WO2021053340A1 - Appareil et procédé de commande pour augmenter la capacité de puissance d'un système de transmission d'énergie électrique - Google Patents

Appareil et procédé de commande pour augmenter la capacité de puissance d'un système de transmission d'énergie électrique Download PDF

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Publication number
WO2021053340A1
WO2021053340A1 PCT/GB2020/052257 GB2020052257W WO2021053340A1 WO 2021053340 A1 WO2021053340 A1 WO 2021053340A1 GB 2020052257 W GB2020052257 W GB 2020052257W WO 2021053340 A1 WO2021053340 A1 WO 2021053340A1
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Prior art keywords
transformer
harmonic
current
injector
transmission line
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PCT/GB2020/052257
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English (en)
Inventor
Duncan Andrew GRANT
Original Assignee
Grant Duncan Andrew
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
Priority claimed from GB201913453A external-priority patent/GB201913453D0/en
Priority claimed from GBGB1918225.2A external-priority patent/GB201918225D0/en
Application filed by Grant Duncan Andrew filed Critical Grant Duncan Andrew
Publication of WO2021053340A1 publication Critical patent/WO2021053340A1/fr

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    • 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
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/04—Circuit arrangements for ac mains or ac distribution networks for connecting networks of the same frequency but supplied from different sources
    • 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
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/26—Arrangements for eliminating or reducing asymmetry in polyphase networks
    • 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
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/50—Arrangements for eliminating or reducing asymmetry in polyphase networks

Definitions

  • the invention herein described relates to apparatus which is located at the star point of three-phase transformer windings which are connected to the three-phase transmission line at each end of the line, this apparatus having the purpose of injecting a triple harmonic waveform in all phases simultaneously and the method of controlling this injection apparatus.
  • This permits the transmission line (overhead lines or cable-based) to carry more power.
  • Fig. 1 shows how the ratio of peak value to fundamental amplitude of a composite waveform (sine wave plus third harmonic) is reduced by the addition of the third harmonic.
  • Fig. 1 shows a sine wave at fundamental frequency only (dashed line) and a composite waveform with 1/6 amplitude third harmonic added (solid line). It has been shown that the addition of a third harmonic of 1/6 amplitude is the optimal ratio of third harmonic amplitude to fundamental amplitude for enhancing the amplitude of the fundamental of the composite waveform while keeping the peak value of the composite waveform constant..
  • the ratio of fundamental voltage amplitude to peak voltage is increased by 15.6% in the composite waveform.
  • the theory with relevant calculations are set out in prior art 1 .
  • the power transmitted by a three-phase transmission line (associated with the fundamental frequency voltage and current waveforms) may be derived from the following equation:
  • Vs is the rms sending end voltage (line to neutral - if a neutral existed)
  • V T is the rms receiving end voltage (line to neutral - if a neutral existed)
  • V is the rated line voltage (line to neutral if a neutral existed)
  • S lf is the phase angle between the sending end and receiving end voltage waveforms at 1f
  • X is the inductance of each phase of the line (positive sequence inductance). Line resistance is neglected.
  • Figure 2 shows how that triple harmonics may be injected in all three phases simultaneously by applying the 3f voltage waveform to the star point of the sending-end transformer TF1 .
  • Injection can be via the secondary of an injection transformer with an inverter providing a 3f supply to its primary.
  • the voltage waveform of the three phases with respect to ground now includes a triple frequency waveform.
  • the star point of the receiving-end transformer TF2 is left floating (ora delta winding is used) so that the 3f waveforms are not passed through the transformer Triple frequency currents are not injected into the three phase lines since there is no return path for the currents (apart from some parasitic capacitance to ground the effects of which may require management).
  • Prior Art 2 discusses such an arrangement.
  • Figure 3 shows triple-frequency waveforms injected at both ends of the line by the use of injection transformers connected to the star points of the relevant transformers.
  • the virtue of adding the 3f waveforms at both ends of the transmission line is that it allows a continuous change in 3f phase along the line to match the change in phase of the 1f waveform which results from power flow.
  • the rate of phase change along the line at 3f will have to be three times the rate of phase change of the 1f waveform if the ideal line-ground waveform (Fig. 1) is to be preserved along the length of the transmission line. Consequently currents with a frequency of 3f will flow along the lines of the transmission system with the earth completing the circuit.
