US4423374A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Unbalanced current detector for three phase electrical system
Assignee: Bendix Corp
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Filing: 1981-09-21
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Granted: 1983-12-27
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Expires: 2001-09-21
Abstract
Abstract An unbalanced current detector for a three phase electrical system of the type including a current transformer (4, 6, 8) for each phase (φA, φB, φC) and a burden resistor (16) which receives a rectified output of the current transformer is disclosed. The harmonic content of a rectified ripple voltage developed across the burden resistor (16) is applied to a filter (20) for extracting desired frequencies and rejecting other frequencies, and the filter output is applied to a level detecting and amplifying circuit (54) the output of which is applied to an indicator (77) to indicate an unbalanced current condition.
Inventors
- 👤 Charles M. Hansen, Jr.
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-31 08:09
CPC Classifications
G; G01; G01R; G01R29/00; G01R29/16
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
114 words
For use with a three phase electrical system of the type including a current transformer for each of the three phases, means for rectifying the outputs of the current transformers and a resistor connected to the rectifying means for performing a current vector addition, with a ripple voltage having a particular harmonic content developed across the resistor, apparatus for detecting an unbalanced phase current condition comprising: means responsive to the ripple voltage for passing the highest value of a selected harmonic of the system nominal frequency without significant attenuation; and means connected to the filter means for detecting when the nominal system harmonics exceed a predetermined threshold commensurate with the unbalanced phase current condition.
Claim 2
Dependent Claim
114 words
For use with a three phase electrical system of the type including a current transformer for each of the three phases, means for rectifying the outputs of the current transformers and a resistor connected to the rectifying means for performing a current vector addition, with a ripple voltage having a particular harmonic content developed across the resistor, apparatus for detecting an unbalanced phase current condition comprising: means responsive to the ripple voltage for passing the highest value of a selected harmonic of the system nominal frequency without significant attenuation; and means connected to the filter means for detecting when the nominal system harmonics exceed a predetermined threshold commensurate with the unbalanced phase current condition.
Claim 3
Dependent Claim
37 words
Apparatus as described by claim 1, including: circuit means connected to the means responsive to the ripple voltage for filtering the output therefrom to remove the DC component of the ripple voltage developed across the burden resistor.
Claim 4
Dependent Claim
35 words
Apparatus as described by claim 2, including: other circuit means connected to the output of the first mentioned circuit means for adjusting the gain of the output therefrom and for rectifying the gain adjusted output.
Claim 5
Dependent Claim
35 words
Apparatus as described by claim 1, including: indicating means connected to detecting means and responsive to the output therefrom for indicating when the predetermined threshold commensurate with the unbalanced phase current condition has been exceeded.
Claim 6
Dependent Claim
171 words
A three phase electrical system comprising: a current transformer for each of the three phase; rectifying means for each of the current transformers, each of which is connected to a corresponding current transformer for rectifying the output therefrom; resistor means connected to each of the rectifying means for performing a current vector addition, with a voltage having a particular harmonic content being developed across the resistor means; means connected to the resistor means and responsive to the voltage developed thereacross for passing the highest value of a selected harmonic of the system nominal frequency without significant attentuation; circuit means connected to the filter means for removing the DC component of the voltage developed across the resistor means; other circuit means connected to the first mentioned circuit means for amplifying and rectifying the remaining AC components of the voltage developed across the resistor means; and means connected to the other circuit means for detecting when the nominal system harmonics exceed a predetermined threshold which is indicative of a three phase current unbalance.
Claim 7
Dependent Claim
171 words
A three phase electrical system comprising: a current transformer for each of the three phase; rectifying means for each of the current transformers, each of which is connected to a corresponding current transformer for rectifying the output therefrom; resistor means connected to each of the rectifying means for performing a current vector addition, with a voltage having a particular harmonic content being developed across the resistor means; means connected to the resistor means and responsive to the voltage developed thereacross for passing the highest value of a selected harmonic of the system nominal frequency without significant attentuation; circuit means connected to the filter means for removing the DC component of the voltage developed across the resistor means; other circuit means connected to the first mentioned circuit means for amplifying and rectifying the remaining AC components of the voltage developed across the resistor means; and means connected to the other circuit means for detecting when the nominal system harmonics exceed a predetermined threshold which is indicative of a three phase current unbalance.
Claim 8
Dependent Claim
62 words
Apparatus as described by claim 1, wherein: each of the phase currents has the same nominal frequency; the ripple voltage developed across the resistor has a predetermined frequency other than the nominal frequency when the phase currents are balanced; and an unbalanced phase current condition produces voltage components at frequencies other than the predetermined frequency and commensurate with the degree of unbalance.
Claim 9
Dependent Claim
50 words
Apparatus as described by claim 6, wherein: the means responsive to the ripple voltage for passing the highest value of a selected harmonic of the system nominal frequency without significant attenuation passes the voltage components at frequencies other than the predetermined frequency while blocking the voltage at the predetermined frequency.
Claim 10
Dependent Claim
35 words
Apparatus as described by claim 1, wherein: the means responsive to the ripple voltage for passing the highest value of a selected harmonic of the system nominal frequency without significant attenuation includes a low-pass filter.
Claim 11
Dependent Claim
36 words
Apparatus as described by claim 1, wherein: the means connected to the filter means for detecting when the nominal system harmonics exceed a predetermined threshold commensurate with the unbalance phase current condition includes a comparator circuit.
References Cited (Backward Citations)
US3783341A
Cited
US4199798A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1986-12-26 | 1987-06-27 | 1987-12-27 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1990-12-26 | 1991-06-27 | 1991-12-27 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1994-12-26 | 1995-06-27 | 1995-12-27 | $7700.00 | Window Closed / Lapsed |