1289646 九、發明說明： 【發明所屬之技術領域】 • 本發明係關於一種超電導電纜等之極低溫電纜的循環 冷卻系統。 【先前技術】 超電導電纜等之極低溫電纜，係經由液態氮或液態氦等 之冷媒而冷卻，其循環冷卻系統方面，如日本特開平8_ 148044號公報中所記載的系統係爲習知者。該循環冷卻系 ® 統，係將冷媒之循環回路做成閉路，在冷媒未氣化的狀態時 可進行循環的冷卻系統。 第2圖係其槪圖，其具有：儲存冷媒33之儲槽單元30、 壓送冷媒33的壓送泵31、將儲槽單元3〇內保持於預定之壓 力的壓力控制機構3 6、將冷媒3 3冷卻到預定溫度的熱交換 單元32、及使冷媒33分流到電纜35 (存在有3條電纜。各 電纜未圖示。）中之閥單元34。 該系統係將從儲槽單元30送出的冷媒33,使用熱交換 ® 單元32而冷卻到預定溫度，將其供給到電纜35，然後再度 回到儲槽單元30之循環周程反覆地進行者。 特許文獻1 :日本特開平8- 148044號公報（申請專利範 圍及第1圖） 〔發明欲解決的課題〕 但是，在上述先前技術之循環冷卻系統中，將電纜35 做爲出發點的情況’儲槽單元30係位於循環回路之上游’ 從該儲槽單元30送出的冷媒33,在使用熱交換單元32冷卻 128.9646 到預定溫度之後，被送入電纜35側。亦即’冷媒33在將電 ★ 纜35冷卻之後回到儲槽單元30,藉由電纜35處之發熱而使 • 冷媒33之溫度上昇，藉由熱膨脹而使冷媒33之體積.增加。 然後，對應於電纜35處之發熱量的變化’冷媒33之體 積亦變化。並且，預料於電纜35之大的發熱量等之情況， 雖然對應於此有預先將冷媒3 3充分地冷卻的需要’但是該 情況之冷媒3 3反而收縮而使其體積減少。 依此方式，藉由冷媒33之溫度變化，而使冷媒33之體 φ 積膨脹或收縮，其液量雖然產生變化，但是在上述回路中電 纜35之冷卻部或配管等之儲槽單元30以外的各構成品之體 積係爲一定，因此冷媒液量之變化部分必須在儲槽單元30 內之容積中被吸收。從而，儲槽單元30之冷媒儲存容積， 必須設計成使回路內之冷媒液量的變化可被吸收，其結果， 有將儲槽單元30做成大容積的需要。或者，爲了將儲槽單 元30內之冷媒量保持一定，而有設置冷媒量之調整機構以 進行調整作業的需要。尤其，在系統內之冷媒總量爲越大之 # 情況，或溫度變化越大的系統時，儲槽單元在考慮該體積膨 脹、收縮而有做成大容積的需要，或者需要有大能力之冷媒 量調整機構。 本發明之目的在提供一種極低溫電纜之循環冷卻系 統，其可解決上述先前技術之循環冷卻系統的問題，而可將 儲槽單元小型化，並且，不需要儲槽單元內之冷媒量調整機 構或調整作業。 【發明說明】 ,1289646 〔解決課題之設施〕 本發明之極低溫電纜的循環冷卻系統，係將具有使儲槽 % 單元內之冷媒量保持於一定之冷媒溫度調整機構，做爲其特 I 徵，藉由該特徵而達成上述目的。 即，本發明極低溫電纜之循環冷卻系統，係具有儲存冷 媒的儲槽單元、及利用從該儲槽單元送出的冷媒將電纜冷卻 的電纜冷卻部，將從該電纜冷卻部送出的冷媒，再度返回到 該儲槽單元中而作循環的極低溫電纜之循環冷卻系統，其特 # 徵爲：其具有使儲槽單元內之冷媒量保持於一定之冷媒溫度 調整機構。 在上述極低溫電纜之循環冷卻系統中，冷媒量調整機構 亦可由對應於檢測冷媒溫度的感測器之檢測結果，而調整冷 卻能力之熱交換單元所形成。 在上述極低溫電纜之循環冷卻系統中，檢測冷媒溫度的 感測器，亦可位於電纜冷卻部之冷媒出口的附近。 在上述極低溫電纜之循環冷卻系統中，熱交換單元亦可 • 位於電纜冷卻部的冷媒出口與朝向儲槽單元的冷媒返回口 之間。 在上述極低溫電纜之循環冷卻系統中，熱交換單元之冷 卻能力之調整，可藉由熱交換單元運轉用電力或電源頻率之 調整而進行。 〔發明之效果〕 本發明之極低溫電纜之循環冷卻系統，具有使儲槽單元 內之冷媒量保持於一定之冷媒溫度調整機構，因此在儲槽單 1289646 壤 元內，並不需要附加吸收冷媒之體積變化用的容積，因而可 * 使儲槽單元小型化。並且，亦不需要儲槽單元內之冷媒體積 ' 調整機構或調整作業。 並且，檢測冷媒溫度的感測器位於電纜冷卻部之出口附 近，且將熱交換單元設置於電纜冷卻部之冷媒出口與儲槽單 元之冷媒返回口之間的情況，可更確實地對應於電纜之發熱 的變化，而進行熱交換單元之冷卻能力之調整，並可防止使 電纜之發熱造成冷媒之體積變化的影響，直接傳到儲槽單元 φ 側，因此可更正確地使儲槽單元內之冷媒量被保持一定。 並且，使熱交換單元之冷卻能力之調整’藉由熱交換單 元運轉用電力或電源頻率之調整而進行之情況中，經常地在 滿載電力下運轉，而過度冷卻之情形，與使用加熱器等加熱 而進行溫度調整之先前技術的系統比較，熱交換單元之消耗 電力爲少即可，因此可節省能源。 【實施方式】 使儲槽單元內之冷媒量保持於一定之冷媒溫度調整機 • 構，係具有將系統內之冷媒溫度保持一定之功能者，因而舉 示由檢測冷媒溫度的感測器及對應該感測器之檢測結果而 調整冷卻能力之熱交換單元等構成爲其代表例。對應於由感 測器檢測的冷媒溫度之變化，使熱交換單元的冷卻能力增加 (將溫度降低之時）或減少（將溫度提高之時）’而使冷媒溫度 保持一定。 檢測冷媒溫度的感測器，只要做成即使在極低溫時’仍 可正確且感度良好地檢測者的話，其種類不予限定。在本發 ,1289646 明之極低溫電纜之循環冷卻系統中，對冷媒溫度之變化影響 最大者，通常係電纜之發熱量的變化。從而，將該感測器設 * 置於電纜冷卻部之出口附近時，可迅速地檢測到電纜發熱量 的變化，因而可進行感度高之冷媒溫度調整，故較受採用。 熱交換單元亦只要爲具有充分的冷卻能力，可對應冷媒 溫度之變化而做冷卻能力之調整的話，其種類不予限定。冷 卻能力之調整方法亦不特別加以限定，先前技術之冷卻系統 中多數採用的方式，即，亦可採用使具有對應於冷媒溫度變 # 化推測最大値之電力以上之滿載電力的熱交換單元，經常以 滿載電力運轉，冷媒溫度過度下降之時，使用位於熱交換單 元之熱交換部的加熱器進行加熱而調整的方法。但是，使冷 卻能力之調整，藉由熱交換單元運轉用電力或電源頻率之調 整而進行的話，不需要由加熱器進行加熱，因而冷卻需要的 能量可被節約，故較爲採用。 電源頻率之調整，例如藉由變頻器進行。熱交換單元之 冷卻能力係依存於頻率，例如從60Hz做成30Hz運轉時，冷 ®卻能力變化1/2。 在本發明極低溫電纜之循環冷卻系統中，雖然冷媒係從 儲槽單元被送出，但是在檢測冷媒溫度的感測器位於電纜冷 卻部之出口附近時，熱交換單元亦可設置於儲槽單元與電纜 冷卻部之間。在電纜之發熱爲大，且電纜冷卻部之出口附近 之溫度上昇時，可使熱交換單元之冷卻能力增加，因而可抑 制冷媒溫度之上昇。 但是，此時，電纜冷卻部，即，發熱部係位於熱交換單 1289646 元之下游側，因此無法迅速地對應於電纜之發熱量的變化而 作冷媒溫度的調整，進而無法根據冷媒溫度之變化對應於冷 β 媒之體積變化而迅速地調整。亦即，即使由於電纜之發熱量 變化，使冷媒溫度變化，其結果使冷媒之體積增加或減少之 時，體積增加或減少的冷媒本身無法直接地做溫度調整，因 此亦無法迅速地對應於冷媒體積之變化。其結果，使感度高 之調整變成困難。 因而較佳爲，熱交換單元被設置於電纜冷卻部之冷媒出 # 口與朝向儲槽單元的冷媒返回口之間。特別更佳的形態爲， 檢測冷媒溫度的感測器係位於電纜冷卻部之出口附近，且， 熱交換單元設置於電纜冷卻部之冷媒出口與朝向儲槽單元 的冷媒返回口之間。