Gas compressor

Abstract

To provide a gas compressor capable of switching from a star connection to a delta connection of an electric motor at starting even if conditions such as ambient temperature of the gas compressor in which the starting torque of the gas compressor changes are different.SOLUTION: A gas compressor is equipped with an oil feeding system 10 that includes a pump 11 mechanically connected to an electric motor 4 driving compressor bodies 2 and 3 and supplies oil of the pump 11 to the compressor bodies, a pressure sensor 16 that detects the pressure of the oil flowing the oil feeding system 10, a starting device 31 that can switch a connection state of the electric motor 4 between a first connection changing it to a star connection and a second connection changing it to a delta connection, and a control device 40 that controls the starting device 31. The control device 40 sets the starting device 31 to the first connection at the time of starting the compressor bodies, determines whether or not a detection pressure value of the pressure sensor 16 is a pressure threshold value Pth or more during the starting of the compressor bodies, and switches the starting device 31 from the first connection to the second connection when it is determined that the detection pressure value is the threshold value Pth or more.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a gas compressor, and more particularly to a gas compressor driven by an electric motor. [Background technology]

[0002] Gas compressors use an electric motor as the prime mover of the compressor itself. A star-delta connection is widely used as a starting method for the electric motor that drives the gas compressor. The star-delta connection is used when the gas compressor starts up (when the electric motor is in the low rotational speed range), and then switches to a delta connection after a predetermined time (e.g., about 15 seconds) has elapsed since the start of startup. This method has the advantage that it allows for the construction of a starting device for the electric motor at a relatively low cost compared to other methods. However, this starting method can cause the electric motor to trip due to excessive current flow if the electric motor is only able to accelerate to a rotational speed that is insufficient compared to the maximum or rated speed when switching from star connection to delta connection.

[0003] A known method for starting a compressor using a star-delta connection is the technology described in Patent Document 1, for example. The technology described in Patent Document 1 aims to optimize the startup time of the electric motor by setting the time for which current is supplied to the electric motor using a star connection to an appropriate time depending on the temperature of the lubricating oil in the compressor. Specifically, the compressor startup method described in Patent Document 1 measures the temperature of the oil that lubricates the compressor body, derives the star time, which is the time for which current is supplied to the electric motor using a star connection, based on the measured oil temperature, and switches from star connection to delta connection when the derived star time has elapsed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-78607 Summary of the Invention [Problem to be solved by the invention]

[0005] The startup time of a gas compressor's electric motor, i.e., the time it takes for the electric motor to reach its maximum or rated speed from the start of startup, varies depending on the magnitude of the load torque applied to the electric motor. The load torque is the torque required to accelerate the compressor body of the gas compressor. The load torque varies, for example, depending on the ambient temperature of the gas compressor. When the ambient temperature of the gas compressor changes, the temperature of the lubricating oil supplied to the compressor body changes, which changes the starting torque of the compressor body. The load torque can vary not only depending on the ambient temperature of the gas compressor, but also on differences in the flow rate of lubricating oil supplied to the compressor body and other factors.

[0006] The technology described in Patent Document 1 derives the star time based on the measured temperature of the lubricating oil in the compressor. That is, the timing (star time) for switching from star connection to delta connection is estimated using the lubricating oil temperature, which has little direct correlation with the rotation speed of the electric motor. For this reason, with this technology, if the starting torque of the compressor body changes due to factors other than the ambient temperature of the gas compressor (such as the amount of lubricating oil supplied), it is difficult to determine the appropriate timing for switching from star connection to delta connection, i.e., whether the electric motor has reached its maximum speed or rated speed.

