Protective relaying system

Claim 2

A protective relaying system comprising: reference output circuit means for producing a digital signal; conversion means coupled to said reference output circuit means for receiving said digital signal and for converting said digital signal into a reference signal; processing means coupled to said conversion means for receiving said reference signal, for inverting said reference signal into an inverted reference signal, and for selecting one of said reference signal and said inverted reference signal to produce a digital reference output signal, said processing means including means for producing a selection signal; selection means for receiving a plurality of input signals from a source, said selection means being coupled to said processing means for receiving said selection signal and for selecting one of said plurality of input signals to produce a selected input signal based on said selection signal; digital to analog converter means coupled to receive said digital reference output signal from said processing means for converting said digital reference output signal into an analog reference signal; and comparison means coupled to receive said selected input signal from said selection means and coupled to receive said analog reference signal from said digital to analog converter means for comparing said selected input signal with said analog reference signal and for producing a decision signal in digital form according to the result of the comparison; wherein said processing means is coupled to receive said decision signal from said comparison means for processing said decision signal to produce a relay output signal.

Claim 3

A protective relaying system comprising: reference output circuit means for producing a digital signal; processing means including means for producing a permission signal and means for producing a selection signal; conversion means coupled to receive said digital signal from said reference output circuit means and coupled to receive said permission signal from said processing means for converting said digital signal into a digital reference signal in response to said permission signal; selection means coupled to receive a plurality of input signals from a source and coupled to receive said selection signal from said processing means for selecting one of said plurality of input signals to produce a selected input signal in response to said selection signal; digital to analog converter means coupled to receive said digital reference signal from said conversion means for converting said digital reference signal into an analog reference signal; and comparison means coupled to receive said selected input signal from said selection means and coupled to receive said analog reference signal from said digital to analog converter means for comparing said selected input signal with said analog reference signal and for producing a decision signal in digital form according to the result of the comparison; wherein said processing means is coupled to receive said decision signal from said comparison means for processing said decision signal to produce a relay output signal.

Claim 4

A protective relaying system comprising: reference output circuit means for producing a digital signal; processing means including means for producing a permission signal and means for producing a selection signal; conversion means coupled to receive said digital signal from said reference output circuit means and coupled to receive said permission signal from said processing means for converting said digital signal into a digital reference signal in response to said permission signal; selection means coupled to receive a plurality of input signals from a source and coupled to receive said selection signal from said processing means for selecting one of said plurality of input signals to produce a selected input signal in response to said selection signal; digital to analog converter means coupled to receive said digital reference signal from said conversion means for converting said digital reference signal into an analog reference signal; and comparison means coupled to receive said selected input signal from said selection means and coupled to receive said analog reference signal from said digital to analog converter means for comparing said selected input signal with said analog reference signal and for producing a decision signal in digital form according to the result of the comparison; wherein said processing means is coupled to receive said decision signal from said comparison means for processing said decision signal to produce a relay output signal.

Claim 5

The protective relaying system as recited in claim 2, wherein: said processing means further includes means coupled to said conversion means for receiving said digital reference signal and for checking said digital reference signal.

Claim 6

The protective relaying system as recited in claim 3, wherein: said permission signal includes a first enabling signal and a second enabling signal; said conversion means includes a first conversion unit means and a second conversion unit means; said first conversion unit means being coupled to receive said digital signal from said reference output circuit means and coupled to receive said first enabling signal from said processing means for converting said digital signal into a first reference signal in response to said first enabling signal; said second conversion unit means being coupled to receive said digital signal from said reference output circuit means and coupled to receive said second enabling signal from said processing means for converting said digital signal to form an inverted reference signal in response to said second enabling signal; said first reference signal and said inverted reference signal forming said digital reference signal.

Claim 7

A protective relaying system, comprising: reference output means for producing a reference output signal; processing means including means for producing a selection signal; first selection means for receiving a plurality of input signals from a source, said first selection means being coupled to said processing means for receiving said selection signal and selecting one of said input signals to produce a selected input signal based on said selection signal; and comparison means coupled to receive said selected input signal from said first selection means and coupled to receive said reference output signal from said reference output means for comparing said selected input signal with said reference output signal and for producing a decision signal in digital form according to the result of the comparison; wherein said processing means is coupled to receive said decision signal from said comparison means for processing said decision signal to produce a relay output signal; and wherein said processing means further includes means for producing a switching signal, and wherein said reference output means comprises, first reference unit means for producing a first reference signal, second reference unit means for producing a second reference signal, and switching means coupled to receive said first and second reference signals from said first and second reference unit means and coupled to receive said switching signal from said processing means for selecting one of said first and said second reference signals as said reference output signal under control of said switching signal.

