JPS6314586B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for replenishing a low-pressure boiling helium bath in a superconducting generator rotor with helium from a helium storage tank at ambient pressure.

[Conventional technology]

In order to achieve high reliability during operation of a rotating electric machine equipped with a rotating superconducting field winding, liquid helium must be supplied to ensure trouble-free operation of the rotating electric machine even in the event of a failure of the cooling system. It is necessary to be informed. The disconnection of this rotating electrical machine from the cooling system is simply ensured by connecting a liquid helium storage tank between them. The pressure in this storage tank is preferably atmospheric or slightly overpressured to avoid contamination of the liquid helium from impurities in the surrounding atmosphere.

The superconducting rotor windings are boiled under a reduced pressure of a few tenths of bar to obtain high current densities.
It is thereby preferably cooled with helium having a boiling temperature of T<4.2K. This low pressure in the rotor can be easily maintained by the desired guidance of the exhaust gas flow, which leaves the rotor at atmospheric pressure after absorbing the lost heat. No additional pumps are required to obtain the low pressure in the rotor cooling section.

The incoming helium is relaxed by a throttle valve to the low pressure present in the rotor (Joule-Thomson relaxation).
It has already been proposed to do so (A. Bejan,
“Improved Thermal Design of the Cryogenic
Cooling System for a Superconducting
Synchronous Generator”，Thesis MIT
(1974); U.S. Pat. No. 4,056,745). This valve must be actively adjusted depending on the helium flow required by the rotor.

Other proposals (U.S. Pat. No. 4,085,529 and No.
No. 4,082,967), it is based on the fact that the helium flow entering the rotor has a relatively large gas content due to heat losses in the transfer tubes. The rotating supply pipe is then constructed in such a way that liquid and gas are spatially separated in at least a radial section of the supply pipe. The radial pressure variation in this supply tube is provided by rotation-based vapor compression. This supply tube is used to store liquids in boiling water at low pressure.
It opens where the liquid pressure is equal to the pressure in the air column. This replenishment system is self-regulating as long as the vapor content does not become too low. In order to ensure stable operation even in the case of large helium flows, it is necessary to generate the necessary vapor components by heating the phase shift tube, if necessary.

Other methods are described in "Cryogenics" 17 , 429 (1977). In this case, the liquid is introduced through radial supply pipes and is fed into the boiling helium at low pressure at the point where equal liquid pressure is present. The radius over which the feeding takes place is larger than when feeding a gas-liquid mixture. It is for example 50Hz
For example, in the case of a rotor of Another drawback is that only pure liquid is conveyed through the radial supply tubes.

[Problem that the invention seeks to solve]

The object of the invention is to enable the replenishment of boiling and rotating helium baths under reduced pressure, independent of the vapor composition of the helium to be supplied and independent of the size of the rotor receiving the supply. The purpose is to provide a replenishment method.

[Means for solving problems]

This purpose, according to the invention, is to supply liquid helium from a helium storage tank at ambient pressure to a boiling helium bath at low pressure in the rotor, so that during the flow from the helium storage tank to the helium bath, a portion of the liquid helium is in the gas phase. The liquid and gas phases of the helium that has changed into This is achieved by introducing the helium bath into a helium bath.

The introduction of liquid helium into the helium bath is advantageously carried out at a position farther from the axis of rotation of the rotor than the liquid-vapor interface of the helium bath.

[Effect]

In the present invention, liquid helium is supplied from a helium storage tank to a phase separator, and a portion of the liquid helium is converted into a gas phase while flowing to the phase separator. In the phase separator, the gas phase and liquid phase are separated by the centrifugal action caused by the rotation of the rotor, and the gas phase is immediately drawn out from the phase separator to the outside, leaving only the liquid phase in the liquid phase portion of the helium bath inside the rotor. supplied to

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. FIG. 1 schematically shows part of the generator.

Liquid helium flows out of a helium storage tank (not shown) under pressure p ₀ (p ₀ 1 bar) through a stationary conduit 1 (FIG. 1) insulated by a vacuum jacket 10; It flows into a phase separator 2 which is connected to a rotor 9. The phase separator 2 mainly consists of branches 11 for different conduits 4 and 12 with at least one outlet 3 on the periphery. Due to the rotation about the axis of rotation 8 passing through the center of the phase separator 2, the gas phase components occurring in the supply conduit 1 are separated from the liquid, so that the liquid collects in a region 13 along the periphery of the phase separator 2. If the rotational speed is high enough, separation also occurs at the horizontal axis of rotation 8. For example, the centrifugal acceleration at the operating speed of a synchronous generator of 50 Hz is already more than 100 times greater than the gravitational acceleration at a distance of 1 cm from the rotation axis.

The liquid is conducted through conduits 4, 12 into the helium bath 5 to be supplied. The helium in this helium bath 5 boils near the rotating shaft 8 at a pressure p ₁ smaller than the pressure p ₀ , and the liquid phase bath in the rotor and
The interface with the gas phase is located at a distance R ₁ from the axis 8.

