Pre-lubrication system for a generator set

Abstract

A method and apparatus for pre-lubricating an engine of a generator set has a primary oil pump 110 and a secondary oil pump 152. In use, the secondary oil pump is configured to circulate oil through the engine 202 via a pathway which bypasses the primary oil pump, and a controller 180 selectively activates the secondary oil pump in response to a monitored voltage of a primary power supply for the primary pump. The primary oil pump power supply may be AC and the secondary oil pump power supply may be DC, and the secondary pump control may be activated for example if the AC line-to-line voltage falls below a threshold. The DC power supply may be provided by at least one battery 160, and sensing 182, 184 and switching 162, 164 apparatus may be connected between the pumps and the controller. The arrangement can be mounted on a skid 220 using anti-vibration mounts, and the skid may include a pair of opposed side members 12, a plurality of cross members 14, and the primary pump. The secondary pump and / or the controller may be mounted on a side member. In the event of a loss of primary oil pump power, such as AC power, the arrangement ensures engine pre-lubrication from the secondary pump, for example via a DC battery source.

Description

The present invention relates to a pre-lubrication system for an engine, and in particular to a pre-lubrication system for lubricating an engine of a generator set prior to start-up of the generator set. Some generator sets comprise a generator, coupled to an internal combustion engine, such as a gas (e.g. lean burn natural gas), petrol or diesel engine. The engine drives the generator in order to generate electrical power. The engine and generator run at a fixed speed of typically 1500 rpm or 1800 rpm to provide 50Hz or 60Hz AC voltage to a load. The generator set may be used in prime-power mode as the main source of power to utility loads, or in stand-by mode to supply critical loads in case of main distribution grid failure. In either case, it may be necessary to shut down and subsequently restart the generator set, for example, for servicing or grid management. During operation of an internal combustion engines, a lubricant such as engine oil is typically circulated throughout the engine to reduce friction and wear on moving parts. The oil creates a separating film between surfaces of adjacent moving parts to minimize direct contact between them, decreasing friction and reducing wear. However, on initial start-up of the engine, there may be little or no lubricant present in some or all components of the engine. When an insufficiently lubricated engine is initially activated, dry start-up friction can cause wear on moving parts. Generator set engines may therefore be provided with a pre-lubrication (“prelube”) system, which circulates lubricant throughout the engine, to lubricate (or prime) the engine before it is started, thereby to decrease dry startup friction and prolong the life of the engine. A known pre-lubrication system can include a pre-lubrication (or priming) pump having AC power, (e.g., utility / mains power), to operate. In the event of a loss of AC power (such as during a total outage of utility power), or if the pre-lubrication pump is not operating, the engine may not be sufficiently pre-lubricated. Pre-lubrication can vary among types of generator set, for example a multi-turbo generator set can be provided with a cyclic pre-lubrication function, whilst a single-turbo generator can have a single cycle of pre-lubrication prior to starting the engine. According to a first aspect, a pre-lubrication system for pre-lubricating an engine of a generator set includes: a primary pump configured to receive power from a primary power supply and to circulate oil though the engine; a secondary pump, configured to receive power from a secondary power supply, wherein the secondary pump is configured to circulate oil through the engine via a pathway which bypasses the primary pump; and a controller configured to control the secondary pump, wherein the controller is configured to monitor a voltage of the primary power supply and to selectively activate the secondary pump in dependence on the monitored voltage. The systems and methods described herein can provide an improved pre-lubrication system for a generator set. The pre-lubrication system may provide the advantage that, by providing a secondary pump configured to receive power from a secondary power supply and to circulate oil through the engine via a pathway which bypasses the primary pump, it may be possible to ensure that the engine is sufficiently pre-lubricated in the event of a fault preventing or restricting operation of the primary pump, such as a loss of or reduction in power from the primary power supply or a malfunction of the primary pump or associated component. The pre-lubrication system can provide a secondary pre-lubrication system for an engine, which can be installed in parallel to a primary pre-lubrication pump. The secondary pre-lubrication system comprises a pump which can run from a secondary power supply, and may therefore be operated in the event of a full or partial loss of function of the primary pre-lubrication pump, for example as a result of a malfunction of one or more components or connections, or a failure of the primary power supply. The secondary pre-lubrication pump may be able to run a full pre-lubrication cycle from start to finish if the primary pre-lubrication pump fails to activate, or the secondary pump may be able to take over from the primary pre-lubrication pump if the primary pre-lubrication pump fails after activation and before the required pre-lubrication cycle is complete. It may also be possible for the primary pump and the secondary pump to operate simultaneously if for example power received from the primary power supply is reduced but still available. In this case, the secondary pump may supplement the pumping action of the primary pump. The primary power supply may be an AC power supply and the secondary power supply may be a DC power supply. The AC power supply may comprise utility power or any other AC power source such as one or more other generator sets or renewable energy sources. The AC power supply may be single phase, three phase, or any other number of phases. The DC power supply may comprise one or more batteries or any other appropriate DC power source such as a DC power supply unit. The pre-lubrication system may enable a pre-lubrication cycle to be completed in the event of the failure of an AC power supply, for example during a total outage of utility I mains power. The DC pre-lubrication pump can take over from the AC pre-lubrication pump if it fails part-way through a pre-lubrication cycle. Alternatively, if the AC pre-lubrication pump fails to activate, the DC pre-lubrication pump can start and complete a full pre-lubrication cycle, i.e. an engine of a generator set may be provided with “black-start” capability. If appropriate, the secondary pump may