BACKGROUND OF THE INVENTION

The invention relates to a mining vehicle and to a method for energy supply of a mining vehicle.

In mines, rock drilling rigs and other mining vehicles are used to perform operations according to work cycles of mining work devices at preplanned work sites. After the necessary tasks according to a work cycle, such as borehole drilling, have been performed, the mining vehicle is moved to the next work site and a new work cycle is started. In underground mines in particular, mining vehicles are generally used, the driving energy for operations according to the work cycles being electricity from an electrical network of the mine. By contrast, transfer drives between work sites are performed by means of driving energy obtained by using a combustion engine, typically a diesel engine, whereby electric cables or the like do not restrict the transfer drives. However, exhaust gases and noise from a combustion engine cause problems in mines. In addition, a combustion engine occupies a lot of space on the carriage of the vehicle and necessitates regular maintenance. A combustion engine also has adverse effects on fire safety in the mine, since it has hot surfaces and it is also necessary to store and handle flammable fuel in the vehicle and the mine.

Mining vehicles that are continuously connected to the electrical network of the mine are also used in mines. These mining vehicles have an electric motor, and typically one with a constant rotation speed. Power required by the work phase may then be adjusted with hydraulic components, and the electric motor obtains the electric current and load power defined by the energy consumption of the work phase from the electrical network of the mine. Further, the movement of the mining vehicle is then typically bound to the electrical network or at least to a cable connected thereto, the cable being coiled in the mining vehicle or at the fixed electrical network. BRIEF DESCRIPTION OF THE INVENTION

It is an object of the present invention to provide a new type of mining vehicle and a method for its energy supply.

The invention is characterised by the features of the independent claims. Embodiments of the invention are presented in the dependent claims. In the presented solution, a mining vehicle comprises at least one mining work device, at least one three phase AC electric motor for powering the at least one mining work device, a three phase connecting device connectable to a supply cable for supplying electric current to the mining vehicle from a supply grid and a current reducer unit for compensating for reactive power. The stator windings or coils of the electric motor are connectable to delta connection or configuration and to star connection or configuration. On a certain lower nominal voltage of the supply grid the stator windings or coils of the motor are connected to delta connection and on a certain higher nominal voltage of the supply grid the stator windings or coils of the motor are connected to star connection. The current reducer unit comprises at least three single phase capacitor units. The three single phase capacitor units are connected to delta connection while the stator windings or coils of the motor are connected to delta connection, and the three single phase capacitor units are connected to star connection while the motor is connected to star connection. The mining vehicle is thus easily connectable to different supply grids having different nominal voltages. The same electric motor may be used in a lower supply voltage and in a higher supply voltage. Correspondingly, the same current reducer unit may be used in a lower supply voltage and in a higher supply voltage.

According to an embodiment, each single phase capacitor unit is connected in parallel with a corresponding stator coil of the motor. Capacitor wirings may be connected to a terminal box for connecting the motor. Thus, the connections and structure of the mining vehicle are simple and reliable.

According to a further embodiment, the terminal box may comprise first terminals and second terminals, the stator coils or windings being connected to the first terminals and the second terminals and, correspondingly, the capacitor wirings are connected to the first terminals and the second terminals. The terminals are connectable by connecting strips for forming the delta connection or the star connection. Assembling the connecting strips for connecting the stator windings or coils of the motor to delta connection simultaneously connects the capacitor units to delta connection, and, correspondingly, assembling the connecting strips for connecting the stator windings or coils of the motor to star connection simultaneously connects the capacitor units to star connection. Modifications to the mining vehicle are thus easily and reliably performed. Consequently, it is ensured that when the stator windings or coils of the motor are connected to delta connection, the capacitor units are simultaneously connected to delta connection, and, correspondingly, when the stator windings or coils of the motor are connected to star connection, the capacitor units are simultaneously connected to star connection.

According to a further embodiment, the mining vehicle further comprises a power electronics device, the power electronics device supplying reactive current as per need. In such a solution the current reducer unit may provide a constant amount of reactive current and the power electronics device supplies reactive current for adjusting the power factor to a specified level.

