AU2012265005B2

AU2012265005B2 - Method for operating a generator in an electrical system, and electrical system having such a generator

Info

Publication number: AU2012265005B2
Application number: AU2012265005A
Authority: AU
Inventors: Jorn Grundmann; Rainer Hartig; Peter Kummeth; Peter Van Hasselt
Original assignee: Siemens Energy Global GmbH and Co KG
Current assignee: Siemens Energy Global GmbH and Co KG
Priority date: 2011-05-30
Filing date: 2012-05-22
Publication date: 2015-03-12
Anticipated expiration: 2032-05-22
Also published as: ES2791033T3; KR101807345B1; AU2012265005A1; WO2012163731A2; EP2702685A2; WO2012163731A3; DE102011076681A1; EP2702685B1; KR20150139633A; KR20140007946A

Abstract

During the operation of a generator (10) in an electrical system (1), particularly in a stand-alone system, such as an onboard power supply system on a ship or an offshore platform, wherein the electrical system (1) comprises a first subsystem (2) having a first rated voltage (UN1) and at least one second subsystem (3) having a second rated voltage (UN2), wherein the first rated voltage (UN1) is higher than the second rated voltage (UN2), wherein the generator (10) has a field winding (11) which, in a normal mode of the generator (10), in which it supplies current to the first subsystem (2), has a first field current applied to it which matches the first rated voltage (UN1) of the first subsystem (2), and wherein the generator (10) comprises a cooling device (12) for cooling the field winding (11), the aim is to keep down-times or impairments in the electrical system (1) in the event of failure of the cooling device (12) as low as possible without the need for additional emergency power supply devices. The invention allows this by virtue of the generator (10) being switched, following failure of the cooling device (12), from the normal mode to an emergency mode, in which it supplies current to the second subsystem (3), wherein in the emergency mode the field winding (11) has a second field current applied to it which is lower than the first field current and which matches the second rated voltage (UN2) of the second subsystem (3).

