Cooling method and system

Description of the invention

The invention relates to a cooling system and method, in particular a cryogenic cooling method and a fluid cooling system for a synchronous machine having a rotor winding on a coil exhibiting high temperature superconductivity. In particular, the invention relates to an evaporative cooling system for supplying cryogenic fluid to the rotor and for re-cooling the used coolant fed back from the rotor and a cooling method therein.

High-temperature superconducting generators require very reliable, low-cost cryotechnical cooling equipment to be commercially viable. In order to achieve high reliability, redundant components of the cryotechnical quench equipment are used in existing cryotechnical equipment. The necessity to use redundant components in the case of HTS rotor cryo-cooling systems is due to the inadequate reliability of these components and the requirement for an uninterrupted supply of cooling fluid.

However, due to the use of redundant components of cryotechnical devices, the cost of these systems increases significantly. In addition, existing cryogenic cooling systems require frequent maintenance due to their inadequate reliability and system redundancy. Accordingly, the operating cost of these systems is relatively high.

The cost of purchasing and operating existing cryogenic cooling systems significantly increases the cost of machines with HTS rotors. These high costs have contributed to the hitherto commercial impracticability of incorporating HTS rotors into commercially available synchronous machines. Hence there is an essential and as yet unmet need for a cryogenic cooling system that is less expensive to build, inexpensive to operate, and capable of reliably delivering cryogenic cooling fluid to the HTS rotor.

Synchronous electrical machines with magnetizing coil windings include, but are not limited to, rotating generators, rotating motors, and linear motors. These machines typically include a stator and rotor that are electromagnetically coupled. The rotor may include a multi-pole rotor core and one or more coil windings installed on the rotor core. The rotor cores contain a solid material with high magnetic permeability, for example an iron rotor.

Conventional copper windings are commonly used in the rotors of synchronous electrical machines. However, the electrical resistance of copper windings (although small by conventional measures) is sufficient to cause significant heating of the rotor and reduce the energy efficiency of the machine. Recently, superconducting (SC) coil windings have been developed. SC windings effectively have no resistance and are very advantageous rotor coil windings.

Iron core rotors saturate at an air-gap field strength of about 2 Tesla. Known superconducting rotor designs use air core designs, with no iron in the rotor, achieving an air-gap magnetic field greater than 3 Tesla. These strong magnetic fields in the air-gap help to increase the power density of the electric machine, and as a result result in a significant reduction in the weight and size of the machine. Superconducting air core rotors require large amounts of superconducting wire. These large amounts of SC wire, in addition to requiring a large number of coils, add to the complexity of the coil supports and increase the cost of the SC coil and rotor windings.

Superconducting rotors have superconducting coils cooled with liquid helium, the spent helium being discharged back as room temperature helium gas. The use of liquid helium for cryogenic cooling requires the continuous re-condensation of the returned room temperature gaseous helium, and such re-liquefaction presents significant reliability problems and requires considerable auxiliary power. Accordingly, there is a need for a cryo-cooling system that re-condenses hot, spent coolant returned from the rotor. The re-liquefied coolant should then be available for reuse as an HTS rotor coolant.

A fluid cooling system for supplying cryogenic coolant to the high temperature superconducting rotor, comprising a cryogenic storage tank for storing the cryogenic liquid coolant and an inlet transport line connecting the storage tank to the rotor and providing a path for the liquid coolant from the storage tank to the rotor, the reservoir being the storage is placed higher than the rotor, and the liquid fluid

The cooling is fed to the rotor by gravity, according to the invention, the storage vessel comprises an upper vapor region and a lower liquid region, and furthermore the system comprises a recapacitor coupled to the upper steam region of the storage vessel.

A method of cooling a superconducting coil with an excitation winding in a rotor of a synchronous machine using an elevated cryogenic storage tank, the method storing the cryogenic coolant in a storage tank which is located higher than the rotor, allowing the coolant to flow under the action of gravity from the tank storage to the rotor, the coil with the excitation winding is cooled with a coolant, the coolant is returned to the storage tank and a part of the coolant vapor is condensed in the storage tank or in the return line, according to the invention it is characterized in that the operation of condensing a part of the coolant vapor is stopped and part of the coolant vapor is condensed, and during the the step of stopping condensation of a portion of the coolant vapor continues the flow of coolant from the storage tank to the rotor.

Additionally, during the step of stopping the condensation of a portion of the coolant vapor from condensing, the upper portion of the vapor is released.

Additionally, during the step of stopping condensation of a portion of the coolant vapor, the pressure of the coolant in the storage tank is increased.

The operation of increasing the pressure of the coolant in the storage tank is performed in the rotor cooling phase.

A highly reliable cryotechnical cooling system was developed for the HTS rotor for the synchronous machine. This quench system ensures a continuous supply of coolant to the HTS rotor. Moreover, this quench system is economical in construction and operation. This reliability and economy of the cooling system enables the development of a commercially viable synchronous machine with the HTS rotor.

