US3588290A

US3588290A - Cooling system for supplying liquid coolant to windings of an electrical machine

Info

Publication number: US3588290A
Application number: US888486A
Authority: US
Inventors: Franz Kreutzkampf
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1969-12-29
Filing date: 1969-12-29
Publication date: 1971-06-28
Anticipated expiration: 1988-06-28

Abstract

A STATIONARY COOLANT TERMINAL HEAD IS PROVIDED AT THE END OF THE ROTOR SHAFT OF AN ELECTRICAL MACHINE AND COVER SUCH END AS A HOUSING. AN ANNULAR RING CHANNEL IS PROVIDED AROUND PART OF THE SHAFT HAVING AN AXIAL BORE FORMED THERETHROUGH. A COOLANT INLET CHAMBER AND A COOLANT OUTLET CHAMBER ARE PROVIDED IN THE TERMINAL HEAD ADJACENT EACH OTHER AND ARE CONNECTED TO THE AXIAL BORE OF THE SHAFT. AN INTERMEDIATE WALL PORTION SEPARATES THE COOLANT INLET AND OUTLET CHAMBERS. SHAFT PACKING AT THE INTERMEDIATE WALL PORTION SEALS AND SEPARATES THE COOLANT INLET AND OUTLET CHAMBERS FROM EACH OTHER. A FRONT FACE INLET TO THE AXIAL BORE OF THE SHAFT IS PROVIDED IN THE TERMINAL HEAD. A DEFLECTION CHANNEL IS PROVIDED IN THE TERMINAL HEAD BETWEEN THE COOLANT INLET CHAMBER AND THE FRONT FACE INLET. A PUMP IN THE TERMINAL HEAD SUPPLIED COOLANT FROM THE COOLANT INLET CHAMBER TO THE AXIAL BORE OF THE SHAFT IN A DIRECTION OPPOSITE THE PREDETERMINED DIRECTION IN WHICH COOLANT FLOWS THROUGH THE AXIAL BORE VIA THE DEFLECTION CHANNEL AND THE FRONT FACE INLET. THE PUMP IS ON THE SIDE OF THE COOLANT INLET CHAMBER OPPOSITE THAT OF THE COOLANT OUTLET CHAMBER.

Description

United States Patent [72] inventor Franz Kreutzkamp! Primary ExammerD. Fr Duggan Aachen. Germany AIlarneys-Cur! M. Avery, Arthur E. Wilfond, Herbert L. [2|] Appl. No 888.486 Lerner and Daniel J. Tick [22] Filed Dec. 29,1969 [45] Patented Jane 28. D71 (73] Assignee Slmens Alttiengellschaft Munich Gummy ABSTRACT: A stationary coolant terminal head is provided 4 at the end of the rotor shaft of an electrical machine and CPVCIS such end as 3 housing. An annular ring channel is pl'O- cooLAN-l- To mamas AN ELECTRICAL vided around part of theshaft having an axial bore formed MACHINE therethrough. A coolant inlet chamber and a coolant outlet H Ch 3 D in chamber are provided in the terminal head adjacent each "v t other and are connected to the axial bore of the shaft. An in- 152] 417/370 termediate wall portion separates the coolant inlet and outlet 310/61 chambers. Shaft packing at the intermediate wall portion seals [5 I] Int. Cl. "02k 9/19 and separates the coolant inlet and fl t chambers f each Field of Search 3 l0/54- other A from f inlet to the axia] bore f the h f is 4 1 7/369 370 vided in the terminal head. A deflection channel is provided in the terminal head between the coolant inlet chamber and the [56] Ram, Cm front face inlet. A pump in the terminal head supplied coolant UNITED STATES PATENTS from the coolant inlet chamber to the axial bore of the shaft in 3,067,690 l2/l962 Kramer et al. 3 l0/63X a direction opposite the predetermined direction in which 3,1 5,839 l2/l963 Pollalt et al. 4 l 7/369X coolant flows through the axial bore via the deflection channel 3,220,350 I 1/1965 White .7 4 1 7/3 X and the front face inlet. The pump is on the side ofthe coolant 3,445,696 5/1969 Erickson 3 l 0/6lX inlet chamber opposite that of the coolant outlet chamber.

