Power generating unit for generating electrical power, power grid with such a power generating unit, and method for operating such a power generating unit on a power grid

Abstract

Power generating unit (3), designed to generate electrical power, with - a first electric machine (5), with - a first drive unit (9) generating waste heat, which is configured to drive the first electric machine (5), with - a second electric machine (7), and with - a second drive unit (11) which is configured to drive the second electric machine (7) and to use waste heat from the first drive unit (9) to drive the second electric machine (7), wherein - the first electric machine (5) and the second electric machine (7) can be connected to the same power grid (1), characterized by - a fault handling device (13) which is configured to detect at least one specific fault in the power network (1), to electrically disconnect the second electrical machine (7) from the power network (1) in response to the at least one specific fault, and at the same time to keep the first electrical machine (5) electrically connected to the power network (1).

Description

[0001] The invention relates to a power generation device, a power grid with such a power generation device and a method for operating such a power generation device on a power grid.

[0002] A power generating device of the type discussed here, configured for generating electrical power, comprises a first electric machine and a first drive unit that generates waste heat, the first drive unit being configured to drive the first electric machine. The power generating device also comprises a second electric machine and a second drive unit, the second drive unit being configured to drive the second electric machine and to utilize waste heat from the first drive unit to drive the second electric machine. The first electric machine and the second electric machine are, and in particular are, connected to the same electrical network.Such a combination of a primary drive unit generating waste heat, which drives an electric machine to generate electrical power, with a secondary drive unit utilizing the waste heat of the primary drive unit and driving another electric machine, serves in particular to increase the efficiency of power generation units, whereby the waste heat of the primary drive generation unit is not released unused into the environment, but rather can be used to generate additional electrical power.

[0003] To ensure grid stability in an electricity network, the grid operator sets requirements for the power generation facilities connected to the grid. These requirements can vary depending on the voltage level of the grid, the size and rated power of the generators, and their design. If the rated power of the first and second electrical machines of the power generation facility differ significantly, differences arise—particularly due to their design—which necessitate that the two electrical machines meet different requirements of the grid operator. An example of this is the dynamic requirements of the German grid connection guidelines. These guidelines require power generation facilities to operate under specific fault conditions.The power generating units must not disconnect from the grid within a so-called fault ride-through curve and must simultaneously provide reactive power to ensure grid stability. The various fault ride-through curves differ significantly between different electrical machines, particularly depending on their rated power.

[0004] Typically, the rated power of the second electric machine, which is driven by waste heat from the first drive unit, is low compared to the rated power of both the first drive unit and the first electric machine, making the electrical power produced in this way specifically expensive. If the second electric machine is then required to also meet the requirements of the grid operator, particularly those arising from grid connection guidelines, this would further increase the cost of the electrical power generated by the second electric machine.Furthermore, a second electrical machine that remains connected to the power grid even in the event of a fault requires a frequency converter in the electrical connection between the second machine and the grid. Such a frequency converter is a very expensive component that significantly contributes to the cost of the electrical power provided by the second machine. Additionally, grid feed-in monitoring and further components for the second electrical machine are required.

[0005] German patent DE 39 00 612 A1 discloses a power generating device configured to generate electrical power, comprising a first electric machine with a first drive unit that generates waste heat and is configured to drive the first electric machine. The power generating device further comprises a second electric machine with a second drive unit configured to drive the second electric machine and to utilize waste heat from the first drive unit to drive the second electric machine. The first electric machine and the second electric machine can be connected to the same power grid. If a fault is detected in the power grid, both electric machines are disconnected from the power grid in response to the fault. Other such power generating devices are also disclosed in US 2014 / 0 062 097 A1 and DE 10 2010 044 889 A1.

[0006] The invention is based on the objective of creating a power generation device, a power grid with such a power generation device and a method for operating such a power generation device on a power grid, without the aforementioned disadvantages occurring.

[0007] The problem is solved by creating the subject matter of the independent claims. Advantageous embodiments result from the dependent claims.