also supplement the primary pump if it is unable to produce sufficient flow. The system may further comprise a suction conduit for receiving oil from the engine and a discharge conduit for discharging oil to the engine. The suction conduit may be arranged to receive oil from an engine sump. For example, the suction conduit may comprise a connector for connecting the suction conduit to the sump. The discharge conduit may be arranged to discharge oil to an engine oil gallery. For example, the discharge conduit may comprise a connector for connecting the discharge conduit to the oil gallery. The primary pump may have an output coupled to the discharge conduit and / or an input coupled to the suction conduit. The secondary pump may have an output coupled to the discharge conduit and / or an input coupled to the suction conduit. For example, the secondary pump may be coupled to a bypass discharge conduit and a bypass suction conduit. The bypass discharge conduit may be coupled to the discharge conduit, and the bypass suction conduit may be coupled to the suction conduit. An output of the secondary pump may be coupled to the discharge conduit via a discharge three-way connector. For example, the bypass discharge conduit may be coupled to the discharge conduit via a discharge three-way connector. A one-way valve may be provided between the primary pump and the discharge three-way connector, and the one-way valve may be arranged to prevent flow of oil into the primary pump during use of the secondary pump. This may provide bypassing of the primary pump whilst the secondary pump is being operated, thereby to prevent the primary pump from being motored whilst the secondary pump is being operated. The one-way valve may be provided in the discharge conduit. Alternatively, the one-way valve may be provided integrally within the primary pump or within the discharge three-way connector. Providing the one-way valve within the discharge three-way connector may reduce a number of components required. An input of the secondary pump may be coupled to the suction conduit via a suction three-way connector. For example, the bypass suction conduit may be coupled to the suction conduit via a suction three-way connector. A one-way valve may be provided between the secondary pump and the suction three-way connector; the one-way valve may be arranged to prevent flow of oil into the secondary pump during use of the primary pump. The secondary pump may thereby be prevented from being motored whilst the primary pump is being run. The controller may be configured to activate the secondary pump in response to a monitored voltage being below a voltage threshold value. The prelubrication system may further comprise a voltage sensor configured to sense at least one voltage of the primary power supply, such as a line to line voltage and / or a line to neutral voltage. The controller may be configured to activate the secondary pump in response to receiving a voltage reading (for example, line to line voltage or line to neutral voltage) from the voltage sensor of below a voltage threshold value. The controller may therefore activate the secondary pump if an insufficient voltage is being supplied to the primary pump. The controller may be configured to calculate a difference between a minimum value and a maximum value of line to line voltage readings of the primary power supply, and to activate the secondary pump if the difference is equal to or above a difference threshold value. For example, in the case of a three-phase AC power supply, the controller may activate the secondary pump if one phase-to-phase voltage is different from another phase-to-phase voltage by more than the difference threshold. The controller may therefore not activate the secondary pump if a non-significant voltage drop is calculated, i.e. a voltage drop which is below the difference threshold value, which can be expected when the power supply to the primary pump is operating normally. However, if the controller calculates a voltage drop of equal to or greater than the difference threshold value, which is indicative of a partial loss of primary power supply to the primary pump, the secondary pump can be activated. The difference threshold value may be, for example, 25% of the maximum value of line to line voltage, i.e. the controller 180 may determine whether the minimum detected line to line voltage is more than 25% lower than the maximum detected line to line voltage, although of course other values such as 50%, 40%, 30%, 20% or 10% could be used instead. The system may further comprise a voltage sensor for sensing a voltage of the secondary power supply. The controller may be further configured to monitor a voltage of the secondary power supply and to inhibit operation of the secondary pump if the voltage is below a threshold. The controller can therefore inhibit operation of the secondary pump if the secondary power supply is below an operational voltage. This may be the case, for example, if the secondary power supply comprises one or more batteries and the batteries are not sufficiently charged. The controller may also be able to send feedback to a generator interface box unit. A user may then take action to ensure a sufficient voltage can be provided by the secondary pump, and allow the controller to resume operation of the secondary pump. The controller may be arranged to receive a pre-lubrication signal and to activate the secondary pre-lubrication system in response to the pre-lubrication signal. The pre-lubrication signal may be a signal indicating that pre-lubrication is required. The pre-lubrication signal may signal may be, for example, a signal which is asserted by a change in state, or a command sent by a communications link, or any other form of signal which can be acted on by the controller. This may enable the controller to initiate, or continue, a pre-lubrication cycle by the secondary pre-lubrication system, in response to a signal sent from a generator interface unit or other component. Thus, the controller may be configured to activate the secondary pump in dependence on both a pre-lubrication signal and the monitored voltage. The controller may be arranged to deactivate the secondary pre-lubrication system in response to the pre-lubrication signal ceasing. Alternatively the controller may be arranged to deactivate the DC pre-lubrication system in response to any other form of signal or command. When an engine has been sufficiently pre-lubricated, the pre-lubrication signal may be terminated (or an end command could be sent, for example, by an engine control module or a generator interface unit). In response, the controller may deactivate the secondary pump if it is running at the time the pre-lubrication signal is terminated. The primary pump, if active, may also be deactivated either by the controller or another device such as a switch. The controller may be configured to store an end time of a most recent pre-lubrication cycle and / or operation of the engine, and to calculate a time lapse since the end