Abstract:
A wind turbine is provided having a gearbox containing a lubrication medium, a pump for circulating the lubrication medium, and a gearbox lubrication suction pipe for transporting the lubrication medium from the gearbox to the pump. A heater is in thermal connection to, at least a portion of, the gearbox lubrication suction pipe. This heater is used to heat the lubrication medium contained within the gearbox lubrication suction pipe to a temperature where damage to the pump is avoided.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to rotary machines and more particularly, to a lubrication heating system for operating wind turbines in cold weather environments. 
     Generally, a wind turbine includes a rotor having multiple blades. The blades are attached to a rotatable hub, and the blades and hub are often called the rotor. The rotor transforms mechanical wind energy into a mechanical rotational torque that drives one or more generators. The generators are generally, but not always, rotationally coupled to the rotor through a gearbox. The gearbox steps up the inherently low rotational speed of the turbine rotor for the generator to efficiently convert the rotational mechanical energy to electrical energy, which is fed into a utility grid. Gearless direct drive wind turbine generators also exist. The rotor, generator, gearbox and other components are typically mounted within a housing, or nacelle, that is positioned on top of a base that may be a truss or tubular tower. 
     The gearboxes need to be lubricated to function effectively. Typically, oils are used for lubrication in a gearbox, and the oil heats up during operation of the gearbox. A heat exchanger can be used to cool the oil, and a suction pipe typically exits the gearbox and feeds into a circulating pump. The circulating pump is used to force the oil through the heat exchanger, and the cooled oil is then directed back to the gearbox. 
     In extremely cold environments (e.g., less than about −10 degrees C.), the lubrication oil used in the gearbox can become very viscous or thick. This cold and viscous oil resists flow and the circulating pump can be damaged if run when the oil is very cold. In some known solutions an external heater and pump are connected to the oil sump of the gearbox. This oil sump heater takes a long time to heat up all the oil in the gearbox sump and requires a large amount of energy. The result is a long delay during cold weather operation, waiting for the oil to come up to a minimum temperature, until the wind turbine can begin producing power, as well as lower overall efficiency due to the large power drain imposed by the oil sump pump/heater. 
     Accordingly, a need exists in the art for a system that will quickly heat the oil entering a circulating pump used with a gearbox, and that does not require a large amount of power or time to operate. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one aspect of the present invention a wind turbine is provided comprising a gearbox containing a lubrication medium, a pump for circulating the lubrication medium, and a gearbox lubrication suction pipe for transporting the lubrication medium from the gearbox to the pump. A heater is in thermal connection to, at least a portion of, the gearbox lubrication suction pipe. This heater is used to heat the lubrication medium contained within the gearbox lubrication suction pipe to a temperature where damage to the pump is avoided. 
     In another aspect, a wind turbine is provided comprising a gearbox containing a lubrication medium, a pump for circulating the lubrication medium, and a gearbox lubrication suction pipe for transporting the lubrication medium from the gearbox to the pump. A heater is located on, at least portions of, the gearbox lubrication suction pipe. The heater is used to heat the lubrication medium contained within the gearbox lubrication suction pipe to a temperature where damage to the pump is avoided. 
     In a further aspect, a heating system for a lubrication medium used in a gearbox is provided. The system comprises a pump for circulating a lubrication medium, heating means for heating a portion of the lubrication medium and a suction pipe connected between the gearbox and the pump. The suction pipe is used for transporting the lubrication medium from the gearbox to the pump. A temperature monitoring system for monitoring a first temperature activates the heating means when the first temperature is below a threshold value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of an exemplary wind turbine generator; 
         FIG. 2  is a fragmentary cross-sectional schematic illustration of a nacelle that may be used with the exemplary wind turbine generator shown in  FIG. 1 ; 
         FIG. 3  is a block diagram illustration of a prior art gearbox lubrication heating system; 
         FIG. 4  is a block diagram illustration of the lubrication heating system according to one embodiment of the present invention; 
         FIG. 5  is a block diagram illustration of the lubrication heating system according to another embodiment of the present invention; and 
         FIG. 6  is a block diagram illustration of the lubrication heating system according to yet another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a schematic illustration of an exemplary wind turbine  100 . In the exemplary embodiment, wind turbine  100  is a horizontal axis wind turbine. Alternatively, wind turbine  100  may be a vertical axis wind turbine. Wind turbine  100  has a tower  102  extending from a supporting surface  104 , a nacelle  106  mounted on tower  102 , and a rotor  108  coupled to nacelle  106 . Rotor  108  has a rotatable hub  110  and a plurality of rotor blades  112  coupled to hub  110 . In the exemplary embodiment, rotor  108  has three rotor blades  112 . In an alternative embodiment, rotor  108  may have more or less than three rotor blades  112 . In the exemplary embodiment, tower  102  is fabricated from tubular steel and has a cavity (not shown in  FIG. 1 ) extending between supporting surface  104  and nacelle  106 . In an alternate embodiment, tower  102  is a lattice tower. The height of tower  102  is selected based upon factors and conditions known in the art. 
