Test and measurement or T&M

  • Test & measurement - Is your resistance low or are you getting hot?

    Low resistance measurement is a well-established technique that can be used almost anywhere electrical conductivity is important - its applications range from checking the quality of earth bonds to verifying the density of graphite electrodes in aluminium refineries. Recently, however, thermal imaging has been proposed as a simple and effective solution in many of the same applications. But is it?

    Low resistance measurement is a well-established technique that can be used almost anywhere electrical conductivity is important - its applications range from checking the quality of earth bonds to verifying the density of graphite electrodes in aluminium refineries. Recently, however, thermal imaging has been proposed as a simple and effective solution in many of the same applications. But is it?

    The real answer is that both low resistance testing and thermal imaging have their place so, in order to decide which to use where, let's take a look at the strengths and weaknesses of each.

    A big benefit of low resistance testing is it can detect problems even when there is no current (other than the test current) flowing in the object under test. This makes it very suitable for applications such as checking weld quality, verifying the performance of lightning protection bonds, confirming the integrity of aircraft structures and testing earth systems.
    Low-resistance testing is also invaluable in manufacturing applications, particularly where it is necessary to test subassemblies rather than complete systems, and for checking new or modified electrical installations prior to energisation. Thermal imaging is unlikely to be suitable for any of these applications.

    A further benefit of low-resistance testing is that it provides straightforward numerical results, which can easily be recorded and, even more useful, trended as part of a predictive maintenance programme.

    Having said that, low-resistance testing does, of course, have its limitations. It can't, for example, be used on live equipment. For equipment that's in service, therefore, it's necessary to arrange for the supply to be isolated before carrying out the test, which is not always convenient. In addition, if there are many connections to test, low-resistance testing can be time consuming.

    Turning now to thermal imaging, it is a good way of checking for overloads and unbalanced loads, which can't be done with a low-resistance tester. Thermal imagers also have non-electrical applications, such as finding the locations of heat loss from buildings, and detecting mechanical faults such as worn bearings in a motor, which heat up because of excessive friction.

    Thermal imaging also has the reputation of being easy to use, but that's not always the case - the operator needs to understand what they are seeing and to be able to interpret the results. For example, is a transformer overheating, or is it at its normal operating temperature? What is the load on the equipment while the test is being carried out? At what point does the temperature rise become a problem?

    In high-voltage environments, such as an electrical substation, a further complication is that is often not safe to get close enough to the equipment to image it clearly. In addition, items such as fuses and circuit breakers are usually mounted in metal enclosures, and thermal imaging will not work through metal.

    It is often unsafe to remove covers or open doors with the supply switched on but, by the time the supply is isolated and the covers removed, the equipment will have cooled significantly, making the thermal imaging data of dubious value.

    It can also be difficult to accurately relate the thermal image to the equipment being evaluated, and it is sometimes necessary to take a normal digital photograph and then use a PC to overlay this with the thermal data. Finally, trending thermal images to identify changes over time is not particularly straightforward.

    Thermal imaging is, as we have seen, a very useful technique but it complements rather than replaces low-resistance testing. And there are many applications where nothing but a low-resistance test will do. It does, however, pay to take a little care in selecting a low-resistance test set if it is to offer maximum versatility and convenience.

    For example, it is all too easy to make an accidental connection to a live supply when attempting to carry out low-resistance tests, particularly when testing busbar bonds and battery straps in UPS installations. It is important, therefore, the instrument is suitably protected.

    In many test sets, this protection is provided by a fuse, but this is not particularly convenient as, if a suitable replacement is not to hand, the instrument is not useable until a replacement can be obtained. Better low-resistance testers, such as those in the Megger DLRO10 family, are intrinsically protected against connection to live supplies. With these instruments, it's possible to carry on testing normally as soon as the errant supply has been properly isolated.

    It is also important to select an instrument that can supply a test current appropriate to the application - ideally, it should offer a choice of test currents covering a wide range. This is because high test currents can, in some cases, cause unwanted heating of the test piece, while in other cases the heating caused by high currents is actually desirable, as it can help to reveal weaknesses such as broken strands in a multi-core cable.

    Similarly, the usefulness of low test currents is also dependent on the application. Low currents may be a problem in some circumstances, as they make not break through the contamination in bonds. In other circumstances, however, this may be a benefit, because the same situation can provide a useful indication that contamination is present!

    In addition, a low test current combined with test current reversal may eliminate the need for temperature compensation of the results, and it also has the benefit of extending battery life in portable instruments.

