Electrical system, mining or tunnelling machine and method of operating an electrical system

Abstract

The electrical system for a mining or tunnelling machine comprises a grid connection interface (1) for connecting the electrical system to an external alternating current power grid (2), at least one alternating current motor (3), a first power supply line (4) for supplying alternating current from the external power grid (2) to said at least one alternating current motor (3), and a second power supply line (5) for supplying electric power from the external power grid (2) to said at least one alternating current motor (3) The second power supply line (5) comprises means (6) for converting alternating current supplied from the external power grid (2) to direct current, and means (7) for converting the direct current to alternating current for supplying the alternating current to said at least one alternating current motor (3).

Description

[0001] Electrical system, mining or tunnelling machine and method of operating an electrical system

[0002] Technical field of the invention

[0003] The present invention concerns an electrical system, as defined in claim 1 . The invention further concerns a mining or tunnelling machine and a method of operating an electrical system.

[0004] Background of the invention

[0005] Many machines used in mining and tunnelling are provided with a grid connection interface that allows the machines to be connected to a power grid of a mine or a tunnel construction site. This allows the electrical equipment of the machines to be powered by external power supply, and the use of internal combustion engines and batteries can be avoided.

[0006] A problem relating to mining and tunnelling machines comprising electrical systems that are connectable to external power grids is that the power grids of mines and tunnel construction sites can operate at different voltages. The voltages commonly used vary between 380 V and 1000 V. The same machines can thus not be used everywhere, but machines with different electrical systems are needed. This increases the complexity of manufacturing of mining and tunnelling machines. Also, in case of rental machines that are moved from site to site, different machines are needed for different power grids, which makes efficient use of the rental machines difficult.

[0007] Similar problems may be encountered with other electrical systems that need to be connectable to power grids with different voltages.

[0008] Summary of the invention

[0009] An object of the present invention is to provide an improved electrical system for a mining or tunnelling machine. Another object of the invention is to provide an improved method of operating an electrical system comprising at least one alternating current motor and being connectable to an external alternating current power grid.

[0010] According to the invention, the electrical system comprises a grid connection interface for connecting the electrical system to an external alternating current power grid, at least one alternating current motor, a first power supply line for supplying alternating current from the external power grid to said at least one alternating current motor, and a second power supply line for supplying electric power from the external power grid to said at least one alternating current motor. The second power supply line comprises means for converting alternating current supplied from the external power grid to direct current, and means for converting the direct current to alternating current for supplying the alternating current to said at least one alternating current motor.

[0011] In the method according to the invention, when the external power grid operates at a voltage that is within a voltage range determined for a first operating mode, alternating current is supplied from the external power grid to said at least one alternating current motor without voltage conversion, and when the external power grid operates at a voltage that is within a voltage range determined for a second operating mode, the alternating current supplied by the external power grid is converted to direct current, the direct current is converted to alternating current, and the alternating current converted from the direct current is supplied to said at least one alternating current motor.

[0012] The system and the method according to the invention allow the same electrical system to be connected to power grids having different voltage levels. This simplifies the manufacturing of the electrical systems, as different configurations are not needed for different power grids. Mining and tunnelling machines comprising the electrical system according to the invention can be used in mines and at tunnel construction sites regardless of the voltage of the local power grid, allowing thus efficient use of the machines.

[0013] The mining or tunnelling machine according to the invention comprises an electrical system defined above.

[0014] According to an embodiment of the invention, the first power supply line is configured to be connected to power grids operating at voltages that are within a voltage range determined for a first operating mode, and the second power supply line is configured to be connected to power grids operating at voltages that are within a voltage range determined for a second operating mode. The motor can be powered directly by the alternating current for example when the voltage of the external power grid corresponds to a rated voltage of the alternating current motor.

[0015] According to an embodiment of the invention, the electrical system is configured to connect said at least one alternating current motor to said first power supply line via a star connection. By connecting the motor to the first power supply line via a star connection, the upper end of the voltage range of power grids to which the electrical system can be connected is raised. However, the motor could be connected to the first power supply line also via a delta connection. The connection could also be selected based on the grid voltage.

[0016] According to an embodiment of the invention, the electrical system is configured to connect said at least one alternating current motor to said second power supply line via a delta connection. By connecting the motor to the second power supply line via a delta connection, lower voltages can be used in the AC / DC and DC / AC conversions.

