Moving forward with tan-delta high voltage insulation testing

Though recent tan-delta test sets in the market, which are widely used to assess insulation in high-voltage electrical apparatus, combine versatility with convenience, there is room for further improvement. - Vince Oppedisano

Modern tan-delta (power factor) test sets, particularly those which offer intelligent temperature correction and automatic voltage dependence detection, are a widely used option to assess the condition of insulation in high-voltage electrical apparatus such as transformers, bushings, circuit breakers, cables, lightning arresters and rotating machinery.

Recent test sets of this type combine versatility with convenience and greater ease of use than older models, but there is room for further improvements. It is, interesting to look at some of the latest enhancements and the benefits they provide.

In the user interface, even small improvements could increase operator convenience as well as providing valuable time savings.

Examples of this type of improvement include simplified set-up page layout and the pre-programming of the most commonly used options, such as frequency variation test mode and selecting default test object temperature of 20ºC.

As their products become more widely used, instrument manufacturers draw on field experience, particularly when those products incorporate major functional innovations such as intelligent temperature correction.
This lets them refine these novel functions to enhance the accuracy, repeatability and comparability of test results.

Report generation is, an important aspect of the operation of all but the most basic instruments. Data management and report generating software for power instruments has, sometimes had a reputation for being complicated and inflexible.

Much progress has been made to address these issues, with the latest instruments offering facilities for generation of reports in the same convenient formats whether using built-in software or software running on an external PC. Careful selection of defaults by the manufacturer simplifies and speeds the work of report production.

With complex test instruments like high-voltage tan-delta test sets, it’s easy to focus on the instrument itself while paying scant attention to test leads and other key accessories. As users point out, these items are just as important as the tester. The test leads, are the essential link between the instrument and the object under test; inferior or damaged test leads not only make life more difficult for the user, they can be a very real safety hazard.

In response to this issue, developments now being seen in the market place include high-voltage test cables with terminations for connection to the test specimen that offer significantly enhanced strength and durability. This means that, even if the termination is dropped from a height – a relatively common occurrence when, for example testing large transformers – the risk of damage is greatly reduced.

Tan-delta testing is increasing in popularity not only in the industrialised nations but also in the emerging economies where the climatic conditions can be particularly demanding.

This presents a challenge for the instrument manufacturers as their products necessarily incorporate high-voltage components yet there is constant pressure from users to minimise size and weight.

The best manufacturers are now successfully addressing this challenge by upgrading their designs and revising their choice of components to ensure that their instruments operate reliably in high-temperature, high-humidity.

Accessories need to be suitable for use in the same demanding climatic conditions as the instrument itself. This has led to the introduction of improved and more durable high-voltage strobes with rugged connectors and optional extended-reach cables.

Naturally, purchasers of tan-delta test sets like to get the best possible value from their investment and many of them buy accessory kits.

Recently, some of these have become even better value for money by including humidity and temperature probes rather than separate and somewhat less convenient temperature and humidity meters. Oil test cells are also popular accessories.

The latest types offer a convenient option for carrying out informative oil testing on a small scale in the field without the delays inevitably associated with sending the samples to a laboratory for testing.

The best of the new oil test cells can be used at temperatures up to 100 ºC and can be heated by a standard oil bath heater. Provided that they contain oil, cells can also handle voltages up to 10 kV.

One final area that frequently receives less attention than it deserves is carrying cases. Many users are moving away from traditional soft carrying cases, possibly because these generate a false sense of security in relation to the level of protection they really offer.

Increasingly, their place is being taken by rigid transport cases that hold the instrument, test leads and accessories.

These cases are inevitably somewhat heavier than soft cases, but the use of modern plastics materials in their construction means that the weight difference has now been greatly reduced without sacrificing the level of protection provided.

It would be easy to dismiss the changes discussed in this article as insignificant and, in comparison with the introduction of a completely new instrument; this would of course be true. Nevertheless, when taken together, these apparently minor changes can make life a lot easier for those who regularly use high-voltage tan-delta test sets in their daily work.

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