SERIES-PARALLEL FLOW COOLING APPARATUS

Abstract: A series-parallel flow cooling apparatus having both advantages in series and parallel flow systems which is obtained by combining a construction of series flow system with that of parallel flow system wherein a by-pass air duct (15) provided with an inlet (17) in a prescribed position is disposed in addition to a semiconductor cooling air duct (12), whereby temperatures of thyristor element junctions (3) are uniformalized, the cooling air flow is minimized, and reduc­ tion for power of whose auxiliary machineries is intended.

Description: SERIES-PARALLEL FLOW COOLING APPARATUS BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a series-parallel flow cooling apparatus utilized for semiconductors for electric power as well as thyristor valves for dc power transmission wherein semiconductors such as thyristor elements and the like are employed. Description of the Prior Art When cooling apparatuses utilized for semiconductor devices for electric power, valves for dc power transmission or the like wherein semiconductors such as thyristor elements and the like are employed are classified in accordance with cooling system, they are divided broadly into three categories, i.e., water cooling, oil cooling and air cooling systems. Among them, series flow system or seriesparallel flow system is usually utilized in case of water cooling and oil cooling, whilst parallel flow system is utilized in case of air cooling in most cases. Meanwhile water cooling is often utilized, because cooling performance thereof is excellent. In general, however, semiconductor devices for electric power are operated at high voltages so that there is a problem in insulation, and solution for such problem is a technical question. In case of oil cooling, there is such a disadvantage in that since semiconductors are immersed in insulating oil, the weight thereof is considerably heavy, besides such oil sticks to parts of the semiconductors and the like, even if the insulating oil has been extracted from the apparatus in case of maintenance and inspection, or the like case thereof so that such apparatus is troublesome in handling. In case of air cooling, parallel flow system of open-air type has been often adopted. And in case of such parallel flow system, there is such an advantage that a temperature difference between a plurality of thyristor elements is small, whilst there are also such disadvantages that much cooling air flow is required so that the cooling construction therefor must be large-scale one. In addition to the above, there is a danger of causing drift, i.e., such a state where cooling air flow is not uniformly supplied to cooling fins for thyristor elements in a semiconductor device for electric power in which a great many thyristor elements are used. In such condition as mentioned above, junction temperatures of the respective thyristor elements become naturally unhomogeneous and as the result, electrical characteristics of the thyristor elements are adversely affected. Furthermore, when such junction temperature of a thyristor element increases abnormally up to around 1250 C, the thyristor element is damaged. For these reasons, since it -is required to previously increase cooling air flow, there is such a disadvantage that power of an auxiliary machinery, for example, power of a blower must be increased. On one hand, in case of series flow system, there is proposed such a conventional apparatus as shown in Figs. 1 - 4 wherein reference numeral 1 designates a tank for supplying a cooling gas which consists of an upper tank 2 being provided with an exhaust port 2a for the cooling gas and a lower tank 3 being provided with a feed port 3a for the gas. A cooler 4 for dissipating heat generated in thyristor elements described hereunder outside is disposed in between the exhaust port 2a and the feed port 3a. The cooler 4 is provided with fans 4a on the side wall thereof. A blower 5 for circulating cooling gas which is placed between the lower tank 3 and the cooler 4 to connect them with each other thereby to pass the gas therethrough. Each module 6 consists of each module insulating air duct 7, each thyristor element 8 contained in such a module insulating air duct 7, and each cooling fin 9, and the module is supported by an insulating stanchion 10. The module insulating air duct 7 comprises cells 7a each containing the thyristor element 8 as well as the cooling fin 9 and a cell 7b for containing electrical parts which is placed in between these cells 7a as shown in Figs. 2 and 3. The whole bottom of the electrical part cell 7b is closed with a blind cap 7c as shown in Fig. 3 so that gas flows only through the cells 7a positioned on the opposite sides of the module insulating air duct 7. A semiconductor cooling air duct 12 is formed by piling up the modules 6 so as to