Electromagnetic induction device

Abstract: An electromagnetic induction device has coils (2) of a plurality of phases and a duct (6) through which a cooling medium is introduced into the coils to cool these coils. Guides (7A, 7B) are provided in the duct (6) so as to realize a substantially uniform distribution of the cooling medium to all coils (2). The flow rates of the cooling medium through the coils (2) is substantially uniformalized so that the coils (2) exhibit substantially the same temperature rise. As a consequence, any difference in the life between the coils (2) is substantially eliminated.

Description: The present invention relates to an electromagnetic induction device comprising a tank a plurality of coils and a cooling medium cooling said coils. a duct defined in said tank for introducing said cooling medium into said coils. Such a device is known from DE-A-3341 626. Fig. 3 of the accompanying drawings is a schematic sectional view of a 3-phase electromagnetic induction device as an example of conventional electromagnetic induction devices. Referring to this Figure, a tank 1 accommodates coils 2A, 2B and 2C of A, B and C phases which form major part of the electromagnetic induction device and which are illustrated schematically. These coils 2A, 2B and 2C will also be collectively referred to as coils 2. One end of a lower coolant pipe 3 is connected to and open in a lower portion of the tank 1 so as to introduce a flow of a coolant to a space under the electromagnetic induction device. Upper coolant pipes 4, each connected at its one end to a cooler (not shown), are connected at its other end to a top wall of the tank 1. A coolant duct 8 is defined between the bottom wall of the tank 1 and a partition plate 5 which extends across a lower portion of the tank. The partition plate 5 has openings which provides coolant inlets 5A, 5B and 5C for introducing the coolant to the coils 2A, 2B and 2C of the respective phases. In this known electromagnetic induction device, a flow of a coolant produced by a blower is supplied into the coolant duct 8 through the lower coolant pipe 3 and is then introduced, as indicated by arrows, into the coils 2A, 2B and 2C of the respective phases through the coolant inlets 5A, 5B and 5C formed in the partition plate 5, thereby to cool these coils 2A, 2B and 2C. The coolant after cooling the coils 2A, 2B and 2C is then introduced into the cooler through the upper coolant pipes 4. Thus, the flow of the coolant is forced by a blower into the coolant duct 8. Thus, the flow of the coolant is distributed to the coils 2A, 2B and 2C. In the distributed coolant flow from the coolant duct 8 to respective coils 2A,2B and 2C, a deceleration caused by flow distribution of the coolant acts as a pressure build-up in the coolant, and the pipe frictional resistance causes a pressure drop in the coolant. As a consequence, the coolant is distributed to the coils 2 unevenly such that the flow rate is smallest in the coil 2A of the phase A nearest to the lower coolant pipe 3 and greatest in the coil 2C of the phase C remotest from the lower coolant pipe 3. The uneven distribution of the coolant to the coils 2A, 2B and 2C causes a difference in the rate of convey of heat from these coils to the cooler. Consequently, the coil 2A of the phase A in which the coolant flow rate is smallest may exhibit a temperature rise to a level exceeding the rated temperature. This promotes deterioration of the insulating material forming the coils 2 to shorten the life of the electromagnetic induction device. DE-3341626 shows a transformer with a duct for supplying cooling air to a plurality of coils. Uniform airflow in each coil is achieved by varying the diameter of the duct and the connecting channels to each coil. FR-A-1291617 shows using baffle plates to reduce variation of flow rate in different channels of a car radiator. Accordingly, an object of the present invention is to provide an electromagnetic induction device in which the flow rates of the coolant in the coils of all phases are equalized to ensure a uniform temperature rise of these coils, with a relatively simple construction. According to the invention, there is provided an electromagnetic induction device, comprising: (a) a tank, (b) a partition plate extending across a lower portion of the tank and defining, with a bottom wall and side walls of the tank, a coolant duct of uniform cross-section, (c) a plurality of coils disposed within the tank, (d) a plurality of coolant inlets individually defined in the partition plate below the respective coils, for introducing coolant into said coils, (e) a coolant duct inlet at one end of the duct, (f) outlet means in an upper portion of the tank, and (g) at least two baffle plates one of which is disposed in every region between adjacent coolant inlets and extending into the duct, said baffle plates having different surface areas, the areas increasing with distance from the coolant duct inlet, to establish a substantially uniform distribution of coolant to the respective coils, wherein said baffle plates are provided on the upper wall of said duct. For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made by way