DE2923496A1 - METHOD AND DEVICE FOR REFILLING HELIUM INTO THE ROTOR OF A SUPRAL-CONDUCTING GENERATOR - Google Patents

Description

' at-

NUCLEAR RESEARCH CENTER Karlsruhe, May 25, 1979 KARLSRUHE GMBH PLA 79 24 Ga / str

Method and device for refilling helium into the rotor of a superconducting generator

-1-

030050/0539

Description:

The invention relates to a method and a device for refilling liquid helium from an under ambient pressure standing helium storage container in a helium bath of the rotor of a superconducting generator boiling at negative pressure, whereby a part of the helium changes into the vapor phase during the conversion and the liquid phase at a distance from the axis of rotation is fed into the helium bath.

To achieve high reliability in the operation of electrical machines with rotating supra] ei bender excitation winding appears it is necessary to supply the liquid helium in such a way that an undisturbed operation even in the event of a malfunction is guaranteed at the refrigeration system. This "decoupling" the electrical machine from the refrigeration system is easily handled by an intermediate storage tank for liquid Helium guaranteed. The pressure in this storage container is expediently at atmospheric pressure or to avoid it of contamination of the liquid helium from the unbound atmosphere - at low overpressure.

To achieve a high current density, the superconducting rotor winding is expediently cooled with helium, which is below boils under reduced pressure of a few tenths of a bar and thus a boiling temperature of T <4.2. K has. This negative pressure in the rotor can be maintained in a simple manner by appropriate guidance of the exhaust gas flow (the exhaust gas leaves after Absorption of heat loss by the rotor at bypass pressure. Additional Pumps are not required to achieve a negative pressure in the cold part of the rotor).

It has already been suggested (A.Bej an, "Improved Thermal Design of the Cryogenic Cooling System for a Superconducting Synchroneous Generator ", Thesis, MIT (1974) rUS-PS 4.o56..745)

-3 -

030050/0 53 9

.1

to relax the incoming helium through a throttle valve to the negative pressure present in the rotor (Joule-Thomson relaxation) . The valve must be actively regulated according to the helium flow required in the rotor.

In other proposals (US-PS 4, o85,529 and 4, o82,967) assumed that the helium flowing into the rotor as a result of the thermal losses in the transfer line has a relatively large proportion of gas. The rotating feed line is designed so that - at least in the radially extending Part of the feed line - spatially separate liquid and gas. The pressure curve in this line is through the rotation-related compression of the steam given. This line ends at the point in the liquid boiling under negative pressure, where their hydraulic pressure is the same as that in the column of intestines. This refill system is self-regulating as long as the The proportion of steam is not too low. In order to ensure safe operation even with a large helium flow, consideration is given to by a heater in the transfer line to generate the required proportion of steam if required.

Another method is described in "Cryogenics 17,429 (1977). In this case, a liquid is introduced through a radial feed line and at the point in the underpressure Boiling helium is fed in, where the hydraulic pressures are equal. The radius at which the feed takes place, is greater than when a vapor-liquid mixture is fed in. For a 50 Hz rotor, it must be greater than ο.33 m, for example. Another disadvantage is that only pure liquid is conveyed through the radial feed line.

The object on which the invention is based is to provide a refilling method and devices for this purpose which have a Refilling of a rotating helium bath boiling under reduced pressure regardless of the steam part of the to be fed Helium and also regardless of the size of the rotor to be supplied.

O300n £ ö / '0539

The solution to this problem is described in the features of claims 1 and 2. The features of claim 3 give an advantageous development of the invention Establishment again.

The invention is described in more detail below with reference to an exemplary embodiment by means of FIGS. 1 and 2, the Fig. 1 shows the schematic structure of a generator

The liquid helium does not flow through the fixed line 1 (Fig.l), which is insulated with a vacuum jacket Io Helium storage tank shown in more detail, which is under the pressure P (p -J ^ 1 bar) and opens into one connected to the rotor 9 Phase separator 2. The phase separator 2 consists of essentially of a branch piece 11 for various pipes 4 and 12 with at least one outlet 3 on the Periphery. As a result of the rotation about the axis of rotation 8, to which the phase separator 2 is concentric, the one in the supply line becomes 1 accumulating vapor fraction separated from the liquid, so that the liquid 13 collects at the periphery. (If the speed is high enough, the separation also takes place when the rotor axis 8 is horizontal Centrifugal acceleration at the operating speed of a synchronous generator of 50 Hz already at a distance of 1 cm loo times greater than the acceleration of gravity).

