AUXILIARY REFRIGERATION SYSTEM AND OPERATING METHOD
Auxiliary refrigeration system used to refrigerate a wind turbine's gearbox (10) when the main refrigeration system (20) is inoperative due to low outside temperatures. The auxiliary equipment (30) is installed inside the nacelle and comprises a pressure limiting valve (31), an exchanger and a motor fan (M), all of them connected to a control cabinet that activates or deactivates the auxiliary refrigeration equipment (30) based on the exterior temperature Text, the temperature of the refrigerant at the outlet of the main circuit Tsc, and the gearbox temperature Tm.
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The object of the invention is to refrigerate a wind turbine's gearbox by means of an auxiliary system when the main refrigeration equipment fails due to bad weather conditions.
BACKGROUND OF THE INVENTIONWind turbines are machines that are installed in all types of locations and are subjected to hard external conditions. Thus, in locations with low temperatures, the viscosity of the gearbox's oil increases to the point that solidified oil lumps are formed. The optimal place for the oil to solidify is in the refrigeration equipment which is in contact with the outside. When the main refrigeration system fails owing to partial solidification of the oil used for refrigeration, problems arise with the temperature reached by the gearbox, the relevant alarm goes off and the wind turbine is stopped.
During normal operation, the gearbox oil goes through the main refrigeration system, which refrigerates it as needed. As is well known, the oil's viscosity increases inversely and exponentially with temperature. The loss of charge of the viscous fluid going through the refrigeration equipment depends linearly on the viscosity; with low temperatures, half-solidified oil lumps are formed and the gearbox oil no longer flows through the main refrigeration equipment.
To avoid the consequences of a lack of gearbox refrigeration, auxiliary exchangers are used to refrigerate the gearbox when needed.
Patent CN 101196176 takes into account the problems caused by low temperatures and uses an auxiliary exchanger that preheats the oil used in the main refrigeration system so that it can be impelled by the pump. This is not the best possible solution, as the amount of heat that needs to be applied to the oil in the main refrigeration system requires the use of an excessively large (which makes its location inside the nacelle difficult) and costly preheater.
Patent WO2008131766 also uses an auxiliary preheater to exchange heat with the main refrigeration system when the latter suffers the consequences of low temperatures and increased oil viscosity. The design shown in this patent prevents excessive oil refrigeration, so that the circuit is not blocked, but does not take into account the possibility of blockage following an extended stoppage of the wind turbine. Because with the wind turbine stopped, none of the heat exchange circuits work, and they may become blocked at low temperatures.
In view of the above, it is believed that none of the known patents solves the gearbox refrigeration problem in such a way that the machine's performance at low temperatures is improved simply, within the space existing inside the nacelle, and cost-effectively.
DESCRIPTIONOne object of this invention is to install an interior auxiliary exchanger applied directly to the gearbox for its refrigeration, which starts operating when the main refrigeration equipment has failed due to the low temperatures existing outside the wind turbine.
Another object of this invention is to establish the necessary mechanical connections between the auxiliary exchanger and the gearbox, so as to prevent the gearbox oil from reaching the maximum operating temperature and enable the machine to be stopped.
Another object of the invention is to establish the appropriate electrical circuit between the auxiliary exchanger, the main refrigeration equipment and the gearbox, in order to achieve the oil's refrigeration.
And finally, another object of the invention is to establish the control method to be followed for determining the failure in the main refrigeration equipment and the activation of the auxiliary exchanger, managing the response and the connection and disconnection of the auxiliary exchanger while awaiting for the main refrigeration equipment's operation to be restored.
The gearbox is a component that is installed between the mechanical transmission system, or drive train, of a wind turbine and the electrical generator, given that the turbine's rotation speed does not usually match the generator's speed. This mechanical component needs to be refrigerated.
As shown in
The auxiliary refrigeration system is controlled basically by means of two parameters: the refrigeration circuit through which the oil flows and the activation-deactivation of the electrical pump (11).
The circuit through which the oil flows is controlled automatically by the pressure limiting valve (31) located at the beginning of the auxiliary circuit. When charge losses exceed a given pressure, this valve (31) opens and the oil flows through the auxiliary circuit. As soon as the value drops below that pressure, the valve closes and the oil once again flows through the main circuit. The activation pressure value is calculated based on the size of the gearbox and of the refrigeration circuit, and varies for different machine sizes.
The activation of the mechanical elements (motor fans) of both circuits depends on 3 parameters:
-
- External temperature Text.
- Oil temperature at the outlet of the main refrigeration equipment Tsc.
- Oil temperature in the gearbox sump Tm.
- All of the temperature sensors are connected to the control cabinet, which controls the wind turbine's components.
As shown in
On the other hand, if the outside temperature Text exceeds TBT, activation of the main refrigeration system (20) will result from the gearbox temperature, Tm.
Restoring refrigeration system operation following a machine stoppage can be a complex process. If the main refrigeration equipment (20) was blocked prior to the stoppage or viscosity is lost and it is blocked while it is stopped, it will remain blocked when the wind turbine is started up again. With auxiliary exchanger (30) of the invention, the gearbox (10) refrigeration requirements could be met from the moment the machine is restarted, since inside the nacelle it is protected from the low temperatures existing outside the wind turbine.
Claims
1. Auxiliary refrigeration system (30) of the type used to refrigerate a wind turbine's gearbox (10) when the main refrigeration equipment (20) is inoperative, wherein said auxiliary system is installed inside the nacelle with no contact with the outside and incorporates a pressure limiting valve (31) and is connected between the established outward (12) and return (13) paths from the gearbox (10) sump and regulated by a refrigerant impelling electrical pump (11).
2. Auxiliary refrigeration system according to claim 1, which comprises an exchanger and a motor fan (M), all of them connected to a control cabinet that activates or deactivates the non-return pressure limiting valve (31).
3. Operating method for a refrigeration system for a gear box comprising a conventional refrigerating circuit through which refrigerant flows and the activation-deactivation of the electrical pump (11) that impels such refrigerant, and an auxiliary exchanger circuit comprising a valve and an auxiliary exchanger, which method comprises:
- if the pressure in said valve (31) of the auxiliary refrigeration circuit exceeds the allowable charge losses, the auxiliary exchanger circuit opens, and once a maximum temperature is exceeded in the gearbox, the auxiliary exchanger (30) is switched on (30);
- Based on the outside temperature, the logic regulating the auxiliary circuit or the main circuit is activated;
- if the measurements of the refrigerant temperature at the outlet of the main circuit, are equal to or less than a given temperature, and the temperature at the outlet of the gearbox sump exceeds a given temperature setpoint, the electrical pump (11) and the auxiliary exchanger (30) are switched on.
4. Operating method for an auxiliary refrigeration system according to claim 3, wherein the pressure valve (11) starts operating upon reaching 6 bar.
5. Operating method for an auxiliary refrigeration system according to claim 3, wherein the electrical pump (11) and the auxiliary exchanger (30) are switched on if:
- the outside temperature is below TBT and
- the temperature (pressure or flow) at the outlet of the main circuit Tsc, is equal to or less than the temperature of the oil whose viscosity is causing charge losses such that it cannot be impelled by the installed pump (or equal to zero in the case of pressure and flow) and
- the gearbox temperature Tm, is greater than a safety value in order to prevent the oil from reaching a critical temperature.
Type: Application
Filed: Oct 4, 2010
Publication Date: Apr 14, 2011
Applicant:
Inventors: Carlos BRITO GARCIA , Ricardo ALCALDE AYALA
Application Number: 12/896,953
International Classification: F25B 7/00 (20060101); F25B 43/00 (20060101);