US1936781A - Mercury arc rectifier construction - Google Patents

Description

Nov. 28, 1933. A' ATHERTQN 1,936,781

MERCURY ARC RECTIFIER CONSTRUCTION Filed Sept. 2, 1931 2 Sheets-$heet 1 WITNESSES: INVENTOR E14 Alfred L, A f/verzo/v BY In. J 6%. MW

ATTORNEY Nov. 28, 1933. ATHERTON 1,936,781

MERCURY ARC RECTIFIER CONSTRUCTION Filed Sept. 2, 1931 2 Sheets-Sheet 2 I 1 I l i 4 i l WITNESSES: NVENTOR AZ/red L. Aziverzon. a /Z j W ATTORNEY Patented Nov. 28, I933 UNETEE STATES MERGUR'IL ARE BEQTIFHER CONSTR Alfred Wes ting Parser v OFFICE UCTION Atherten, Verona, Pa, assignor to reuse Electric a Manufacturing. Com- My invention relates to a mercury arc rectifier and particularly to a metal-tank rectifier of small size and high efficiency and capacit The metal-tank mercury-arc rectifiers constructed prior to my invention have been provided with a large central condensing chamber surrounded by an anode-chamber, and a mercury cathode, usually centrally located, coo, erated with a plurality of anodes. When high currents are rectified by these prior devices a great quantity of mercury vapor is given off by the cathode and must necessarily be condensed in order to keep the vapor pressure in the rectifier at the proper value.

In order to secure the necessary condensing area the central coolers or condensing chambers have been made of large size which in turn has pushed the anodes to a great distance from the cathode and increasedthe length of the rectifying arcs. 7

This construction has given rise to tanks of enormous size in which the arc drop is of the ord r of 20 or 40 volts, with a consequent energy-loss of huge proportions. Since this energy appeared mostly as heat in a substantially complete vacuum, the Working parts were necessarily at high temperature.

The introduction of these high temperatures to a safe working order has introduced still further losses.

Apparently this form of construction was the result of a mistaken idea concerning the nature of the vapor-flow from the cathode. It has long been known that the quantity of vapor flowing from the cathode to the anodes exerted a material influence on the operating characteristics of the rectifier.

It has been heretofore believed that the mercury-vapor leaving the cathode acted very much like a jet and flowed substantially in a straight line. Consequently the centralc ndensing ch 2 her in direct communication With the cathode was believed to be the best method of eliminating vapor-flow into the anode spaces. However, it

was suspected that a certain amount of mercury-. In order sufiicient cooling to reduce causing difficultie tion, the mercury vapor, instead of flowing as a jet-develops a complete randomness of direction immediately after it is released from the cathode, or if an arc-guard is used, immediately beyond the termination of the arc-guard, so that the vapor behaves as any other high-pressure gas released in a low-pressure area and moves outin all directions.

The rectifier of my invention takes account of the nature of vapor-flow from the cathode, and instead of trying to confine the vapor to a central condenser and excluding it from a large anodearea, I have clustered the anodes in closely spaced relation, both with respect to each other and with respect to the cathode, and I have excluded the vapor from this relatively small area, While permitting it to flow freely into the remainder of the tank.

The anodes are placed as close togetherias is convenient mechanically, and they are enclosed in a common shield having openings adjacent to the anode faces for the passage of the arcs, thus eliminating the customary confining shields and grids, and leaving the arcs substantially unconfined, while materially reducing the arc-length. The short, substantially unimpeded arc reduces the arc-drop; from 40 volts of the conventional rectifier to approximately 12 volts. 1

However, I still found that sufiicient mercuryvapor entered the anode-chamber to have a deleterious influence on stability. In order to prevent I the vapor from the cathode fromentering the anode-space, I have provided-an auxiliary source of mercury vapor from which vapor of sufficient pressure and-quantity to counteractthe vaporflOW from the cathode is conducted to the anodechamber. This auxiliary vapor-flow prevents the highly ionized vapor from the cathode from coming into direct contact with the anodes and materially reduces the probability of back-fire in the rectifier.

I have found that there are accumulations of non-condensing gases at various places in the rectifier and that these accumulations depend on the flow of the nercury-vapor from the cathode to the condensing surfaces. Apparently, when the mercury-vapor flows into a closed pocket, the Walls of which are condensing surfaces, the foreign gas is carried along and retained in the pocket by the continued flow of vapor. Any instability thereupon permits this foreign gas to flow out,

troduced by'the presence of the foreign gas itself.

It is quite probable that unanodes. tensions 16 on the main shield 12, extending be- The accumulation of foreign gas will continue until it is sufiicient to have a pronounced effect on the now of the mercury-vapor, at which time the vapor is prevented from reaching some of the condensing surface. The vapor is, therefore, deflected and as a result the accumulated foreign gas can flow out of the pocket and, particularly if in the vicinity of the anodes, may cause backfire in the rectifier.

Since it is apparent that there is always some foreign gas to contend with, this problem becomes one of major importance. In fact, it may be the greatest source of difficulty with rectifiers.

