FORM – 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
OVERHEAD TANK
ROMAX TECHNOLOGY LIMITED
a British company
of, Romax Technology Centre University of Nottingham Innovation Park, Triumph
Road Nottingham Nottinghamshire NG7 2TU, Great Britain
Inventors:
1. SHIELD, David
2. SCOTT, David
3. JOHNSTONE, Gary

THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED. 2

Technical Field
The present invention is concerned with rotating machines having a lubrication reservoir which feeds key components by gravity, such that in some operating conditions, lubricant from the reservoir may continue to be supplied to the rotating machine, even in the absence of electrical power with which to operate pumps.
Background Art
A wind turbine drivetrain typically comprises an aerodynamic rotor supported on a rotor shaft, which itself is supported on one or more rotor bearings, mounted in the turbine structure. The rotor shaft is torsionally connected to a gearbox, which increases the rotational speed. The output of the gearbox is connected to a generator, which converts the mechanical power into electrical power. The turbine is typically also equipped with an electric power converter, which modifies the electrical output of the generator to meet the requirements of the electrical grid to which the turbine is connected.
The rotor bearings, gearbox gears and bearings, generator bearings, and various other mechanical components in the drivetrain are supplied with pressurised lubricating oil pumped from a reservoir through an arrangement of pipes and nozzles. This oil serves both to lubricate the working surfaces of these components, and remove excess heat generated at these surfaces during operation.
The oil reservoir may be formed by the gearbox housing, such that the oil is substantially retained within the same enclosed volume as the rotating parts of the gearbox. Some of the rotating parts may be situated partially or entirely below the level of the oil, such that their rotation may distribute oil around the gearbox. Such arrangements are referred to as ‘wet sump’. 3

Alternatively, the oil reservoir may comprise an enclosed volume separated from the enclosed volume occupied by the rotating parts of the gearbox. This volume may be integral to the gearbox housing, or it may take the form of a separate tank, located below the gearbox housing, and connected to the gearbox housing by a pipe, channel, or conduit in such a way that oil which is distributed to the gearbox components will drain from the gearbox housing into the oil reservoir under the influence of gravity. Such arrangements are referred to as ‘dry sump’.
A dry sump arrangement may be considered advantageous for wind turbines during normal operation. In a wet sump arrangement, some or all of the rotating components may pass through the oil as they rotate. This causes a drag force to act on the rotating components, reducing the overall efficiency of the drivetrain. Additionally, the continual churning of the oil may degrade its properties, and will introduce air bubbles into the oil, which may cause problems with pumping, filtering, and cooling the oil in other parts of the lubrication system.
Conversely, a wet sump arrangement may be considered advantageous in the case of non-operation of the pumped lubrication system, as the passage of some or all of the rotating components through the oil will cause the oil to be distributed around the machine, achieving at least some lubrication function. Some existing machines which operate according to a dry sump arrangement incorporate a valve in the drain conduit which can be closed to retain some oil in the machine housing during non-operating periods, thus replicating the function of a wet sump arrangement.
Existing wind turbine drivetrains equipped with a lubrication system as described above may be expected to function satisfactorily in normal operating conditions. However outside these conditions there are a number of problems which arise, and for which the present invention seeks to provide solutions. 4

