Insulating-liquid immersed electrical machine

Abstract: An insulating liquid immersed electrical machine com­ prises a hermetically sealed tank (1) containing the electric­ al machine (4) and insulating liquid (5) arranged between the electrical machine (4) and the tank (1). The tank (1) includes deformable means (72) through which gas and liquid cannot pass and whose shape is variable so that the volume receiving the insulating liquid (5) between the tank (1) and the electrical machine (4) is variable. The insulating liquid (5) completely fills the receiving volume in the tank (1). Pressurizing means (7, 73) are provided for adjusting the shape of the deformable means (72) so that the pressure of the insulating liquid (5) in the tank (1) is kept at a suitable degree for preventing the insulating liquid (5) from vaporizing.

Description: The present invention relates to an electrical machine which is immersed in non-flammable insulating liquid for cooling the electrical machine and for increasing insulating strength in the electrical machine. A prior art insulating-liquid immersed inductor comprises, as shown in JP-A-63-241909, an inductor body including an iron core and a coil, and a hermetically sealed tank in which the inductor body is arranged, non-flammable insulating-liquid fills a part of a space between the inductor body and the hermetically sealed tank to immerse the inductor body therein, and the other part of the space is filled by pressurized insulating gas. A part of the pressurized insulating gas is absorbed in the non-flammable insulating-liquid so that the volume of the pressurized insulating gas decreases in the tank. In the above prior art insulating-liquid immersed inductor, when the pressure in the hermetically sealed tank is decreased according to the decrease of temperature in the tank, the absorbed insulating gas returns to gas, so that the insulating-liquid includes a great number of bubbles therein. The bubbles of the insulating gas cause the insulating strength to decrease in the inductor, because the insulating strength of the insulating gas is lower than that of the insulating liquid between the coated wires of the inductor. JP-A-61-128506 discloses an insulating-liquid immersed electrical machine with the features included in the first part of claim 1. The known apparatus employs oil as the insulating liquid which is pressurised above atmospheric to increase the insulating property of the oil. OBJECT AND SUMMARY OF THE INVENTION It is an object of the present invention to provide an insulating-liquid immersed electrical machine in which the insulating-liquid does not include or absorb gas and is prevented from vaporising. This object is met by the invention as defined in claim 1. In the insulating-liquid immersed electrical machine according to the invention, the pressurizing means for adjusting the shape of the deformable means ensures that the pressure of the perfluorocarbon insulating-liquid in the tank is kept at a suitable degree for preventing the perfluorocarbon insulating-liquid from vaporizing, whereby the perfluorocarbon insulating-liquid does not vaporize even when the receiving volume is changed. Therefore, gas bubbles decreasing insulating strength in the electrical machine are not generated in the perfluorocarbon insulating-liquid. Fig. 1 is a partially cross-sectional view showing an embodiment of the insulating-liquid immersed electrical machine according to the present invention. Fig. 2 is a schematic cross-sectional view showing a part of a coil used in the insulating-liquid immersed electrical machine according to the present invention. Fig. 3 is a diagram showing boiling point characteristics relative to absolute pressure in perfluorocarbon liquid used in the insulating-liquid immersed electrical machine according to the present invention. Figs. 4 and 5 are partially cross-sectional views showing change in shape of deformable means of the insulating-liquid immersed electrical machine according to the present invention, which deformable means is deformed according to change in temperature. Figs. 6 to 10 are partially cross-sectional view showing other embodiments of the insulating-liquid immersed electrical machine according to the present invention. In an embodiment of