     Blades  112  are positioned about rotor hub  110  to facilitate rotating rotor  108  to transfer kinetic energy from the wind into usable mechanical energy, and subsequently, into electrical energy. Blades  112  are mated to hub  110  by coupling a blade root portion  120  to hub  110  at a plurality of load transfer regions  122 . Load transfer regions  122  have a hub load transfer region and a blade load transfer region (both not shown in  FIG. 1 ). Loads induced in blades  112  are transferred to hub  110  via load transfer regions  122 . 
     In the exemplary embodiment, blades  112  have a length between about 50 meters (m) (164 feet (ft)) and about 100 m (328 ft). Alternatively, blades  112  may have any length. As the wind strikes blades  112 , rotor  108  is rotated about rotation axis  114 . As blades  112  are rotated and subjected to centrifugal forces, blades  112  are subjected to various bending moments and other operational stresses. As such, blades  112  may deflect and/or rotate from a neutral, or non-deflected, position to a deflected position and associated stresses, or loads, may be induced in blades  112 . Moreover, a pitch angle of blades  112 , i.e., the angle that determines blades  112  perspective with respect to the direction of the wind, may be changed by a pitch adjustment mechanism (not shown in  FIG. 1 ) to facilitate increasing or decreasing blade  112  speed by adjusting the surface area of blades  112  exposed to the wind force vectors. Pitch axes  118  for blades  112  are illustrated. In the exemplary embodiment, the pitches of blades  112  are controlled individually. Alternatively, the pitches of blades  112  may be controlled as a group. 
     In some configurations, one or more microcontrollers in a control system (not shown in  FIG. 1 ) are used for overall system monitoring and control including pitch and rotor speed regulation, yaw drive and yaw brake application, and fault monitoring. Alternatively, distributed or centralized control architectures are used in alternate embodiments of wind turbine  100 . 
       FIG. 2  is a fragmentary cross-sectional schematic view of nacelle  106  of exemplary wind turbine  100 . Various components of wind turbine  100  are housed in nacelle  106  atop tower  102  of wind turbine  100 . Pitch drive mechanisms  130  (only one illustrated in  FIG. 2 ) modulates the pitch of blades  112  along pitch axis  118  (both shown in  FIG. 1 ). 
     Rotor  108  is rotatably coupled to an electric generator  132  positioned within nacelle  106  via rotor shaft  134 , sometimes referred to as low speed shaft  134 , a gearbox  136 , a high speed shaft  138 , and a coupling  140 . Forward and aft support bearings  152  and  154 , respectively, are positioned within and are supported by nacelle  106 . Bearings  152  and  154  facilitate radial support and alignment of shaft  134 . Rotation of shaft  134  rotatably drives gearbox  136  that subsequently rotatably drives shaft  138 . Typically, a lubrication oil is used within gearbox  136 . Shaft  138  rotatably drives generator  132  via coupling  140  and shaft  138  rotation facilitates generator  132  production of electrical power. Gearbox  136  and generator  132  are supported by supports  142  and  144 , respectively. In the exemplary embodiment, gearbox  136  utilizes a dual path geometry to drive high speed shaft  138 . Alternatively, main rotor shaft  134  is coupled directly to generator  132  via coupling  140 . 
     Also positioned in nacelle  106  is a yaw adjustment mechanism  146  that may be used to rotate nacelle  106  and rotor  108  on axis  116  (shown in  FIG. 1 ) to control the perspective of blades  112  with respect to the direction of the wind. Mechanism  146  is coupled to nacelle  106 . Meteorological mast  148  includes a wind vane and anemometer (neither shown in  FIG. 2 ). Mast  148  is positioned on nacelle  106  and provides information to the turbine control system that may include wind direction and/or wind speed. In alternative embodiments, mast  148  can be mounted on hub  110  and extend in a direction in front of rotor  108 . 
     A portion of the turbine control system resides within control panel  150 . The turbine control system (TCS) controls and monitors various systems and components of wind turbine  100 . A plurality of sensors are distributed throughout wind turbine  100  and the status of various conditions (e.g., vibration level, temperature, etc.) are monitored. The sensed conditions are utilized by the TCS to control various subsystems of wind turbine  100 . In one example, the ambient temperature or temperature of the oil in the gearbox sump can be sensed and compared to a lower threshold value. If the temperature of either or both of these values is below the threshold, a heater could be activated to warm the gearbox oil to above the threshold value. When a higher predetermined value (e.g., minimum recommended operating temperature of gearbox lubricating oil) is reached the heater may be de-activated. 