time; and to compare the time lapse with a pre-determined threshold. This may enable, for example, the controller to signal to an engine control module or a generator interface unit that a pre-lubrication cycle is not currently required as the time lapse since the last cycle is below a threshold, and that the engine will therefore still be sufficiently pre-lubricated from the previous cycle. The pre-lubrication system may further comprise mounting means, for mounting the primary pump and / or the secondary pump on a skid of the generator set. The mounting means may comprise anti-vibration mounts. The primary and secondary pumps could therefore be mounted on a skid, and the generator set which they are provided to pre-lubricate could also be mounted on the skid. The anti-vibration mounts can act to isolate the pumps from any vibrations during operation of the generator set. In a second aspect, a skid for a generator set comprises a pre-lubrication system according to the first aspect. The skid may comprise a pair of opposed side members and a plurality of cross members, and the primary pump, the secondary pump and / or the controller may be mounted on a side member. In a third aspect, a generator set comprises a generator, an engine, and a pre-lubrication system according to the first aspect. The primary pump and the secondary pump may be fluidly connected to an oil sump of the engine and to an oil gallery of the engine. The generator set may further comprise a generator interface unit arranged to receive inputs from and / or provide outputs to a user of the generator set. The generator interface unit may be arranged to send commands and / or signals to the controller and / or to receive feedback signals from the controller. The controller may therefore receive operational commands and / or signals from the generator interface unit, and send feedback back to the generator interface unit. The generator interface unit may be arranged to send a pre-lubrication signal (which may indicate that pre-lubrication is required) to a switch between the primary power supply and the primary pump. The generator interface unit may be arranged to send a pre-lubrication signal (which may be the same as or different from that sent to the switch) to the controller. A pre-lubrication cycle may therefore be initiated in response to a signal sent from the generator interface unit. Alternatively, a pre-lubrication start command could be sent from another component, such as an engine control module. The generator interface unit may be arranged to terminate a pre-lubrication signal (or send a pre-lubrication end command) to the switch between the primary power supply and the primary pump, for example, when pre-lubrication is completed or no longer required. The generator interface unit may be arranged to terminate a pre-lubrication signal (or send a pre-lubrication end command) to the controller. When an engine has been sufficiently pre-lubricated, a pre-lubrication cycle may therefore by ended in response to a signal from the generator interface unit. Alternatively, a pre-lubrication end command could be sent from another component, such as an engine control module. The feedback signals may include fault signals, and the fault signals may be displayed on a user interface (such as a display) of the generator set interface unit. This may allow an operator of the generator set to view fault signals received from the controller so that appropriate action may be taken to correct the fault. In a fourth aspect, a method of pre-lubricating an engine of a generator set, by a pre-lubrication system comprising a primary pump configured to receive power from a primary power supply and to circulate oil though the engine; and a secondary pump, configured to receive power from a secondary power supply and to circulate oil through the engine via a pathway which bypasses the primary pump, is provided. The method comprises: monitoring a voltage of a primary power supply, and in dependence on the monitored voltage selectively activating the secondary pump. The method may enable an engine of a generator set to be pre-lubricated by a secondary pump on failure (or partial failure) of a primary pump or its power supply, thereby allowing the engine to be started without the risk of damage which would otherwise result from dry-start-up friction, thereby prolonging the life of the engine. The primary pump may be activated in response to receiving a pre-lubrication signal. The pre-lubrication signal may be issued by a generator interface unit of the generator set, in response to a user input into a user interface (such as a keypad, touch screen and so forth) of the generator interface unit, and / or automatically prior to start-up of the engine. A pre-lubrication cycle could therefore be initiated manually or automatically. The pre-lubrication signal may be issued at predefined regular time intervals. This may enable intermittent pre-lubrication of an engine. The method may further comprise receiving line to line voltage readings from a voltage sensor which is configured to sense line to line voltages across the primary power supply and the primary pump. The voltage sensor may be positioned between a switch for activating the primary pump, and the primary pump. The secondary pump may be activated in response to receiving a line to line voltage reading from the voltage sensor of below a voltage threshold value. The method may further comprise calculating a difference between a minimum value and a maximum value of line to line voltage readings taken across the primary power supply, and activating the secondary pump if the difference is equal to or above a difference threshold value. The method may further comprise monitoring a voltage of the secondary power supply, and inhibiting operation of the secondary pump if the voltage is below a threshold. The method may further comprise receiving a pre-lubrication signal and activating a pre-lubrication process in response to the pre-lubrication signal. The method may also comprise deactivating the pre-lubrication process in response to the pre-lubrication signal ceasing. The method may further comprise storing an end time of a most recent full pre-lubrication cycle or engine operation and calculating a time lapse since the end time; and comparing the time lapse with a pre-determined threshold. The method may be at least partially carried out by a controller. The method may further comprise a generator interface unit sending commands and / or signals to the controller and receiving feedback signals from the controller. The fault signals may be displayed on a user interface of the generator set interface unit. Preferred embodiments will now be described by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows schematically a generator set; Figure 2 shows schematically a generator set and a pre-lubrication system in an embodiment; Figure 3 shows schematically a pre-lubrication system in an embodiment connected to an engine; Figure 4 shows a part of a pre-lubrication system in one