The application of ultrasonic techniques for location of partial discharges(PD) in power transformers is now well established -for example as described in references 1 and 2. A sound wave produced by a partial discharge inside a transformer must in general pass through various barriers on its way to a transducer attached to the outside of the tank wall. If the PD source is located deep inside the coils, the acoustic signal generated by the discharge may not be detectable because of the attenuation of the signal and the relatively poor sensitivity of the detecting system. Enhancement of the signal can be realised using signal averaging techniques. However, for a transformer having more than one PD source and large interference, averaging of the acoustic signals from different sources may lead to confusing results even when a combined electric and acoustic technique is used.The present paper describes a method by which these problems may be minimised or overcome. The electrical pulses on the HV and neutral terminals of a transformer and the outputs of two acoustic transducers attached to the tank wall were measured by a four channel digital transient recorder. The ratio of magnitudes of the electrical signals after filtering by a digital filter[3,41 of a predetermined frequency band for the winding was used to discriminate acoustic signals from different PD sources. The signals from the same PD source were then averaged resulting in significant suppression of the interference from mechanical vibration and from other PD sources. Tests on a 330kV/fl/3SMVA transformer in service have given encouraging results. An increase of the acoustic detection sensitivity by 20-40dB has been achieved.
This paper describes t h e initial experiences of t h e Snowy Mountains Hydro-Electric Authority with O n t a r i o Hydro P a r t i a l Discharge Analyser (PDA) technology. T h e f a c t o r s necessitating modification of t h e standard XLPE c a b l e coupler a n d its installation method a r e described. S o m e initial PDA test m e a s u r e m e n t results and t h e i r i n t e r p r e t a t i o n a r e presented.Comparisons a r e m a d e b e t w e e n P D A a n d o t h e r discharge d e t e c t o r measurements.T h e significant improvement in t h e Authority's knowledge of t h e condition of i t s g e n e r a t o r s t a t o r windings as a result of initial PDA m e a s u r e m e n t s is noted and it is concluded t h a t P D A condition monitoring will b e a n i m p o r t a n t tool in f u t u r e m a i n t e n a n c e s t r a t e g i c planning in t h e Snowy Mountains Scheme.
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