Claim 8

A protective relaying system, comprising: reference output means for producing a reference output signal; processing means including means for producing a selection signal; first selection means for receiving a plurality of input signals from a source, said first selection means being coupled to said processing means for receiving said selection signal and selecting one of said input signals to produce a selected input signal based on said selection signal; and comparison means coupled to receive said selected input signal from said first selection means and coupled to receive said reference output signal from said reference output means for comparing said selected input signal with said reference output signal and for producing a decision signal in digital form according to the result of the comparison; wherein said processing means is coupled to receive said decision signal from said comparison means for processing said decision signal to produce a relay output signal; and wherein said processing means further includes means for producing a switching signal, and wherein said reference output means comprises, first reference unit means for producing a first reference signal, second reference unit means for producing a second reference signal, and switching means coupled to receive said first and second reference signals from said first and second reference unit means and coupled to receive said switching signal from said processing means for selecting one of said first and said second reference signals as said reference output signal under control of said switching signal.

Claim 9

The protective relaying system as recited in claim 5, wherein said first and second reference unit means each comprise: a power source having first and second terminals; an output terminal; a first resistor coupled between said first terminal of said power source and said second output terminal; a plurality of second resistors, each of said plurality of second resistors having first and second terminals, each of said first terminals of said plurality of second resistors being coupled to said output terminal; and second selection means coupled between said second terminal of said power source and said second terminals of said plurality of second resistors for selectively coupling each of said second terminals of said plurality of resistors to said second terminal of said power source.

Claim 10

The protective relaying system as recited in claim 3, which further comprises: a plurality of full-wave rectifier means coupled between said source of said plurality of input signals and said selection means for full-wave rectifying said plurality of input signals.

Claim 11

The protective relaying system as recited in claim 7, which further comprises: a plurality of input transformer means coupled between said source of said plurality of input signals and said plurality of full-wave rectifier means for converting said plurality of input signals into a plurality of transformed input signals having predetermined voltage levels.

Claim 12

A protective relaying system, comprising: reference output means for producing a reference output signal; processing means including means for producing a selection signal; first selection means for receiving a plurality of input signals from a source, said first selection means being coupled to said processing means for receiving said selection signal and selecting one of said input signals to produce a selected input signal based on said selection signal; and comparison means coupled to receive said selected input signal from said first selection means and coupled to receive said reference output signal from said reference output means for comparing said selected input signal with said reference output signal and for producing a decision signal in digital form according to the result of the comparison: wherein said processing means is coupled to receive said decision signal from said comparison means for processing said decision signal to produce a relay output signal; and wherein said processing means further includes means for producing a switching signal, and wherein said reference output means comprises, first reference unit means for producing a first reference signal, inverting means coupled to receive said first reference signal from said first reference means for inverting said first reference signal to produce an inverted reference signal, and switching means coupled to receive said first reference signal from said first reference unit means, coupled to receive said inverted reference signal from said inverting means, and coupled to receive said switching signal from said processing means for selecting either of said first reference signal and said inverted reference signal as said reference output signal under control of said switching signal.

Claim 13

A protective relaying system, comprising: reference output means for producing a reference output signal; processing means including means for producing a selection signal; first selection means for receiving a plurality of input signals from a source, said first selection means being coupled to said processing means for receiving said selection signal and selecting one of said input signals to produce a selected input signal based on said selection signal; and comparison means coupled to receive said selected input signal from said first selection means and coupled to receive said reference output signal from said reference output means for comparing said selected input signal with said reference output signal and for producing a decision signal in digital form according to the result of the comparison: wherein said processing means is coupled to receive said decision signal from said comparison means for processing said decision signal to produce a relay output signal; and wherein said processing means further includes means for producing a switching signal, and wherein said reference output means comprises, first reference unit means for producing a first reference signal, inverting means coupled to receive said first reference signal from said first reference means for inverting said first reference signal to produce an inverted reference signal, and switching means coupled to receive said first reference signal from said first reference unit means, coupled to receive said inverted reference signal from said inverting means, and coupled to receive said switching signal from said processing means for selecting either of said first reference signal and said inverted reference signal as said reference output signal under control of said switching signal.