  • Prior art 3 describes the injection of triple frequency components at the sending end of a transmission line with a triple frequency voltage component being injected at the receiving end transformer star point by allowing triple frequency current to flow to ground through a passive load.
  • the use of a second triple frequency injection arrangement at the receiving end is mentioned without further explanation.
  • the invention addresses the problems which arise when the system shown in Figure 3 is used in practice.
  • the injectors of the triple frequency component replace solid and direct connections to ground which would represent normal practice. Normal practice would be to connect both star points to ground. Alternatively normal practice could be to connect only one star point to ground with the other star point left floating or with a delta winding employed at the other transformer.
  • the chosen system has the star points at both ends connected to injectors with one end of each injector grounded. This creates problems which we now identify.
  • the main purpose of the injectors is to impose a 3f voltage waveform at the star point of the 1 f transformer windings.
  • a further purpose of the injectors is to hold the voltage of the star point otherwise at OV (ground potential).
  • the three-phase set of currents in the three phases of the transmission line will be unbalanced (in magnitude or phase or both). This imbalance can give rise to negative sequence currents at 1f and zero sequence currents at 1f. As with positive sequence currents, negative sequence currents will also sum to zero at the star point. However, zero sequence currents at 1f at the star point will be cophasal and will be additive. These zero sequence currents must flow through the injector without giving rise to any deviation of the star point voltage from the required 3f voltage waveform. Hence, the injector must ideally have zero impedance to 1f currents under normal operating conditions.
  • Heavily unbalanced currents can arise during fault conditions. Typical faults are line-to-line accidental connections (shorts) or line-to-ground shorts. There are two ways in which the injectors can respond to these conditions.
  • the injector can continue to operate as it does under normal conditions - that is continuing to present a low (ideally zero) impedance to 1f currents. This will require that the injectors can carry abnormally high currents fora short time (until protection equipment operates to isolate or clear the fault). However, provided the injectors can restrain the rise of 1f voltage at the star point, the injectors will not need a voltage rating above that required for their injector role (i.e. 1 /6 th of the 1f line to ground voltage). As described later, if a back-to-back pair of SCRs (Silicon Controlled Rectifiers) are located in parallel with the injection transformer these SCRs can be turned on under fault conditions to provide an alternative path for the 1f current.
  • SCRs Silicon Controlled Rectifiers
  • the injector can become an open circuit. This prevents the injector having to carry excessive current but the injector will be exposed to a high voltage - possibly full line-to-line 1f voltage.
  • the injector may therefore have a role to play in fault current limitation and fault clearing if the injectors at each end of the transmission line can be made to act in coordination. However, this comes at the cost of an increase in the VA rating of the injector transformer.
  • I- f the current in each line at frequency 1f
  • I 3 f the current in each line at frequency 3f
  • the VA rating of the transformer 20 can be obtained approximately by multiplying the 3f voltage rating V .
  • the type of injector on which the invention is based comprises a single phase transformer and triple frequency power source as shown in Figure 4.
  • An aspect of the invention is that, when appropriately driven and appropriately controlled, the transformer can simultaneously act as a voltage transformer at 3f and a current transformer at 1 f, thereby injecting a 3f voltage waveform while any 1f current flowing in the injection-side winding is balanced by equal and opposing ampere-turns from the other winding of the transformer.
  • a further aspect of the invention is that when the currents at 1 f in the injection transformer attains a predefined maximum allowed value, the transformer is disconnected from its 3f power supply, thereby permitting the injection transformer to saturate and conduct the 1f current in the injection-side winding with minimal voltage drop.
  • a further aspect of the invention is that when the current through the injection-side winding of the injection transformer reaches a predetermined level, a pair of back-to back SCRs (silicon Controlled Rectifiers) connected across the injection-side winding are turned on to provide an alternative path for the 1f current.
  • a pair of back-to back SCRs silicon Controlled Rectifiers
  • a further aspect of the invention is the use of a control loop to operate the power supply to the injector transformer in such a manner that the voltage at the star point of the 1f transformer is forced to follow the required 3f voltage waveform (with the required amplitude and phase with respect to the line-to-ground voltage waveforms of the transmission line) while suppressing any deviation from that desired waveform so that the 1f voltage appearing at the transmission line starpoint is always zero with respect to ground.