Description

1 Method for operating a generator in an electrical system, and electrical system having such a generator Aspects of the present disclosure relate to a method for operating a generator in an electrical system, and to an electrical system having such a generator. Stand-alone electrical systems on board ships or offshore platforms often have a plurality of voltage levels with different rated voltages in each case. Each of these voltage levels constitutes a separate subsystem. Large electrical loads such as e.g. propulsion drive motors are supplied, for example, with electrical energy from a first subsystem having a rated voltage of 3.3 kVAC. On the other hand, auxiliaries for operating these large loads, as well as other low-voltage loads such as e.g. lighting, ventilation, air conditioning, public address system, automation systems, etc. are supplied with electrical energy from a second subsystem having a smaller rated voltage of 400 VAC, for example, or another subsystem again supplied from the second subsystem. The electrical energy for the first subsystem having comparatively the largest rated voltage is usually produced by one or more generators connected to the first subsystem which feed electrical energy to said first subsystem. All the subsystems are often electrically interconnected back to back in rated voltage sequence via voltage converters (e.g. transformers) so that the generator or generators ultimately supply electrical energy via the first subsystem to the thereto connected second subsystem for example, via the second subsystem in turn to a third subsystem which is connected to 9481787 2 the second subsystem, and via the latter in turn to other lower-order subsystems. The generators are frequently embodied as a synchronous machine having a rotating field winding which, during normal operation of the generator in which it supplies power to the first subsystem, has a first field current applied to it which is matched to the rated voltage of the first subsystem. The generator often also comprises a cooling device for cooling the field winding or rather for additionally cooling the entire generator, said cooling device usually being supplied with power from the second subsystem or from another subsystem supplied directly or indirectly from the second subsystem. Such a cooling device is necessary especially if the field winding is embodied as a superconductor winding, in particular a high temperature superconductor (HTS) winding. The cooling device then comprises, for example, a cold head which is in turn back-cooled by a cooling circuit having a compressor. Complete or partial failure of the cooling device, e.g. because of a fault in the electrical system or a defect of the cooling device itself, results in heating of the field winding. Depending on the duration of the malfunction, the field winding may heat up so strongly that it can no longer be operated using the first rated current and therefore the generator can no longer feed current to the first subsystem, as it does not achieve the required rated voltage. 9481787 3 In order to compensate at least to some extent for such a power supply failure, an emergency power supply (e.g. an additional diesel unit) can be provided which, however, requires additional space which is at a premium on a ship or an offshore platform, and constitutes an additional cost factor. WO 00/13304 discloses a method for controlling a generator, wherein the field current is reduced if a limit temperature of the generator is exceeded. With regard to a method for operating a generator in an electrical system or rather for an electrical system having such a generator, an object of the present invention is to minimize adverse effects or even downtimes of the electrical system in the event of cooling device failure, without the need for additional emergency power supply devices. This object is achieved by a method for operating a generator in an electrical system, wherein the electrical system comprises a first subsystem having a first rated voltage, and at least one second subsystem having a second rated voltage, the first rated voltage being greater than the second rated voltage, wherein the generator has a field winding which, during normal operation of the generator in which it feeds current to the first subsystem, has a first field current applied to it which is matched to the first rated voltage of the first subsystem, and wherein the generator comprises a cooling device for cooling the field winding, wherein, in the event of cooling device failure, the generator is switched from normal mode to emergency mode in which it feeds current to the second subsystem, wherein during emergency operation the field winding has a second field 9481787 4 current applied to it which is smaller than the first field current and which is matched to the second rated voltage of the second subsystem. Aspects of the present disclosure are based on the insight that, after heating of the field winding, although it is no longer possible for the first field current to be applied to the field winding, it is still possible for a second field current to be applied to it which is reduced in accordance with the higher temperature of the field winding and is therefore smaller than the first field current. Although such a reduced field current reduces the generator's output voltage such that current can no longer be fed to the first subsystem, the output voltage can still be sufficient to enable current to be fed to the second subsystem having a lower rated voltage than the first subsystem. By switching the generator from normal to emergency mode, an emergency power supply can therefore be provided for the second subsystem and other subsystems directly or indirectly supplied therefrom without significant downtimes, and without the need for additional emergency power supply devices. In the case of a generator having an HTS field winding and normally supplying a subsystem having a rated voltage of 3.3 kVAC, a second field current amounting to only some 12 % of the first field current would be sufficient to establish a second subsystem having a rated voltage 400 VAC. For machines containing soft iron, the second field current can even be less than 10 % of the first field current. If cooling device failure was caused by a defect in the cooling device itself, the cooling device can be repaired during the period of emergency operation and then re activated. If failure of the cooling device was due to failure 9481787 5 of its power supply, this emergency mode enables the power supply for the cooling device to be restored and therefore cooling of the field winding to be recommenced. This advantage comes in particularly