[0007] The present invention has been made to solve the above problems, and an object of the present invention is to provide a gas compressor that can switch the electric motor from star connection to delta connection at appropriate timing during startup, even if conditions that change the starting torque of the gas compressor, such as the ambient temperature of the gas compressor, are different. [Means for solving the problem]

[0008] The present application includes multiple means for solving the above problems. For example, the present application includes a compressor main body that compresses gas, an electric motor that drives the compressor main body, and a pump that is mechanically connected to and driven by the electric motor and includes an oil supply system that supplies oil discharged from the pump to the compressor main body, a pressure sensor that detects the pressure of the oil flowing through the oil supply system, a starting device that is electrically connected to the electric motor and has an electric circuit that is switchable between a first connection that establishes a star connection and a second connection that establishes a delta connection for a winding of the electric motor, and a control device that controls the connection of the electric circuit of the starting device, wherein the control device is configured to set the electric circuit of the starting device to the first connection when startup of the compressor main body is initiated, to perform a switching determination that determines whether a pressure value detected by the pressure sensor during startup of the compressor main body is equal to or greater than a pressure threshold value, and to switch the electric circuit of the starting device from the first connection to the second connection when the control device determines in the switching determination that the pressure value detected by the pressure sensor is equal to or greater than the pressure threshold value. [Effects of the Invention]

[0009] According to the present invention, since there is a correlation between the rotation speed of the electric motor that drives the compressor body and the pump and the oil supply pressure from the pump, by monitoring the oil supply pressure from the pump driven by the electric motor that drives the compressor body when the compressor body is started, it is possible to determine the appropriate timing for switching the connection state of the electric motor from star connection to delta connection. Therefore, even if the conditions that change the starting torque of the gas compressor, such as the ambient temperature of the gas compressor, are different, the starting device can switch the electric motor from star connection to delta connection at the appropriate time when the gas compressor is started. Problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a system diagram showing a schematic configuration of a gas compressor according to an embodiment of the present invention. [Figure 2] 2 is a flowchart showing an example of a startup procedure of the gas compressor performed by a control device that constitutes a part of the gas compressor according to the embodiment shown in FIG. [Figure 3] 4 is a graph showing the relationship between the rotation speed of the electric motor and the supply pressure from the pump when the gas compressor according to the embodiment shown in FIG. 1 is started up. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of a gas compressor according to the present invention will be described with reference to the drawings. In this embodiment, a screw gas compressor is used as an example of the gas compressor. However, the present invention can be applied to any gas compressor driven by a three-phase electric motor, such as a scroll gas compressor or a reciprocating gas compressor.

[0012] [One embodiment] The configuration of a gas compressor according to one embodiment will be described with reference to Fig. 1. Fig. 1 is a system diagram showing a schematic configuration of a gas compressor according to one embodiment. In Fig. 1, black arrows indicate the flow of working fluid or lubricating oil in the gas compressor.

[0013] In Fig. 1, gas compressor 1 is configured as a screw-type compressor. Gas compressor 1 includes a low-pressure front-stage compressor body 2 that compresses and discharges sucked gas, a high-pressure rear-stage compressor body 3 that further compresses and discharges the compressed gas discharged from front-stage compressor body 2, and an electric motor 4 that drives front-stage compressor body 2 and rear-stage compressor body 3. A gas filter 6 is disposed on the suction side of front-stage compressor body 2. The discharge side of front-stage compressor body 2 and the suction side of rear-stage compressor body 3 are connected via an intercooler 7. The discharge side of rear-stage compressor body 3 is connected to an aftercooler 8.

[0014] The front-stage compressor body 2 and the rear-stage compressor body 3 each include a pair of screw rotors that mesh with each other and rotate, multiple bearings that rotatably support the pair of screw rotors, and a casing that houses the pair of screw rotors and the multiple bearings (FIG. 1 shows a schematic diagram, and each component is not shown). The pair of screw rotors and the casing surrounding them form multiple working chambers. The multiple working chambers move axially as the pair of screw rotors rotate. As the pair of screw rotors rotate, the front-stage compressor body 2 and the rear-stage compressor body 3 draw in gas through a gas filter 6 as the volume of the working chamber increases, compressing the gas as the volume of the working chamber decreases, and finally discharging the compressed gas. The front-stage compressor body 2 and the rear-stage compressor body 3 are, for example, oil-free screw compressors that do not supply oil to the working chambers and have timing gears that synchronize the rotation of the pair of screw rotors.