the insulating-liquid immersed electrical machine according to the present invention, as shown in Fig. 1, an inductor body 4 having an iron core 2 and a coil 3 is contained by a hermetically sealed tank 1. Incombustible and insulating liquid 5 fills a volume between the tank 1 and the inductor body 4 to cool the inductor body 4 and to increase insulating strength in the inductor body 4. The non-flammable liquid 5 is perfluorocarbon liquid whose main component is C₈F₁₆O. The tank 1 contains a radiator 6 for cooling the perfluorocarbon liquid 5 heated by the operation of the inductor body 4. Tank volume adjusting means 7 is arranged at an upper portion of the tank 1 to adjust a volume capable of receiving the perfluorocarbon insulating-liquid 5 for surrounding the inductor body 4 in the tank 1 and to pressurize the perfluorocarbon insulating-liquid 5 to, for example, more than the atmospheric pressure. The tank volume adjusting means 7 has a hermetically sealed cover 71 fixed to the tank 1 and a flexible or deformable member or sheet 72 through which gas and liquid cannot pass, which defines a chamber 73 together with the cover 71 and which defines the tank volume capable of receiving the perfluorocarbon insulating-liquid 5 together with the tank 1. Since the deformable member 72 can deform, the volume capable of receiving the perfluorocarbon insulating-liquid 5 in the tank 1 is changable. Pressurized gas 73 (the chamber 73 and the pressurized gas arranged therein are donated by the identical reference numerals "73" ) is inserted into the chamber 73 to press the deformable member 72 and to adjust the shape of the deformable member 72 so that the tank volume is adjusted according to the volume of the perfluorocarbon insulating-liquid 5 and the perfluorocarbon insulating-liquid 5 in the tank 1 is pressurized to, for example, more than the atmospheric pressure (about 0.1 MPa) and less than 0.3 MPa. The pressure of the gas 73 is determined to set the pressure of the perfluorocarbon insulating-liquid 5 at a suitable degree for preventing the perfluorocarbon insulating-liquid 5 from vaporizing even when the temperature of the perfluorocarbon insulating-liquid 5 is increased by the heat of the inductor body 4 or by the air surrounding the tank 1. The gas 73 may be, for example, atmosphere or insulating gas or inert gas. Since the gas 73 and the perfluorocarbon insulating-liquid 5 cannot pass through the deformable member 72 and the perfluorocarbon insulating liquid 5 fills completely the tank volume capable of receiving the perfluorocarbon insulating-liquid 5 in the tank 1, gas is not included or absorbed by the perfluorocarbon insulating-liquid 5. Therefore, bubbles of the gas are not generated, even when the temperature of the perfluorocarbon insulating-liquid 5 is increased and/or the pressure of the perfluorocarbon insulating-liquid 5 in the tank is decreased. In the structure of the coil 3 as shown in Fig. 2, a passage 32 for the perfluorocarbon insulating-liquid 5 extends radially between coated wires 31 of the coil 3. A width of the insulating liquid passage 32 is indicated by D in Fig. 2. The perfluorocarbon insulating-liquid 5 flows in the passage 32 to cool the inductor body 4 and the temperature of the perfluorocarbon insulating-liquid 5 is increased by the heat generated by the operation of the inductor body 4. The heated perfluorocarbon insulating-liquid 5 flows to the radiator 6 for cooling the perfluorocarbon insulating-liquid 5 so that the temperature of the perfluorocarbon insulating-liquid 5 surrounding the inductor body 4 is kept at a low degree. Therefore, the perfluorocarbon insulating-liquid 5 can cool the inductor body 4 effectively and the insulating characteristic of the perfluorocarbon insulating-liquid 5 is not decreased. Since the perfluorocarbon insulating-liquid 5 is pressurized to, for example, more than 0.1 MPa and less than 0.3 MPa through the deformable member 72 by the pressurized gas 73, the boiling point of the perfluorocarbon insulating-liquid 5 is set at a high degree, as shown in Fig. 3. Therefore, bubbles of vaporized perfluorocarbon insulating-liquid are not generated, for example, in the insulating liquid passage 32 between the coated wires 31 of the coil 3, even when the inductor