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COOLING SYSTEM FOR SUPPLYING LIQUID COOLANT TO WINDINGS OF AN ELECTRICAL MACHINE DESCRIPTION OF THE INVENTION The invention relates to a cooling system for electrical machinery. More particularly, the invention relates to a cooling system for supplying liquid coolant to the windings of an electrical machine.

Reference is made to German Disclosure Document No. l,488,04l, published Apr. l7, I969.

The cooling system of the invention includes a pump positioned at one end of the rotor of the electrical machinery. A coolant terminal head at the same end of the rotor includes a coolant inlet and a coolant outlet connected to an axial bore through the shaft of the electrical machine and to an annular duct or ring channel surrounding a part of the shaft having the bore formed therethrough. Shaft packing seals and insulates the coolant inlet and the coolant outlet from each other.

Cooling systems have become increasingly important in recent years, particularly liquid cooling systems for the rotor winding and, if necessary, the stator winding of a turbogenerator. A known liquid cooling system of such type is described in French Pat. No. 1,350,388. In the system described by the French patent, the rotor of the coolant pump is provided at the stub shaft of the coolant terminal head. This causes the pump to be driven directly by the electrical machine. Although the French patent does not disclose additional details for a constructive design, the suction chamber of the pump and the pump rotor must be followed in axial sequence by the pressure chamber and the interior of the supply duct. The pressure chamber of the pump, provided on the outer front face of the supply duct, should be connected via a sealed shaft gap to the outlet chamber coaxially arranged around said supply duct. Due to the relatively high pressure gradient between the pressure chamber and the outlet chamber, as well as in the immediate vicinity of the chambers, stronger output packing or sealing must be provided in the known system in order to avoid an increase in leakage losses.

The principle object of the invention is to provide a new and improved cooling system for supplying liquid coolant to the windings of an electrical machine.

An object of the invention is to provide a cooling system for supplying liquid coolant to the winding of an electrical machine, wherein effective scaling is provided between the pressure chamber of the pump and the coolant outlet chamber of the system, at a relatively low output.

An object of the invention is to provide a cooling system for supplying liquid coolant to the windings of an electrical machine, which system functions with efficiency, effectiveness and reliability.

In accordance with the invention, a pump which supplies the coolant into the axial bore through the shaft, supplies said coolant in a flow direction opposite that of the coolant in said bore. The coolant is supplied to the system via a series connected coolant inlet chamber. The outlet side is connected to a pressure chamber which functions to deflect the coolant. The pressure chamber surrounds the front face supply opening of the axial bore. On the side opposite that of the pump, the coolant inlet chamber is adjacent a coolant outlet chamber. The coolant inlet and outlet chambers are separated from each other by an intermediate wall and shaft packing or sealing.

The invention is based upon the recognition that a loop having opposite-running flow paths provides for the coolant a particularly favorable correlation between the pressure chamber and the coolant outlet chamber, as well as the suction chamber, when the packing or sealing is effective. It is particularly advantageous in this connection to provide axially sequential chambers for the pressure chamber, the coolant inlet chamber and the coolant outlet chamber between the end of the shaft and the coolant terminal head surrounding, as a housing, the end of the shaft and the rotor of the pump. This produces particularly favorable conditions for the packing or sealing within the coolant terminal head, as well as with regard to the atmosphere. This type of scaling is of primary importance, since impairments to the flow ofthe coolant must be prevented via the air or oxygen. That is, the output separation or preparation of the coolant must be kept very low.

Another advantage of the invention is that the pressure chamber connected to the outlet side of the pump is easily and readily accessible from the outside, so that outside ducts for supplying the cooling channels of the stator or liquid annular seals may be easily connected to said pressure chamber. In a preferred embodiment of the invention, the coolant outlet chamber of the coolant terminal head is sealed against the atmosphere by a double liquid ring seal. The part of the double liquid ring seal on the inside is in the pressure chamber of the coolant terminal head and the part ofsaid ring seal on the outside is in an outside sealing liquid path, supplied from outside the system. Double liquid ring seals are known and described in German Pat. No. DAS l,047,299. The aforedescribed German patent, however, discloses the sealing of the stator gas chamber of an electrical machine with regard to the outer chamber. An intermediate gas chamber is provided between the two liquid ring seals and is charged with a blocking gas pressure corresponding to the gas pressure of the machine.

