Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J13/00—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
  • H02P9/00—Arrangements for controlling electric generators for the purpose of obtaining a desired output
  • H02P9/10—Control effected upon generator excitation circuit to reduce harmful effects of overloads or transients, e.g. sudden application of load, sudden removal of load, sudden change of load
  • H02P9/107—Control effected upon generator excitation circuit to reduce harmful effects of overloads or transients, e.g. sudden application of load, sudden removal of load, sudden change of load for limiting effects of overloads
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
  • H02H1/00—Details of emergency protective circuit arrangements
  • H02H1/0061—Details of emergency protective circuit arrangements concerning transmission of signals
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J13/00—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network
  • H02J13/00006—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network characterised by information or instructions transport means between the monitoring, controlling or managing units and monitored, controlled or operated power network element or electrical equipment
  • H02J13/00016—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network characterised by information or instructions transport means between the monitoring, controlling or managing units and monitored, controlled or operated power network element or electrical equipment using a wired telecommunication network or a data transmission bus
  • H02J13/00017—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network characterised by information or instructions transport means between the monitoring, controlling or managing units and monitored, controlled or operated power network element or electrical equipment using a wired telecommunication network or a data transmission bus using optical fiber
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J13/00—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network
  • H02J13/00032—Systems characterised by the controlled or operated power network elements or equipment, the power network elements or equipment not otherwise provided for
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J13/00—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network
  • H02J13/00032—Systems characterised by the controlled or operated power network elements or equipment, the power network elements or equipment not otherwise provided for
  • H02J13/00036—Systems characterised by the controlled or operated power network elements or equipment, the power network elements or equipment not otherwise provided for the elements or equipment being or involving switches, relays or circuit breakers
  • H02J13/0004—Systems characterised by the controlled or operated power network elements or equipment, the power network elements or equipment not otherwise provided for the elements or equipment being or involving switches, relays or circuit breakers involved in a protection system
• • H02J13/0086—
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02K—DYNAMO-ELECTRIC MACHINES
  • H02K19/00—Synchronous motors or generators
  • H02K19/16—Synchronous generators
  • H02K19/36—Structural association of synchronous generators with auxiliary electric devices influencing the characteristic of the generator or controlling the generator, e.g. with impedances or switches
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
  • H02P9/00—Arrangements for controlling electric generators for the purpose of obtaining a desired output
  • H02P9/14—Arrangements for controlling electric generators for the purpose of obtaining a desired output by variation of field
  • H02P9/26—Arrangements for controlling electric generators for the purpose of obtaining a desired output by variation of field using discharge tubes or semiconductor devices
  • H02P9/30—Arrangements for controlling electric generators for the purpose of obtaining a desired output by variation of field using discharge tubes or semiconductor devices using semiconductor devices
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
  • Y02B90/00—Enabling technologies or technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02B90/20—Smart grids as enabling technology in buildings sector
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
  • Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
  • Y04S40/00—Systems for electrical power generation, transmission, distribution or end-user application management characterised by the use of communication or information technologies, or communication or information technology specific aspects supporting them
  • Y04S40/12—Systems for electrical power generation, transmission, distribution or end-user application management characterised by the use of communication or information technologies, or communication or information technology specific aspects supporting them characterised by data transport means between the monitoring, controlling or managing units and monitored, controlled or operated electrical equipment
  • Y04S40/124—Systems for electrical power generation, transmission, distribution or end-user application management characterised by the use of communication or information technologies, or communication or information technology specific aspects supporting them characterised by data transport means between the monitoring, controlling or managing units and monitored, controlled or operated electrical equipment using wired telecommunication networks or data transmission busses

Definitions

• the present invention relates generally to design, control, operation and protection of power converters and in particular to power converters comprising synchronous machines with rotor windings.
• the invention also concerns electric power plants comprising controllable synchronous machines, and control of such plants.
• Electrical machines can in general be used for both generator operation and motor operation.
• a mechanical power is converted into an electric power.
• the conversion takes place in the opposite direction, i.e. from an electrical power to a mechanical one.
• An electrical power converter thus comprises electrical machines in both these aspects.
• Electrical power converters are today to a large extent composed by synchronous machines, at least for electrical power 'converters that are intended for connection to general electric power networks. It is very important that the operation of synchronous machines takes place in concordance with the electric power network they are connected to and discrepancies normally result in losses or inefficient utilisation. One therefore often wishes to control the operational modes of the synchronous machines in a fast and efficient manner. Such a control can e.g. comprise control of the power 'conversion, relation between reactive and active power, torque, frequency and rotational speed, voltages, currents, overload protections etc. Generally, a synchronous machine thus constitutes a converter for active power and at the same time a simple and easily available setting tool for reactive power.
• a power electronic converter which controls the current that passes through the rotor windings.
