments. Like the PEL-102 and PEL-103, the AEMC PEL-105 can also be remotely monitored, either by connecting it into a LAN (by plugging into an Ethernet point), by WiFi, or even by connecting it to a GSM modem. Sometimes, it is necessary to leave something recording in a remote place, but with this level of connectivity, you can now leave it and remotely access it from somewhere else, as long as there is an internet connection. The PEL-105 has only just been released, so it’s still early to tell, but the indications are there at the moment, that it’s poised to do extremely well in the power quality analyser market, here in Australis, because for the level of features that are available, the price of the PEL-105 is to say the least, extremely competitive.

HT Italia offer a similar unit, but without a screen in the form of the PQA820. Although this is also weatherproof, like the PEL-105 and the AEMC 8435 (more about that one later) the functionality is reduced. It is phase powered, and it has 4 flexible current probes, but the only way to monitor the PQA820 is to connect it to the HTAnalysis app (which works with Android and iOS) and view it in real time. Not having a screen is one of those things, especially with a power quality analyser that you miss a lot if you don’t have it. Most users tend to want to see the screen on the device and be able to scroll through the parameters once it’s recording. The other thing about the PQA820 is that it will only measure up to 1,000A (AC) so if you need to go higher than this, you need a different power analyser.

HT also make the VEGA78, the PQA823 and the PQA824 power quality analysers. These are more traditional in design, with colour screens, waveform diagrams, vector (phasor) diagrams and so on. In fact, the HT Italia meters can measure most power related things, and the PQA824 is very fast, being able to capture voltage transients to a resolution of 5 micro seconds, but the price is quite high for all of this speed, and the memory is internal with a 15MB limit, although this can be expanded with a Flash Memory Card, rather than the SD cards used by AEMC. The VEGA78 is the cheapest of the three units, and records quite a few parameters, but you will lose out on flicker and inrush current, however the VEGA78 compares with the AEMC PEL-105 on pricing, but for most customers they tend to either look at one of the AEMC high end power quality analysers, such as the AEMC 8336 or AEMC 8435, or go for the PEL-103 and PEL-105 as they have very up to date functionality and a no nonsense, simple to use interface.

For those customers looking at the upper end of the scale, and preferring a power quality analyser with a host of more advanced features, the AEMC 8336 tends to be the instrument of choice. Although the AEMC 8333 may be cheaper, like the PEL-103 it does not have a neutral current sensor and calculates it’s neutral current, plus it also has a built in memory, rather than the more flexible removable SD card option, and for most customers looking at the top end of the market, the neutral current sensor and the ability to expand the memory are essential. When you look at the recordings, and more to the point the space that the recording data occupies in terms of the available memory, the harmonics are the one thing that occupy more space within the memory than any other single parameter. Record harmonics and you need a decent size of available memory to cope with it. Most users looking at something like the AEMC 8336 or even the 8435 would not entertain the thought that harmonics is not important, particularly when you consider the impact that harmonics have on the neutral current in a three phase distribution system, and the further impact caused by the neutral carrying too much current, beyond it’s design capabilities.

When you look at something like the AEMC 8336 (the AEMC 8435 is quite similar but in a weatherproof housing with weatherproof sensors and a few differences) then you are getting a very capable, top of the range power quality analyser. The AEMC 8336 has a multitude of features, designed for complete power quality analysis in a range of three phase, split phase and single phase distribution systems. You have four current inputs and five voltage inputs, so direct recording of neutral current and voltage is possible. On top of that the AEMC 8336 has a large colour display with waveform graphs, phasor (vector) diagrams, and various tabulated data. The user can manipulate the display and select different families of data for real time analysis.