[0015] The intercooler 7 is, for example, an air-cooled heat exchanger, and cools the high-temperature compressed gas discharged from the front-stage compressor body 2. The aftercooler 8 is, for example, an air-cooled heat exchanger, and cools the high-temperature compressed gas discharged from the rear-stage compressor body 3.

[0016] An oil supply system 10 is connected to the front-stage compressor body 2 and the rear-stage compressor body 3. The oil supply system 10 supplies lubricating oil to the front-stage compressor body 2 and the rear-stage compressor body 3 for lubricating the bearings of the screw rotors and timing gears. The oil supply system 10 includes, in order from the upstream side, a pump 11 that supplies lubricating oil to the front-stage compressor body 2 and the rear-stage compressor body 3, an oil cooler 12 that cools the lubricating oil supplied from the pump 11 to the front-stage compressor body 2 and the rear-stage compressor body 3, and an oil filter 13 that filters impurities contained in the lubricating oil supplied from the pump 11 to the front-stage compressor body 2 and the rear-stage compressor body 3. The pump 11 is mechanically connected to and driven by an electric motor 4 that drives the front-stage compressor body 2 and the rear-stage compressor body 3. A discharge line of the pump 11 is connected via a pressure regulating valve 14 to a gear case 26 of a gear device 20 (described later). The pressure regulating valve 14 is configured to open when the discharge pressure of the pump 11 reaches or exceeds a set pressure. By opening, the pressure regulating valve 14 releases excess pressure to the gear case 26, and has the function of maintaining a substantially constant pressure of the lubricating oil supplied to the bearings and timing gears of the front-stage compressor body 2 and the rear-stage compressor body 3.

[0017] A pressure sensor 16 and a temperature sensor 17 are installed downstream of the oil filter 13 in the oil supply system 10. The pressure sensor 16 detects the pressure of the oil discharged from the pump 11 and flowing through the oil supply system 10. Like existing pressure sensors, the pressure sensor 16 of this embodiment detects the pressure of the lubricating oil flowing out of the oil filter 13 and introduced into the front-stage compressor body 2 and the rear-stage compressor body 3, and has the function of monitoring the supply pressure of the lubricating oil to the front-stage compressor body 2 and the rear-stage compressor body 3. The temperature sensor 17 detects the temperature of the lubricating oil introduced into the front-stage compressor body 2 and the rear-stage compressor body 3 after being cooled by the oil cooler 12.

[0018] The front-stage compressor body 2 and the rear-stage compressor body 3 are mechanically connected to the electric motor 4 via a gear device 20. The pump 11 of the oil supply system 10 is also mechanically connected to the electric motor 4 via the gear device 20. The gear device 20 includes a motor-side bull gear 21 and a motor-side pinion 22 provided on the shaft of the electric motor 4, a front-stage pinion 23 provided on the shaft of the screw rotor of the front-stage compressor body 2 and meshing with the motor-side bull gear 21, a rear-stage pinion 24 provided on the shaft of the screw rotor of the rear-stage compressor body 3 and meshing with the motor-side bull gear 21, a pump-side gear 25 provided on the shaft of the pump 11 and meshing with the motor-side pinion 22, and a gear case 26 that houses these gears 21, 22, 23, 24, and 25. The driving torque of the electric motor 4 is transmitted from the motor-side bull gear 21 to the front-stage compressor body 2 via the front-stage pinion 23, and from the motor-side bull gear 21 to the rear-stage compressor body 3 via the rear-stage pinion 24. The driving torque of the electric motor 4 is also transmitted from the motor-side pinion 22 to the pump 11 via the pump-side gear 25. The lower part of the gear case 26 stores lubricating oil for the oil supply system 10. That is, the gear case 26 also functions as a storage tank for the lubricating oil for the oil supply system 10. The lubricating oil for the oil supply system 10 circulates between the gear case 26 and the front-stage compressor body 2 and the rear-stage compressor body 3.

