Electrically operated civil engineering machine, and method for operating the civil engineering machine

Abstract

The invention relates to an electrically operated civil engineering machine and to a method for electrically operating the civil engineering machine, having a mobile carrier device, at least one electrical consumption unit, at least one supply device by means of which electric current is supplied from an external energy source, which supplies electric current in alternating voltage with a first frequency and a first voltage value, the supply device having a first supply unit, which is arranged remote from the mobile carrier device and is connected to the external energy source, and having a second supply unit, which is arranged on the carrier device and is connected to the first supply unit via a connecting line for transmitting electric current. According to the invention, it is provided that the first supply unit has a frequency converter, which converts a frequency of the alternating voltage of the supplied current to a second frequency that is higher than the first frequency, and a first transformer, which increases the alternating voltage to a second voltage value, and that the electric current is transmitted from the first supply unit via the connecting line to the second supply unit on the carrier device with the second frequency and the second voltage.

Description

[0001] ||J wunderlich & heim

[0002] WH PATENTANWÄ LTE

[0003] B 3789

[0004] ELECTRICALLY OPERATED CIVIL ENGINEERING MACHINE AND METHOD FOR OPERATING THE CIVIL ENGINEERING MACHINE

[0005] The invention relates to an electrically operated underground construction machine with a mobile carrier unit, at least one electrical consumption unit, at least one supply device for supplying electric current from an external energy source which supplies electric current in alternating voltage with a first frequency and a first voltage value, wherein the supply device comprises a first supply unit which is arranged remotely from the mobile carrier unit and is connected to the external energy source, and a second supply unit which is arranged on the carrier unit and is connected to the first supply unit via a connecting line for the transmission of electric current, according to the preamble of claim 1.

[0006] The invention further relates to a method for electrically operating a civil engineering machine, comprising a mobile carrier device, at least one electrical consumption unit, and at least one supply device through which electric current is supplied from an external energy source, which provides electric current in alternating voltage with a first frequency and a first voltage value, wherein the supply device comprises a first supply unit, which is arranged remotely from the mobile carrier device and is connected to the external energy source, and a second supply unit, which is arranged on the carrier device and is connected to the first supply unit via a connecting line for transmitting electric current, according to the preamble of claim 14. Electrically operated civil engineering machines have been known for some time, for example from EP 4 245 923 B1.Such civil engineering machines can be used particularly at work sites where noise and exhaust fumes are undesirable, such as those that can be more prevalent with combustion engine-powered civil engineering machines. Due to the high energy requirements of such electrically powered civil engineering machines, they have a power supply device for drawing electrical energy from an external power source, especially an electrical grid. This requires the provision of a suitable electrical connection.

[0007] During operation, a trenching machine can have a high energy demand, requiring electrical power of up to 1 megawatt or more. This high power must be transmitted by the connecting cable that links the mobile trenching machine to a stationary feed unit of the feed system. Depending on the power to be transmitted, these cables, in the case of a multi-core cable configuration, can have a diameter of up to 20 cm or more. Such connecting cables are very expensive due to the high material requirements, particularly copper, and are also very difficult to handle due to their dimensions, requiring forklifts or cranes for transport on the construction site.

[0008] EP 4 012 109 B1 discloses the use of a swiveling mounting and connection device for attaching a power supply cable to the superstructure of a construction machine. The larger and heavier the cable, the more complex the corresponding mountings for the cable on the machine become. Moving the machine on the construction site with a connected cable is also very difficult with a thick cable.

[0009] Several concepts exist for transmitting electrical energy to mobile construction machinery. According to one concept, a high or medium voltage from an external power source is transformed down to the operating voltage of the construction machine using a stationary transformer before being transmitted to the machine. This requires only a frequency converter on the machine to convert the alternating current into a direct current operating voltage. However, this method results in relatively high power losses during transmission and necessitates connecting cables with large cross-sections, which can easily reach 20 cm² or more. Since these cables are typically made of copper, they are also quite heavy.The connecting cables, which can easily reach lengths of 100 meters or more, are very heavy, can only be handled with lifting equipment, and are ultimately very expensive. They can represent a cost of around €100,000 or more.