藉由該形態，可進行直接對應於電纜發 熱的變化之熱交換單元的冷卻能力之調整，而且熱交換單元 可將冷卻到預定溫度的冷媒供給到儲槽單元，因此熱膨脹或 熱收縮不會對冷媒之體積變化有直接的影響，故可更正確地 將儲槽單元內的冷媒量保持於一定。 Φ 以下，將參照第1圖而具體地說明上述特別更佳的形態。 第1圖之系統，係以儲槽單元1、熱交換單元2、閥單 元3、電纜冷卻部4、及檢測冷媒溫度之感測器5 (以下只稱 感測器5)做爲主要構成要素。 儲槽單元1係儲存冷媒C之閉鎖容器，其具有冷媒循環 用之壓送泵7及壓力控制機構9。冷媒C係藉由該壓送泵7 加壓而循環，其吐出壓力係藉由儲槽單元內之傍通閥8作調 整。壓送泵7係考慮冷媒之循環回路中之壓力降低’而爲了 -10- ,128.9646 獲得必要流量所使用者。 雖然壓送泵7亦可設置成獨立於儲槽單元1之外部，但 * 是如本例將其設置於儲槽單元1內之時，可共用真空隔熱容 器，故可達成系統製造成本的降低。而，P1係測定儲槽單 . 元1內之壓力的壓力計，P2係測定壓送泵7之吐出部壓力 的壓力計，符號20係保護儲槽單元1之壓力過度上昇的安 全閥，符號21係不使大氣等流入儲槽單元1內之逆止閥。 並且，雖然壓力控制機構9係供給氣體G而將儲槽單元 1內之壓力保持大致一定，因而將冷媒C保持於不氣化的狀 - 態，但是其在本發明中並不需要。供給的氣體G，係使用沸 點或三態點比冷媒C更低者，例如冷媒C爲液態氮之時，係 使用氦氣。 在上述之先前技術的循環冷卻系統中，雖然設置有將儲 ' 槽單元1內之冷媒量維持一定之冷媒自動補給機構（例如， 液位計及與其測定結果連動的供給器之組合），但是在本發 明中該機構基本上並不需要。 • 閥單元3具有將從儲槽單元1通過配管1 5送出的冷媒之 分流而供給到電纜冷卻部4之功能。在本例中，爲了將冷媒 C均勻地供給到位於電纜冷卻部4內之3相電力電纜，在閥 單元3內將冷媒C分歧’在每個分歧上設置有流量計12、 流量調整閥13及傍通閥14。 通過閥單元3輸送的冷媒C被供給到電纜冷卻部4。在 本例中係爲，從電纜冷卻部4之一端供給，在另一端將3相 部分的冷媒C綜合成一起而排出，並返回到熱交換單元2側 -11- 1289646 % ι 的構成。 在電纜冷卻部4內，雖然藉由冷媒C而將個別之電纜冷 ' 卻，但是藉由一方電纜之發熱而使冷媒C之溫度上昇。並 _ 且，溫度之上昇量，係由電纜之發熱量變化（即電流的變化） . 而變動。 設置於電纜冷卻部4之冷媒出口附近的感測器5檢測冷 媒C的溫度，其檢測結果被回授到熱交換單元2之電力調整 機23。從感測器5送出之冷媒C通過配管1 6而被送出到熱 ，交換單元2。 - 熱交換單元2係將從感測器5送出之冷媒C冷卻到預定 溫度者。在本例中，冷凍機10之冷頭11被接觸到銅塊上， ^ 該銅塊上卷繞有冷媒C之輸送管，藉由固體熱傳導作熱交 換。並且雖然在本例中，係使用1台熱交換單元2，但是冷 卻能力1台爲不充足之時，亦可串聯2台以上。 在本例中之熱交換單元2，係被設置於感測器5之出口 側配管1 6之下游側，且朝向儲槽單元1之冷媒C返回配管 ® 的上游側。即，其係位於電纜冷卻部4之冷媒出口與朝向儲 槽單元1之冷媒返回口之間。 雖然冷凍機10係接受來自於熱交換單元用之電源22的 電力供給而運轉，但是在該電源22與冷凍機1 〇之間設置有 熱交換單元運轉用之電力調整機23。如上所述，感測器5 檢測的溫度被回授，而控制電力調整機23。因而，可進行熱 交換單元2之冷卻能力的調整，而將朝向儲槽單元1之返回 口的溫度控制成一定，因而防止由於冷媒C之溫度變動造成 1289646 冷媒C之體積的變動。電力調整機23方面，亦可使用將熱 交換單元2中的電源頻率數任意變化的變頻器。 * 而，來自發熱部，亦即，來自電纜冷卻部4而存在於熱 交換單元2間的冷媒量爲多之時，由於該冷媒的熱膨脹或熱 收縮將使體積變化變成大。從而，使該冷媒量做成少較佳， 熱交換單元2位於電纜冷卻部4之冷媒出口附近，即感測器 5之出口的附近較佳。 從熱交換單元2送出的冷媒C，通過配管15而返回儲 _槽單元1。 儲槽單元1、熱交換單元2、閥單元3個別地被收容於 真空隔熱容器18中，構成循環回路的配管15,16亦被真空 隔熱層所覆蓋。因此，可使冷卻系統全體的熱損失變小。.而， 各單元1，2,3，1 5,16之真空隔熱，亦可整體而非個別地進行。 產業上利用之可行性 本發明之極低溫電纜之循環冷卻系統，雖然可被做爲超 電導電纜等在被冷媒所冷卻的狀態下所使用的電纜之冷卻 ^ 系統而使用，但是尤其在要求小型化或機構的簡單化之時適 用。 【圖式簡單說明】 第1圖係顯示本發明之極低溫電纜的循環冷卻系統之一 例的槪略圖。 第2圖係先前技術之極低溫電纜的循環冷卻系統之一例 的槪略圖。 【元件符號說明】 -13- 1289646 j 1，30…儲槽單元 2.32.. .熱交換單元 3，34 ...閥單元 4.. .電纜冷卻部 5.. .感測器 7，3 1 ...壓送栗 8 ...傍通閥 9···壓力控制機構 1 0 ...冷凍機 1 1…冷頭 1 2 ...流量計 13…流量調節閥 14.. .傍通閥 15,16…配管 18.. .真空隔熱容器 20…安全閥 ® 21...逆止閥 2 2…電源 23···電力調整機 C...冷媒 G...氣體 P1，P2···壓力計 -141289646 IX. Description of the invention: [Technical field to which the invention pertains] The present invention relates to a circulating cooling system for a cryogenic cable such as a superconducting cable. [Prior Art] A cryogenic cable such as a superconducting cable is cooled by a refrigerant such as liquid nitrogen or liquid helium, and the system described in Japanese Laid-Open Patent Publication No. Hei No. Hei 8-148044 is a conventional one. This recirculating cooling system is a cooling system that allows the circulation circuit of the refrigerant to be closed and to circulate when the refrigerant is not vaporized. Fig. 2 is a plan view showing a sump unit 30 for storing a refrigerant 33, a pressure feed pump 31 for pumping a refrigerant 33, and a pressure control mechanism 36 for holding the sump unit 3 at a predetermined pressure. The heat exchanger unit 32 that cools the refrigerant to a predetermined temperature and the valve unit 34 that divides the refrigerant 33 