    Finally, ease of use is a crucial factor. For maximum convenience in day-to-day use, the test set should have an intuitive user interface, and it should perform tests quickly and efficiently, otherwise it will rapidly become a constant source of irritation rather than a useful tool.
    In conclusion, it's clear that both thermal imaging and low-resistance testing are invaluable techniques and the ideal situation is to have access to test equipment for both. Only then can you be absolutely certain of providing a definitive answer to the question that we've all, at one time or another, asked - is your resistance low, or are you getting hot?

  • Test and measurement - Increasing the power of test data management

    Advances in electrical safety testing data collection and management systems have significant benefits, says Jim Wallace of Seaward

    With advances in technology making everything faster, smarter and smaller, and computer programs streamlining data management for even greater efficiency, the needs of those contractors and engineers involved in test and measurement work have never been better catered for.

    Advances in test instrumentation mean new lightweight, Bluetooth enabled hand held instruments complete safety test sequences very quickly and with the minimum of fuss - no matter whether installation testing or portable appliance testing is involved.

    Over time the introduction of advanced microprocessor based testers, powerful software-based record keeping systems and PDAs, mobile phones or specialist modems to transmit test results, have succeeded in helping the test engineer or contractor to provide a faster, more efficient electrical safety testing service.

    All these advances have been made in recognition of the need to improve and also to enable them to add value to the test process. The result has been not only better operating efficiencies, but also an enhanced relationship with customers and end users, generating important new business opportunities in the process.

    With the ever present need to undertake inspection and testing quickly without compromising quality, there is increasing importance on the linkage between test instrumentation used in the field and central test records systems that produce test certification and other test reports.

    Rather than simply ‘electrical testers', in broad terms the most advanced 17th edition testers and portable appliance (PAT) test instruments might now be regarded more as test data collection tools - gathering the important measurements and checks carried out on electrical systems and equipment.

    On a practical level there is now greater emphasis on the ability to enhance the transfer of this data between the tester and the database - and particularly on how the collected data is acquired, interrogated, managed and presented for more effective control of safety testing programmes.

    In this respect new innovations in both test instrumentation and record keeping software programs have not only brought electrical engineers and PAT service companies opportunities to provide more efficient test services, but have also created a means of real differentiation between the services offered by different electrical contractors.

    17th edition testing

    For example, in 17th edition testing the latest specialist instrumentation incorporates an electronic copy of the inspection and test certificate within the hand held tester - and in the process becomes a combined multi-function electrical tester and data logger.

    Onboard electronic certificate software enables electrical installation test and inspection data to be recorded directly by the tester using a replica of the inspection and test certificate which is displayed on the instrument.

    During inspection and testing, the user can navigate around the onboard certificate and when measured values are required, the results are automatically placed in the correct certificate fields.

    Once all inspection and test data has been collected, onboard software scans the certificate and warns the user if any fields appear to be incomplete or invalid. The integral ‘certificate assistant' also holds many of the commonly used tabulated values, such as earth loop impedance tables, avoiding the need to take bulky reference material onsite.

    When inspection and testing is complete, the certificate held inside the tester can be transferred to main PC records for the completion of certificates which can be printed or supplied in electronic format to customers in line with the 17th edition wiring regulations.
    The latest version of this program enables test results obtained from larger individual sites, such as shopping malls or commercial office complexes, can be merged onto one certificate.
    Another new feature is the ability to ‘clone' certificates from an existing master document. This allows the user to select an existing certificate and use this as a template to create multiple certificates for identical or similar electrical installations - for example of the type required for a housing development of the same type of properties and electrical systems.
    As a result, not only does the combined inspection, testing and certification system eliminate the need to record results on a dummy certificate while inspection and testing is being carried out, it also means that the often cumbersome and problematic use of PDAs, smart phones and laptops for test data transfer is avoided. 

    The new instrument incorporates Bluetooth download and upload of data to and from PC certification and record keeping systems and a wide variety of certificate templates can be loaded into the tester using the accompanying PC software.

    The specially developed software program includes all required 17th edition certification and can print onto ECA, NAPIT and NICEIC stationery.

    The result is a highly efficient and effective 17th edition inspection, testing and certification system with full traceability and reduced likelihood of human error in the recording and transfer of test data.

    Portable Appliance Testing
    In the PAT testing sector powerful test data management packages are available to facilitate the two-way transfer of data between the tester and the test records software.

