Patent US5283708A successfully refreshed from Google Patents.
US5283708A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Overload current protection apparatus
Assignee: Allen Bradley Co LLC
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Filing: 1992-09-23
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Granted: 1994-02-01
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Expires: 2012-09-23
Abstract
Abstract A device protects an electric load, such as a motor, from excessive current levels. The current flows from a source to the load through a switch and a primary winding of a current sensing transformer. The voltage across a secondary winding of the current sensing transformer is rectified to produce a voltage which is measured to determine the level of current through the load. The voltage across the secondary winding also powers components of the device. In a first mode of operation, current from the secondary winding is applied to charge a power supply capacitor. In a second mode of operation the level of the rectified voltage is sensed to produce a sample of the level of the current flowing through the load. From this sample the change in temperature of the load since a previous sample is calculated and used to derive the present load temperature. When the present load temperature exceeds a defined threshold level, the switch is opened to disconnect the load from the electricity source.
Inventors
- 👤 Richard W. Waltz
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-07 13:12
CPC Classifications
H; H02; H02H; H02H6/00; H02H6/005; H02H1/00; H02H1/06; H02H1/063; H02H1/066; H02H3/00; H02H3/08
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
144 words
An overload protection device, for controlling the application of multi-phase electric current for a source to a load, comprising a switch coupled to the source for selectively connecting the load to the source; means for periodically sensing a level of current flowing between the source and the load; means for detecting a phase imbalance in the current flowing from the source to the load; means, responsive to the sensed level of current and to said means for detecting a phase imbalance, for deriving a change in temperature of the load since a previous sensing of the level of current; means for combining the change in temperature with a previous load temperature value to determine the present temperature of the load; and means for activating said switch to disconnect the load from the source when the present temperature of the load exceeds a threshold level.
Claim 2
Dependent Claim
144 words
An overload protection device, for controlling the application of multi-phase electric current for a source to a load, comprising a switch coupled to the source for selectively connecting the load to the source; means for periodically sensing a level of current flowing between the source and the load; means for detecting a phase imbalance in the current flowing from the source to the load; means, responsive to the sensed level of current and to said means for detecting a phase imbalance, for deriving a change in temperature of the load since a previous sensing of the level of current; means for combining the change in temperature with a previous load temperature value to determine the present temperature of the load; and means for activating said switch to disconnect the load from the source when the present temperature of the load exceeds a threshold level.
Claim 3
Dependent Claim
200 words
An overload protection device, for controlling the application of multi-phase electric current from a source to a load, comprising a switch coupled to the source for selectively connecting the load to the source; means for periodically sensing a level of current flowing between the source and the load; means for deriving a change in temperature of the load since a previous sensing of the level of current by calculating the change in temperature according to the expression: ##EQU4## where ΔC is a change in temperature that occurs during time interval Δt, C trip is a temperature of the load at which the load should be disconnected from the source, C is the temperature of the load, τ is a thermal time constant, i is the sensed level of current, i.sub.μ is a constant that defines an overload current level, and n is a relationship constant of the sensed level of current to its heating effect; means for combining the change in temperature with a previous load temperature value to determine the present temperature of the load; and means for activating said switch to disconnect the load from the source when the present temperature of the load exceeds a threshold level.
Claim 4
Dependent Claim
200 words
An overload protection device, for controlling the application of multi-phase electric current from a source to a load, comprising a switch coupled to the source for selectively connecting the load to the source; means for periodically sensing a level of current flowing between the source and the load; means for deriving a change in temperature of the load since a previous sensing of the level of current by calculating the change in temperature according to the expression: ##EQU4## where ΔC is a change in temperature that occurs during time interval Δt, C trip is a temperature of the load at which the load should be disconnected from the source, C is the temperature of the load, τ is a thermal time constant, i is the sensed level of current, i.sub.μ is a constant that defines an overload current level, and n is a relationship constant of the sensed level of current to its heating effect; means for combining the change in temperature with a previous load temperature value to determine the present temperature of the load; and means for activating said switch to disconnect the load from the source when the present temperature of the load exceeds a threshold level.