The liquid is fed through the line 4 and / or 12 into the helium bath 5 to be supplied - with a surface at a distance R from the axis 8 - which _{boils near the axis of rotation 8 at the pressure P 1} , which is less than ρ . The vapor occurring in the phase separator is led out of the rotor 9 or phase separator 2 through the coaxial external line 6. The radius Ro of the vapor space 11 in the phase separator 2 is kept at a value to be specified by the level controller 7. The liquid level in the phase separator 2 must be actively controlled. Such level regulators 7 are well known. Temperature-dependent measuring sensors (carbon resistance thermometers or superconducting detectors), for example, serve as level regulators 7. The level compensation can be done either by changing the pressure in the helium storage tank or by pressure changes. U "^ Gi4socufi ^^ i -follow. This is the same technique as with non-rotating

Systems.

In the bath 5 to be refilled, the phase boundary Rl is set so that at the feed point 14 of the line 4 and 12 of the the same hydraulic pressure is present as in the helium bath 5.

In Fig. 2 it is indicated how the pressures in the radial line 4 and 12 (there is also a cylindrical feed line iriög- · borrowed) and in the helium bath 5 as a function of the distance R to the axis of rotation 8 and as a function of the radii of the phase boundaries R and R, change. The example describes typical conditions in a large superconducting turbo runner 9 with 50 Hz speed and 1 m diameter. In the center of the rotor 9 there is a pressure of 0.41 bar, e.g. as a result of the Self-pumping effect in the exhaust gas circuit can be assumed.

The dashed curve (a) describes the pressure curve of p _o = 1 bar and the solid (b) curve for the pressure P ₁ = 0.41 bar. The other curves describe the pressures in the liquids that adjoin these vapor spaces outside the radii R and R. These families of curves indicate the limits within which the radii R, R and R ₂ can be varied.

To show the range in which the steam and feed radii can vary, three examples are given in FIG. It it is required in each case that a vapor radius of R, = 0.1 m is established in the helium bath. When the feed is at the points

^R 2A ^{= O / 2 m} ' ^R 2B ~ °' ^{35 m or R} 2C ~ ° ^{'45 m er} f ° lgt> the level in the phase separator must be adjusted to the radii R _Λ , R or R _n .

α. / τ. Oil Ov ^

be regulated.

In the calculation that leads to the result shown in FIG leads, it must be taken into account that the thermodynamic State of helium during compression due to centrifugal force

-6-

030050/0539

acceleration changes greatly. The helium is in the feed line 4 and / or 12 no heat is supplied or withdrawn. This means that these lines must preferably be made of material with poor thermal conductivity (e.g. stainless steel). The pressure increase in the single-phase liquid is calculated from the change in state

h (R) - h (o) = 1 W ² R ² (1)

s = const, (2)

where h is the specific enthalpy and s is the specific entropy. The steam is along the phase boundary in the state diagram compressed so that

² _ r _o ² ) '

where ρ is the density of the saturated steam. The relationships; (i) _t J s

(2) and (3) can also be verified experimentally.

The main advantages of the invention are that the liquid and the gas of the inflowing helium i-n one im Rotor 9 integrated phase separator 2 are separated. The liquid is fed into the rotor 9 at a suitable point 4 and / or 12 and the gas is returned through a separate line 6. The location of the feed 4 and / or 12 can be freely selected within wide limits. The system works independently on the size of the vapor content in the helium. Result from this the further advantages of the high operational reliability,

-7-

0300 50/0 53 9

the adaptability to different types of rotor concepts and the clear separation of liquid and vapor.

030050/0539

Blank page

Claims (3)

NUCLEAR RESEARCH CENTER Karlsruhe, May 24, 1979 KARLSRUHE GMBH - PLA 7924 Ga / str Patent claims: (1.j method of replenishing liquid helium from a \ - 'under ambient pressure helium reservoir in a boiling under reduced pressure helium of the rotor of a superconductive generator with a portion of the helium passes in the conversion in the vapor phase and the liquid phase at a distance is fed into the helium bath to the axis of rotation, characterized in that the liquid and gaseous phases of helium are separated in a phase separator (2) integrated in the rotor (9), and that the gaseous phase is led out of the phase separator (2). 2. Device for performing the method according to claim 1, characterized in that a implementation (1,6) for the Feeding of the two phases into the phase separator (2) is provided, and that the implementation (1,6) as a coaxial line is formed, through whose outer tube (6) the gaseous phase is removed from the phase separator (2). 3. Device according to claim 2, characterized in that at least one line (4 and / or 12) from the phase separator (2) to the helium bath (5) is provided at a distance from the axis of rotation (8). -2- 030050/0539