    In this way engineers can pre-program or upload their testers directly from the PC with the necessary equipment details and testing information required before the day's work begins and then download updated results directly into the records programme at the end of the shift.

    The same software programs can also be used to create asset registers for customers, print test certificates and output test reports in different formats.

    The use of Bluetooth enabled testers further enhances this flexibility and means that for large PAT service and contracting organisations the effective use of data management software can greatly improve the margins associated with operating efficiencies gained for remote or off site working.

    For more specific monitoring of PAT productivity in the field special software is also available that works alongside the PAT results database to provide a clear picture of tester usage.

    Special time manager software provides clear information on the test activity of individual users and engineers - providing such details as time of test, number of tests undertaken and time between jobs.

    Analysis of such information enables service or contract managers to understand how often testers are being used, identify improvements in staff training and help field staff to test faster and work more efficiently.

    In terms of customer service improvements, another innovation is the use of PAT management software to identify and plan re-testing schedules quickly and effectively.

    This feature works through specialist software that constantly monitors the test records stored in a PAT results database, automatically triggering re-test notices for those that are approaching the next test date.

    The pre-trigger feature enables re-test schedules to be highlighted prior to appliances becoming overdue for test, with special e mail alerts being sent to customer contact personnel to give advance warning of the presence of any potentially unsafe electrical equipment in the workplace.

    The system can also be configured to submit formal re-test price quotations with the alerts for a complete test scheduling and costing proposal, boosting repeat business and enhancing the levels of customer support provided.

    For all types of electrical test and measurement activity, the combination of innovative test instrumentation with sophisticated record keeping programs provide real practical benefits to contractors - reducing costs, increasing revenue and improving productivity.

    In addition, integrated test systems can also play a significant role in enabling a contractor to provide a truly professional approach and this can only help in the long-term development of their business.

  • Test & measurement - Smarter choices in electrical testing

    Jim Wallace of Seaward, explains how advances in test technology have increased the range of test instrument options available to contractors

    For contractors involved in electrical testing there has never been a wider choice of test instruments available.

    In recent years the instrumentation industry has been at the forefront of innovation and technical advances. These changes have been made in recognition of the situation for electrical companies, particularly during difficult economic conditions, the challenge is to balance the provision of efficient, high quality test services with a competitive price tag and value for money offering.

    The test companies that flourish will be those that combine a fast and effective service that does not compromise the quality of testing undertaken - and who can build on existing customer relationships.
    In fact customer service and satisfaction levels have become a crucial area for electrical test companies. With less work around existing relationships become even more important. It follows that an ability to enhance existing customer services through the provision of a cost-effective and added-value test service can do much to both reinforce a company's reputation and maintain a positive profile with influential prospects.

    In addition, as well as a wide variety of testers available, the ability to provide a seamless link between test instruments used in the field and central test record systems that produce test certification and other reports also takes on even greater importance.

    The good news for large and small contractors is advances in test instrumentation mean a range of options are available to meet specific test needs - and budgets - for periodic electrical installation testing or portable appliance testing.

    In 17th edition testing
    The HSE's Guidance Note GS38 provides guidance to electrically competent people involved in electrical testing, diagnosis and repair. The note identifies three main test instrument categories - those that detect voltage, those that measure voltages and those that measure current, resistance and (occasionally) inductance and capacitance.

    The first named forms an essential part of the procedure for proving a system dead before starting work, whilst the other categories are more concerned with commissioning and testing procedures and fault finding.

    Guidance note GS38 provides details of the risks associated with the use of unsatisfactory test equipment and includes a list of safety precautions and requirements all professional electricians should be aware of.

    However, in terms of selecting appropriate 17th Edition test instruments, electrical contractors are broadly faced with a choice between ‘multifunction/combination' testers or single application specific testers.

    As the name implies the latter are designed to carry out one specific function - RCD testing, insulation, earth resistance etc - and the ‘all in one' type testers are single units designed to carry out a wide range of tests including earth loop, insulation resistance, continuity, RCDs etc.

    Choice invariably depends on the scope of work to be carried out, but increasingly it is the multifunction testers that have become the preferred tools of the trade for those involved in 17th Edition testing. This is for both practical reasons, in terms of using one meter constantly rather than swapping and changing between testers, and also for budget considerations - buying, maintaining and calibrating one combination tester is invariably cheaper than buying three separate ones.

    Multifunction 17th Edition testers carry out the required circuit tests and display the test reading for transfer onto the test certificate manually or alternatively, readings can be recorded on a PDA and transferred to a desktop application for certificate printing. Some testers are also linked with smart phone and portable laptop applications which work in the same way by gathering test data collected in the field for subsequent transfer onto a master certificate.