Claim 5
Dependent Claim
190 words
An overload protection device, for controlling the application of multi-phase electric current from a source to a load, comprising a switch coupled to the source for selectively connecting the load to the source; means for periodically sensing a level of current flowing between the source and the load; means for deriving a change in temperature of the load since a previous sensing of the level of current by calculating the change in temperature per a given time interval (ΔC/Δt) according to the expression: ##EQU5## where K is a constant, i is the sensed level of current, i.sub.μ is a constant that defines an overload current level, C is the present temperature, C trip is a temperature of the load at which the load should be disconnected from the source, and n is a relationship constant of the sensed level of current to its heating effect; means for combining the change in temperature with a previous load temperature value to determined the present temperature of the load; and means for activating said switch to disconnect the load from the source when the present temperature of the load exceeds a threshold level.
Claim 6
Dependent Claim
190 words
An overload protection device, for controlling the application of multi-phase electric current from a source to a load, comprising a switch coupled to the source for selectively connecting the load to the source; means for periodically sensing a level of current flowing between the source and the load; means for deriving a change in temperature of the load since a previous sensing of the level of current by calculating the change in temperature per a given time interval (ΔC/Δt) according to the expression: ##EQU5## where K is a constant, i is the sensed level of current, i.sub.μ is a constant that defines an overload current level, C is the present temperature, C trip is a temperature of the load at which the load should be disconnected from the source, and n is a relationship constant of the sensed level of current to its heating effect; means for combining the change in temperature with a previous load temperature value to determined the present temperature of the load; and means for activating said switch to disconnect the load from the source when the present temperature of the load exceeds a threshold level.
Claim 7
Dependent Claim
169 words
An overload protection device, for controlling the application of multi-phase electric current from a source to a load, comprising: a switch coupled to the source for selectively connecting the load to the source; means for periodically sensing a level of current flowing between the source and the load; means for deriving a change in temperature of the load since a previous sensing of the level of current by calculating the change in temperature primarily as a mathematical power function of the presently sensed level of current in accordance with a term: K.sub.1 (i).sup.n where K 1 is a constant, i is the sensed level of current and the exponent n is a relationship constant of the sensed level of current to its heating effect; means for combining the change in temperature with a previous load temperature value to determine the present temperature of the load; and means for activating said switch to disconnect the load from the source when the present temperature of the load exceeds a threshold level.
Claim 8
Dependent Claim
169 words
An overload protection device, for controlling the application of multi-phase electric current from a source to a load, comprising: a switch coupled to the source for selectively connecting the load to the source; means for periodically sensing a level of current flowing between the source and the load; means for deriving a change in temperature of the load since a previous sensing of the level of current by calculating the change in temperature primarily as a mathematical power function of the presently sensed level of current in accordance with a term: K.sub.1 (i).sup.n where K 1 is a constant, i is the sensed level of current and the exponent n is a relationship constant of the sensed level of current to its heating effect; means for combining the change in temperature with a previous load temperature value to determine the present temperature of the load; and means for activating said switch to disconnect the load from the source when the present temperature of the load exceeds a threshold level.
Claim 9
Dependent Claim
16 words
The device of claim 4, wherein the exponent n is within the range 2.20 to 2.78.
Claim 10
Dependent Claim
60 words
The device of claim 4 wherein the change in temperature of the load is additionally derived by calculating the change in temperature also as a linear function of the previously calculated temperature in accordance with a term: -K.sub.2 C K 2 is a constant and C is the temperature of the load as previously calculated during the last calculation cycle.
Claim 11
Dependent Claim
16 words
The device of claim 6, wherein the exponent n is within the range 2.20 to 2.78.
References Cited (Backward Citations)
US75296A
Cited
US3223587A
Cited
US4213165A
Cited
US4337837A
Cited
US4271447A
Cited
US4423459A
Cited
US4428021A
Cited
US4689712A
Cited
US4685022A
Cited
US4703389A
Cited
US5057962A
Cited
US8805973B2
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1997-01-31 | 1997-08-02 | 1998-02-01 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2001-01-31 | 2001-08-02 | 2002-02-01 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2005-01-31 | 2005-08-02 | 2006-02-01 | $7700.00 | Window Closed / Lapsed |