Yokogawa power meter provides superior accuracy for measuring transformer losses at SMIT Transformers

Phil Black - PII Editor 27/08/2009

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The Yokogawa WT3000 digital power analyser is at the heart of a test system being used by Smit Transformers NV, one of Europe”s leading manufacturers of high-power transformers for power distribution networks, to provide accurate measurement of power losses.

Smit Transformers, part of the SGB-Smit Group and based at Nijmegen in the Netherlands, manufactures very large (up to “house sized”) transformers for use in power stations and substations. These units are designed for 3-phase operation with voltages up to 525 kV and power ratings up to 1000 MVA.

At these power levels, the power losses which are inherent in every transformer design can have a significant effect. A typical large transformer may suffer losses of around 0.25%of its total output, which can equate to a value of 2.5 MW for a 1000 MVA transformer: a figure which represents a considerable sum of money for the utility operator. It is therefore important for the transformer manufacturer to know the exact value of the power loss before the unit is shipped to the customer.

The need for accuracy in these loss measurements is further emphasised by the fact that even an error of as little as 1% in the measured value could still represent an error of 25 kW: again, a significant amount in financial terms. The situation is further complicated by the fact that these measurements need to be made at very low power factors – as low as 0.001 – where accuracy becomes an even more sensitive issue.

Smit Transformers uses a number of transformer test systems incorporating proprietary power meters. However, for these particular tests, combining very high power levels with extremely low power factors, the standard meters proved insufficiently accurate. As a result, Smit”s engineers decided to use the Yokogawa WT3000, which is renowned for its high accuracy.

Not only does the accuracy of the WT3000 meet the requirements of the transformer manufacturer – particularly at low power factors – the instrument also offers two other important benefits. Firstly, its multiple inputs enable it to carry out simultaneous measurements on all three phases, whereas previously Smit Transformers had used three separate wattmeters – one for each phase. Secondly, the built-in oscilloscope-type display on the WT3000 allowed engineers to view the current and voltage waveforms, so that they could see in real time the effects of those harmonics that can affect measurement results at low power factors.

To ensure that the measured results were correct, Smit Transformers then confirmed the calibration of the test system using the services provided by one of the world”s leading standards organisations: the Canadian Metrology Institute (part of the National Research Council of Canada). The extremely positive result of these tests, verifying an error of less than 10 parts per million, persuaded Smit Transformers to standardise on the Yokogawa WT3000 digital power analyser for use with all their transformer test systems.

For further information please contact:

Terry Marrinan
European Test & Measurement Centre
Yokogawa Europe BV
Euroweg 2
3825 HD Amersfoort
The Netherlands

Tel: +31 (0) 88 464 1811
Fax: +31 (0) 88 464 1111

E-mail: terry.marrinan@nl.yokogawa.com
http://tmi.yokogawa.com