• power electronic converters here generally mean means that influence amplitude, phase and/ or frequency of an electrical current, which inter alia comprises ac-to-dc-converters, dc-to-ac-converters, frequency converters, phase shifters and different types of current amplifying means as well as combinations thereof.
• the magnetisation of synchronous machines with rotor windings can be carried out in two ways. It can either be made brushless, by use of a magnetisation machine, or by slip rings and brushes. In the latter method, the current that will be provided to the rotor windings is transferred between the stationary and the rotating part of a synchronous machine by an arrangement of brushes and slip rings.
• Such a solution has, however, all the problems that are connected with movable contacting tools, such as sparking, interferences, material wear etc. Many larger synchronous machines are therefore today using so called brushless magnetisation. Brushless magnetisation takes place by means of a co- rotating exciter machine and a power electronic converter.
• Power electronic converters rotating with the shaft in the form of ac-to-dc-converters, are present since about 25 years as brushless exciters for feeding the field winding in the rotor.
• the power electronic converter being co-rotating with the shaft is substantially/ most often designed with diodes, and the field current is controlled via the stator current of the exciter, so that the electronics of the power electronic converter on-board in the rotor is simple to design in traditional analogous technique.
• ABB brochure "Brushless exciter”, SEGEN/HM 8-001 One example of an embodiment of a brushless exciter is apparent from the ABB brochure "Brushless exciter", SEGEN/HM 8-001. From the brochure, it is evident that the exciter is an alternating current machine, whose stator is provided with sailent poles and whose rotor has a three-phase alternating current winding for exciting a power electronic converter. The direct voltage of the power electronic converter is then connected to the field winding of the synchronous machine. The voltage of the synchronous machine can be regulated by influencing the magnetisation of the exciter via its field winding.
• PSS Power System Stabilizer
• Such a system is described in the American patent US 3,671,850, where one uses radio communication to determine the control angle for the thyristors in the rotating thyristor rectifier.
• analogous technique is used, which makes the system difficult to dynamically adapt, at changes of parameters included in the regulation, such as the resistance of the rotor.
• slip rings and brushes both the ac-to-dc-converter and the control electronics are typically stationary, whereby the readymade current is transferred to the rotor.
• a special embodiment of magnetisation at a with constant rotational speed rotating electrical machine is described in the patent application PCT/EP 98/007744, for "Power flow control" in a transmission line.
• the stator windings of the electrical machine are here connected in series with the conductors of the transmission line without connected neutral point.
• the rotor of the electrical machine is provided with two or three 90 or 120 degrees, respectively, electrically phase-shifted direct-current rotor windings for control of amplitude and phase of the voltage of the electrical machine.
• the excitation of the rotor windings takes place via a co-rotating magnetisation exciter and power electronic converter (ac-to-dc-converter) for each one of the rotor windings.
• safety devices are connected to most synchronous machines, which should supervise the condition of the synchronous machines and in an appropriate manner interrupt or limit such operation that may damage the machine or be disadvantageous for the operation of the electric power network.
• the safety devices may consist of pure protections, turning off the operation at noticed faults. They may also consist of limitation devices, which in a suitable manner changes or limits the operation to permitted conditions.
• the limits for the level a synchronous machine can be utilised is often set by considerations regarding temperatures, e.g. the temperatures of the stator and field windings.
• the currents in the windings, permitted by the safety and limiting devices, are in general estimated by means of simple theoretical models.
• a limit for the current is typically set by the magnetisation equipment. This may have a limit at e.g. nominal field current.
• Larger machines are often equipped with a field current limiter that besides a momentary limiter may comprise a time delay that allows for a certain over-current during a shorter period. This limitation is, however, static and does not take the actual thermal condition of the synchronous machine into account.
• the stator winding at alternating current machines is normally protected by an over-current protection. At overload of the machine, such as that the current exceeds a limit that is given by nominal power, the machine is disconnected.
• Synchronous machines may be equipped with a stator current limiter and /or an under- magnetisation limiter. These limiters may either automatically control the field current or give an alarm to the machine operator, which manually can control the field current and in such a way control the reactive power so that the operational point is kept within the permitted working area in a well-known "P-Q-circle diagram", which for anyone skilled in the art often is called capability diagram.
• Alternating current machines with a power over 5 MVA are today equipped with resistive temperature meters (e.g. PtlOO elements) that are placed in or in close vicinity to the stator winding. These give a good information about the working temperature of the winding. These are connected to a protection that disconnects the machine when the temperature reaches over a certain limit. These limits are typically determined from the temperature class or from measurements during the commissioning of the machine.
• resistive temperature meters e.g. PtlOO elements
• a problem with machine protections and machine limiters according to prior art is that they in many cases are based on coarse static models about loss generation and conduction, and temperature rise.
• the actual conditions, such as variation in the temperature of the ambience, are generally considered very little.
• large safety margins have to be used. In less extreme cases, this leads to that the protections are tripped unnecessarily early in a process.