The steam itself generated in the phase separator passes through the coaxial outer tube 6 around the jacket 10 to the phase separator 2.
is discharged from. The radius R ₀ of the gas-liquid interface in the vapor chamber 11 of the phase separator 2 is maintained at a predetermined value by the level regulator 7 . The liquid level in the phase separator 2 must be actively regulated. Level regulators 7 of this type are well known. As the level regulator 7, for example, a temperature sensor (carbon resistance thermometer or superconducting detector) is used. Level balancing can be achieved by varying the pressure within the helium reservoir or by varying the pressure of the gas output of the coaxial outer tube 6. This can use similar techniques as in non-rotating systems.

In the bath 5 to be replenished, the conduits 4 and 12
At a distance R ₁ from the axis of rotation 8 such that the same liquid pressure as in the helium bath 5 exists at the supply point 14 of
A phase boundary occurs at this point. The feed point 14 is located at a distance R ₂ from the axis of rotation 8 .

FIG. 2 shows that the pressure in the radial conduits 4, 12 (which may be cylindrical supply pipes) and the helium bath 5 is determined by the distance R from the axis of rotation 8 and by the distance of the phase boundary. It shows how it changes depending on R ₀ and R ₁ . This example shows a typical relationship for a large superconducting turbo rotor 9 with a rotation speed of 50 Hz and a diameter of 1 m. It is assumed that along the axis of rotation 8 of the rotor 9 there is a pressure of 0.41 bar which can be adjusted in the exhaust circuit, for example by a self-pumping effect.

The dashed curve a shows a pressure change of p ₀ =1 bar, the solid curve corresponds to a pressure p ₁ =0.41 bar. The other curves show the pressure in the liquid bordering these vapor spaces outside the radii R ₀ and R ₁ . These curves show at which boundaries the radii R ₀ , R ₁ and R ₂ can change.

Three examples are shown in FIG. 2 to illustrate the range in which the steam radius and feed radius can vary. R ₁ = 0.1m in helium bath 5, respectively.
is required to produce a vapor radius of . _R2A =
0.2 m, R _2B = 0.35 m or R _2C = 0.45 m, the gas-liquid interface in phase separator 2 must be adjusted to radius R _0A , R _0B or R _0C . No.

In the calculations leading to the results shown in FIG. 2, it must be taken into account that the thermodynamic state of helium changes dramatically during centrifugal compression.

Helium absorbs or releases no heat in the supply conduits 4 and/or 12. This means that these conduits must be made of a material with particularly poor thermal conductivity (special steel). The pressure rise in a single phase liquid is calculated from the change of state h(R) - h(O) = 1/2ω ² R ² (1) and s = constant (2). However, h is the characteristic enthalpy and s is the characteristic entropy. Since steam is compressed along the phase boundary in the phase diagram, the steam pressure at the phase boundary is given by:

∫ ^p(r1) _p(r0) 1/ρsdp=1/2ω ² (r ₁ ² − r ₀ ² ) (3) holds. where ρs is the density of saturated steam, r ₁ is the radius of the phase boundary (= R ₁ ), r ₀ is the radius of the steam output from the bath (0), and p (r ₁ ) and p (r ₀ ) are the corresponding pressures. It is. Relational expressions (1), (2), and (3) have also been confirmed experimentally.

In the present invention, the helium liquid and gas flowing from the helium storage tank are separated in a phase separator 2 built into the rotor 9;
or 12 to the rotor 9, and the gas is returned through another tube 6. This feeding point can be freely selected within a wide range. The method works regardless of the amount of helium gaseous component.

〔Effect of the invention〕

According to the present invention, the gas phase helium contained in the liquid helium supplied from the helium storage tank is separated in the phase separator built into the rotor, and only the liquid phase helium is contained in the helium bath inside the rotor. Since it is supplied away from the central axis, that is, to the liquid phase, the vapor chamber in the phase separator and the gas phase of the helium bath in the rotor are not directly connected, and there is no helium between them. Due to the presence of a liquid column, there is no pressure difference between the stationary and rotating parts.
This has the following effects: troubles due to helium gas leakage can be prevented, high operational reliability can be obtained, and it can be adapted to various rotor structures.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of the apparatus of the present invention, and FIG. 2 is an explanatory diagram of the operation of the present invention. 1... Supply conduit, 2... Phase separator, 3... Outlet, 4, 12... Conduit, 5... Helium bath, 6...
... Coaxial outer tube, 7 ... Level adjuster, 8 ... Rotating shaft, 9 ... Rotor.

Claims (1)

[Claims] 1. Liquid helium is supplied from a helium storage tank under ambient pressure to a helium bath boiling at low pressure in the rotor, and a portion of the liquid helium changes into a gas phase while flowing from the helium storage tank to the helium bath. The liquid and gas phases of helium are separated in a phase separator fixed to the rotor, the separated gas phase is drawn out from the phase separator, and only the liquid phase is separated from the rotor at a distance from the rotation axis. A helium replenishment method for a superconducting rotor characterized by introducing helium into a helium bath. 2. The method according to claim 1, wherein the introduction of liquid helium into the helium bath is carried out at a position farther from the rotation axis of the rotor than the liquid-gas phase interface of the helium bath.