US3381248A - Magnetic pressure liquid circuit breaker - Google Patents

Description

April 30, 1968 H. P. FURTH 3,381,248

MAGNETIC PRESSURE LIQUID CIRCUIT BREAKER Filed Oct. 23, 196E J2 1:]! g l:

I 1 1 I I LII I I II 59 55 INVENTOR.

HAROLD P F (/1? TH 5296;. 5: ynfl 41 9 45 ,arroelvek United States Patent 3,381,248 MAGNETIC PRESSURE LIQUID CHRCUIT BREAKER Harold P. Furth, Berkeley, Calif. Filed Oct. 23, 1965, Ser. No. 593,370 1 Claim. (Cl. 335-51) ABSTRACT OF THE DISCLOSURE The present invention relates to a magnetic circuit breaker for breaking the electrical circuit between a pair of electrically conductive liquids. A magnetic field generated by a coil in the vicinity of the liquids interacts with current induced in the liquids to generate magnetic pressure which forces apart the liquids thereby breaking the electrical circuit.

This invention relates to electrical current circuit breakers and more particularly to devices and methods for rapidly interrupting an electric current in a liquid by magnetic pressure.

The increasing use of electrical circuits carrying large currents and high voltages has dictated the need for more efficient switching circuits. In a copending application entitled, Liquid Level Current Circuit Breaker, filed on July 26, 1965, Serial No. 474,762, now abandoned, by Harold P. Furth, there is disclosed an electrical current circuit breaker which utilizes magnetic pressure to interrupt a current circuit between a solid electrode and a conducting liquid. Such a circuit breaker offers many advantages over the prior art including extremely fast operation and ability to switch large currents of high voltages. While the above mentioned circuit breaker offers many advantages over the prior art, certain problems are created by the action between the solid electrode and the liquid metal conductor. There is a tendency to are during the switching which erodes the ends of the solid electrode. Since the switching may occur at a very high frequency, the surface of the solid electrode is eventually eroded to the point of requiring replacement. Accordingly it is an object of this invention to provide a circuit breaker for opening a current circuit in a fast time without erosion of the electrodes.

The device of this invention overcomes the problem of erosion of the electrodes by interrupting a current between a pair of liquid metal electrodes. Magnetic pressure of extremely large force instantaneously forces the liquid metal electrodes apart to break the current circuit. A fast interruption of a large current high voltage circuit is realized without arcing sufficient to cause any serious erosion during continuous operation.

It is therefore another object of this invention to provide an improved electrical circuit breaker activated by magnetic pressure.

It is still another object of this invention to provide a means for breaking the electrical circuit between a pair of liquid conductors.

It is a further object of this invention to provide a circuit breaker which is not subject to arcing.

It is a still further object of this invention to interrupt a current between a pair of liquid conductors by creating a magnetic field which reacts to generate magnetic pressure to break the circuit between the conductors.

Other objects and advantages of the present invention will become apparent from the following description and appended claims.

In the drawing:

FIGURE 1 is a view of a circuit breaking switch according to a preferred aspect of the invention.

FIGURE 2 is a partial view of the switch of FIG. 1

Patented Apr. 30, 1968 showing the position of the liquid when magnetic pressure has been applied to open the circuit.

FIGURE 3 is a view of a second aspect of the invention in which the pulse generating coils are located outside of the main switch.

FIGURE 4 is a view of the device of FIG. 3 when magnetic pressure has been applied.

FIGURE 5 is a view of another aspect of the invention in which the pulse generating coils are located above the liquid only.

FIGURE 6 is a view of the device of FIG. 5 in open condition.

According to a principal aspect of the invention an electrical current flowing between liquid metal electrodes is interrupted by magnetic pressure which forces the liquid apart. A liquid metal pool is separated into a pair of electrodes by an insulating bridge with current flowing between the electrodes during the closed position of the switch. A pair of interrupter coils are mounted in relationship with the electrodes with magnetic pressure generated by activation of the coils forcing the liquid electrodes apart during the open position of the switch.