The cryotechnical quench system is a closed loop gravity fed evaporative cooling system for the High Temperature Superconducting (HTS) rotor. The system includes a high cryogenic storage tank, vacuum jacketed conveying lines supplying liquid cryogenic medium to the rotor and reflux steam to the storage tank, and a cryogenic cooling device in the vapor space of the storage tank to re-condense the vapor. The cryotechnical unit may be a Gifford-McMahon single stage cryotechnical unit or an impulse tube with an integral or separate compressor. The cryogenic fluid may be neon, hydrogen, or some other such type of refrigerant.

The subject matter of the invention is shown in the exemplary embodiments in the drawing, in which fig. 1 is a simplified side view of a superconducting (SC) rotor in the stator, fig. 2 - a simplified perspective view of an oval superconducting (SC) coil having passages for a cooling gas, fig. 3 simplified diagram of a cryogenic cooling system for supplying coolant to a superconducting (SC) rotor.

Fig. 1 shows an exemplary synchronous generator 10 having a stator 12 and a rotor 14. The rotor includes magnetizing winding coils which fit snugly inside the cylindrical vacuum space 16 for the rotor in the stator. The rotor is inserted into the vacuum space 16 in the rotor stator. As the rotor rotates inside the stator, the magnetic field 18 (shown in dashed lines) generated by the rotor and the rotor coils moves / spins in the stator and produces an electric current in the stator coil windings 19. This current is transferred to the outside by the generator as electric power

The rotor 14 has a generally longitudinally extending axis 20, and a generally solid rotor core 22. The solid core 22 with high magnetic permeability is typically made of a ferromagnetic material such as iron. In a low power density superconducting machine, the iron core is used to reduce the magnetomotive force (MMF) and thus reduce the amount of wire in the superconducting (SC) coil required for the coil winding. For example, the solid iron core of the rotor may be magnetically saturated with a gap magnetic field strength of about 2 Tesla.

The rotor 14 supports at least one longitudinally extending oval winding 34 of high temperature superconducting (HTS) coils. The HTS coil winding may, in contrast, be a saddle-shape or may have some other shape suitable for a particular HTS rotor design. The coil support system described in this document is for the winding of an oval SC coil. The coil support system may be adapted to a coil configuration other than the oval coil installed on the solid rotor core.

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The rotor includes end shafts 24, 30 which embrace the rotor core 22 on both sides and are supported by bearings 25. The collector end shaft 24 has a cryogenic transport connection 26 that connects to a source of cryogenic coolant used to cool the SC coil windings in the rotor. The cryogenic fluid transport connector 26 includes a stationary segment connected to a source of cryogenic cooling fluid, and a rotary segment that supplies cooling fluid to the HTS coil. The collector end shaft 24 also includes a collector 78 for electrical connection to the rotating SC coil winding. The shaft 30 at the driving end of the rotor may be driven by the clutch 32 of the power turbine 32.

Figure 2 shows an exemplary oval winding 34 of a magnetizing coil. The coils 34 of the rotor magnetizing winding include a high temperature superconducting (SC) coil 36. Each SC coil includes a conductor with high temperature superconductivity such as BSCCO (Bi_xSr_xCa_xCu_xABOUT_x) laminated in an epoxy impregnated winding composite. For example, a BSCCO 2223 wire assembly can be laminated, bonded, and wound into a solid epoxy-impregnated coil.

HTS wire is brittle and easy to damage. The HTS coil is usually wound with layers of epoxy impregnated tape. The HTS tape is rolled into a precise shape to ensure tight dimensional tolerances. The tape is wound on a spiral to form the oval SC coil 36.

The dimensions of the oval coil depend on the dimensions of the rotor core. Typically, each oval coil surrounds the magnetic poles of the rotor core and is parallel to the rotor axis. The HTS coil windings are continuous around an oval shape. The SC coils form a resistance-free electric current path around the rotor core and between the magnetic poles of the core.

Coil winding 34 includes fluid channels 38 for cryogenic coolant. The channels may extend around the outer edge of the SC coil 36. Transition channels bring coolant to the coil and remove heat from the coil. The coolant maintains the low temperature, for example 27K, in the coil winding necessary to provide the superconductive conditions associated with the absence of electrical resistance to the coil. The cooling channels at one end of the rotor core have inlet and outlet fluid ports 112. These fluid (gas) ports 112 connect the SC coil cooling channels 38 to the cryogenic fluid port 26.

FIG. 3 schematically shows a cryoprotection system 50 for an HTS 10. The cryogenic storage vessel 52 or Dewar vessel stores the liquid cryogen. The reservoir is located at a height 54 above the HTS generator. The height of the tank above the rotor is proportional to the required pressure of the fluid flowing into the rotor and inversely proportional to the density of the coolant. Due to the elevation of the reservoir to a certain height, the force of gravity displaces the coolant from the cooling reservoir to the rotor joint 26 and into the SC coils 34. The force of gravity does not dissipate, requires no maintenance, and is free. Thus, the gravity fed cooling system is highly reliable and low cost.

