On-line detection of partial discharge in electrical power systems

Abstract

A method and apparatus for on-line detection of partial discharge events in an a.c. power system, in which high frequency electromagnetic pulses generated by partial discharge events are detected and analyzed in the frequency domain and the time domain to determine the type and location of the partial discharge event. The phase relationship between the partial discharge events and the on-line power signal is also examined to help indicate severity of the insulation anomaly giving rise to the partial discharge events.

1 . Apparatus for on-line location of partial discharge events in an a.c. power system during operation of the system while a.c. power is being applied through a power cable to a load, which includes: 
 a coupler for operative connection to the cable and responsive to current flowing through the cable for detecting high frequency electromagnetic pulses in the cable generated by partial discharge events caused by continuing application of a.c. power to the system,    a spectrum analyzer including means for operating said spectrum analyzer in a first mode of operation for analyzing pulses from said coupler in the frequency domain to identify a frequency at which partial discharge pulses of greatest magnitude are received at said coupler, and in a second mode of operation in the time domain at the frequency identified in said first mode of operation to identify a relationship between occurrence of said pulses and cycles of the a.c. power in the system, and    means for determining location of partial discharge events in the power system as a function of said frequency at which partial discharge pulses of greatest magnitude occur and said relationship between said pulses and cycles of a.c. power.    
     
     
         2 . The apparatus set forth in  claim 1  including: 
 a pulse phase analyzer for determining phase angle between said pulses detected by said coupler and a.c. power applied to the system, and  
 means for determining as a function of said phase angle a type of fault in the system that causes said partial discharge pulses.  
 
     
     
         3 . The apparatus set forth in  claim 2  including: 
 an antenna for receiving electromagnetic interference from the atmosphere surrounding the power cable, and  
 a differential amplifier connected between said coupler and said spectrum analyzer for subtracting said electromagnetic interference from said partial discharge pulses detected at said coupler.  
 
     
     
         4 . The apparatus set forth in  claim 1  wherein said coupler comprises an inductive coupler for removably exteriorly surrounding the cable to detect partial discharge current pulses in the cable.  
     
     
         5 . Apparatus for on-line analysis of location of partial discharge events during operation of an a.c. power system in which a.c. power is being applied through a cable to a load, which includes: 
 first means for detecting in the cable high frequency electromagnetic pulses generated by partial discharge events in the power system caused by continuing application of a.c. power to the system,    second means for analyzing said pulses detected by said first means in the frequency domain to identify a frequency component of greatest magnitude in said pulses and the frequency of said component,    third means for analyzing pulses detected by said first means in the time domain at the frequency of said component identified by said second means to determine a phase relationship between said frequency component and cycles of the a.c. power in the system,    fourth means for identifying location of partial discharge events in the power system as a function of said frequency of said frequency component identified by said second means and said phase relationship determined by said third means,    fifth means for determining a phase relationship between pulses detected by said first means and the a.c. power being applied to said system, and    sixth means for determining a type of fault in said system that causes said partial discharge events as a function of said phase relationship determined by said fifth means.    
     
     
         6 . The apparatus set forth in  claim 5  wherein said first means includes means for detecting said pulses within a selected frequency range.  
     
     
         7 . The apparatus set forth in  claim 6  wherein said first means includes means for filtering within said selected frequency range said high frequency pulses generated by partial discharge events in the power system against high frequency signals in the surrounding atmosphere.  
     
     
         8 . The apparatus set forth in  claim 7  wherein said means for filtering said high frequency pulses includes means for detecting high frequency signals in the surrounding atmosphere within said selected frequency range, and means for subtracting said high frequency signals in the surrounding atmosphere from said pulses.  
     
     
         9 . The apparatus set forth in  claim 8  wherein said selected frequency range includes the VHF frequency range.