embodiment; Figure 5 shows a pre-lubrication system in an embodiment; Figure 6 shows the pre-lubrication system mounted on a generator set skid; Figure 7 shows some of the electrical components in the pre-lubrication system, and a generator set interface box; and Figure 8 shows steps taken by a pre-lubrication system in one embodiment. Figure 1 shows schematically a generator set (genset). The generator set 200 comprises an engine 202 and a generator 204 which are mechanically coupled to each other. The engine 202 and the generator 204 are each mounted to a skid (bed frame) 220. The engine 202 includes an oil sump 206 containing oil, and a main oil distribution gallery 208. During operation of the engine 202, a main oil pump (not shown) circulates oil from the engine sump 206 through the main oil distribution gallery 208, thereby reducing friction between moving parts of the engine 202. The generator set 200 includes a generator set interface box (GIB) 210, which includes an interface 212. Figure 2 shows schematically a generator set 200 and a pre-lubrication system 100 in an embodiment. The pre-lubrication system 100 is mounted to the skid 220, and is connected to the oil sump 206 and to the main oil gallery 208 of the engine 202. A DC pre-lubrication system controller 180 of the pre-lubrication system 100 is in communication with the GIB 210 via an electrical connection 136. The controller 180 can therefore receive commands and / or signals from, and send feedback back to, the GIB 210. Figure 3 shows schematically a pre-lubrication system 100 connected to an engine 202. Referring to Figure 3, pre-lubrication system 100 comprises a controller 180, a primary, AC pre-lubrication system 108, and a secondary, DC pre-lubrication system 150 installed in parallel with the AC pre-lubrication system 108. The AC pre-lubrication system 108 comprises an AC pre-lubrication pump 110, and the DC pre-lubrication system 150 comprises a DC pre-lubrication pump 152. The AC pre-lubrication system 108 and the DC pre-lubrication system 150 are each fluidly connected to the engine 202 and can be used independently of one another (or concurrently) to circulate a lubricating medium such as oil through the engine 202 as further explained below. The AC pump 110 of the AC pre-lubrication system 108 is connected to an AC power supply I source 130. The AC power supply 130 could be provided by a utility I mains power supply or any other source. In one embodiment, the AC power supply is a three-phase power supply with a nominal voltage of, for example, of 380-480V, although other numbers of phases and nominal voltages could be used instead. The GIB 210 is connected to an AC system switch 162 positioned between the AC power supply 130 and the AC pump 110. The GIB 210 can thereby control the AC pump 110 via the AC system switch 162. The switch 162 comprises a plurality of contactors, and the controller 180 is arranged to open and close the contactors, in order to connect or disconnect the AC pump 110 from the AC power supply 130. The AC system switch 162 may comprise a miniature circuit breaker (MCB), which will trip to interrupt the AC power supply 130 to the AC pump 110 in the event of a short-circuit or an overload. Alternatively or in addition, a circuit breaker could be provided elsewhere between the AC power supply 130 and the AC pump 110. An AC system voltage sensor 182 is connected between the AC system switch 162 and the AC pump 110, and is configured to continually sense voltages of the AC power supply 130. The AC system voltage sensor 182 may sense line to line voltages. A line to line voltage is the voltage between any two given phases of the AC power supply. For a three phase power supply, the line to line voltage would be the voltage between any two of the three phases. The AC system voltage sensor 182 is in communication with the controller 180, to send line to line voltage readings to the controller 180, thereby allowing the controller 180 to selectively activate the DC pre-lubrication system 150 based on the voltage readings, as further explained below. The DC pump 152 of the DC pre-lubrication system 150 is connected to a DC power supply 160, such as a battery source. The battery source could, for example, comprise one or more batteries, such as 12V or 24V batteries. The battery source could be provided by starter batteries used to start the engine, or could be a dedicated pre-lubrication battery, or a combination of the two. The controller 180 is connected to a DC system switch 164 positioned between the DC power supply 160 and the DC pump 152. The controller 180 can thereby control the DC pump 152 via the DC system switch 164. The switch comprises one or more contactors, and the controller 180 is arranged to open and close the contactors in order to connect and disconnect the DC power supply 160 to and from the DC pump 152. A DC system voltage sensor 184 is connected between the DC power supply 160 and the DC pump 152, and is configured to detect a voltage across the DC power supply 160. The voltage sensor 184 is in communication with the controller 180, to send DC voltage readings to the controller 180. Figure 4 shows part of the pre-lubrication system 100 (the controller 180 is omitted from this figure). Figure 5 shows the pre-lubrication system 100 including the controller 180. Referring to Figures 3 to 5, the AC pump 110 has an output port coupled to a discharge hose 112 via a connector 192a, and an input port coupled to a suction hose 114 via a connector 192b. The discharge hose 112 is connectable, at an end distal to the AC pump 110, to the main oil gallery 208 of the engine 202, via a connector 192c. The suction hose 114 is connectable, at an end distal to the AC pump 110, to the sump 206 of the engine 202, via connector 192d. A fluid circulation pathway is defined, connecting the AC pump 110 with the engine 202 via the discharge hose 112 and the suction hose 114. The AC pump 110, when activated, circulates oil from the engine sump 206 through the main oil gallery 208 of the engine 202, thereby to pre-lubricate the engine 202. The DC pump 152 has an output port coupled to a bypass discharge hose 154 via connector 194a, and in input port coupled to a bypass suction hose 156 via a connector 194b. The bypass discharge hose 154 is coupled, at an end distal to the DC pump 152, to the discharge hose 112, via a first three-way connector, comprising a first T-piece connector 140. In the embodiments of Figures 4 and 5, the first T-piece connector 140 is positioned adjacent to the AC pump 110. However, the first T-piece connector 140, or another form of three-way connector, could alternatively be provided part-way along the discharge hose 112, for example as illustrated schematically in Figure 3. The bypass suction hose 156 is coupled, at an end distal to the DC pump 152, to the suction hose 114 via a second three-way connector, comprising a second T-piece connector 144. In the embodiments of Figures 4 and 5, the second T-piece connector 144 is positioned adjacent to the connector 