The mining vehicle may comprise one or more of the following mining work devices: a rock drilling machine, bolting machine, shotcreting device, scaling device, injection device, blasthole charger, loader, dumper, measuring device, or drilling, sealing and propellant feeding equipment used in small-charge excavation. The rock drilling machine may be a face drilling device or a device used in production hole drilling, that is a long-hole drilling device that drills boreholes in a fan shape. The mining work device may be an actuator used in handling undetached rock and may perform several consecutive operations according to a given work cycle. Typically, several similar operations are performed with the mining work device at one work site. These operations may be defined in an excavation plan, such as a drilling plan, charging plan, or a corresponding mining plan. The mining work device is usually arranged on a boom with which the device is moved during the work cycle. On the other hand, the mining work device may be arranged on a corresponding support or support structure in a mining vehicle, supporting the device during its work cycle.

BRIEF DESCRIPTION OF THE FIGURES

Some embodiments of the invention will be described in more detail in the attached drawings, in which

Figure 1 is a schematic side representation of a mining vehicle, in this case a rock drilling rig,

Figure 2 is a diagram of an energy supply arrangement of a mining vehicle,

Figure 3 is a schematic diagram showing details of connecting a motor and a current reducer unit and

Figure 4 is a schematic diagram of a single phase capacitor unit. In the figures, some embodiments of the invention are shown simplified for the sake of clarity. Similar parts are marked with the same reference numbers in the figures.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 shows a rock drilling rig, which is one example of a mining vehicle 1 equipped with one or more mining work devices 2. The rock drilling rig comprises a carriage 3 that may be moved by means of drive equipment 4. The drive equipment 4 comprises one or more drive motors 5 and one or more power transmission means 6 for transmitting drive power to one or more wheels 7. The drive power transmission may comprise a mechanical gear system and mechanical power transmission members or, alternatively, the drive power transmission may be hydraulic or electric. There may be one or more booms 8 arranged on the carriage 3, and the boom may be equipped with a mining work device 2. In the embodiment shown in Figure 1 , the first boom 8a is a drilling boom, at the outermost end of which there is a rock drilling unit 9 comprising a feed beam 10, along which a rock drilling machine 1 1 can be moved by means of a feed device 12. The rock drilling machine 1 1 may comprise a percussion device 13 for generating impact pulses on a tool and a rotating device 15 for rotating the tool 14 around its longitudinal axis. There may be several of these drilling booms 8a in the rock drilling rig. By way of example, a second boom 8b is shown to comprise a bolting device 1 6, with which rock bolts can be arranged in pre-drilled boreholes to support the excavated rock cavern. In the embodiment of Figure 1 , a third boom 8c is equipped with a measuring device 17 for measuring drilled boreholes. Other alternative mining work devices 2 include injection devices used in feeding sealing material into rock, shotcrete processing devices, scaling equipment, devices used in small-charge excavation, and devices for feeding explosives.

The mining vehicle 1 is run in accordance with the excavation plan of the mine 18, or a corresponding predrafted plan, to a work site 19 where the mining work device 2 performs operations according to the work cycle, which takes a relatively long time. For instance, the work cycle of a rock drilling machine may include drilling several boreholes defined in the drilling plan at the work site 19. Further, drilling of each borehole typically consists of several work phases, such as collaring, actual drilling, changing extension rods and drill bits, and dismantling extension rod equipment after drilling. Performing a drilling work cycle at the work site 19 may take several hours, sometimes even an entire work shift. Correspondingly, charging, bolting, measuring, and injecting are often quite time-consuming operations. Generally, the use of a mining work device 2 has to do with drilling a borehole or further processing a finished hole. This then means handling undetached rock.

Figure 1 further shows that the mine 18 has an electrical network or a supply grid 20 that may be fixedly constructed or it may consist of a modifiable network. The supply grid 20 is typically a three-phase alternating current network. When the mining vehicle 1 is at the work site 19, its mining work device 2, hydraulic system and any necessary auxiliary systems are mainly driven by electrical energy obtained from the supply grid 20. The mining vehicle 1 may be connected to the supply grid 20 with one or more supply cables 21 . The supply cable 21 may be arranged on a reel 22 and it may be equipped with a suitable connector 23 that may be connected to the supply terminal of the electrical network 20. Alternatively, the reel 22 and the cable 21 may be arranged in the mine 18, and the supply cable 21 is connected to the mining vehicle 1 . The mining vehicle 1 comprises an electric motor 26, which is connected via a connecting device 24 to the supply grid 20. In the mining vehicle 1 , hydraulic pressure is produced by a hydraulic pump 27. The hydraulic pump is rotated by the electric motor.