body 4 begins to operate or even when the electrical current flowing in the coated wires 31 increases rapidly, that is, even when the temperature of the perfluorocarbon insulating-liquid 5 is increased rapidly. In this way, the insulating strength of the perfluorocarbon insulating-liquid 5 is always kept at a high degree. Further, although width D of a prior art insulating liquid passage is about 5 mm, the width D of the insulating liquid passage 32 according to the present invention may be small, for example, less than 2 mm, because the gas is not absorbed by the perfluorocarbon insulating-liquid 5, the bubbles of vaporized perfluorocarbon insulating-liquid are not generated and the kinematic viscosity 0.8 cts of the perfluorocarbon liquid (C₈F₁₆O) is significantly smaller than the kinematic viscosity 7.5 cts of mineral oil. Therefore, the size of the inductor body 4 may be small. If the pressure of the perfluorocarbon insulating liquid 5 and the pressure of the gas 73 is kept between 0.1 MPa and 0.3 MPa, the tank 1 and the cover 71 do not require a special structure for resisting pressure. For the perfluorocarbon insulating-liquid 5, a suitable volume of the chamber 73 defined by the deformable member 72 with the cover 71 is determined as follows. Please refer to Figs. 4 and 5. On the basis of Boyle's and Charles' law, when the surrounding temperature ϑ is -25°C, the volume of the perfluorocarbon insulating-liquid 5 is V L , the volume of the gas 73 is V G , the pressure of the gas 73 is P G , the temperature of the gas 73 is T as shown in Fig. 4, and when the surrounding temperature ϑ is 80°C, the volume of the perfluorocarbon insulating-liquid 5 is V L ′, the volume of the gas 73 is V G ′, the pressure of the gas 73 is P G ′, the temperature of the gas 73 is T′ as shown in Fig. 5, the relations among these parameters are shown by the following formulas (1), (2) and (3) (P G *V G )/T = (P G ′*V G ′)/T V G = X*V L V G ′ = X*V L - V L *β*(ϑ′-ϑ) (X is a rate of V G relative to V L . β is the expansion coefficient of the perfluorocarbon insulating-liquid 5.) When the formulas (2) and (3) are combined with the formula (1) (P G *X*V L )/T = P G ′*V L *{X-β*(ϑ′-ϑ)}/T. X/{X-β*(ϑ′-ϑ)} = (P G ′*T)/(P G *T′) According to the formula (5), when P G is 0.1 MPa, T is 253 (273-20) K, ϑ is -20°C, P G ′ is 0.3 MPa, T′ is 358(273+85) K, ϑ′ is 85°C and β is 15.4*10⁻⁴ (1/°C) X = 0.3 Therefore, the suitable volume of the chamber 73 is 30 percent of the volume of the perfluorocarbon insulating liquid 5, when the surrounding temperature ϑ is -25°C. In this embodiment, the reliability of the insulating strength is improved and the stable insulating characteristic is kept. Further, the size of the coil may be small, the tank does not require the special structure for resisting pressure, and a low-cost insulating-liquid immersed electrical machine can be provided. Another embodiment of the insulating-liquid immersed electrical machine according to the present invention, as shown in Fig. 6, has the tank volume adjusting means 7 including a case 74 which is detachably mounted on the tank 1 and whose inside communicates with the inside of the tank, and a valloon-shaped deformable member 75 whose volume is variable, in which the pressurized gas 73 is inserted to adjust the volume of the balloon-shaped deformable member 75 for pressurizing the perfluorocarbon insulating-liquid 5 and which is contained by the case 74. The gas 73 and the perfluorocarbon insulating-liquid 5 cannot pass through the deformable member 75 and the perfluorocarbon insulating-liquid 5 fills completely a volume capable of receiving the perfluorocarbon insulating-liquid 5 in the tank 1 and the case 74. The case 74 may be arranged at an upper portion of the tank 1 or at a side portion thereof. In this structure, the insulating strength is improved and the size of the insulating-liquid immersed electrical machine may be small during transportation thereof because of the detachable structure of the tank volume adjusting means 7. Another embodiment of the insulating-liquid immersed electrical machine according to the present invention, as shown in Fig. 7, has the tank volume adjusting means 7 including a balloon-shaped deformable member 76 whose outer volume is variable, in which