Means and method for measuring power system frequency

Claim 3

The method as in claim 1 wherein said signal is sampled from 8 to 24 times for each of said first and second cycle of said signal.

Claim 4

The method as in claim 1 wherein said signal is sampled 12 times for each of said first and second cycle of said signal.

Claim 5

The method as in claim 1 wherein said first and second cycles are consecutive.

Claim 6

The method as in claim 1 wherein said sampling is repeated at predetermined intervals.

Claim 7

The method as in claim 5 wherein said sampling is performed once every ten cycles of said signal.

Claim 8

The method as in claim 5 wherein said sampling is performed once every other cycle of said signal.

Claim 9

The method as in claim 1 wherein generating said first phasor comprises: generating a component of said first phasor from each of said data values associated with the first cycle of said signal in accordance with the following expression: ##EQU13## wherein: V 1 =first cycle data values; Δt=sampling period; N=samples per cycle; and k=summation index; and summing each of the components determined from the data values associated with the first cycle to produce said first phasor.

Claim 10

The method as in claim 8 wherein generating said second phasor comprises: generating a component or said second phasor from each of said data values associated with the second cycle of said signal in accordance with the following expression: ##EQU14## wherein: V 2 =second cycle data values Δt=sampling period; N=samples per cycle; and k=summation index; and summing each of the components determined from the data values associated with the second cycle to produce said second phasor.

Claim 11

The method as in claim 1 further comprising: generating the inverse tangent of the ratio of the imaginary portion of said frequency deviation phasor (IMAG (D)) divided by the real portion of said frequency deviation phasor (REAL(D)), wherein said inverse tangent is indicative of the frequency deviation of said signal from said predetermined reference frequency; and supplying said inverse tangent to display means for providing an indication of the frequency deviation.

Claim 12

The method as in claim 10 wherein said inverse tangent is determined in accordance with the following formula: ##EQU15## wherein x represents the ratio of the imaginary portion of said frequency deviation phasor divided by the real portion of said frequency deviation phasor.

Claim 13

The method as in claim 10 further comprising: generating a signal from said inverse tangent representative of an actual system frequency; supplying said actual system frequency to display means for providing an indication of the actual system frequency.

Claim 14

The method as in claim 1 further comprising: generating an over-frequency warning if the imaginary portion of said frequency deviation phasor (IMAG(D)) is greater than the real portion of said frequency deviation phasor (REAL(D)) times tan 2π(f 1 -f o )/f o , wherein f 1 is a predetermined upper frequency limit and if REAL(D) is greater than zero; generating an over-frequency warning if IMAG(D)<REAL(D)·tan 2π(f x -f o )/f o and if REAL (D) is less than zero; generating an under-frequency warning if IMAG(D)<REAL(D)·tan 2π(f x -f o )/f o wherein f x is a predetermined lower frequency limit and if REAL(D) is greater than zero; and generating an under-frequency warning if IMAG(D)>REAL(D)·tan 2π(f x -f o )/f o is less than zero.

Claim 15

The method as in claim 13 wherein said signal is representative of the frequency of a power system and generating an over-frequency warning comprises: removing power supplying said power system; and providing an indication of said over-frequency warning.

Claim 16

The method as in claim 13 wherein said signal is representative of the frequency of a power system and generating an under-frequency warning comprises: removing power supplying said power system; and providing an indication of said under-frequency warning.

Claim 17

The method of claim 1 further comprising displaying the frequency deviation of said signal from said predetermined reference frequency.

Claim 18

The method of claim 1 wherein generating a first and second phasor comprises generating a discrete Fourier transform for each of said first and second cycle of said signal, respectively, from the data values respectively associated with said first and second cycle of said signal.

Claim 21

The method as in claim 18 wherein sampling at least one of the phases comprises sampling all the phases.

Claim 22

The method as in claim 18 further comprising adding the respective phase deviation phasors to form a frequency deviation phasor (D), wherein the angle of said frequency deviation phasor with respect to the real axis is indicative of frequency deviation of said signal from said predetermined reference frequency.