[0017] According to an embodiment of the invention, the second power supply line comprises a harmonic filter arranged before the means for converting alternating current supplied from the external power grid to direct current. The harmonic filterfilters harmonic frequencies that could disturb the electrical system.

[0018] According to an embodiment of the invention, said at least one alternating current motor is configured to be operated at voltages of at least 220 V. The alternating current motor could be configured to be operated at voltages of at least 350 V.

[0019] According to an embodiment of the invention, the means for converting the direct current to alternating current are configured to produce alternating current having a voltage in the range of 220-1000 V.

[0020] According to an embodiment of the invention, the electrical system comprises at least one transformer connectable to the alternating current supplied from the power grid and configured to transform the voltage of the power grid to a predetermined voltage level for powering one or more additional loads. As the alternating current motor is powered either directly by the grid voltage or by the alternating current produced by the AC / DC and DC / AC converters, the power required from the transformer can be relatively small. According to an embodiment of the invention, the mining or tunnelling machine is configured to spray concrete.

[0021] In the method according to an embodiment of the invention, the alternating current in the voltage range determined for the second operating mode is fed to a harmonic filter before converting the alternating current to direct current.

[0022] According to an embodiment of the invention, the voltage is increased when the alternating current is converted to the direct current.

[0023] According to an embodiment of the invention, part of electric power received from the power grid is supplied as alternating current at the voltage level of the power grid to a transformer, and the voltage is transformed by the transformer to a predetermined voltage level for powering one or more additional loads.

[0024] Brief description of the drawings

[0025] Embodiments of the invention will be described below in more detail with reference to the accompanying drawings, in which

[0026] Fig. 1 shows as a block diagram parts of an electrical system according to an embodiment of the invention,

[0027] Fig. 2 shows as a flowchart the method according to the invention, and

[0028] Fig. 3A-3G show alternative ways of operating the electrical system.

[0029] Detailed description of embodiments of the invention

[0030] Figure 1 shows as a block diagram parts of an electrical system according to an embodiment of the invention. The electrical system is configured for a mining or tunnelling machine. The mining or tunnelling machine could be any machine that is configured to carry out tasks relating to mining or tunnel construction. The mining or tunnelling machine could be, in particular, a concrete spraying machine, which is configured to spray concrete onto the walls or roof of an underground space, such as a mine or tunnel. The mining or tunnelling machine could also be some other machine, such as a scaler, braker or rock drill. The mining or tunnelling machine can be a moveable vehicle. The electrical system according to the invention comprises a grid connection interface 1 . The grid connection interface 1 is configured to allow the electrical system to be connected to an external alternating current power grid 2. The external alternating current power grid 2 can be a power grid of a mine or a tunnel construction site. However, the power grid 2 does not need to be a fixed power grid, but the external power grid means here any power supply that can be connected to the grid connection interface 1 . Alternating current could thus be supplied to the electrical system for example from an aggregate unit that comprises a generator and an internal combustion engine driving the generator.

[0031] The grid connection interface 1 is configured to allow the electrical system to be connected to external power grids 2 with at least two different voltages. The grid connection interface 1 may be configured to allow the electrical system to be connected to a power grid 2 operating at any voltage within a predetermined voltage range. However, the grid connection interface 1 can be configured to allow the electrical system to be connected only to power grids 2 operating at certain voltages or in certain voltage ranges within the predetermined voltage range. The predetermined voltage range could have a lower limit of at least 200 V. The predetermined voltage range could have an upper limit of at most 1100 V.

[0032] The external power grid 2 may be a three-phase power grid. The grid voltage (line voltage) of the external power grid 2 could be, for instance, in the range of 380-1000 V. The phase voltage of the power grid 2 could thus be 219-577 V. However, the voltage ranges could also be different. The grid connection interface 1 can be configured to allow the electrical system to be connected to power grids 2 operating at a predetermined frequency or predetermined frequencies or in a predetermined frequency range. The frequencies can include, for instance, 50 Hz and / or 60 Hz.

[0033] The grid connection interface 1 can comprise any components needed to electrically connect the electrical system to the external power grid 2. The grid connection interface 1 can further comprise for example means for measuring the voltage of the power grid 2.