[0008] The problem is solved in particular by creating a power generating unit of the type mentioned above, which includes a fault handling unit configured to detect at least one specific fault in the power grid. The fault handling unit is further configured to electrically disconnect the second electrical machine from the power grid in response to the at least one specific fault, that is, when the at least one specific fault is detected, while simultaneously keeping the first electrical machine electrically connected to the power grid. The power generating unit thus configured offers advantages compared to the prior art.Because the second electrical machine is selectively disconnected from the power grid in the event of a fault, it no longer needs to meet the grid operator's requirements, allowing for a simpler and more cost-effective design. In contrast, the first electrical machine remains connected to the grid and thus still fulfills the grid operator's requirements, contributing to grid stability and, in particular, providing reactive power for grid stabilization. The grid operator's requirements are reduced to the combination of the first drive unit and the first electrical machine, simplifying and reducing the cost of designing the entire power generation system. Once at least one specific fault has resolved, the second electrical machine can be reconnected to the grid.The effort associated with certifying the entire power generation system is significantly reduced and brought to a lower overall level because only the first drive unit, in combination with the first electric machine, needs to meet the grid operator's requirements. Since the second electric machine is electrically disconnected from the grid in the event of a fault, additional components such as an inverter, a frequency converter, grid feed-in monitoring, and the like can be omitted on the second electric machine side. This significantly reduces the power-specific costs associated with the electrical power generated by the second electric machine. At the same time, the overall system efficiency is increased.

[0009] An electrical machine is understood to be, in particular, a device designed to convert mechanical energy, especially rotational energy, into electrical energy, wherein the electrical machine is ultimately designed to generate electrical power when mechanical power is supplied to it. The electrical machine is therefore, in particular, designed or operable as a generator.

[0010] The first electric machine is preferably designed for a first, higher rated power, while the second electric machine is preferably designed for a second, lower rated power, wherein the second rated power is lower than the first rated power, and wherein the first rated power is higher than the second rated power. The second electric machine is preferably supplied with power derived exclusively from the waste heat of the first drive unit via the second drive unit. This inherently results in a lower rated power for the second electric machine, since the waste heat output of the first drive unit is typically lower than its rated power.This implies that, with regard to grid stability and the provision of reactive power, it is relatively irrelevant whether the second electrical machine remains connected to the grid or is electrically disconnected. The majority of the electrical power is generated by the first electrical machine and fed into the grid anyway. Furthermore, with regard to the provision of reactive power to ensure grid stability, it can be stated that any reactive power that could potentially be provided by the second electrical machine is ultimately dispensable, and in particular negligible, compared to the reactive power provided by the first. Therefore, from the perspective of the grid operator, there is no significant disadvantage to the second electrical machine being disconnected from the grid in the event of a fault.Rather, the first electric machine enables the provision of reactive power in sufficient quantity, even in relation to the total power output of the power generation device.

[0011] Preferably, the fault handling device is designed as a control unit of the power generation device, or it is part of a control unit of the power generation device. It is also possible that the fault handling device – particularly in the form of control software or a control module of control software – is implemented in the control unit of the power generation device.

[0012] According to a further development of the invention, the power generating unit comprises a first circuit breaker configured for electrically connecting—and, accordingly, disconnecting—the first electrical machine from the power grid. The power generating unit also comprises a second circuit breaker, which can be operated independently of the first circuit breaker and is configured for electrically connecting—and disconnecting—the second electrical machine from the power grid. The circuit breakers are operatively connected—in particular, independently of each other—to the fault handling unit, so that they can be operated by the fault handling unit.It is possible that at least one fault exists, different from the at least one specific fault, in which the first electrical machine is also electrically disconnected from the power grid by opening the first circuit breaker, controlled by the fault handling device. This can be done, in particular, to protect the power generating equipment, and specifically the first electrical machine, from damage. The fault handling device is specifically designed to control the second circuit breaker when the at least one specific fault occurs, causing it to open and thus electrically disconnecting the second electrical machine from the power grid. In contrast, in this case, the first circuit breaker is either not controlled, so it remains closed, or it is controlled to remain closed, so that the first electrical machine remains electrically connected to the power grid.