• a load drop or fault in the electric power network causes an unfavourable distribution of reactive and active power, this may easily lead to a temperature and/ or current increase in certain parts of an alternating current machine.
• the material may then be classified in a material class, whereby the temperature limit of the class normally is used for all materials included in the class.
• a machine manufacturer uses the material in his construction, whereby he adds his own constructional margins.
• the vendor of a machine may specify certain permitted operational conditions, but when an operator works out his own operator instructions, further safety margins are added in order to compensate for minor mistakes in the operation. This gives in many cases a total margin that is so large that only a too small part of the possible performance of the material is utilised, which today in many cases is not economically optimum.
• a general object of the present invention is to provide a synchronous machine with intelligence in order to be able, in an improved manner, to reach an optimum control of the operational conditions of the machine.
• An object with the present invention is also to utilise measurements of, to the rotating parts of an electrical machine, associated electrical and mechanical quantities as basis for the control.
• mechanical quantities also comprises thermal quantities.
• Another object is to, by continuous supervision of critical quantities, utilise in the synchronous machine existing constructional margins for an efficient operation and a flexible protection of the machine.
• a subordinated object with the present invention is to provide an electrical machine, where processing and/ or measurement of to rotating parts of the electrical machine associated quantities takes place locally, in direct connection to the actual part of the electrical machine.
• a further object with the present invention is to provide an electric power plant with increased possibilities to planned and/or co-ordinated power changes.
• a synchronous machine which comprises a power electronic converter device, a winding provided rotor with a co-rotating processing unit, and a similarly co-rotating communication unit for wireless information transfer to a stationary unit. Also at least one co-rotating sensor exists at the rotor for measuring of mechanical and/ or electrical quantities associated with the rotor.
• Fig. 1 shows a block diagram of an embodiment according to the present invention, with brushless magnetisation
• Fig. 2 shows a block diagram of another embodiment according to the present invention, with magnetisation via slip rings and brushes;
• Fig. 3 shows a block diagram of a third embodiment according to the present invention, with double rotor windings;
• Fig. 4 is a combined capability and phasor diagram for a synchronous machine in generator operation;
• Fig. 5a shows a block diagram of an electric power plant with two synchronous machines according to the present invention
• Fig. 5b shows a block diagram for communicating electric power plants
• Fig. 6 shows a flow diagram for a control method for a synchronous machine according to the present invention.
• Fig. 7 shows a flow diagram for a control method for an electric power plant according to the present invention.
• a basic embodiment of the present invention is schematically illustrated in Fig. 1.
• a synchronous machine generally denoted by 1, comprises a stator 2 and a rotor 3.
• the stator 2 is provided with alternating current windings 4, through which, during operation, an alternating current flows, which is provided by supply terminals 5.
• the rotor 3 is arranged around a rotating shaft 6, and comprises rotor windings 7 or field windings. These rotor windings 7 are during operation provided with magnetisation current that is controlled by a power electronic converter 8.
• the synchronous machine 1 is provided with a, with the rotating shaft 6, co-rotating processing unit 10.
• the co- rotating processing unit 10 is connected to a, with the rotating shaft 6, co- rotating communication means 11.
• This communication means 11 is arranged to send and receive data by a wireless information transfer.
• the co- rotating processing unit 10 is furthermore connected to the power electronic converter 8, for control of its operation.
• a stationary processing unit 12 is connected to a stationary communication means 13.
• the stationary communication means 13 is arranged to send and receive data through the wireless information transfer with the co-rotating communication means 11.
• the stationary processing unit 12 is preferably also connected to additional external processing units via at least one communication device 14.
• co-rotating sensors 15, 16 and 17 sense mechanical and/ or electrical quantities, which are associated with the rotor 3, and the sensors 15, 16 and 17 are connected to the co-rotating processing unit 10 for transmission of measurement data.
• the sensors 15 and 16 measure the temperature of the rotor winding 7 and the sensor 17 measures the actual magnetisation current of the rotor.
• a number of stationary sensors 18, 19 and 20, which sense mechanical and/ or electrical quantities associated with stationary parts of the synchronous machine 1 are connected to the stationary processing unit 12 for transmission of measurement data.
• the sensors 18 and 19 measure the temperature of the stator winding 4 and the sensor 20 measures the actual current of the stator.
• the co-rotating processing unit 10 treats the measurement data that is transferred from the co-rotating sensors, 15, 16 and 17, and data received form the stationary processing unit 12, if any. Based on these treated data, the co-rotating processing unit 10 controls the function of the power electronic converter 8 in an appropriate way.
• This basic concept makes it possible to control the synchronous machine 1 in a dynamic and efficient way.
• With the rotor 3 associated quantities are measured locally, which normally gives a higher reliability than remote measurements.