The mining vehicle 1 is equipped with the connecting device 24, through which the electricity supplied from the supply grid 20 is connected to different devices of the mining vehicle 1 . The connecting device 24 is a three phase connecting device connectable to the supply cable 21 for supplying electric current to the mining vehicle from the supply grid 20.

The mining vehicle 1 is also equipped with at least one auxiliary energy source 25. The auxiliary energy source 25 may be a battery, a supercapacitor or their combination, for example, or any other suitable energy source that may be charged.

Figure 2 shows some parts of the mining vehicle very schematically. The electric motor 26 is connected to the supply grid 20. The electric motor 26 rotates the hydraulic pump 27. The electric motor 26 is a three phase alternating current electric motor.

The electric motor 26 also comprises a shaft 28. When electric energy is supplied from the supply grid 20 to the electric motor 26, the rotor of the electric motor is rotated. The shaft 28 is connected to the rotor of the electric motor 26, and thereby the electric energy from the supply grid 20 rotates the shaft 28.

The shaft 28 is connected to rotate the hydraulic pump 27. When rotated, the hydraulic pump 27 produces hydraulic pressure to the hydraulic system of the mining vehicle. The hydraulic system of the mining vehicle is denoted by reference numeral 29.

The hydraulic pressure in the hydraulic system 29 is used for supplying power to the mining work devices 2, for example. The hydraulic pressure may also be used for driving a hydraulic system of the driving equipment, such as steering and braking, for example.

The energy source 25 is connected via an inverter 30 to the supply grid 20. The inverter 30 is a power electronics device that is used for charging the auxiliary energy source 25. The inverter 30 may also be used for discharging the auxiliary energy source 25. Discharging the auxiliary energy source means that energy from the auxiliary energy source 25 is supplied via the inverter 30 for further use in the mining vehicle or even to the supply grid.

The auxiliary energy source 25 may be connected to the drive motor 5 via the inverter 30. Energy from the auxiliary energy source 25 may thus be used for the transfer drive of the mining vehicle 1 , for example.

During full power drilling, for example, it is also possible to supply energy from the auxiliary energy source 25 to the mining work device 2, whereby a boost mode is achieved. In the boost mode, energy is supplied to the mining work device from the supply grid 20 and from the energy source 25. During the boost mode, the load of the electric motor 26 to the supply grid 20 may thus be decreased by simultaneously supplying energy to the mining work device from the energy source 25.

It is also possible to supply energy to the mining work device 2 from the energy source 25 only. Thus, so-called low power drilling could be achieved even if the supply grid 20 were not able to supply energy, for example.

The inverter 30 is connected to a bus bar 31 . The electric motor 26 is also connected to the bus bar 31 . Other electric motors, such as a water pump and a compressor, may also be connected to the bus bar 31 .

A DC bus bar 32 may be provided between the inverter 30 and the auxiliary energy source 25. Other components, such as a cabin heater, may also be connected to the DC bus bar 32. The mining vehicle also comprises a current reducer unit 33. The current reducer unit 33 is a compensation device that is used for compensating for reactive power.

The mining vehicle comprises a terminal box 36 for connecting the electric motor 26. The current reducer unit 33 may be connected to the same terminal box 36.

The vehicle may also comprise a power factor meter 34. The power factor meter 34 may also be connected to the bus bar 31 .

The vehicle comprises a control unit 35. Measuring results are guided to the control unit 35 and the control unit 35 controls the devices of the vehicle.

The AC electric motor 26 is a cage induction motor that requires a magnetisation current which is reactive current. If this reactive current is not compensated for at the motor the reactive current oscillates between the motor and the supply grid, thus loading the supply cable 21 . The reactive current supplied via the supply cable 21 decreases the supply voltage. Low supply voltage causes overheating of the electric motors, starting problems, and dangerous situations regarding the short-circuit protection. Compensating for the reactive current raises the supply voltage, which in turn decreases the current of the electric motors and minimizes their warming.

The power factor meter 34 measures how much compensation is needed for compensating for the reactive current. The current reducer unit 33 may be a controllable compensation device in which case it is connected at the electric motor by a controllable thyristor switch, for example. In such a case the control unit 35 may control the thyristor switch to control the current reducer unit 33 to supply the reactive current. However, the current reducer unit may also be a fixed compensation device in which case it is directly connected at the electric motor and thus constantly provides a constant amount of reactive current. Such a solution is simple, reliable and cost effective.