The AEMC 8336 also can store searches and record up to 210 transients. The user can also take screen shots and download the data into the supplied DataView software and can set up to 40 types of alarms with up to 7 active ones and another 16,362 recorded. Apart from this, True Inrush current is a feature of the AEMC 8336, which can be RMS + Peak or RMS only as well as full harmonics up to 50^th order. I harmonic mode the AEMC can capture and record both individual harmonics as well as RMS distortion, for both the phases and the neutral individually. Being able to also capture various power functions, including power distortion, active power, reactive power, apparent power, power factor, energy consumption, and all of these can be recorded to IEEE1459 with a setting in the power analyser.

The backup battery in the AEMC 8336 is also very long, allowing the AEMC 8336 to run in recording mode for up to 25 hours (according to the manufacturer), although most of the time the power quality meter will be simply plugged into a socket outlet to keep it mains powered. All of the PowerPad III units (AEMC 8333, 8336, 8435) are advanced level power quality analysers, but saying that, they are still simple to set up and use. The same DataView software program is supplied with all AEMC power quality analysers for downloading the data and compiling customized reports which can be sent to customers either as email attachments, or printed documents.

All AEMC power quality analysers and Kyoritsu power quality analysers are “plug and play” instruments, which effectively means that as soon as you plug a certain type of current probe into it, the meter will recognize the type of current clamp being used and eliminate any mistakes caused by the user not setting the power analyser up correctly.

The Kyoritsu brand of power quality analyser are also a fairly popular instrument. Although they do not have the same level of functionality as the AEMC power analysers, the Kyoritsu 6315 is a very capable meter indeed, but again it comes down to user choice. Kyoritsu is a very well known brand in Australia and to an extent that can equate to more sales, as we find a lot of customers buy on recommendation within the industry, and why wouldn’t they?. Recommendation is the most powerful form of sales lead there is. You see something being used by someone else, or see – for example a power quality report from a certain brand and model of power quality meter, and you are more likely to be pre-disposed to buy that same one.

The Kyoritsu family consists of only 2 models, the Kyoritsu 6305 and the Kyoritsu 6315. Basically, the difference between them is that the Kyoritsu 6305 is classed as a power meter, and offers what must be the most simple user interface on the market. There’s a keypad and a rotary dial and if you turn the rotary dial anti-clockwise as far as it goes, that’s the Off position. Click it to the right and you go to the Set Up function allowing you to configure the recording. Click to the right again and you get the Wiring Check position, so that when the voltage leads and current probes are in place, any incorrect connection is highlighted immediately. Click to the right again and you are in the Demand position. Right next to that is the Start/Stop button which allows for fast and easy recording. The final position allows the data to be checked and downloaded to a PC. Simple as that.

The screen on the Kyoritsu 6305 is a large LCD display, and it’s simplicity and large numbers have something appealing about it. There are no harmonics though with this meter, it’s simply for recording power, but not for fully analyzing it. I guess the purpose of the Kyoritsu 6305 is to allow power consumption, voltage, current and those sorts of things to be measured, but not for recording of harmonics and distortion, and that probably explains why there isn’t a neutral current and voltage sensor – because there is no need for it. If you are interested in the amount of neutral current and potentially exploring the cause of it, then the Kyoritsu 6315 or one of the other power quality analysers is where you should be heading.

Both the Kyoritsu 6305 and the Kyoritsu 6315 have included software and also will work with the Kyoritsu Android app, but the main difference (apart from the colour screen on the Kyoritsu 6315) is that the 6315 is a power quality analyser, rather than a power meter. By this what is meant is that it can record a much wider range of power functions and parameters, such as full harmonic analysis, and because of this it has more input channels. The simplicity is still there and the Kyoritsu 6315 even has a single button labelled “Quality” which automatically records various functions associated with analysis of power issues. It’s a very simple to use meter, with a really nice range of features, and the built in Bluetooth and app makes it very versatile.

All in all, the final decision is based on many things, and the whole purpose to writing this article was to differentiate between the various power quality analysers, and also to explain some of the terms and help you to understand why you should monitor certain things and why. However, feel free to call us on 1800 837 837 if you would like some further guidance on selection of a suitable power analyser and speak to one of our experts.