ln the cooling system of the invention, the pressure of the sealing liquid supplied from the pressure chamber of the coolant path of the double liquid ring seal and the pressure of the sealing liquid of the outside sealing liquid path are equally maintained or adjustable to a pressure difference which is such that a slight amount of coolant, which is balanced by the introduction of additional liquid, may be removed by a pressure reducer from the sealed coolant via the sealing liquid path which is supplied from an outside source. The coolant volume supplied to the liquid ring sealing or of the volume of outside liquid is automatically regulated, so that such volumes are at equal pressures. The coolant pumped in the coolant paths of the rotor, and, if necessary, the stator, does not contact the atmosphere, so that losses of the coolant are completely eliminated under all circumstances. The pressures may be somewhat different, however, in a manner whereby a very small volume of the coolant transfers to the other externally supplied sealing liquid path due to the somewhat higher pressure on the sealing side charged with the coolant. The small amount of coolant is then removed together with the sealing liquid. This arrangement is recommended when it is desired to continually renew the coolant with freshly supplied coolant. The primary coolant for the cooling system of the invention is water having a high degree of purity.

In another embodiment of the invention, at least one duct is connected to the pressure chamber behind the pump at the front side of the shaft for the removal of a portion of the coblant supplied by the pump, to be utilized for the coolant path of the stator. in this manner, the pump on the rotor shaft may be utilized simultaneously for pumping the coolant for the rotor and for the stator. The simultaneous cooling of the rotor and stator windings by the pump seated on the machine shaft is known, as evidenced by German Pat. No. DAS l,l59,558. The pump is a pot pump and the coolant, emerging from the rotor through a central bore, mixes with a coolant volume which is fed from the pot pump directly into the stator winding. Accordingly, the invention permits the distribution of coolant flow or currents behind the pump, into two completely separate paths for the stator and rotor windings and permits the regulation of their ratio to each other, as well as their magnitudes, in a specific manner. To accomplish this, it is especially preferable to be able to utilize a first regulating member to change the coolant behind the pump via a deflection channel system. A first regulating member may be positioned between the pressure chamber at the front face of the shaft and the axial bore of the rotor. The first regulating member may be a manually or automatically operated throttle or spindle member. It is advantageous for simple coolant regulation for the rotor and the stator, to provide the supply duct from the pressure chamber of the coolant tenninal head to the stator with a second regulating member which regulates the mo lant supplied to the stator and which functions automatically.

in order that the invention may be readily carried into effect, it will now be described with reference to the accompanying drawings, wherein:

FIG. 1 is a schematic diagram, partly in axial section, of an embodiment of the cooling system of the invention utilized with a turbogenerator;

FIG. 2 is a sectional view of an embodiment of the outside seal ofthe coolant terminal head ofthe embodiment of FIG. I; and

FIG. 3 is a schematic diagram, partly in axial section, of a modification of the embodiment of FIG. 1 as utilized with a turbogenerator.

In the FIGS. the same components are identified by the same reference numerals.

In FIG. 1, a rotor shaft 1 has an axial or central bore 2 formed therethrough. Liquid coolant is supplied via the axial bore 2 of the shaft 1. An annular ring channel 3 for the rotor coolant is positioned coaxially around the shaft 1 and around the axial bore formed therethrough. The ring channel 3 is provided around the portion or part 11 of the shaft 1 having a greater diameter then the remainder of said shaft and may be subdivided into a plurality of outlet channels. The diameter of the shaft 1 is reduced at the end 12 of said shaft. At its end 12, the shaft has a diameter which is ofa dimension which permits only the axial bore 2 to be formed therethrough.

A coolant terminal head 4 is provided around the shaft 1 at its end 12 and around the area 11 of said shaft. The coolant terminal head 4 has a coolant inlet chamber 15 through which coolant is supplied to the axial bore 2 of the shaft 1. The coolant terminal head 4 also has an outlet chamber 17 through which coolant flows after emerging from the rotor, via the ring channel 3. The coolant inlet chamber 15 and the coolant outlet chamber 17 are separated from each other by a wall 13 and a shaft packing 14 at said wall. The coolant terminal head 4 functions as a housing for the rotor of a pump 5 mounted on the end 12 of the shaft 1.