192d for connecting to the engine sump 206. However, the second T-piece connector 144, or another form of three-way connector, could alternatively be provided part-way along the suction hose 114, for example as illustrated schematically in Figure 3. The DC pump 152 is thereby fluidly connected with the engine 202. In the embodiments of Figures 4 and 5, the fluid pathway between the DC pump 152 and the engine 202 comprises the bypass discharge hose 154, the discharge hose 112, and the bypass suction hose 156. In the embodiment of Figure 3, wherein the T-piece connectors are located part-way along the respective hoses, the fluid connection between the DC pump 152 and the engine 202 comprises the bypass discharge hose 154, part of the discharge hose 112, part of the suction hose 114, and the bypass suction hose 156. The DC pump 152, when activated, circulates oil from the engine sump 206 through the main oil gallery 208 of the engine 202, thereby to pre-lubricate the engine 202. The pathway around which the DC pump 152 circulates oil therefore bypasses the AC pump 110. A one way I non-return valve 188 (indicated schematically in Figure 3) is provided between the DC pump 152 and the first T-piece connector 140, to prevent oil flowing into the DC pump 152 during use of the AC pump 110. The valve 188 could be provided part way along the bypass discharge hose 154 as illustrated in Figure 3, or could be provided integrally within the DC pump 152, or integrally within the first T-piece connector 140. A one way I non-return valve 186 (indicated in Figure 3) is also provided between the AC pump 110 and the first T-piece connector 140, to prevent oil flowing into the AC pump 110 during use of the DC pump 152. The valve 186 could be provided part way along the discharge hose 112, as shown in Figure 3, or could be provided integrally within the AC pump 110, or integrally within the first T-piece connector 140. Figure 6 shows the pre-lubrication system 100 mounted on a generator set skid in one embodiment. Referring to Figure 6, the generator set skid 220 comprises a pair of opposing side members 12, cross members 14 (one of which is shown in Figure 6), and a pair of engine mounts 16. The side members 12 and cross members 14 have an l-shaped cross section, and may be for example rolled steel joists. The side members 12 extend parallel to each other in a longitudinal direction. The cross members 14 extend between the pair of side members 12. The engine mounts 16, arranged to support the engine, are provided on top of one of the cross members 14. Other cross members and the appropriate mounts (not shown) are also provided for mounting the generator 204 and other components of the generator set to the skid 220. The AC pump 110 comprises a plurality of anti-vibration mounts 224 (two of which are visible in Figures 4 to 6), by which it is attached to the skid 220. The DC pump 152 is similarly provided with a plurality of anti-vibration mounts 228 (two of which are visible in Figures 4 to 6), by which it is attached to the skid 220. In the arrangement of Figure 6, the AC pump 110 and the DC pump 152 are each mounted on an inside of one the side members 12 via their respective anti-vibration mounts 224, 228. The controller 180 is mounted to the top of the same side member 12. The anti-vibration mounts 224, 228 act to isolate the AC and DC pumps from any vibrations from the engine. The controller 180 is hard mounted via a bracket 230 to a side member 12 of the skid 220, to isolate any operational vibrations. The controller 180 could alternatively be mounted via anti-vibration mounts. A battery pack forming the DC power supply 160 is provided on an opposing side of the side member 12 to which the AC pump 110 and DC pump 152 are mounted. Figure 7 shows some of the electrical components, and the electrical connections between the components, in an embodiment of the pre-lubrication system. Referring to Figure 7, pre-lubrication system 100 comprises AC pump 110, DC pump 152, DC power supply 160, AC system switch 162, controller 180 and control relay 138. The AC pump 110 receives power from a three-phase AC supply 130, via the AC system switch 162. The DC pump 152 receives power from the DC supply 160 via controller 180 and the contacts 139 of the control relay 138. Also shown in Figure 7 is priming logic circuitry 211 which is part of a generator interface box (GIB) 210. An output of the priming logic circuitry 211 is connected to an input terminal of the switch 162 and to an input terminal of the control relay 138. Although a three-phase AC supply is shown in Figure 7, an AC supply with a different number of phases, such as a single phase, could be used instead. In this embodiment, the following three types of pre-lubrication are available: 1. Manual. If the engine is not in a run state and a manual input (GIB button) is active, then the system turns on the pre-lubrication system. Exceptions may be provided, for example, for fire stop and e-stop states. 2. Pre-start. This runs the pre-lubrication system when the user requests an engine start and before cranking the engine. Generally, the oil pressure will be required to meet an oil pressure threshold within a specified time, and if it does not meet this threshold then the engine is considered not pre-lubricated. Pre-start may also run during vent and start cycles. 3. Intermittent. The pre-lubrication process may run at defined intervals as well as during the vent and start cycles. In this embodiment, the main control of the priming pump is through the priming logic circuitry 211 in the GIB 210. The priming control logic 211 provides a negative signal whenever the pump is required to run. This negative signal controls both the AC system switch 162 and the relay 138. The relay 138 sends a separate negative signal to the controller 180. The control relay 138 is provided in order to separate the priming control logic 211 from the controller 180 and avoid the possibility of unwanted interaction between the two. In operation, when pre-lubrication of the engine is required, the priming control logic 211 sends out a negative signal for the generator set priming pump to run. This will close the contactors in the switch 162, which will connect the AC (utility) supply 130 to the AC priming pump 110. If the AC supply 130 is available, this turns on the AC pump 110, causing oil to be circulated through the engine. In parallel with this, the relay 138 is also operated and applies a negative signal to the controller 180 via the contacts 139 of the control relay 138. This will call the DC pump 152 to engage. However, within the controller 180, there is a slight delay between receiving the signal to run the DC pump 152 (via relay 138) and actually switching the DC supply 160 onto the pump itself. During this delay, the controller 180 monitors the AC voltage at the AC priming pump 110. If the AC voltage is deemed to be present, the controller 180 will not switch DC voltage supply 160 onto the DC pump 152. However, if AC voltage is not measured at the AC