into the cable 35 (there are three cables, each of which is not shown). This system cools the refrigerant 33 sent from the sump unit 30 to a predetermined temperature using the heat exchange unit 32, supplies it to the cable 35, and then returns to the cycle of the sump unit 30 to repeat the cycle. [Patent Document 1 and No. 1 148 044] (Application of the Invention and Fig. 1) [Problems to be Solved by the Invention] However, in the above-described prior art circulating cooling system, the case where the cable 35 is used as a starting point is stored. The tank unit 30 is located upstream of the circulation loop. The refrigerant 33 sent from the tank unit 30 is cooled to 128.9646 by the heat exchange unit 32 to a predetermined temperature, and then sent to the cable 35 side. That is, the refrigerant 33 returns to the sump unit 30 after cooling the electric cable 35, and the temperature of the refrigerant 33 rises due to heat generated at the cable 35, and the volume of the refrigerant 33 increases due to thermal expansion. Then, the volume of the refrigerant 33 corresponding to the change in the amount of heat generated at the cable 35 also changes. Further, in the case where the heat generation amount of the cable 35 is large, it is necessary to sufficiently cool the refrigerant 3 3 in advance. However, in this case, the refrigerant 3 3 is contracted to reduce the volume. In this manner, the temperature of the refrigerant 33 changes, and the volume φ of the refrigerant 33 expands or contracts, and the amount of liquid changes. However, in the circuit, the cooling unit of the cable 35 or the storage unit 30 such as piping is used. The volume of each component is constant, and therefore the change in the amount of refrigerant liquid must be absorbed in the volume in the sump unit 30. Therefore, the refrigerant storage volume of the sump unit 30 must be designed such that the change in the amount of the refrigerant liquid in the circuit can be absorbed, and as a result, there is a need to make the sump unit 30 into a large volume. Alternatively, in order to keep the amount of refrigerant in the sump unit 30 constant, there is a need to provide an adjustment mechanism for the amount of refrigerant to perform an adjustment operation. In particular, when the total amount of refrigerant in the system is larger, or the system with a larger temperature change, the tank unit needs to have a large volume in consideration of the volume expansion and contraction, or requires a large capacity. Refrigerant volume adjustment mechanism. SUMMARY OF THE INVENTION An object of the present invention is to provide a circulating cooling system for an extremely low temperature cable which can solve the problems of the above-described prior art circulating cooling system, and can miniaturize the tank unit and eliminate the need for a refrigerant amount adjusting mechanism in the tank unit Or adjust the job. [Description of the Invention] 1289646 [Facilities for Solving the Problem] The circulating cooling system for the cryogenic cable of the present invention has a refrigerant temperature adjusting mechanism for keeping the amount of refrigerant in the tank % unit