The outlet of the pump rotor 5 is connected to a first pressure chamber 7 in the coolant terminal head 4 via a deflection channel 6. The first pressure chamber 7 is provided at a front face inlet 8 at the opening of the axial bore 2 of the rotor shaft 1. The first pressure chamber 7 is thus connected to the axial bore 2 of the shaft 1 via the front face inlet 8. Labyrinth packing or sealing 9 is utilized to pack the end 12 of the shaft 1 with regard to the pressure chamber 7 and the deflection channel 6 in the coolant terminal head 4.

The pump 5 supplies the coolant from the coolant inlet chamber 15, which simultaneously constitutes the suction chamber of said pump, in a flow direction opposite that of the coolant in the axial bore 2. The pump 5 draws the coolant into the first pressure chamber 7, which functions to deflect said coolant and which surrounds the front face inlet 8. The coolant outlet chamber 17 is closely adjacent the coolant inlet chamber 15 but is on the opposite side of said coolant inlet chamber from the side closer to the pump 5. A nozzle 16 is provided at the coolant inlet chamber 15 for connection with the coolant supply duct from a return cooling system, or separation or preparation plant, not shown in FIG. 1 to maintain the clarity of illustration.

The coolant flows through the ring channel 3 into the coolant outlet chamber 17 and is removed from said coolant outlet chamber via a nozzle 18, to the return coolant preparation or separation plant. Since the suction chamber of the pump 5 and the coolant inlet chamber 15 are identical, said coolant inlet chamber may be next-adjacent the coolant outlet chamber 17. Furthermore, the shaft packing 14 may be designed for relatively low pressure, since the pressure drop in the outside coolant path between the coolant inlet chamber 15 and the coolant outlet chamber 17 is relatively small compared to the pressure drop within the cooling paths of the machine.

A double liquid ring seal 20 is provided outside the coolant outlet chamber 17 for packing between the coolant terminal head 4 and the shaft part 11. The double liquid ring packing 20 comprises a ring 21 which surrounds the shaft 1 at its section, part or portion 11 with very little clearance. The ring 21 has two

ring gaps

22 and 23 formed therein. One of the ring gaps 22 is closer to the end 12 of the shaft 1 and is supplied with a small volume of coolant, serving as a packing, for a second pressure chamber 25 via a bore 24.

The first pressure chamber 7 is connected to the second pressure chamber 25 via a duct 26. A pressure reducing valve 26a is provided in the duct 26 between the first and

second chambers

7 and 25. The other ring gap 23 is farther from the end 12 of the shaft 1 than the first ring gap 22 and is supplied with a sealing liquid from a pressure chamber 23 via a channel 27. The pressure chamber 28 is connected to an outside or external sealing liquid supply duct via a channel 29. When the coolant utilized in the first ring gap 22 is water having a high degree of purity, the coolant utilized for the second ring gap 23 may comprise tap water or water having a poor degree of purity. The coolant utilized in the second ring gap 23 may thus comprise a condensate. Additional labyrinth packing includes sealing or packing strips 31, 32 and 33.

The double liquid ring packing 20 functions in a manner which requires that the pressure of the sealing liquid supplied to the second ring gap 23 be kept the same or a little less than the pressure of the coolant utilized as the sealing means in the first ring gap 22. If this condition is fulfilled, the result, during operation, is that a coolant supplied to the first ring gap 22 is a sealing fluid which may penetrate to the coolant outlet chamber 17 in the direction of an arrow 35. This is due to the fact that the liquid pressure in the first ring gap 22 is greater than the pressure in the coolant outlet chamber 17.

When the pressures in the first and

second ring gaps

22 and 23 of the double liquid ring packing 20 are equal, there is no flow of fluid between them. However, the sealing liquid supplied to the second ring gap 23 may flow from said second ring gap, in the direction of the arrow 36, into a chamber 38 between shaft 1 and the coolant terminal head 4. The sealing liquid which thus flows from the second ring gap 23 is removed via a duct 39 opening from the chamber 38. If the pressure in the first ring gap 22 is greater than the pressure in the second ring gap 23, some coolant may flow into said second ring gap and may also flow out via the chamber 38. The lost coolant is then replaced by fresh coolant supplied to the system.