useful if the cooling device, preferably also other auxiliary units for operating the generator, is/are supplied with power from the second subsystem or from another subsystem which is directly or indirectly supplied from the second subsystem. As soon as the field winding has then been cooled down again to a predefined operating temperature, the generator can be switched back from emergency mode to normal mode in which it supplies current to the first subsystem. According to one embodiment, the generator is only switched from normal mode to emergency mode when a predefined period of time has elapsed after failure of the cooling device or when heating of the field winding to a predefined temperature has been detected. This is based on the insight that, by appropriate design and implementation of the generator, a time period or temperature can be defined in which or up to which, despite failure of the cooling device, the field winding of the generator can still have the first field current applied to it, i.e. receive full excitation. This time period or this temperature is essentially determined by the utilization of the conductor (in the case of a superconductor by the margin between the operating current and the critical current of the winding at the operating point), resulting in a maximum permitted winding temperature above the normal operating temperature at which the full first field current in the field winding is only just permissible. This time period or temperature can be selectively controlled in conjunction with the thermal losses in the rotor and the integral heat capacity thereof. 9481787 6 The generator is preferably embodied as a synchronous machine having a rotating field winding. The advantages of aspects of the present disclosure come in particularly useful if the field winding is embodied as superconductor winding, in particular a high temperature superconductor (HTS) winding, as there is then a particular cooling requirement for the field winding. The advantages of aspects of the present disclosure also come in particularly useful if the electrical system is embodied as a stand-alone system, in particular as an electrical system on a ship or offshore platform, as there the number of generators is limited and therefore the probability of electrical system malfunction is greater than in an interconnected system. This applies particularly if the subsystems are electrically linked via one or more voltage converters, in particular transformers. By feeding the first subsystem having the first rated voltage, the other subsystems having comparatively lower rated voltages can then be supplied, thereby obviating the need for separate generators or other energy producers for the other subsystems. However, failure of the feed to the first subsystem also results in power supply failure for the other subsystems. In respect of the electrical system, this problem is solved by an electrical system comprising: - a first subsystem having a first rated voltage and a second subsystem having a second rated voltage, the first rated voltage being greater than the second rated voltage, - at least one generator having a field winding, wherein the generator, during normal mode in which it feeds current to the first subsystem, can have a first field current applied to it 9481787 7 which is matched to the first rated voltage of the first subsystem, - wherein the generator comprises a cooling device for cooling the field winding, wherein the generator is designed such that it can be switched from normal operation to an emergency mode in which it feeds current to the second subsystem, wherein in emergency mode the field winding can have a second field current applied to it which is smaller than the first field current and which is matched to the second rated voltage of the second subsystem. The advantages mentioned for the method apply correspondingly to the electrical system according to aspects of the present disclosure. To supply power, the cooling device, and preferably also other auxiliaries for operating the generator, is/are connected to the second subsystem or another subsystem directly or indirectly fed from the second subsystem. Although it is basically also possible for electrical system operating personnel to switch manually from normal mode to emergency mode, the electrical system preferably comprises an open and/or closed loop control device for automated switching from normal mode to emergency mode. Open and/or closed loop control of the field current is also possible using the open and/or closed loop control device. The open and/or closed loop control device is preferably designed such that it switches the generator from normal mode to emergency mode only after a predefined time period has elapsed after failure of the cooling device or when heating of the field winding to a specified temperature has been detected. 9481787 8 According to a further advantageous embodiment, the open and/or closed loop control device is designed such that it switches the generator from emergency mode to normal mode after the field winding has cooled down to a specified temperature. According to a particularly simple embodiment in design terms, the electrical system has a two-way switch for optionally connecting the generator to the first or the second subsystem. The generator is advantageously embodied as a synchronous machine having a rotating field winding. The field winding is preferably embodied as a superconductor winding, in particular as a high temperature superconductor (HTS) winding. According to a particularly advantageous embodiment, the electrical system is embodied as a stand-alone system, in particular as an electrical system on a ship or offshore platform. According to another advantageous embodiment, the subsystems are interconnected via one or more voltage converters, in particular transformers. The disclosed advantages for the method and its advantageous embodiments apply correspondingly to the electrical system according to aspects of the present disclosure and its respective corresponding advantageous embodiments. Embodiments of the present disclosure according to features set forth in the sub-claims will now be explained in greater detail with reference to an exemplary embodiment in the 9481787 9 drawing. This shows an electrical system 1 embodied as a stand-alone system. Said electrical system 1 is, for example, an electrical system on a ship or offshore platform. The electrical system 1 comprises a first subsystem 2 having a first rated voltage UN1 and a second subsystem 3 having a second rated voltage UN2, the first rated voltage UN1 being greater than the second rated voltage UN2. The first subsystem 2 is, for