Claim 23

The method of claim 19 further comprising adding the respective phase deviation phasors to form a frequency deviation phasor (D), wherein the angle of said frequency deviation phasor with respect to the real axis is indicative of frequency deviation of said signal from said predetermined reference frequency.

Claim 24

The method as in claim 18 wherein said sampling is repeated at predetermined intervals.

Claim 25

The method as in claim 18 wherein said sampling of said first cycle is performed once every other cycle of said signal.

Claim 26

The method as in claim 18 wherein said signal is sampled 12 times for each of said first and second cycles of said respective phases.

Claim 27

The method as in claim 18 wherein said respective first and second cycle of said at least one of the phases are consecutive.

Claim 28

The method as in claim 22 wherein said sampling of said first cycle is performed once every ten cycles of said signal.

Claim 29

The method as in claim 22 wherein said sampling of said first cycle is performed once every other cycle of said signal.

Claim 30

The method as in claim 19 wherein said respective first and second cycle of each respective phase are consecutive.

Claim 31

The method as in claim 19 wherein said sampling is repeated at predetermined intervals.

Claim 32

The method as in claim 29 wherein said sampling of said first cycle is performed once every ten cycles of said signal.

Claim 33

The method as in claim 29 wherein said sampling of said first cycle is performed once every other cycle of said signal.

Claim 34

The method of claim 18 wherein generating said first phasor comprises: generating a component of said first phasor from each of said data values associated with the first cycle of said signal in accordance with the following expression: ##EQU16## wherein: Vα 1 =first cycle data values; α=phase indicator; Δt=sampling period; N=samples per cycle; and k=summation index; and summing each of the components determined from the data values associated with each respective first cycle to produce said first phasor.

Claim 35

The method of claim 32 wherein generating said second phasor comprises: generating a component of said second phasor from each of said data values associated with the second cycle of said signal in accordance with the following expression: ##EQU17## wherein: Vα 2 =second cycle data values; α=phase indicator; Δt=sampling period; N=samples per cycle; and k=summation index; and summing each of the components determined from the data values associated with each respective second cycle to produce said second phasor.

Claim 36

The method of claim 19 wherein generating said first phasor comprises: generating a component of each said respective first phasor from each of said data values associated with the respective first cycle of said signal in accordance with the following expression: ##EQU18## wherein: Vα 1 =first cycle data values; α=phase indicator; Δt=sampling period N=samples per cycle; and k=summation index; and summing each of the components determined from the data values associated with each respective first cycle to produce each said respective first phasor.

Claim 37

The method as in claim 34 wherein generating said second phasor comprises: generating a component of each said respective second phasor from each of said data values associated with the respective second cycle of said signal in accordance with the following expression: ##EQU19## wherein: Vα 2 =second cycle data values; α=phase indicator; Δt=sampling period; N=samples per cycle; and k=summation index; and summing each of the components determined from the data values associated with each respective second cycle to produce each said respective first phasor.

Claim 38

The method as in claim 20 further comprising: generating the inverse tangent of the ratio of the imaginary portion of said frequency deviation phasor (IMAG(D)) divided by the real portion of said frequency deviation phasor (REAL(D)) wherein said inverse tangent is indicative of the frequency deviation of said signal from said predetermined reference frequency; and supplying said inverse tangent to display means for providing an indication of the frequency deviation.

Claim 39

The method as in claim 36 wherein said inverse tangent is determined in accordance with the following formula: ##EQU20## wherein x represents the ratio of the imaginary portion of said frequency deviation phasor divided by the real portion of said frequency deviation phasor.

Claim 40

The method as in claim 36 further comprising: generating a signal from said inverse tangent representative of an actual system frequency; and supplying said actual system frequency to display means for providing an indication of the actual system frequency.