priming pump 110 (or is below one or more thresholds), the controller 180 will recognise this as an AC failure and subsequently switch the DC supply 160 onto the DC pump 152. By measuring AC voltage at the AC pump itself and not at the utility supply terminals, the DC back-up system can recognise either a loss of AC voltage due to utility failure or instances where the switch 162 has either failed, been erroneously switched to an off position or tripped following an AC priming pump fault. This may provide a reasonably high level of back-up against failure of the AC priming system. When the AC supply 130 is operating normally, i.e. under a healthy three-phase utility supply, after the pre-lubrication signal has been sent out by the GIB 210, and the AC switch 162 has opened to provide power from the AC supply 130 to operate the AC pump 110, the AC pump 110 will then operate to circulate oil through the engine thereby to initiate a pre-lubricate cycle. If the AC supply 130 is operating sufficiently, the controller 180 will detect that one or more of the line-to-line voltages received from the AC system voltage sensor 182 is above a threshold, or that the difference between the maximum line-to-line voltage and the minimum line-to-line voltage is below a threshold, and will not switch on the DC power supply 160 to operate the DC pump 152. However, if the controller 180 detects that one or more of the line-to-line voltages is below a threshold, or the difference between the maximum line-to-line voltage and the minimum line-to-line voltage exceeds a threshold, it will proceed to connect the DC supply 160 to the DC pump 152. This turns on the DC pump 152, which then circulates oil through the engine. Figure 8 shows steps taken by pre-lubrication system in one embodiment. The DC pre-lubrication system may be a system 100 as described with reference to earlier figures. Further reference numerals are provided below in accordance with the earlier figures. A pre-lubrication signal is issued by the GIB 210 when pre-lubrication of the engine 202 is required. The pre-lubrication signal may be issued by the GIB 210 for various reasons. For example, a user may have manually input a pre-lubrication run command into the interface 212, or the GIB 210 may be configured to issue the signal automatically prior to start-up of the engine 202. The GIB 210 may additionally be configured to issue the signal at predefined regular or non-regular time intervals, to provide intermittent pre-lubrication of the engine 202. Referring to Figure 8, the priming start command, i.e. the pre-lubrication signal, is received in parallel by the AC system switch, and by the DC system controller 180, at step 300. When the AC system switch 162 receives the pre-lubrication signal, at step 302, it closes its contactors. If AC power is available, the AC pump 110 begins to operate, to begin a pre-lubrication cycle, by circulating oil throughout the engine. Step 304 is an optional time lapse check by the DC system controller 180 The controller 180 may be configured to store an end time of a most recent full pre-lubrication cycle (or operation of the engine), and on receiving a pre-lubrication signal, to compare a time lapse since the last cycle with a threshold. An engine will be optimally lubricated immediately after the end of a full pre-lubrication cycle, and will remain sufficiently lubricated for a certain amount of time following the full pre-lubrication cycle. For example, an engine could remain sufficiently pre-lubricated for 15 minutes following a full pre-lubrication cycle. Therefore, when the controller 180 receives the pre-lubrication signal from the GIB 210, it may compare, at optional step 304, a time lapse TL, i.e. an amount of time which has passed, since an end time of the most recent full pre-lubrication cycle, to predetermined threshold TTL. If the time lapse TL is greater than the predetermined threshold TTL, the controller 180 will proceed to step 308 as described below. If the time lapse TL is less than the predetermined threshold TTL, the controller 180 may inhibit proceeding to step 308, and may, at optional step 321, send a signal back to the GIB 210, i.e. to communicate to the GIB 210 that no pre-lubrication (priming) is required at the present time. The voltage sensor 182 which is provided between the AC system switch 164 and the AC pump 110 continually senses the line to line voltages, V, of the AC power supply 130. A line to line voltage is the voltage between any two given phases of the AC power supply, i.e. for a three phase power supply, each line to line voltage is the voltage between two of the three phases. At step 308, the controller 180 receives the line to line voltage readings from the AC system voltage sensor 182. At step 310, the controller 180 compares the line to line voltage values received from the AC system voltage sensor 182 to a first threshold value, T1. The first threshold value T1 is a predetermined value. The first threshold value T1 could be set dependent upon the nominal supply voltage of the AC power supply. For example, for a three-phase power supply with a nominal supply voltage of 380-480V, the predetermined minimum threshold value T1 could be 250V AC. The threshold value T1 could be set as a certain percentage of a nominal supply voltage. The percentage could be, for example, 75% or any other appropriate value. A line to line voltage reading, i.e. a voltage reading between two of the phases of the AC power supply, of less than the first threshold T1 value, indicates that the power being supplied by the AC power supply 130 is insufficient to power the AC pump 110. This could be caused by a failure of the AC power supply 130 (e.g. full outage or non-availability of utility I mains power), or as a result of the AC power supply 130 being interrupted by the tripping of a circuit breaker within the AC system switch 162 on malfunction of one or components of the AC system 108, or of the generator set. Therefore a line to line voltage of less than the first threshold value T1 indicates a fault condition (step 316). If the controller 180 does not receive any line to line voltage values of less than the first threshold value T1, it proceeds to step 312. At step 312, the controller 180 identifies a minimum detected line to line voltage Vmin and a maximum detected line to line voltage, Vmax, and calculates a voltage drop, by calculating a difference between the minimum and maximum detected line to line voltages, △V, i.e. AV = Vmax - Vmin. Following step 312, at step 314, the controller 180 compares the difference between the detected minimum and maximum line voltages, AV, to a second threshold value T2. During normal operation of the AC power supply 130 the phase-to-phase voltages will remain substantially constant, and any voltage drop AV will be nonsignificant, i.e. any voltage drop will remain below the second threshold value T2. However, a voltage drop of equal to or greater than the second threshold value is indicative of a partial loss of AC power supply to the AC