example, a medium-voltage system having a rated voltage UN1 = 3.3 kVAC, and the second subsystem 3 a low voltage system having a rated voltage UN2 = 400 VAC. For redundancy reasons, the first subsystem 2 in turn consists of two sections 2', 2'' which can be linked via a system interconnection 20. Correspondingly, the subsystem 3 in turn consists of two sections 3', 3'' which can be linked via a system interconnection 30. The two subsystems 2, 3 are coupled via transformers 40 so that, by feeding current to the first subsystem 2, the second subsystem 3 can also be supplied with current. From the first subsystem 2, large electrical loads such as e.g. electric propulsion drive motors 6 are supplied with electrical energy via a transformer 4 and a converter 5 in each case. From the second subsystem, auxiliaries 7 for operating said large loads as well as other low-voltage loads 8 such as e.g. lighting, ventilation / air conditioning, public address system and automation systems are supplied with electrical energy. Each generator 10 embodied as a synchronous machine and having a rotating field winding 11 is available for generating power for its respective section 2', 2'' of the first subsystem 2. 9481787 10 The field winding 11 is embodied as a superconductor winding, in particular a high temperature superconductor (HTS) winding. Each generator 10 is additionally assigned a cooling device 12 for cooling the (HTS) field winding 11. The cooling device 12 is connected to the second subsystem 3 for its power supply. The field winding 11 is supplied with direct current from a DC supply device 13. During normal operation in which it feeds current to the first subsystem 2, the generator 10 can have a first field current applied to it which is matched to the rated voltage UN1 of the first subsystem 2. The generator is also designed such that it can be switched from normal operation to an emergency mode in which it feeds current to the second subsystem 3, wherein in emergency mode the field winding 11 can have a second field current applied to it which is smaller than the first field current and which is matched to the rated voltage UN2 of the second subsystem 3. For open and/or closed loop control of the operating mode of the generator (i.e. normal mode or emergency mode) and therefore of the field current through the field windings 11, an open and/or closed loop control device 14 is provided which comprises, for each of the field windings 11, a sensor 15 or some other suitable device (e.g. physical model based) for measuring or determining the temperature of the respective field winding 11. A two-way switch 16 is used for optionally connecting the respective generator 10 to the first subsystem 2 or to the second subsystem 3. 9481787 11 In normal mode, each of the generators 10 feeds current directly to the first subsystem 2. Here the open and/or closed loop control device 14 controls the two DC supply devices 13 such that the respective field winding 11 has a first field current applied to it which is matched to the rated voltage UN1 of the first subsystem 2. The field winding 11 of the generators 10 is cooled by its respective cooling device 12 which is supplied with current from the second subsystem 3. If cooling of the field winding 11 of one of the generators 10 fails due to a fault in the subsystem 3 or a defect in the cooling device 12 itself, for example, the open and/or closed loop control device 14 initially waits for a specified time for the cooling device 12 to resume its cooling function. This time period is essentially determined by the utilization of the conductor (in the case of the HTS conductor by the margin between the operating current and the critical current of the winding at the operating point), resulting in a maximum permitted winding temperature above the normal operating temperature at which the first field current in the field winding 11 is only just permissible. If cooling of the field winding 11 by the cooling device 12 is not resumed until this time has elapsed, the open and/or closed loop control device 14 switches the generator 10 in question from normal mode to emergency mode in which it feeds current directly to the second subsystem 3. To do so, the open and/or closed loop control device 14 disconnects the generator 10 from the first subsystem 2 by means of the two-way switch 16 and connects it to the second subsystem 3. The open and/or closed loop control device 14 also controls the DC supply device 13 of the relevant generator such that the respective field winding 11 has a second field current applied to it 9481787 12 which is smaller than the first field current and which is matched to the rated voltage UN2 of the second subsystem 2. Alternatively, instead of waiting for the specified time to elapse before switching from normal mode to emergency mode, it is also possible for the temperature of the field winding 11 to be determined by the open and/or closed loop control device 14 via the sensor 15 or another suitable device and the switchover from normal mode to emergency mode to take place when it is detected that the maximum permitted winding temperature has been reached. As a result, the serviceability of the generator 10 in question is extended and an emergency power supply for the second subsystem 3 or more specifically the affected section 3', 3'' of the second subsystem and any other subsystems directly or indirectly fed therefrom is provided by the generator 10 in question. This means that a separate emergency power supply device is unnecessary. In the case of a defect of the cooling device 12, the latter can now be repaired. If the failure of the cooling device 12 was due to failure of the power supply in the second subsystem 3, the power supply can be restored by the now available direct feeding of the second subsystem 3 by the generator 10 in question. The open and/or closed loop control device 14 measures the temperature of the field winding 11 via the sensor 15. When the field winding 11 has cooled down to a specified temperature, the open and/or closed loop control device 14 switches the generator 10 in question from emergency mode to normal mode again. 9481787 13 To do so, the open and/or closed loop control device 14 disconnects the generator 10 from the second subsystem 3 by means of the two-way switch 16 and re-connects it to the first subsystem 2. In addition, the open and/or closed loop control device 14 controls the DC supply device 13 of the generator 10 such that the latter's field winding 11 again has the first field current applied to it which is matched to the rated voltage UN1 of the first subsystem 2. Full operability of the electrical system 1 is now restored. 9481787

