Eaton Corporation

Westinghouse Electric Corporation

Rick A Hurley

Mark E Innes

Birch L DeVault

Nelson R Palmer

Bruce R Quayle

Parker A Bollinger, Jr

A control circuit for electrical contactors, starters and the like which include one or more pairs of separable main contacts is controlled by an electromagnet assembly. In order to reduce, if not eliminate, audible noise generated by the electromagnet assembly, the electrical current to the electromagnetic assembly is regulated to minimize the rate of change of magnetic flux therethrough to thereby reduce, if not eliminate, audible noise. By regulating the electrical current to the electromagnet assembly, the power consumption of the electromagnet assembly is reduced which, in turn, reduces undesirable heating of a solenoid coil within the electromagnet assembly.

Ultrasonic coil current regulator

An electromagnetic switch includes separable contacts, an electromagnet having a coil which is energized to close and hold closed the separable contacts, a power supply for applying current to the coil, and a closed-loop control circuit for sensing and regulating, throughout a contact closure cycle, the current applied to the coil to a selected current reference. The current reference may include a closing current reference for closing the contacts and a holding current reference for holding the contacts closed. The control circuit may include a microcomputer for generating the current reference and, further, may include a first switching circuit and an associated control circuit for actuating the first switching circuit between enabled and inhibited states, a second switching circuit and an associated control circuit for actuating the second switching circuit between conductive and non-conductive states, a feedback circuit for sensing the coil current and generating a related feedback signal, and a comparator circuit for comparing the current reference and the feedback signal, and for inhibiting the second switching circuit whenever the feedback signal is greater than the current reference. The microcomputer may include control signals defining states corresponding to a predetermined closing current reference and a predetermined holding current reference. One of the control signals may attenuate the feedback signal, in order to provide the closing current reference. The electromagnetic switch may alternatively include a circuit for generating a time-variable current reference in order to substantially follow a predetermined magnet pull curve of the electromagnet.

Electromagnetic device with current regulated closure characteristic

An electrical contactor has first and second contacts movably mounted to engage for achieving continuity in an electrical circuit, via an electromagnet and armature defining a magnetic circuit with an air gap that closes in a first position of the contactor and opens in a second position of the contactor. A controller switches an alternating current voltage to the coil of the electromagnet during a timed portion of each AC half cycle, and senses the current level in the coil in a feedback loop. The controller adjusts the voltage-on time to achieve a predetermined average current as needed for accelerating the armature or coasting during a closing operation, for holding the armature in place when closed, etc. In order to sense whether the contactor is presently open or closed, the controller monitors and stores the phase angle between the previous voltage zero crossing and the time of voltage turn-on. When the inductance of the magnetic circuit including the electromagnet and armature changes rapidly due to opening or closing of the air gap between them, the controller detects a corresponding variation in the phase angle. The controller is preferably a microprocessor, programmed to normalize the phase angle over a range of coil drive voltages. The microprocessors of a number of such contactors can communicate in order to effect coordinated operations.

Electronic interlock for electromagnetic contactor

A controller such as a programmable logic controller (PLC) is coupled to a load such as a contactor or motor starter through an interface that operates over a range of DC or AC voltage and couples a Start output of the controller to the load through a low current switch such as an opto-relay. The interface has a charging circuit coupled to the controller output, with a switching transistor, a load resistor and a capacitor in series. The low current switch is operated from accumulated charge in the capacitor and couples power to the load device. Charging of the capacitor to a threshold switches off of the transistor for an interval timed by a one-shot, during which the low current switch remains activated due to current draining from the capacitor. In an AC embodiment with a triac controller output, the capacitor continues to power the low current switch for the remainder of the positive AC half cycle, regardless of the triac, which may cease conduction due to lack of sufficient loading. The circuit substantially reduces the current dissipation of an interface between a PLC and a motor starter or contactor. The interface can include optically isolated signalling in both directions, including feed back of contact status and trip indications to inputs of the PLC.

Reduced wattage PLC interface

A multiphase contactor with solid state circuity gating rectified pulses to an electromagnetic coil to close and hold closed contacts for each phase, sequentially for each successive opening of the contactor adjusts the delay angle of the last pulse to rotate the sequence in which the individual phase currents are interrupted. By alternately making the last pulse positive or negative the polarity of the interrupted current alternates to further promote even contact wear.

Microprocessor based electrical contactor with distributed contactor

The coil holding current of a contactor is regulated to the lesser of two measurements of coil current during each cycle of the full-wave rectified control voltage to compensate for induced flux in the coil generated by load current through the main contacts of the contactor, thereby preventing uncontrolled drop out of the contactor.

Coil current regulator with induced flux compensation in an

A method and apparatus for remotely displaying information about heat in a motor having an associated motor-starting contactor with an overload relay system is provided. The apparatus includes a suitably programmed microprocessor which obtains a signal representative of current in the motor, squares the current and multiplies by time. This actual I.sup.2 t value is then used to calculate a signal representative of a relationship between the actual I.sup.2 t value and a target value at which the contacts of the motor-starting contactor will open due to an overload current situation. This relationship is preferably a percentage which is then displayed on either an LED bar type display or a digital display. The display may also include a 'trip' indicator and a 'reset allowed' indicator.

Apparatus for displaying thermal condition of motor controller

Control circuitry is disclosed for electrical starters, contactors and the like having a starting winding and a serially coupled holding winding wherein the holding winding is shorted until the separable main contacts have closed which includes circuitry which obviates the need for relatively precise sensing of the position of the separable main contacts to control the holding winding. In one embodiment of the invention, the unshorting of the holding winding is delayed a predetermined number of cycles after the separable main contacts have closed to avoid the necessity of relatively accurate mechanical sensing of the position of the separable main contacts. In this embodiment a relatively less expensive field effect transistor or the like is used to short out the holding winding until the separable main contacts have closed. This allows the use of a relatively less expensive limit switch with a substantially smaller DC capability. In alternate embodiments of the invention, control circuits are provided which allow the limit switch normally used for sensing the position of the separable main contacts, to be eliminated altogether, thus further reducing the cost of the device as well as the labor cost involved for adjustment of the limit switch.

Double DC coil timing circuit

A microprocessor controlled electrical contactor monitors the voltage and peak current produced by a first voltage pulse gated to the coil of the contactor electromagnet and adjusts the conduction angle of the second pulse to deliver a constant amount of electrical energy to the electromagnet coil despite variations in coil resistance and supply voltage so that the contactor contacts can be consistently closed with low impact velocity and minimum contact bounce. Normally, the third and subsequent pulses are gated to the coil at constant conduction angles selected so that the contacts consistently touch and seal on a preselected pulse with declining coil current. Under marginal conditions, determined by the peak current produced by the first pulse, the third and subsequent pulses are gated at substantially full conduction angles to assure contact closure. If the voltage or current produced by the first pulse is below a predetermined value, closure is aborted.

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Fletcher, NC, United States of America

Rick A Hurley