The inverter 30 is such that, in addition to charging or discharging the auxiliary energy source 25, it is capable of supplying reactive current. If the current reducer unit 33 cannot supply enough reactive current, the control unit 35 may control the inverter 30 to supply reactive current. Supplying reactive current by the inverter 30 does not substantially consume the energy of the auxiliary energy source 25. The only energy consumed is caused by the losses of the inverter. Therefore it is advantageous to supply by the inverter 30 as much reactive current as possible and/or needed while the inverter 30 is not used for charging or discharging the auxiliary energy source 25, for example, or whenever possible. Naturally, if the need for reactive current is less than the maximum value of the reactive current the inverter is able to supply the inverter supplies only the needed amount. On the other hand, if the need for reactive current is equal to or higher than the maximum value of the reactive current the inverter is able to supply, the inverter supplies as much reactive current as possible.

Instead of the inverter 30, the power electronics device may also be a motor drive mechanism or a charging device, for example.

Figure 3 shows the connection of the electric motor 26 and the current reducer unit 33 as depicted in Figure 2 but in a more detailed manner. Electricity is supplied to the terminal box 36 via a motor feed line 37.

The stator coils or windings 38 of the electric motor 26 are connected to the terminal box 36 by motor wirings 39. Correspondingly, the single phase capacitor units 40 are connected to the terminal box 36 by capacitor wirings 41 .

Each single phase capacitor unit 40 is connected in parallel with a corresponding stator coil 38 of the electric motor 26. Thereby it is simple and easy to ensure that the single phase capacitor units 40 are connected to delta connection while the stator coils of the motor are connected to delta connection and that they are connected to star connection while the stator coils of the motor are connected to star connection.

The terminal box 36 comprises first terminals U1 , V1 and W1 and second terminals U2, V2 and W2. The first stator coil 38 is connected between the terminals U1 and U2, and, correspondingly, the first single phase capacitor unit 40 is connected between the terminals U1 and U2. The second stator coil 38 is connected between the terminals V1 and V2, and, correspondingly, the second single phase capacitor unit 40 is connected between the terminals V1 and V2. The third stator coil 38 is connected between the terminals W1 and W2, and, correspondingly, the third single phase capacitor unit 40 is connected between the terminals W1 and W2.

The stator coils of the electric motor 26 are connected to star connection by assembling a connecting strip 42 to connect the second terminals U2, V2 and W2. The connecting strip 42 for performing the star connection is depicted in Figure 3 by a dash and dot line. The stator coils of the electric motor 26 are connected to delta connection by assembling connecting strips 42 such that a first connecting strip 42 connects the terminals U1 and W2, a second connecting strip 42 connects the terminals V1 and U2 and a third connecting strip 42 connects the terminals W1 and V2. The connecting strips 42 for performing the delta connection are depicted in Figure 3 by dashed lines.

Because the single phase capacitor units 40 are connected in parallel with corresponding stator coils 38 and they are both connected to the first terminals U1 , V1 and W1 and the second terminals U2, V2 and W2, connecting the stator coils of the electric motor 26 by the connection strip 42 to star connection simultaneously connects the capacitor units 40 to star connection, and, correspondingly, assembling the connecting strips 42 to connect the stator coils of the electric motor 26 to delta connection simultaneously connects the capacitor units to delta connection.

A star delta switch could also be used for connecting the stator coils of the electric motor 26 and the capacitor units 40 to star connection or to delta connection. However, the selection between the star connection and delta connection is typically made only once before the mining vehicle is connected to the supply grid 20. Furthermore, the use of the connecting strips 42 is simple and reliable. Therefore it is cost effective to use connecting strips 42 instead of a star delta switch. The connecting strips may be made of copper or aluminium, for example.

According to an embodiment, the supply grid 20 has a nominal voltage of 400 V. The stator coils of the electric motor 26 are then connected to delta connection before the mining vehicle is connected to the supply grid 20. If the same mining vehicle is connected to another supply grid having a nominal voltage of 690 V, the stator coils of the electric motor 26 are connected to star connection. However, the same electric motor 26 is used without any other substantial modifications. According to the invention, the current reducer unit 33 comprises single phase capacitor units 40 that are connected to delta connection while the stator coils of the motor 26 are connected to delta connection and connected to star connection while stator coils of the motor 26 are connected to star connection. Thereby the same current reducer unit 33 is used in connection with both the supply grids, without any other substantial modifications. Thus the need for different components is minimal although the mining vehicle may be used in connection with supply grids having different nominal voltages.