Before proceeding to a detailed description of the device of the invention a brief discussion of the principles defining the operation of the device of the invention will be made. As described in the copending application referred above, a rapid displacement of liquid metal can be accomplished by pulsing on a magnetic field of strength B in a coil at the surface of the liquid metal. The pulse risetime is made sufiiciently short so that the associated skin depth in the liquid metal is smaller than the dimension of the region of liquid metal that is to be displaced. The pulsed magnetic field is effectively excluded from the volume of the liquid metal and exerts a pressure B /S on r the surface of the liquid. If B is expressed in gauss, then where V is the mass density of the metal and T is in seconds. If D is, for example, .5 cm. and B is 25,000 gauss and if the liquid metal is sodium, with V=1 gm./ 0111. then the time is sec. The skin depth in liquid sodium for t=l00 sec. is .3 cm., so it may be readily seen that the pulsed magnetic field is in fact effectively excluded from the volume of the liquid metal. It is this principle of interaction between a magnetic field and the skin of a liquid metal which produces magnetic pressure to force liquid electrodes apart and break the current circuit between them.

Referring now to the drawing and in particular to FIGS. 1 and 2 there is illustrated a principal aspect of the invention. In FIG. 1 a pair of liquid metal electrodes are produced by the structure including an outer liquid metal pool 16 and an inner liquid pool 14 which are suitably enclosed by a casing 17. The pools 14 and 16 are separated by insulator tubes 21 having coils 19 mounted thereon. The coils 19 are suitably located a short distance below the level of the pools 14 and 16 so that during the position of the switch when current is flowing between the pools 14 and 16 current flows through the bridge 15, which is that portion of the liquid above the coils 19 between the pools 14 and 16. The switch includes a solid center electrode 13 which is connected to a terminal 11 responsively connected to the initial source of current. The lower end of the electrode 13 is immersed in the inner liquid pool 14 and suitably insulated from the outer casing 17. The terminal 12 completes the current path by being conductively connected to the outer casing 17 which is a metallic conductor. Thus when the circuit is in the closed position, current fiows from the terminal 11 through Located above the tubes 21 and coils 19 are corresponding tubes 20 and coils 18 which interact with the coils 19, in a manner to be described to provide the magnetic pressure for forcing the liquid pools 14 and 16 apart. The coils 18 and 19 are mounted in close relationship so that the coils 18 are just above the level of the pools 14 and 16 and the coils 19 are just below the level of the pools. Electrical pulse current for the coils 18 and 19 is provided by a suitable source of high voltage large current, through corresponding leads 22 for the coils 18, and leads 23 for the coils 19. It is to be noted that the level of the pools 14 and 16 is slightly depressed as illustrated in FIG. 1 during operation which is caused by the magnetic pressure exerted during the flow of current through the center electrode 13 when the circuit is completed.

Turning now to the operation of the device of FIG. 1 when the circuit is interrupted, as shown in the partial view of FIG. 2, current is interrupted between the liquid pools 14 and 16 by magnetic pressure generated by the interaction between the magnetic fields created by the coils 18 and 19 and the current flowing on the surface of the pools 14 and 16. A current pulse of high magnitude in the coils 18 and 19 generates magnetic fields whose lines of force are illustrated in FIG. 2. The current in the coils 18 produces lines of force shown by the lines 24 and the current in the coils 19 produces lines of force 25. The interaction between these lines of force and the current induced in the skin of the pools 14 and 16 in the vicinity 15 generates magnetic pressure. This pressure forces the liquid pools apart thus breaking the bridge 15 as shown in FIG. 2. Since the device is cylindrical in structure, the pools 14 and 16 are completely electrically separated by reason of the magnetic force in the region of the bridge 15.

