US2130309A - Current conductor support - Google Patents

Description

Sept. 13, 1938. 1.. s. NERGAARD CURRENT CONDUCTOR SUPPORT Filed Sept. 18, 1937 INVENTOR LEON .5. IVERGAARD BY ATTORNEY.

' ductors.

Patented Sept. 13, 1938 UNITED STATES PATENT OFFICE CURRENT CONDUCTOR SUPPORT Application September 18, 1937, Serial No. 164,471

5 Claims.

This invention relates to means for supporting and sealing conductors of alternating current in a wall such as the envelope of an electron discharge device.

In power tubes large current carrying leads, such as the filament conductors, are usually supported by cup-shaped bushings or thimbles of metal sealed along their rims to the glass wall of the envelope, the conductors passing centrally through the bottom of the thimbles. As the filament leads usually enter the envelope side-byside, the current flows in opposite directions in the leads and produces circular electromagnetic lines of force surrounding each of the two con- When these lines are produced by alternating current, they cut the walls of the thimbles and induce circulating currents and considerable heat loss.

An object of my invention is to make a bushing or thimble for lead-in conductors to minimize circulating currents and heat losses in the thimble induced by the currents flowing in the conductors.

The circular electromagnetic lines of force about each of two parallel conductors are, be-

cause of their mutual repulsion, eccentric with respect to those conductors. I have found that if the cylindrical walls of a thimble surrounding the conductors are placed eccentric with the conductors and concentric with the lines of force which cut the cylinder, circulating currents and heating is reduced. As the circular lines of force collapse and expand about the conductors axial electromotive forces are induced in the thimble. Since all points on each cutting line pass simultaneously through the wall of the thimble in my improved construction, the net E. M. F. around any closed loop in the thimble is zero and no circulating current results. If the lines of force are irregular because of extraneous electromagnetic influence or because of three or more juxtaposed current carrying conductors, it is proposed according to my invention to so shape and space the side of thimble that all points on each cutting line of force pass simultaneously through the side of the thimble.

The characteristic features of my invention are pointed out with particularity in the claims and one embodiment is described in the accompanying specification and appended drawing in which Figure 1 is a sectional perspective view of my novel lead-in seal, and

Figure 2 is an end view of my novel lead-in seal showing diagrammatically the magnetic field distribution.

The structural embodiment of my invention chosen for the purpose of illustrating the characteristic features of my invention and shown in Figure 1 comprises a vitreous wall I representative of the envelope of an electric device such as the wall of an electron discharge device with two conductors 2 and 3 passing through and sealed in the Wall by cup-shaped bushings or thimbles 4 and 5. The rims of the thimbles are sealed, preferably gas-tight, in the vitreous wall, which may be of glass, and the conductors 2 and 3 may either be continuous metal rods passed through openings in the bottom of the thimbles, or the conductors may be in two coaxial portions joined as by welding to opposite faces of the bottoms of the thimbles. The parallel conductors may be connected on one side of the wall to any desired circuit, or, in the case of a radio tube, they may be connected to electrodes in the tube. The conductors may serve, for example, to supply alternating current of high ampltiude to a filament or they may function as the Lecher wire conductors of a long line tuning system of a high frequency oscillator or amplifier.

The magnetic field distribution about two parallel conductors of the same diameter carrying current in opposite directions is represented by electromagnetic lines of force 6, Figure 2, each line being circular and eccentric with respect to the conductor which it encircles. If the tubular sides of the thimbles are concentric about the leads, the magnetic field strength will not be the same at each point on the periphery of the thimbles and each line as it cuts the walls of the thimbles induces unequal voltages at each point on the thimble periphery. Since the induced voltages vary from point-to-point along the periphery of the thimble, eddy currents and heating losses result.

According to the characteristic feature of my invention, the thimbles are so placed that their peripheries coincide and are concentric with the cutting lines of force, the centers of thimbles being placed outward on a line through the centers of the conductors so that induced voltages are the same at each point on the periphery. It has been determined mathematically that, if the conductors have equal diameters and the thimbles have equal mean diameters, the relation of the distance between centers of the conductors l1, the

distance between centers of the thimbles la, the diameter of the leads d1, and the average diameter of the thimbles dz is From this relation, the distance between the centers of each conductor and its thimble may readily be calculated. If, however, the diameters of conductors 2 and 3 are unequal, and are di and d2, the distance m1 between the centers of thimble 4 and its conductor 2 and the distance m2 between the centers of conductor 3 and its thimble 5 may be determined from the following formulae:

in which Z is the distance between the centers of the two conductors, L is the distance between the centers of the two thimbles and D1 and D2 are, respectively, the diameters of the thimbles. If a third conductor lies parallel to conductors 2 and 3, the lines of magnetic force are no longer circular, but are of an irregular shape, the only requirement according to my invention being that the wall of the thimble be so shaped as to coincide with the particular line of force cutting it.

My novel bushing or thimble for supporting the sealing lead-in conductors in a vitreous wall minimize circulating currents and heat losses in the thimbles induced by currents flowing in the conductors.

I claim:

1. In combination, a wall, a plurality of alternating current carrying conductors extending through openings in said wall, means for supporting said conductors in said openings com prising cup-shaped thimbles with the tubular sides of the thimbles joined to said wall in the opening, the bottom portion of each thimble being joined to one of the conductors, and said tubular sides of the thimbles being shaped to coincide with electromagnetic lines of force cutting the tubular sides.

2. In combination, a plurality of cup-shaped thimbles with tubular sides and a bottom portion, a current carrying conductor extending through each of said thimbles and attached to said bottom portion, each point on the sides of the thimbles being so spaced from the conductors as to be simultaneously cut by each electromagnetic line of force passed through the sides of the thimble by current flowing in the conductors.

3. In combination a wall, two parallel conductors extending through said wall, two cup-shaped thimbles each being joined along its rim to the wall and at its bottom to one of said conductors, the center of each thimble being spaced outwardly from the center of its conductor on a line through the centers of the conductors.

4. In combination a plurality of metal cylinders, an alternating current carrying conductor extending longitudinally through each of said cylinders and supported in spaced relation to the sides of said cylinders, the center of each conductor being displaced from the center of its surrounding metal cylinder.

5. In combination, a wall, openings in said wall, metal cylinders attached to said wall in the openings, and an alternating current carrying conductor extending through each cylinder and supported in spaced relation to the sides of the cylinder, each conductor being eccentric with respect to its cylinder.

LEON S. NERGAARD.

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