constant, and is a special feature thereof. With the feature, the above object is achieved. That is, the circulating cooling system for the cryogenic cable of the present invention has a storage tank unit for storing the refrigerant, and a cable cooling unit for cooling the cable by the refrigerant sent from the storage tank unit, and the refrigerant sent from the cable cooling unit is re-circulated. The circulating cooling system of the cryogenic cable that is returned to the storage tank unit for circulation is characterized in that it has a refrigerant temperature adjustment mechanism that keeps the amount of refrigerant in the storage tank unit constant. In the above-described circulating cooling system for extremely low temperature cables, the refrigerant amount adjusting mechanism may be formed by a heat exchange unit that adjusts the cooling capacity corresponding to the detection result of the sensor for detecting the temperature of the refrigerant. In the above-described cryogenic cable circulating cooling system, the sensor for detecting the temperature of the refrigerant may be located in the vicinity of the refrigerant outlet of the cable cooling portion. In the above-described cryogenic cable circulating cooling system, the heat exchange unit may also be located between the refrigerant outlet of the cable cooling section and the refrigerant return port facing the storage tank unit. In the above-described circulating cooling system for extremely low temperature cables, the adjustment of the cooling capacity of the heat exchange unit can be performed by adjusting the power or power frequency of the heat exchange unit. [Effects of the Invention] The circulating cooling system for the cryogenic cable of the present invention has a refrigerant temperature adjusting mechanism for keeping the amount of refrigerant in the storage tank unit constant. Therefore, it is not necessary to additionally absorb the refrigerant in the storage tank 1289646. The volume for volume change makes it possible to miniaturize the tank unit. Moreover, there is no need for a cold media product 'adjustment mechanism or adjustment work in the tank unit. Further, the sensor for detecting the temperature of the refrigerant is located near the outlet of the cable cooling portion, and the heat exchange unit is disposed between the refrigerant outlet of the cable cooling portion and the refrigerant return port of the sump unit, and can more reliably correspond to the cable. The change of the heat generation, and the adjustment of the cooling capacity of the heat exchange unit, and the influence of the volume change of the refrigerant caused by the heating of the cable can be prevented, and directly transmitted to the φ side of the sump unit, so that the sump unit can be more correctly The amount of refrigerant is kept constant. Further, in the case where the adjustment of the cooling capacity of the heat exchange unit is performed by the adjustment of the heat exchange unit operation power or the power source frequency, the operation is often performed under full load power, and excessive cooling is performed, and a heater or the like is used. Compared with the