[0010] Another concept involves installing a first transformer at the stationary first feed unit to generate a high voltage and a second transformer at the construction machine to then transform the high voltage down to the operating voltage. This allows for a reduction in the cross-sectional area of ​​the connecting cable. However, the transformers required for this are very large and can each have a volume of well over one cubic meter. This can be particularly problematic when installed on a mobile construction machine with limited installation space.

[0011] A third concept involves supplying electricity from a construction site distribution box, which in certain cases can be provided by the energy supplier. The construction machine then requires an onboard charger, which manages the supply and provision of electrical energy via specialized power electronics. This type of energy transmission is technically complex and only feasible in specific situations. Furthermore, the transmittable power is limited.

[0012] The various known concepts will be explained in more detail below in connection with Figures 3 to 5.

[0013] The invention is based on the task of providing an electrically operated underground construction machine and a method for this purpose, with which a particularly efficient transfer of electrical energy to the construction machine is achieved.

[0014] According to the invention, the problem is solved, firstly, by an electrically operated underground construction machine with the features of claim 1 and, secondly, by a method with the features of claim 14. Preferred embodiments of the invention are specified in the dependent claims.

[0015] The construction machine according to the invention is characterized in that the first feed unit comprises a frequency converter configured to convert the frequency of the AC voltage of the supplied current to a second frequency higher than the first frequency, and a first transformer configured to increase the AC voltage to a second voltage value higher than the first voltage value, and that the electric current from the first feed unit can be transmitted via the connecting line to the second feed unit at the carrier device with the second frequency and the second voltage. A first aspect of the invention lies in increasing the frequency of the alternating current for the transmission of electrical energy. This frequency increase simplifies energy transmission and, in particular, significantly reduces the size of the transformers required.Preferably, small, easily transportable transformers can be used, some of which can even be carried without lifting equipment and are about the size of a suitcase. This saves space on the construction site and especially on the excavation machine. Another aspect of the invention is increasing the voltage of the alternating current for the transmission of electrical energy. Increasing the voltage simplifies energy transmission and reduces power losses. Furthermore, another advantage is that the required cross-sectional area of ​​the connecting cable is inversely proportional to the voltage of the alternating current being transmitted. Thus, the cross-sectional area of ​​the connecting cable can be significantly reduced, which noticeably improves its handling and transportability and leads to a significant reduction in material, weight, and therefore also costs.

[0016] In particular, the combination of these two aspects results in a significant simplification and improvement in the transmission of electrical energy to a construction machine, which can require high electrical power of up to 1 megawatt or more on a construction site. Furthermore, only conventional electrotechnical components are required, and complex power electronics can be largely avoided. An electrically operated construction machine according to the invention can be a purely electric machine or a hybrid machine, which, in addition to electric drives, can also include a conventional drive, in particular an internal combustion engine. Preferably, construction machines can be equipped with batteries, since no cable is normally connected during setup. Battery operation is practical and very convenient for loading and unloading onto the low-loader.

[0017] A preferred embodiment of the invention comprises a second supply unit on the carrier device, comprising a second transformer configured to change the second voltage value to a third voltage value, in particular to reduce it, and a rectifier configured to convert the alternating current of the supplied power into a direct current voltage. The second transformer is preferably configured to change the high voltage set for power transmission to an operating voltage of the construction machine, in particular to reduce it. The second transformer can also be very compact, in particular even portable. This allows for quick conversion, retrofitting, or adaptation to a local power grid.With a downstream rectifier, the alternating voltage can be changed to a direct voltage preferred on the construction machine, which can preferably be fed into an intermediate circuit of the construction machine.

[0018] Furthermore, it can be advantageous that the DC voltage of the intermediate circuit can be generated very easily by a bridge rectifier. This is mainly due to the high frequency used for transmission.