• These reliable measurement data are sent to the co-rotating processing unit 10 via permanent connections, which present very large bandwidths and constitute thus no obstacle for the communication.
• the co- rotating processing unit 10 treats the incoming measurement data locally, and can, based on this, give control signals to the power electronic converter how a continued operation should be.
• the aspects of the magnetisation of the rotor that are determined by quantities achieved from the rotor are preferably controlled by signals that are treated totally within the rotating part of the synchronous machine. The invention thus gives a double function.
• the co-rotating processing unit 10 extracts these data and transfer them to the stationary processing unit 12 via the communication means 11, 13.
• the stationary processing unit 12 takes thereafter care of these data for further processing.
• the stationary processing unit 12 extracts appropriate information, and sends it via the communication means 11, 13 to the co- rotating processing unit 10. This is also valid for data and instructions that are obtained from other places and are intended for the co-rotating processing unit 10.
• the co-rotating processing unit 10 then controls the power electronic converter 8 by means of received data.
• the control of the synchronous machine can, as is indicated above, also comprise "external" data, which may be constituted by technical, economical, administrative as well as other control information.
• the actual data exchange with information about the condition of the synchronous machine as well as of the electric power network can be performed in close relation to the synchronous machine, for instance via different supervision units, which are further described below.
• the co-rotating positioning of the processor unit also provides a possibility for autonomous operation of the rotor, during possible breakdowns in the communication with stationary parts. A fault on the communication devices may thereby not mean an immediate turning-off of the whole machine, but the machine may continuously be run, even though more carefully.
• the co-rotating processing unit can thereby control the operation of the rotor according to predetermined guidelines independent of the stationary parts.
• Such a communication may e.g. be constituted by brushes and slip rings or parallel similar communication paths, which are activated when needed.
• a so-called inverted synchronous machine 26 is used as a magnetisation machine.
• the stator windings 4 of the main machine are connected to an electric power network via the supply connections 5 and a power transformer 23.
• a smaller power transformer 22 converts the alternating voltage in the supply connections 5 in order to supply an AC-to-DC converter 21 with suitable alternating current.
• the AC- to-DC converter 21 is controlled by the stationary processing unit 12, so that the stator 24 of the magnetisation machine 26 is supplied with an appropriate direct current.
• An alternating current is then induced in the rotor windings 25 of the magnetisation machine 26, which current constitutes the exciting current to the power electronic converter 8.
• the power electronic converter 8 is in this case preferably a thyristor rectifier.
• an asynchronous machine with multiphase windings can be used as magnetisation machine. This has the advantage that it can supply power also to a rotor at standstill.
• Fig. 2 shows another embodiment of the present invention. This is in large similar to the embodiment shown in fig. 1 and similar parts are denoted by the same reference numbers and are not further discussed. Only the existent differences are described here below.
• an arrangement with slip rings and brushes 31 is used to transfer the magnetisation current to the rotor 3.
• the information concerning the desired control of the magnetisation current is in this case transferred from the co-rotating processing unit 10 to the stationary processing unit 12.
• a power electronic converter 30 is then controlled by the stationary processing unit 12 according to the instructions achieved from the co-rotating processing unit 10.
• the power electronic converter 30 is in this case positioned stationary, which means that the need for communication between the processing units 10, 12 in general increases.
• Fig. 3 shows a further embodiment of the present invention. Also this embodiment has large similarities with Fig. 1, and similar parts are denoted by the same reference numbers and are not further discussed. Only the existent differences are described here below.
• the rotor 3 is provided with two field windings 38, 39. These field windings are arranged with displaced magnetic axes.
• the windings 38 and 39 are supplied with current from a double power electronic converter 40 via the connection lines 41 and 42, respectively.
• the embodiment in Fig. 3 is provided with a synchronous machine 26 as magnetisation machine.
• the device with double field windings has certain advantages concerning controllability, stability and so on. Such a type of machine is advantageously used together with an electrical machine according to the earlier mentioned patent application PCT/ EP98/ 007744.
• the rotor 3 is in the embodiment in Fig. 3 provided with a number of additional sensors 43-46, which are connected to the co-rotating processing unit 10.
• Two sensors 43, 44 are arranged to the connection lines 41 and 42, respectively, in such a way that they can sense both the current and the voltage in the respective connection line 41 and 42, respectively.
• a vibration sensor 45 is arranged at the rotor body for detection of vibrations of the rotor, and a torque sensor 46 is also arranged at the rotor shaft 6, for measuring the shaft torque. Also these functions are described more in detail below.
• the angle between the voltage vector and the so-called q axis, determined by the rotating magnetic flux, is referred to as the load angle.
• This angle constitutes a mechanical quantity, which can be measured via a, with the rotor co-rotating, sensor by for instance determining when the voltage vector reaches its maximum in relation to the rotating magnetic flux vector.
• the load angle constitutes an important parameter in order to determine the stability properties of the generator towards the external electric power network, which is described further below.