Claim 14

The protective relaying system as recited in claim 9, wherein said first reference unit means comprises: a power source having first and second terminals; an output terminal; a first resistor coupled between said first terminal of said power source and said output terminal; a plurality of second resistors, each of said plurality of second resistors having first and second terminals, each of said first terminals of said plurality of second resistors being coupled to said output terminal; and second selection means coupled between said second terminal of said power source and said second terminals of said plurality of second resistors for selectively coupling each of said second terminals of said plurality of resistors to said second terminal of said power source.

Claim 15

A protective relaying system, comprising: processing means including means for producing a selection signal and means for producing a digital reference output signal; selection means for receiving a plurality of input signals from a source, said selection means being coupled to said processing means for receiving said selection signal and selecting one of said input signals to produce a selected input signal based on said selection signal; digital to analog converter means coupled to receive said digital reference output signal from said processing means for converting said digital reference signal into an analog reference signal; and comparison means coupled to receive said selected input signal from said selection means and coupled to receive said analog reference signal from said digital to analog converter means for comparing said selected input signal with said analog reference signal and for producing a decision signal in digital form according to the result of the comparison; wherein said processing means further includes, means for producing a first reference signal, means for inverting said first reference signal to form an inverted reference signal, and switching means coupled to receive said first reference signal and said inverted reference signal for selecting one of said first reference signal and said inverted reference signal to form said digital reference output signal; and wherein said processing means is coupled to receive said decision signal from said comparison means for processing said decision signal to produce a relay output signal.

Claim 16

A protective relaying system, comprising: processing means including means for producing a selection signal and means for producing a digital reference output signal; selection means for receiving a plurality of input signals from a source, said selection means being coupled to said processing means for receiving said selection signal and selecting one of said input signals to produce a selected input signal based on said selection signal; digital to analog converter means coupled to receive said digital reference output signal from said processing means for converting said digital reference signal into an analog reference signal; and comparison means coupled to receive said selected input signal from said selection means and coupled to receive said analog reference signal from said digital to analog converter means for comparing said selected input signal with said analog reference signal and for producing a decision signal in digital form according to the result of the comparison; wherein said processing means further includes, means for producing a first reference signal, means for inverting said first reference signal to form an inverted reference signal, and switching means coupled to receive said first reference signal and said inverted reference signal for selecting one of said first reference signal and said inverted reference signal to form said digital reference output signal; and wherein said processing means is coupled to receive said decision signal from said comparison means for processing said decision signal to produce a relay output signal.

Claim 17

The protective relaying system as recited in claim 11, which further comprises: reference output circuit means for producing a digital signal; wherein said means for producing said first reference signal in said processing means is coupled to receive said digital signal from said reference output circuit means for converting said digital signal into said first reference signal.

Claim 18

A protective relaying system comprising: reference output circuit means for producing a digital signal; processing means coupled to receive said digital signal from said reference output circuit means for converting said digital signal to produce a digital reference output signal, said processing means including means for producing a selection signal; selection means for receiving a plurality of input signals from a source, said selection means being coupled to said processing means for receiving said selection signal and for selecting one of said plurality of input signals to produce a selected input signal based on said selection signal; digital to analog converter means coupled to receive said digital reference output signal from said processing means for converting said digital reference output signal into an analog reference signal; and comparison means coupled to receive said selected input signal from said selection means and coupled to receive said analog reference signal from said digital to analog converter means for comparing said selected input signal with said analog reference signal and for producing a decision signal in digital form according to the result of the comparison; wherein said processing means is coupled to receive said decision signal from said comparison means for processing said decision signal to produce a relay output signal, wherein said processing means further includes means for producing a first read signal and a second read signal, and wherein said reference output circuit means comprises, first reference unit means for producing a first digital reference signal, second reference unit means for producing a second digital reference signal, and means coupled to said processing means for receiving said first read signal and said second read signal, for selecting one of said first digital reference signal and said second digital reference signal in response to said first and second read signals to produce said digital signal.