It is to be expected that there will be periods when the turbine is operating outside normal operating conditions, due to lack of wind, planned maintenance, a fault in some component or sub-system of the turbine itself, a fault in the electrical grid, or when the turbine has been constructed but not connected to the grid infrastructure. During these periods, the turbine may be stationary (no wind, or because the rotor has been locked in position for safety while maintenance is carried out), or it may be rotating at low speed and torque. In either case, although these situations do not require a large oil flow rate for cooling, it is necessary to maintain some oil flow to the working surfaces in order to prevent damage, both during the period of non-operation, and immediately after turbine operation is resumed. Examination of existing wind turbine drivetrains which have failed in service indicates that failure is often initiated during these periods, rather than during normal running, and that inadequate lubrication is a contributing factor.
Existing wind turbine drivetrains commonly seek to provide lubrication during non-operating periods through the inclusion of a mechanical oil pump within the gearbox, which is caused to operate by the rotation of the drivetrain. The intent is that, even if electrical power is not available, some lubrication will continue to be provided as long as the turbine rotor is rotating. However during non-operating conditions, the turbine rotor may not be rotating continually, at a sufficient speed, and in a single direction. It is common for the rotor to be stationary, rotating extremely slowly in a single direction, or oscillating backwards and forwards. A mechanical oil pump may not provide sufficient oil for lubrication under such conditions.
Furthermore, the mechanical pump in existing systems simply circulates the oil around the same circuit as in normal running. This circuit is configured, typically by means of valves, nozzles, and restricting orifices, to supply a large portion of the oil to the gear meshes for cooling when running at full rated power. During non-operational periods, it is more important that sufficient oil is provided to the bearings. Existing mechanical pump systems will continue to distribute the oil flow according to the 5

proportions determined by the normal operational requirements, albeit at a much reduced flow rate. There is therefore a risk that the oil supply to the bearings will be insufficient, and that bearings will be damaged during non-operational periods.
An additional measure taken in some existing drivetrains is to design the various bearing supports such that they do not drain fully. This ensures that a small amount of oil is trapped at each bearing position when the turbine is shut down, and this small amount of oil continues to provide some lubrication during non-operational periods. However, any such arrangement is also likely to trap contaminant particles, potentially accelerating bearing failure.
It will be seen therefore that a system in which lubricant flow could be maintained during non-operating conditions, and where the ability of the lubricant flow to carry away contaminant particles was not compromised, and furthermore where the lubricant flow could be prioritised to those components where it is most required, would be advantageous to the lifetime reliability of a wind turbine.
Disclosure of Invention
According to an embodiment of the present invention, there is provided a lubrication arrangement for a rotating machine, which has components to be lubricated. The lubrication arrangement has a lubricant reservoir and a first arrangement of one or more conduits. The reservoir is located above the components and is connected to the first arrangement of conduits. The first arrangement of conduits includes outlets positioned so as to direct a lubricant passing through the first arrangement of conduits to a first set of components. This means that under certain operating conditions, the lubricant is caused to flow by gravity from the reservoir to the one or more components via the first arrangement of conduits.
Preferably, the first set of components may include one or more bearings. 6

Preferably, the lubrication arrangement may also include a second arrangement of one or more conduits. The reservoir is connected to the second arrangement of conduits. The second arrangement of conduits includes outlets positioned so as to direct a lubricant passing through the second arrangement of conduits to a second set of components.
Preferably, the second set of components may include one or more gear meshes.
Preferably, the lubrication arrangement may also include one or more valves which determine a flow of lubricant through the first and second arrangements of conduits. A division of lubricant flow between the first set of components and the second set of components may be different, according to the operating conditions.
Preferably, the second arrangement of conduits may additionally incorporate one or more pumps.
Preferably, the rotating machine has an outlet for lubricant and a pump to transfer lubricant from the outlet to the lubricant reservoir.
Preferably, the lubrication arrangement has a second lubricant reservoir located below the one or more components to be lubricated, and which is configured to receive a flow of lubricant from the components to be lubricated.
Preferably, the second reservoir may have a capacity smaller than a total volume of oil in the lubrication arrangement, such that when the lubricant reservoir is empty, the second reservoir will be full, and the remaining proportion of the total volume of oil will remain within a housing of the rotating machine and the lubrication arrangement will be a wet sump arrangement. 7

