Harmonic measuring instrument for AC power systems with latched indicator means
First Claim
1. An apparatus for measuring voltage harmonics and current harmonics on an alternating current power system comprising:
- a. means for sensing a harmonic voltage and a harmonic current coupled to the alternating current power system;
b. means for comparing both the harmonic voltage to a predetermined voltage threshold and the harmonic current to a predetermined current threshold, said means for comparing coupled to the means for sensing; and
c. means for indicating when either the predetermined voltage threshold is exceeded, the predetermined current threshold is exceeded or both the predetermined voltage threshold and the predetermined current threshold are exceeded simultaneously, the means for indicating coupled to the means for comparing.
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Abstract
An instrument for measuring voltage harmonics and current harmonics on AC (alternating current) power systems. The instrument includes the ability to determine when threshold limits have been exceeded for harmonics. The instrument also includes timing thresholds whose inputs are activated when the harmonic thresholds are exceeded. A single harmonic threshold is applied to measurements from multiple phases on poly-phase systems by comparing the square root of the sum of the squares of measurements from each phase to the harmonic threshold. Three indicators show when voltage harmonic limits are exceeded, current harmonics limits are exceeded, or both voltage and current harmonic limits are exceeded simultaneously.
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Citations
20 Claims
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1. An apparatus for measuring voltage harmonics and current harmonics on an alternating current power system comprising:
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a. means for sensing a harmonic voltage and a harmonic current coupled to the alternating current power system; b. means for comparing both the harmonic voltage to a predetermined voltage threshold and the harmonic current to a predetermined current threshold, said means for comparing coupled to the means for sensing; and c. means for indicating when either the predetermined voltage threshold is exceeded, the predetermined current threshold is exceeded or both the predetermined voltage threshold and the predetermined current threshold are exceeded simultaneously, the means for indicating coupled to the means for comparing. - View Dependent Claims (2, 3, 4, 5)
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6. An apparatus for measuring voltage harmonics and current harmonics on an alternating current power system comprising:
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a. means for sensing a harmonic voltage coupled to the alternating current power system; b. means for sensing a harmonic current coupled to the alternating current power system; c. means for comparing the harmonic voltage to a predetermined voltage threshold, said means for comparing coupled to the means for sensing a harmonic voltage; d. first means for indicating when the harmonic voltage exceeds the predetermined voltage threshold, the first means for indicating coupled to the means for comparing the harmonic voltage; e. means for comparing the harmonic current to a predetermined current threshold, said means for comparing coupled to the means for sensing a harmonic current; f. second means for indicating when the harmonic current exceeds the predetermined current threshold, the second means for indicating coupled to the means for comparing the harmonic current; and g. third means for indicating when both the harmonic voltage exceeds the predetermined voltage threshold and the harmonic current exceeds the predetermined current threshold, the third means for indicating coupled to the means for comparing the harmonic voltage and the means for comparing the harmonic current. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13)
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14. An apparatus for measuring voltage and current harmonics on an alternating current power system having a power line conductor and a power neutral conductor, comprising:
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a. a current transformer coupled to the power line conductor; b. a burden resistor coupled to the current transformer for producing a first voltage signal which represents a current flowing in the power line conductor; c. a first amplifier coupled to the burden resistor for adjusting the first voltage signal; d. a first filter coupled to the first amplifier for removing undesired frequencies from the first voltage signal; e. an attenuator coupled to the power line conductor and the power neutral conductor for receiving a second voltage signal which represents a voltage difference between the power line conductor and the power neutral conductor; f. a second amplifier coupled to the attenuator for adjusting the second voltage signal; g. a second filter coupled to the second amplifier for removing undesired frequencies from the second voltage signal; h. a first analog-to-digital converter coupled to the first filter for converting the analog first voltage signal to a first digital time-domain signal; i. a second analog-to-digital converter coupled to the second filter for converting the analog second voltage signal to a second digital time-domain signal; j. means for processing digital signals coupled to the first and the second analog-to-digital converters for converting the first time-domain signal to a first frequency-domain representation having a plurality of current harmonics representing the current in the power line and for converting the second time-domain signal to a second frequency-domain representation having a plurality of voltage harmonics representing the voltage difference between the power line conductor and the power neutral conductor; k. a control subsystem coupled to the means for processing digital signals for determining if any of the current harmonics received from the means for processing digital signals circuit exceeds a predetermined current threshold and if any of the voltage harmonics received from the digital signal processing circuit exceeds a predetermined voltage threshold; and l. a display coupled to the control subsystem for indicating if any of the frequency-domain representations do exceed a predetermined threshold. - View Dependent Claims (15, 16, 17, 18, 19, 20)
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Specification