allow the cells 7a to communicate with each other. Reference numeral 13 designates an insulating air duct for introducing gas into a module 6, and which supports the modules 6 piled up and at the same time, insulates current flowing through the modules 6. Reference numeral 14 designates a blow-off air duct for conducting the gas passing through the modules 6 to the cooler 4. Next, operation of such conventional series flow cooling apparatus as mentioned above will be described. A cooling gas supplied from the blower 5 enters first the lower tank 3, and the cooling gas is introduced to the cells 7a of each module 6 through the insulating air duct 13. In this case, the gas passes through only the cells 7a of each module 6, i.e., the semiconductor cooling air duct 12, during this passage, the gas moves upwardly while absorbing heat produced by the thyristor elements 8 and is collected in the blow-off air duct 14. Accordingly, the cooling gas on this occasion rises in temperature by such a quantity which is determined by thermal capacity, air flow and total calorific value. The gas of such increased temperature is subjected to heat exchange by means of the open air at the time when the gas passes through the cooler 4, whereby the gas is again cooled, and then circulation of such gas is again repeated from the blower 5. Fig. 4 is a graphical representation illustrating cooling characteristics of module portions in the course of circulation of such cooling gas wherein the modules 6 are piled up in series in eight stages to form a column, and two of such columns are disposed in parallel to each other. In the graph, the position of stage of the respective modules 6 is plotted as abscissa and velocity of flow as well as rise in temperature as ordinates, respectively, wherein symbol VD designates flow velocity in the front of a fin, VF flow velocity in a fin, Tg temperature rise of the gas, and TSCR temperature rise of a thyristor element junction, respectively. As apparent from Fig. 4, in such a conventional series flow system, the flow velocity VD in the front of a fin and the flow velocity VF in a fin are substantially constant, so that temperatures rise with a constant gradient in respect of the temperature rise Tg of gas and the temperature rise TSCR of a thyristor element junction. For example, there is a temperature difference of about 8 deg. between the temperatures of thyristor element junctions in the first and eighth modules. Accordingly, the temperatures of thyristor element junctions vary so that electrical characteristics of, the thyristor elements are adversely affected. SUMMARY OF THE INVENTION The present invention has been made to eliminate disadvantages of such a conventional apparatus as mentioned above and an object of the invention is to provide a series-parallel flow cooling apparatus having both advantages in series and parallel flow systems and obtained by combining a construction of series flow system with that of parallel flow system wherein a by-pass air duct provided with an inlet in a prescribed position is disposed in addition to a semiconductor cooling air duct, whereby temperatures of thyristor element junctions are uniformalized, its cooling air flow is minimized, and reduction for power of auxiliary machineries is intended. Other objects and advantages of the present invention will become apparent from the description of the following preferred embodiment by referring to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an elevational view showing a conventional series flow cooling apparatus; Fig. 2 is a perspective view showing a conventional module insulating air duct; Fig. 3 is a perspective view showing the bottom of the module insulating air duct in Fig. 2; Fig. 4 is a graphical representation illustrating cooling characteristics of the conventional series flow cooling apparatus; Fig. 5 is an elevational view showing an embodiment of the series-parallel flow cooling apparatus according to the present invention; Figs. 6 and 7 are perspective views each showing the bottom of a module insulating air duct according to the present invention; Fig. 8 is a perspective view showing a throttle plate utilized for the module insulating air duct of the invention; ; Figs. 9 and 10 are perspective views each showing the module insulating air duct of the invention being provided with gas inlets; Fig. 11 is a graphical representation illustrating cooling characteristics of the series-parallel flow cooling apparatus in accordance with the present invention; and Fig. 12 is a graphical representation illustrating characteristic curves of a blower utilized in the apparatus of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described hereinbelow by referring to Figs. 5 - 12 wherein the same parts with those of Figs. 1 - 4 are designated by the same reference numerals. Module insulating