Substation load distribution monitor system
First Claim
1. A method of monitoring power distribution equipment carrying voltage and current to distribute electrical power, said monitoring method comprising the steps of:
- sampling periodic waveforms representative of said current and said voltage within said power equipment to obtain samples which are substantially equally spaced in time so that said samples have a sample period, said samples having magnitudes and wherein a value derived from said magnitudes of said samples is used as feedback to maintain a sample rate such that a period of the periodic waveforms is substantially an integer multiple of said sample period; and
analyzing said sample values by means of a discrete Fourier Transform to obtain a relative phase between the voltage and current waveforms.
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Abstract
The monitoring and control system of the present invention provides a distributed intelligence, data acquisition and control system which collects and analyzes large amounts of data representing power usage from a power distribution substation. Using a Discrete Fourier Transform, the system provides accurate tracking of the primary frequency of the voltage and current waveforms in the power equipment, and determines the relative phase between the voltage and current waveforms. The system provides real time monitoring of power usage and real time control of various functions in the substation.
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Citations
11 Claims
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1. A method of monitoring power distribution equipment carrying voltage and current to distribute electrical power, said monitoring method comprising the steps of:
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sampling periodic waveforms representative of said current and said voltage within said power equipment to obtain samples which are substantially equally spaced in time so that said samples have a sample period, said samples having magnitudes and wherein a value derived from said magnitudes of said samples is used as feedback to maintain a sample rate such that a period of the periodic waveforms is substantially an integer multiple of said sample period; and analyzing said sample values by means of a discrete Fourier Transform to obtain a relative phase between the voltage and current waveforms.
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2. A method of determining the relative phase between a periodic voltage waveform and a periodic current waveform carried in power equipment, said determining method comprising the steps of:
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simultaneously sampling said periodic current waveform and said periodic voltage waveform at a sampling rate to obtain first and second sets of sample values, said first set of sample values comprising a representation of said periodic current waveform with discrete sample values substantially equally spaced in time to define a first sample period, said second set of sample values comprising a representation of said periodic voltage waveform with discrete sample values substantially equally spaced in time to define a second sample period and wherein a feedback value derived from said first and second sets of sample values is used as feedback to automatically adjust said sample rate to insure that a period of said periodic current waveform is substantially an integer multiple of said first sample period and a period of said periodic voltage waveform is substantially an integer multiple of said second sample period; applying a discrete Fourier Transform to the first and second sets of sample values of said periodic voltage waveform and said periodic current waveform to obtain a phase of said periodic voltage waveform and a phase of said periodic current waveform; and comparing the phase of said periodic voltage waveform and said periodic current waveform to obtain a relative phase between said periodic voltage waveform and said periodic current waveform. - View Dependent Claims (3, 4, 5, 6, 7)
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8. A method of taking an integer number of sample values per cycle of a periodic voltage or current waveform carried by power equipment, said method comprising the steps of:
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sampling said periodic voltage or current waveform at a selected sampling rate corresponding to a first expected frequency to obtain a first set of samples equally spaced in time to define a first sample period and covering substantially a first cycle of said periodic voltage or current waveform; transforming the samples from said first set of samples by means of a discrete Fourier Transform to obtain a first X transform value and a first Y transform value; sampling said periodic voltage or current waveform at said selected sampling rate to obtain a second set of samples equally spaced in time to define a second sample period, said second set of samples covering at least a portion of a second cycle of said periodic voltage or current waveform; transforming at least one of the samples from said second set of samples by means of a discrete Fourier Transform to obtain a second X transform value and a second Y transform value; comparing said first Y transform value with said second X transform value; and adjusting said selected sampling rate in response to said comparison to insure that a period of said periodic voltage or current waveform is substantially an integer multiple of said first and second sample periods. - View Dependent Claims (9, 10, 11)
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Specification