[0013] The second circuit breaker is preferably located on one side of the first electrical machine upstream of the first circuit breaker, so that the first electrical machine can remain connected to the power grid via the first circuit breaker, while at the same time the second electrical machine can be electrically disconnected from the power grid. It is also possible, for example to start up the power generating unit, to close the second circuit breaker while the first circuit breaker is open, so that the first electrical machine is electrically connected to the second electrical machine, but both electrical machines are electrically disconnected from the power grid via the first circuit breaker.For example, when starting up the power generation unit, the two electrical machines can first be electrically connected to each other before a connection to the power grid is established for both electrical machines via the first circuit breaker.

[0014] According to a further development of the invention, the electrical connection of the second electric machine to the power grid is provided without a frequency converter. This means, in particular, that no frequency converter is provided in the electrical connection of the second electric machine to the power grid. Since the second electric machine is disconnected from the power grid in the event of a fault, a frequency converter can be advantageously omitted, thereby saving considerable costs associated with power generation by the second electric machine. Preferably, no inverter and / or grid feed-in monitoring is provided in the electrical connection of the second electric machine to the power grid either. These components are unnecessary because the second electric machine is electrically disconnected from the power grid in the event of a fault.

[0015] According to a further development of the invention, the first electrical machine is designed as a synchronous machine. In this case, a frequency converter between the first electrical machine and the power grid can be advantageously omitted. Furthermore, a synchronous machine as the first electrical machine in the operation of the power generation unit offers advantages compared to an asynchronous machine, particularly with regard to ensuring grid stability during normal, fault-free operation.

[0016] Alternatively or additionally, it is preferred that the second electrical machine be designed as an asynchronous machine. This allows for a particularly cost-effective design of the second electrical machine, especially its drive connection to the second drive unit. An asynchronous machine can be used without difficulty as the second electrical machine in the power generation unit proposed here, since it does not have to meet the grid operator's requirements in the event of a fault, as it is then disconnected from the power grid. If this were not the case, and the second electrical machine were to remain connected to the power grid even in the event of a fault, an asynchronous machine could hardly meet the grid operator's requirements without additional components, which would significantly increase the specific costs of the electrical power generated by the second electrical machine.In contrast, using a synchronous machine as a second electrical machine is less advantageous with regard to waste heat utilization, especially with regard to unsteady waste heat generation, so it is advantageous if an asynchronous machine can be used as a second electrical machine.

[0017] According to a further development of the invention, the second drive unit is designed as a cycle unit for carrying out a thermodynamic cycle. The cycle unit is thermally connected to the first drive unit to utilize waste heat from the first drive unit. This enables very efficient use of the waste heat from the first drive unit.

[0018] A cycle process device is understood to be, in particular, a device that is suitable and configured for carrying out a thermodynamic cycle. Such a cycle process device includes, in particular, a conveying device, preferably a pump, for conveying a cycle process medium along a flow path for the cycle process medium of the cycle process device. Along the flow path – preferably in this order in the direction of flow of the cycle process medium – the conveying device, an evaporator, a power unit, and a condenser are provided, wherein the cycle process medium absorbs heat in the evaporator, namely waste heat from the first drive unit, and at least a portion of the absorbed heat is released by the cycle process medium in the power unit and converted into mechanical work.A remaining portion of the heat absorbed by the process medium in the evaporator is preferably released back into the external environment of the cycle in the condenser, downstream of the engine. The process medium is then pumped back to the evaporator, where the cycle begins anew.

[0019] The cycle process device is preferably configured to carry out a thermodynamic cycle using an organic cycle medium. This makes it possible to select a cycle medium that can absorb a suitable amount of heat for efficient cycle operation even at a comparatively low temperature level – especially compared to water – and which can have a lower boiling point than water. It is therefore particularly possible to evaporate such an organic cycle medium at a comparatively low temperature level. This makes such an organic cycle medium especially suitable for utilizing waste heat – particularly from an internal combustion engine. The cycle process device is particularly preferably configured to carry out an organic Rankine cycle (ORC).Such a cyclical process is particularly suitable for utilizing waste heat, especially from an internal combustion engine.