Claim 19

A protective relaying system comprising: reference output circuit means for producing a digital signal; processing means coupled to receive said digital signal from said reference output circuit means for converting said digital signal to produce a digital reference output signal, said processing means including means for producing a selection signal; selection means for receiving a plurality of input signals from a source, said selection means being coupled to said processing means for receiving said selection signal and for selecting one of said plurality of input signals to produce a selected input signal based on said selection signal; digital to analog converter means coupled to receive said digital reference output signal from said processing means for converting said digital reference output signal into an analog reference signal; and comparison means coupled to receive said selected input signal from said selection means and coupled to receive said analog reference signal from said digital to analog converter means for comparing said selected input signal with said analog reference signal and for producing a decision signal in digital form according to the result of the comparison; wherein said processing means is coupled to receive said decision signal from said comparison means for processing said decision signal to produce a relay output signal, wherein said processing means further includes means for producing a first read signal and a second read signal, and wherein said reference output circuit means comprises, first reference unit means for producing a first digital reference signal, second reference unit means for producing a second digital reference signal, and means coupled to said processing means for receiving said first read signal and said second read signal, for selecting one of said first digital reference signal and said second digital reference signal in response to said first and second read signals to produce said digital signal.

Claim 20

A protective relaying system comprising: reference output circuit means for producing a digital signal; processing means coupled to receive said digital signal from said reference output circuit means for converting said digital signal to produce a digital reference output signal, said processing means including means for producing a selection signal; selection means for receiving a plurality of input signals from a source, said selection means being coupled to said processing means for receiving said selection signal and for selecting one of said plurality of input signals to produce a selected input signal based on said selection signal; digital to analog converter means coupled to receive said digital reference output signal from said processing means for converting said digital reference output signal into an analog reference signal; comparison means coupled to receive said selected input signal from said selection means and coupled to receive said analog reference signal from said digital to analog converter means for comparing said selected input signal with said analog reference signal and for producing a decision signal in digital form according to the result of the comparison; wherein said processing means is coupled to receive said decision signal from said comparison means for processing said decision signal to produce a relay output signal; wherein said processing means further includes, means for producing a first write signal and a second write signal, said processing means converting said digital signal into an expanded digital signal having a longer bit length than the bit length of said digital signal, said processing means separating said expanded digital signal into a lower bit signal and an upper bit signal; first latch means being coupled to receive said lower bit signal and said first write signal from said processing means for latching said lower bit signal to produce a lower bit reference signal upon receipt of said first write signal; second latch means being coupled to receive said upper bit signal and said second write signal from said processing means for latching said upper bit signal to produce an upper bit reference signal upon receipt of said second write signal; and said digital to analog converter means being coupled to said first latch means for receiving said lower bit reference signal and coupled to said second latch means for receiving said upper bit reference signal as said digital reference output signal.

Claim 21

A protective relaying system comprising: reference output circuit means for producing a digital signal; processing means coupled to receive said digital signal from said reference output circuit means for converting said digital signal to produce a digital reference output signal, said processing means including means for producing a selection signal; selection means for receiving a plurality of input signals from a source, said selection means being coupled to said processing means for receiving said selection signal and for selecting one of said plurality of input signals to produce a selected input signal based on said selection signal; digital to analog converter means coupled to receive said digital reference output signal from said processing means for converting said digital reference output signal into an analog reference signal; comparison means coupled to receive said selected input signal from said selection means and coupled to receive said analog reference signal from said digital to analog converter means for comparing said selected input signal with said analog reference signal and for producing a decision signal in digital form according to the result of the comparison; wherein said processing means is coupled to receive said decision signal from said comparison means for processing said decision signal to produce a relay output signal; wherein said processing means further includes, means for producing a first write signal and a second write signal, said processing means converting said digital signal into an expanded digital signal having a longer bit length than the bit length of said digital signal, said processing means separating said expanded digital signal into a lower bit signal and an upper bit signal; first latch means being coupled to receive said lower bit signal and said first write signal from said processing means for latching said lower bit signal to produce a lower bit reference signal upon receipt of said first write signal; second latch means being coupled to receive said upper bit signal and said second write signal from said processing means for latching said upper bit signal to produce an upper bit reference signal upon receipt of said second write signal; and said digital to analog converter means being coupled to said first latch means for receiving said lower bit reference signal and coupled to said second latch means for receiving said upper bit reference signal as said digital reference output signal.

Claim 22

The protective relaying system as recited in claim 13, or 14, wherein said processing means further includes: means for converting said digital signal into a first reference signal; means for inverting said first reference signal to form an inverted reference signal; and switching means coupled to receive said first reference signal and said inverted reference signal for selecting one of said first reference signal and said inverted reference signal to form said digital reference output signal.