    The latest generation 17th Edition testers eliminate the use of intermediary devices by storing a replica of the test certificate within the tester so test data can be automatically incorporated onto the certificate as testing is undertaken.

    In this way the instrument combines the functions of a multifunction test instrument and data logger. When inspection and testing is complete, the certificate held inside the tester can be transferred to accompanying PC software for the completion and print out of formal certificates.

    As a result the time consuming (and therefore costly) practice of recording results on paper, a dummy certificate or a PDA is avoided. In addition, because the tester warns the user if any certificate fields appear  incomplete or invalid, verification of data can be carried out on site immediately and without return visits.

    Recently the concept on ‘on board certification' in testers has been extended with additional features aimed at large testing organisations or the testing of large premises.

    For example, the moist advanced 17th Edition testers now have the ability to upload certificates generated on a PC into multiple testers. This is particularly useful in situations where a number of test personnel might be working on the same large installation, such as a hospital development or shopping mall and enables specific test work to be allocated to a number of engineers very easily.
    Once testing has been undertaken, the software enables test results downloaded separately from different testers to be merged into a single certificate for the premises concerned.

    Another new feature is the ability to ‘clone' certificates from an existing master document. This allows the user to select an existing certificate and use this as a template to create multiple certificates for identical or similar electrical installations.

    The cloned certificates will contain all of the distribution boards and circuit details held in the original and therefore represents an easy way of generating certificates for, say, 20 or more  houses on a street which all have the same electrical configuration.

    In these combined testing and certification testers, all data transfer between the PC and the instrument can be achieved easily using Bluetooth connectivity. This means a certificate can be uploaded to the tester, the required test and inspection carried out and the information downloaded to a PC and the final certificate printed directly onto pre-printed NICEIC, ECA, ECA Select or Napit stationery.

    With such a wide range of test instruments and accessories to choose from, electricians and contractors involved in 17th Edition electrical testing can be sure the right test package solution is available to meet their specific needs and budget.

    In recent years substantial technical development has gone into the development of new test instrumentation so the ‘tester' can now be used in a much more effective manner - improving operational efficiencies, adding value to the test process and enhancing customer relationships.

  • Test & measurement - Putting engineers back in control

    IEC 61850, the new standard for substation data networks, is creating a lot of interest and  excitement. It's also creating more than a few challenges, says Romain Douib of Megger, not least for substation control engineers who spend their lives creating and working on interlocking schemes

    One of the biggest challenges substation control engineers face, is not how to implement interlocking schemes based on IEC 61850, but how to test them. The problem is particularly acute, because at present IEC 61850 is being more widely used for interlocking than it is in protection applications.
    Of course, options do exist for testing IEC 61850 interlocking schemes. However, these almost always involve the use of protective relay test set that supports IEC 61850. This approach, however, is far from ideal. The first concern is that, in most cases, control engineers are not protection engineers. They are unlikely, therefore, to be familiar with the operating a protective relay test set. They could, of course, learn, but that's a pretty steep learning curve for something that is not central to their work.
    Another issue is protective relay test sets are necessarily costly, since they incorporate high-performance precision amplifiers and other elements that are expensive to develop and produce. Yet these are not needed for testing interlocking schemes, so using a relay test set in this application is not only overkill, it also needlessly ties up expensive capital equipment.

    It's clear there is a pressing need for a reasonably priced instrument that is simple to use and provides all of the facilities needed for testing IEC 61850 interlocking schemes, but does not incorporate the expensive extras needed for protective relay testing.

    It's not difficult, in principle at least, to imagine how such a test set would work. First of all, it would monitor the Goose messages IEC 61850 installations use to communicate and it would convert them to the ordinary type of on/off binary signal that control engineers are used to working with in non-networked installations.

    The test set would also be capable of working in the opposite direction. That is, it should take signals from ordinary contacts and convert them into appropriate Goose messages. In effect, a test set of this kind is simply an interface between the Goose messages on the bus and the electromechanical world of the control engineer.

    Of course, there's rather more to be considered than this very basic overview initially suggests. For example, the conversion between Goose messages and binary signals must be fast enough so as not to materially affect the timing of the interlocking system. In practice, a conversion time of less than a millisecond, which is achievable with careful design, will be fast enough to satisfy the most demanding of requirements.

