US2937321A

US2937321A - Current limiting in the windings of electromagnetic devices

Info

Publication number: US2937321A
Application number: US671599A
Authority: US
Inventors: Richard O Decker; Leonhard Werner
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1957-07-12
Filing date: 1957-07-12
Publication date: 1960-05-17
Anticipated expiration: 1977-05-17
Also published as: JPS3627195Y1

Description

y 1960 R. o. DECKER ET AL 2,937,321

CURRENT LIMITING IN THE WINDINGS OF ELECTROMAGNETIC DEVICES Filed July 12, 1957 WITNESSES INVENTORS ,6 Richard Q Decker a a W wo rmr Leonhard $17 WW M6,

ATTORNEY CURRENT LIMITING IN THE WINDINGS OF ELECTROMAGNETIC DEVICES Richard 0. Decker, Murrysville, and Werner Leonhard, Edgewood, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application July 12, 1957, Serial No. 671,599

Claims. or. 317-156) Our invention relates to an electromagnetic control system, and, more particularly, toa system for limiting the current in the winding, or coil, of an electromagnetic device designed to be energized with alternating current but in use is being supplied with a direct current, or 'at least one having a large direct-current component.

The coil of a solenoid operated valve, solenoid actuated clutch, designed to be normally operated from a source of alternating current, or the coil of an alternating-current contactor, each represents an impedance highly dependentonthe position of the armature, or other movable part with reference to the other parts of the magnetic circuit involved. In a contactor, for example, in open conditions the impedance is small, but the impedance increases rapidly as the armature moves from its unactuated position to its fully actuated position. That is, the impedance increases with a decrease of the air gap in the magnetic circuit with the inductance being a maximum when the air gap is closed. When such a device is operated from a stiff alternating-current voltage source, the contactor takes a high current surge which produces enough force to pull the contactor in even though the air gap is large. As soon as the air gap closes, the impedance increases rapidly and in consequence the current is reduced to a safe value, sufiicient to hold the contactor in.

This inherent current limiting characteristic which allows an economical design, is the distinguishing feature between alternating-current and direct-current contactors.

With the extensive use of magnetic amplifiers in control circuits, having half wave rectified direct current output alternating-current contactors are'at times connected in the output circuit of the magnetic amplifier. If an alternating-current coil is thus energized from a magnetic amplifier, namely, a magnetic amplifier having a half-wave direct-current output, then the coil has to be redesigned, which is impractical, or some other means have to be provided, as current limiting resistors cut in by extra relays or auxiliary contacts on the contactor.

One broad object of our invention is the provision of static means for limiting the current in an inductive load when energized with a direct current.

Another broad object of our invention is the provision of controlling the output of a magnetic amplifier supplying an inductive load as a function of the impedance of the load.

These objects here stated are merely illustrative. Other objects and advantages will become more apparent from a study of the following specification, ing drawing, in which:

Figure 1 is a diagrammatic showing of the simplest embodiment of our invention; and

Figure 2 is a somewhat more elaborate diagrammatic showing of our invention.

In Fig. 1, a generally conventional alternating-current contactor, ACC, is shown connected in the output circuit of a substantially conventional half-wave magnetic amplifier MAI.

This invention is, however, not restricted in use to the and the accompany.

- in control winding 7 2,937,321 Patented May 17, 1960 shown. The magnetic circuit carries the control windings- 9 and 14 and the main winding 2. The main winding 2 is connected in a circuit that may be traced from the lefthand terminal 1 of a suitable source of single-phase alternating current, main winding 2, rectifier 3, poled as indicated, conductor 4, armature actuating winding 5, conductor 6 to the right-hand terminal 7 of the alternatingcurrent supply.

The control winding 14 is connected in a circuit from alternating-current terminal 12, rectifier 13, poled as indicated, control winding 14 to the alternating-current terminal 15. The alternating currents supplied to terminals 1 and 7, and 12 and 15 are in phase with instant polarities as shown. The voltage on terminals 12 and 15 may be made variable, may be arranged to have a directcurrent component of a selected value, or be of a direct current character of a selected value. Usually in this circuit, voltage between terminals 12 and 15 is a resetting voltage that is opposed by a control signal. arrangement, when there is no control signal, the voltage between terminals 12 and 15 resets the core during its resetting half cycle, which half cycle is the half cycle when terminal 12 is positive and when terminal 15 is negative, and during the following gating half cycle, when the polarities at terminal 12 and 15 are as shown in Fig. 1, substantially no current fiows in the output circuit, namely, the circuit including the coil, or actuating winding 5.