[0019] The electric motor 4 is a three-phase electric motor having three-phase windings. The electric motor 4 is electrically connected to a starting device 31 and is configured to be connected to a power source 100 via the starting device 31. The starting device 31 has an electric circuit (not shown) that can switch the connection state of the windings of the electric motor 4 between a first connection in which the windings are star-connected and a second connection in which the windings are delta-connected. By switching the connection of the electric circuit, it is possible to adjust the current or voltage applied to the electric motor 4 from the power source 100. The starting device 31 is configured to switch the electric circuit between the first connection (star connection) or the second connection (delta connection) in response to a switching command Cs from the control device 40. The power source 100 may be an external power source to the gas compressor 1 or may be a part of the configuration of the gas compressor 1.

[0020] When an operation command signal is input from an operation switch or an external control panel (neither of which are shown), the control device 40 controls the connection of the electrical circuit of the starting device 31 to supply power from the power source 100 to the electric motor 4 and start the gas compressor 1 (the front-stage compressor body 2 and the rear-stage compressor body 3). The control device 40 employs a star-delta connection as the starting method for the electric motor 4. The control device 40 of this embodiment is characterized in that, during start-up of the gas compressor 1 (electric motor 4), the pressure of the lubricating oil discharged by the pump 11 and flowing through the oil supply system 10 is monitored by a pressure sensor 16, and the timing of switching from the star connection to the delta connection is determined based on the detected value of the pressure sensor 16. The method of starting the gas compressor 1 (electric motor 4) by the control device 40 will be described in detail below.

[0021] Next, the operation (driving) of the gas compressor according to one embodiment will be described with reference to Fig. 1. In normal operation of the gas compressor, the front-stage compressor body and the rear-stage compressor body (electric motor) are controlled to be driven at a substantially constant rotation speed.

[0022] In the gas compressor 1 having the above-described configuration shown in FIG. 1, the rotational driving force of the electric motor 4 is transmitted from the motor-side pull gear 21 of the gear device 20 to the front-stage pinion 23 and the rear-stage pinion 24, thereby rotating the front-stage compressor body 2 and the rear-stage compressor body 3. As a result, gas (e.g., air) is drawn into the front-stage compressor body 2 through the gas filter 6. The drawn gas is compressed by the front-stage compressor body 2 and then discharged to the intercooler 7. The high-temperature compressed gas discharged from the front-stage compressor body 2 is cooled by the intercooler 7 before being drawn into the rear-stage compressor body 3. The cooled compressed gas is further compressed by the rear-stage compressor body 3 and then discharged to the aftercooler 8. The high-temperature, high-pressure compressed gas discharged from the rear-stage compressor body 3 is cooled to a desired temperature by the aftercooler 8 and then supplied to an external device (not shown).

[0023] Furthermore, the rotational driving force of the electric motor 4 is transmitted from the motor-side pinion 22 of the gear device 20 to the pump-side gear 25, thereby driving the pump 11 of the oil supply system 10 to rotate. As a result, the lubricating oil stored in the gear case 26 of the gear device 20 is pumped by the pump 11 to the oil cooler 12. The lubricating oil discharged from the pump 11 is cooled by the oil cooler 12, and impurities are filtered out by the oil filter 13. The cooled and purified lubricating oil is supplied to the front-stage compressor body 2 and the rear-stage compressor body 3 (bearings, timing gears, etc.). When the discharge pressure of the pump 11 exceeds the set pressure, the pressure regulating valve 14 is opened. Therefore, the discharge pressure of the pump 11 is maintained approximately constant.

[0024] The pressure and temperature of the lubricating oil (lubricating oil flowing on the most downstream side of the oil supply system 10) introduced into the front-stage compressor body 2 and the rear-stage compressor body 3 are detected by a pressure sensor 16 and a temperature sensor 17, respectively. The pressure sensor 16 outputs a detection signal corresponding to the detected pressure value of the lubricating oil to the control device 40. The temperature sensor 17 outputs a detection signal corresponding to the detected temperature value of the lubricating oil to the control device 40. The control device 40 monitors the state (pressure and temperature) of the lubricating oil supplied to the front-stage compressor body 2 and the rear-stage compressor body 3 based on the detection signal from the pressure sensor 16 and the detection signal from the temperature sensor 17.