pump 110, i.e. a loss of one of the phases of the AC power supply, or of a significant voltage drop on one of the phases. The second threshold value T2 could be determined by the controller 180 based on the detected maximum line to line voltage Vmax. For example, the second threshold value T2 could be determined by the controller 180 as being a certain percentage, e.g. 25%, of the detected maximum line to line voltage Vmax, i.e. the controller 180 determines whether the minimum detected line to line voltage Vmin is more than 25% lower than the maximum detected line to line voltage Vmax. If the controller 180 does not detect, at step 314, a voltage drop AV which is equal to or in excess of the second threshold value T2, it proceeds to step 400. In step 400, the controller determines whether the pre-lubrication signal has ceased. When the engine 202 is sufficiently pre-lubricated, the GIB 210 stops sending the pre-lubrication signal to the controller 180 and the AC system switch 164. If the pre-lubrication signal has not ceased, then the controller returns to step 308. Therefore, whilst sufficient operation of the AC pre-lubrication system 108 is maintained, the controller 180 continually monitors received voltages, i.e. by repeating the voltage monitoring cycle of steps 308, 310, 312, 314, until the pre-lubrication signal ceases (or a cease command is received). When the pre-lubrication signal ceases, the method ends. If, at step 314, the controller 180 detects a voltage drop AV which is equal to or in excess of the second threshold value T2, a fault condition is indicated (step 316). After a fault condition has been indicated (either as a result of the outcome of step 310 or step 314), at step 322 the controller 180 activates the DC pre-lubrication system 150, by activating the DC pump 152, by closing the contactors in the DC system switch 164. As an optional additional step following step 322, the controller 180 may be configured to check, at step 318, that a voltage of the DC power supply 160 (as sensed by the DC system voltage sensor 164), is equal to or above a predetermined required voltage, Vreq. The voltage of the DC power supply 160 may be insufficient for the DC pre-lubrication pump 152 to function for example, as a result of a malfunction, or if the batteries are insufficiently charged, or are at mid- to end- of life. For example, if the DC power supply 160 comprises a 24V battery source, the controller 180 may be configured to check that at least 20V is available to the DC pump 152. If the voltage of the DC power supply 160 is below the pre-determ ined threshold Vreq, the controller 180 may be configured to inhibit operation of the DC pre-lubrication system 150, and to send a fault signal to the GIB 210 (step 320). The fault condition may be presented to a user, for example, it may be displayed on the interface 212; the user may then take action to replace the DC power supply 160, and allow the controller 180 to continue on to step 322 to activate the DC pre-lubrication system 150. If the voltage of the DC power supply 160 is not below the pre-determined threshold Vreq, operation of the DC pre-lubrication system 150 is maintained. After the controller 180 has activated the DC pre-lubrication system 150, the DC pre-lubrication system 150 then takes over the pre-lubrication cycle, i.e. the DC pump 152 acts, instead of the AC pre-lubrication pump 110, to circulate oil from the engine sump 206 throughout the main oil gallery 208 of the engine 202, thereby to pre-lubricate the engine 202. In some circumstances (for example, low but not completely absent AC voltage), the DC pump may operate together with the AC pump. When the engine 202 is sufficiently pre-lubricated, the GIB 210 ceases the pre-lubrication signal to the controller 180 and the AC system switch 164. When the AC system switch 164 stops receiving the pre-lubrication signal, at step 404, it closes its contactors, thereby disconnecting the AC pump 110 from the AC supply 130 and ceasing any operation of the AC pump 110. When the controller 180 detects that the pre-lubrication signal has ceased at step 402, it proceeds to deactivate the DC pre-lubrication system at step 406. The pre-lubricated engine 202 can then be safely started whilst avoiding or reducing any risk of damage to the engine 202 due to start-up friction. In accordance with a method of pre-lubrication, the controller 180 can selectively activate the DC pre-lubrication system 150, based on one or more line to line voltage readings sensed across the AC power supply and the AC pump. The DC pre-lubrication system 150 can therefore be used to initiate a pre-lubrication cycle (e.g. in the event of a full loss or AC I utility power, a generator set with “black start” capability is provided), and then complete the required pre-lubrication cycle. Furthermore, if a pre-lubrication cycle is started by the AC pre-lubrication system 108, but before the cycle has run for the required amount of time, the AC power to the AC pump fails (e.g. as a result of utility power failure or malfunction of an AC system component), the DC pre-lubrication system can take over and complete the required pre-lubrication cycle. An engine of a generator set is therefore protected against risk of damage due to dry start-up friction, even if the AC pre-lubrication system fails in the event of full or partial loss of an AC power supply or a malfunction of the AC pre-lubricating system. Wear and tear or other damage to the engine caused by dry start-up is thereby avoided, and the life expectancy of the engine is increased. Certain steps are discussed above in relation to the method of Figure 8. However, alternative embodiments may omit certain steps or may include further or alternative steps and / or may carry out the steps in a different order. For example, whilst the method of Figure 8 compares the voltage readings to a first threshold in step and then a voltage drop to a second threshold, in alternative embodiments the controller 180 could selectively activate the DC pre-lubrication system 150 based on voltage readings which have been processed in a different manner, or compared to a different threshold or a plurality of different thresholds. The controller 180 may send other communications I signals I feedback to the GIB 210, or to other devices. Other communications could include, for example, further fault condition I error notifications such as breaker tripped, pump timed out, low battery, or system ready notifications. These communications could be sent as a generic failure signal such as “DC prelube system failure”, and displayed to a user, for example via the interface 212 of the GIB 210. The user may then analyse the controller 180 to determine the type of fault which has occurred. Embodiments of the invention have been described above by way of example only, and various modifications are possible. Features of one embodiment may be used with any other embodiment. Other modifications in detail will be apparent to the skilled person within the scope of the claims.