the pressurized gas 73 is inserted to adjust the volume of the balloon-shaped deformable member 75 for pressurizing the perfluorocarbon insulating-liquid 5 at a suitable degree and which is contained by the tank 1. The gas 73 and the perfluorocarbon insulating-liquid 5 cannot pass through the deformable member 75 and the perfluorocarbon insulating-liquid 5 fills completely a volume capable of receiving the perfluorocarbon insulating-liquid 5 surrounding the inductor body 4 in the tank 1. In this structure, the insulating strength is improved, the volume of the perfluorocarbon insulating-liquid 5 filling completely the volume capable of receiving the perfluorocarbon insulating-liquid 5 surrounding the inductor body 4 in the tank 1 may be small, and the volume of the gas 73 also may be small because the required volume of the perfluorocarbon insulating-liquid 5 is small. Therefore, the size of the insulating-liquid immersed electrical machine is small. Another embodiment of the insulating-liquid immersed electrical machine according to the present invention, as shown in Fig. 8, has the structure shown in Fig. 1 and solid insulating members 10 arranged between the inductor body 4 and the tank 1. In this structure, the insulating strength is improved, the volume of the perfluorocarbon insulating-liquid 5 filling completely the volume capable of receiving the perfluorocarbon insulating-liquid 5 surrounding the inductor body 4 in the tank 1 may be small, and the volume of the gas 73 also may be small because the required volume of the perfluorocarbon insulating-liquid 5 is small. Therefore, the size of the insulating-liquid immersed electrical machine is small. Another embodiment of the insulating-liquid immersed electrical machine according to the present invention, as shown in Fig. 9, has the inductor body 4 having the iron core 2 and the coil 3, the hermetically sealed tank 1 containing the inductor body 4 and the radiator 6. Tank volume adjusting means 7 is arranged at an upper portion of the tank 1. The tank volume adjusting means 7 has the deformable member 72 which defines the chamber 73 together with the portion 71 of the tank 1 and which defines the tank volume capable of receiving the perfluorocarbon insulating-liquid 5 together with the tank 1. Pressurized gas is inserted into the chamber 73. The perfluorocarbon insulating-liquid 5 fills completely the tank volume capable of receiving the perfluorocarbon insulating-liquid 5 in the tank 1. The solid insulating members 10 are arranged between the inductor body 4 and the tank 1. A second tank 11 is connected to the chamber 73 through a conduit 13 and a pressure response discharge valve 12 which connects the chamber 73 to the second tank 11 only when the pressure in the chamber 73 increases more than a predetermined degree. The predetermined degree is set less than the resisting pressure strength of the tank 1 or the portion 71 thereof. Therefore, the pressure in the chamber 73 or in the tank 1 is prevented from increasing more than the predetermined degree or the resisting pressure strength of the tank 1, so that the tank 1 is prevented from being destroyed by a pressure greater than the resisting pressure strength of the tank 1. If the deformable member 72 is destroyed, the perfluorocarbon insulating-liquid 5 flows into the second tank 11 so that the perfluorocarbon insulating-liquid 5 does not flow to the outside. The pressure response discharge valve 12 has an electrical switch which cuts off the supply of electric current to the inductor body 4 only when the pressure response discharge valve 12 which connects the chamber 73 to the second tank 11 is activated as stated above. In another embodiment of the insulating-liquid immersed electrical machine according to the present invention, as shown in Fig. 10, the inductor body 4 having the iron core 2 and the coil 3 is contained by the hermetically sealed tank 1. The non-flammable perfluorocarbon insulating-liquid 5 fills the tank volume between the tank 1 and the inductor body 4. The tank 1 contains the radiator 6 for cooling the liquid 5. At least one tank volume adjusting means 7 is arranged at an upper portion of the tank 1 to adjust a volume capable of receiving the perfluorocarbon insulating-liquid 5 for