  • the voltage at the star point at frequency 1f is held at zero under normal conditions, including unbalance load conditions.
  • it injects at the start point a voltage waveform of frequency 3f.
  • the invention is equally applicable to new-build and retrofit (injectors being added to an existing transmission system) situations.
  • Figure 1 shows a sine wave at fundamental frequency and a composite waveform with 1/6 amplitude third harmonic added.
  • Figure 2 shows a transmission line with a third harmonic voltage injected at one end.
  • Figure 3 shows a transmission line with a third harmonic voltage injected at both ends.
  • Figure 4 shows an injector arrangement.
  • Figure 5 shows a control arrangement of the injector in which the ampere-turns at 1 f in each of the injector transformer windings are brought to equality by measuring the current in each winding.
  • Figure 6 shows a control arrangement in which the control system allows for the generation of a 3f sinusoidal voltage waveform at the injector terminals while suppressing any deviation from that voltage waveform, such as might be produced by the passage of 1f current through the injector.
  • Figure 7 shows an overall injector layout with the addition of a pair of back-to-back SCRs across the injector which provide an additional path for current flow from the star point of the 1f transmission line transformer to ground.
  • Figure 1 shows a waveform composed of a sine wave plus 1 /6 th third harmonic.
  • Figure 2 shows a transmission system with third harmonic injection at one end only.
  • Figure 3 shows the system to which the invention applies.
  • a three-phase transmission line is formed by the conductors 1 , 2, 3.
  • a single conductor is shown for each phase but in some transmission line each phase may comprise several conductors in parallel.
  • the invention is applicable to this arrangement also.
  • the three conductors 1 ,2,3, may be overhead lines or insulated cables. In a cable-based system the lines will be individually sheathed with the sheaths at ground potential.
  • the transformer 4 will be called the sending end transformer.
  • the transformer 5 will be called the receiving end transformer. It will be understood that power can be made to flow in either direction along an ac transmission line and hence the transformers are only labelled “sending end” and “ receiving end” for the purposes of this description within which power is supposed to flow from the transformer 4 to the transformer 5.
  • the three-phase winding 6 of transformer 4 is called the primary winding of this transformer and is connected to a three-phase source of power consisting of a three-phase set of voltage waveforms of frequency 1f.
  • the three-phase winding 7 of transformer 4 is the secondary winding of transformer 4.
  • This secondary winding 7 is connected to the three lines 1 ,2,3 of the transmission line.
  • the star point of the three-phase winding 7 would normally (in conventional practice) be connected to earth 8.
  • a sinusoidal voltage waveform at 3f is injected between earth 8 and the star point 9 of the secondary winding 7.
  • This 3f waveform is injected by the injector 10 and has amplitude approximately one-sixth of that of the 1f voltage waveform (line-neutral, where the neutral is imagined and is at earth potential).
  • the primary winding 11 of transformer 5 is connected to the receiving end of the transmission line (comprising lines 1 ,2,3 ).
  • the star point 14 of transformer winding 11 is connected to earth 13 through injector 12.
  • the secondary three-phase winding 15 of transformer 5 is connected to the load or part of the grid which is receiving the power transmitted by the sending end transformer 4.
  • the impedance which lines 1 ,2,3 present to the flow of 1 f current is usually mainly inductive, so that as an approximation it can be said that power flow through the transmission line is achieved by a phase difference between the sending end and the receiving end and that a VAR (Volt Amps Reactive) flow is achieved by a voltage difference between the sending and receiving end voltages.
  • a phase difference between the sending end and the receiving end
  • a VAR Volt Amps Reactive
  • the 3f waveform injected by injector 10 will need to be ahead in phase of the 3f waveform injected by injector 12 by three time the phase difference between ends of the transmission line at 1f.
  • the phase difference between ends of the transmission line at 3f will cause cophasal currents to flow at 3f in the lines 1 ,2,3.