Claim 41

The method as in claim 20 further comprising: generating an over-frequency warning if the imaginary portion of said frequency deviation phasor IMAG(D)) is greater than the real portion of said frequency deviation phasor (REAL(D)) times tan 2π(f 1 -f o )/f o , wherein f 1 is a predetermined upper frequency limit and if REAL(D) is greater than zero; generating an over-frequency warning if IMAG(D)<REAL(D)·tan 2π(f 1 -f o )/f o and if REAL (D) is less than zero; generating an under-frequency warning if IMAG(D)<REAL(D)·tan 2π(f x -f o )/f o , wherein f x is a predetermined lower frequency limit and if REAL(D) is greater than zero; and generating an under-frequency warning if IMAG(D)>REAL(D)·tan 2π(f x -f o )/f o and if REAL (D) is less than zero.

Claim 42

The method as in claim 39 wherein said signal is representative of the frequency of a power system and generating an over-frequency warning comprises: removing power supplying said power system; and providing an indication of said over-frequency warning.

Claim 43

The method as in claim 39 wherein said signal is representative of the frequency of a power system and generating an under-frequency warning comprises: removing power supplying said power system; and providing an indication of said under-frequency warning.

Claim 44

The method as in claim 18 wherein generating a first and second phasor comprises generating a discrete Fourier transform for each of said first and second cycles of each said at least one of the phases, respectively, from the data values respectively associated with said first and second cycles of said signal.

Claim 45

Apparatus for determining the frequency deviation of a system signal from a predetermined reference frequency (f o ), comprising: first transform means adapted to receive a first plurality of samples indicative of a first cycle of said system signal for generating the discrete Fourier transform of said first cycle of said system signal in response to said first plurality of samples; second transform means adapted to receive a second plurality of samples indicative of a second cycle of said system signal for generating the discrete Fourier transform of said second cycle of said system signal in response to said second plurality of samples, wherein said first cycle of said system signal precedes said second cycle of said system signal; multiplying means coupled to the output of each of said first and second transform means, respectively, for multiplying the discrete Fourier transform of said second cycle of said system signal by the complex conjugate of the discrete Fourier transform of said first cycle of said system signal to form a frequency deviation phasor; and conditioning means coupled to the output of said multiplying means for providing signals indicative of under-frequency and over-frequency, respectively, of said system signal with respect to said predetermined reference frequency.

Claim 46

Apparatus for determining the frequency deviation of a system signal from a predetermined reference frequency (f o ), comprising: first transform means adapted to receive a first plurality of samples indicative of a first cycle of said system signal for generating the discrete Fourier transform of said first cycle of said system signal in response to said first plurality of samples; second transform means adapted to receive a second plurality of samples indicative of a second cycle of said system signal for generating the discrete Fourier transform of said second cycle of said system signal in response to said second plurality of samples, wherein said first cycle of said system signal precedes said second cycle of said system signal; multiplying means coupled to the output of each of said first and second transform means, respectively, for multiplying the discrete Fourier transform of said second cycle of said system signal by the complex conjugate of the discrete Fourier transform of said first cycle of said system signal to form a frequency deviation phasor; and conditioning means coupled to the output of said multiplying means for providing signals indicative of under-frequency and over-frequency, respectively, of said system signal with respect to said predetermined reference frequency.

Claim 47

The apparatus of claim 43 further comprising: arc tangent means coupled to said multiplying means for generating the inverse tangent of said frequency deviation phasor, said inverse tangent indicative of the frequency deviation of said system signal from said predetermined reference frequency; and display means coupled to said arc tangent means for providing an indication of said frequency deviation of said system signal.

Claim 48

The apparatus of claim 43 wherein said system signal is representative of the frequency of a power system and further comprising switching means coupled to said conditioning means for stopping the supply of power to said power system in response to said under-frequency and said over-frequency signals, respectively.

Claim 49

The apparatus of claim 43 further comprising: arc tangent means coupled to said multiplying means for generating the inverse tangent of said frequency deviation phasor; frequency conversion means coupled to said arc tangent means for generating a frequency signal indicative of the frequency of said system signal; and display means coupled to said frequency conversion means for providing an indication of the frequency of said system signal.