Claims

1. A method for operating a generator in an electrical system, wherein the electrical system comprises a first subsystem having a first rated voltage and at least one second subsystem having a second rated voltage , the first rated voltage being greater than the second rated voltage , wherein the generator has a field winding which during normal operation of the generator in which it feeds current to the first subsystem has a first field current applied to it which is matched to the first rated voltage of the first subsystem, and wherein the generator comprises a cooling device for cooling the field winding , wherein, after failure of the cooling device, the generator is switched from normal mode to emergency mode in which it feeds current to the second subsystem, wherein in emergency mode the field winding has a second field current applied to it which is smaller than the first field current and which is matched to the second rated voltage of the second subsystem.

2. The method as claimed in claim 1, wherein the cooling device and/or other auxiliaries for operating the generator , is/are supplied with power from the second subsystem or from another subsystem which is fed directly or indirectly from the second subsystem.

3. The method as claimed in one of the preceding claims, wherein the generator is switched from emergency mode to normal mode when the field winding has cooled down to a specified temperature.

4. The method as claimed in one of the preceding claims, wherein the switching of the generator from normal mode to emergency mode only takes place when a predefined time period 9481787 15 has elapsed following failure of the cooling device or when heating of the field winding to a specified temperature is detected.

5. The method as claimed in one of the preceding claims, wherein the generator is embodied as a synchronous machine having a rotating field winding.

6. The method as claimed in one of the preceding claims, wherein the field winding is embodied as a superconductor winding.

7. The method as claimed in one of the preceding claims, wherein the electrical system is embodied as a stand-alone system.

8. The method as claimed in one of the preceding claims, wherein the first and second subsystems are interconnected via one or more voltage converters.

9. An electrical system, comprising - a first subsystem having a first rated voltage (UN1) and a second subsystem having a second rated voltage (UN2), the first rated voltage being greater than the second rated voltage, - at least one generator having a field winding, wherein during normal operation in which it feeds current to the first subsystem the generator can have a first field current applied to it which is matched to the first rated voltage of the first subsystem, - wherein the generator comprises a cooling device for cooling the field winding, the generator being designed to switch from a normal mode to an emergency mode in which the generator feeds current to the 9481787 16 second subsystem, wherein in the emergency mode a second field current is applied to the field winding which is smaller than the first field current and which is matched to the second rated voltage of the second subsystem.

10. The electrical system as claimed in claim 9, wherein, for power supply, the cooling device and/or other auxiliaries for operating the generator is/are connected to the second subsystem or to another subsystem supplied directly or indirectly from the second subsystem.

11. The electrical system as claimed in one of claims 9 to 10, further comprising: an open and/or closed loop control device for switching the generator from the normal mode to the emergency mode.

12. The electrical system as claimed in claim 11, wherein the open and/or closed loop control device is designed such that the control device switches the generator from the normal mode to the emergency mode after a specified time has elapsed following failure of the cooling device or after heating of the field winding to a specified temperature is detected.

13. The electrical system as claimed in claim 10 or 11, wherein the open and/or closed loop control device is designed to switch the generator from the emergency mode to the normal mode when the field winding has cooled down to a specified temperature.

14. The electrical system as claimed in one of claims 9 to 13, further comprising: a two-way switch for optionally connecting the generator to the first subsystem or to the second subsystem. 9481787 17

15. The electrical system as claimed in one of claims 9 to 14, wherein the generator is a synchronous machine having a rotating field winding.

16. The electrical system as claimed in one of claims 9 to 15, wherein the field winding is implemented as a superconductor winding.

17. The electrical system as claimed in one of claims 9 to 16, wherein the electrical system is embodied as a stand-alone system.

18. The electrical system as claimed in one of claims 9 to 17, wherein the first and second subsystems are interconnected via one or more voltage converters .

19. The invention as claimed in one of claims 6 o 16, wherein the superconductor winding is a high temperature superconductor (HTS) winding.

20. The invention as claimed in one of claims 7 or 17, wherein the electrical system is a stand-alone system on a ship or offshore platform.

21. The invention as claimed in one of claims 8 or 18, wherein the one or more voltage converters are transformers. 9481787