Claims

1. A pre-lubrication system for pre-lubricating an engine of a generator set, the system comprising:a primary pump configured to receive power from a primary power supply and to circulate oil though the engine;a secondary pump, configured to receive power from a secondary power supply, wherein the secondary pump is configured to circulate oil through the engine via a pathway which bypasses the primary pump; anda controller configured to control the secondary pump, wherein the controller is configured to monitor a voltage of the primary power supply and to selectively activate the secondary pump in dependence on the monitored voltage.

2. A pre-lubrication system as claimed in claim 1 wherein the primary power supply is an AC power supply and the secondary power supply is a DC power supply.

3. A pre-lubrication system as claimed in claim 2 wherein the AC power supply comprises utility power and the DC power supply comprises one or more batteries.

4. A pre-lubrication system as claimed in any of the preceding claims wherein the primary pump is coupled to a suction conduit and a discharge conduit, and the secondary pump is coupled to a bypass suction conduit and a bypass discharge conduit; wherein the bypass suction conduit is coupled to the suction conduit, and the bypass discharge conduit is coupled to the discharge conduit.

5. A pre-lubrication system as claimed in claim 4 wherein the bypass discharge conduit is coupled to the discharge conduit via a discharge three-way connector, and wherein a one-way valve is provided between the primary pump and the discharge three-way connector, wherein the one-way valve is arranged to prevent flow of oil into the primary pump during use of the secondary pump.

6. A pre-lubrication system as claimed in claim 5 wherein the one-way valve is provided in the discharge conduit, or is provided integrally within the primary pump or within the discharge three-way connector.

7. A pre-lubrication system as claimed in any of claims 4 to 6, wherein the bypass suction conduit is coupled to the suction conduit via a suction three-way connector, and wherein a one-way valve is provided between the secondary pump and the suction three-way connector, wherein the one-way valve is arranged to prevent flow of oil into the secondary pump during use of the primary pump.

8. A pre-lubrication system as claimed in any of the preceding claims, wherein the controller is configured to activate the secondary pump in response to a monitored voltage being below a voltage threshold value.

9. A pre-lubrication system as claimed in any of the preceding claims, further comprising a voltage sensor configured to sense a line to line voltage of the primary power supply.

10. A pre-lubrication system as claimed in claim 9, wherein the controller is configured to activate the secondary pump in response to receiving a line to line voltage reading from the voltage sensor of below a voltage threshold value.

11. A pre-lubrication system as claimed in claim 9 or 10, wherein the controller is configured to calculate a difference between a minimum value and a maximum value of line to line voltages of the primary power supply, and to activate the secondary pump if the difference is equal to or above a difference threshold value.

12. A pre-lubrication system as claimed in any of the preceding claims wherein the controller is further configured to monitor a voltage of the secondary power supply, and to inhibit operation of the secondary pump if the voltage is below a threshold.

13. A pre-lubrication system as claimed in any of the preceding claims wherein the controller is arranged to receive a pre-lubrication signal, and to activate the secondary pre-lubrication system in response to the pre-lubrication signal.

14. A pre-lubrication system as claimed in any of the preceding claims wherein the controller is configured to store an end time of a most recent full pre-lubrication cycle and to calculate a time lapse since the end time; and to compare the time lapse with a pre-determined threshold.

15. A pre-lubrication system according to any of the preceding claims, further comprising mounting means, for mounting the primary pump and / or the secondary pump on a skid of the generator set.

16. A pre-lubrication system as claimed in claim 15, wherein the mounting means comprises anti-vibration mounts.

17. A skid for a generator set, the skid comprising a pre-lubrication system according to any of the preceding claims.

18. The skid as claimed in claim 17, wherein the skid comprises a pair of opposed side members and a plurality of cross members, and wherein the primary pump, the secondary pump, and / or the controller are mounted on a side member.

19. A generator set comprising a generator, an engine, and a pre-lubrication system according to any one of claims 1 to 16, wherein the primary pump and the secondary pump are fluidly connected to an oil sump of the engine and to an oil gallery of the engine.

20. A generator set as claimed in claim 19, further comprising a generator interface unit arranged to send command signals to the controller and / or to receive feedback signals from the controller.

21. A generator set as claimed in claim 20, wherein the generator interface unit is arranged to send a pre-lubrication signal to the controller, and to a switch between the primary power supply and the primary pump.

22. A generator set as claimed in any of claims 19 to 21 wherein the feedback signals include fault signals, and wherein the fault signals are displayed on a user interface of the generator set interface unit.

23. A method of pre-lubricating an engine of a generator set, by a pre-lubrication system comprising a primary pump configured to receive power from a primary power supply and to circulate oil though the engine; and a secondary pump, configured to receive power from a secondary power supply and to circulate oil through the engine via a pathway which bypasses the primary pump; the method comprising:monitoring a voltage of the primary power supply, and in dependence on the monitored voltage selectively activating the secondary pump.

24. A method as claimed in claim 23 wherein the primary pump is activated in response to receiving a pre-lubrication command, wherein the pre-lubrication command is issued by a generator interface unit of the generator set, in response to a user input into an interface of the generator interface unit, and / or automatically prior to start-up of the engine.

25. A method as claimed in claim 24 wherein the pre-lubrication command is issued at predefined regular time intervals.

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