Undervoltage circuit breaker with an electromagnet

Details Undervoltage circuit breaker with an electromagnet Undervoltage circuit breaker with an electromagnet

1998-02-12

2001-05-15

Ballato, Josie (Department: 2836)

Electricity: electrical systems and devices

Safety and protection of systems and devices

With specific voltage responsive fault sensor

Reexamination Certificate

active

06233129

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an undervoltage circuit breaker for monitoring the voltage of a single-phase or multi-phase system including an electromagnet for triggering a switching device, and a driver circuit that supplies power to the electromagnet. The driver circuit includes a rectifier circuit for obtaining a direct current from the system, a capacitance and a threshold circuit for interrupting a holding current that keeps the electromagnet in an energized condition when the voltage of the system falls below a predetermined level. The driver circuit is designed as a pulse generator to generate a holding current that is essentially independent of the line voltage when the latter is sufficiently high. The driver circuit also contains an operational amplifier that is controlled by a timer and an electronic switch that is controlled by the operational amplifier and is connected in series with the electromagnet and with a resistor, wherein the voltage dropping at the resistor is applied to the timer. The capacitance is designed as an energy storage device to supply power to the electromagnet if triggering is to be delayed.
BACKGROUND INFORMATION
A conventional undervoltage circuit breaker with these features is described in U.S. Pat. No. 4,890,184.
Although undervoltage circuit breakers are used in electrical installations to prevent damage to loads whose operating voltage must not fall below a predetermined level, it may nevertheless be desirable not to have each voltage reduction lead to shutdown of the load. In particular, it may be desirable to disregard brief interruptions or brief dropping of the voltage below a minimum. This is accomplished by the above-mentioned delay in triggering. The small space provided in compact low-voltage circuit breakers, for example, for installation of an undervoltage circuit breaker does not, however, usually make it possible to accommodate capacitors with a suitably large capacitance in addition to the electromagnet and the components of the driver circuit. Likewise, it is not usually possible to accommodate suitable capacitors outside the switching device because the installation space provided for the power switch in switchgear or control cabinets is dimensioned only for the power switch. Therefore, the delay that can be achieved is limited to relatively small values.
One of the objects of the present invention is to create a predetermined required triggering delay when there is an undervoltage, using a smallest possible capacitance.
SUMMARY OF THE INVENTION
An undervoltage circuit breaker according to the present includes:
a series circuit of another electronic switch and a resistor is connected in parallel to another resistor which is in series with an electromagnet,
the resistor of the series circuit has a lower resistance than the resistor that is connected in series with the electromagnet, and
an additional electronic switch can be controlled by a threshold circuit.
Thus, a current flowing through the electromagnet can be reduced to a minimum required holding current when the voltage to be monitored drops below a limit value and triggering is to occur after a time delay. Due to a reduction in the holding current, energy content of the capacitance is better utilized to generate a longer possible time delay.
As explained above, an essential property of the undervoltage circuit breaker according to the present invention provides that a relatively long time delay can be achieved while using a comparatively small capacitance. Therefore, an electromagnet, a respective driver circuit and a capacitor which is provided as the energy storage device for the delay time can be combined to form a single unit. A further embodiment of the undervoltage circuit breaker according to present invention provides that the driver circuit (which includes the capacitor) is arranged on a printed circuit board that matches the width of the electromagnet and extends beyond the electromagnet M in the longitudinal direction, with the total capacitance required provided by at least one capacitor that is mounted on the part of the circuit board projecting beyond the electromagnet in such a way that substantially the only space required is the space that extending in the longitudinal direction of the electromagnet.


REFERENCES:
patent: 3843908 (1974-10-01), Priegnitz
patent: 4025823 (1977-05-01), Lang et al.
patent: 4183071 (1980-01-01), Russell
patent: 4205261 (1980-05-01), Franklin
patent: 4331996 (1982-05-01), Matsko et al.
patent: 4356526 (1982-10-01), Russell
patent: 4890184 (1989-12-01), Russell

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