prior art system in which the temperature is adjusted by heating, the heat exchange unit can consume less power, thereby saving energy. [Embodiment] The refrigerant temperature adjustment mechanism for keeping the amount of refrigerant in the storage tank unit constant has a function of keeping the temperature of the refrigerant in the system constant. Therefore, the sensor and the pair for detecting the temperature of the refrigerant are shown. A heat exchange unit or the like that adjusts the cooling capacity according to the detection result of the sensor is constituted as a representative example. Corresponding to the change in the temperature of the refrigerant detected by the sensor, the cooling capacity of the heat exchange unit is increased (when the temperature is lowered) or decreased (when the temperature is raised), and the temperature of the refrigerant is kept constant. The sensor for detecting the temperature of the refrigerant is not limited as long as it can be detected accurately even when it is extremely cold. In the circulating cooling system of the cryogenic cable of the present invention, 1289646, the greatest influence on the change of the temperature of the refrigerant is usually the change of the heat generation of the cable. Therefore, when the sensor device is placed near the exit of the cable cooling portion, the change in the amount of heat generated by the cable can be quickly detected, so that the temperature of the refrigerant having high sensitivity can be adjusted, which is preferable. The heat exchange unit is not limited as long as it has sufficient cooling capacity and can be adjusted for the cooling capacity in response to changes in the temperature of the refrigerant. The method for adjusting the cooling capacity is also not particularly limited. In the prior art, the cooling system is mostly employed, that is, a heat exchange unit having a full load power equal to or higher than the power estimated to be the maximum temperature of the refrigerant may be used. When the temperature of the refrigerant is frequently lowered and the temperature of the refrigerant is excessively lowered, the heater placed in the heat exchange unit of the heat exchange unit is heated and adjusted. However, since the adjustment of the cooling capacity is performed by adjusting the power or the power frequency of the heat exchange unit, it is not necessary to heat the heater, so that the energy required for cooling can be saved. The adjustment of the power frequency is performed, for example, by a frequency converter. The cooling capacity of the heat exchange unit depends on the frequency. For example, when operating at 30 Hz from 60 Hz, the cooling capacity is changed by 1/2. In the circulating cooling system of the cryogenic cable of the present invention, although the refrigerant is sent out from the sump unit, the heat exchange unit may be disposed in the sump unit when the sensor for detecting the temperature of the refrigerant is located near the outlet of the cable cooling portion. Between the cable cooling section. When the heat generation of the cable is large and the temperature near the outlet of the cable cooling