  • the return path for these currents is through the earth via earth connections 8 and 13. If a return path of well defined resistance is preferred then a neutral wire 15 can be connected between the earth end of injector 10 and the earth end of injector 12. This wire will need to be earthed in at least one location (e.g. 8 or 13) so that the voltage of the transmission line is referenced to earth. This is an important consideration with respect to line insulator voltage rating and transformer insulation voltage rating.
  • Some overhead transmission lines will include an earth wire suspended above the wires carrying the three-phases, the main purpose being to shield the phase wires from lightning.
  • This conductor may also provide a return path for the 3f current which flows along the transmission line phases in transmission systems which have a 3f injector at both ends.
  • Cable- based transmission lines are likely to use metal-sheathed cables in which the metal sheaths can provide a return path for the 3f current.
  • Figure 4 shows a schematic diagram of an injector (10 and 12).
  • the injector unit control system must achieve two basic goals in normal operation, defined as suppressing 1f ampere turns in the transformer while generating a 3f voltage waveform at the star point.
  • the line-to-ground amplitude of this 3f waveform is approximately 1 /6 th of the line-ground voltage of the transmission system at 1f.
  • three phase transformer 4 is included in the diagram (in this case the sending end transformer 4).
  • the injector is based on a single-phase transformer 20.
  • the secondary 21 of this single-phase transformer 20 is connected between earth and the star point 9 of the 1 f, three-phase transformer 4.
  • the primary 22 of the single-phase transformer 20 is connected to a 3f power supply unit 25 which acts as an ac source of frequency 3f.
  • the 3f power unit 25 comprises an inverter 26, which produces the 3f voltage waveform of required amplitude, and a source of dc 28 which supplies dc to the inverter via the dc link 27.
  • the dc source 28 is connected to an ac supply 29 which may be single-phase, as shown, or three-phase if this is more convenient.
  • the 1f ac supply 29 may be derived from the transmission line or the incoming 1 f lines to transformer 4 or the outgoing 1 f lines to transformer 5 or from any other ac source. Power may flow in either direction along the transmission line due to the line currents at 3f. Hence it will be necessary to accommodate a power flow in either direction in the dc link 27. Hence either the dc link 27 will need an arrangement to dump power from the dc link 27 (unlikely given the inefficiency of such an arrangement) or the rectifier 28 will need to be able to handle reverse power flow ( from dc to ac).
  • the rectifier 28 becomes an inverter and the arrangement in unit 25 is more correctly called a back-to-back inverter pair.
  • a back-to-back inverter any other suitable frequency changing converter may be employed such as a cycloconverter or matrix converter.
  • the link 27 between units 28 and 26 may need to include elements appropriate to the technology chosen for power unit 25, such as a dc link reservoir capacitor where 26 is a voltage source inverter or a series inductor where 26 is a current source inverter.
  • Ideal normal operating conditions are defined as no faults and a balanced load (the three-phase set of currents in the transmission line are balanced).
  • the same 3f voltage waveform is added to each of the three 1f voltage waveforms (line to neutral or line to ground. Since neutral and ground should ideally be at the same potential).
  • a three-phase set of voltage waveforms is produced by the transformer 4 and these are applied to the lines 1 ,2,3.
  • the operation of the 3f power unit 25 is controlled by the control unit 30.
  • the amplitude and frequency and phase of the 3f voltage waveform applied to the primary 22 of the injector transformer 20 is controlled by the control unit 30.
  • This unit will ensure that the 3f frequency is exactly three times that of the 1 f grid and that the 3f and 1f waveforms are phase locked which ensures that at the sending end the zero crossings of the 3f waveform coincide with the zero crossings of each of the 1f waveforms as illustrated in Figure 1.
  • the control unit sets the amplitude of the 3f waveform at 1 /6 th of the amplitude of the line-ground voltage at 1 f in the transmission system, with some small difference in 3f voltage between injector 10 and injector 12 being permitted to give exact control of the waveform shape along the transmission line.
  • the control unit is able to set the frequency, phase and amplitude of the 3f waveform with respect to the same variables at 1f because of the information it receives from one of the phases of the three-phase transformer 4 via the signal line 31.
  • Signal line 32 provides a signal at earth potential permitting the voltage waveform at the starpoint 9 of the transformer relative to earth to be measured via signal line 33.