Preferably, the lubrication arrangement has one or more pumps operable to cause lubricant to flow from the second lubricant reservoir to the lubricant reservoir. The lubrication arrangement may also have a means for sensing a level of lubricant in the reservoir and/or in the second reservoir, and the one or more pumps operate according to a predetermined level of lubricant. The one or more of the one or more pumps may be operated by means of electrical power from: an electrical grid, a battery, a generator, a photovoltaic panel, or a wind turbine. The one or more of the one or more pumps may be operated by a human operator.
Preferably, the rotating machine may be a gearbox, a transmission or a generator.
According to a further embodiment of the present invention, there is provided a gearbox comprising the lubrication arrangement as described in the preceding paragraphs above.
According to a further embodiment of the present invention, there is provided a wind turbine comprising the lubrication arrangement as described in the preceding paragraphs above.
Brief Description of Drawings
The present invention will now be described, by way of example only, with references to the accompanying drawings, in which:
Figures 1 and 2 show lubrication arrangements for a wind turbine drive train; and
Figure 3 shows an external view of an offshore wind turbine.
Best mode for Carrying out the Invention
Referring now to Figure 1, rotating machine 7, for example a wind turbine drivetrain, contains a number of gears, bearings, and other components which must be supplied by with oil. 8

The oil, after it has been distributed within the rotating machine, flows through pipe, channel, or conduit 8 into lower reservoir 9. Lower reservoir 9 is situated substantially below the rotating machine such that the flow requires only the influence of gravity to occur. In this embodiment, lower reservoir 9 is represented as a separate component, however in other embodiments it may be attached to, or formed as an integral part of the housing of the rotating machine. In alternative embodiments lower reservoir 9 and pump 10 may be removed completely and replaced with a conduit looping below the rotating machine and pump 4 or an additional pump in upper reservoir 2 capable of raising the oil from the lower conduit into upper reservoir 2.
One or more pumps 10 are provided which take oil from lower reservoir 9, and cause it to be transferred by another conduit to upper reservoir 2. In this embodiment, upper reservoir 2 is represented as a separate component, however in other embodiments it may be attached to, or formed as an integral part of the housing of the rotating machine. Between the pump and upper reservoir 2, the oil is passed through oil conditioning system 1, which may comprise various systems for heating, cooling, filtering, and monitoring the condition and cleanliness of the oil.
Upper reservoir 9 has one or more outlets. One of the outlets is provided with one or more pumps 4 which cause the oil to be transferred to first inlet 6 of the rotating machine.
A second outlet of upper reservoir 2 or a branch of the first outlet is provided with valve 3, arranged such that it prevents flow during normal operation of the rotating machine, but permits flow during periods of non-operation. Valve 3 may be held in the closed position by electrical signal, by pressure in the conduit between pump 4 and first inlet 6, or by some other signal which will cause it to return to the open position in the event of turbine shutdown or electrical power loss. During such periods, valve 3 permits oil to flow via a conduit to second inlet 5 of the rotating machine. Upper reservoir 2 is situated substantially above the drivetrain such that oil flow via this second outlet requires only the influence of gravity to occur. An alternative 9

embodiment would be to place an oil distribution manifold between the rotating machine and the upper reservoir instead of two separate inlets to the rotating machine.
Oil entering the first inlet is divided and distributed to a number of components of the rotating machine, according to the proportions required by each of the components during normal operation of the machine.
Oil entering the second inlet is divided and distributed to a number of components of the rotating machine, according to the proportions required by each of the components during non-operating conditions. The number of components to which oil entering the second inlet is distributed may be different to the number of components to which oil entering the first inlet is distributed.
During normal operation, valve 3 is held in the closed position, and the entirety of the oil flow is passed by pump 4 into the first inlet, where it is distributed amongst the mechanical components. The oil then drains via the conduit 8 into lower reservoir 9, and is then returned to upper reservoir 2 by the one or more pumps 10, passing through the oil conditioning system 1.
In the event of a period of non-operation where electrical power is still available, oil may continue to be circulated according to this regime. Alternatively, pumps 4 and 10 may be stopped, and valve 3 caused to open. This will permit oil to flow, under the influence of gravity, into second inlet 5, where it is distributed amongst those mechanical components considered most important for lubrication during non-operating conditions. This may include for example, bearings.
It will be apparent that after a period of time, the oil contained within upper reservoir 2 will be exhausted, and the oil flow to the machine will cease if no further action is taken. It is advantageous therefore to equip the lubrication arrangement with a level sensor, fitted to either the lower or upper reservoirs, which will cause a signal to be sent to the control system when a predefined proportion of the total oil volume has 10

