Methods for providing generator stator winding ground fault protection

Abstract

The present invention includes a method for providing ground fault protection to a generator. The method includes determining the existing state of the generator and second, determining the updated alarm or trip conditions of a relay connected to the generator in view of the existing state of the generator. This includes estimating a ratio of the magnitude of the 3 rd harmonic neutral voltage to the magnitude of the 3 rd harmonic terminal voltage of a generator, along with calculating the residual 3 rd harmonic voltage from the estimated 3 rd harmonic ratio. From this, a comparison is made between the energy of the residual voltage with a fractional energy of the 3 rd harmonic neutral voltage. Based on this comparison, an alarm or trip condition is signaled when the energy of the residual voltage is greater than the fractional energy of the 3 rd harmonic neutral voltage. The invention further includes adaptive relays and systems utilizing the adaptive relays, along with methods of producing power using the adaptive relays.

What is claimed is: 
     
         1 . A relay, comprising:
 a processor capable of being programmed with alarm or trip conditions for a relay; and   a program for the processor that establishes the conditions for the relay based on an existing state of a generator or electrical system.   
     
     
         2 . The relay of  claim 1  wherein the program determines the existing state of the generator or electrical system by estimating a ratio of the magnitude of the 3 rd  harmonic neutral voltage to the magnitude of the 3 rd  harmonic terminal voltage. 
     
     
         3 . The relay of  claim 1 , wherein the program determines the existing state of the generator or electrical system by estimating a ratio of the phasor of the 3 rd  harmonic neutral voltage to the phasor of the 3 rd  harmonic terminal voltage. 
     
     
         4 . The relay of  claim 2  wherein the program calculates a residual 3 rd  harmonic voltage. 
     
     
         5 . The relay of  claim 4  wherein the program establishes modified characteristic of a generator or electrical system relay based on the calculated energy of the residual 3 rd  harmonic voltage over at least six data points as compared to a fraction of the calculated energy of the 3 rd  harmonic neutral voltage over the same data points. 
     
     
         6 . The relay of  claim 5  wherein the program establishes the conditions for the relay in real time. 
     
     
         7 . The relay of  claim 2  wherein estimating the ratio comprises an iterative technique to estimate the ratio of the magnitude of the 3rd harmonic neutral voltage and the magnitude of the 3rd harmonic terminal voltage. 
     
     
         8 . The relay of  claim 7  wherein the iterative technique is selected from recursive weighted least-squares (RWLS), exponentially-weighted-past RWLS (EWP-RWLS) or a Kalman adaptive filter (KAF). 
     
     
         9 . An article of manufacture, comprising:
 a programmable relay, wherein the relay signals an alarm or trip condition when an energy of a residual 3rd harmonic voltage n the existing state of a generator or electrical system including a generator is greater than a fractional energy of a 3rd harmonic neutral voltage in the existing state of a generator or electrical system including a generator.   
     
     
         10 . The article of  claim 7  wherein the alarm or trip condition of the relay is set in real time. 
     
     
         11 . The article of  claim 7  wherein the residual 3rd harmonic voltage is calculated from an estimated 3rd harmonic ratio. 
     
     
         12 . The article of  claim 9  wherein the estimated 3rd harmonic ratio is estimated by comparing a magnitude of the 3rd harmonic neutral voltage to a magnitude of the 3rd harmonic terminal voltage of the generator. 
     
     
         13 . The article of  claim 12  wherein estimating the ratio comprises an iterative technique to estimate the ratio of the magnitude of the 3rd harmonic neutral voltage and the magnitude of the 3rd harmonic terminal voltage. 
     
     
         14 . The article of  claim 13  wherein the iterative technique is selected from recursive weighted least-squares (RWLS), exponentially-weighted-past RWLS (EWP-RWLS) or a Kalman adaptive filter (KAF). 
     
     
         15 . The article of  claim 7  wherein the estimated 3rd harmonic ratio is calculated by using an adaptive algorithm wherein the generator power factor, the magnitude or phasor of the 3rd harmonic neutral voltage, and the magnitude or phasor of the 3rd harmonic terminal voltage are used to estimate the 3rd harmonic ratio.