1 ROCK DRILLING DEVICE BACKGROUND OF THE INVENTION [0001] The invention relates to rock drilling equipment provided with electrically operated operation devices and means for connecting the rock drilling equipment to an electrical network. [0002] Typically, operation devices of rock drilling rigs are electrically operated. In such a case, at least at work points during working phases, a rock drilling rig is connected to an electrical network. Particularly at tunnel sites and other contract work sites, a rock drilling rig is only used for a short period of time of its entire life span, and after being used at one site the rock drilling rig is transferred for use at another site. A transfer from one site to another will succeed only if the voltage level of the electrical networks at the sites is the same. If the voltage level of the electrical networks at different sites is different, the voltage level should be transformed by a transformer to suit an operation device of the rock drilling rig, but in practice the size of such a necessary transformer and thus the difficulty of its handling and the subsequent costs are so great that rock drilling rigs are only used at sites wherein the voltage level of the electrical network feeding the rock drilling rigs suits their operation devices. BRIEF DESCRIPTION OF THE INVENTION [0003] DELETED [0004] In accordance with the present invention there is provided a rock drilling equipment provided with electrically operated operation devices and means for connecting the rock drilling equipment to an electrical network, wherein the rock drilling equipment comprises a voltage transformation means for transforming a voltage level as necessary either from higher to lower or from lower to higher, the rock drilling equipment is provided with electrically operated operation devices whose voltage levels are different in magnitude, and the rock drilling equipment is provided with connecting means for feeding some of the electrically operated operation devices directly from the electrical network and for feeding some of the electrically operated operation devices via the voltage transformation means, whereby it is possible to select by the connecting means the operation devices to be fed directly from the electrical network on the basis of their voltage levels. [0005] An advantage of the rock drilling equipment described herein is that rock drilling equipment or device which is provided with electrically operated operation devices and means for connecting the rock drilling equipment to an electrical network is also pro 3540820_1 (GHMatters) P90610AU 25/07/2012 WO 2011/080391 PCT/F12010/051086 2 vided with a voltage transformation means for transforming a voltage level. The rock drilling equipment is further provided with electrically operated operation devices having at least two different voltage levels, i.e. the rock drilling equip ment is provided with electrically operated operation devices whose voltage levels are different in magnitude, and the rock drilling equipment is provided with connecting means for feeding some of the electrically operated operation devices directly from the electrical network and for feeding some of the electri cally operated operation devices via the voltage transformation means. This enables rock drilling equipment to be achieved which may be used connected to electrical networks having at least two different voltage levels. However, the size of the voltage transformation means provided in the rock drilling equip ment is not very large since electricity has to be fed therethrough to only some of the operation devices of the rock drilling equipment. Preferably, the voltage transformation means is a transformer, in which case it is possible to utilize the same device both when raising the voltage level and when lowering the volt age level. A transformer has a simple and reliable structure, and in an applica tion according to the invention its volume and weight are also reasonable enough for the transformer to be used in rock drilling equipment. BRIEF DESCRIPTION OF THE FIGURES [0006] Some embodiments of the invention are described in closer detail in the accompanying drawings, in which Figure 1 is a schematic side view showing a rock drilling rig, and Figure 2 shows a diagram of an electricity feeding arrangement of a rock drilling rig. [0007] For the sake of clarity, the figures show some embodiments of the invention in a simplified manner. In the figures, like reference numerals identify like elements. DETAILED DESCRIPTION OF THE INVENTION [0008] Figure 1 shows a rock drilling rig 1 which is provided with one or more mining work devices 2. The rock drilling rig 1 comprises a carriage 3 which is movable 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 WO 2011/080391 PCT/F12010/051086 3 hydraulic or electric. The carriage 3 may be provided with one or more booms 8 which may be equipped with a mining work device 2. In the embodiment shown in Figure 1, a first boom 8a is a