US1535883A - Electric-furnace control - Google Patents

Description

April 28, 1925. 1,535,883

I H. A. WINNE ELECTRIG FURNACE CONTROL Filed Nov. 25, 1921 Invehtor: Harry A.Winhe His Attorneg.

Patented Apr. 28, 19 25.

UNITED STATES PATENT OFFICE.

HARRY A. WINNE, OF SCHENECTADY, NEW YORK, ASSIGNOR'TO GENERAL ELECTBIC p COMPANY, A COBPORATION OF NEW YORK. y 4 V Enorme-ruana@ CONTROL.

Application filed November 23, 1921. Serial No. 517,401.

To all whom it 'may concern:

Be it known that I', HARRYVA. WINNE, a citizen of the United States, residing at Schenectady, in the county of Schenectady, State of'Ne'w York, have invented certain new and useful Improvements in Electric- Furnace Controls, of, which the following is a specification.

My invention relates to the control of electricfurnaces and has for its object the provision of means whereby an improved reguw lation of the furnace current is obtained in a simple and eflicent'manner.

My invention relates more specifically t'o the control of an electric are furnace in.

controllng the electric motor which operates` the electrode. With this arrangement there is under some conditions possibility of a hunting action of the moving member of p the contact making ammeter due to lag in some of the circuit controlling parts and also due in part to momentum in themotor arma ture and electrodes moved thereby. One of the objects of my invention is to overcome this tendency. p

In carrying-out my invention I provide means whereby the moving'member of the controlling means, such as the contact making ammeter, is supplied with a positive force tending to return it to neutral position as soon as it makes a contact which starts the motor for shifting the electrodes. This causes themember to be pulled away from the stationary contact earlier in the operating cycle than would ordinarily be the case. The result is that a closer regulation of the current is obtained .without the objcctionable hunting action of the mo'vable member. Other objects andpurposes of my inj vention will appear in the course of the following specification in which I have shown ny invention embo'died in concrete form for purposes of illustration. I

Referring to the accompany'ing drawing i in which I have shown the parts more or less which has a screw threade'd relation with a. screw 10 connected with the electrode' whereby the electrode will be moved up and down very slowly through this speed red1icing gear. The field of the motor F is suppled from the direct current mains 11 and 12, there being a resistanc'e R in' the field circuit controlled by a cont actor' 13 for varying the speed of the moton...- Reversing switches 14: and 15 are provided for reversing the motor armature current which is supplied from the mains 11 and 12 "an'd adynamc brake resistance 16 controlled by a contactoi' 17 conncle across khe motor temnas is provi e or uic sto t e motor after the power i s cut ta. lb canical interlocks 18 and 19 cooperate with an extension 20 on the moving element of the contactor 17 for preventing the closing of one of the reversing contactors until the contactor 17, which controls the dynamic braking circuit, opens due to the substantial stopping of the motor. The two reversing ing ammeter having an Operating coil 21 connectedto-a current transformer 22 in 'the supply conductor 8, a resistance 23 be- ,control to manual control and vice versa.

contactors are controlled by a contact makt When the switch 31 is in position to bridge whereas when it is moved over so as to enu gage the contact 33, the control will be manual through the push buttons 34 and 35.

As thus far described it will be seen that assuming that the switch 31 is in engagement with the contaets 32 the control of the electrode 5 will be automatically effected in accordance with the variations in 'the current 'of the sup ply conductor 8. If,

for inst'ance, current 'in the conductor 8 becomes too high the contactmaking ammeter will operate to make contact at 27 and energize the reversing contactor 14 whereby the electrode will be raised to reduce the current. On the other hand, if the current in the conductor 8 becomes too low the con-g tact is made at 26 so as to energize the contactor 15 and close the motor circuit in a direction to lower the electrode; Each time one of the reversing contactors opens 'to open the motor armature circuit the con tactor 17 wilL'close ,toestablish a dynamic braking circuit through the resistance 16 and the other reversing contactor cannot close until the contactor 17 'is opened by the slowing d'own of the motor substantially to rest. When the switch 31 is 'in the auto natic position; namely, in engagement with the contacts 32, the contactor 13 Will close so as to short circuit the resistance R and reduce the speed of the motor. When the switch 31 is moved into engagenent with the contact 33 the control of the reversing' contactors will be through the push buttons' 34 and 35. In this position, however, the conta'ctor 13 will be open and the resistance R will be in series with the field so as to speed up the motor. There will therefore be a 'higher speed of the motor during manual v which is energized to move the member in either direction depending upon which of the contacts 26 or 27 isengaged. This winding 36 is energized across the direct currentsupply circuit 11, 12`either through resistances 7' or 7-' and one of the reversingcontactors 14, 15. 'Whencontactor 14 closes due to the engagement'of the arm 24 with the contact 27, a. circuit is completed through the winding 36 from the supply line 11 through the'resistance-r, winding 36, and the upper switch arm of contactor 14 to line 12. The energization of winding 36 is now in a direction to force the. arm.24 upward out of engagementwith the contact 27. If

