Electricity: motive power systems – Automatic and/or with time-delay means – Responsive to thermal conditions
Reexamination Certificate
2000-02-15
2001-10-02
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Automatic and/or with time-delay means
Responsive to thermal conditions
C318S473000, C361S025000
Reexamination Certificate
active
06297607
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to control systems for motor starters, and more particularly to a method and apparatus to compensate a motor starter for increases in temperature.
Many electrical devices use one form or another for thermal protection. One of the most common forms of temperature protection includes the use of thermistors, which are heat sensitive resistors that change resistive value with temperature change. Typically, the thermistor is connected to an electronic monitoring circuit which is set to react to a predetermined resistance value. When that resistance value is reached, the electronic monitoring circuit disconnects, or connects, the temperature protection circuits, which then turn the device off. Most electrical devices use a single thermistor for protection. Therefore, the level of protection provided is solely dependent on the location of that single thermistor. In other words, the thermal protection in reality protects only one small portion of the device. In larger devices, many components can be damaged before the thermal protection turns off the device. Another problem with such systems is that they provide little warning or assistance in diagnosing the cause of shutting down the device. Further, in some applications or processes, it is critical that the electrical device not be shutdown. In such processes, it would be desirable to have some indication of an overheating condition while keeping the process running.
Another common method of thermal protection is the use of a bimetallic element or disk mounted within the device to open or close a circuit. Such devices change shape with heat due to a differential thermal expansion between the two metals that form the physical configuration. As the device changes shape, it exerts a physical force on a switch, or on a set of contacts, to change the state of an electrical circuit. That is, a normally opened circuit, for example, will close to activate a temperature protection circuit when the bi-metal strip deforms to a deflection point that corresponds to a temperature indicating an overheating condition. This form of thermal protection requires calibration by hand-bending or tweaking for each particular device. Further, accuracy is suspect after field adjustments are made and such bi-metal devices typically require invasive connections between components, thereby reducing manufactureability, increasing the cost of the component, and increasing the overall size of the electrical equipment.
An electrical device with thermal compensation adjusts the starting characteristics of the controller to compensate for the additional ambient temperature. This compensation adjusts or increases the output of the device to compensate for the increasing internal resistance of the device caused by heating. Typically, such temperature compensation requires the use of mechanical components, such as the aforementioned bimetallic elements to sense the temperature and adjust the output accordingly. Since thermal compensation ranges are relatively small, several device configurations are required in order to cover an entire product line. Further, thermal compensation adds additional cost to the manufacturing of the device because of the additional components.
It would be desirable to have a thermal compensation and protection scheme that eliminates the need of these additional components to avoid the need for having variations of the product for different temperature ranges.
SUMMARY OF THE INVENTION
The present invention provides a motor starter thermal compensation and protection control that solves the aforementioned problems without adding significant cost to the overall system.
A motor starter thermal compensation and protection control, according to the present invention, includes an ambient temperature sensor to sense ambient temperature and provide an ambient temperature signal indicative of the ambient temperature of a motor starter, and at least one pole temperature sensor in thermal communication with an electrically conducting bus in the motor starter that produces a pole temperature signal indicative of a temperature of the electrically conducting bus. A processing unit is connected to the ambient temperature sensor and the at least one pole temperature sensor and is programmed to periodically acquire the ambient and pole temperature signals to determine an operating temperature of the motor starter, and monitor any changes in the operating temperature of the motor based on the periodic acquisitions of the ambient and pole temperature signals. The output of the motor starter is then adjusted based on the change in operating temperature so that the output of the electrical device is constant as the operating temperatures increase. This avoids the need of the electrical rating on the device to be sized larger than is required to compensate for the additional ambient heat in order to operate at the rated load.
In accordance with another aspect of the invention, a motor starter control for thermally protecting a motor and a motor starter includes an ambient temperature sensor for sensing ambient temperature and creating ambient temperature signals, and a pole temperature sensor for sensing a pole temperature in the motor starter and creating pole temperature signals therefrom. A memory is provided for periodically storing ambient and pole temperature signals, and a processor is used for comparing current ambient and pole temperature signals to previous ambient and pole temperature signals stored in memory. The processor is also used for increasing an FLA adjustment to the motor when current ambient and pole temperature conditions cause a previous FLA adjustment to be inadequate to start the motor due to increases in internal resistance.
In accordance with yet another aspect of the invention, a method of thermally protecting a motor and motor starter includes the steps of periodically monitoring an ambient temperature and a pole temperature of each pole in a motor starter and recording the periodically monitored ambient and pole temperatures. The process next includes comparing present ambient and pole temperatures to previously recorded ambient and pole temperatures and preventing a motor from starting if the temperature comparison reaches a maximum parameter and an FLA adjustment is at a motor limit.
Various other features, objects and advantages of the present invention will be made apparent from the following detailed description and the drawings.
REFERENCES:
patent: 3585451 (1971-06-01), Day, III
patent: 4207602 (1980-06-01), Kussy et al.
patent: 4434390 (1984-02-01), Elms
patent: 5220478 (1993-06-01), Innes et al.
patent: 5525881 (1996-06-01), Desrus
patent: 5539601 (1996-07-01), Farag
patent: 5998893 (1999-12-01), Fowler et al.
patent: 6087800 (2000-07-01), Becker et al.
patent: 6122153 (2000-09-01), Becker
Eaton Corporation
Leykin Rita
Nappi Robert E.
Ziolkowski Timothy J.
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