Figure 4 shows a schematic diagram of a single phase capacitor unit 40. In this embodiment the capacitor unit 40 comprises a capacitor card comprising a printed circuit board with box type film capacitors. The capacitor unit 40 shown in Figure 4 comprises three capacitor levels 43. In each capacitor level 43, single capacitors 44 are connected in parallel to reach the needed capacitance level. The capacitor levels 43 formed by the parallel capacitors 44 may then be connected in series to have a sufficient voltage rating.

The capacitor unit 40 comprises a first terminal 45, a second terminal 46 and a third terminal 47. The capacitor wirings 41 are connected to the first terminal 45 and to the second terminal 46 when the needed voltage rating of the capacitor unit 40 is low and the capacitor wirings 41 are connected to the first terminal 45 and the third terminal 47 when the voltage rating of the capacitor unit 40 is high. Thus, according to an embodiment, the capacitor wirings 41 are connected to the first terminal 45 and to the second terminal 46 when the voltage is less than 500 V and the capacitor wirings 41 are connected to the first terminal 45 and to the third terminal 47 when the voltage is more than 500 V. Thereby the capacitor unit 40 may be used in connection with a very wide variety of different voltage levels. In Figure 4 balancing resistors, for example, are not shown for the sake of clarity.

Instead of the capacitor card 40 shown in Figure 4, the single phase capacitor unit 40 may comprise at least one conventional cylinder- shaped capacitor. Furthermore, the single phase capacitor unit 40 may comprise two or more conventional cylinder- shaped capacitors connected in parallel.

According to an embodiment the current reducer unit is

dimensioned such that the power factor is not optimal for all cases. Thus, although on a low voltage the power factor is 0.99, for example, on a high voltage the power factor is allowed to be as low as 0.95, for example. Thus, in certain situations the reactive current is not totally compensated for. Thereby, however, the amount of different components used in the current reducer unit 33 is low.

In the following Table 1 shows different voltage/frequency pairs for an induction motor (75 kW, 4-pole, IE3). In this example four different motors for 20 different voltage/frequency pairs are used. One current reducer unit (CRU) fits to all voltages/frequencies if the current reducer unit is made with printed circuit board capacitor cards. CRU connection A means that the CRU is internally connected for lower voltage. CRU connection B means that the CRU is internally connected for higher voltage. Table 1 shows the power factors with and without compensation at nominal power. Also the relative current reduction is shown. If a power electronics device is used for fine tuning of the reactive power compensation, it is possible to have a unity power factor in each voltage/frequency pair. Main idea behind the CRU dimensioning is to find the best possible compromise to have an adequate reactive power compensation and at the same time fit to as many different voltage/frequency pairs as possible. The relative current reduction ΔΙ is shown at nominal power. During normal work cycle the current reduction of average current is, however, typically 1 .5 times higher, for example. Thus, if the current reduction shown in the Table 1 is 10 %, for example, the current reduction of average current may be 15 %. This is due to the fact that during the work cycle the motor often runs idle thereby mainly consuming reactive current only, which is now

Table 1

A separate drive motor 5 is not necessarily needed but the electric motor 26 may produce the drive power needed. In that case the power transmission means 6 are connected to the shaft 28 of the electric motor 26.

The mining vehicle 1 may comprise one or more electric motors 26. The mining vehicle 1 may also comprise one or more hydraulic pumps 27. The electric motor 26 may rotate one or more hydraulic pumps 27, or each hydraulic motor 27 may comprise an electric motor of its own.

It should be mentioned that, in this specification, a mine refers to underground mines and opencast mines. Further, the method and the mining vehicle may be used at contract work sites, for example when excavating different rock facilities. Therefore, a contract work site may also be considered a type of mine. At contract work sites, an external electrical network may be modifiable, such as an aggregate on a movable carriage.

In some cases, the features described in this specification may be used as such, regardless of other features. On the other hand, the features described in this specification may also be combined to provide various combinations as necessary.

The drawings and the related description are only intended to illustrate the idea of the invention. The invention may vary in its details within the scope of the claims.

It will be obvious to a person skilled in the art that, as technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.