[0034] The electrical system comprises at least one alternating current motor 3. The alternating current motor 3 can be any kind of electric motor that is configured to be powered by alternating current. The alternating current motor 3 could be, for instance, an induction motor or a synchronous motor. The alternating current motor 3 is configured to be operable using at least one voltage or voltage range that is within the predetermined voltage range of the external power grids 2.

[0035] The alternating current motor 3 can be used for operating any kind of device of the mining or tunnelling machine. For instance, in a concrete spraying machine the motor 3 could be used for operating a pump that is configured to pump the concrete. In some other mining or tunnelling machine, the motor 3 could be used for operating some other actuator of the machine. Alternatively, the motor 3 could be configured to drive a hydraulic pump that is configured to produce hydraulic power for various functions of the mining or tunnelling machine. The electrical system could comprise two or more alternating current motors 3, which could be used for the same purpose or for different purposes.

[0036] The electrical system comprises a first power supply line 4 for supplying alternating current from the external power grid 2 to the alternating current motor 3. Via the first power supply line 4, the alternating current can be supplied to the alternating current motor 3 at the same voltage level as the voltage of the external power grid 2. There is thus no transformer between the power grid 2 and the motor 3. In a three-phase system, the motor 3 can be connected to the first power supply line 4 either in a delta connection or in a star connection. If the motor 3 is connected to the first power supply line 4 in star, the phase voltage of the motor 3 is the line voltage divided by 3. If the motor 3 is connected to the first power supply line 4 in delta, the phase voltage of the motor 3 is the same as the line voltage. The electrical system can comprise means for switching the connection of the first power supply line 4 and the alternating current motor 3 between the delta connection and star connection. The means for switching the connection can be either manually or automatically operable.

[0037] The electrical system further comprises a second power supply line 5 for supplying electric power from the external power grid 2 to the alternating current motor 3. The second power supply line 5 comprises means 6 for converting alternating current supplied from the external power grid 2 to direct current, i.e. an AC / DC converter. The second power supply line 5 further comprises means 7 for converting the direct current to alternating current, i.e. a DC / AC converter, for supplying the alternating current to the alternating current motor 3. The AC / DC converter 6 and DC / AC converter 7 can be separate devices or they can be integrated into a single unit.

[0038] Because of the second power supply line 5 that comprises the AC / DC converter 6 and the DC / AC converter 7, the electrical system can be connected to any external power grid 2 having a voltage in a certain voltage range. If the voltage of the power grid 2 is suitable for operating the alternating current motor 3, alternating current can be supplied directly from the power grid 2 to the motor 3. In case a different voltage is needed, electric power can be supplied to the motor 3 via the second power supply line 5, which allows converting the voltage to a voltage level allowing operation of the alternating current motor 3. The DC / AC converter 7 also allows setting the frequency of the alternating current to a suitable level for operating the alternating current motor 3.

[0039] In the embodiment of figure 1 , the second power supply line 5 comprises a harmonic filter 8 arranged before the AC / DC converter 6. The harmonic filter 8 is configured to filter harmonic frequencies that could disturb the electrical system.

[0040] In the embodiment of figure 1 , the electrical system further comprises a transformer 9. The transformer 9 is connectable to the alternating current supplied from the power grid 2 and configured to transform the voltage of the power grid 2 to a predetermined voltage level for powering one or more additional loads 10. The additional loads 10 can be any other electric power consumers than the alternating current motor 3 that is powered directly by the grid current or by the power transmitted via the second power supply line 5. The additional loads 10 can comprise even alternating current motors. The transformer 9 is configured to have a fixed output voltage and a variable input voltage. The transformer 9 can be configured to be operable using any input voltage in the predetermined voltage range of the electrical system. Alternatively, the transformer 9 could be configured to be operable using input voltages corresponding to the voltages that are used for operating the alternating current motor 3. In the embodiment of figure 1 , the transformer 9 is connected to the grid voltage of the external power grid 2. However, the transformer 9 could also be connected in the second power supply line 5 between the DC / AC converter 7 and the motor 3. The electrical system 7 comprises a control system 11 . The control system 11 is configured to control at least the operation of the AC / DC converter 6 and the operation of the DC / AC converter 7. The control system 11 can further control the operation of the grid connection interface 1 and / or the operation of the transformer 9.