air ducts 7 placed on from the 6th. stage to the 8th. stage in the present embodiment are identical to conventional ones, whilst module insulating air ducts placed on from the 1st. to the 5th stages are ones each of which is formed, as shown in the perspective view of Fig. 6, in such that, for example, a rectangular opening 7d is defined on a blind cap 7c of a conventional module insulating air -'duct 7 in the central part thereof so that a cooling gas can circulate through cells 7a and an air duct cell 7e. Reference numeral 15 designates a by-pass air duct which is formed by piling up modules 6 so as to allow air duct cells 7d to communicate with each other, and the by-pass air duct 15 communicates with a lower tank 3. A throttle plate 16 is attached to the 1st. module 6-ll) and which regulates flow rate balance of the cooling gas. The throttle plate 16 involves an opening 16a having a shape corresponding to that of the rectangular opening 7d of the blind cap 7c as shown in, for example, Figs. 7 and 8. Circular holes 7h and 16b are bored in the blind cap 7c and the throttle plate 16 in their respective corresponding positions to each other. Then, the throttle plate 16 is attached to the blind cap 7c by means of bolts, nuts and the like through the circular holes 7h and 16b, respectively, so that area of the rectangular opening 7d is adjusted to a suitable opening area. Gas inlets 17 are defined on the side wall of the by-pass air duct 15 in a position corresponding to a prescribed#position of the module 6 (the module in the 5th. stage in this embodiment) and which are for supplying a cold gas fed from-the lower tank 3 to a semiconductor cooling air duct 12 corresponding to the modules from the 6th stage on through the by-pass air duct 15. The gas inlets 17 are defined on the side walls of an air duct cell 7e of a module insulating air duct 7 in a prescribed stage as shown in Figs. 9 and 10, and the gas inlets permit the central air duct cell 7e to communicate with the cells 7a positioned on the right and left sides of the air duct cell 7e. Next, operation of the series-parallel flow cooling apparatus according to the present invention will be described hereinbelow. The cooling gas which was supplied from the blower 5 and has been in the lower tank 3 is separated into a component which passes through the insulating air duct 13 and then flows into the semiconductor cooling air duct 12 through the cells 7a of each module 6 and the other component which flows into the by-pass air duct 15 disposed in the central part of the tank. In this case, temperature of the cooling gas passing through the semiconductor cooling air duct 12 rises with upward movement thereof, because of heat generation of the thyristor elements 9 contained in the cells 7a, whilst the cooling gas passing through the by-pass air duct 15 accompanies no rise in temperature, more specifically, this cooling gas is never heated until the gas flows into the cells 7a of the module 6 through the gas inlets 17 defined on the side wall of the module 6-(5) in the 5th. stage in the present embodiment so that such gas described above is supplied to the semiconductor cooling air duct 12 corresponding to the modules 6 from the 6th. stage on while keeping the gas cold. Accordingly, the cold gas supplied from the by-pass air duct 15 through the gas inlets 17 flows together with the gas heated which has passed through the semiconductor cooling air duct 12 composed of the modules 6 below the 5th. stages into the cells 7a of the modules 6-(6) from the 6th. stage on so that thermal resistance of cooling fins 9 becomes small. As the result, the junction temperature of thyristor elements decreases Fig. 11 is a graphical representation illustrating cooling characteristics of the module part in the course of circulation of such cooling gas as mentioned above. In the modules from the lst stage 6-(1) to the 5th. stage 6-(5), since flow rate of the cooling gas supplied to the cells 7a decreases by the amount of flow rate of the gas passing through the by-pass air duct 15, values of a flow velocity VD in the front of a fin and a flow velocity VF in a fin become small. Because of influence of such phenomenon as mentioned above, a temperature rise TSCR of a thyristor element is about 5 deg. higher than that of a conventional one. However, since cold gas is again supplied through the gas inlets 17 at the modules from the 6th. stage 6-(6) on, flow velocity increases so that the cooling characteristics of temperature rise TSCR of the thyristor element junctions become similar to those of a conventional series flow system. As is apparent from Fig. 11, the temperature rise TSCR of thyristor element junction indicates substantially uniform distribution of temperature over the modules from the 1st. stage 6-(1) to the 8th. stage 6-(8). Under the circumstances, it is