passed from the upper reservoir to the lower reservoir. This signal may cause pump 10 to operate until the level in the upper reservoir is replenished. Thus this second lubrication regime may be maintained indefinitely, consuming less energy than is necessary to maintain the first lubrication regime.
If the period of non-operation is caused by a lack of electrical power, the lubrication arrangement will operate according to this second regime, distributing oil under the influence of gravity. However if the absence of electrical power prevents pump 10 from operating, oil flow will only be sustained until the oil contained within the upper reservoir is exhausted.
Lower reservoir 9 may advantageously be designed to have a capacity less than the total volume of oil contained within the lubrication arrangement. If this is so, when the supply of oil in upper reservoir 9 is exhausted, lower reservoir 9 will be full, and the remaining proportion of the total oil volume will remain within the machine housing. In this way, the machine will behave as if it is a wet sump machine, and some level of lubrication will be maintained indefinitely. This achieves a similar function to existing designs of lubrication arrangement, without the requirement for a valve to retain oil within the gearbox. Alternatively, such a valve may be included.
Additionally, provision may be made for the replenishment of the upper reservoir by means other than the use of power from the electrical grid. Pump 10, or an alternative pump connected between the lower and upper reservoirs, may be operated using an external power source. The external power source may be a battery or other energy storage device, an auxiliary generator mounted in the turbine nacelle or brought to the turbine by a maintenance crew, one or more solar photovoltaic panels mounted on the outer surfaces of the turbine nacelle, or some other source.
An alternative embodiment of the invention is shown in Figure 2. In this embodiment, pump 10 both transfers oil from the lower reservoir to the upper reservoir, and maintains the upper reservoir at a pressure required for distribution of 11

oil through first inlet 6. This permits pump 4 to be omitted. Pressure relief valve 11 and return conduit 12 are provided to ensure the design pressure is not exceeded and damage is not caused to components.
The conduit between the upper reservoir and the first inlet is connected to upper reservoir 2 at a point at, or proximal to, the top of the reservoir. This ensures that while the upper reservoir is pressurised, oil will pass into the conduit and thus into the first inlet of the machine. However when the machine is not operating, valve 3 is open, and the level of oil in the upper reservoir begins to drop, oil will cease to pass through the conduit leading to the first inlet, and thus will only reach the machine via the second inlet.
Figure 3 is a perspective view of an example of a wind turbine. Although an offshore wind turbine is shown, it should be noted that the description below may be applicable to other types of wind turbines. The wind turbine 402 includes rotor blades 404 mounted to a hub 406, which is supported by a nacelle 408 on a tower 410. Wind causes the rotor blades 404 and hub 106 to rotate about a main axis. This rotational energy is delivered to a powertrain having the lubrication arrangement described above and housed within the nacelle 408.
It will be apparent that the embodiments described above are only some of the ways in which the invention claimed may be implemented.
Industrial Application
The present invention is concerned with rotating machines having a lubrication reservoir which feeds key components by gravity, such that in some operating conditions, lubricant from the reservoir may continue to be supplied to the rotating machine, even in the absence of electrical power with which to operate pumps. It will be seen therefore that the system described above in which lubricant flow could be 12

maintained during non-operating conditions, and where the ability of the lubricant flow to carry away contaminant particles was not compromised, and furthermore where the lubricant flow could be prioritised to those components where it is most required, would be advantageous to the lifetime reliability of a wind turbine. 13