portion rises, the cooling capacity of the heat exchange unit can be increased, so that the temperature of the refrigerant can be increased. However, at this time, the cable cooling portion, that is, the heat generating portion is located on the downstream side of the heat exchange unit 1,289,646, so that the temperature of the refrigerant cannot be quickly adjusted in accordance with the change in the amount of heat generated by the cable, and the temperature of the refrigerant cannot be changed according to the temperature of the refrigerant. It is quickly adjusted corresponding to the volume change of the cold beta medium. That is, even if the temperature of the refrigerant changes due to a change in the amount of heat generated by the cable, as a result of increasing or decreasing the volume of the refrigerant, the refrigerant which is increased or decreased in volume cannot be directly adjusted in temperature, and therefore cannot quickly correspond to the refrigerant. Volume change. As a result, it becomes difficult to adjust the sensitivity. Therefore, it is preferable that the heat exchange unit is disposed between the refrigerant outlet of the cable cooling unit and the refrigerant return port facing the storage unit. In a particularly preferred embodiment, the sensor for detecting the temperature of the refrigerant is located near the outlet of the cable cooling portion, and the heat exchange unit is disposed between the refrigerant outlet of the cable cooling portion and the refrigerant return port facing the storage unit. With this configuration, the adjustment of the cooling capacity of the heat exchange unit directly corresponding to the change in cable heating can be performed, and the heat exchange unit can supply the refrigerant cooled to the predetermined temperature to the sump unit, so that thermal expansion or heat shrinkage does not The volume change of the refrigerant has a direct influence, so that the amount of refrigerant in the tank unit can be more accurately maintained. Φ Hereinafter, the above-described particularly preferable form will be specifically described with reference to Fig. 1 . The system of Fig. 1 is mainly composed of a sump unit 1, a heat exchange unit 2, a valve unit 3, a cable cooling unit 4, and a sensor 5 for detecting the temperature of the refrigerant (hereinafter referred to as a sensor 5). . The sump unit 1 is a lock container for storing the refrigerant C, and has a pressure feed pump 7 for circulating refrigerant and a pressure control mechanism 9. The refrigerant C is circulated by pressurization by the pumping pump 7, and the discharge pressure is adjusted by the bypass valve 8 in the sump unit. The pressure feed pump 7 is a user who obtains the necessary flow rate for -10-, 128.9646 in consideration of the pressure drop in the circulation circuit of the refrigerant. Although the pressure feed pump 7 can also be disposed independently of the outside of the sump unit 1, when the * is disposed in the sump unit 1 as in this example, the vacuum heat insulating container can be shared, so that the system manufacturing cost can be achieved. reduce. Further, P1 is a pressure gauge for measuring