Recursive estimation in digital distance relaying system

Claim 3

The method of digital distance relaying claimed in claim 1 wherein said method further comprises the steps of electronically storing prior to the detecting of the fault pairs of distinct collections of numbers, said collection pairs respectively corresponding to said pairs of postfault line current and line voltage data; and utilizing each pair of said pairs of distinct collections of numbers in the recursive calculating in response to each said pair of postfault line current and line voltage data to which said each said pair corresponds.

Claim 4

The method of digital distance relaying claimed in claim 1 wherein said recursive electronic calculating is performed during parallel processing said voltage estimation procedure and said current estimation procedure.

Claim 5

The method of digital distance relaying claimed in claim 1 wherein said two state variables of said voltage estimation procedure correspond to amplitudes in quadrature, and said three state variables of said current estimation procedure correspond to amplitudes in quadrature and a transient waveform component.

Claim 6

The method of digital distance relaying claimed in claim 1 wherein each of said estimation procedures is in accordance with discrete Kalman Filtering.

Claim 9

The method of digital distance relaying claimed in claim 6 wherein said method further comprises the steps of electronically storing prior to the detecting of the fault a first table of sets of numbers, the sets respectively corresponding to the data for each voltage from said successive sampling, said first table being successively accessed by said first calculating means in said recursively automatically computing said voltage waveform state estimates; and electronically storing prior to the detecting of the fault a second table of sets of numbers, the sets respectively corresponding to the data for each current from said successive sampling, said second table being successively accessed at least by said second calculating means in said recursively automatically computing said current waveform state estimates.

Claim 10

In a distance relay having circuit breaker means for isolating a fault in one section of an alternating voltage transmission system, means having a first pair of input terminals energized by the voltage of said line and a second pair of input terminals energized by the current of said line, for providing periodic samples of said voltage and said current to calculating means; said calculating means being effective to determine the existence of the fault in response to an onset of the fault somewhere in said section and to provide an initial set of estimates including (A) cosine waveform state variable estimates respectively for said voltage and said current occurring subsequent to the onset of said fault, (B) negative sine waveform state variable estimates respectively for said voltage and said current occurring subsequent to the onset of said fault, and (C) at least one transient waveform state variable estimate for said current occurring subsequent to the onset of said fault, said calculating means further being effective to provide an updated set of said estimates all of said state variables during the time period between each pair of consecutive ones of said periodic samples subsequent to the onset of said fault on the basis of the most nearly previous sample of said voltage and the most nearly previous sample of said current and the most nearly previously provided set of said estimates, said calculating means being able to so provide an updated set of said estimates at least twice during the first half cycle after the onset of said fault, utilizing as to sampling data for computing said estimates only samples of said voltage and said current subsequent to the onset of said fault, said calculating means being effective to utilize the cosine waveform state variable estimates and the negative sine state variable estimates so updated in determining whether said fault is located in said one section of said transmission system and to trip said circuit breaker means substantially only when said fault is determined to be located in said one section.

Claim 11

In a distance relay having circuit breaker means for isolating a fault in one section of an alternating voltage transmission system, means having a first pair of input terminals energized by the voltage of said line and a second pair of input terminals energized by the current of said line, for providing periodic samples of said voltage and said current to calculating means; said calculating means being effective to determine the existence of the fault in response to an onset of the fault somewhere in said section and to provide an initial set of estimates including (A) cosine waveform state variable estimates respectively for said voltage and said current occurring subsequent to the onset of said fault, (B) negative sine waveform state variable estimates respectively for said voltage and said current occurring subsequent to the onset of said fault, and (C) at least one transient waveform state variable estimate for said current occurring subsequent to the onset of said fault, said calculating means further being effective to provide an updated set of said estimates all of said state variables during the time period between each pair of consecutive ones of said periodic samples subsequent to the onset of said fault on the basis of the most nearly previous sample of said voltage and the most nearly previous sample of said current and the most nearly previously provided set of said estimates, said calculating means being able to so provide an updated set of said estimates at least twice during the first half cycle after the onset of said fault, utilizing as to sampling data for computing said estimates only samples of said voltage and said current subsequent to the onset of said fault, said calculating means being effective to utilize the cosine waveform state variable estimates and the negative sine state variable estimates so updated in determining whether said fault is located in said one section of said transmission system and to trip said circuit breaker means substantially only when said fault is determined to be located in said one section.

Claim 12

The distance relay claimed in claim 8 wherein said calculating means comprises first, second, and third processor means, said first processor means being effective to provide said initial set of estimates and said updated set of estimates as to said voltage; said second processor means being effective to determine the existence of the fault and to provide said initial set of estimates and said updated set of estimates as to said current; said third processor means being effective to determine whether said fault is located in said one section and to trip said circuit breaker means.

Claim 13

The distance relay claimed in claim 9 wherein said calculating means further comprises first memory means associated with said first processor means having stored therein a first table of sets of numbers, the sets respectively corresponding to the periodic samples of said voltage, said first memory means being accessible by said first processor means for a respective distinct one of said sets of numbers in updating said estimates during the time period between each pair of consecutive ones of said periodic samples of said voltage; and second memory means associated with said second processor means having stored therein a second table of sets of numbers, the sets in the second table respectively corresponding to the periodic samples of said current, said second memory means being accessible by said second processor means for a respective distinct one of said sets of numbers in said second table in updating said estimates for said current during the time period between each pair of consecutive ones of said periodic samples of said current.