Claim 23

The protective relaying system as recited in claims 1, 4, 5, 9, 13 or 14, which further comprises: a plurality of input transformer means coupled between said source of said plurality of input signals and said selection means for converting said plurality of input signals into a plurality of transformed input signals having predetermined voltage levels.

Claim 24

The protective relaying system as recited in claim 16, which further includes input signal processing means coupled between said plurality of input transformer means and said selection means, said signal processing means comprising: bandpass filter means coupled to receive said plurality of transformed input signals from said plurality of input transformer means for filtering each of said plurality of transformed input signals and for producing a plurality of filtered input signals, said plurality of filtered input signals being supplied to said selection means; and difference circuit means coupled to receive said plurality of transformed input signals from said plurality of input transformer means and coupled to receive said plurality of filtered means for producing a plurality of difference input signals, said plurality of difference input signals being supplied to said selection means, each of said plurality of difference input signals being the difference between a corresponding one of said plurality of transformed input signals and a corresponding one of said polurality of filtered input signals.

Claim 25

A protective relaying system, comprising: reference output means for producing a reference output signal; processing means including means for producing a selection signal; first selection means for receiving a plurality of input signals from a source, said first selection means being coupled to said processing means for receiving said selection signal and selecting one of said input signals to produce a selected input signal based on said selection signal; and comparison means coupled to receive said selected input signal from said first selection means and coupled to receive said reference output signal from said reference output means for comparing said selected input signal with said reference output signal and for producing a decision signal in digital form according to the result of the comparison; wherein said processing means is coupled to receive said decision signal from said comparison means for processing said decision signal to produce a relay output signal only when said decision signal becomes a predetermined logic value consecutively for a predetermined number of times, and wherein said reference output means comprises, a power source having first and second terminals, an output terminal, a first resistor coupled between said first terminal of said power source and said output terminal, a plurality of second resistors, each of said plurality of second resistors having first and second terminals, each of said first terminals of said plurality of second resistors being coupled to said output terminal, and second selection means coupled between said second terminal of said power source and said second terminals of said plurality of second resistors for selectively coupling each of said second terminals of said plurality of resistors to said second terminal of said power source.

Claim 26

A protective relaying system, comprising: reference output means for producing a reference output signal; processing means including means for producing a selection signal; first selection means for receiving a plurality of input signals from a source, said first selection means being coupled to said processing means for receiving said selection signal and selecting one of said input signals to produce a selected input signal based on said selection signal; and comparison means coupled to receive said selected input signal from said first selection means and coupled to receive said reference output signal from said reference output means for comparing said selected input signal with said reference output signal and for producing a decision signal in digital form according to the result of the comparison; wherein said processing means is coupled to receive said decision signal from said comparison means for processing said decision signal to produce a relay output signal only when said decision signal becomes a predetermined logic value consecutively for a predetermined number of times, and wherein said reference output means comprises, a power source having first and second terminals, an output terminal, a first resistor coupled between said first terminal of said power source and said output terminal, a plurality of second resistors, each of said plurality of second resistors having first and second terminals, each of said first terminals of said plurality of second resistors being coupled to said output terminal, and second selection means coupled between said second terminal of said power source and said second terminals of said plurality of second resistors for selectively coupling each of said second terminals of said plurality of resistors to said second terminal of said power source.

Claim 27

A protective relaying system, comprising: reference output means for producing a reference output signal; processing means including means for producing a selection signal; selection means for receiving a plurality of input signals from a source, said selection means being coupled to said processing means for receiving said selection signal and selecting one of said input signals to produce a selected input signal based on said selection signal; comparison means coupled to receive said selected input signal from said selection means and coupled to receive said reference output signal from said reference output means for comparing said selected intput signal with said reference output signal and for producing a decision signal in digital form according to the result of the comparison; a plurality of input transformer means coupled between said source of said plurality of input signals and said selection means for converting said plurality of input signals into a plurality of transformed input signals having predetermined voltage levels; and input signal processing means coupled between said plurality of input transformer means and said selection means, said signal processing means comprising, bandpass filter means coupled to receive said plurality of transformed input signals from said plurality of input transformer means for filtering each of said plurality of transformed input signals and for producing a plurality of filtered input signals, said plurality of filtered input signals being supplied to said selection means, and difference circuit means coupled to receive said plurality of transformed input signals from said plurality of input transformer means and coupled to receive said plurality of filtered input signals from said bandpass filter means for producing a plurality of difference input signals, said plurality of difference input signals being supplied to said selection means, each of said plurality of difference input signals being the difference between a corresponding one of said plurality of transformed input signals and a corresponding one of said plurality of filtered input signals; wherein said processing means is coupled to receive said decision signal from said comparison means for processing said decision signal to produce a relay output signal only when said decision signal becomes a predetermined logic value consecutively for a predetermined number of times.