FIG. 2 is an axial sectional view of another embodiment of the double liquid ring packing 20 of the embodiment of FIG. 1. In the embodiment of FIG. 2 the double liquid ring packing comprises two separate sealing rings 41 and 42. The sealing ring 41 is closer to the end 12 of the shaft 1 than is the sealing ring 42. The sealing rings 4| and 42 are spaced from each other and are provided with first and second ring gaps, respectively. The first sealing ring 41 has a ring gap 43 formed therein and the second sealing ring 42 has a ring gap 44 formed therein. The first sealing ring 41 is provided in a pressure chamber 45 and the second sealing ring 42 is provided in a pressure chamber 46.

The first ring gap 43 of the first sealing ring 41 is provided with coolant from the pressure chamber 7 via the pressure chamber 45 and a duct 47. The ring gap 44 of the second sealing ring 42 is provided with sealing liquid from an external source of sealing liquid via the pressure chamber 46 and a duct 48. An annular chamber 49 is provided in the space between the first and second sealing rings 41 and 42. Mixed water flows through the chamber 49 and around a collar 50 formed in the rotor shaft 1. The provision of the collar 50 in the chamber 47 permits the reduction of the volume ofsealing liquid supplied to the ring gap 44 of the second sealing ring 42 from the externally supplied sealing liquid path. Satisfactory sealing or packing is still possible in the system, in the sealing liquid path, even when there is no supply of sealing liquid.

in the embodiment of FIG. 3, the rotor coolant is regulated in a simple manner. A throttle or spindle member 52 is threadedly engaged in a wall 4a of the coolant terminal head 4. A throttle head 51 is provided at the end of the spindle 52. The spindle 52 is movable in axial directions by rotation via a manual wheel 53, so that the throttle head 51 moves toward and away from the axial bore 2 of the shaft, as desired. The movement of the throttle head 5! permits the variation of the size of the coolant inlet gap 54 relative to the axial bore 2 of the shaft 1. The spindle 52 may be rotated, and thereby move axially, by any suitable automatic or other means such as, for example, a servosystem.

FIG. 3 illustrates the entire system of cooling paths for an electrical machine in a rotor and stator liquid cooling system. ln FIG. 3, the stator has a stator winding 60. The coolant is prepared in a coolant preparation and return coolant plant 6i. The coolant in the stator cooling path is regulated by a regulator 62. A pressure regulator 63 and a pressure reducer 64 regulate the coolant supplied as a sealing fluid from the coolant path to the right half of the liquid ring packing 20. A duct or supply conduit 66 is provided for the sealing liquid of the left half of the liquid ring packing 20. The sealing liquid is provided from an external or an outside source. A pressure regulator 65 is provided in the supply conduit 66.

The mode of operation of the cooling system of the invention is readily followed in FIG. 3. The coolant flows from the coolant plant 6], where the coolant is prepared and returned, at its initial temperature to the coolant inlet chamber ofthe pump 5. The coolant is supplied from the coolant plant to the nozzle 16 of the coolant inlet chamber 15 via a supply duct 61a and is supplied by the pump rotor, at a specific pressure, to the pressure chamber 7 of the coolant terminal head 4. The pressure chamber 7 of the coolant terminal head is connected in parallel with two coolant paths.

The two coolant paths to which the pressure chamber 7 is connected are the rotor coolant path and the stator coolant path. The rotor coolant path comprises the pressure chamber 7, the inlet gap 54 of adjustable dimensions, the axial bore 2 of the shaft 1, the rotor winding path (not shown in the FlGS., in order to maintain clarity of illustration), the ring channel 3, the coolant outlet chamber 17, the nozzle 18 of said coolant outlet chamber, a duct 61b and the coolant plant 61.

The stator coolant path comprises the pressure chamber 7, the outlet duct or channel 70 formed through the coolant terminal head 4, a supply duct 67, the stator cooling path regulator 62, the stator winding path 60, a return duct 68 and the coolant plant 61.

As indicated by FIG. 3, the cooling system of the invention permits the exact adjustment of the volume of coolant in a simple manner by utilizing the common, rotor-driven pump 5 for both the stator and rotor coolant paths. The volume of the coolant is regulated in accordance with operational requirements and the regulation may be automatic. A multistage pump may be utilized instead of the single stage pump 5. The spindle 52, for regulating the volume of the rotor coolant, may be replaced by a rotary member which is shifted when rotated, relative to slots formed through a wall (not shown in the FIGS.) of the coolant terminal head 4 positioned opposite the axial bore 2 of the shaft 1.

