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T&D World Magazine

Sweep Frequency Response Analyzer Diagnoses Power Transformers

Omicron offers a FRA (Frequency Response Analysis) measurement device for detecting possible damage to the windings or the magnetic core of a power transformer after transportation or after high short-circuit and inrush currents.

The FRAnalyzer uses the frequency sweep method. The input amplifiers work with a small bandwidth to prevent interference signals being superimposed on the measurement signal. This increases the accuracy particularly in the lower frequency range, where faults in the core can usually be detected. For higher frequencies, where the condition of the windings is investigated, this principle is also sensitive as the generated signal has constant amplitude over the whole frequency range. The internal 24 MBit AD converter of the FRAnalyzer enables it to operate at a high accuracy.

To identify changes, which can be quite small, the FRA measurement results are compared to a fingerprint of the transformer taken in a healthy condition. For the essential improvement of the reliability and repeatability of the measurement itself, Omicron has developed a connection technique using a pair of aluminum braids instead of the error prone connection with a wire. A patent for this technique is pending.

FRAnalyzer is controlled by a versatile, powerful software package. The connection between FRAnalyzer and the PC is established via the USB interface and can be operated over a distance of up to 30 m. The software also includes complete vector and network analyzer functionality that supports the measurement of transformer short circuit impedances.

The battery operation of the unit allows a mains independent operation of FRAnalyzer for up to four hours and also eliminates possible interferences by avoiding a galvanic connection to the 50/60 Hz mains.

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