Apparatus and method for detecting power of a three phase alternating current system
First Claim
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1. An electric power detector for a three-phase alternating current voltage supply comprising:
- means for detecting the current of a first phase of said supply,means for detecting the line to line voltage between said first phase and a second phase of said supply,means for computing the phase difference of the current detected by said current detecting means with respect to the line to line voltage detected by said line to line voltage detecting means,means for comparing the magnitude of said computed phase difference with a phase difference α
(30°
≦
α
≦
60°
),means for subtracting 30°
from said computed phase difference when the comparison produces a phase difference larger than α
,means for adding 30°
to said computed phase difference when the comparison produces a phase difference less than α
, andmeans for computing the electric power of the supply using the resultant phase difference of said subtraction or addition as a power factor angle.
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Abstract
An electric power detector for a three-phase AC voltage supply which measures the current of one phase and the voltage between the one phase and another phase and computes the phase difference between the voltage and the current, decides the phase rotation direction by comparing the phase difference with a specified angle, and obtains a power factor angle by adding or subtracting 30° to or from the phase difference corresponding to the result of the decision to produce a power factor angle for computing three-phase power.
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Citations
9 Claims
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1. An electric power detector for a three-phase alternating current voltage supply comprising:
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means for detecting the current of a first phase of said supply, means for detecting the line to line voltage between said first phase and a second phase of said supply, means for computing the phase difference of the current detected by said current detecting means with respect to the line to line voltage detected by said line to line voltage detecting means, means for comparing the magnitude of said computed phase difference with a phase difference α
(30°
≦
α
≦
60°
),means for subtracting 30°
from said computed phase difference when the comparison produces a phase difference larger than α
,means for adding 30°
to said computed phase difference when the comparison produces a phase difference less than α
, andmeans for computing the electric power of the supply using the resultant phase difference of said subtraction or addition as a power factor angle. - View Dependent Claims (2, 3, 4, 5)
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6. An electric power detector for three-phase alternating current voltage supply which is changeable in phase rotation comprising,
means for detecting the current of a first phase of said supply, means for detecting the line to line voltage between said first phase and a second phase of said supply, first means for computing the phase difference and direction of phase rotation of the current detected by said current detecting means with respect to the line to line voltage detected by said line to line voltage detecting means, means for adding 30° - to or subtracting 30°
from said computed phase difference corresponding to the direction of the phase rotation, andsecond means for computing the electric power of the supply using the resultant phase difference produced by said addition or subtraction as a power factor angle. - View Dependent Claims (7)
- to or subtracting 30°
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8. A method for computing the power (W) of a three-phase alternating current supply comprising the steps of:
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detecting the current (I) of one phase of said supply, detecting the line to line voltage (V) between said one phase and another phase of said supply, computing the phase difference (N) between the detected current (I) and line to line voltage (V), comparing the magnitude of the computed phase difference (N) with a phase difference angle α
(30°
≦
α
≦
60°
), andsubtracting 30°
from or adding 30°
to the computed phase difference (N) depending if the comparison is larger or smaller than α
to produce a resultant phase angle (θ
) andcomputing the power (W) of the supply using the resultant phase angle (θ
). - View Dependent Claims (9)
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Specification
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Current AssigneeTsubakimoto Chain Company
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Original AssigneeTsubakimoto Chain Company
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InventorsKitayoshi, Haruyoshi, Tamaki, Atsuhiko
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Primary Examiner(s)NGUYEN, VINH P
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Application NumberUS07/980,917Time in Patent Office994 DaysField of Search322/141, 322/142, 322/107, 364/483, 364/481, 364/492, 324/140, 324/103 RUS Class Current324/107CPC Class CodesG01R 21/06 by measuring current and vo...G01R 21/133 by using digital techniqueG01R 31/42 AC power supplies