Claim 50

Apparatus for determining the frequency deviation of a system signal from a predetermined reference frequency (f o ), said system signal including a plurality of phases, comprising: a first plurality of transform means each respectively adapted to receive a first plurality of samples indicative of a respective first cycle of each phase of said system signal for generating the respective discrete Fourier transform of said respective first cycle of each phase of said system signal in response to said respective first plurality of samples; a second plurality of transform means each respectively adapted to receive a second plurality of samples indicative of a respective second cycle of each phase of said system signal for generating the respective discrete Fourier transform of said respective second cycle of each phase of said system signal in response to said respective second plurality of samples, wherein each said respective first cycle of each phase of said system signal precedes each said respective second cycle of each phase of said system signal; a plurality of multiplying means each respectively coupled to the output of one of said first and one of said second plurality of transform means, respectively, both said one of said first and said one of said second transform means adapted to receive samples from the same phase of said system signal, each of said multiplying means, respectively, multiplying the discrete Fourier transform of said second cycle of said respective phase of said second cycle of said respective phase of said system signal by the complex conjugate of the discrete Fourier transform of said first cycle of said respective phase of said system signal to form a plurality of respective phase deviation phasors; adder means having inputs respectively coupled to the output of each of said plurality of multiplying means for summing each of said respective phase deviation phasors to form a frequency deviation phasor (D); and conditioning means coupled to the output of said adder means for providing signals indicative of under-frequency and over-frequency, respectively, of said system signal with respect to said predetermined reference frequency.

Claim 51

Apparatus for determining the frequency deviation of a system signal from a predetermined reference frequency (f o ), said system signal including a plurality of phases, comprising: a first plurality of transform means each respectively adapted to receive a first plurality of samples indicative of a respective first cycle of each phase of said system signal for generating the respective discrete Fourier transform of said respective first cycle of each phase of said system signal in response to said respective first plurality of samples; a second plurality of transform means each respectively adapted to receive a second plurality of samples indicative of a respective second cycle of each phase of said system signal for generating the respective discrete Fourier transform of said respective second cycle of each phase of said system signal in response to said respective second plurality of samples, wherein each said respective first cycle of each phase of said system signal precedes each said respective second cycle of each phase of said system signal; a plurality of multiplying means each respectively coupled to the output of one of said first and one of said second plurality of transform means, respectively, both said one of said first and said one of said second transform means adapted to receive samples from the same phase of said system signal, each of said multiplying means, respectively, multiplying the discrete Fourier transform of said second cycle of said respective phase of said second cycle of said respective phase of said system signal by the complex conjugate of the discrete Fourier transform of said first cycle of said respective phase of said system signal to form a plurality of respective phase deviation phasors; adder means having inputs respectively coupled to the output of each of said plurality of multiplying means for summing each of said respective phase deviation phasors to form a frequency deviation phasor (D); and conditioning means coupled to the output of said adder means for providing signals indicative of under-frequency and over-frequency, respectively, of said system signal with respect to said predetermined reference frequency.

Claim 52

The apparatus of claim 47 further comprising: arc tangent means coupled to said adder means for generating the inverse tangent of said frequency deviation phasor, said inverse tangent indicative of the frequency deviation of said system signal from said predetermined reference frequency; and display means coupled to said arc tangent means for providing an indication of said frequency deviation of said system signal.

Claim 53

The apparatus of claim 47 wherein said system signal is representative of the frequency of a power system, said apparatus further comprising switching means coupled to said conditioning means for stopping the supply of power to said power system in response to said under-frequency and said over-frequency signals, respectively.

Claim 54

The apparatus of claim 47 further comprising: arc tangent means coupled to said adder means for generating the inverse tangent of said frequency deviation phasor; frequency conversion means coupled to said arc tangent means for generating a frequency signal indicative of the frequency of said system signal; and display means coupled to said frequency conversion means for providing an indication of the frequency of said system signal.