[0019] To ensure the smoothest possible operation of the construction machine, a further development of the invention provides that the first feed unit has a filter designed to filter out interference frequencies, preferably arranged between the external power source and the frequency converter. Such a filter can prevent or largely suppress interference frequencies that can be generated by the first feed unit and that can have a particularly negative impact on a power grid that may serve as an external power source. Furthermore, a filter can contribute to the return of recuperatively generated excess power from the construction machine to the power grid. The filter can reduce the harmonic oscillations that are fed back into the grid as feedback (interference). Various feed-in regulations with different limit values ​​apply to this.By using different filters, these feedback effects can be adapted to the various requirements.

[0020] For efficient energy transmission, it is further advantageous if the first supply unit includes a choke designed to provide a specific inductance, preferably arranged between the frequency converter and the first transformer. The use of a choke and the resulting assurance of a specific inductance has a positive effect on the operation of the downstream transformer and thus on the entire circuit arrangement.

[0021] It should be noted that a filter and a choke are also conventional electrotechnical components or elements, which are robust and do not require complicated power electronics.

[0022] In principle, various suitable alternating current frequencies can be used for the electrically operated excavation machine. According to one embodiment of the invention, it is particularly advantageous for the frequency converter to be designed as a high-frequency converter, which is configured to increase the first frequency, preferably in the range up to 200 Hz, and in particular approximately 50 Hz, to a high frequency as a second frequency, preferably in a range above 1 kHz, and in particular between 1 kHz and 20 kHz. With such a high frequency, particularly compact transformer sizes can be achieved, which can be within a volume of 0.5 m x 0.5 m x 0.5 m. In contrast, conventional box-type transformers with the usual mains frequencies can have side lengths of up to 2 m and a volume of several cubic meters.

[0023] According to one embodiment of the invention, the size advantage can be improved in particular by designing the first transformer as a high-frequency transformer, which is connected downstream of the frequency converter and is designed to increase the first voltage value, which is preferably in the range up to 500 V, in particular about 400 V, to a high voltage as a second voltage value, which is preferably in a range above 1 kV, in particular between 1 kV and 20 kV.

[0024] According to a further development of the invention, it is preferred that the first feeding unit and / or the second feeding unit are each enclosed in a housing and designed to be transportable. The feeding units, which are preferably equipped with a weatherproof housing, can be designed to be particularly compact and robust. They can be easily transported, so that they can be reliably used on construction sites and can also be retrofitted or adapted to a local power grid.

[0025] A further advantageous embodiment of the electrically operated excavation machine is achieved by designing the second transformer as a high-frequency transformer, which is configured to reduce the second voltage value, preferably a high voltage, to an operating voltage of the excavation machine as the third voltage value, which is preferably in the range between 500 V and 2000 V. By using a high frequency, preferably in the range above 1 kHz, particularly between 1 kHz and 20 kHz, a particularly compact size for a transformer, especially on the excavation machine, can be achieved. Preferably, two high-frequency transformers, but only one frequency converter, can be provided.

[0026] A preferred embodiment of the underground construction machine according to the invention can be further achieved by connecting the second feed unit, in particular the rectifier of the second feed unit, to a DC intermediate circuit of the underground construction machine for power supply. The at least one electrical load unit of the underground construction machine is connected to this DC intermediate circuit for power supply. The DC intermediate circuit enables efficient energy distribution at the underground construction machine, even during recuperation. All or virtually all electrical load units of the underground construction machine, in particular the electric drives, are connected to the DC intermediate circuit. By using a rectifier, a direct current can be generated from the high-frequency alternating current at the underground construction machine relatively easily and with low power losses.

[0027] According to the invention, a particularly energy-efficient design of the underground construction machine is achieved by connecting at least one accumulator to the DC intermediate circuit for power storage. This makes it possible, in particular, to temporarily store the larger quantities of electricity generated during recuperation, which cannot be used directly by the underground construction machine. This increases the energy efficiency of the underground construction machine.

[0028] It is particularly advantageous that the excavation machine has at least one recuperation device for recovering energy and converting it into electricity, and that the supply device is designed to feed electricity back to the external energy source, in particular a power grid. This allows even large quantities of recuperatively generated electrical energy, which cannot be directly consumed or temporarily stored by the excavation machine itself, to be used effectively.