WE CLAIM:
1. A lubrication arrangement for a rotating machine, the rotating machine having components to be lubricated, the lubrication arrangement comprising:
a lubricant reservoir; and
a first arrangement of one or more conduits;
in which the reservoir is located above the components and is connected to the first arrangement of conduits, and in which the first arrangement of conduits includes outlets positioned so as to direct a lubricant passing through the first arrangement of conduits to a first set of components;
wherein, under certain operating conditions, the lubricant is caused to flow by gravity from the reservoir to the one or more components via the first arrangement of conduits.
2. A lubrication arrangement according to claim 1, in which the first set of components includes one or more bearings.
3. A lubrication arrangement according to claim 1 or claim 2, additionally comprising:
a second arrangement of one or more conduits;
in which the reservoir is connected to the second arrangement of conduits, and in which the second arrangement of conduits includes outlets positioned so as to direct a lubricant passing through the second arrangement of conduits to a second set of components.
4. A lubrication arrangement according to claim 3, in which the second set of components includes one or more gear meshes.
5. A lubrication arrangement according to claim 3 or claim 4, additionally comprising one or more valves which determine a flow of lubricant through the first and second arrangements of conduits. 14

6. A lubrication arrangement according to any of claims 3 to 5, in which a division of lubricant flow between the first set of components and the second set of components is different, according to the operating conditions.
7. A lubrication arrangement according to any of claims 3 to 6, in which the second arrangement of conduits additionally incorporates one or more pumps.
8. A lubrication arrangement according to any preceding claim, in which the rotating machine includes:
an outlet for lubricant, and
a pump to transfer lubricant from the outlet to the lubricant reservoir.
9. A lubrication arrangement according to any preceding claim, additionally comprising a second lubricant reservoir, the second lubricant reservoir located below the one or more components to be lubricated, and configured to receive a flow of lubricant from the components to be lubricated.
10. A lubrication arrangement according to claim 9, in which the second reservoir has a capacity smaller than a total volume of oil in the lubrication arrangement, such that when the lubricant reservoir is empty, the second reservoir will be full, and the remaining proportion of the total volume of oil will remain within a housing of the rotating machine and the lubrication arrangement will be a wet sump arrangement.
11. A lubrication arrangement according to claim 9 or claim 10, additionally comprising one or more pumps operable to cause lubricant to flow from the second lubricant reservoir to the lubricant reservoir.
12. The lubrication arrangement according to claim 11, additionally comprising a means for sensing a level of lubricant in the reservoir and/or in the second reservoir, 15

and in which the one or more pumps operate according to a predetermined level of lubricant.
13. A lubrication arrangement according to claim 11 or claim 12, in which one or more of the one or more pumps may be operated by means of electrical power from an electrical grid.
14. A lubrication arrangement according to claim 11 or claim 12, in which one or more of the one or more pumps may be operated by means by means of electrical power supplied by a battery.
15. A lubrication arrangement according to claim 11 or claim 12, in which one or more of the one or more pumps are operated by means by means of electrical power supplied by a generator.
16. A lubrication arrangement according to claim 11 or claim 12, in which one or more of the one or more pumps are operated by means by means of electrical power supplied by a photovoltaic panel.
17. A lubrication arrangement according to claim 11 or claim 12, in which one or more of the one or more pumps are operated by means by means of electrical power supplied by a wind turbine.
18. A lubrication arrangement according to claim 11 or claim 12, in which one or more of the one or more pumps are operated by a human operator.
19. A lubrication arrangement according to any preceding claim, in which said rotating machine is a gearbox, a transmission or a generator.
20. A lubrication arrangement substantially as described herein with reference to the drawings.
21. A gearbox comprising the lubrication arrangement according to any preceding claim.
22. A wind turbine comprising the lubrication arrangement according to any preceding claim.