[0020] The power machine is preferably connected to the second electric machine in a drive-related manner, so that the second electric machine can be driven by the power machine of the cycle process device.

[0021] A power machine is understood to be, in particular, a device designed to convert energy from the cyclic process medium, especially thermal energy, pressure energy, and / or flow energy, into mechanical energy, wherein the mechanical energy is preferably available at an output shaft of the power machine. The power machine is, in particular, driven by the cyclic process medium. Preferably, the power machine is designed as a turbomachine or as a positive displacement machine.

[0022] The power engine is preferably selected from a group consisting of a turbine, a scroll expander, a Roots expander, a reciprocating engine, and a vane engine. The power engine configurations mentioned here are particularly suitable for use as a power engine in a cyclic process, especially an organic Rankine cycle.

[0023] According to a further development of the invention, the first drive unit is designed as an internal combustion engine. In particular, the combination of the first electric machine with the first drive unit is preferably designed as an internal combustion engine-generator unit, especially as a so-called genset. The internal combustion engine can be designed, in particular, as a stationary internal combustion engine, especially for the stationary provision of electrical power. The internal combustion engine is particularly preferably designed as a gas engine. It is then preferably used in a stationary gas-fired power plant for the generation of electrical power.

[0024] The internal combustion engine is preferably designed as a reciprocating piston engine. One embodiment of the internal combustion engine is preferably used in a stationary configuration, for example, for stationary power supply in emergency power operation, continuous load operation, or peak load operation, in which case the internal combustion engine preferably drives a generator. The internal combustion engine is preferably designed as a diesel engine, a gasoline engine, or a gas engine for operation with natural gas, biogas, special gas, or another suitable gas. In particular, when the internal combustion engine is designed as a gas engine, it is suitable for use in a combined heat and power plant for stationary power generation.

[0025] The internal combustion engine is preferably thermally connected to the second drive unit, i.e., to the cycle unit, in such a way that waste heat from the internal combustion engine can be supplied to the second drive unit from an exhaust gas stream and / or from a coolant circuit of the internal combustion engine.

[0026] In particular, it is possible that the evaporator of the cycle is heated directly or indirectly by exhaust gas from the internal combustion engine. Alternatively or additionally, a coolant circuit of the internal combustion engine can be thermally connected directly or indirectly to the evaporator of the cycle. In particular, it is possible that the evaporator is directly permeated by exhaust gas and / or coolant from the internal combustion engine.

[0027] According to a further development of the invention, the fault handling device is configured to detect a single-phase, two-phase, and / or three-phase short circuit in the power grid as at least one specific fault. In the event of such a short circuit, a voltage dip occurs in the power grid, and a short-circuit current must be supplied by the power generating unit to ensure grid stability. In this case, the short-circuit current is supplied by the first electrical machine, while the second electrical machine is electrically disconnected from the power grid.

[0028] It is particularly preferred that the rated power of the second electrical machine be at most 10%, preferably at most 7%, preferably at most 5% of the rated power of the first electrical machine. The second electrical machine is therefore not capable of making a significant contribution to stabilizing the power grid, so that it can be electrically disconnected from the grid in the event of a fault without any serious adverse effects on grid stability. Conversely, enormous cost savings result in connection with the design and control of the second electrical machine if it is disconnected from the grid in the event of a fault and thus does not have to meet the existing requirements of the grid operator.

[0029] The problem can also be solved by creating a power grid that includes at least one power generation unit according to one of the previously described embodiments. In connection with the power grid, the advantages that have already been explained in connection with the power generation unit become particularly apparent.

[0030] The power grid is preferably designed as a medium-voltage network. The exemplary embodiments of a power generation unit described here are preferably used at the medium-voltage network level for public electricity supply. Additionally or alternatively, it is preferably provided that the power grid is designed as a regional or supra-regional power grid.