Electrical arcing during the interruption of current between the pools 14 and 16 is greatly minimized by reason of the separation between a pair of liquid electrodes as opposed to the prior art devices wherein solid electrodes were used. Additionally arcing between the liquid pools 14 and 16 and the coils 18 and 19 is greatly reduced by the action of the magnetic lines of force. As seen in FIG. 2 the lines of force 24 and 25 have horizontal components which act to force the liquid pools 14 and 16 apart at the bridge 15 and vertical components which tend to cause any radial are generated to be rapidly elongated thereby extinguishing the arc. This is realized since the radially outer part of the arc will move in the opposite azimuthal direction from its radially inner part. In that event the opposite direction movement of the lines of force 24 and 25 elongate the arc thereby extinguishing it.

To further prevent arcs from being generated dun'ng the interruption of current between the pools 14 and 16 there is included a high pressure gas, such as argon, within the casing in the region 30 above the pools 14 and 16.

In order to further minimize arcing, a layer of oil may be placed on the surface of the pools 14 and 16. The combination of the methods described above elfectively eliminate any erosion of the solid parts of the device from arcing thereby contributing to a long life for the device. The magnetic field, as shown in FIG. 2, causes any arcs to move in a direction orthogonal to the initial are current and the magnetic field vector. Since the magnetic field vector is in two directions along the length of the are as seen by the arrows 32 and 33, for example, the local arc velocity will also change its sign thereby distorting and elongating the arc.

In FIGS. 3 and 4 there is illustrated another aspect of the invention in which a pair of coils 41 and 42 are located outside of the casing 43 of the device. The central solid electrode 44 is formed in a diamond shape to facilitate the parting of the liquid during the interrupting phase. As seen in FIG. 4 when coils 41 and 42 are energized, the region 46 joining the liquid electrodes 47 and 48 becomes void of liquid due to the magnetic pressure which forces the liquid away. The liquid moves away from the point 49 on the edge of the solid electrode 44 thereby tending to suppress any arcs. Similarly the region in the vicinity of the coil 42 has its liquid forced away by the generated magnetic pressure.

Another aspect of the invention is illustrated in the drawing in FIGS. 5 and 6 which show a device in which liquid is separated in two regions by the action of two coils displaced above the liquid level. The coils 51 and 52 located on either side of the central solid electrode 53 each produce a force to separate the liquid in a pool 55 in the regions 56 and 57 where insulating tubes 58 and 59 extend from the bottom of the pool to a position just below the level of the liquid pool.

The liquid level current interrupting device of the invention provides a distinct advantage over other circuits by utilizing a pair of liquid electrodes as the contacting electrodes. Arcing is almost eliminated thereby producing an extremely long life for the device. Additionally the magnetic pressure operation produces a tremendously fast is practically nonexistent due to the presence of liquid switching time in the operation of the device. Overheating electrodes.

While the invention has been disclosed herein with respect to the embodiments illustrated in the drawing, it will be readily apparent that numerous variations and modifications may be made within the spirit and scope of the invention. For example, as previously described, a number of different locations for the current coils may be utilized to produce the most eifective magnetic pressure on the liquid conductors.

I claim:

1. In a circuit breaker, the combination comprising:

a liquid metal enclosed in a metallic casing,

insulating means in said casing for separating said liquid metal into inner and outer pools,

said insulating means extending to a height just below the surface of said pools to form a bridge region between said pools,

means for applying current to said metal casing and said liquid metal to provide a circuit between said inner and outer pools through said bridge region,

and means for generating magnetic pressure in said bridge region to force said liquid apart in said bridge region,

said means for generating magnetic pressure comprising a pair of coils in said bridge region, one of said coils above the liquid level, and the other said coil below said liquid level, and means for pulsing said coils to 4/1895 Lernp 33550 1/1911 Lohr 200l52 BERNARD A. GIL'HEANY, Primary Examiner.

H. BROOME, Assistant Examiner.

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