drilling boom whose outer end is pro vided with a rock drilling unit 9 comprising a feed beam 10 along which a rock drilling machine 11 may be moved by means of a feed device 12. The rock drilling machine 11 may comprise a percussion device 13 for generating im pact pulses on a tool, and a rotating device 15 for rotating the tool 14 around a longitudinal axis. The rock drilling rig may be provided with a plurality of such drilling booms 8a. For the sake of example, it is shown that a second boom 8b comprises a bolting device 16 for enabling rock bolts to be inserted into pre drilled holes to support the excavated rock cavern. In the embodiment of Fig ure 1, a third boom 8c is provided with a measuring device 17 for enabling drilled holes to be measured. Other alternative mining work devices 2 also in clude e.g. injection devices used for feeding a sealing material in to rock, de vices used in small-charge excavation, and devices for feeding explosives. [0009] Figure 1 also schematically illustrates an electrical network 18 which may be fixedly built or it may consist of a modifiable network. Typi cally, the electrical network 18 is a three-phase alternating current network. When the rock drilling rig is at a work point, its mining work devices, hydraulic system, and necessary auxiliary systems are mainly powered by electric en ergy available from an outside electrical network. The rock drilling rig 1 may be connected to the electrical network 18 by one or more connecting cables 19. The connecting cable 19 may be arranged on a reel 20 and it may be provided with a suitable connector 21 which may be connected to a supply connector of the electrical network 18. Alternatively, the reel 20 and the cable may be ar ranged fixedly in connection with the electrical network 18, and the connecting cable 19 is connected to the rock drilling rig 1. The rock drilling rig 1 is further equipped with a connecting device 22 via which electricity to be fed from the electrical network 18 is conveyed to different operation devices of the rock drill ing rig 1. The structure and operation of the connecting device 22 are de scribed in closer detail in connection with Figure 2. [0010] First, the connecting device 22 is provided with a circuit breaker 23 for enabling the rock drilling rig 1 to be connected to the electrical network 18 and for enabling the rock drilling rig 1 to be disconnected from the electrical network 18. The connecting device 22 is provided with switches 24a and 24b for selecting which side of a transformer 25 is connected to the elec- WO 2011/080391 PCT/F12010/051086 4 trical network 18. The switches 24a and 24b are thus arranged such that when one of the switches 24a, 24b is closed, the other one is open, correspondingly. The switches 24a and 24b may be manually controlled. The operation of the switches 24a and 24b may also be automatic, in which case they may be con trolled automatically on the basis of measurement of the feeding voltage. [0011] In Figure 2, designations 26a to 26e and 27 illustrate differ ent electrically operated operation devices of a rock drilling rig. For instance, designations 26a and 26c may describe feeding of electricity to mining work devices 2, i.e. designations 26a to 26c may describe power units of the rock drilling rig 1 that are powered by an electric motor. Designation 26b may de scribe an electric motor of a compressor of the rock drilling rig 1. Designation 26d, again, may describe a water pump of the rock drilling rig 1. Designation 26e, again, may describe e.g. a socket that may be used for connecting auxil iary functions, such as an immersion pump, to the rock drilling rig 1. Designa tion 27, again, may describe low voltage auxiliary functions of the rock drilling rig, such as lights or electricity feeding systems necessitated by control units, that are fed via a control transformer 28. Typically, the control transformer transforms the voltage of these auxiliary functions to be e.g. 24 volts. Electri cally operated operation devices of the rock drilling rig that are fed via the con necting device 22 may thus be e.g. mining work devices 2 of the rock drilling rig, its drive equipment 4, compressors, pumps and other auxiliary devices as well as other corresponding electrically operated devices. [0012] In terms of their voltage level, the electrically operated opera tion devices of the rock drilling rig 1 are divided into two different voltage lev els; in Figure 2, such levels are designated by Ul and U2. The transformer 25, again, is configured to transform voltage level U1 into voltage level U2, and vice versa. The position of the switches 24a, 24b, again, is selected according to the voltage level of the electrical network 18. If the voltage level of the elec trical network 18 is U1, the switch 24a is closed and the switch 24b is opened. In such a case, electrically operated operation devices having voltage level U1 are fed directly from the electrical network while electrically operated operation