the pressure in the storage tank unit, P2 is a pressure gauge for measuring the pressure of the discharge portion of the pressure feed pump 7, and reference numeral 20 is a safety valve for protecting the pressure of the storage tank unit 1 from excessively rising, symbol The 21 system is a check valve that does not allow the atmosphere or the like to flow into the sump unit 1. Further, although the pressure control means 9 supplies the gas G to keep the pressure in the sump unit 1 substantially constant, the refrigerant C is held in an unvaporized state, but it is not required in the present invention. The supplied gas G is one in which the boiling point or the triplet point is lower than the refrigerant C. For example, when the refrigerant C is liquid nitrogen, helium gas is used. In the above-described circulating cooling system of the prior art, a refrigerant automatic replenishing mechanism that maintains a constant amount of refrigerant in the tank unit 1 (for example, a combination of a level gauge and a feeder linked to the measurement result) is provided. This mechanism is basically not required in the present invention. The valve unit 3 has a function of supplying the refrigerant sent from the sump unit 1 through the pipe 15 to the cable cooling unit 4 by shunting the refrigerant. In this example, in order to uniformly supply the refrigerant C to the three-phase power cable located in the cable cooling unit 4, the refrigerant C is diverged in the valve unit 3, and the flow meter 12 and the flow rate adjusting valve 13 are provided in each of the divisions. And the valve 14 is closed. The refrigerant C sent through the valve unit 3 is supplied to the cable cooling portion 4. In this example, the supply is supplied from one end of the cable cooling unit 4, and the refrigerant C of the three-phase portion is combined and discharged at the other end, and returned to the heat exchange unit 2 side -11 - 1289646 % ι. In the cable cooling unit 4, although the individual cables are cooled by the refrigerant C, the temperature of the refrigerant C rises due to the heat generated by one of the cables. And _, and the rise in temperature is caused by the change in the heat generation of the cable (ie, the change in current). The sensor 5 provided near the refrigerant outlet of the cable cooling unit 4 detects the temperature of the refrigerant C, and the detection result is fed back to the power conditioner 23 of the heat exchange unit 2. The refrigerant C sent from the sensor 5 is sent to the heat exchange unit 2 through the pipe 16. - The heat exchange unit 2 is a person who cools the refrigerant C sent from the sensor 5 to a predetermined temperature. In this example, the cold head 11 of the refrigerator 10 is brought into contact with the copper block. ^ The copper block is wound with a transfer tube of the refrigerant C for heat exchange by solid heat conduction. Further, in this example, one heat exchange unit 2 is used, but when the cooling capacity is insufficient, two or more units may be connected in series. The heat exchange unit 2 in this example is disposed on the downstream side of the outlet side pipe 16 of the sensor 5, and