[0029] Another preferred embodiment of the electrically operated underground construction machine is that the frequency converter is equipped with a current or power measurement function, particularly for so-called voltage droop control in the DC link. This can further improve energy efficiency.

[0030] In principle, electrically powered civil engineering machinery can be designed to carry out any type of civil engineering work or process. It is particularly advantageous if the machinery is configured as a drilling rig, a diaphragm wall excavator, a vibrator, or a pile driver. A drilling rig for civil engineering can be, in particular, a pile drilling rig, which is used to install foundation piles in the ground. A diaphragm wall excavator can be a trench cutter with milling wheels or a diaphragm wall grab with grab buckets. A vibrator can include a vibration device for driving piles or planks into the ground. A pile driver can be designed for driving piles into the ground.

[0031] The invention further relates to a method for electrically operating a civil engineering machine, in particular as previously described. The method according to the invention is characterized in that the first supply unit comprises a frequency converter, which converts one frequency of the AC voltage of the supplied current to a second frequency that is higher than the first frequency, and a first transformer, which increases the AC voltage to a second voltage value that is higher than the first voltage value, and that the electric current is transmitted from the first supply unit via the connecting line to the second supply unit at the carrier device with the second frequency and the second voltage. On the carrier device, which comprises a second transformer, the second voltage is then reduced to a third voltage value that is lower than the second voltage value.A rectifier bridge can then be used to generate a direct current from the alternating current, which can be fed into an intermediate circuit. This method allows the previously described advantages to be achieved when operating a deep-construction machine.

[0032] A further advantageous embodiment of the method according to the invention is achieved by designing the second transformer as a high-frequency transformer, which reduces the second voltage value, preferably a high voltage, to an operating voltage of the excavation machine as the third voltage value, which is preferably in the range between 500 V and 2000 V. By using a high frequency, preferably in the range above 1 kHz, in particular between 1 kHz and 20 kHz, a particularly compact size for a transformer, especially at the excavation machine, can be achieved. Preferably, a total of two high-frequency transformers, but only one frequency converter, can be used.

[0033] The invention is further explained below with reference to preferred embodiments, which are shown schematically in the drawings. In the drawings, Fig. 1 shows a side view of a deep-construction machine according to the invention;

[0034] Fig. 2: a schematic representation of an arrangement for energy transmission for a civil engineering machine according to the invention;

[0035] Fig. 3: a schematic representation of an arrangement for energy transmission according to a first concept in the prior art;

[0036] Fig. 4: a schematic representation of an arrangement for energy transmission according to a second prior art concept; and

[0037] Fig. 5: a schematic representation of an arrangement for energy transmission according to a third concept in the prior art.

[0038] An electrically operated underground construction machine 10 according to the invention, comprising a carrier unit 12, is shown in Fig. 1. The carrier unit 12 preferably comprises a crawler chassis as an undercarriage 14, on which a superstructure 16 can be rotatably mounted. A control unit 60 for the underground construction machine 10 can be located in an operator's cabin of the superstructure 16. In particular, a beam-like machine component, especially a mast 20 shown here, can be adjustably mounted on the superstructure 16, preferably via a linkage mechanism 18, to form a lifting device. The mast 20 can preferably be designed as a pole 21 with a linear guide 24 along the mast 20 and can have a substantially vertical position during operation.The beam-like machine component, in particular the mast 20, can also be directly connected to the superstructure 16 via a joint (not shown) arranged in the lower region of the beam-like machine component and one or more actuating cylinders (not shown). Likewise, it is also possible, according to the invention, that the beam-like machine component, instead of the mast 20, is an articulated boom (not shown) which can be adjustably arranged on the superstructure 16.

[0039] According to the illustrated embodiment, the mast 20 can preferably be designed as a mast 21 with a linear guide 24 on its front side. A work carriage 38 with a rotary drilling drive 36, which in particular includes at least one electric motor, can be mounted vertically along the linear guide 24. This allows the underground construction machine 10 to be configured as a drilling rig. The drawing shows an exemplary middle position of the rotary drilling drive 36 as well as a lower position with a dashed line.