[0031] A medium-voltage network is understood to be, in particular, an electricity grid or part of an electricity grid designed for distributing electrical power over distances ranging from a few kilometers to 100 km, especially in rural areas. Such a medium-voltage network is preferably operated at a high voltage of 10 kV, 20 kV, or 30 kV. A medium-voltage network primarily serves to supply electricity to a region comprising several localities, at least one town, or at least one district. Medium voltage is generally understood to be a high voltage in the range of more than 1 kV up to and including 52 kV, and optionally up to 63 kV.

[0032] The problem is also solved by providing a method for operating a power generating unit, in particular a power generating unit according to one of the previously described embodiments, on a power grid, in particular on a power grid according to one of the previously described embodiments, wherein the method comprises the following steps: Electrical power is generated with a first electrical machine, wherein the first electrical machine is driven by a first drive unit. Waste heat from the first drive unit is used in a second drive unit to drive a second electrical machine. Electrical power is generated with the second electrical machine, which is driven by the second drive unit.The electrical power generated by the first electrical machine and the power generated by the second electrical machine is fed into the same, and in particular, identical, power grid. The power grid is monitored for at least one specific fault, and the second electrical machine is electrically disconnected from the power grid when this fault occurs. The first electrical machine remains electrically connected to the power grid when the fault occurs, meaning it is kept connected to the power grid. The advantages of this method are particularly evident in the advantages already described in connection with the power generation device and the power grid.

[0033] At least one specific fault is preferably considered to be a single-phase, two-phase or three-phase short circuit in the power grid, and the power grid is specifically monitored for such a short circuit.

[0034] The description of the power generation device and the power grid, on the one hand, and the method, on the other, are to be understood as complementary to each other. Features of the power generation device and / or the power grid that have been explicitly or implicitly explained in connection with the method are preferably, individually or in combination, features of a preferred embodiment of the power generation device and / or the power grid. Method steps that have been explicitly or implicitly described in connection with the power generation device and / or the power grid are preferably, individually or in combination, steps of a preferred embodiment of the method. This embodiment is preferably characterized by at least one method step that is conditioned by at least one feature of an inventive or preferred embodiment of the power generation device and / or the power grid.The power generation unit and / or the power grid are preferably characterized by at least one feature which is caused by at least one process step of an inventive or preferred embodiment of the process.

[0035] The invention is explained in more detail below with reference to the drawing. The single figure shows a schematic representation of an embodiment of a power grid with an embodiment of a power generation device.

[0036] The single figure shows a schematic representation of an embodiment of a power grid 1 with a power generating unit 3 comprising a first electric machine 5 and a second electric machine 7. The first electric machine 5 and the second electric machine 7 are configured to generate electrical power, the first electric machine 5 having a higher rated power than the second electric machine 7, which correspondingly has a lower rated power. In particular, the rated power of the second electric machine is preferably at most 10%, preferably at most 7%, preferably at most 5% of the rated power of the first electric machine.

[0037] The power generating unit 3 also includes a first, waste heat-generating drive unit 9, which is configured to drive the first electric machine 5. The power generating unit 3 also includes a second drive unit 11, which is configured to drive the second electric machine 7, the second drive unit 11 being further configured to utilize waste heat from the first drive unit 9 to drive the second electric machine 7.

[0038] The first electric machine 5 and the second electric machine 7 can be connected to the power grid 1, preferably - especially outside of a fault or malfunction - also connected to the power grid 1.

[0039] The power generating unit 3 has a fault handling unit 13, which is configured to detect at least one specific fault, in particular a single-phase, two-phase and / or three-phase short circuit, in the power grid 1. The fault handling unit 13 is further configured to electrically disconnect the second electrical machine 7 from the power grid 1 in response to the at least one specific fault, that is, when the at least one specific fault is detected, and at the same time to leave the first electrical machine 5 connected to the power grid 1, that is, to keep it electrically connected to it.