[0041] The first power supply line 4 can be connected to power grids 2 operating at voltages that are within a voltage range determined for a first operating mode. The second power supply line 5 can be connected at least to power grids 2 operating at voltages that are within a voltage range determined for a second operating mode. The grid connection interface 1 and / or the control system 11 can comprise means for detecting the grid voltage and to automatically connect either the first power supply line 4 or the second power supply line 5 to the power grid 2 based on the detected voltage. Alternatively, or in addition, the grid connection interface 1 and / or the control system 11 can comprise means for allowing either the first power supply line 4 or the second power supply line 5 to be manually connected to the power grid 2.

[0042] In the method according to the invention, the voltage of the external power grid 2 is determined. As shown in figure 2, if the external power grid 2 operates at a voltage that is with-in a voltage range determined for the first operating mode, alternating current is supplied from the external power grid 2 to the alternating current motor 3 without voltage conversion (step 101 ). If the external power grid 2 operates at a voltage that is within a voltage range determined for the second operating mode, the alternating current supplied by the external power grid 2 is converted to direct current (step 102), the direct current is converted to alternating current (step 103), and the alternating current converted from the direct current is supplied to the alternating current motor 3 (step 104).

[0043] The electrical system can be configured to determine the voltage of the external power grid 2 automatically and to connect either the first power supply line 4 or the second power supply line 5 to the external power grid 2. Alternatively, this could be done manually.

[0044] A voltage range determined for the first operating mode is a voltage range in which the operation of the alternating current motor 3 is allowed. The voltage range determined for the first operating mode can correspond to a rated voltage of the alternating current motor 3. The rated voltage refers here to an allowed voltage range around a nominal voltage of the alternating current motor 3. The motor may have two or more nominal voltages, such as nominal voltages for delta and star connections. The motor 3 may thus have two or more rated voltages. There can thus be two separate voltage ranges determined for the first operating mode. One of the voltage ranges can correspond to the rated voltage of the motor 3 in a star connection and one of the voltage ranges can correspond to the rated voltage of the motor 3 in a delta connection. A voltage range determined for the first operating mode can be narrower than a rated voltage of the alternating current motor 3 to allow fluctuations in the voltage of the external power grid 2. For instance, if the rated voltage of the alternating current motor is the nominal voltage + / - 10%, the voltage range determined for the first operating mode could be the nominal voltage of the motor + / - 5%.

[0045] Figures 3A to 3G show examples of possible voltage ranges in different operating modes of the electrical system. In figures 3A to 3G, Vs denotes the nominal voltage of the alternating current motor 3 when connected in star and VD denotes the nominal voltage of the alternating current motor 3 when connected in delta. The dotted voltage ranges depict operation in the first operating mode and the hatched voltage ranges depict operation in the second operating mode.

[0046] In the embodiment of figure 3A, there is only one voltage range RS determined for the first operating mode. Voltage range RS corresponds to the rated voltage Vs of the alternating current motor 3 when connected in star or is a narrower voltage range around the nominal voltage. In the embodiment of figure 3A, the upper end of the rated voltage of the motor 3 when connected in star is also the upper limit of the predetermined voltage range of the electrical system. If the voltage of the external power grid 2 is within voltage range RS, electric power is supplied to the alternating current motor 3 via the first power supply line 4. Any voltage below voltage range RS belongs to the voltage range R1 determined for the second operating mode. If the voltage of the external power grid 2 is within voltage range R2, electric power is supplied to the alternating current motor 3 via the second power supply line 5.

[0047] In the embodiment of figure 3B, voltage range RS is identical to the corresponding voltage range RS of figure 3A. However, in the embodiment of figure 3B, the electrical system has another voltage range RD determined for the first operating mode. Voltage range RD corresponds to the rated voltage of the alternating current motor 3 when connected in delta or is a narrower range around the nominal voltage. If the voltage of the external power grid 2 is within voltage range RS or within voltage range RD, electric power is supplied to the motor 3 via the first power supply line 4. Voltage range R1 , which is a voltage range determined for the second operating mode, is between voltage range RS and voltage range RD. The electrical system has another voltage range R2 determined for the second operating mode. Voltage range R2 is below voltage range RD. If the voltage of the external power grid 2 is within voltage range R1 or within voltage range R2, electric power is supplied to the motor 3 via the second power supply line 5.