     Gearboxes typically need lubrication to function effectively. This lubrication is often in the form of an oil. When oil is warm, it flows readily and is non-viscous, but when oil is cold it becomes viscous and resists flow. Referring to  FIG. 3 , many known gearboxes use a circulating pump  310  to circulate warm or hot oil through a heat exchanger  320 . The heat exchanger is used to cool lubricating oil, and then returns the cooled oil back to the gearbox  136 . 
     In cold weather operation (e.g., less than about −10 degrees C.), the lubricating oil used in the gearbox becomes very viscous. The circulating pumps  310  used in conjunction with gearboxes can be damaged by the viscous oil. For example, the vanes of the pump could break when forced to pump viscous fluids (e.g., lubricating oils). The term “cold” is somewhat relative and refers to a temperature when a lubricating medium becomes viscous. For example, some lubricating oils may become viscous at about +10 degrees C. The present invention can be used at any temperature and/or in any application where a viscous lubricating medium needs to be heated to become less viscous. 
     In some known solutions to this problem, and as illustrated in  FIG. 3 , an external heater and pump  330  is connected to the oil sump of gearbox  136 . Typically, two pipes  335  are connected between the heater and pump  330  and the oil sump of gearbox  136 . One pipe  335  transfers oil from the gearbox to the heater and pump  330 , and the other pipe  335  returns warned oil back to the oil sump of gearbox  136 . 
     Once the oil in gearbox  136  has warmed to a minimum operating temperature, pump  310  can be energized and transfer oil out of gearbox  136  via suction pipe  340 . Pump  310  can include an internal valve (not shown) for selectively discharging oil into gearbox return pipe  350  or into heat exchanger input pipe  360 . Typically, when the oil in gearbox heats up enough to require cooling by heat exchanger  320 , it is normally returned to gearbox  136  via pipe  370 . In alternative embodiments, the oil may pass through pump  310  before returning to gearbox  136 . 
     Given enough time and power the system illustrated in  FIG. 3  does work, although it takes a long time to heat all the oil in the oil sump to a minimum operating temperature. A large amount of power is also required during this process. The disadvantages to this approach include the large amount of power required to operate the heater and pump  330 , the capital cost of the heater and pump  330  components, the long time period required to heat the oil and the lost income from waiting to operate the machinery (e.g., a wind turbine). This last factor can have a large impact in wind farms that may comprise hundreds of wind turbines. Every minute lost in generating power adds up to a substantial monetary amount when factored over the course of a year and multiplied by the number of turbines in a typical wind farm. 
       FIG. 4  illustrates one embodiment of the present invention that drastically reduces the time required to start operating a wind turbine in cold environments. The weakest link in the system shown in  FIG. 4  is the pump  310 . This pump  310  is the most likely element to fail in cold weather environments. The cause of this failure is most often associated with viscous oil or lubricant. The viscous oil causes the vanes (or other parts) of pump  310  to break. The solution, as embodied by aspects of the present invention, is to heat up the oil just before it enters pump  310 . There is no need to heat up all the oil in the gearbox  136  first. The oil located in oil sump outlet pipe  410  consists of a small amount of oil and a low thermal mass, when compared to the total oil capacity of the oil contained in gearbox  136 . In alternative embodiments, oil sump outlet pipe  410  could be located at any point on the gearbox  136 , as long as a supply of oil can be transferred to pump  310 . 
     A heated wrap  420  can be placed around pipe  410 , and this wrap  420  can be used to heat the oil contained within pipe  410 . The heated wrap  420  can be a blanket like device having electrically heated wires or cables, a hot air jacket or heat transfer device. The heated wrap  420  could also be embedded within the walls of pipe  410  (e.g., electrically powered heating wires within the pipe wall). A portion or the entirety of pipe  410  can be covered with the heated wrap  420 . The heated wrap  420  can be attached to pipe  410  with any suitable fasteners (e.g., hook and loop, cable ties, magnets, etc.). Power can be supplied via a standard electrical plug (not shown) and the wrap  420  can be configured to run on AC or DC power. 
     One major advantage to this system is that only a small amount of power is needed to power heated wrap  420 . Another advantage is that since only a small amount of oil is heated (i.e., only the oil contained within pipe  410 ) the resulting low thermal mass of oil heats up very quickly. The pump  310  is constantly fed a supply of warm oil and can begin operation much faster than in the system shown in  FIG. 3 . Another advantage is that the wind turbine can begin to operate sooner, thereby the oil present in gearbox  136  will begin to heat up via frictional forces and aid in the oil warming process. 
