Electricity: electrical systems and devices – Control circuits for electromagnetic devices – Systems for magnetizing – demagnetizing – or controlling the...
Reexamination Certificate
1999-11-24
2001-06-12
Sherry, Michael J. (Department: 2836)
Electricity: electrical systems and devices
Control circuits for electromagnetic devices
Systems for magnetizing, demagnetizing, or controlling the...
C361S187000
Reexamination Certificate
active
06246562
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a control device of an electromagnet comprising at least one holding coil connected in series with an electronic switch to the terminals of a supply voltage of the coil, means for measuring the holding current flowing in the holding coil, control means for controlling the electromagnet comprising means for regulating the holding current connected to the means for measuring the holding current and to a control electrode of the electronic switch, and power supply means of the control means.
Circuit breakers generally comprise a certain number of electrical auxiliaries, more particularly closing electromagnets (XF) or opening electromagnets. Two types of opening electromagnets, or voltage trip releases, are generally provided. They comprise an electromagnet which must be actuated when certain conditions having to cause opening of the circuit breaker are met with. An under-voltage release (MN) causes opening of the circuit breaker when the voltage of the power system to be protected drops below a certain threshold, and a shunt release (MX) causes opening of the circuit breaker when the power system voltage exceeds another threshold.
For control of an electromagnet, it is known (FR-A-2,133,652) to temporarily supply a relatively high inrush current, followed by a lower holding current. This can be achieved either with a device comprising a single coil, in which the current is switched to constitute the holding current, or with a double coil formed by an inrush coil and a holding coil. It is also known to regulate the inrush and holding currents to preset levels (FR-A-2,568,715). This device is supplied by a power supply circuit which dissipates a non-negligible power and is therefore both costly and voluminous.
Voltage supply of the circuits of a control device of an electromagnet may require production of an auxiliary supply voltage. The document EP-A-353,533 proposes using for this purpose the voltages induced in a control coil of the electromagnet when the transistors connected in series with the coil are turned off. This embodiment does not enable the current flowing in the coil to be regulated since a part of this current is branched off to the power supply circuit.
SUMMARY OF THE INVENTION
The object of the invention is to achieve a device enabling the holding current to be regulated simply while supplying the supply voltages necessary for the device inexpensively and in a small volume.
According to the invention, this object is achieved by the fact that the power supply means of the control means are connected in series with the holding coil and the electronic switch in such a way as to be supplied by the holding current, the means for measuring the holding current comprising a measuring circuit connected in parallel with the power supply means and comprising in series an additional electronic switch and a measuring resistor, the control means being connected to the terminals of the resistor and to a control electrode of the additional electronic switch in such a way as to turn the additional electronic switch on periodically.
REFERENCES:
patent: 4729056 (1988-03-01), Edwards et al.
patent: 5214561 (1993-05-01), Morita
patent: 5754386 (1998-05-01), Barbour et al.
patent: 5930104 (1999-07-01), Kadah et al.
patent: 0 353 533 A1 (1990-02-01), None
Parkhurst & Wendel LLP
Schneider Electric Industries SA
Sherry Michael J.
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