[0040] A rope 40 can be guided over a mast head 22 at the upper end of the mast 20. At one end of the rope, a preferably telescopic Kelly bar 32 with an exemplary auger 34 for forming a deep-drilling tool 30 can be provided. The Kelly bar 32 can be guided by a sleeve-shaped drive wheel of the rotary drilling drive 36 on the working carriage 38, so that torque can be transmitted from the rotary drilling drive 36 to the Kelly bar 32, for example, via drive strips (not shown). The auger 34 for creating a borehole in the ground can be arranged at the lower end of the Kelly bar 32. The drilling tool can, in principle, be of any design and, in particular, may include an auger 34 or a drill bucket.

[0041] From the Kelly bar 32, the cable 40 can be guided via pulleys 26 at the mast head 22 along the mast 20 to a winch 46 in the superstructure 16. The winch 46 is driven by an electric motor 50, which can also be operated in a recuperation mode. The Kelly bar 32 with the auger 34 can be raised and lowered by the cable 40 via the winch 46. During lowering, potential energy can be converted into electrical energy by the electric motor 50 and supplied to an intermediate circuit, which is described in more detail below.

[0042] An actuator 28 with a winch on the mast 20 allows the work carriage 38 with the rotary drilling drive 36 to be raised via a further actuating cable 29. By driving the actuator 28 in the opposite direction, the work carriage 38 with the rotary drilling drive 36 can also be lowered. Likewise, the work carriage 38 can be pulled downwards by the actuator 28. The rotary drilling drive 36 can be formed by a power rotary head with at least one additional electric motor. The actuator 28 can also be equipped with an electric motor (not shown), which can also be operated in recuperation mode. The work carriage 38 with the rotary drilling drive 36 can also be considered part of the deep-drilling tool 30.The control unit 60 controls at least one electric motor 50 for operating the cable winch 46 and preferably also the further electric motor for operating the actuator 28 designed as a winch.

[0043] For power supply, a schematically depicted carrier device 12 of an electrically operated underground construction machine according to the invention is connected to an external electrical power source 5, which is preferably a power grid. The external power source 5 can, in particular, provide an alternating current with a first voltage value, which is preferably an alternating voltage in the range up to 500 V, in particular approximately 400 V, and with a first frequency, which is preferably in the range up to 200 Hz, in particular approximately 50 Hz.

[0044] According to the invention, the external energy source 5 is connected to the carrier device 12 via a feed device 62, which comprises a stationary first feed unit 70 and a second feed unit 80 on the carrier device 12. A connecting line 90 extends from the first feed unit 70 to the second feed unit 80 on the carrier device 12 of the underground construction machine to conduct electrical current. The connecting line 90 can have a length of approximately 100 m or more.

[0045] According to the illustrated embodiment, the first feed unit 70 can include a frequency converter 74, which is configured to convert a first frequency of the alternating voltage of the supplied current to a second frequency that is higher than the first frequency and preferably between 1 kHz and 20 kHz. An electrotechnical component, a filter 72, can be connected upstream of the first feed unit 70, which is configured to filter out interference frequencies.

[0046] Furthermore, the first feed unit 70 comprises a first transformer 78, which is configured to increase the alternating voltage of the current from a first voltage value from the external energy source 5 to a second voltage value that is higher than the first voltage value. The second voltage value can, in particular, be between 1 kV and 20 kV. A choke 76, which is configured to provide a specific inductance, can be arranged between the frequency converter 74 and the first transformer 78 of the first feed unit. The electrical components of the first feed unit 70 can be enclosed by a housing 71, which is preferably designed to be transportable. The electrical current, modified by the first feed unit 70 with an increased frequency and voltage, is transmitted via the connecting line 90 to the second feed unit 80 on the carrier device 12 of the underground construction machine.