When a control signal is present, the voltage between terminals 12 and 15 is opposed during the resetting half cycle. The control signal must, of course, be of sufiicient magnitude to block the rectifier 13 during the resetting half cycle. Therefore, no flux reset occurs and a heavy current will flow in coil 5 which half cycle is a gating half cycle. On the immediately subsequent resetting half cycle some current will flow in the circuit from conductor 6, through conductor 8, device 50 when used, conductor as indicated, to conductor 4. This current in control wind ing 9 will be small in comparison to the current that flows 9 in subsequent resetting half cycles after the contactor ACC pulls in. After the contactor ACC pulls in, a relatively heavy current flows in control winding 9 during the resetting half cycles. The reason for the current flow in winding 9 during the resetting half cycles is because of the inductive nature of the coil 5. The current in winding 9 thus increases as the contactor pulls in. The winding relation of the control winding 9 with respect to the windings 2 and 14 is such that the ampere turns increase the resetting of the core of the magnetic amplifier MAI. This increased resetting reduces the output of the gating cycles. Since the magnitude of the current in coil 9 is here directly related to the position of the armature with respect to the stationary portion of the magnetic circuit, it is apparent we have provided a reliable, dependable, and self-adjusting current limiting For this during the next half cycle,

10, rectifier 11 poled 3 The contactor ACC is interconnected with a magnetic amplifier MA2 such that the feed-back circuit in parallel with coil 5 includes conductor 8, device 50 when used, control winding 9 on magnetic amplifier MA2, rectifier 11, poled as indicated, to conductor 4. The magnetic 5 amplifier MA2 is also provided with a control winding 33. in the adjustable voltage circuit including negative terminal 31, adjustable resistor 32, control, or bias, winding 33, and conductor 34 to the positive terminal 35.

A more positive feed-back signal than obtained with 1 the circuit shown in Fig. I, can be obtained with the circuit arrangement shown in Fig. 2. The magnetic amplifier MA3 has main, or output, windings 41, and control windings 42 and 43. Winding 42 is the feedback winding receiving its signal from magnetic amplifier MA2. Here magnetic amplifier MA3 serves as a preamplifier for magnetic amplifier MAI. The polarities indicated in Fig. 2 for the terminals 12 and 15, I and 7, and I8 and 23, are the instantaneous polarities for the resetting half cycle of magnetic amplifier MA3, for the gating half cycle of poses the effect of the control signal in winding 43.

A control signal of sufiicient magnitude resets magnetic amplifier MAS which then does not reset magnetic amplifier MAI and current flows in the output circuit of magnetic amplifier MAI.

Magnetic amplifier MA2 may be so biased that it is cut off for all currents in control winding 9 less than a selected value, namely for all current values present as long as the contactor ACC is open. With magnetic amplifier MA2 cut-oft, no feedback signal is fed to magnetic amplifier MA3. When the contactor ACC closes and thus effects a higher inductance of coil 5, heavy current flows in control winding 9.

The winding relation of winding 9 with respect to windings 22 and 33 is such that the ampere turns decrease the resetting of the core of magnetic amplifier MA2.

When the output of magnetic amplifier MA2 increases, due to the decreased resetting current, current is supplied to the feedback winding 42 on magnetic amplifier MAS. This current in the feedback winding 42 opposes the control signal in winding 43 and increases the output voltage of magnetic amplifier MA3 and thus reduces the output voltage of magnetic amplifier MAI. The aim of protecting the coil 5 against unsafe current values is thus attained, while safely holding the armature A in actuated position.

When the control signal in winding 43 of magnetic amplifier MAS is removed, the voltage output of magnetic amplifier is at full value and magnetic amplifier MAI is substantially cut off. The contactor ACC thus drops out.

tions and arrangements are possible all falling within the spirit and scope of our invention.