  • closed loop control within the control unit 30 can ensure that the correct amplitude of 3f waveform is applied to starpoint 9 under all circumstances.
  • the current in the secondary winding of the 3f transformer 20 is monitored by current sensor 34 with the signal being sent to the control unit 30 by signal line 35. Monitoring of the current supplied to the star point 9 is best achieved by this method since current in the primary winding 22 of the transformer 20 includes the 3f magnetising current for transformer 20.
  • the commands from the control unit 30 to the 3f power unit 25 are conveyed via signal path 36.
  • the 3f transformers 20 at each end of the transmission line operate as voltage transformers at frequency 3f.
  • VAR flow is also possible particularly when there is a voltage difference at 3f between the sending and receiving end of the transmission line. VAR flow will not require the inverter power supply 25 to handle power or draw power from the source 29 or sink power into the source 29.
  • a voltage at 1f should not be generated the star point 9. It is preferable that the 3f transformer 20 should behave as a short circuit to ground, emulating the situation which obtains in normal 1f operation without 3f injection, Hence no flux must be generated at 1 f in the transformer 20. To ensure that this is the case, a current at 1f must flow in the primary 22 of transformer 20 such that the ampere-turns at 1 f in the two windings cancel each other out with respect to flux production. This is how a current transformer operates. Hence the transformer 20 operates simultaneously as a voltage transformer at 3f and a current transformer at 1f. The control unit 30 can cause this to happen in two alternative manners.
  • Ampere turn matching The ampere-turns in winding 21 at frequency 1f are determined from a current measurement made by the current transducer 34.
  • the ampere turns in winding 22 at frequency 1f are determined from a current measurement made by the current transducer 40.
  • the 1f current in winding 22 is controlled so that the ampere turns in the two windings cancel each other. This arrangement is described further in the section dedicated to Figure 5.
  • the source 26 which drives the primary winding 22 of the injector transformer 20 can be of fundamentally of the voltage source type or current source type. It will be understood that a voltage source converter can be converted to a current source supply by the addition of a local current control loop and that a current source convertor can be converted to a voltage source inverter by the addition of a local voltage control loop. Economics are likely to influence the choice of converter type. In the following it is assumed that the generator (inverter) 26 which drives the primary of the injector transformer 20 is a voltage-source inverter.
  • a voltage source inverter used for 26 can respond rapidly to demanded voltage change (within the limit imposed by its maximum current capability given that it has to charge or discharge line capacitance).
  • a current source inverter used for 26 can respond rapidly to demanded current change (within the limit imposed by its maximum voltage capability given that it has to add or reduce the current in a circuit containing inductance.
  • Injector 10 and injector 12 can operate independently of each other. Each can generate a 3f voltage waveform of the required amplitude and phase by reference to the amplitude and phase of the 1f waveform at their respective ends of the transmission line. However, for the purposes of fault management and other system control advantages the two injector control units 10 and 12 may be in communication - via signal wires, optical fibres, signals impressed on the 1f transmission wires, or by radio or microwave communication.
  • the control arrangement must be able to deal with overload conditions or fault conditions.
  • the injector transformer must be protected against operating beyond its normal VA rating. Under the conditions of unbalanced line currents the VA rating requirement of transformer 20 is likely to be dominated by the amount of 1f zero sequence current flowing through winding 21 .
  • the control circuit measures this current through the current sensor 34 and can determine if the short-term VA rating of the 3f transformer 20 is being exceeded and take appropriate action. A large 1f current through the winding 21 can be occasioned by a fault on the transmission line.
  • the transformer 20 is therefore now operating as a saturable reactor with very low impedance while saturated. Hence the transformer 20 acts very much like a solid connection to earth. This is a situation much preferred by power system designers when there is a fault on the transmission line.
  • Figure 5 shows a control arrangement in which power supply 25 employs a voltage source inverter 26 as the output stage.
  • a signal-level generator 45 produces a 3f sinewave to be used as the model for the generation at the inverter terminals of a 3f voltage waveform of the required amplitude (approximately l/6 th of the line-neutral (or line-ground) voltage of the power transmission system).
  • This signal passes through a summing node 46.
  • the sensor 34 detects the instantaneous current flowing in the primary 21 of the injection transformer.
