It is still common practice in sub-station testing to use separate instruments for each type of test. This situation, however, is about to change. There are many compelling reasons to move away from separate instruments in favour of a multi-functional test set, including:
1.Users always have all of the test facilities they need readily at hand; no need to go back to the van or, worse, back to base to fetch another instrument for the next test. Plus, a single multifunction tester is much easier to transport than several individual instruments.
2.Multi-functional test sets cost less than the individual instruments that would be needed to cover the same range of testing requirements; e.g., four single-function test instruments = four displays, four user interface systems, four enclosures, etc. = more money than one multifunction instrument with one display, one UI system, one enclosure, etc.
3.Reduces testing time, thus saves money; only one instrument to unpack, power up and configure; the same cable set is used for a whole range of measurements, so the connections only need to be made once; and, when carrying out a range of tests, users of multifunction instruments move quickly and easily from app to app, rather than having to go from instrument to instrument.
4.Less operator training is required; users of separate instruments need to familiarise themselves with the quirks of each, whereas users of well-designed multifunction testers enjoy a consistent user interface across all functions, which means that the learning process is simplified. This begs the question then, if multifunction instruments have so much to offer, why are they not used more frequently for substation testing? The reasons are interesting:
a.Inertia. If separate instruments have always been used in the past and have delivered satisfactory results, why change? The simple answer is that change brings the benefits above.
b.Cost. If an additional single-function instrument is all that´s needed to complement instruments already owned, why spend extra on a multifunction tester that will duplicate at least some of the functionality of the existing instruments? The answer is an investment for the future. Buy a multifunction tester and it will probably be unnecessary to replace the single-function instruments as they come to the end of their lives.
c.Until recently, few, if any, adequately specified instruments were available. This is not particularly surprising, as designing and manufacturing a versatile, convenient, dependable and easy-to-use multifunction tester for use in substations presents many challenges.
A multifunction test instrument design that can lead a migration from single-function instruments must:
Be capable of generating high currents and voltages yet remain easy to transport. For users with interests that cover a wide geographical area, it is highly desirable for the instrument to weigh less than the international maximum shipping weight of 32 kg for check-in luggage on passenger flights.
Alleviate the potential conflict between versatility and ease of use. There´s little point in producing a multifunction instrument that can perform a wide range of tests if many of the tests are difficult to access and set up. This only leads to user frustration and ultimately dissatisfaction with the product, however impressive its claimed abilities may be.
Fortunately, recent advances in instrument design and technology have made it possible to produce multifunction testers for substation and other power applications that address both of these issues, making them truly attractive to users. An excellent example is a recently released integrated transformer and substation test system.
This compact unit, the main section of which weighs just 26 kg, provides comprehensive facilities for testing power transformers, current transformers, potential transformers, circuit breakers, rotating machines and many other items of substation equipment. The base unit can generate AC current up to 800 A, DC current up to 100 A, AC voltage up to 2.2 kV and DC voltage up to 300 V. With optional accessories, the AC capabilities can readily be extended to 2,000 A and 12 kV.
The voltages and currents generated by the instrument can be controlled and measured with a high degree of precision, allowing it to be used for an exceptionally wide range of applications that includes, for example, turns ratio, winding resistance and excitation current measurements in transformers; contact resistance, impedance and tan delta/power factor testing; main and resistor contact timing in circuit breakers; and primary injection testing in LV, MV and HV equipment of almost any type.
The challenge of delivering a simple user interface and experience in view of this vast range of capabilities has been met by making use of the latest colour touch-screen technology and by designing the user interface so that it presents functions in the form of apps (´virtual instruments´). When the user has decided what to measure and has selected the app/instrument to work with from the start screen, the display shows only those elements that are appropriate to that function.
For example, if the winding resistance instrument is selected, the screen simply shows the output current, the output voltage and the measured resistance. The user selects a test current and starts measuring. Users, who prefer test guidance from the instrument, just enter the configuration and the unit provides connection diagrams and a table showing the sequence of measurements.
Provision is also made for full manual testing with a generic instrument app that allows the user to freely select outputs, measurement inputs and the way in which the measured data should be processed.
This remarkable new multifunction substation test set - the Megger TRAX - conveniently and cost effectively replaces a whole battery of conventional single-function instruments. Let the migration begin!
Author: Peter Fagerstrom - Business unit manager
If you would like to know more about Megger´s product, please write to Pratyush.Sinha@megger.com