We claim as our invention:

1. In an electric system of control, in combination, an inductive load the energization of which is to be controlled, said inductive load in use having a variable impedance, a magnetic amplifier having a magnetic circuit and having a main winding and two control windings, all of said windings being interlinked with the magnetic circuit, a rectifier, a pair of terminals in use energized with single-phase alternating current, a circuit including the main winding, the rectifier, and the inductive load connected across said terminals, means for so energizing one of the control windings to effect a selected effective degree of saturation of the magnetic circuit to thus energize the inductive load with pulsating direct current of a magnitude dependent on the selected effective degree of saturation of the magnetic circuit and the impedance of the inductive load, and means for energizing the second control winding as a function of the impedance of the inductive load to decreased the saturation of the magnetic circuit with a rise of the impedance of the inductive load.

2. In an electric system of control, in combination, an inductive load normally in use having the characteristic to rapidly increase its impedance upon energization with alternating current but the impedance of which rises less rapidly if energized with pulsating direct current, a magnetic amplifier in use suitably energized and having an output circuit for producing pulsating direct current, circuit means for connecting the inductive load to the output circuit of the magnetic amplifier, and control means responsive to the rise of impedance of the inductive load to decrease the output of the magnetic amplifier as a function of the rise of impedance of the inductive load.

3. In a system of control, in combination, an inductive load unit in use upon energization manifesting a rise in impedance, a magnetic amplifier having a magnetic 0 core, a main winding on the core, and rectifier connected to energize the load unit from a suitable source of alternating current, a control winding for the magnetic amplifier so wound on the core to effect operation of the magnetic amplifier so as to energize the load unit, a sec- 5 ond control winding for the magnetic amplifier, said sec- Either method of precedure, as shown in Fig. 1 or Fig. 50

2, however, gives a safe and efficient means of limiting the current in coil 5 after the contactor has operated. The result is that an alternating-current contactor can be operated from a half move source with a current limit scheme that does not require resistors and auxiliary contacts.

For some applications it is desirable to indicate the condition of the circuit including the coil 5. The device 50 is shown interconnected with this circuit. The device 50 may be a meter, or signal light indicating whether or not contactor ACC has operated. The device 50 may also constitute control means for effecting operation of other circuitry depending on the operation of contactor ACC.

While we have shown and described but two embodiments of our invention, it is apparent that other modifica-- ond control winding being interconnected with the load unit and so disposed on the core to effect a decrease in the magnetic amplifier output with a rise in impedance of the load unit.

4. he system ofcontrol, in combination, an inductive load unit in use upon energization manifesting a rise in impedance, a magnetic amplifier having a main winding and rectifier connected to energize the load unit from a suitable source of alternating current, a control winding .for the magnetic amplifier to effect operation of the magnetic amplifier so as to effect energization of the load unit, a second control winding for the magnetic amplifier and a second rectifier, poled in opposition to the first rectifier, connected in series with the second control winding, said second control winding and second rectifier being connected in parallel with the load unit, the second control winding being so wound with respect to the other windings of the magnetic amplifier to decrease the output of the magnetic amplifier with a rise in impedance of the load unit.

5. In an electric system of control, in combination, an inductive load unit in use, upon initiation of its energization, manifesting a rise in impedance, at first magnetic amplifier having a main winding and rectifier connected in series therewith comprising the output circuit of the magnetic amplifier, said output circuit in use being connected to a suitable source of alternating current and being'connected to energize the load units, said magnetic amplifier having a control winding for selecting the triggering point of the magnetic amplifier, and havljr ing a second control winding for altering the output of the magnetic amplifier, a second magnetic amplifier having a main winding connected in series with a rectifier, the second control winding of the first magnetic amplifier and a suitable source of alternating current, said second magnetic amplifier having a bias winding for selecting its triggering point and having a second control winding and a rectifier connected in series therewith, this second control winding and series connected rectifier being connected in parallel with the load unit with this rectifier being poled in opposition to the pol-ing of the rectifier in series with the main winding of the first magnetic amplifier.

References Cited in the file of this patent UNITED STATES PATENTS 2,518,865 Cartotto Aug. 15, 1950 2,706,764 Mitchell Apr. 19, 1955 2,747,109 Montner May 22, 1956 2,816,260 Scorgie Dec. 10, 1957 2,849,662 Britten Aug. 26, 1958