Cryogenic refrigerator and control method therefor

Abstract

A cryogenic refrigerator (10) which generates a cryogenic temperature by compressing and expanding a working gas in a closed loop (11). The cryogenic refrigerator comprises a bypass line (22) allowing a high-pressure portion and a low-pressure portion to communicate with each other, a gas storage tank (24) located midway in the bypass line and having pressure regulation valves (23a, 23b) on the high-pressure side and the low-pressure side, respectively, and a pressure control unit (26) controlling the pressure regulation valves. The pressure control unit (26) controls the pressure regulation valves (23a, 23b) so that the pressure in the gas storage tank (24) is equal to the pressure in the closed loop at room temperature and in a stopped state and so that the pressure in the gas storage tank (24) is between the pressures in the high-pressure portion and in the low-pressure portion and is close to the pressure in the low-pressure portion in an operating state.

Description

BACKGROUND OF THE INVENTION[0001]1. Technical Field of the Invention[0002]The present invention relates to a cryogenic refrigerator having a cooling capacity of cooling a cooled object up to cryogenic temperatures and a control method therefor.[0003]2. Description of the Related Art[0004]A cryogenic refrigerator (for example, a Brayton cycle refrigerator or an Ericsson cycle refrigerator) is used to cool down high temperature superconducting (HTS) equipment (for example, a superconducting transmission cable, a superconducting transformer, a superconducting motor, a superconducting coil for storing superconducting power, a large accelerator, a nuclear fusion test facility, MHD power generation, a superconducting coil, or the like).[0005]For example, in the case of using the cryogenic refrigerator for cooling the high temperature superconducting equipment, the lowest temperature is 65K, 40K, 30K, 20K, or the like, though it depends on the type and application of a superconducting wire...

AI Technical Summary

Benefits of technology

[0022]The present invention has been devised in order to solve the above problems. Specifically, it is an object of the present invention to provide a cryogenic refrigerator and a control method therefor, the cryogenic refrigerator having a cooling capacity of cooling a cooled object up to a predetermined cryogenic temperature, capable of maintaining the pressure in a high-pressure portion at a substantially constant level from a room temperature in a stopped state to a cryogenic temperature in an operating state without using a pressure vessel whose pressure resistance exceeds a predetermined pressure (for example, 1 MPa) and without discharging or supplying a working gas, and capable of preventing a reverse rotation of a compressor even in the case of an emergency stop.

[0030]According to the cryogenic refrigerator and the method of the present invention, the cryogenic refrigerator comprises a bypass line which allows a high-pressure portion and a low-pressure portion in the closed loop, which constitutes the cryogenic refrigerator, to communicate with each other and a gas storage tank which is located midway in the bypass line and has pressure regulation valves on the high-pressure side and the low-pressure side, respectively, and therefore it is possible to set the pressure of the entire system, which includes the closed loop, the bypass line, and the gas storage tank, to a predetermined reference pressure or lower by controlling the pressure regulation valves (for example, maintaining the pressure regulation valves to be fully opened in the stopped state) so that the pressure in the gas storage tank is equal to the pressure in the closed loop at room temperature and in a stopped state. Moreover, this enables the pressures on the inlet side and outlet side of the compressor to be equalized in the stopped state of the refrigerator, and therefore it is possible to prevent a reverse rotation of the compressor caused by a pressure difference between the inlet side and the outlet side of the compressor after the stop.

[0032]Therefore, the capacity of the gas storage tank is set so that the pressure in the gas storage tank is able to be maintained at a predetermined reference pressure or lower level at room temperature in the stopped state and so that the pressure in the high-pressure portion is able to be maintained at a predetermined operating pressure level in the operating state in which the cryogenic temperature is generated, thereby enabling the cryogenic refrigerator to have a cooling capacity of cooling an cooled object up to a predetermined cryogenic temperature and to maintain the pressure in the high-pressure portion at a substantially constant level from the room temperature in the stopped state to the cryogenic temperature in the operating state without using a pressure vessel whose pressure resistance exceeds a predetermined pressure (for example, 1 MPa) and without discharging or supplying the working gas.

Problems solved by technology

While the working gases (helium, neon, and the like) for use in the foregoing cryogenic refrigerator have extremely low liquefaction temperatures and therefore are excellent in preventing liquefaction in the inside of an expander, there is a problem that the working gases are very expensive.

In this case, discharging the working gas to the outside causes a great loss of the expensive working gas, and bleeding the working gas to the pressure vessel causes excess pressure resistance of the pressure vessel.

In this case, there is a problem that an excess load is applied to the compressor on start-up.

Furthermore, if the refrigerator is suddenly stopped in an emergency stop or the like, the working gas on the high-pressure side flows backward passing through the compressor and the compressor turns in reverse, which adversely affects a drive system or the like in some cases.

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