of example to the accompanying drawings, in which: Fig. 1 is a schematic sectional view of an electromagnetic induction device in accordance with an embodiment of the present invention; Fig. 2 is a graph showing the flow rates of a coolant distributed to coils of respective phases of the electromagnetic induction device shown in Fig. 1; Fig. 3 is a schematic sectional view of a conventional electromagnetic induction device; and Fig. 4 is a graph showing the flow rates of a coolant distributed to coils of respective phases of the conventional electromagnetic induction device shown in Fig. 3. The invention will be more fully understood from the following description of the preferred embodiment. Fig. 1 is a schematic sectional view showing an embodiment of the electromagnetic induction device of the present invention. In this figure, the same reference numerals are used to denote the same parts or members as those appearing in Fig. 3 showing the conventional device, and detailed description of such parts or members is omitted. A coolant duct 6 is defined between the bottom wall of a tank and a partition plate 5 which separates the duct 6 from the space accommodating the coils 2. A coolant which is preferably an insulating gas such as SF₆ gas for cooling the coils 2A, 2B and 2C of the respective phases is forced by a blower into the cooling duct 6. The partition plate 5 is provided at its portions between the coolant inlets 5C and 5B and between the coolant inlets 5B and 5A with flow-rate regulating guides 7A and 7B. Although not exclusive, the flow rate regulating guides 7A, 7B may be baffle plates as illustrated. The dimensions or projecting lengths of the flow rate regulating guides are determined to realize a uniform distribution of the coolant to the coils 2. More specifically, the dimension of the flow rate regulating guide 7A is determined such that about one third (1/3) of the coolant supplied by the blower is introduced into the coil 2A of the phase A through the coolant inlet 5A, while two thirds (2/3) of the same are directed to the coils 2B and 2C of the phases B and C. Similarly, the dimension of the flow rate regulating guide 7B between the coolant inlets 5B and 5C is so determined that half (1/2) the amount of coolant which has passed over the flow rate regulating guide 7A, i.e., one third (1/3) of the total amount supplied by the blower, is introduced into the coil 2B through the coolant inlet 5B and the remaining half, i.e., one third (1/3) of the total amount is introduced into the coil 2C through the coolant inlet 5C. Thus, in the electromagnetic induction device of the present invention, the flow rate regulating guides 7A, 7B provided in the coolant duct 6 function as flow resistors which impose resistance to the flow of the coolant, so as to enable the coolant to be supplied substantially uniformly into the coils 2A, 2B and 2C, as will be seen from Fig. 2. Consequently, difference in temperature between the coils 2A, 2Band 2C of the respective phases is substantially eliminated . In the illustrated embodiment, the flow rate regulating guides 7A and 7B are attached to the partition plate 5 which forms upper wall of the duct 6. This, however, is only illustrative and the flow rate regulating guides may be provided at any suitable positions where they can realize the substantially uniform distribution of the coolant, e.g., on the bottom wall of the tank 1 facing the duct 6. As will be understood from the foregoing description, in the electromagnetic induction device of the present invention, flow rate regulating means are provided to realize a substantially uniform distribution of the coolant to the coils of the respective phases, by virtue of the flow rate regulating guides provided in the coolant duct. As a result, all the coils exhibit substantially the same temperature rise, thus contributing to prolongation of the life of the device.

Claims: An electromagnetic induction device, comprising: (a) a tank (1), (b) a partition plate (5) extending across a lower portion of the tank and defining, with a bottom wall and side walls of the tank, a coolant duct (6) of uniform cross-section, (c) a plurality of coils (2A, 2B, 2C) disposed within the tank, (d) a plurality of coolant inlets (5A, 5B, 5C) individually defined in the partition plate below the respective coils, for introducing coolant into said coils, (e) a coolant duct inlet (3) at one end of the duct, (f) outlet means (4) in an upper portion of the tank, and (g) at least two baffle plates (7A, 7B) one of which is disposed in every region between adjacent coolant inlets and extending into the duct, said baffle plates having different surface areas, the areas increasing with distance from the coolant duct inlet, to establish a substantially uniform distribution of coolant to the respective coils, wherein said baffle plates are provided on the upper wall of said duct. An electromagnetic induction device according to claim 1 wherein said cooling medium is sulfur hexafluoride.

Inventors: YOSHIKAWA TORU C O MITSUBISHI, YOSHIKAWA, TORU, C/O MITSUBISHI DENKI K.K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1991
Main classification: H01F27
IPC codes: H01F27