devices having voltage level U2 are fed via the transformer 25, which thus transforms the voltage level U1 of the electrical network into voltage level U2. [0013] In a similar manner, again, if the voltage level of the electrical network 18 is U2, the switch 24b is closed and the switch 24a is opened. In such a case, electrically operated operation devices having voltage level U2 WO 2011/080391 PCT/F12010/051086 5 are fed directly from the electrical network 18 while electrically operated opera tion devices having voltage level U1 are fed via the transformer 25, which transforms voltage level U2 into voltage level U1. [0014] Thus, in both cases, only some of the electrically operated operation devices are fed via the transformer 25, i.e. the basis of dimensioning the transformer 25 is thus smaller than the total power of the rock drilling rig. The power of the mining work devices 2, i.e. the power units of rock drilling rigs, may be of the order of 30 to 100 kW. The power of compressors and pumps, again, may be e.g. of the order of 5 to 15 kW. The power of other auxil iary devices and the like, again, may typically be of the order of couple of kilo watts. Consequently, the total power of the rock drilling rig may be e.g. of the order of 250 kW. If such a rock drilling rig is to be used in two different voltage levels, a prior art solution would require a 300 kVA transformer. In the present solution, however, only some of the electrically operated operation devices have to be fed via the transformer, in which case the size of the transformer may be e.g. 160 kVA. The weight and in particular the volume of the trans former then remain quite small, so it is structurally and economically reason able to place the transformer in connection with the rock drilling rig. [0015] Preferably, then, the electrically operated operation devices are divided into different voltage levels as evenly as possible, which enables the size of the transformer 25 to be dimensioned to be of the order of almost half the total power of the rock drilling rig. Preferably, the electrically operated operation devices are divided into the different voltage levels such that the summed-up total power of the electrically operated operation devices having the greater summed-up total power is no more than 75%, preferably no more than 60%, of the total power of the rock drilling rig. [0016] The basic principle may be that the power units of the rock drilling rig are divided into different voltage levels, since typically their propor tion of the total power of the rock drilling rig is the largest. Other electrical de vices, again, are divided into different voltage levels such that the power distri bution is as even as possible. If the number of power units provided in the rock drilling rig is an odd number, one voltage level may include only power units while other electrically operated operation devices are included in another volt age level. If the rock drilling rig comprises e.g. three power units, a first voltage level may include two power units while a second voltage level may include one power unit as well as all the rest of the electrically operated operation de- 6 vices. If the rock drilling rig comprises only one power unit, it is included in a first voltage level while all the rest of the electrically operated operation devices are included in a second voltage level. [0017] As examples of a voltage level to be used, it may be put forward that a first voltage level is 1000 V and a second voltage level is 690 V. Another example of voltage levels may be that a first voltage level is 1000 V and a second voltage level is 400 V. The transformer 25 may also be such that its one side is provided with two different voltage levels available by utilizing e.g. an intermediate tap. In such a case, the voltage level of the first side of the transformer may thus be 1000 V and the voltage levels of the other side of the transformer may be e.g. 690 V and 400 V, the latter being utilizable from the intermediate tap. [0018] In some cases, the features disclosed in the present application may be used as such, irrespective of other features. On the other hand, when necessary, the features disclosed in the present application may be combined so as to provide different combinations. [0019] The drawings and the related description are only intended to illustrate the idea of the invention. The details of the invention may vary within the scope of the claims. [0020] Instead of a transformer, some other device enabling a voltage level to be transformed from higher to lower and in another usage situation again from lower to higher may also be used as a voltage transformation means. Such a solution may be produced e.g. by two inverters, thus comprising a rectification part, an intermediate circuit, and an inversion part which enables the voltage level to selected as desired. [0021] In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention. 3540820_1 (GHMatters) P90810.AU 25/07/2012