A Yokogawa power meter provides superior accuracy for measuring transformer losses at SMIT Transformers
Yokogawa's 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 three-phase operation with voltages up to 525kV and power ratings up to 1000MVA.
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 per ent of its total output, which can equate to a value of 2.5MW for a 1000MVA 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.
A need for accuracy in these loss measurements is further emphasised by the fact that even an error of as little as one per cent in the measured value could still represent an error of 25kW: 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.
Need for high accuracy
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, an instrument known for its high accuracy.
Not only does the accuracy of the WT3000 meet the requirements of the transformer manufacturer — particularly at low power factors — but 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 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 ten parts per million, persuaded Smit to standardise on the WT3000 digital power analyser for use with all its transformer test systems.
