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 12:34
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.
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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 |