[0047] According to the illustrated embodiment, the second feed unit 80 on the carrier device 12 can have a second transformer 82, which is configured to change, and in particular reduce, the second voltage value to a third voltage value, namely an operating voltage of the excavation machine. The third voltage value can be in a range preferably between 700 V and 2 kV. Other value ranges are possible. Furthermore, the second feed unit can include a rectifier 84, which is configured to convert the AC voltage of the supplied current into a DC voltage. It can be particularly advantageous that a second frequency converter is unnecessary due to the rectifier.

[0048] The second feed unit 80 can be connected via the rectifier 84 to a DC intermediate circuit 52 of the excavation machine 10 for power supply, to which an inverter 56 and / or several electrical load units 50a and 50b of the excavation machine can be connected for supplying electrical current. At least one accumulator 54 can also be connected to the DC intermediate circuit 52 for power storage.

[0049] The feeding device 62 according to the invention for a civil engineering machine 10 enables efficient transmission of electrical energy.

[0050] Several concepts are known for the transmission of electrical energy to a mobile construction machine, which are schematically illustrated in Figures 3 to 5.

[0051] According to a first concept shown in Fig. 3, a high or medium voltage from an external energy source 5 for electrical current is transformed down to the operating voltage of the construction machine by means of a stationary transformer 78' before being transmitted to a carrier device 12 of the construction machine and via a connecting line 90'. A frequency converter 74' is required on the construction machine to convert the frequency of an alternating voltage into an operating DC voltage for the electrical load unit 50a. However, this results in relatively high power losses during energy transmission and requires connecting lines 90' with large conductor cross-sections, which can easily be 20 cm² or more. These connecting lines are unwieldy and involve high costs.

[0052] A second concept, as shown in Fig. 4, involves providing a first transformer 78" at a stationary power supply unit to generate a high voltage and a second transformer 82" at the construction machine to then transform the high voltage down to the operating voltage. A frequency converter 74" can then supply the electrical load unit 50a. This allows for a reduction in the cross-sectional area of ​​a connecting cable 90". However, the transformers 78" and 82" required for this are very large and can each have a volume well over one cubic meter. This can be problematic, especially when installed on a mobile construction machine. A third concept is illustrated in Fig. 5. The electrical current from an external energy source 5 is supplied via a construction site distribution box 94, which in certain cases can be provided by the energy supplier.The construction site distribution panel can typically provide an alternating current of, for example, 400 V and a frequency of 50 Hz. The construction machine then requires a so-called on-board charger 86, which, via special power electronics, manages the supply and provision of electrical energy to a DC intermediate circuit 52'" with a battery 54'" for energy storage, a connected frequency converter 74'", and electrical load units 50a. This type of energy transmission is technically complex and limited in the power that can be transmitted. This type of energy transmission is only possible in certain cases.

Claims

II* wunderlich & heim WH PATENTANWÄ LTE -15- B3789 PATENT CLAIMS 1 Electrically powered civil engineering machine with a mobile carrier device at least one electrical consumption unit (50), at least one supply device (62) for supplying electric current from an external energy source (5) which supplies electric current in alternating voltage with a first frequency and a first voltage value, wherein the supply device (62) a first feed unit (70), which is arranged remotely from the mobile carrier device (12) and is connected to the external power source, and a second feed unit (80) which is arranged on the carrier device (12) and is connected to the first feed unit (70) via a connecting line (90) for the transmission of electrical current, characterized by that the first supply unit (70) comprises a frequency converter (74) configured to convert the frequency of the AC voltage of the supplied current to a second frequency which is higher than the first frequency, and a first transformer (78) configured to increase the AC voltage to a second voltage value which is higher than the first voltage value, and that the electric current from the first feed unit (70) via the connecting line (90) to the second feed unit (80) on the carrier device (12) can be transmitted with the second frequency and the second voltage.

2. Electrically operated underground construction machine according to claim 1 , characterized by that the second supply unit (80) on the carrier device (12) has a second transformer (82) which is configured to change the second voltage value to a third voltage value, in particular to reduce it, and preferably a rectifier (84) which is configured to convert the alternating voltage of the supplied current into a direct voltage.