    Next, it is clearly necessary to be able to associate particular Goose messages with specific inputs and outputs on the test set. This is best accomplished with software but, if it is to be intuitive and easy to work with, the software needs to be carefully designed. Further refinements can also be envisaged. For example, LEDs that provide instant visual confirmation of the state of the instruments binary inputs and outputs would be an important benefit for users.

    The ideas mentioned in this article have driven the development of Megger's new Goose Message Interface.. This embodies a number of unique technical features for which patents are pending, and offers the most efficient and cost-effective solution currently available to the challenge of testing IEC 61850-based substation interlocking schemes.

    That is, however, by no means the limit of the capabilities of the Goose Message Interface. While it may not be particularly interesting to control engineers, the unit can also be used to adapt a conventional protection relay test set so that it can be used to test IEC 61850 protection schemes. This is a big benefit for users that already have protection relay test sets - whether they are units supplied by Megger or by others - as it is offers a very straightforward and cost-effective upgrade path.
    It also creates an attractive option for consultants and smaller organisations who can now purchase a Goose Message Interface and a modestly priced relay test set, to cover all their relay and interlocking test requirements for both conventional and IEC 61850 schemes.

    Equipment that allows convenient and dependable testing of IEC 61850 interlocking schemes has, until now, been difficult or even impossible to find. This situation has now been addressed by Megger's Goose Message Interface, an instrument that provides the added bonus of facilitating the testing of IEC 61850 protection schemes.

  • Test & Measurement - Top tips for cabling and test fixture safety

    In general, test cabling and test connections must all be designed to minimise resistance (R), capacitance (C), and inductance (L) between the device under test (DUT) and the used source-measure unit (SMU) explains the applications engineering team at Keithley Instruments

    To minimise resistance, use heavy gauge wire wherever possible, and definitely within the test fixture itself. The gauge required will depend on the level of current being carried; for example, for cabling that must carry 40A, a 12 gauge cable is probably necessary. For guidance on choosing cabling for higher current levels, refer to construction industry wire gauge tables, such as the one available at: www.powerstream.com/Wire_Size.htm. Check the ‘Maximum amps for chassis wiring" column to find the wire gauge needed to carry the level of current involved.

    Low-resistance cabling is critical to preventing instrument damage. Choose cables with resistances of less than 30 milliohms/meter or lower for 10A pulses. Keep cable lengths as short as possible and always use low-inductance cables (such as twisted-pair or low-impedance coax types), heavy gauge cable in order to limit the voltage drop across the leads. Ensure the voltage drop won't be excessive by checking the SMU's Voltage Output Headroom spec. For example, if you were using a Keithley Model 2602A (pictured above) SMU to output 20V, the test leads should have no more than 3V of voltage drop across them to avoid inaccurate results or instrument damage. It is specified for a maximum voltage of 3V between the HI and SENSE HI terminals and a maximum voltage of 3V between LO and SENSE LO. 

    Although many believe guarding can minimise the effects of cable charging, this is typically more of a concern for high voltage testing than for high current testing. Four-wire Kelvin connections must be kept as close to the DUT as possible; every millimetre makes a difference.

    Also, it should be noted 0voltage readback should be done with the SMU that's forcing voltage, because the current-sourcing SMU's voltage readings will all vary quite a bit due to the connections, and will differ from what is actually seen at the DUT.

    The jacks used on the test fixture should be of known high quality. For example, some red jacks use high amounts of ferrous content to produce the red colouring, which can lead to unacceptably high levels of leakage due to conduction. The resistance between the plugs to the case should be as high as possible and in all cases >1010 ohms.

    Many published test setups recommend adding a resistor between the SMU and the device's gate when testing a FET or IGBT. When pulsing large amounts of current through these kinds of devices, they tend to oscillate. Inserting a resistor on the gate will dampen these oscillations, thereby stabilising the measurements; because the gate does not draw much current, the resistor does not cause a significant voltage drop.

    If voltages in excess of 40V will be used during the test sequence, the test fixture and SMUs must have the proper interlock installed and be operated in accordance with normal safety procedures.