Claim 28

A protective relaying system, comprising: reference output means for producing a reference output signal; processing means including means for producing a selection signal; selection means for receiving a plurality of input signals from a source, said selection means being coupled to said processing means for receiving said selection signal and selecting one of said input signals to produce a selected input signal based on said selection signal; comparison means coupled to receive said selected input signal from said selection means and coupled to receive said reference output signal from said reference output means for comparing said selected intput signal with said reference output signal and for producing a decision signal in digital form according to the result of the comparison; a plurality of input transformer means coupled between said source of said plurality of input signals and said selection means for converting said plurality of input signals into a plurality of transformed input signals having predetermined voltage levels; and input signal processing means coupled between said plurality of input transformer means and said selection means, said signal processing means comprising, bandpass filter means coupled to receive said plurality of transformed input signals from said plurality of input transformer means for filtering each of said plurality of transformed input signals and for producing a plurality of filtered input signals, said plurality of filtered input signals being supplied to said selection means, and difference circuit means coupled to receive said plurality of transformed input signals from said plurality of input transformer means and coupled to receive said plurality of filtered input signals from said bandpass filter means for producing a plurality of difference input signals, said plurality of difference input signals being supplied to said selection means, each of said plurality of difference input signals being the difference between a corresponding one of said plurality of transformed input signals and a corresponding one of said plurality of filtered input signals; wherein said processing means is coupled to receive said decision signal from said comparison means for processing said decision signal to produce a relay output signal only when said decision signal becomes a predetermined logic value consecutively for a predetermined number of times.

Claim 29

A protective relaying system, comprising: processing means including means for producing a selection signal and means for producing a digital reference output signal; selection means for receiving a plurality of input signals from a source, said selection means being coupled to said processing means for receiving said selection signal and selecting one of said input signals to produce a selected input signal based on said selection signal; digital to analog converter means coupled to receive said digital reference output signal from said processing means for converting said digital reference signal into an analog reference signal; comparison means coupled to receive said selected input signal from said selection means and coupled to receive said analog reference signal from said digital to analog converter means for comparing said selected input signal with said analog reference signal and for producing a decision signal in digital form according to the result of the comparison; a plurality of input transformer means coupled between said source of said plurality of input signals and said selection means for converting said plurality of input signals into a plurality of transformed input signals having predetermined voltage levels; and input signal processing means coupled between said plurality of input transformer means and said selection means, said signal processing means comprising, bandpass filter means coupled to receive said plurality of transformed input signals from said plurality of input transformer means for filtering each of said plurality of transformed input signals and for producing a plurality of filtered input signals, said plurality of filtered input signals being supplied to said selection means, and difference circuit means coupled to receive said plurality of transformed input signals from said plurality of input transformer means and coupled to receive said plurality of filtered input signals from said bandpass filter means for producing a plurality of difference input signals, said plurality of difference input signals being supplied to said selection means, each of said plurality of difference input signals being the difference between a corresponding one of said plurality of transformed input signals and a corresponding one of said plurality of filtered input signals; wherein said processing means is coupled to receive said decision signal from said comparison means for processing said decision signal to produce a relay output signal only when said decision signal becomes a predetermined logic value consecutively for a predetermined number of times.

