The present invention relates to a rotating machine; and, more particularly, the invention relates to a rotating machine having a rotor winding assembly in which a direct cooling system is employed.
In a rotating machine of the type used in electric power generation equipment in which a gas turbine and a steam turbine are adopted as a drive source, in order to reduce an increase in temperature of a rotor winding during electric power generation, a direct cooling system has been employed widely. In such a direct cooling system for a rotating machine, a cooling gas is brought into direct contact with a winding conductor which constitutes the rotor winding for cooling the winding conductor. Among the known direct cooling systems for rotating machines, Japanese application patent publication No. Hei 5-48058 discloses a radial flow cooling system for a rotating machine which has characteristics such that the structure thereof is constituted simply and heat exchange is carried out with a high efficiency.
The construction of a radial flow cooling system for a rotating machine has, in association with a slot for receiving a rotor winding, another slot, which is a sub-slot, for carrying cooling gas. The sub-slot has a different shape than that of the rotor winding slot and is formed to extend in an axial direction of the rotor. A cooling gas is supplied to the sub-slot from an end portion of the rotor, and the cooling gas first flows in an axial direction and then flows through ventilation holes in a radial direction of the rotor. The cooling gas passes through the ventilation holes which are formed in the rotor winding and goes through a ventilation hole of a creepage block serving as an insulation member and a ventilation hole of a wedge for fixing the rotor winding. The gas is then discharged to a gap which is formed between the rotor and the stator. In the course of passing through the rotor winding in this way, the rotor is cooled.
In the rotor winding, the winding conductor is laminated with plural turns stacked in the radial direction of the rotor, and by applying electricity thereto, a magnetic flux which is proportional to the number of turns of the winding conductor is generated. The winding conductor has the same cross-sectional shape for all of the turns and the abovestated various ventilation holes are provided with the same shape.
Herein, recently, much of the electric power equipment has been constructed to accommodate an increase in electric power demand; however, there is still a need to increase the generator capacity to a required level. With an increase in the generator capacity and with the same constitution as that of the conventional rotating machine, since it is required to have an even larger current and voltage, there a big problem concerning provision of ways to restrain the temperature rise in an interior portion of the generator. When the generator capacity becomes large, a direct cooling system is adopted; and, in such a direct cooling system, the heat exchange is carried out directly between the cooling gas and the rotor winding, namely, the above stated radial flow system is employed in the generator.
A generator which employs a radial flow system is constituted as shown in FIG. 5, and a temperature rise in the generator can be restrained with the use of such a system. Namely, the generator has an air ventilation passage in which a cooling gas (air) is pressurized using fans 2, which are installed at both end portions of a rotor iron core 1, and the cooling gas passes through a space between the rotor iron core 1 and a stator iron core 3 and then is returned again to the fan 2. In the course of its flow through the air ventilation passage, the cooling gas passes through a cooling means 4, which is provided in the air ventilation passage and carries out the required heat exchange to provide cooling, so that a temperature rise in the generator can be restrained.
The construction of the rotor iron core 1 of the radial flow system is shown in FIG. 6. As shown in FIG. 6, the rotor iron core 1 is constituted mainly of plural coil slots 5, which are formed near an outer peripheral face in the axial direction of the rotor iron core 1 and are disposed with a predetermined spacing in a circumferential direction of the rotor iron core 1. A rotor winding 7 is received in each of the coil slots 5, and the bottom of each coil slot 5 communicates with a sub-slot 6 which has a narrower width than the coil slot 5. The rotor iron core 1 has wedges 8 for fixing the rotor windings 7 in the coil slots 5 against the centrifugal force produced by a rotation of the generator, and creepage blocks 9 are provided for insulating between the wedges 8 and the rotor windings 7.
After a part of the cooling air 11 pressurized by the fan 2 has entered the sub-slot 6 from an end portion of the rotor, the cooling air 11 flowing into the sub-slot 6 is branched to plural air ventilation holes 10 (10a, 10b, 10c) which are spaced apart in the axial direction of the rotor winding 7. The respective branches of cooling air 11 flow in the holes 10 through the rotor winding 7 in the radial direction of the rotor and pass into an air gap which is formed between the rotor iron core 1 and the stator iron core 3 through the air ventilation hole 10c provided in the creepage block 9 and the air ventilation hole 10b provided in the wedge 8. The discharged cooling air 11 flows in the stator iron core 3 toward an outer peripheral side of the stator iron core 3 in a radial direction, and after the cooling air 11 is cooled by a cooling means 4, the cooling gas returns to the air input side of the fan 2.