[0048] The embodiment of figure 3C is similar to the embodiment of figure 3A. However the upper end of the rated voltage of the alternating current motor 3 connected in star does not form the upper end of the predetermined voltage range of the electrical system, but the components of the second power supply line 5 can handle higher voltages. There is thus another voltage range R2 determined for the second operating mode. If the voltage of the external power grid 2 is within voltage range R1 or within voltage range R2, electric power is supplied to the motor 3 via the second power supply line 5.

[0049] The embodiment of figure 3D is similar to the embodiment of figure 3C. However, there is another voltage range RD determined for the first operating mode. Voltage range RD corresponds to the rated voltage of the alternating current motor 3 when connected in delta or is a narrower range around the nominal voltage. If the voltage of the external power grid 2 is within voltage range RS or within voltage range RD, electric power is supplied to the motor 3 via the first power supply line 4. There are three voltage ranges R1 , R2, R3 determined for the second operating mode. Voltage range R1 is between voltage range RS and RD, voltage range R2 is above voltage range RS and voltage range R3 is below voltage range RD. If the voltage of the external power grid 2 is within one of voltage ranges R1 , R2, R3, electric power is supplied to the motor 3 via the second power supply line 5.

[0050] In the embodiment of figure 3E, there is one voltage range RD determined for the first operating mode. Voltage range RD corresponds to the rated voltage of the alternating current motor 3 when connected in delta or is a narrower range around the nominal voltage. If the voltage of the external power grid 2 is within voltage range RD, electric power is supplied to the motor 3 via the first power supply line 4. There are two voltage ranges R1 , R2 determined for the second operating mode. Voltage range R1 is below voltage range RD and voltage range R2 is above first voltage range RD.

[0051] In the embodiment of figure 3F, the lower limit of the rated voltage of the alternating current motor 3 when connected in delta forms the lower limit of the predetermined voltage range of the electrical system. Voltage range RD corresponds to the rated voltage of the alternating current motor 3 when connected in delta or is a narrower range around the nominal voltage and forms a voltage range determined for the first operating mode. Voltage range R1 is above voltage range RD and forms a voltage range determined for the second operating mode. If the voltage of the external power grid 2 is within voltage range RD, electric power is supplied to the motor 3 via the first power supply line 4. If the voltage of the external power grid 2 is within voltage range R1 , electric power is supplied to the motor via the second power supply line 5.

[0052] The embodiment of figure 3G is similar to the embodiment of figure 3F. However, electric power is supplied to the alternating current motor 3 also in case the voltage of the external power grid 2 is within the rated voltage of the alternating current motor 3 when connected in star, which forms another voltage range (voltage range RS) determined for the first operating mode. There are two voltage ranges R1 , R2 determined for the second operating mode. Voltage range R1 is between voltage range RD and voltage range RS. Voltage range R2 is above voltage range RS.

[0053] Different embodiments of the invention are described below using some numerical values as examples. The alternating current motor 3 could have a nominal voltage Vs 1000 V in a star connection and a nominal voltage VD 575 V in a delta connection. The rated voltage of the alternating current motor 3 could be, for instance, the nominal voltage + / - 10%. In the embodiment of figure 3A, voltage range RS could be, for instance, the nominal voltage of the motor + / - 5%, i.e. 950-1050 V. The lower end of the predetermined voltage range of the electrical system could be, for instance, 380 V. Voltage range R1 would thus be 380-950 V. If the voltage of the external alternating current power grid 2 is 950-1050 V, the first power supply line 4 is connected via the grid connection interface 1 to the power grid 2. The motor 3 is connected to the first power supply line 4 in a star connection. The transformer 9 is connected to the first power supply line 4. The transformer 9 can be configured to transform the voltage of the power grid 2 to 400 Vac, which can be supplied to any additional load 10 of the electrical system.

[0054] If the line voltage of the external power grid 2 is below 950V, the second power supply line 5 is connected via the grid connection interface 1 to the power grid 2. The AC / DC converter 6 converts the AC current to DC current. The voltage of the DC current could be, for instance, 1000 V. The DC current is converted in the DC / AC converter 7 back to AC current. The voltage can be after the DC / AC conversion 575 V. The AC current can be supplied to the alternating current motor 3 that is connected to the second power supply line 5 in a delta connection.

