In a steady-state performance of a salient-pole synchronous machine, the hottest part in the rotor is usually the rotor winding. Any kind of improvement of the cooling effectiveness of the rotor winding contributes to its longer lifespan and increased power/cost ratio in its design and manufacturing. The idea of this invention is to improve the cooling ability of the both wound-type and flat-copper rotor windings by the use of a diamond-based insulation by replacing the paper and polyester-laminate insulation materials that have the main role of electrical insulators. Both of the rotor constructions considered here are represented in
Insulation paper is also applied in the stator slot of electrical machines as ground wall insulation.
The analysis is performed on a salient-pole synchronous machine with wound-type rotor winding with nominal power of Pn=15 MW and voltage Vn=11 kV. At a nominal steady state condition, the measured average temperature of the rotor winding is tmeas=88.8° C. The same operational point is simulated using the thermal-network method and the calculated average temperature is tcalc=93.8° C. The paper sheet between the winding and the aluminium support has thickness of 0.5 mm and all other aforementioned paper layers are 0.72 mm thick. The presumed value of the thermal conductivity of the paper material is kpaper=0.3 [W/m·K]. Just for comparison, the thermal conductivity of the aluminium is kAl=215 [W/m·K], and of the winding kw_across=2.8 [W/m·K] across the conductors and kw_along=333 [W/m·K] along the conductors. The rotor core has thermal conductivity of krc_rad=30 [W/m·K] in radial direction and krc_ax=8 [W/m·K] in axial direction. It is obvious that the paper insulation has tens to hundreds of times lower thermal conductivity than all other materials, and an increase of its value can greatly improve the cooling of the rotor.
The thermal conductivity of the paper insulation could be increased if the paper material is either enriched or fully substituted by a material with higher thermal conductivity. A diamond material will be the right choice because besides the high thermal conductivity, it also acts as an excellent electrical insulator and has good mechanical properties. The thermal conductivity of the diamond is kdiamond=2200 [W/mK], that is even more than 7000 times higher than the paper material. We can conclude that if the paper insulation layer contains a certain amount of diamond-based material, its thermal conductivity will be significantly increased. In order to examine its positive effect on the cooling of the rotor winding, we can gradually increase the thermal conductivity of the paper material up to the value of a pure diamond, and for each value, the average temperature of the rotor winding is calculated. The calculations of the temperatures are summarized in Table. 1. The first row in Table 1 contains the original value of the thermal conductivity and the calculated average temperature of the rotor. After that, all the calculations are repeated for 2, 5, 10, 100 times increased thermal conductivity, and the last calculation is for using a pure diamond material instead of paper material. We can notice that by increasing the thermal conductivity of the paper insulation layer the average temperature of the rotor is significantly reduced, with maximum reduction of 6.8K if a pure diamond is used. However, the largest benefit is achieved when the thermal conductivity is increased only few times. If the thermal conductivity approaches the value of a pure diamond, the benefit is not any more emphasized that much because the overall thermal conduction is limited by the other materials. This conclusion eliminates the need of using pure diamond material if it does not represent a cost-effective solution.
We have not seen any limiting prior art for diamond enriched paper before this application. This means that both flake shaped diamond particles (significantly larger dimensions parallel with the paper surface) and diamond powder with any size—including diamond nanoparticles—of any shape could be applied in the diamond enriched paper patent. The most likely best solution would be to use “large” flake shaped diamond particles, parallel with the surface of the paper mixed into its material and also to use small micro and nano-diamond powder as filling material in the paper-diamond material mixture.
A special case could be a mixture of “large”—bigger than the width of the paper—diamond particles mixed into the paper which would penetrate through the paper surface on both of its sides creating tiny thermal bridges (thermal short circuit) and electrical separators between the copper on one side and the pole shoe on the other. Such thermal bridge creating “rough diamond” paper would require special manufacturing instructions to avoid unnecessary damage to the winding insulation, but it could provide extreme cooling abilities for the rotor winding and/or stator slot wall insulation.
Diamond enriched insulation papers have not existed before this invention. In the proposed structure the diamond particles are held in place by the fibrous substance of the paper itself, without the need of a holding matrix material by default.
Insulation papers for example those consisting of Nomex material have an important high thermal insulation property which is utilized in many applications. In electrical machines the thermal insulation is a disadvantage. Mixing diamond the best solid thermal conductor material into a paper made of thermally insulating fibrous insulation material like Nomex is an unprecedented innovative solution because while it destroys an important property of the insulator, the excellent thermal insulation it benefits the electrical insulation application. Also, contrary to prior art, the diamond particles are maintained in the paper without the need of a solid holding matrix material, as the paper consisting of fibrous substance can hold the diamond particles in place. The addition of any “glue” is not required for the whole volume just a part of it in order to maintain the flexibility of the paper while increasing somewhat the cohesion. When the paper is attached to another carrier, the “gluing” to that surface would also increase the cohesion of the paper.
Number | Date | Country | Kind |
---|---|---|---|
LU100876 | Jul 2018 | LU | national |
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/FI2019/050558 | 7/24/2019 | WO | 00 |