    Many electrical test systems or instruments are capable of measuring or sourcing hazardous voltage and power levels. It's also possible, under single fault conditions (e.g., a programming error or an instrument failure), to output hazardous levels even when the system indicates no hazard is present. These high levels make it essential to protect operators from any of these hazards at all times. Protection methods include:
    - Verify the operation of the test setup carefully before it is put into service.
    - Design test fixtures to prevent operator contact with any hazardous circuit.
    - Make sure the device under test is fully enclosed to protect the operator from any flying debris.
    - Double insulate all electrical connections that an operator could touch. Double insulation ensures the operator is still protected, even if one insulation layer fails.
    - Use high reliability, fail-safe interlock switches to disconnect power sources when a test fixture cover is opened.
    - Where possible, use automated handlers so operators do not require access to the inside of the test fixture or have a need to open guards.
    - Provide proper training to all users of the system so they understand all potential hazards and know how to protect themselves from injury. It's the responsibility of the test system designers, integrators, and installer to make sure operator and maintenance personnel protection is in place and effective.

  • Test & Measurement - Work smarter with PAT records programs

    Jim Wallace of Seaward looks at developments in PAT data management software systems

    With a competitive portable appliance testing market forcing all contractors and PAT contractors to work more efficiently, linking the test functions of tester to effective results programs has taken on increased importance.

    Fortunately, advances in portable appliance testing instrumentation and test data management software means that there are now integrated PAT solutions available that meet the needs of all levels of electrical safety testing.

    In very basic terms PAT testers could be regarded simply as test data collection tools that measure and check the safety of electrical appliances. For fully effective risk management programmes and compliance with workplace safety protocols, how this data is acquired, managed and presented takes on even greater importance.

    As a result, considerable work has also gone into the development of PAT record keeping software systems to enable the user to build and maintain computerised records of test results so that the collected data can be interrogated and used to control electrical safety programmes in a professional and orderly manner.

    In addition, the HSE Memorandum of Guidance on the Electricity At Work Regulations 1989 advises records of maintenance and safety test results should be kept throughout the life of the equipment.

    Software controlled safety testing record systems enable ‘real-time’ records to be maintained, which are easily amended and updated. This enables new equipment to be added and the movement of equipment from one location to another to be tracked.
    Programs used for asset management purposes in this way can search through records very easily and display the record details significantly faster than making changes to a manual paper based system – and with reduced chances of mistakes being made.

    Another advantage is the ease with which re-test schedules can be planned. As the re-test periods for individual items could be anything from three months to four years, it is comparatively easy for test situations and work schedules to become unmanageable. It becomes particularly unwieldy to have someone monitoring a paper record system looking for items which may have remained in use beyond their next test date, particularly when large workplaces or testing contracts can include thousands of appliances.

    Now, matching the availability of different testers, a range of results recording programs possess different features and varying levels of sophistication to meet the needs of all types of PAT testing organisations and personnel.

    Manual data entry systems
    In their most basic form, PAT record keeping programs provide database packages capable of storing and presenting large numbers of test records.

    Because most entry-level PAT testers provide simple pass/fail readings and do not have an internal memory for results storage, complementary software programs at this level permit manual entry of results.

    With these systems, once test results have been entered there can be a range of data manipulation options available that allow different test report templates to be produced – for example, as PDF, TIF or jpeg files.

    In addition some of these elementary or basic level programs also allow different reporting options including the presentation of test histories for individual appliances for comparison or trend analysis purposes.

    More elaborate entry level packages also have the ability to link testing carried out to the automatic generation of invoices – including the option to include the costs of any repairs carried out.

    Once testing has been undertaken and all data entered, it is also possible to produce special ‘certificates of testing’ that can be displayed in workplaces to highlight the electrical safety measured undertaken.

    Direct data download
    For those PAT testers equipped with a memory to record results, basic software packages are also available that enable the direct download of test results into database systems.
    Of course one of the most important considerations for users of PAT testers incorporating an internal memory is the compatibility between the test instrument and the PC program. Most software packages are compatible with different safety tester output formats – although as the range of test instruments has increased over the years it is worth checking with the supplier of your preferred results recording program that your tester will be compatible.
    Some of these types of programs allow both manual and direct download input of data and in broad terms provide the same range of test report options and administrative functions as those described earlier.

    However there are some differences that may be attractive to different types of PAT contractor or user: For example some programs enable test results to be downloaded into existing customer or site specific files – while some download programs produce multiple databases with new results listings being created every time a new set of results is entered.

    Uploading test data
    As PAT testers have become more sophisticated, some have the ability to ‘pre-program’ the instrument with a special testcode (a test routine defined by a numeric sequence) at the start of the working day.

    This is referred to as an upload capability and involves the ability to send an appliance number and testcode from PAT records held on a PC program to the instrument. By uploading this information into the tester, re-testing in the field can be speeded up considerably and detailed test histories can be maintained very easily.