• phase angle which is the angle between voltage and current on the stator side.
• This quantity contains lots of information about the operational conditions of the rotor. Furthermore, it may also be of interest to, preferably simultaneously, measure the true rotor currents, rotor voltages, vibrations of the rotor, partial discharges in the insulation of the rotor, the insulation resistance of the rotor, shaft torque and load angle. If damping windings are used, corresponding quantities are also of interest to know.
• condition of the insulation is important for the control and planning of the operation of the machine.
• the condition of the insulation can be monitored by measuring, either continuously or intermittently, different quantities. The methods will vary depending on the type of winding and voltage. By measuring the insulation resistance between winding and ground (iron parts of the machine), one may detect faults in the insulation, such as for instance mechanical wear, contamination or collection of humidity. For the rotor winding, this can be performed by measuring current and voltage
• Partial discharges are present in cavities in the insulation, but may also be discharges in air between the insulation and iron parts of the machine.
• the winding insulation is normally made with a semiconductive outer coating and measurement of PD therefore gives a good indication of the winding insulation itself.
• the discharge level is normally rather high in traditional insulation (typically larger than 10 000 pC) and it is normally of interest to measure changes in the discharge level in order to detect the degradation of the insulation.
• the voltage is rather low and therefore there is no need for any semiconductive coating between the insulation and the iron parts.
• Measurement of PD will therefore for a traditional design not have the same value.
• a change of the design of the rotor winding such as use of two separate windings, as mentioned above and/ or increased voltage level transients for increased dynamics in the regulation may bring measurements of values of partial discharges up again in order to supervise the condition of the insulation.
• Measurement of the insulation resistance and/ or PD can also be used for the regulation of the operation of the machine itself.
• One will then e.g. during a strong temporary overload of the machine get mechanical tensions between the winding and the iron in the machine since the temperature difference is large. This may in the worst case damage the insulation and continuous measurement of PD can then be used in order to limit the set-point value at temporary overload of the machine. Overload of the machine is discussed further below.
• Additional quantities that can be of interest to measure can e.g. be the mechanical vibrations in the rotor.
• a changed appearance of the vibration spectrum may indicate incipient mechanical problems, and may also bring about changed operation control, in order to avoid inconvenient breakdowns.
• the shaft torque is also information that is of interest for controlling the synchronous machine.
• Such quantities can be measured in a number of conventional ways, e.g. by strain gauges mounted at the shaft. By help of these sensors, torques, both static and oscillating, may easily be detected.
• Information about the shaft torque can for instance be used in order to protect large turbo machines against subsynchronous resonance, SSR.
• SSR may lead to torsion interaction that results in heating of the shaft, which in turn may lead to breakdowns.
• This type of destructive torsion interaction may arise if there are "unfortunate" relations between the eigen- frequencies for the long shaft in a large turbo aggregate (including generator and turbines) and the electric power network.
• the risk for that it may arise subsynchronous (0 - 50 alt. 60 Hz) resonances is largest for large turbo generators in the vicinity of serially compensated power lines. In the following, it will be described how and why one requests to control a synchronous machine.
• FIG 4 a capability diagram is shown, which corresponds to a synchronous machine in stationary operation.
• the synchronous machine is assumed to, in order to simplify the reasoning, have a round rotor.
• P denotes the active power and Q the reactive power to /from the machine.
• the pole voltage has its rated value Us
• IA denotes the stator current
• jXs denotes the synchronous reactance.
• An inner magnetomotoric force EA which is controlled by the field current IF, is formed.
• the current in the windings has given rated values IFN,
• ISN which should not be exceeded during stationary conditions.
• permitted stationary operational conditions are limited to an area within the stator current limitation 57 and the field current limitation 56, where both IF ⁇ IFN and IA ⁇ IAN. This means that the area 53 is not stationary permitted since IA is limiting and the area 54 is not stationary permitted since IF is limiting.
• the rated powers PN and QN correspond to the state when both the stator and rotor currents assume their rated values.
• the temperature in the windings of the rotor in a synchronous motor is a limiting parameter for the ability of the synchronous machine to produce electrical torque as well as its ability to produce reactive power via the winding of the stator to the electric power network.
• Limits for temperatures and currents are often set in order to protect the machine against damaging overloading.
• Existent synchronous machines have, however, often a large thermal margin because of that the designer and operator built in safety margins at the design of the machine or because of that new experience values have been achieved since the machine was set into operation. Creation of standards, customers demands, uncertainty in dimensioning and inherent tolerances in insulation margins, gives for large electrical generators and motors of today a considerable thermal capacity that for the moment can be utilised to increase the power output of the machine.
• One possibility to expand the area for possible operational points is to deliberately allow an accelerated ageing of the insulation material, i.e. a shortening of the life, by letting the machine work at a higher temperature than what is nominally stated. Such an operation may e.g. be performed against a higher economical benefit by this operation. One may thus "sell off a part of the life of the machine" if that is desired.