[0055] If the electrical system was operated according to the embodiment of figure 3B, voltage range RD could be, for instance, 575 V + / - 5%, i.e. 546-604 V. If the voltage of the external power grid 2 was 546-604 V, the first power supply line 4 would be connected via the grid connection interface 1 to the external power grid 2 and the motor 3 would be connected to the first power supply line in a delta connection. If the voltage of the external power grid 2 was 950-1050 V, the first power supply line 4 would be connected via the grid connection interface 1 to the power grid 2. The motor 3 would be connected to the first power supply line 4 in a star connection. If the voltage of the external power grid 2 was outside of these ranges, the second power supply line 5 would be connected to the external power grid 2 via the grid connection interface 1 .

Claims

Claims:1 . An electrical system for a mining or tunnelling machine, the electrical system comprising- a grid connection interface (1 ) for connecting the electrical system to an external alternating current power grid (2),- at least one alternating current motor (3),- a first power supply line (4) for supplying alternating current from the external power grid (2) to said at least one alternating current motor (3), and- a second power supply line (5) for supplying electric power from the external power grid (2) to said at least one alternating current motor (3), wherein the second power supply line (5) comprises means (6) for converting alternating current supplied from the external power grid (2) to direct current, and means (7) for converting the direct current to alternating current for supplying the alternating current to said at least one alternating current motor (3).

2. The electrical system according to claim 1 , wherein the first power supply line (4) is configured to be connected to power grids (2) operating at voltages that are within a voltage range (RS, RD) determined for a first operating mode, and the second power supply line (5) is configured to be connected to power grids (2) operating at voltages that are within a voltage range (R1 , R2, R3) determined for a second operating mode.

3. The electrical system according to claim 1 or 2, wherein the electrical system is configured to connect said at least one alternating current motor (3) to said first power supply line (4) via a star connection.

4. The electrical system according to any of claims 1 to 3, wherein the electrical system is configured to connect said at least one alternating current motor (3) to said second power supply line (5) via a delta connection.

5. The electrical system according to any of the preceding claims, wherein the second power supply line (5) comprises a harmonic filter (8) arranged before the means (6) for converting alternating current supplied from the external power grid (2) to direct current.

6. The electrical system according to any of the preceding claims, wherein said at least one alternating current motor (3) is configured to be operated at voltages of at least 220 V.

7. The electrical system according to any of the preceding claims, wherein the means (7) for converting the direct current to alternating current are configured to produce alternating current having a voltage in the range of 220-1000 V.

8. The electrical system according to any of the preceding claims, wherein the electrical system comprises at least one transformer (9) connectable to the alternating current supplied from the power grid (2) and configured to transform the voltage of the power grid (2) to a predetermined voltage level for powering one or more additional loads (10).

9. A mining or tunnelling machine comprising an electrical system according to any of the preceding claims.

10. The mining or tunnelling machine of claim 9, wherein the machine is configured to spray concrete.

11. A method of operating an electrical system comprising at least one alternating current motor (3) and being connectable to an external alternating current power grid (2), wherein- when the external power grid (2) operates at a voltage that is within a voltage range (RS, RD) determined for a first operating mode, alternating current is supplied from the external power grid (2) to said at least one alternating current motor (3) without voltage conversion (101 ), and- when the external power grid (2) operates at a voltage that is within a voltage range (R1 , R2, R3) determined for a second operating mode, the alternating current supplied by the external power grid (2) is converted to direct current (102), the direct current is converted to alternating current (103), and the alternating current converted from the direct current is supplied to said at least one alternating current motor (3) (104).

12. The method of claim 11 , wherein the alternating current in the voltage range (R1 , R2, R3) determined for the second operating mode is fed to a harmonic filter before converting the alternating current to direct current.

13. The method of claim 11 or 12, wherein the voltage is increased when the alternating current is converted to the direct current.

14. The method of any of claims 11 to 13, wherein part of electric power received from the power grid (2) is supplied as alternating current at the voltage level of the power grid (2) to a transformer (9), and the voltage is transformed by the transformer (9) to a predetermined voltage level for powering one or more additional loads (10).

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