the` contactor 15 is closed due to the closing' of the circuit at contact 26, the circuit will then be from th -supply line 11 through the upper switch arm of con'tactor 15 through clear.

winding 36 and to`-supply line 12 through resistance r'. The current through the winding 36 is'now reversed so ;that the force'` upon the arm 24 is in the downward direc tion tending to break the contact at-26. A

dash pot 37 retards the action ofthe wind ing '36 upon its moving core. It will therefore be seen that whenever the contact is made at either 26 or 27 a force is-set up tending to move the arm back to the central position. The 'result of this is more positve action of the contact making anj meter resulting in a closer calibration with no tendency of the member to hunt. A numerical example will make .this point Assuming that the member 24 balances. in a neutral positionwith' a current of one ampere in the coil 21 'and that a decrease of current .to .95 ampere will cause the electrode 5. .At the same time the-coil 36' willbe energized in a direction tendi'g to lift the arm 24 out of engagement with the contact 27. If the 'force due to the wind*- ing 36 were not present, 'the arm'24 would not tend to separate from contact 27 until the current in the contact making ammeter had actually been reduced to 1.05 amperes and the lag of the mechanism and the over:

travel of the electrode might cause the -current to drop to .95 ampere before the electrode motion actually ceased. The -force set up by the winding 36 may be such that the member 24 will tend to separate' from 'the contact 27 when the current in the winding 22 has been reduced to only- 1.1 amperes. consequently, assuming the sa'me'lag and *overtravel in the mechanism, at the tim the electrode motion' is actually stopped, the current in the coil 22 will have been reduced only to the normal -value of one ampere. In other words, by the provision of-. my arrangement the natural tendency for an overtravel which would result in the continuous vibration or hunting action of the mem-' ber 24 will be to a very large extent overcome While I have described my invention as i embodied in concrete form and as operat ing in a specific manner in accordance with the provisions of the patent statutes, it should be understood that I do not limit my invention thereto, since various modifica tions thereof will suggest themselves to those skilled in the art without departing from the spirit of my invention, the scope of which is set forth in the annexed'claims.

' What I claim 'as new and desire' to se- V electrode cure by Letters Patent of the United States,

1'. A regulating system for e-lectric. furnaces comprising in combination with an 2 an energy supply source therefor, an electrc motor for' moving said electrode, electromagnetic means res nsive to variations in the electrode circut for controlling the. movement of 'said electrode by said motor in two-directions, a. pair of resistance devices connected in series across said supply source, a second electromagnet mechanically connected* to the first, and' electrical connections between one terminal of said secv ond electromagnet and one terminal of said motor and between the other terminal of said second electromagnet and a point between said resistance devices, whereby said second electromagnet is energized to oppose the first upon movement of said electrode in either direction.

2. A regulating system for electric furnaces comprsing in combination with an electrode, an energy supply source therefor,

an electric motor operatively connected to adjust said electrode, "reversing switches for said motor, a contact making ammeter for controlling the reversing switches having a winding in the electrode supply circuit and an element movable by said winding to opposite contact making positions from an intermediate position in accordance with variations in the electrode circuit, a pair of resistances connected in series across said supply source, an electromagnet, an Operating connection between said electromagnet and said element, and electrical connections between one terminal of said electromagnet and one terminal of said motor and between the other terminal of said electromagnet and a point between said resistances' whereby said electrona-gnet is energized through said reversing switches concurrently with said motor to exert a force tending to return said element to its intermediate position.

In witness whereof, I have hereunto set my hand this 22nd day of November, 1921.

HARRY' A. WINNE.

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