• a control of e.g. a power electronic converter means may thus be used to change the operational point in the capability diagram in Fig. 4.
• the operational point may then e.g. be moved outside the area 55, which gives possibilities to a flexible utilisation.
• the operational point may also be changed when measurements indicate that there is a probable fault in the plant, which should give rise to a careful utilisation.
• the operational point may then be moved to a very conservative operational state with additional safety margins, until the reasons for the fault indications are investigated. If e.g. the rotor vibrations increase in an unjustified manner, the shaft torque that arises may e.g. be changed by the choice of rotor current so that the mechanical load on the rotor decreases.
• the synchronous machine is provided by a number of sensors, preferably at both stationary and rotating parts. These sensors may be of the above-discussed types, or for measuring of other quantities that may be though to influence the desired operation of the synchronous machine.
• the sensors are connected to the processing units 10, 12, where a local evaluation of the measurement values is performed.
• the data transfer may here be performed by fixed connections, which easily can give desired bandwidth. In e.g. the cases where measurements from a stationary sensor indicates that the rotor current should be altered, a transfer of information has to be performed between the stationary parts of the synchronous machine to its rotating parts. In the same way, a transfer of information in the opposite direction may also be necessary.
• the amount of transferred data is, however, reduced by the local treatment in the stationary
• control of the power electronic converter can also be performed very fast and flexible.
• the dynamics in the control of the power electronic converter in e.g. Fig. 1 does not any more need to totally rely on control from the stationary parts, but may be performed directly from the local co-rotating processing unit 10, when concerning the information that likewise is obtained from the co-rotating parts.
• the transmission is performed wireless between the rotating and stationary parts.
• a solution with transmission via slip rings and brushes should in principle be possible, but since data transfer in this way often is associated with high noise levels, mechanical wear and uncertainty in reliability, this is not to recommend.
• Wireless communication of different types can be used.
• Transmission with inductive coupling can be used. Frequency modulation and time multiplexing are preferably used in such cases. Inductive coupling does, however, normally demand that one additional mechanical unit is connected to the rotor shaft, with corresponding stationary parts. This increases in an undesirable way the building length for such synchronous machines.
• Infrared communication according to IrDA (Infrared Data
• radio communication is utilised for the wireless information transmission.
• the radio technique is well developed for such applications as a result of the mobility demands concerning computers and telephone equipment.
• Power electronic converters of conventional type give normally rise to electromagnetic disturbances of different kinds. These disturbances are, however, normally mainly below a frequency of 100 MHz, why carrier frequencies over this value should be chosen for the communication. The disturbances of the power electronic converter do thereby not influence the communication in any significant degree.
• the frequency band at 2.45 GHz is e.g. of great interest.
• Bluetooth is a radio interface in the frequency band of 2.45 GHz, which allows terminals to be connected and communicate wireless via a wireless LAN (Local Area Network) with short range.
• LAN Local Area Network
• each unit can communicate simultaneously with several other units.
• Bluetooth uses a spectrum spreading technique with frequency jumps in order to divide the frequency band into several jump channels. During one connection, the transmitters jump from one channel to another in a pseudo- random manner. Wireless communication with up to 721 kbit/s can in this way be guaranteed in the present invention between rotating and stationary parts of the synchronous machine.
• a preferred embodiment of the present invention utilises digital communication. It has during the later decades been a clear trend to miniaturise electronics for signal processing. Telecommunication can be said to be almost totally digital today in its essential parts. Digital communication has today very well developed methods for data compression, filtering, fault correction etc., which is not available in the same way at analogous communication. Signal processing in control and regulation circuits has also been miniaturised and it is easy to implement internal digital signal processing in e.g. power electronic converters, both ac-to-dc-converters and dc-to-ac-converters. To make such circuits with analogue technique does not bring about any additional value, since the digital resolution both concerning amplitude and time is sufficiently high. Digital communication is also to prefer as a result of other aspects such as the possibilities to set and trim the parameters of the regulation circuits remotely. An original parameter setting can thus be exchanged during operation to a modified parameter setting based on earlier operational data.
• the stationary processing unit can be placed in such a position that it can work at normal conditions and consists preferably of a conventional microprocessor, which are well-known to anyone skilled in the art. This is therefore not further described.
• the co-rotating processing unit is on the contrary exposed for more abnormal conditions, e.g. centrifugal forces, vibrations and raised temperatures. These surrounding conditions thus have to be considered at the choice of processor and mechanical design of this and fitting thereof.
• processors are today available, mainly for military use, where the object among other things is to provide reliable shock protections.
• Electric power plant is in this application referring to a construction comprising a group of synchronous machines, which are located within a limited area and are operated in a co-ordinated manner and which preferably belong to the same operator.