    As a result software programs that combine data upload and download features can be used to create fairly sophisticated asset registers for customers, grouping appliances by type or location and helping to track the movement of equipment between departments or different parts of a building.

    Such high level programs also come with a host of other functions and test templates – including the inclusion of ‘view only’ CD files that enable others to have copies of test records from a parent program that can be viewed without having a copy of the original record-keeping program software.

    Other features include sophisticated presentation and reporting options and the ability to link electrical safety testing records with other asset management or maintenance functions - extending the use of these programs for more general facilities management tasks.

    For contractors carrying out PAT testing as part of more general facilities management functions, software programs are available that include the ability to include reports and details of other health and safety related checks on equipment such as emergency lighting, fire alarms and fire extinguishers.

    Networking options have also been developed for these higher level PAT programs - enabling more than one user to access the program at the same time.

    Special programs
    In addition to the range of record keeping database programs a number of special software packages are available to provide specific test management or PAT administrative functions.
    One example is an e-scheduler module that systematically interrogates the PAT test database and automatically identifies when equipment will be overdue for re-test – issuing e-mail alerts to notify customers or departments immediately of all re-test requirements or overdue warnings.

    In this way this special software can be used to highlight and plan re-test schedules, enabling workloads to be managed efficiently. For testers with an upload capability this program can also directly transfer the appropriate test data into test instruments in preparation for on-site testing.

    The system can also be configured to submit formal re-test price quotations with the alerts for a complete test scheduling and costing proposal, boosting repeat business and enhancing the levels of customer support provided.

    Another example of ancillary is special time manager software that provides information on the test activity of individual users and engineers – providing such details as time of test, number of tests undertaken and time between jobs.

    Analysis of such information enables service or contract managers to understand how often testers are being used, identify improvements in staff training and help field staff to test faster and work more efficiently.

    With developments such as these, PAT results recording and data management solutions are available for all organisations involved in portable appliance testing whatever their requirements.

    At all levels PAT record keeping programs provide real practical benefits to contractors – reducing costs, increasing revenue and productivity, improving safety and providing a truly professional approach to test data management that can only help in the long term development of their business.


    Footnote: To help employers learn more about portable appliance testing Seaward has published a free booklet -
    ‘A Common Sense Approach to Electrical Safety in the Workplace’. This describes the importance of implementing inspection and testing measures that are appropriate to the particular working environment and which are in keeping with the specific risks posed. Further details call 0191 586 3511 or visit www.seaward.co.uk

  • Test & measurement - A primary injection primer

    What is primary current injection testing, and what are its applications? What kind of test equipment is needed for primary injection testing, and what features should users expect to find in the latest test sets? The answers to these questions and many more are supplied by Damon Mount of Megger

    Primary current injection testing is most usually associated with high current and high voltage power distribution systems of the type found in an electricity substation, or in a large industrial installation. The principle it is actually very straightforward: a test current is injected into the primary side of a system – which is often but not always some form of protection scheme – to determine how the system behaves at particular levels of current.
    The system under test might, for example, comprise a circuit breaker with an over-current trip relay that operates via a current transformer (CT). By injecting a predetermined current into the circuit breaker, it is possible to determine whether the relay will trip at this current and, if so, how long the current needs to flow before the trip is initiated.

    Something similar, of course, could be achieved by injecting a test current directly into the trip relay – that is, on the secondary side of the CT. This is secondary current injection testing and it is widely used, not least because much lower currents are needed than are typically required for primary injection testing.

    Secondary injection testing is undoubtedly valuable, but it does not check all of the components in the system. In the scenario discussed, it would not, for example, reveal a defective CT. Neither does it truly mimic the operating conditions – the heating effect of the primary current will not be present and, in some types of test, this can significantly affect the results obtained.

    For these reasons, there are many situations where primary injection testing is considered useful if not essential. Because it tends to be somewhat disruptive – the plant under test must be taken out of service and de-energised and then arrangements must be made for the high current connections needed for the test – primary injection is most usually performed as part of the commissioning procedure for new plant or after major modifications have been carried out. In some instances, however, it can also be an invaluable aid to faultfinding.

    Test sets used for primary injection are invariably built specifically for this purpose. Their primary function is to supply a lot of current – tests typically involve injecting currents from 100 A or so up to 20,000 A. Equipment capable of delivering these sorts of currents is never going to be physically small or lightweight, but remarkable strides have been made over recent years in making primary injection test sets more manageable.

