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EP-4125189-B1 - COOLING OF ACTIVE ELEMENTS OF ELECTRICAL MACHINES

EP4125189B1EP 4125189 B1EP4125189 B1EP 4125189B1EP-4125189-B1

Inventors

  • URRESTY, JULIO CESAR
  • RAMTAHAL, SADEO
  • SIWAK, Pawel
  • MUÑIZ CASAIS, CESAR

Dates

Publication Date
20260506
Application Date
20210727

Claims (13)

  1. A method (100) for cooling a generator of a direct drive wind turbine, the generator comprising a rotor (210) including a plurality of active rotor elements (212) which are magnetically and/or electrically active, a stator (220) including a plurality of active stator elements (222) which are magnetically and/or electrically active and an air gap (215) separating the active rotor elements (212) and the active stator elements (222), the method (100) comprising: supplying (110) a cooling fluid (140) to the air gap (215) through one or more primary inlets (236) of the electrical machine (200) for cooling the plurality of active elements (212) of the rotor (210) and/or the plurality of active elements (222) of the stator (220) and extracting the cooling fluid from the electrical machine (200) through one or more primary outlets (256) of the electrical machine (200); characterised in that the method further comprises reversing (120) a direction of flow of the cooling fluid (140) such that the cooling fluid (140) is supplied to the air gap (215) through one or more of the primary outlets (256) and extracted from the electrical machine (200) through one or more of the primary inlets (236), wherein the cooling fluid (140) is supplied in a first direction (150) during a first time period, and the cooling fluid (140) is supplied in a second direction (155) during a second time period, the second direction (155) being opposite to the first direction (151), wherein the first (150) and second directions (155) are substantially axial directions (241).
  2. The method of claim 1, wherein reversing (120) comprises reversing the direction of rotation of one or more fluid displacement devices (310, 310') causing the cooling fluid (140) to flow towards the air gap (215) for cooling the air gap (215).
  3. The method of claim 1, wherein reversing (120) comprises selectively fluidly connecting one or more entry cooling conduits (320) for guiding the cooling fluid (140) towards the air gap (215) with one or more exit cooling conduits (330) for guiding the cooling fluid (140) away from the air gap (215).
  4. The method of claim 3, wherein fluidly connecting comprises operating a plurality of valves (350) for redirecting the cooling fluid (140) through additional cooling conduits (340) connecting one or more entry cooling conduits (320) with one or more exit cooling conduits (330).
  5. The method of any of claims 1 - 4, wherein reversing (120) is performed only once during the expected lifetime of the electrical machine (200).
  6. The method of any of claims 1 - 5, wherein reversing (120) is performed when or after a predetermined temperature threshold (360, 365, 370) of one or more active elements is achieved.
  7. The method of any of claims 1 - 6, wherein the cooling fluid (140) is air.
  8. A direct drive wind turbine comprising a generator and a cooling system (300) fluidly connected to the generator (200); wherein the generator (200) comprises a rotor (210) including a plurality of active rotor elements (212) which are magnetically and/or electrically active, a stator (220) comprising a plurality of active stator elements (222) which are magnetically and/or electrically active, and an air gap (215) separating the active rotor elements (212) and the active stator elements (222); wherein the cooling system (300) comprises one or more entry cooling conduits (320) configured to guide a cooling fluid (140) towards the air gap (215), and one or more exit cooling conduits (330) configured to collect and guide the cooling fluid (140) heated in the air gap (215) away from the electrical machine (200); and characterised in that the cooling system (300) is configured to reverse the direction of flow of the cooling fluid (140).
  9. The direct drive wind turbine of claim 8, wherein the cooling system (300) further comprises one or more cooling fluid displacement devices (310, 310') configured to be rotated in two opposite directions for reversing the direction of flow of the cooling fluid (140).
  10. The direct drive wind turbine of claim 9, wherein the one or more cooling fluid displacement devices (310, 310') are one or more fans.
  11. The direct drive wind turbine of claim 8, wherein the cooling system (300) further comprises one or more additional conduits (340) configured to selectively fluidly connect one or more entry conduits (320) and one or more exit conduits (330).
  12. The direct drive wind turbine of claim 11, wherein the cooling system (300) further comprises one or more valves (350) configured to be operated for allowing or impeding the flow of the cooling fluid (140) through one or more additional conduits (340).
  13. The direct drive wind turbine of any of claims 8 - 12, further comprising: one or more temperature sensors configured to measure a temperature (381, 382, 383) of one or more active rotor elements (212) and/or active stator elements (222); and a controller configured to instruct to change the direction of the flow of the cooling fluid (140) based on temperature measurements of one or more temperature sensors.