[0025] Next, the hardware configuration of a control device constituting a part of a gas compressor according to one embodiment and a method for starting up the gas compressor by the control device will be described with reference to Figures 1 and 2. Figure 2 is a flowchart showing an example of a start-up procedure for the gas compressor by the control device constituting a part of the gas compressor according to the embodiment shown in Figure 1.

[0026] 1, the hardware configuration of control device 40 of gas compressor 1 is configured by a microcomputer including storage device 41 consisting of RAM, ROM, etc., and processing device 42 consisting of CPU, MPU, etc. Storage device 41 pre-stores programs and various information required for starting gas compressor 1. Processing device 42 appropriately reads the programs and various information from storage device 41 and executes processing in accordance with the programs, thereby starting gas compressor 1.

[0027] 2, when an operation command signal is input from an operation switch or an external control panel (neither of which are shown), the control device 40 shown in FIG. 1 starts the startup procedure (startup control flow) of the gas compressor 1. First, the control device 40 sets the electric circuit of the starting device 31 to a first connection in which the windings of the electric motor 4 are connected in a star connection, and supplies power from the power source 100 to the electric motor 4 (whose windings are connected in a star connection) via the starting device 31 set to the first connection (step S10). This initiates startup of the electric motor 4. The startup of the electric motor 4 starts the front-stage compressor body 2 and the rear-stage compressor body 3, and also starts the pump 11.

[0028] Next, the control device 40 determines whether the pressure of the lubricating oil flowing through the oil supply system 10 is equal to or greater than a pressure threshold (step S20). This determines when to switch the winding connection of the electric motor 4 from star connection to delta connection. In a star-delta connection starting method for an electric motor, switching to the delta connection is required when the electric motor reaches or nears its maximum speed or rated speed. In this embodiment, the discharge pressure of the pump 11, which is mechanically connected to and driven by the electric motor 4, changes depending on the increase or decrease in the rotational speed of the electric motor 4. That is, there is a correlation between the rotational speed of the electric motor 4 and the discharge pressure of the pump 11 (see FIG. 3, described later). Therefore, the control device 40 is configured to determine whether the rotational speed of the electric motor 4 has reached an appropriate rotational speed for switching to the delta connection based on the pressure of the lubricating oil discharged from the pump 11 and flowing through the oil supply system 10.

[0029] Specifically, the control device 40 determines whether the pressure detection value Ps from the pressure sensor 16 is equal to or greater than the pressure threshold value Pth. If the pressure detection value Ps is smaller than the pressure threshold value Pth (NO), the process returns to step S20 and repeats step S20 until the pressure detection value Ps from the pressure sensor 16 becomes equal to or greater than the pressure threshold value Pth (YES). If the pressure detection value Ps from the pressure sensor 16 becomes equal to or greater than the pressure threshold value Pth (YES), the control device 40 proceeds to step S30.

[0030] The pressure threshold Pth is, for example, a preset fixed value that is stored in advance in the storage device 41. However, since the pressure of the lubricating oil flowing through the oil supply system 10 varies depending on the detection position, it is necessary to set an appropriate value depending on the installation position of the pressure sensor 16. In this embodiment, the pressure sensor 16 is installed, for example, downstream of the oil filter 13, which is the most downstream side of the oil supply system 10, and detects the pressure of the lubricating oil immediately before being introduced into the front-stage compressor body 2 and the rear-stage compressor body 3. In this case, the pressure of the lubricating oil discharged from the pump 11 indicates a value that is lower than the pump discharge pressure due to pressure losses in the oil cooler 12, the oil filter 13, and pressure losses in the pipelines. Therefore, the pressure threshold Pth is set taking into consideration the discharge pressure or discharge flow rate of the pump 11 when the electric motor 4 is at maximum speed or rated speed (during normal operation of the gas compressor 1), the pressure loss in the oil cooler 12, the pressure loss in the oil filter 13, and the pressure loss in the pipelines.