3. Electrically operated underground construction machine according to claim 1 or 2, characterized by that the first feed unit (70) has a filter (72) which is designed to filter out interfering frequencies, wherein the filter (72) is preferably arranged between the external power source (5) and the frequency converter (74).

4. Electrically operated underground construction machine according to one of claims 1 to 3, characterized in that, that the first feed unit (70) has a choke (76) which is configured to provide a certain inductance, wherein the choke (76) is preferably arranged between the frequency converter (74) and the first transformer (78).

5. Electrically operated underground construction machine according to one of claims 1 to 4, characterized in that, that the frequency converter (74) is designed as a high-frequency converter which is designed to increase the first frequency, which is preferably in the range up to 200 Hz, in particular about 50 Hz, to a high frequency as a second frequency, which is preferably in a range above 1 kHz, in particular between 1 kHz and 20 kHz. -17- 6. Electrically operated underground construction machine according to one of claims 1 to 5, characterized in that, that the first transformer (78) is designed as a high-frequency transformer, which is connected downstream of the frequency converter (74) and is designed to increase the first voltage value, which is preferably in the range up to 500 V, in particular about 400 V, to a high voltage as a second voltage value, which is preferably in a range above 1 kV, in particular between 1 kV and 20 kV.

7. Electrically operated underground construction machine according to one of claims 1 to 6, characterized in that, that the first feed unit (70) and / or the second feed unit (80) are each enclosed by a housing (71) and designed to be transportable.

8. Electrically operated underground construction machine according to one of claims 1 to 7, characterized in that, that the second transformer (82) is designed as a high-frequency transformer, which is designed to reduce the second voltage value, which is preferably a high voltage, to an operating voltage of the underground construction machine (10) as a third voltage value, which is preferably in a range between 500 V and 2000 V.

9. Electrically operated underground construction machine according to one of claims 1 to 8, characterized in that, that the second feed unit (80), in particular the rectifier (84) of the second feed unit (80), is connected to a DC intermediate circuit (52) of the underground construction machine (10) for power supply, to which the at least one electrical consumption unit (50) of the underground construction machine (10) is connected for supply with electrical current.

10. Electrically operated underground construction machine according to claim 9, characterized by that at least one accumulator (54) for power storage is connected to the DC intermediate circuit (52).

11. Electrically operated underground construction machine according to one of claims 1 to 10, characterized in that, that the underground construction machine (10) has at least one recuperation device for recovering energy and converting it into electrical current and that the supply device (62) is designed to return electrical current to the external energy source (5), in particular a power grid, and / or the accumulator (54).

12. Electrically operated underground construction machine according to one of claims 1 to 11, characterized in that, that the frequency converter (74) is equipped with a current or power measurement, in particular for voltage droop control in the DC intermediate circuit (52).

13. Electrically operated underground construction machine according to one of claims 1 to 12, characterized in that, that it is designed as a drilling rig, a diaphragm wall rig, a vibrator rig or a pile driver rig.

4. Method for electrically operating a civil engineering machine (10), in particular according to one of claims 1 to 13, with a mobile carrier device (12), at least one electrical consumption unit (50), at least one supply device (62) through which electric current is supplied from an external energy source (5) which supplies electric current in alternating voltage with a first frequency and a first voltage value, wherein the supply device (62) a first feed unit (70), which is arranged remotely from the mobile carrier device (12) and is connected to the external power source (5), and a second feed unit (80) which is arranged on the carrier device (12) and is connected to the first feed unit (70) via a connecting line (90) for the transmission of electrical current, characterized by , that the first supply unit (70) comprises a frequency converter (74) which converts a frequency of the alternating voltage of the supplied current to a second frequency which is higher than the first frequency, and a first transformer (78) which increases the alternating voltage to a second voltage value which is higher than the first voltage value, and that the electric current is transferred from the first feed unit (70) via the connecting line (90) to the second feed unit (80) on the carrier device (12) with the second frequency and the second voltage.

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