Protective device for an electrical consumer

Details Protective device for an electrical consumer Protective device for an electrical consumer

1995-02-13

1997-02-18

Donovan, Lincoln

Electricity: electrothermally or thermally actuated switches

Thermally actuated switches

337100, H01H 3700

Patent

active

056044763

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a protective device for an electrical consumer disposed in a consumer circuit. The protective device has sensor elements for detecting an operating state of the electrical consumer, and an electronic evaluation and control unit operatively connected to the sensor elements for evaluating and controlling the operating state of the electrical consumer detected by the sensor elements. The protective device further includes a protective switch responsive to the operating state of the electrical consumer detected by the sensor elements for interrupting the consumer circuit. The protective switch comprises: a housing and a control circuit disposed at least in part within the housing and including a bimetallic strip and a temperature-dependent resistor operatively associated with the bimetallic strip for deflecting the bimetallic strip for interrupting the consumer circuit, the bimetallic strip thereby defining a deflecting direction. The protective device further includes a power supply unit adapted to be connected to a power supply grid and to respective ones of the sensor elements, the evaluation and control unit, and the protective switch for supplying electrical power to the sensor elements, the evaluation and control unit and the protective switch.
Protective devices of this kind are known in the industry in highly modified versions. The technical principle can be described as follows: The switch acts as an interface between a consumer circuit and a control circuit. As a function of a measured physical variable within the operating state of the electrical consumer, a control device with a sensor outputs an electrical measurement signal to the control circuit. The control circuit in turn experiences a flow of a control current that is variable as a function of the measurement signal.
The physical variable--such as current, water level, temperature, pressure, acceleration and the like--can be measured at the electrical consumer connected into the consumer circuit. Alternatively, it may be an extreme physical variable, such as the current of the other circuit or the ambient temperature. If a limit value for the electrical measurement signal is exceeded, the switch, utilizing the deflection force of the bimetallic strip, interrupts the current lines of the electrical consumer. This is intended to protect the consumer against damage from the effect of certain physical variables.
Protective devices of the type described above serve for instance to monitor electrical rotary pumps, which are used in a heating, fresh water or service water system. As a rule, the operating states of the electrical consumers that are essential to the particular operating state of the pump are monitored. The winding temperature of a motor, for instance, has a definitive influence on its service life. High winding temperatures cause premature destruction of the motor. In known protective devices the motors therefore shut off, in the case of measured temperatures in excess of a given temperature limit value.
German Utility Model DE 91 07 139 U1 discloses such a protective device for monitoring the winding temperature of electric motors. The protective device has a protective switch with stationary and movable contacts for switching the power supply connections of the electrical consumer. The switching events of the protective switch are controlled by a control device. The control device essentially includes a control circuit. A temperature probe that monitors the winding temperature of the electric motor is electrically connected to the control circuit. The control circuit also contains a positive temperature coefficient (PTC) resistor for heating a bimetallic disk disposed in the protective switch.
The temperature probe functions as a sensor and outputs an electrical measurement signal to the control circuit. If a temperature limit value is exceeded, the electrical measurement signal is high enough to switch a semiconductor switch in the conducting direction and thereby cause a control current to flow through the

REFERENCES:
patent: 3019319 (1962-01-01), Anderson
patent: 3636426 (1972-01-01), Buiting
patent: 3893054 (1975-07-01), Marcoux et al.
patent: 4281358 (1981-07-01), Plouffe et al.
O. Fleig "Proper Protection for LV Motors" In: Siemens Energy & Automation, vol. IX, No. 1, Apr. 1, 1989, Berlin, DE, pp. 18-22.

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