important to take flow rate balance between the gases passing through the modules 6 as well as the by-pass air duct 15, respectively, into consideration in case of the series-parallel flow system according to the present invention. As a means for adjusting such balance of pressure loss, it is effective to provide the aforesaid throttle plates 16 or to regulate opening area of the gas inlets 17. Fig. 12 is a graphical representation illustrating characteristic curves which are obtained by comparing a conventional series flow system with the series-parallel flow system according to the present invention with the use of blowers having identical performance with each other wherein numeral 18 designates Q-H curve, 19 pressure loss characteristic curve of the conventional series flow system, and 20 pressure loss characteristic curve of the seriesparallel flow system according to the present invention, respectively. In case of the present series-parallel flow system, as a result of actual measurement or the like, pressure loss is smaller by AH than that of-the conventional series flow system shown in Fig. 1 so that flow rate of the blower 5 increases by AQ. For instance, the minimum flow rate required is represented by Q1, and if only cooling gas is supplied with the flow rate Q1, it is possible to previously reduce power of the blower 5 by such increment EQ Namely, power in case of a conventional series flow system is given by the following equation: EMI11.1 On the other hand, if the minimum flow rate required is represented by Q11 power in case of the present seriesparallel flow system is as follows: : EMI12.1 and as a result, reduction , reductlon EMI12.2 (KW) is attained. In this connection, if it is not intended to particularly reduce power of the blower 5, temperature rise TSCR of the thyristor element junction comes to be lower by an amount corresponding to the increment AQ of flow rate. As described above, a construction of series flow system is combined with that of parallel flow system, and a by-pass air duct provided with an inlet in a prescribed position is disposed in addition to a semiconductor cooling air duct for cooling semiconductors such as thyristors and the like in the series-parallel flow cooling apparatus according to the present invention. As the result, the series-parallel flow cooling apparatus of the invention has very excellent advantages such as uniformalization of temperatures of thyristor element junctions, improvement of electrical characteristics, minimization of cooling air flow, reduction of power, elevation of cooling efficiency and the like. Although the specific case of cooling thyristor elements has been described in the above embodiment, the present invention is, of course, applicable for any types of semiconductor which must be cooled. Furthermore, any construction can be applied to the rectangular opening of module insulating air duct and the throttle plate so far as they can effectively regulate the flow rate balance.

Claims: WHAT IS CLAIMED IS: 1. A series-parallel flow cooling apparatus comprising: a tank provided with a feed port and an exhaust port for circulating a cooling gas; a plurality of modules being aligned vertically in said tank and involving semiconductors such as thyristor elements and the like; a semiconductor cooling air duct communicating with said modules and allowing said gas to flow thereinto to effect cooling of said semiconductors; a by-pass air duct being formed so as to communicate with said modules and communicating with said feed port for gas in said tank; and gas inlets each of which is defined on a side wall of said by-pass air duct being composed of said modules in a prescribed position and replenishing a fresh cooling gas supplied from said feed port into said semiconductor cooling air duct. 2. A series-parallel flow cooling apparatus as claimed in claim 1, wherein an opening is defined on a blind cap in the central part of a module insulating air duct of said module. 3. A series-parallel flow cooling apparatus as claimed in claim 2, wherein a throttle plate having an opening of a shape corresponding to that of the opening of said blind cap is disposed on the lower part of said module in order that area of the opening of said blind cap is regulated to obtain a suitable opening area. 4. A series-parallel flow cooling apparatus as claimed in claim 1, wherein said gas inlet is defined in such that a central air duct cell is permitted to communicate with cells formed on opposite sides thereof.

Inventors: MATSUMURA, SUSUMU KANSAI ELECTRIC POWER CO., INC., NITTA, TOHEI C/O MITSUBISHI DENKI K.K., TAKAHASHI, NOBUYOSHI C/O MITSUBISHI DENKI K.K., TAKAHASHI, YASUHIDE C/O MITSUBISHI DENKI K.K.
Applicants: MATSUMURA, SUSUMU, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1983
Main classification: H05K7
IPC codes: F25D1, H01L23, H05K7