[0031] In step S20, if the pressure detection value Ps from the pressure sensor 16 reaches or exceeds the pressure threshold value Pth (if YES), the control device 40 switches the electric circuit of the starting device 31 from the first connection to the second connection (step S30). That is, the connection state of the windings of the electric motor 4 is switched from star connection to delta connection. Specifically, the control device 40 outputs a switching command Cs to the starting device 31. As described above, there is a correlation between the rotation speed of the electric motor 4 and the discharge pressure of the pump 11. Therefore, when the pressure detection value Ps from the pressure sensor 16 reaches or exceeds the pressure threshold value Pth, it is assumed that the rotation speed of the electric motor 4 has reached an appropriate rotation speed for switching to the delta connection.

[0032] Next, the operation at the time of startup of a gas compressor according to one embodiment will be described with reference to Figures 1 to 3. Figure 3 is a graph showing the relationship between the rotation speed of the electric motor and the supply pressure from the pump at the time of startup of the gas compressor according to the embodiment shown in Figure 1. In Figure 3, the horizontal axis T represents the elapsed time from the start of startup of the gas compressor, the right vertical axis R and the solid line represent the rotation speed of the electric motor, and the left vertical axis P and the dashed line represent the supply pressure of lubricating oil from the pump in the oil supply system to the front-stage compressor and the rear-stage compressor.

[0033] When an operation command signal is input, control device 40 shown in Fig. 1 starts starting gas compressor 1 (when elapsed time T shown in Fig. 3 is 0). Specifically, control device 40 sets the electrical circuit of starting device 31 to a first connection that sets the winding connection state of electric motor 4 to star connection, and supplies power from power source 100 to electric motor 4 via starting device 31 (step S10 shown in Fig. 2).

[0034] This starts the activation of the electric motor 4 shown in Fig. 1. The activation of the electric motor 4 starts the front-stage compressor body 2 and the rear-stage compressor body 3, and also starts the pump 11 of the oil supply system 10. As shown in Fig. 3, the electric motor 4 is accelerated by the supply of power from the power source 100, and the rotation speed gradually increases according to the elapsed time T from the start-up. As the rotation speed of the electric motor 4 increases, the rotation speed of the pump 11 of the oil supply system 10 also increases. As a result, the pressure P of the lubricating oil supplied from the pump 11 to the front-stage compressor body 2 and the rear-stage compressor body 3 gradually increases according to the elapsed time T from the start-up.

[0035] At this time, the control device 40 determines whether the pressure P (the value detected by the pressure sensor 16) of the lubricating oil supplied from the pump 11 to the front-stage compressor body 2 and the rear-stage compressor body 3 is equal to or greater than the pressure threshold value Pth, thereby determining the timing to switch from the star connection to the delta connection (step S20 shown in FIG. 2). In FIG. 3, during the period when the elapsed time T is from 0 to Ts, the supply pressure P (the value detected by the pressure sensor 16) of the lubricating oil from the pump 11 does not reach the pressure threshold value Pth, so the control device 40 maintains the starting device 31 in the first connection (repeatedly repeating step S20 shown in FIG. 2), thereby maintaining the supply of power to the electric motor 4, whose windings are connected in a star connection.

[0036] When the supply pressure P of lubricating oil from the pump 11 (the value detected by the pressure sensor 16) reaches the pressure threshold value Pth, that is, when the elapsed time T is Ts, the control device 40 switches the connection state of the windings of the electric motor 4 from star connection to delta connection (step S30 shown in FIG. 2). At this time (when the elapsed time Ts) the rotation speed of the electric motor 4 has reached the maximum speed or rated speed Rr due to the acceleration of the electric motor 4 caused by the power supply. Therefore, an excessive current does not flow through the electric motor 4, and the start-up of the electric motor 4 can be completed.

[0037] In this way, in this embodiment, when the electric motor 4 (gas compressor 1) is started, the supply pressure of lubricating oil from the pump 11, which is correlated with the rotational speed of the electric motor 4, is monitored to determine the appropriate timing for switching the connection state of the electric motor 4 from star connection to delta connection.

