Portable Accuracy: Voltage Transformer Testing and Calibration

Voltage transformers can be found in many locations within energy supply networks. Their duties include protecting supply networks and accurately recording primary voltage levels for power determination.

Omi Figure 1 Setup

by Markus Jäger

Voltage transformers can be found in many locations within energy supply networks. Their duties include protecting supply networks and accurately recording primary voltage levels for power determination. To perform these duties correctly, however, they require regular tests and calibration based on operator directives or national regulations. OMICRON's new VOTANO 100 test system combines mobility with a high level of accuracy in a single system.

Until now, precise testing of the ratio accuracy of voltage transformers was a major undertaking. Highly accurate measurement solutions are complex systems, made up of various devices that are calibrated and extremely accurate. This includes a high-voltage source, a reference transformer, a set of standard burdens, measuring bridges for comparative purposes, and a computer to evaluate all of the measured data. Transporting all of this equipment to the testing location can often be awkward. The time and costs involved are immense. Smaller testing solutions typically lack the necessary accuracy or are incapable of taking all of the different burdens into account. So, the only viable alternative is often to remove the voltage transformer and send it to a testing institute for accurate calibration. This, however, is also time and cost-intensive.

Figure 1: VOTANO 100 and VBO1-a safe combination

Precise Mobile Testing

VOTANO 100 combines mobility and accuracy, reducing testing efforts to a minimum. The basis for this combination is the examination of the voltage transformer as an electrical model that is captured and then mathematically simulated by VOTANO 100. This model was developed on the basis of the CT Analyzer.

Safe and Lightweight Package

The VBO1 voltage booster comes with VOTANO 100. It supplies the primary side of the transformer with a maximum reference voltage of 4 kV for the ratio measurement. The VBO1 is positioned near the test object, while the test engineer operates VOTANO 100 in a secure area outside of the high-voltage environment. The compact dimensions provide easy, convenient transport. The combined total weight of both devices is less than 33 pounds.

In a single pass, winding resistance, short-circuit impedances, ratio and the magnetic characteristics curve of inductive and capacitive voltage transformers are determined. During this process, VOTANO 100 assesses voltage transformers with up to five secondary windings-for both no-load and standard load operating conditions.

Accurate

The measurement method offers a high degree of accuracy-VOTANO 100 achieves a measurement tolerance of 0.05 percent. This allows voltage transformers with Institute of Electrical and Electronics Engineers (IEEE) accuracy class of 0.15 to be precisely calibrated on site with regard to their ratio and phase error.

With VOTANO 100, OMICRON is introducing a high-precision mobile voltage transformer testing system that is easy to use where it is needed-in the field.

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