• An electric power plant according to the above definition may typically consist of a number of synchronous machines, transformers, lines, cables, bus bars, disconnecting switches and circuit breakers and accompanying measuring and setting tools.
• the power conversion of the electric power plant can be influenced by the machine as well as other parts in the plant, such as phase compensating equipment, to which shunt reactors and shunt and serial capacitors can be counted.
• HVDC High Voltage Direct Current
• FACTS Flexible AC Transmission Systems
• the above mentioned components may furthermore be used in order to control the stationary and transient behaviour of the electric power network in normal operation as well as in fault cases.
• An electric power network is in this application referring to a network of connected electric power plants, which typically are spread over a wider geographical area.
• the transmission capability in the electric power network may break down very fast by that the maximum point on the so called PV-curve is passed or by that there are further disconnections of remaining production units as a result of overload.
• the limitation in the amount of transmitted power depends in many electric power networks on shortage of reactive power, above all at critical positions and not on that thermal limits for transmission lines are exceeded.
• Reactive power can not, unlike for active power, be transported any longer distances. This means that reactive power constitutes a "local" resource, which must be available in the area where it is needed, for instance after a disturbance.
• the reactive power is closely related to the voltage in the electric power network, while the active power in similar way is strongly connected to the frequency.
• a way to control the reactive power is to introduce phase compensating elements in the electric power network or the electric power plant.
• Another measure for controlling the amount of reactive power may be to change the operational conditions for alternating current machines, e.g. synchronous machines, in order to get these to change the reactive power with respect to the present situation in the electric power network or electric power plant. Contributing causes to that a voltage collapse arises may be a high active as well as reactive load level (stressed electric power network), insufficient reactive resources (at least locally) together with different types of disturbances in the electric power network.
• phase compensating equipment thus constitutes, together with the possibilities for an improved utilisation of the reactive resources in synchronous machines, important resources in order to control power flows in the electric power networks.
• the present invention gives, however, possibilities for utilising different existing margins in machines in a more efficient and flexible way in order e.g. to be able to increase the reactive power without decreasing the total utilisation of the machine.
• Synchronous machines according to the present invention can thus be utilised by an electric power network or electric power plant in order to balance the relation between active and reactive power, in particular at critical situations.
• Fig. 5a and 5b show schematically an electric power plant, in which a number of synchronous machines 62 are included. Together with control equipment for the machine, the synchronous machine constitutes a machine unit 71.
• Each machine unit 71 constitutes a part of an electric power plant (according to earlier definition), which via power lines or cables 61 is connected to an electric power network 60.
• the machines are equipped with local processing units 64, 68 and communication devices 69, 70 according to the present invention and data concerning the properties, operational conditions and status, both instantly and historically, of the machine can be available in a stationary processing unit 64 and /or a co-rotating processing unit 68 at each machine.
• a group of machine units 71 is generally controlled by a production management unit 66.
• a number of communication devices 65 are established between the machine units 71, i.e. the stationary 64 and/or co-rotating processing units 68 of the machines and the production management unit 66. If for instance a fault occurs in the network, or if the electric power need is abnormal, the production management unit 66 can transfer information about this to the different processing units 64, 68, possibly related to a wish or demand of temporary being able to operate the machines in a specific manner. The respective processing units 64, 68 may in their turn inform the production management unit 66 about its present operational state and if any tendencies to network instability have been detected.
• Such a configuration becomes particularly powerful if the production management unit 66 has access to the present operational state for the different machines, i.e. e.g. to temperature measurement values or other interesting quantities.
• the control of the synchronous machines 62 via the production management unit 66 may be based on internal measurement signals as well as local, regional or central input signals. Examples of internal measurement quantities are temperature measurement values from stator as well as rotor.
• the frequency constitutes an example of an interesting locally measurable input signal to a production management unit 66, while examples of regional and global input signals can be constituted by different indicators, for instance based on eigenvalue calculations, which states the risk for voltage instability.
• the production management unit 66 has access to both the present operational state for the different machines and stored information about how large constructional margins that are to be utilised in each of the machines, this can be utilised in order to continuously update the operational plans for how one should be able to handle different types of faults or operational situations.
• the updating of operational plans can be built on mathematical relations for instance in the form of optimisation tools such as optimum load distribution, OPF, and stability indicators e.g. based on eigenvalue calculations as well as on measured, calculated or extrapolated data for the response of the machines with respect to interference of protections or limiters. If the production management unit 66 knows that a certain machine has a large margin to utilise, this can be requested at a fault situation, maybe in order to be able to rescue other machines with less margin in the network.
• a database with data about the different machines is thus to prefer.
• the database comprises among other thing the data that has been measured with the above described sensors. Such information can at a later stage be used for analysis in order to increase the knowledge about the behaviour of the plant at normal operation as well as at disturbances. The information can also be used to analyse the efficiency of the plant and to be able to plan future operational ways.