Claim 30

A protective relaying system, comprising: processing means including means for producing a selection signal and means for producing a digital reference output signal; selection means for receiving a plurality of input signals from a source, said selection means being coupled to said processing means for receiving said selection signal and selecting one of said input signals to produce a selected input signal based on said selection signal; digital to analog converter means coupled to receive said digital reference output signal from said processing means for converting said digital reference signal into an analog reference signal; comparison means coupled to receive said selected input signal from said selection means and coupled to receive said analog reference signal from said digital to analog converter means for comparing said selected input signal with said analog reference signal and for producing a decision signal in digital form according to the result of the comparison; a plurality of input transformer means coupled between said source of said plurality of input signals and said selection means for converting said plurality of input signals into a plurality of transformed input signals having predetermined voltage levels; and input signal processing means coupled between said plurality of input transformer means and said selection means, said signal processing means comprising, bandpass filter means coupled to receive said plurality of transformed input signals from said plurality of input transformer means for filtering each of said plurality of transformed input signals and for producing a plurality of filtered input signals, said plurality of filtered input signals being supplied to said selection means, and difference circuit means coupled to receive said plurality of transformed input signals from said plurality of input transformer means and coupled to receive said plurality of filtered input signals from said bandpass filter means for producing a plurality of difference input signals, said plurality of difference input signals being supplied to said selection means, each of said plurality of difference input signals being the difference between a corresponding one of said plurality of transformed input signals and a corresponding one of said plurality of filtered input signals; wherein said processing means is coupled to receive said decision signal from said comparison means for processing said decision signal to produce a relay output signal only when said decision signal becomes a predetermined logic value consecutively for a predetermined number of times.

Claim 31

A protective relaying system, comprising: processing means including means for producing a selection signal and means for producing a digital reference output signal; selection means for receiving a plurality of input signals from a source, said selection means being coupled to said processing means for receiving said selection signal and selecting one of said input signals to produce a selected input signal based on said selection signal; digital to analog converter means coupled to receive said digital reference output signal from said processing means for converting said digital reference signal into an analog reference signal; comparison means coupled to receive said selected input signal from said selection means and coupled to receive said analog reference signal from said digital to analog converter means for comparing said selected input signal with said analog reference signal and for producing a decision signal in digital form according to the result of the comparison; and reference output circuit means for producing a digital signal; wherein said processing means further includes means coupled to said reference output circuit means for receiving said digital signal and for converting said digital signal into said digital reference output signal, and wherein said processing means is coupled to receive said decision signal from said comparison means for processing said decision signal to produce a relay output signal only when said decision signal becomes a predetermined logic value consecutively for a predetermined number of times.

Claim 32

A protective relaying system, comprising: processing means including means for producing a selection signal and means for producing a digital reference output signal; selection means for receiving a plurality of input signals from a source, said selection means being coupled to said processing means for receiving said selection signal and selecting one of said input signals to produce a selected input signal based on said selection signal; digital to analog converter means coupled to receive said digital reference output signal from said processing means for converting said digital reference signal into an analog reference signal; comparison means coupled to receive said selected input signal from said selection means and coupled to receive said analog reference signal from said digital to analog converter means for comparing said selected input signal with said analog reference signal and for producing a decision signal in digital form according to the result of the comparison; and reference output circuit means for producing a digital signal; wherein said processing means further includes means coupled to said reference output circuit means for receiving said digital signal and for converting said digital signal into said digital reference output signal, and wherein said processing means is coupled to receive said decision signal from said comparison means for processing said decision signal to produce a relay output signal only when said decision signal becomes a predetermined logic value consecutively for a predetermined number of times.

Claim 33

The protective relaying system as recited in claims 2, 21, 13 or 14, which further comprises: a plurality of full-wave rectifier means coupled between said source of said plurality of input signals and said selection means for full-wave rectifying said plurality of input signals.

Claim 34

The protective relaying system as recited in claims 11 or 12 which further comprises: a plurality of input transformer means coupled between said source of said plurality of input signals and said selection means for converting said plurality of input signals into a plurality of transformed input signals having predetermined voltage levels.

Claim 35

The protective relaying system as recited in claim 22, which further comprises: a plurality of input transformer means coupled between said source of said plurality of input signals and said plurality of full-wave rectifier means for converting said plurality of input signals into a plurality of transformed input signals having predetermined voltage levels.

Claim 36

The protective relaying system as recited in claim 23, which further includes input signal processing means coupled between said plurality of input transformer means and said selection means, said signal processing means comprising: bandpass filter means coupled to receive said plurality of transformed input signals from said plurality of input transformer means for filtering each of said plurality of transformed input signals and for producing a plurality of filtered input signals, said plurality of filtered input signals being supplied to said selection means; and difference circuit means coupled to receive said plurality of transformed input signals from said plurality of input transformer means and coupled to receive said plurality of filtered input signals from said bandpass filter means for producing a plurality of difference input signals, said plurality of difference input signals being supplied to said selection means, each of said plurality of difference input signals being the difference between a corresponding one of said plurality of transformed input signals and a corresponding one of said plurality of filtered input signals.