In the rectifier of my invention, this source of trouble is removed, as the auxiliary vapor-stream is supplied from a portion of the rectifier from which impurities and foreign gas are excluded. The auxiliary Vapor-stream prevents gas from other parts of the rectifier from entering the anode-chamber, while the fiow of gas around the anodes produces a pumping action to remove any gas generated at the anodes and to carry it to the condensing chamber from which it is most easily pumped by any suitable means. I

By the use of my clustered anodes, together with short are lengths, the rectifier, according to my construction, is of much smaller size than rectifiers of similar capacity, according to conventional designs.

Also, by the shortening of the arc-length and the elimination of the restricting shields and the control-grids, made possible by the use of the auxiliary vapor blast, the power-loss in the arcs has been materially reduced, so that the efficiency of the rectifier has been materially increased. Less energy-loss results in less cooling-surface, and thus still smaller and moreeificient rectifiers are produced.

Other objects and advantages of my invention will be apparent from the following detailed description, taken in conjunction with the accompanying drawings, in which,

Figure 1 is a sectional elevation of a preferred embodiment of my invention,

Fig, 2 is a sectional plan view along line II-II of Fig. 1 showing the interior arrangement,

Fig. 3 is a sectional elevation of a modification,

Fig. 4 shows a further modification, and

Fig. 5 is a cross-sectional view on line V-V of Fig. 4.

In the embodiment of my invention, according to Figs. 1 and 2, the rectifier comprises a watercooled metal tank 1 of substantiallycylindrical construction, having an insulated cathode plate 2 secured thereto, the cathode plate carrying an annular cathode pool 5 and a central auxiliary pool 6 fed from the cathode pool by a duct 7, but shielded from the rectifying arc, so as to be distinct and separate from the cathode 5.

A plurality of anodes 10 are nested as closely together as is mechanically convenient and are surrounded by a single shield 12 of a size suiiicient to enclose the anode space. The shield 12 is provided, near its bottom and adjacent to the anode faces, with openings 14 for the rectifying arcs.

It is characteristic of vapor-electric devices that where objects at high differences of potential are separated by very short distances the potential gradient is such that there is little likelihood of breakdown, and since the shields are at substantially cathode potential it is desirable that the shields approach closely to the bodies of the Therefore I provide partitions or exvide an anode-chamber 22, leaving only the radial openings 14 for the rectifying arcs. However, since these radial openings 14 are in proximity to the anode surfaces, the main portion of the rectifying arcs are outside of the anode chamber 22 and are substantially unconfined.

Surrounding the anode-chamber and occupying the remainder of the tank is a condensing chamber 25 directly open to the vapor from the cathode 5 and provided with one or more ring coolers 26.

The auxiliary mercury pool 6 is provided with a suitable heater 30 of any desired type for producing mercury vapor. Immediately above this auxiliary pool is a conduit or chimney 31 for conducting the mercury vapor to the anode chamber 22, preferably to the top wall 18 of the anode chamber 22, which is depressed in a substantially conical form in proximity to the chimney 31. This conical depression acts as a spreader for directing the mercury vapor from the chimney 31 toward the anodes 10, so that the auxiliary vaporflow passes around the anodes, and sweeps over the surfaces thereof in the direction of the radial arc passages, so that the direction of the auxiliary vapor-flow in the arc passages is opposite In addition to the pumping action of the auxiliary vapor, the counter-flow or counter-pressure in the anode chamber produces a constant fiow or condition of vapor in the vicinity of the anodes, as distinguished from the gusty, turbulent gasfiow believed to exist in previous rectifiers. probably follows from the fact that the vapor is produced steadily and because, as a result of the shape of the stack 31 and the cooperating baffle 18, the auxiliary vapor flows in stream-lines, while in the previous devices the vapor was released principally in the vicinity of the cathode spot or spots with resultant swirls and eddies.

The cathode spot on an annular cathode appears reluctant to move away from the keepelive, resulting in unequal arc lengths from the various anodes and unequal arc losses, if only one keepalive is used.

The rectifier of my invention is provided with a plurality of keep-alives 35 so spaced that a cathode spot is always maintained adjacent to each of the anodes or group of anodes, so that the arcs are of approximately the'sarne length. I have provided radial shields 36 for partitioning the condensing chamber 25 into a plurality of chambers corresponding to the number of keepbeen reconstructed to better cooperate with the smaller annular cathode.

Because of the absence of cooling surfaces around the auxiliary pool, the mercury therein is normally at about the same temperature as the mercury in the cathode, so that only a comparatively small amount of heat is needed, in the heater 3-9, to produce sufficient auxiliary vapor to counteract the tendency of the cathode-vapor to enter the anode-chamber.

In the modification according to Figs. l and 5, the anodes 16 have been clustered adjacent to the sides or" a substantially rectangular tank, the clustered anodes being provided with a common shield to provide anode chambers at the sides of the tank, and a longitudinally extending centrally located cooling chamber. The anodes cooperate with a conventional centrally located cathode 42.

Each of the anode-chambers is provided with an auxiliary mercury pool having a chimney e for supplying auxiliary vapor to the anode spaces.