[0040] The fault handling device 13 is part of a control device 15, which is specifically designed for controlling and, in particular, for network regulation of the power generation device 1. Alternatively, it is also possible that the fault handling device 13 is provided separately from such a control device 15.

[0041] The power generating unit 3 has a first circuit breaker 17, which is configured to electrically connect the first electric machine 5 to the power grid 1 and to disconnect the first electric machine 5 from the power grid 1. Furthermore, the power generating unit 3 has a second circuit breaker 19, which is configured to electrically connect the second electric machine 7 to the power grid 1 and to disconnect the second electric machine 7 from the power grid 1. In particular, the second circuit breaker 19 is operatively connected to the fault handling device 13, so that the second circuit breaker 19 can be opened to disconnect the second electric machine 7 from the power grid 1 when at least one specific fault is detected by the fault handling device 13.The first circuit breaker 17 is preferably operatively connected to the control unit 15, and optionally also to the fault handling unit 13, so that it can be opened and closed by the control unit 15.

[0042] The second circuit breaker 19 is located on one side of the first electric machine 5 and also of the second electric machine 7, upstream of the first circuit breaker 17. This allows, firstly, the second electric machine 7 to be disconnected from the power grid 1 without simultaneously disconnecting the first electric machine 5 from the power grid 1. Secondly, particularly for starting up the power generating unit 3, the second circuit breaker 19 can be closed while the first circuit breaker 17 is open, in order to first connect the two electric machines 5 and 7 electrically to each other before they are connected together to the power grid 1.

[0043] It is evident that the electrical connection of the second electric machine 7 to the power grid 1 is free of a frequency converter. Therefore, no frequency converter is installed in the electrical connection between the second electric machine 7 and the power grid 1. This allows the second electric machine 7, including its connection to the power grid 1, to be constructed very simply and cost-effectively. Furthermore, it is evident that the second electric machine 7 does not have to meet any specific requirements of the power grid operator in the event of a fault, as it is disconnected from the power grid 1 by opening the second circuit breaker 19. This significantly reduces the specific costs of the electrical power generated by the second electric machine 7, since both the machine itself and its connection to the power grid 1 can be designed more simply and cost-effectively.

[0044] The first electric machine 5 is preferably designed as a synchronous machine. The second electric machine 7 is preferably designed as an asynchronous machine. This allows the second electric machine 7 to be implemented in a particularly cost-effective and technically simple manner.

[0045] The second drive unit is designed here as a cycle unit 21, which is configured to carry out a thermodynamic cycle, in particular on an organic cycle medium, and preferably to carry out an organic Rankine cycle (ORC). The cycle unit 21 is thermally connected to the first drive unit 9, as shown here by arrow P, to utilize the waste heat from the first drive unit 9.

[0046] The cycle process device 21 also has a power machine 23, which can be driven by the cycle process medium of the cycle process device 21, and which is operatively connected to the second electric machine 7 for its drive.

[0047] The first drive unit 9 is designed as an internal combustion engine, in particular as a reciprocating piston engine, and most preferably as a gas engine. In particular, the first drive unit 9 and the first electric machine 5 form a motor / generator unit, which is also referred to as a genset.

[0048] The power grid 1 is preferably designed as a medium-voltage grid, as a regional grid and / or as a supra-regional power grid.

[0049] In a method for operating the power generating unit 3 on the power grid 1, electrical power is preferably generated by the first electric machine 5, which is driven by the first drive unit 9. Waste heat from the first drive unit 9 is used in the second drive unit 11 to drive the second electric machine 7. Electrical power is generated by the second electric machine 7, which is driven by the second drive unit 11. The electrical power generated by the first electric machine 5 and the electrical power generated by the second electric machine 7 are fed into the same power grid 1. The power grid 1 is monitored for at least one specific fault by means of the fault handling unit 13.If at least one specific fault occurs, in particular a single-phase, two-phase and / or three-phase short circuit in the power grid 1, the second electrical machine 7 is disconnected from the power grid 1 by means of the second circuit breaker 19. In contrast, the first electrical machine 5 remains electrically connected to the power grid 1 when at least one specific fault occurs; the first circuit breaker 17 therefore remains closed when at least one specific fault occurs.