       FIG. 5  illustrates another embodiment of the present invention. Heated wrap  520  comprises a heated cover that covers pump  310  and pipe  410 . In alternative embodiments, the heated wrap  520  may cover all or a portion of pump  310  and/or all or a portion of pipe  410 . The heated wrap may comprise a single piece or may comprise two or more individual pieces that can be used to cover all or portions of pump  310  and/or pipe  410 . The heated wrap  520  could also be extended to cover all or a portion of pump outlet pipe  350 . Heating the oil exiting the pump  310  and entering gearbox  136  via pipe  350  could benefit the pump by reducing the pushing resistance experienced by the pump. 
     In alternative embodiments the heated wrap could be configured to cover all or a portion of gearbox  136 . In one embodiment, only the lower portion of the gearbox could be heated, and in other embodiments the entire gearbox, or majority of the gearbox could be heated by one or more heated wraps. It is also contemplated by aspects of the present invention that one or more wraps could be used to cover and heat, all or portions of, the gearbox  136 , outlet pipe  410 , pump  310 , and inlet pipe  350 . 
     As described above in conjunction with  FIG. 4 , heated wrap  520  can be comprised of a blanket like device having electrically heated wires or cables, a hot air jacket or heat transfer device. The heated wrap  520  could also be embedded within the walls of pipe  410  (e.g., electrically powered heating wires within the pipe wall) and/or the casing of pump  310 . A portion of or the entirety of pipe  410  and/or pump  310  can be covered with the heated wrap  520 . The heated wrap  520  can be attached to pipe  410  and/or pump  310  with any suitable fasteners (e.g., hook and loop, cable ties, magnets. etc.). Power can be supplied via a standard electrical plug (not shown) and the wrap  520  can be configured to run on AC or DC power. 
     Referring to  FIG. 6 , the temperature control system  610  can be utilized to monitor and control the heated wrap  420 ,  520 . A plurality of temperature monitoring sensors can be used to monitor the temperature of the oil in the gearbox, the temperature of the oil in pipe  410 , the temperature of pipe  410 , the temperature of the oil in pump  310 , the temperature of pump  310  and the ambient temperature. Based on the data received, the temperature control system can determine if the heated wrap should be activated. As one example, if the ambient temperature was about −10 degrees C and the oil temperature in the gearbox sump and/or the oil temperature in the suction pipe  410  was below a predetermined threshold value, then the heated wrap  420 ,  520  could be energized. Readings would be monitored at predetermined intervals, and when the oil reached a specific temperature, then the heated wrap could be deactivated. 
     In some applications, the pipes or hoses used in a gearbox system are formed of a rubber or elastomeric material, and this rubber material can be damaged by oil that is too hot. It will be understood that the terms “pipe” or “pipes” and “hose” or hoses” are used interchangeably, and the present invention can be applied to any type of pipe or hose used in a machine requiring the lubrication medium to be heated. Additional aspects of the present invention can be utilized to monitor the temperature of pipe  410 , and if this temperature exceeded or was approaching a maximum recommended temperature (i.e., the oil was making the pipe or hose too hot), then the heated wrap could be deactivated. The temperature control system may also decide to instruct pump  310  to route the oil through heat exchanger  320  to cool the oil. In additional embodiments, the heated wrap itself could contain a self-regulating device that deactivates itself when an over-temperature condition is approaching. The temperature control system  610  could also be controlled by the turbine control system (TCS). In some wind turbines the TCS monitors and controls a variety of subsystems (e.g. pitch motors, yaw drive, power converter, etc.). 
     In additional aspects of the present invention, the wrap  420 ,  520  could comprise heating and/or cooling means. The cooling means could be used if the oil in pipe  410  or pump  310  became too hot. In some applications, it may be possible for oil, over a predetermined temperature, to damage the pipe  410  and/or pump  310 . Accordingly, a cooling means integrated with wrap  420 ,  520  could be used to cool oil which has become too hot. The cooling means could comprise a length of conduit or tubing that contains a heat transfer medium. The conduit could be connected to an external or internal heat exchanger, or to a refrigeration device. In one example embodiment, the conduit used for cooling could be connected to heat exchanger  320 . 
     The various aspects of the present invention herein described provide a system for quickly and efficiently heating or cooling the lubrication medium (e.g., oil) used in gearboxes. The oil is heated prior to entering the circulating pump and only a small thermal mass of oil is heated (i.e., compared to the entire volume of oil used for gearbox lubrication). The result is a very quick start up time for machines utilizing gearboxes in cold weather environments. Any engine, vehicle or machine requiring a gearbox could employ the invention herein described. One application is in the use of wind turbines, and the present invention enables a quick start-up time during cold weather operation, while reducing the costs of prior solutions. 
     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.