surrounding the inductor body 4 in the tank 5 and to pressurize the perfluorocarbon insulating-liquid 5. The tank volume adjusting means 7 has a bellows 76 which is fixed to the tank 1, through which gas and liquid cannot pass and whose inside communicates with the inside of the tank 1 to define the tank volume capable of receiving the perfluorocarbon insulating-liquid 5 together with the tank 1. Since the bellows 76 can deform to change its internal volume, the volume capable of receiving the perfluorocarbon insulating-liquid 5 in the tank 1 is changable. A spring 78 arranged between the tank 1 and the bellows pressures through a piston plate 77 the bellows 76 to adjust the shape of the bellows 76 so that the tank volume is adjusted according to the volume of the perfluorocarbon insulating-liquid 5 and the perfluorocarbon insulating-liquid 5 in the tank 1 is pressurized to, for example, more than the atmospheric pressure (about 0.1 MPa) and less than 0.3 MPa. The pressing force of the spring 78 is determined to set the pressure of the perfluorocarbon insulating-liquid 5 at a suitable degree for preventing the perfluorocarbon insulating-liquid 5 from vaporizing even when the temperature of the perfluorocarbon insulating-liquid 5 is increased by the heat of the inductor body 4 or by the air surrounding the tank 1. The perfluorocarbon insulating-liquid 5 fills completely the tank volume capable of receiving the perfluorocarbon insulating-liquid 5 in the tank 1. A required volume V for compensating a change in volume of the insulating liquid 5 is determined by a following formula (6) V = β*(ϑ′-ϑ)*V L = 15.4*10⁻⁴*105*V L = 0.16 V L Therefore, an adjustable internal volume of the bellows 76 may be 16 percent of the volume of the perfluorocarbon insulating-liquid 5, so that the size of the insulating-liquid immersed electrical machine may be small.

Claims: An insulating-liquid immersed electrical machine comprising a hermetically sealed tank (1) containing an insulating liquid (5) and the electrical machine (4) immersed therein, wherein the tank (1) includes deformable means (72; 75; 76) through which gas and liquid cannot pass, which together with the tank (1) forms a receiving volume capable of receiving the insulating liquid (5) between the tank (1) and the electrical machine (4) and the shape of which is variable so that the receiving volume is variable, wherein the insulating liquid (5) completely fills the receiving volume in the tank (1), and wherein pressurising means (73; 78) is provided for adjusting the shape of the deformable means (72; 75; 76) so that the pressure of the insulating liquid (5) in the tank (1) is greater than the atmospheric pressure, characterised in that the insulating liquid (5) is perfluorocarbon and the pressurising means (73; 78) is adapted to keep the pressure of the insulating liquid (5) at a suitable degree for preventing it from vaporising. The machine of claim 1, wherein the pressurising means (73) is pressurised gas pressing on the deformable means (72; 75). The machine of claim 1, wherein the pressurising means (78) is a spring pressing on the deformable means (76). The machine of claim 1, wherein the deformable means (72) is a flexible sheet forming the receiving volume with the tank (1). The machine of claim 1, wherein the deformable means (76) is a bellows forming the receiving volume with the tank (1). The machine of claim 1, wherein the deformable means (75) is a balloon-shaped member and the pressurising means (73) is pressurised gas filled therein. The machine of claim 6, wherein the balloon-shaped member (75) is contained in the tank (1). The machine of claim 6, wherein the balloon-shaped member (75) is contained in a case (74) communicating with the tank (1). The machine of claim 2, wherein the pressurised gas is contained in a chamber which is connected to a second tank (11) via a pressure-responsive discharge valve (12) only when the pressure in the tank (1) exceeds a predetermined degree, so that the pressure in the tank (1) is decreased.

Inventors: ENDOO KAORU, NAKATAKE RYOJI, SAKAMOTO TAKESHI, UWANO YOSHITO, ENDOO, KAORU, NAKATAKE, RYOJI, SAKAMOTO, TAKESHI, UWANO, YOSHITO
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1990
Main classification: H01F27
IPC codes: H01F27