  • the signal 41 passes through a low-pass or band-pass filter 47 which passes the If signal but blocks the 3f signal.
  • the signal in signal line 48 therefore represents the If component of the current in winding 21.
  • Sensor 40 detects the instantaneous current flow in the transformer winding 22.
  • the signal passes through low-pass or band-pass filter 49 so that the signal 50 represents the If current supplied to winding 22.
  • the sensitivity of sensors 34 and 40 are set to take account of the number of turns in windings 21 and 22 respectively so that the output of the two sensors are equal when the ampere turns provided by windings 21 and 22 are equal.
  • the output of summing node 51 is an error signal 53 representing the difference between the If ampere turns in the windings 21 and 22.
  • the error signal 53 is fed to summing node 46.
  • the signal 54 which is fed to the inverter 26 is a 3f waveform model for the inverter to reproduce plus an additional signal component which will have the effect of increasing or reducing the current in winding 22 in the appropriate sense to suppress If flux in the core of the transformer 20.
  • the effect is to reduce or increase the instantaneous voltage of the inverter 26 so as to ensure the that error signal 53 tends to zero and that the ampere turns applied to the core of transformer 20 at frequency If tends to zero. Since with zero flux at If created in the core of transformer 20 the voltage at If across the transformer winding 21 will also be zero and hence the injector will have zero reactance to ground at If. Due to lag in the open loop transfer function of this control arrangement (for example between current in the transformer winding 22 and voltage applied to this winding) appropriate compensation techniques will need to be used with this control arrangement to ensure optimal performance.
  • Elements 45, 46, 47, 48, 49, 50, 51, 53 of the control system illustrated in Figure 5 are likely to be located within the control unit 30 of Figure 4.
  • the signal line 54 will be included in the overall signal feed arrangement 36 of Figure 4.
  • Signal line 31 is also required to provide a If reference signal for the 3f waveform generator 29 to allow the generator to provide a signal of the required frequency, phase and magnitude.
  • Figure 6 shows an alternative control arrangement in which power supply 25 employs a voltage source inverter 26 as the output stage.
  • a signal-level generator 45 produces a 3f sinewave to be used as the model for the generation 3f voltage waveform at the terminals of the inverter 26. The required amplitude of this is approximately l/6 th of the line-neutral (line-ground) voltage of the power transmission system.
  • This signal passes through a summing node 46.
  • the voltage of the star point 9 with respect to ground is sensed via signal wire 33.
  • a voltage attenuator may be included in this signal path. Earth potential is also supplied to summing node 60 via the signal line 32.
  • the summing node 60 produces a signal 61 which is a measurement of the instantaneous voltage relative to earth of the star point 9.
  • Amplifier 62 produces a signal of the appropriate amplitude, this signal then being fed to summing node 46.
  • Summing node 46 compares the measured voltage at the star point 9 with the 3f model signal provided by signal generator 45.
  • Signal 64 is the resulting error signal. Error signal 64 is used to control the instantaneous voltage output of the converter 26 in the power supply 25. When there is no If zero sequence current flowing in winding 21, the voltage across winding 21 will be an amplified version of the 3f signal produced by signal generator 45. Thus a sinusoidal voltage waveform of the required amplitude is injected at the star point 9.
  • Elements 45, 46, 60, 61, 62, 64 of the control system illustrated in Figure 6 are likely to be located within the control unit 30 of Figure 4.
  • the signal line 64 will be included in the overall signal feed arrangement 36 of Figure 4.
  • Signal line 31 is also required to provide a If reference signal for the 3f waveform generator 29 to allow the generator to provide a signal of the required frequency, phase and magnitude.
  • FIG. 7 shows the injector arrangement as described previously but with the addition of a back-to-back pair of SCRs (Silicon Controlled Rectifiers) connected in parallel with the winding 21 of the injector transformer 20.
  • SCR 71 and SCR 72 provide an alternative method of providing a low impedance path to ground from the If transformer star point 9. This path may be used in the event of a very large If current attempting to flow to ground (for example, under fault conditions on the transmission line) and greatly reduces the current flowing through winding 21.
  • the inverter 26 is turned off during this time.