While the invention has been described by means of specific examples and in specific embodiments I do not wish to be limited thereto, for obvious modifications will occur to those skilled in the art without departing from the spirit and scope of the invention.

lclaim:

l. A cooling system for supplying liquid coolant to the windings of an electrical machine having a rotor and a shaft having an axial bore formed therethrough and coolant flowing through said axial bore in a predetermined direction, said cooling system comprising:

a stationary coolant terminal head at the end of the shaft of the machine;

an annular ring channel around part of the shaft having the axial bore formed therethrough;

a coolant inlet chamber in said coolant terminal head;

a coolant outlet chamber in said coolant terminal head, each of said coolant inlet chamber and coolant outlet chamber being connected to the axial bore of said shaft and being adjacent each other;

an intermediate wall portion separating said coolant inlet and outlet chambers;

shaft packing at said intermediate wall portion sealing and separating the coolant inlet and outlet chambers from each other;

a front face inlet to the axial bore of the shaft in the coolant terminal head;

a deflection channel in the coolant terminal head between said coolant inlet chamber and said front face inlet; and

a pump on the coolant terminal head at the end of the rotor of the machine for supplying coolant from the coolant inlet chamber to the axial bore of the shaft in a direction opposite the predetermined direction via the deflection channel and the front face inlet, said pump being on the side of the coolant inlet chamber opposite that ofthe coolant outlet chamber.

2. A cooling system as claimed in claim I, further comprising a first pressure chamber at the end of the shaft in the coolant terminal head, and wherein said coolant terminal head surrounds the end of the shaft as a housing, the coolant inlet chamber is adjacent said pressure chamber along said shaft and the coolant outlet chamber is adjacent said coolant inlet chamber along said shaft.

3. A cooling system as claimed in claim 1, further comprising a second pressure chamber in said coolant terminal head, an outside sealing liquid path supplied from outside said system, and double liquid ring packing sealing said coolant outlet chamber from the atmosphere, said double liquid ring packing having an interior portion in the second pressure chamber and an exterior portion in the outside sealing liquid path.

4. A cooling system as claimed in claim 1, further comprising first deflection regulating means in the coolant terminal head for regulating the coolant pressure ofthe rotor coolant of the pump.

5. A cooling system as claimed in claim 2, wherein the electrical machine has a stator and said pump supplies coolant through the stator, and further comprising a duct opening from the first pressure chamber for removing a portion of the coolant supplied by the pump for the coolant path of the stator ofthe electrical machine.

6. A cooling system as claimed in claim 3, further comprising a duct connecting said first and second pressure chambers, pressure regulating means and pressure reducing means in said duct, said pressure regulating means adjusting the pressure of the sealing liquid from the pressure chamber in the coolant path of the double liquid ring packing and adjusting and maintaining the pressure of the sealing liquid of the outside sealing liquid path to a pressure difference which is such that a small volume of coolant, balanced by the supply of additional liquid, may be removed from the closed coolant path by the pressure reducing means via the outside sealing liquid path.

7. A cooling system as claimed in claim 3, wherein said double liquid ring packing comprises a sealing ring having two ring gaps formed therein, one of said ring gaps being closer to the end of the shaft and being supplied with coolant under pressure and the other of said ring gaps being farther from the end of the shaft and being supplied with sealing liquid from the outside sealing liquid path.

8. A cooling system as claimed in claim 3, wherein said double liquid ring packing comprises two sealing rings spaced from each other, one of said sealing rings having a ring gap formed therein for supplying coolant from the first pressure chamber and the other of said sealing rings having a ring gap formed therein for supplying sealing liquid in the outside sealing liquid path.

9. A cooling system as claimed in claim 4, wherein said first deflection regulating means is located between the axial bore of the shaft and the first pressure chamber.

from the first pressure chamber for removing a portion of the coolant supplied by the pump for the coolant path of the stator of the electrical machine, and second regulating means in said duct for regulating the volume of coolant supplied to said stator.

(233 UNl'lL-ID STAIES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,5 9 Dated October 26, 1971 Inventofls) Franz Kreutzkampf" I: is certified that error appears in the above-identified patent; and that: said Letters Patent are hereby corrected as shown below:

The name of the assignee should read --Siemens Aktiengesellschaf Signed and segled this 28th day Cf March 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK 'Attesting Officer Commissioner of Patents