The cooling system is a closed loop. Coolant from reservoir 52 flows through an inlet transport element that connects the reservoir to the rotor interface 26. The coolant passes through a vacuum jacketed cooling channel in the end shaft 24 and through cooling channels 38 around the SC coils 36. The coolant keeps the coil at cryogenic temperature by evaporative cooling and keeps the coils superconducting. The used coolant, usually in the form of cold gas, exits the coil through cooling passage 38, flows through vacuum jacketed cooling channels in the end shaft and through cooling connection 26. Return conveying line 58 carries the return coolant from the rotor to the storage tank 52. Supply lines and transport are provided with a vacuum jacket and therefore well insulated. Vacuum insulation of the conveying lines minimizes heat transfer losses in the coolant as it flows from the reservoir to the rotor, and from the rotor to the reservoir.

The coolant is usually dead, such as neon or hydrogen. Suitable temperature values ​​for HTS superconductors are typically less than 30K, preferably around 27K. Cryogenic fluids most suitable for cooling the SC coils in the HTS rotor are hydrogen, which can cool the coil to 20K, and neon, which can cool the coil to 20K. cool the SC coil at 27K. The liquid neon exits the reservoir 52 of the cryoprotectant at a temperature of, for example, about 27K. A liquid cryogen is typically used in the storage vessel 52 to supply the HTS rotor with liquid coolant. A vacuum jacketed inflow conveyor line ensures that the liquid coolant from the storage tank enters the rotor at substantially the same temperature as the liquid remaining in the tank.

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The coolant evaporates as it flows around the SC coils. The evaporation of the coolant cools the SC coils and ensures that the coils operate under superconducting conditions. The evaporating coolant flows as cold gas from the HTS rotor through the return line 58 to the cooling tank 52. The return line is sized to pass the cold cooling gas from the rotor to the upper vaporized space 60 of the tank 52. The tank vapor space is vertically above the liquid space 62 of the tank. The vapor space and the liquid space in the reservoir may be a single continuous volume within the reservoir, or they may be separate chambers hydraulically connected to one another.

Re-condensation of the gaseous coolant in the storage vessel is accomplished by a cold head reconditioner 64. The condenser receives heat from the gaseous coolant in the reservoir so that the fluid condenses to a liquid and flows down to the liquid region of the reservoir. The capacitor need not be operated continuously while the reservoir supplies liquid coolant to the HTS rotor. The liquid coolant in the reservoir provides an uninterrupted supply of coolant to the HTS rotor. Thus, the recapacitor can be operated while the HTS continues to run. The capacitor can temporarily stop working without having to take the rotor out of operation during the repair of the recapacitor. When the HTS rotor is shut down for normal operation, the tank may be operated via the service funnel 66.

The cryogenic quench device 64 may include one or more Gifford-McMahon blocks or cold head pulsing tube blocks needed to provide the cooling capacity of the HTS rotor. The cryotechnical quench device may be a recapacitor that condenses vapor into a liquid. Typically, redundant cryoprotection blocks should not be needed. No excess capacity for the cryogenic quench device is needed because the cryogen storage vessel has sufficient liquid coolant capacity reserve to allow the cryopreservation blocks 64 to be shut down for maintenance or replacement without affecting the operation of the rotor. The storage volume of the vessel is sized to provide a sufficient amount of liquid for the rotor during the recapacitor shutdown period, for example, one day, in which case the typical storage capacity for a neon-cooled HTS rotor would be about 100 liters. During the shutdown periods of the cryogenic quench, the cooling system operates in an open loop so that the coolant vapors returned from the rotor are ejected to the surrounding atmosphere via the exhaust outlet 66. The lost cryogenic fluid is replenished by refilling the storage tank after the cryogenic quench block is restored to operation.

In operation, the liquid cryogenic agent is fed by gravity from the liquid space 62 to the transport connection 26 of the superconducting rotor. The cooling liquid circulates through the heat exchanger tubes 38 in contact with the exterior of the HTS coil, and cools the coil by transferring the boiling heat. The gaseous cooling steam returns from the rotor transport connection 26 via the vacuum jacketed return transport line 58 to the top (space 60) of the storage tank. The driving force for circulating the cooling fluid in a closed loop system is caused by the pressure difference resulting from the difference in the weight of the column 54 of the heavy inlet liquid and the column 54 of the light return gas.

The cold head 64 of the cryogenic quench device operates in the steam space 60 of the storage tank to recondensate the steam. Upon recondensation of the coolant, the fluid returns to the liquid region of the reservoir and is available for reuse to cool the HTS rotor. The system is a closed loop system that reuses the coolant and avoids fluid leakage. However, the system may operate as an open loop system if the cryotechnical device is not in operation. Moreover, the rotor cooling system of the present invention can be effectively used to cool the core in open loop operation by applying pressure to the vapor space of the storage tank to force larger amounts of liquid through the rotor if needed to cool it rapidly.

The cooling system 50 is economical and reliable. The operation of the system is based on the force of gravity and the use of a reservoir that ensures uninterrupted supply of coolant in an inexpensive manner. The system also minimizes potential failures, as no intensive systems and maintenance, such as cryotechnical cooling, are needed to ensure continuous operation.

While the invention has been described in conjunction with an embodiment that is presently considered to be the most advantageous and practicable, it is obvious that the invention is not intended to be limited to the described embodiment but, on the contrary, is considered to cover all embodiments according to the invention. the essence of the attached reservations.