The quantity of ionized vapor given off the cathode during operation is directly de- Consequently the vapor-pressure in the rectifier increases with the load. The increased vapor-pressure tends to force ionized vapor into the anode-spaces so that it is desirable to vary the auxiliary vapor pressure to counteract the increased-vapor pressure from the cathode. This may be accomplished by varying the input into the heaters in response to load-variations. If direct current is use in the heaters they may be connected in series with the output of the rectifier, or if 1 alternating current is supplied to the heaters the same response to load conditions may be secured by supplying the current by current transformers in the supply-leads of the rectifier. By the variation of the capacity of t e heaters in response to load conditions, the optimum quantity of auxiliary vapor may be supplied at all times.

While I have shown and described three embodiments of my invention, it is apparent that changes and modifications can be made therein without departing from the spirit and scope of my invention. I desire, therefore, that only such limitations shall be imposed as are embodied in the accompanying claims or as may be necessitated by the prior art.

I claim as my invention:

1. An evacuated metal-tank mercury-arc rectifier comprising a mercury cathode, said tank including a lar e evacuated cooling chamber adjacent to said cathode, a plurality of anodes so positioned that the are from an anode to the cathode passes through a portion of the cooling chamber, a pool of mercury other than the cathode, and means for producing a stream of mercury-vapor from said pool for counteracting the vapor-stream from the cathode.

2. An evacuated metal-tank mercury-arc rectifier comprising a mercury cathode, said tank including a large evacuated cooling chamber adjacent to said cathode, a plurality of anodes so positioned thatv the are from an anode to the cathode passesthrough'the cooling chamber, a pool of mercury other than the cathode, a heating element for said pool and means fordirect ing a stream of mercury-vapor from said pool through the anode-space, the quantity and velocity of the vapor-stream being suificient to counteract the tendency of the cathode-vapor to enter the anode-space.

A vapor-electric device comprising a metal tank, a plurality of closelyspaced anodes in said tank, a mercury cathode in said tank, a condensing chamber adjacent to said cathode, baiiles for directing mercury-vapor away from said anodes into said condensingchainber, a body of niecury other than said cathode in the' tank, a heater for said body of mercury, and means for conducting vapor from said body of mercury into the vicinity of the anodes and thence in the arc-path.

4. In a vapor-electric device, a mercury cathode, a condensing chamber, an anode chamber, a plurality of anodes in said chamber, the anode chamber being open to the cathode, a pool of mercury separate'from said cathode, a heating element for said mercury pool, and a conduit for conducting mercury vapor from the pool to the anode chamber.

5. A mercury-arc rectifier comprising a container, an annular cathode pool therein, a plurality of anodes nested in said container, a shield around said anodes to provide a small anode chamber, a comparatively large condensing chamber surrounding said anode chamber, a plurality of shields for dividing said anode chamber and said condensing chamber into a plurality of sections, and a keep-alive in each section.

6. A mercury-arc rectifier comprising a metal tank, an annular cathode pool therein, a plurality of anodes clustered in said tank, a shield around said anodes to provide a small anode chamber, a comparatively large condensing chamber surrounding said anode chamber, a plurality of radial shields for dividing said condensing chamber into aplurality of segmental sections,

a keep-alive in each section, a centrally disposed auxiliary mercury pool shielded from the arc, a heating element for said pool, and a chimney for conducting mercury vapor from said pool to said anode chamber. V

7. A mercury-arc rectifier comprising a pluralityof anodes, a shield providing a partially closed anode chamber, a condensing chamber, a vaporizable cathode open to said condensing chamber and an auxiliary source of .mercury vapor for preventing vapor from said cathode from entering the anode chamber.

8. A mercury-arc rectifier comprising a plurality of anodes, a shield providing a partially closed anode chamber, a condensing chamber, a vaporizable cathode open to said condensing chamber, an auxiliary source of mercury vapor for preventing vapor from said cathode from entering the anode chamber, a chimney for conducting vapor from the auxiliary source to the anode chamber, a top shield in the anode chamber shaped to spread the vapor flow evenly the anode and means comprising a source of auxiliary vapor for deflecting the cathode vapor 'from the common anode shield.

10. A mercury-arc rectifier comprising a container, a mercury cathode therein, a plurality of anodes, an anode chamber substantially enclosing said anodes, an opening in said chamber for the passage of the rectifying arc, a body of mercury other than the cathode, vaporizing means for producing mercury vapor from said body of mercury, said means being responsive to load current, and means for conducting the mercury vapor into the anode chamber.

11. A vapor-electric device comprising a vaporizable cathode, a plurality of anodes cooperating with the cathode to produce arc streams of ionized mercury vapor, a condensing chamber separated from said anodes, a source of auxiliary mercury vapor and means for causing said auxiliary vapor to sweep across the surface of said anodes.

12. A mercury-arc rectifier comprising a mercury cathode, a condensing chamber open to said cathode, an anode chamber, a plurality of anodes therein, a source of mercury vapor other than the cathode and means for causing a blast of mercury vapor from said source to flow through.

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