[0050] This does not preclude the existence of at least one other fault, the occurrence of which also opens the first circuit breaker 17 and thus electrically disconnects the power generating unit 3 from the power grid 1.

[0051] Overall, it is evident that the power generation unit 3, the power grid 1, and the method for operating the power generation unit 3 proposed here provide a means of designing a second electric machine 7, driven by waste heat from a first drive unit 9 of a first electric machine 5, in a simpler and, in particular, more cost-effective manner, thus reducing the costs specifically associated with generating electrical power by the second electric machine 7. This is possible, in particular, because the second electric machine 7 is electrically disconnected from the power grid 1 in the event of a fault, meaning it does not have to meet the specific requirements of a power grid operator of the power grid 1, especially regarding the provision of reactive power in the event of a fault.

Claims

[1] Power generating unit (3), designed to generate electrical power, with - a first electric machine (5), with - a first drive unit (9) generating waste heat, which is configured to drive the first electric machine (5), with - a second electric machine (7), and with - a second drive unit (11) which is configured to drive the second electric machine (7) and to use waste heat from the first drive unit (9) to drive the second electric machine (7), wherein - the first electric machine (5) and the second electric machine (7) can be connected to the same power grid (1), characterized by - a fault handling device (13) which is configured to detect at least one specific fault in the power network (1), to electrically disconnect the second electrical machine (7) from the power network (1) in response to the at least one specific fault, and at the same time to keep the first electrical machine (5) electrically connected to the power network (1). [2] Power generating device (3) according to claim 1, characterized by a first circuit breaker (17) which is configured to electrically connect the first electric machine (5) to the power grid (1), and by a second circuit breaker (19) which can be operated independently of the first circuit breaker (17) and which is configured to connect the second electric machine (7) to the power grid (1). [3] Power generating device (3) according to any one of the preceding claims, characterized by, that the electrical connection of the second electrical machine (7) to the power grid (1) is free of a frequency converter. [4] Power generating device (3) according to any one of the preceding claims, characterized by , that a) the first electrical machine (5) is designed as a synchronous machine, and / or that b) the second electrical machine is designed as an asynchronous machine. [5] Power generating device (3) according to any one of the preceding claims, characterized by , that the second drive unit (11) is designed as a cycle unit (21) for carrying out a thermodynamic cycle, wherein the cycle unit (21) is thermally connected to the first drive unit (9) for the use of waste heat from the first drive unit (9). [6] Power generating device (3) according to any one of the preceding claims, characterized by, that the first drive unit (9) is designed as an internal combustion engine. [7] Power generating device (3) according to any one of the preceding claims, characterized by , that the fault handling device (13) is set up to detect a single-phase, two-phase and / or three-phase short circuit in the power network (1) as the at least one specific fault. [8] Power grid (1), comprising at least one power generating unit (3) according to any one of claims 1 to 7. [9] Power grid (1) according to claim 8, characterized by , that the electricity grid is designed as a medium-voltage grid, as a regional electricity grid (1), and / or as a supra-regional electricity grid (1). [10] Method for operating a power generating unit (3) on an electricity network (1), comprising the following steps: - Generating electrical power with a first electrical machine (5) driven by a first drive device (9); - Use of waste heat from the first drive unit (9) in a second drive unit (11) to drive a second electric machine (7); - Generating electrical power with the second electric machine (7) driven by the second drive unit (11); - Feeding the electrical power generated by the first electrical machine (5) and the second electrical machine (7) into an identical power grid (1); - Monitoring the power grid (1) for at least one specific fault, and - Disconnecting the second electrical machine (7) from the power grid (1) when at least one certain fault occurs, wherein - the first electrical machine (5) is kept connected to the power grid (1) when at least one specific fault occurs.

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