• the database thus comprises both historical information concerning the earlier operation of the machines, but also information that is needed to achieve an adequate control of the machines.
• the database may e.g. comprise the response of the machine to earlier occurred disturbances.
• the information stored in the database can as described above be based on measured, calculated as well as extrapolated data and mathematical calculations for instance in the form of optimising tools and eigenvalue calculations. Measurement data and other information that is stored in the database can with advantage be time stamped, for instance by using time specification via GPS satellites in order to synchronise the timing.
• the database can be available directly in the production management unit 66 and/or the local processing units 64, 68.
• the production management unit 66 therefore preferably comprises a memory means for storage of the database.
• the network communication devices 65 can operate according to different communication methods according to prior art. Such methods can be based on fixed connections in the form of e.g. metallic wires or fibre optics, or on wireless transmission, such as radio or radio link.
• a network of communication devices can be formed. Such a network contributes to alternative communication paths, which can be utilised in the cases where one or some of the communication devices by some reason are not available.
• the production management unit 66 can perform calculations and updates of operational plans, for instance by extrapolating earlier measurement data or results from eigenvalue calculations to estimate the condition in the machine, even if one or some of the communication devices and/ or sensors at the occasion do not work.
• the possibility to build up an operationally safe network is of particular large importance for instance at strained operational situations and during the operation recovery after a larger operational disturbance.
• a network supervision unit 72 is responsible for the operation of the electric power network in large, and can in corresponding way as been described above communicate with electric power plants, i.e. the production management units 66, or individual electrical machines 62, in order to be able to receive information about possible margins. These margins can then be used for an optimisation of larger areas or the total operation of the electric power network.
• An electric power network operator has above all an interest in to know available power resources at different places in the network and the possible costs that are associated with utilisation of these.
• the detailed conditions concerning the temperature margins of the individual machines are of less interest, at least for a hierarchically superior electric power network operator. It is also of interest for an operator of an electric power plant to be able to limit the information exchange, since a part of the available information can be used as competitive means against competing operators.
• the main task for the network supervision unit 72 is to guarantee the possibilities for a reliable and economically optimum operation of the electric power network. This may comprise communication of information exchange and set points as well as control signals to both production management units 66, individual electrical machines 62 and electric power networks 60. During normal operational conditions, the control of production management units 66 can be based on economical control signals, while it can be necessary to send direct control commands at serious operational disturbances, with the aim to save the integrity and continuous operation of the electric power network.
• the information exchange between the network supervision unit 72 and the other units should be performed in the form of messages, which besides address and message may comprise safety keys (coding) in order to limit the right to study the information.
• a preferred embodiment of a production management unit 66 in an electric power plant thus comprises at least one means for external communication.
• This means is arranged on one hand to receive and interpret messages from external units, such as e.g. an operator of an electrical power network and on the other hand to send out selected information to the external units.
• An external unit sends a request if the electric power plant can increase its production of active power by 5 %, and to what price this can be done.
• the production management unit 66 of the electric power plant answers with an offer to a certain price. If the external unit can accept the offer, an order about increased power output is sent.
• the production management unit 66 of the electric power plant responds by carrying through the promised increase and sending back a confirmation of the order.
• Fig. 6 shows a flow diagram for a basic control method for a synchronous machine according to the invention.
• the process begins in step 100.
• step 102 a number of rotor quantities are measured, which are collected into a co-rotating processing unit in step 104.
• the co-rotating processing unit evaluates the measurement values in step 106. Rotor information that is of importance for stationary parts, and outer information that is important for the co-rotating processing unit are transferred between stationary and rotating parts in step 108. Based on the evaluated measurement results, the rotor current is then controlled in step 110 and the process is ended in step 112.
• Fig. 7 shows a flow diagram for a basic control method for an electric power plant with at least one synchronous machine according to the invention.
• the process starts in step 100.
• step 102 a number of rotor quantities are measured in the synchronous machine, which are collected into a co- rotating processing unit in step 104.
• the co-rotating processing unit evaluates the measurement values in step 106.
• Rotor information that is of importance for stationary parts of the synchronous machine and/ or the control of the electric power plant, and external information that is of importance for the co-rotating processing unit are transferred between stationary and rotating parts in step 108. Based on the evaluated measurement results, the operation and power conversion of the electric power plant is then controlled in step 111 and the process ends in step 112.

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• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
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• Control Of Eletrric Generators (AREA)

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• 1999
  • 1999-08-27 SE SE9903026A patent/SE9903026L/sv not_active IP Right Cessation
  • 1999-08-27 SE SE516401D patent/SE516401C2/sv not_active IP Right Cessation
• 2000
  • 2000-08-23 WO PCT/SE2000/001604 patent/WO2001017084A1/en active Application Filing
  • 2000-08-23 AU AU68843/00A patent/AU6884300A/en not_active Abandoned

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