Adrian Parker - Application engineer
As infrastructure ages, the incidence of equipment failure is rising and will undoubtedly continue to rise. Whether a failure results in local inconvenience or a widespread loss of power to possibly millions of consumers depends largely on the design and performance of the protective relay system in use. Dependable testing of these systems has therefore never been more important.
The purchase of a modern relay test set is however a substantial investment, so it’s important to make the right choice. Megger has recently made this easier as with its acquisition of Programma, it now offers two ranges of relay test equipment – MPRT and Freja – giving potential users greater choice, and allowing them to select the system which best meets their technical and budgetary requirements.
But what are the differences between the MPRT and the Freja relay test sets, and how do users decide between them? Let’s first look at what the MPRT range has to offer.
Key features of MPRT test sets include constant high-power outputs, a colour touch-screen user interface and flexible hardware configuration. These test sets are currently available in two versions – the MPRT8430, with a maximum output of 30 Amps and 300 Volts and the MPRT8415, which has a maximum output of 15 Amps and 150 Volts.
Both models can be used to test virtually all types of protection relay, from the traditional electromechanical types to the latest microprocessor-based protection schemes, eliminating the expense and inconvenience of having to use different types of test set depending on the type of relay.
To further enhance their versatility, all MPRT systems have been designed to provide a constant power output of 200 VA per phase. This means that they can be used for example, to test high impedance relays and panels of wired relays, without the need for accessory high-power current amplifiers.
Fully automated testing and the management of test files is provided by the AVTS PC-based software package that supports the MPRT system. This provides advanced features including On-line – click on fault, RIO file import and DFR playback, as well as options for metering and transducer testing.
Facilities for semi-automatic and manual testing of protection relays are also provided via the unique Touch-View Interface (TVI), an easy to handle colour touch-screen system connected to the test set’s main power box by a flexible cable. The TVI also allows manual testing of electric power type transducers in single- and three-phase versions.
A further feature of the TVI is that it continuously displays the status including phase vector graphs, of all outputs while computer-controlled testing is in progress. In addition to the measured values, the TVI shows calculated values.
MPRT test systems are available with between one and four output modules, and any unit can be upgraded to a maximum of four channels. Each module provides both a voltage and a current output so that when four modules are fitted, the MPRT is suitable for testing modern integrated relays that in addition to three-phase voltage and current inputs, also require residual voltage and/or current inputs.
Further flexibility is offered by an option which allows MPRT voltage outputs to be reconfigured as current outputs in order to provide up to six current channels for testing three-phase differential relays.
Additional features offered by MPRT protective relay test sets include ten programmable binary inputs, six programmable binary outputs with the capability of Boolean logic control, and facilities for digitally recording fault files in the industry standard COMTRADE format, for later replay with up to 256,000 samples per channel.
Turning now to the Freja 300 range, with key features including easy to use software that makes setting up particularly simple; robust construction; an in-field calibration option; and excellent portability – the Freja 300 model weighs only 15kg. Test sets in this range can be operated with or without a PC. They incorporate a large liquid crystal display that is used in conjunction with front panel keys to select and control test sequences.
Like the MPRT range, the Freja range currently includes two models. Freja 300 can generate outputs of 4 x 150 V (82 VA) and 3 x 15 A (87 VA) or 1 x 45 A (250 VA), whereas the newly launched Freja 306 offers a high power alternative with 6 x 15A (3 x 15A + 3 x 35A) or 1 x 100A (750VA) output. On both models, all outputs can be set independently, and both support static and dynamic testing, including simultaneous ramping of multiple quantities and waveform editing. Freja 306 is available as an upgrade for current Freja 300 users.
For automated testing, Freja 300 test sets are used in conjunction with the Freja Win software package, which allows users to save test setups and results via a standard Microsoft Explorer display, making it easy to create test object structures.
Which of these two versatile ranges of protection relay test sets is the most suitable depends of course on the applications in which it will be used. However it’s possible to give some general guidance.
Where electromechanical relays are to be tested, then the higher output power available from the MPRT 8430 makes it the preferred choice. On the other hand if portability (light weight) and ease of use are a key issue and high output power is not required, the Freja 300 range offers the benefits of lighter weight and smaller size.
While both ranges offer standalone operation, the MPRT with its full-colour Touch View Interface, is substantially more versatile when used without a PC. Arguably the Freja user interface is simpler to use for straightforward tests in standalone mode, but it is less well adapted for complex applications.
Both of the product ranges are supported by excellent software – AVTS for the MPRT test sets, and Freja Win for Freja instruments. However the AVTS package offers features that are of particular benefit to advanced relay test users where technical acceptance is a key issue.
In simple terms, the overall conclusion is that Freja products are an ideal and cost-effective choice for straightforward field applications, while the MPRT test sets offer additional complex test facilities and expansion options that are of particular interest to advanced users, or users with a wide range of protection relay testing requirements.