| In practical application of partial discharge on-line monitoring system inpower transformer based on UHF method, we found the valve has much impact todetection. The paper studies the characteristic of UHF wave in the pipe in case ofbutterfly valve. UHF signal was decayed and distorted a lot when it passed metalvalve plate. The metal pipe is high pass filter. We design the on-line installationdevice of butterfly valve sensor. The head of sensor could easily pass through thevalve plate because of its eccentric structure. The performances of circular/conicalhelix antennas are experimentally studied through partial discharge experiment inoil. The pitch, length and diameter have impact to response characteristic ofantennas. The shorter the pitch is, the higher the signal amplitude is when the lengthof antenna is fixed. Low-frequency characteristic of helix antenna is better if it haslarger diameter. The head wave response velocity of conical spiral antenna is slowerthan that of circular spiral antenna.
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