[0038] As described above, the gas compressor according to one embodiment includes a front-stage compressor body 2 and a rear-stage compressor body 3 (compressor bodies) that compress gas, an electric motor 4 that drives the front-stage compressor body 2 and the rear-stage compressor body 3 (compressor bodies), an oil supply system 10 that includes a pump 11 that is mechanically connected to and driven by the electric motor 4 and supplies lubricating oil (oil) discharged from the pump 11 to the front-stage compressor body 2 and the rear-stage compressor body 3 (compressor bodies), a pressure sensor 16 that detects the pressure of the lubricating oil (oil) flowing through the oil supply system 10, a starting device 31 that is electrically connected to the electric motor 4 and has an electrical circuit that can switch the connection state of the windings of the electric motor 4 between a first connection that sets the windings to a star connection and a second connection that sets the windings to a delta connection, and a control device 40 that controls the connection of the electrical circuit of the starting device 31. The control device 40 is configured to set the electrical circuit of the starting device 31 to the first connection when the startup of the front-stage compressor main body 2 and the rear-stage compressor main body 3 (compressor main body) begins, perform a switching judgment to determine whether the pressure value detected by the pressure sensor 16 during startup of the front-stage compressor main body 2 and the rear-stage compressor main body 3 (compressor main body) is greater than or equal to the pressure threshold value Pth, and when the switching judgment determines that the pressure value detected by the pressure sensor 16 is greater than or equal to the pressure threshold value Pth, switch the electrical circuit of the starting device 31 from the first connection to the second connection.

[0039] According to this configuration, there is a correlation between the rotation speed of the electric motor 4 that drives the front-stage compressor body 2, the rear-stage compressor body 3 (compressor body), and the pump 11 and the supply pressure of the lubricating oil (oil) from the pump 11. Therefore, when the front-stage compressor body 2 and the rear-stage compressor body 3 (compressor body) are started, by monitoring the supply pressure of the lubricating oil (oil) from the pump 11 driven by the electric motor 4 that drives the front-stage compressor body 2 and the rear-stage compressor body 3 (compressor body), it is possible to determine the appropriate timing for switching the connection state of the electric motor 4 from star connection to delta connection. Therefore, even if the conditions that change the starting torque of the gas compressor 1, such as the ambient temperature of the gas compressor 1, are different, the starting device 31 can switch the electric motor 4 from star connection to delta connection at the appropriate time when the gas compressor 1 is started.

[0040] Furthermore, in the present embodiment, the pressure threshold value Pth is a preset fixed value that is stored in advance in the control device 40. According to this configuration, the control flow for starting up the control device 40 can be simplified.

[0041] In this embodiment, the oil supply system 10 includes, in addition to the pump 11, an oil cooler 12 (heat exchanger) that cools the lubricating oil (oil) supplied from the pump 11 to the front-stage compressor body 2 and the rear-stage compressor body 3 (compressor body), and an oil filter 13 (filter) that filters impurities from the lubricating oil (oil) supplied from the pump 11 to the front-stage compressor body 2 and the rear-stage compressor body 3 (compressor body). The pressure sensor 16 is installed downstream of the oil cooler 12 (heat exchanger) and the oil filter 13 (filter) in the oil supply system 10.

[0042] According to this configuration, the installation position of the pressure sensor 16 in the fuel supply system 10 is the same as in the fuel supply system of an existing gas compressor, so there is no need for a new pressure sensor to determine the timing of switching the electric motor 4 from star connection to delta connection when the gas compressor 1 is started, and a pressure sensor with an existing configuration can be used.

[0043] [Other embodiments] The present invention is not limited to the above-described embodiment, but includes various modifications. The above-described embodiment has been described in detail to clearly explain the present invention, and is not necessarily limited to an embodiment having all of the described configurations. In other words, it is possible to add, delete, or replace part of the configuration of one embodiment with other configurations.

[0044] For example, in the above-described embodiment, the front-stage compressor body 2 and the rear-stage compressor body 3 are configured as liquid-free screw compressors in which no liquid, such as oil or water, is injected into the working chambers. However, the front-stage compressor body and the rear-stage compressor body can also be configured as liquid-feed screw compressors in which a liquid, such as oil or water, is injected into the working chambers. If the liquid injected into the working chambers is lubricating oil, the oil supply system 10 of the embodiment can also be configured to supply lubricating oil to the working chambers of the front-stage compressor body and the rear-stage compressor body.