  • the current sensor 34 sends a current measurement to the control unit.
  • control unit 30 determines from this measurement that the appropriate conditions exist (for example a very large If current) then the control circuit can turn on the SCRs (71 and 72) thereby providing a by-pass path for the current.
  • the control unit turns the SCRs (71 and 72) on by sending a current pulse or series of pulses or a continuous current to each of the SCR gates (for SCR 71 gate signals go from output 74 to gate 73 and for SCR 72 gate signals go from output 76 to gate 75).
  • the SCRs (71 and 72) When the current through these SCRs (71 and 72), as sensed by sensor 34, has returned to normal level the SCRs (71 and 72) can be turned off by removal of the gate signals after which the SCRs (71 and &2) will turn off when the current through them falls to zero as it will twice every cycle of the If supply.
  • the operation of the SCRs can advantageously be coordinated with other fault-handling measures.
  • GTOs are an alternative to the SCRs 71 and 72.
  • the three transmission line phases will each carry a current at 3f. These currents will flow in the windings of the 1f three-phase transformers at each end of the transmission line.
  • the voltage generated at 3f at the 1 f transformer terminals will depend on the impedance of the each of the 1f transformerwindings at 3f.
  • the 3f currents in the three transmission line phases will be cophasal (in phase with each other).
  • the three-phase 1f transformer is a three-limb transformer then there will be no circulating path for flux at 3f so the impedance of the windings will be low at 3f and little voltage will be generated at the 1 f transformer terminals at 3f. If on the other hand the 1 f transformers are four-limb, there will be a circulating path for flux at 3f and the impedance of each winding at 3f could be high, permitting a substantial 3f voltage to be generated at the 1f transformer terminals. This will also be the case if the three-phase 1f transformer is made up of three single-phase transformers or single-phase autotransformers.

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Abstract

Troisième injecteur harmonique pour une ligne de transmission de puissance qui est agencée pour fonctionner à une fréquence fondamentale, le troisième injecteur harmonique comprenant : un transformateur doté d'un enroulement primaire et d'un enroulement secondaire ; un circuit d'attaque agencé pour fournir une troisième forme d'onde de tension harmonique à trois fois la fréquence fondamentale à l'enroulement primaire du transformateur ; un premier détecteur conçu pour détecter une composante de fréquence fondamentale d'une forme d'onde de tension à travers l'enroulement secondaire du transformateur ou la forme d'onde de courant dans l'enroulement secondaire du transformateur ; et un dispositif de commande agencé pour commander le circuit d'attaque de façon à fournir du courant à l'enroulement primaire qui génère un flux dans le transformateur qui annule le flux généré par la composante de fréquence fondamentale détectée dans l'enroulement secondaire. Lorsqu'il est entraîné et commandé de manière appropriée, le transformateur peut agir simultanément comme un transformateur de tension en 3f et un transformateur de courant en 1f, ce qui permet d'injecter une forme d'onde de tension 3f tandis que tout courant 1f circulant dans l'enroulement côté injection est équilibré par des tours ampère égaux et opposés à partir de l'autre enroulement du transformateur.
PCT/GB2020/052257 2019-09-18 2020-09-17 Appareil et procédé de commande pour augmenter la capacité de puissance d'un système de transmission d'énergie électrique WO2021053340A1 (fr)

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GB201913453A GB201913453D0 (en) 2019-09-18 2019-09-18 Apparatus and method of control for increasing the power capability of an electrical power transmission system
GB1913453.5 2019-09-18
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GBGB1918225.2A GB201918225D0 (en) 2019-12-11 2019-12-11 Apparatus and method of control for increasing the power capability of an electrical power transmission system

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WO2023052194A1 (fr) * 2021-09-28 2023-04-06 Rolls-Royce Deutschland Ltd & Co Kg Système électrique pour une machine électrique
CN114268102A (zh) * 2021-12-23 2022-04-01 国网江苏省电力有限公司经济技术研究院 基于解析式概率潮流模型的电力系统运行状态量化方法
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WO2024099629A1 (fr) * 2022-11-10 2024-05-16 Innomotics Gmbh Dispositif de compensation permettant de réduire une ou plusieurs oscillations harmoniques dans une machine électrique

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