Description

TECHNICAL FIELD The present disclosure relates to electrical machines, cooling systems and methods for cooling active elements of electrical machines. More in particular, the present disclosure relates to cooling systems and methods for cooling active rotor and/or stator elements of a generator of a wind turbine, e.g. of a direct drive wind turbine. BACKGROUND Electrical machines, such as motors and generators, generally comprise a rotor structure and a stator structure. Large electrical generators may be e.g. electrically excited generators or permanent magnet excited generators (PMG). The rotor of an electrical machine rotates with respect to the stator. The rotor may be the inner structure and the stator the outer structure. The stator in this case thus surrounds, e.g. radially, the rotor. Alternatively, the configuration may be the opposite, i.e. the rotor surrounds, e.g. radially, the stator. Such generators may be used for example in wind turbines. Wind turbines generally comprise a rotor with a rotor hub and a plurality of blades. The rotor is set into rotation under the influence of the wind on the blades. The rotation of the rotor shaft either drives the generator rotor directly ("directly driven") or through the use of a gearbox. A direct drive wind turbine generator may have e.g. a diameter of 6 - 10 meters (236 - 328 inches), a length of e.g. 2 - 3 meters (79 - 118 inches) and may rotate at low speed, for example in the range of 2 to 20 rpm (revolutions per minute). Alternatively, generators may also be coupled to a gearbox which increases the rotational speed of the generator to for example between 50 to 500 rpm or even more. In electrical machines, such as generators of direct drive wind turbines, cooling is generally important. In particular, the active elements of the rotor and the stator, e.g. permanent magnets and coils, may heat up. An increase in temperature of the active rotor and stator elements may lead to failure of the active elements and may reduce the efficiency of the generator. To reduce the temperature of the active elements of the rotor and the stator, a cooling fluid may be run through the air gap separating the active elements. The cooling fluid contacts the active elements and takes heat from them away. A cooling system may be provided for guiding the cooling fluid towards and away from the air gap, and thus removing heat from the active elements of the rotor and the stator. Such a cooling system may comprise a primary or "main" path or loop. A main loop may include a fluid inlet for a main fluid. A main fluid may be carried from the main fluid inlet to the active rotor and stator elements. For example, air may be directed to an air gap between the active rotor and stator elements. During operation, the active elements heat up, and the cooling fluid (which may also be air) is heated up too. The heated main fluid may be then carried away to a main fluid outlet. In some examples, the main fluid outlet and inlet may fluidly communicate with an exterior of the wind turbine, e.g. the air surrounding the nacelle. For example, the cooling system may comprise fans, e.g. in the nacelle, for introducing air from an outside of the wind turbine through the main fluid inlet. Conduits may carry the main loop fluid from the main cooling fluid inlet to the generator air gap, and then conduits may carry the heated main cooling fluid from the generator air gap to the fluid outlet. In other examples, the main fluid inlet and the main fluid outlet may fluidly communicate with a heat exchanger. A secondary path or loop for the cooling fluid may include the heat exchanger. A heat exchanger may comprise a heat exchanger main cooling fluid inlet, a heat exchanger main cooling fluid outlet, a heat exchanger secondary fluid inlet and a heat exchanger secondary fluid outlet. The main cooling fluid (i.e. the fluid used for cooling elements in the air gap, herein generally referred to as "cooling fluid") heated in the generator air gap may be guided into the heat exchanger through the heat exchanger main cooling fluid inlet. A secondary fluid (i.e. a fluid that does not cool elements in the air gap directly but rather is used to cool the main cooling fluid or "cooling fluid") may be introduced into the heat exchanger through the heat exchanger secondary fluid inlet. The secondary fluid may cool the main cooling fluid. The secondary fluid may be removed from the heat exchanger through the heat exchanger secondary outlet and the main fluid may be removed from the heat exchanger through the heat exchanger main outlet. The secondary fluid may for example be water or air. Conduits may be used to guide the heated main cooling fluid inside the heat exchanger and then, once cooled down, out of it. The cooled main cooling fluid may then be directed again towards the air gap between the active elements of the rotor and the stator. SUMMARY In an aspect of the present disclosure, a method for cooling an electrical