    One way this has been achieved is by using modular current sources, so that for lower test currents only one or two sources are needed, but for higher test currents additional current sources can be added. Test sets that adopt this approach are often assembled on wheeled trolleys that can accommodate the control unit plus up to three or four current source modules. This arrangement makes the test sets much easier to handle.

    Test equipment manufacturers have also noted that only a few applications of primary injection testing involve the highest currents – many requirements can be satisfied with test sets rated at no more than 5000 A, which paves the way for smaller mid-range units. In addition, the highest currents are usually only required for a comparatively short time, to test, for example an instantaneous overcurrent relay, so the test sets do not need to be continuously rated for their maximum current output. Once again, this allows size and weight to be reduced.

    Weight and size are not, however, the only areas where progress has been made. Another useful development is the introduction of test sets where the control unit can be connected to the current generator by a comparatively long control cable. This allows the current generator to be placed very close to the equipment under test, thereby minimising the length of the high current test leads needed, which makes testing easier and more practical.

    To ensure versatility, primary injection test sets need to be able to offer options to cope with a wide range of burdens since, if they do not, there is the possibility that they will not be able to deliver the required test current into the impedance presented by the equipment under test plus the test cables. In the best test sets, this issue is addressed by allowing the output voltage of the current generators to be raised at the expense of output current, so that the total power the test set is required to deliver is not increased unduly. This option is particularly valuable when testing CTs, circuit breakers and busbar joints.

    Another option of great value is an integral timer that can be set to inject the test current for an accurately controlled time, preset by the user. This makes it easy to perform complete circuit breaker tripping time tests that encompass both the relay and the CTs, by injecting the actual fault currents. Auxiliary voltage and current measuring inputs facilitate the testing of CTs and good test sets can provide a wide range of data, including impedance, resistance, virtual power, active power, reactive power, and power factor, together, of course, with CT ratio and polarity.

    A fast acting hold feature for the measuring functions, which is provided in conjunction with a “stop” input further enhances usefulness, as it allows readings to be frozen by applying a signal to the stop input. This makes it possible, for example, to record data relating to the exact moment that a protection relay operates during a test. Some instruments, when used for circuit breaker testing, can even be configured to automatically freeze the measurements at the instant the breaker trips without the need to use the stop input.

    A feature that is just starting to become available on the latest primary injection test sets is zero-crossover synchronisation. This ensures that the test current is turned on only at a zero crossing point, which eliminates DC offset effects and also ensures the best possible repeatability for test results.

    One issue that has been perennially troublesome in carrying out primary injection tests has been heating of the equipment under test while setting up and adjusting the test current. This effect has even been known to trip a breaker under test during set up before the test proper has commenced. Work-arounds are available – test engineers can perform the set up very quickly to minimise heating, or they can prevent tripping at least by isolating the trip circuits. Neither of these options is particularly convenient, however.

    Fortunately, there is a better solution, in that test sets are now available with a so-called I/30 function. This, as its name suggests, reduces the programmed current output of the test set by a factor of 30. Since this means that the heating effect is reduced by a factor of 900, test engineers using this function can take as much care and time as they need in setting up the test with absolutely no risk of significant heating. And, when they are ready to start testing, the output current can be returned to normal at the push of a button.

    Some of the principal applications of primary injection testing, including the testing of circuit breakers and CTs, have already been mentioned in this article. Some test sets can, however, also be programmed for more complex functions, such as testing automatic reclosers and sectionalizers.

    Finally, it is worth bearing in mind that the high-capacity current source at the heart of every primary injection test set is also useful in its own right as convenient way of providing current to carry out heat runs on busbars and other types of switchgear assembly, and for testing ground grid installations where the test set is used to inject current between a reference ground and the ground to be tested. Measuring the voltage drop and the percentage of current flowing through the ground grid then enables an accurate assessment to be made of the ground grid’s performance.

    Primary current injection tests are among the most valuable tests that can be carried out on power systems as they take into account the performance of every component and are, therefore, the most reliable way of assessing the performance of the system under real world operating conditions. In the past, however, primary injection testing has been fraught with inconvenience, not least because of the size and weight of the equipment involved, and because of its limited capabilities.

    Fortunately, things have changed and, as we have seen, the latest primary injection test equipment is much more user friendly – and far less back breaking! For all those involved in the commissioning and maintenance of power distribution systems this could, therefore, be a very good time to take a closer look at how primary injection test sets have changed in recent years, and to look again at the benefits that this form of testing undoubtedly offers.

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