returns to the upstream side of the pipe ® toward the refrigerant C of the sump unit 1. That is, it is located between the refrigerant outlet of the cable cooling unit 4 and the refrigerant return port facing the sump unit 1. Although the refrigerator 10 is operated to receive power supply from the power source 22 for the heat exchange unit, a power conditioner 23 for operating the heat exchange unit is provided between the power source 22 and the refrigerator 1 . As described above, the temperature detected by the sensor 5 is fed back, and the power conditioner 23 is controlled. Therefore, the adjustment of the cooling capacity of the heat exchange unit 2 can be performed, and the temperature toward the return port of the sump unit 1 can be controlled to be constant, thereby preventing the volume of the 1289646 refrigerant C from varying due to the temperature fluctuation of the refrigerant C. As the power conditioner 23, an inverter that arbitrarily changes the number of power sources in the heat exchange unit 2 can also be used. * When the heat generating portion, that is, the amount of refrigerant existing between the heat exchanger units 2 from the cable cooling portion 4 is large, the volume change is large due to thermal expansion or thermal contraction of the refrigerant. Therefore, it is preferable to make the amount of the refrigerant less, and the heat exchange unit 2 is located near the refrigerant outlet of the cable cooling unit 4, that is, in the vicinity of the outlet of the sensor 5. The refrigerant C sent from the heat exchange unit 2 is returned to the storage tank unit 1 through the pipe 15. The sump unit 1, the heat exchange unit 2, and the valve unit 3 are individually housed in the vacuum heat insulating container 18, and the pipes 15, 16 constituting the circulation circuit are also covered by the vacuum heat insulating layer. Therefore, the heat loss of the entire cooling system can be made small. Moreover, the vacuum insulation of the units 1, 2, 3, 15 and 16 can also be carried out as a whole rather than individually. Industrial Applicability The circulating cooling system of the cryogenic cable of the present invention can be used as a cooling system for a cable used in a state in which a refrigerant is cooled by a superconducting cable, but is particularly required to be miniaturized. Or when the organization is simplistic. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view showing an example of a circulating cooling system of an extremely low temperature cable of the present invention. Fig. 2 is a schematic diagram showing an example of a circulating cooling system of a cryogenic cable of the prior art. [Description of component symbols] -13- 1289646 j 1,30...storage unit 2.32.. heat exchange unit 3,34 ...valve unit 4.. cable cooling section 5..sensing sensor 7,3 1 ...pressure delivery pump 8 ... 傍 valve 9 · · pressure control mechanism 1 0 ... freezer 1 1 ... cold head 1 2 ... flow meter 13 ... flow control valve 14 .. Valves 15, 16...Pipe 18: Vacuum insulated container 20...Safety valve® 21...Backstop valve 2 2...Power supply 23···Power conditioner C...Refrigerant G...Gas P1, P2 ··· Pressure gauge-14