Acoustic testing of cable joints and bushings in the switchgears
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Acoustic testing of instrument transformers Acoustic testing of the switchgears Acoustic testing of power transformers Implementation of the system of control of electrical insulation characteristics New approaches to monitoring of the technical condition of the switchgear equipment
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In accordance with paragraph 29.13 of "Volumes and standards of testing of electrical equipment", the power cable lines during commissioning should be tested at voltage of 1,00 - 1,73 U nom, 50 Hz. Due to the absence of appropriate test equipment in Russia, there are restricts that allow only monitoring of partial discharges in terminations of cable lines under operating voltage for the first run. Acoustic method is the most effective non-invasive diagnostic method to be implemented under operating voltage. Terminations of Russian production (type МКАПВ 64/110) are the most accidental. In the 90’s in Mosenergo there had been more than 10 accidents of these terminations per year (the total amount of installed terminations was about 300). However, import terminations are also accidental. For example, in 2007 at “City” SS, there was an accident of 110 kV Siemens termination. Therefore, acoustic screening for partial discharges continues to be important.
The main reason for the breakdown of МКАПВ 64/110 is an imperfect technology. Usually acoustic survey is conducted under operating voltage without disconnecting and removing the load. During the acoustic survey РЧРш sensor is installed on the grounded base plate of 110 kV termination, and its signal is detected by "Dolphin" device. The sensitivity of the instrument is such, that it allows you to record the signals of initial level (several pC). This corresponds to the ignition of the first level indicator of "Dolphin". If there are significant acoustic signals above the noise level, the waveform of the ultrasonic signals in two periods of frequency is recorded. The analysis of acoustic signals in the frequency spectrum, with linking the signals to the phase of voltage amplitude and stability is performed. The signals from electrical discharges that have high range of 60h130 kHz and occur twice during the period are unstable to amplitude. Spectrum of the acoustic signal is determined by the software of "AKTAKOM"oscilloscope by fast Fourier transform.
Hazard criteria for partial discharges and problem of making decisions about the urge for repairs are described in "Methods of insulation control for 110 kV switchgears and terminations of jumper cables with polyethylene insulation ..." by Mosenergo. The decision on the recommendations to repair has to be made when partial discharges reach 25-100 pC. Decision on urgent disabling - at the partial discharge level of more than 100 pC. The sound of such discharge process leads to ignition of three to five signals of the "Dolphin".
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