When the above-stated radial flow system is intended to be used for cooling a larger capacity generator than the conventional generator, for example, as stated in Japanese application patent laid-open publication No. Hei 9-2850-52, it is important to set the shape or dimension of the air ventilation hole 10a formed in a rotor winging 7 so as to significantly reduce the air ventilation resistance of the air ventilation passage through the rotor winding 7 from the sub-slot 6, if the cooling efficiency of the generator is to be increased.
However, even when the shape of the air ventilation hole 10a provided on the rotor winding 7 is changed or the cross-sectional area of the air ventilation hole is made large, there are restrictions on such changes in the shape of the air ventilation hole 10b provided in the wedge 8 and the cross-sectional area of the air ventilation hole 10b based on the strength of the wedge 8. The wedge 8 is provided to prevent the rotor winding 7 from flying out of the coil slot 5 of the rotor in response to a strong centrifugal force, so that the wedge 8 must maintain some minimum degree of strength. Accordingly, there is a limitation on the size and shape of the hole 10b of the air ventilation passage, which in turn places a limitation on the amount of cooling air which can pass through the rotor winding 7 from the sub-slot 6.
FIG. 7 shows the shape of the wedge 8. As shown in FIG. 7, the air ventilation hole 10b formed in the wedge 8 has a round circular shape, and the interval between adjacent air ventilation holes 10b is maintained in consideration of the strength aspect of the wedge 8.
The limitation on the size and shape of the air ventilation passage in which the cooling air passes through the rotor winding 7 from the sub-slot 6 and flows into the air gap between the rotor and the stator will be discussed with reference to FIG. 8. FIG. 8 is a view showing a condition in which the rotor winding 7 is received in the coil slot 5 and showing the air ventilation hole 10a of the rotor winding 7 and the air ventilation hole 10c of the creepage block 9, as viewed from the air ventilation hole 10b provided in the wedge 8. As shown in FIG. 8, the shape of the air ventilation hole 10b provided in the wedge 8 is round, however the air ventilation hole 10a provided in the rotor winding 7 has an elliptical shape; accordingly, the shape (ellipse) of the air ventilation hole 10a differs from the shape (circular) of the air ventilation hole 10b.
Regarding the creepage block 9, to maintain an insulating condition between the wedge 8, which is made of a metal material, and the rotor winding 7 to which the current flows and, in addition, to provide sufficient strength to withstand the strong centrifugal force produced by the rotation of the generator, there is a restriction on the size and shape of the air ventilation hole 10c provided in the creepage block 9, similar to the limitation provided on the air ventilation hole 10b in the wedge 8. Further, to maintain the insulating condition between both metal members, the creepage block 9 must be formed to have some degree of thickness and also must be also to maintain some degree of creepage distance.
Further, in the case of a radial flow system, the air ventilation hole 10b provided in the rotor winding 7 is arranged to extend radially relative to the rotating shaft of the generator However, as shown in FIG. 8, the air ventilation hole 10b of the wedge 8 and the air ventilation hole 10a of the rotor winding 7 are not necessarily coincident. With the creepage block 9 being positioned between the wedge 8 and the rotor winding 7, by providing for smooth communication of air through the air ventilation holes 10a of the rotor winding 7 and the air ventilation hole 10b of the wedge 9, the air ventilation loss can be reduced.
For example, a technique is known wherein, to the rotor winding side of the creepage block 9, one axial direction air ventilation groove is formed. However, by this conventional technique of providing one axial direction air ventilation groove in the creepage block 9, the contact area between the rotor winding 7 and the creepage block 9 becomes small; and, since the pressure due to the centrifugal force of the generator acts relatively largely on the creepage block 9, it is necessary to set the groove width of the air ventilation groove of the creepage block 9 to ensure that the creepage block 9 will be crushed.