[0045] In the above-described embodiment, an example has been shown in which the pressure sensor 16 is installed downstream of the oil filter 13 in the oil supply system 10. However, the pressure sensor 16 may be configured to detect the pressure of the lubricating oil discharged from the pump 11 and flowing through the oil supply system 10. For example, the pressure sensor may be configured to be installed downstream of the oil cooler 12 and upstream of the oil filter 13 in the oil supply system 10 (not shown). The pressure sensor may also be configured to be installed upstream of the oil cooler 12 in the oil supply system 10 so as to detect the discharge pressure of the pump 11 (pressure sensor 16 indicated by the dashed dotted line in FIG. 1).

[0046] In the above-described embodiment, the pressure threshold Pth is set to a predetermined fixed value. However, the pressure threshold Pth may be set based on the detection value of the pressure sensor 16 rather than being a fixed value. Specifically, the control device 40 is configured to store, in the storage device 41, a pressure value detected by the pressure sensor 16 during normal operation immediately before the front-stage compressor body 2 and the rear-stage compressor body 3 (gas compressor 1) are stopped when the front-stage compressor body 2 and the rear-stage compressor body 3 (gas compressor 1) are stopped. Furthermore, the control device 40 is configured to set the pressure threshold Pth based on the pressure value of the pressure sensor 16 stored in the storage device 41. The pressure value detected by the pressure sensor 16 during normal operation of the gas compressor 1 indicates the pressure of the lubricating oil (oil) supplied from the pump 11 to the front-stage compressor body 2 and the rear-stage compressor body 3 when the electric motor 4 is operating at maximum speed or rated speed. In other words, the pressure value can be used as an indicator for determining the maximum speed or rated speed of the electric motor 4. According to this configuration, unlike when the pressure threshold Pth is set to a fixed value, there is no need to take into consideration the pressure loss of the oil cooler 12 or the oil filter 13, etc. [Explanation of symbols]

[0047] 1...gas compressor, 2...pre-stage compressor body (compressor body), 3...post-stage compressor body (compressor body), 4...electric motor, 10...oil supply system, 11...pump, 12...oil cooler (heat exchanger), 13...oil filter (filter), 16...pressure sensor, 31...starting device, 40...control device, Pth...pressure threshold

Claims

1. a compressor body that compresses gas; an electric motor that drives the compressor body; an oil supply system including a pump mechanically connected to and driven by the electric motor, the oil being discharged from the pump and supplying the oil to the compressor body; a pressure sensor for detecting the pressure of oil flowing through the oil supply system; a starting device electrically connected to the electric motor and having an electric circuit switchable between a first connection that sets a winding state of the electric motor in a star connection and a second connection that sets a winding state of the electric motor in a delta connection; a control device that controls connection of the electric circuit of the starting device, The control device When the compressor main body starts to start, the electric circuit of the starting device is in the first connection; performing a switching determination to determine whether or not a pressure value detected by the pressure sensor is equal to or greater than a pressure threshold value during startup of the compressor main body; When it is determined in the switching determination that the pressure value detected by the pressure sensor is equal to or greater than the pressure threshold value, the electric circuit of the starting device is switched from the first connection to the second connection. A gas compressor characterized by:

2. 2. The gas compressor according to claim 1, The pressure threshold is a preset fixed value and is stored in advance in the control device. A gas compressor characterized by:

3. 2. The gas compressor according to claim 1, the control device is configured to store, when the compressor body is stopped, a pressure value detected by the pressure sensor in a normal operation state immediately before the compressor body is stopped, The control device sets the pressure threshold value based on the stored pressure value in the switching determination. A gas compressor characterized by:

4. 2. The gas compressor according to claim 1, In addition to the pump, the oil supply system includes a heat exchanger that cools the oil supplied from the pump to the compressor body, and a filter that filters impurities from the oil supplied from the pump to the compressor body, The pressure sensor is installed downstream of the heat exchanger and the filter in the fuel supply system. A gas compressor characterized by:

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