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WO1997007581A1 - Compensateur var statique - Google Patents

Compensateur var statique Download PDF

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Publication number
WO1997007581A1
WO1997007581A1 PCT/GB1996/001935 GB9601935W WO9707581A1 WO 1997007581 A1 WO1997007581 A1 WO 1997007581A1 GB 9601935 W GB9601935 W GB 9601935W WO 9707581 A1 WO9707581 A1 WO 9707581A1
Authority
WO
WIPO (PCT)
Prior art keywords
switching means
current
zero
compensator
capacitor
Prior art date
Legal status (The legal status 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 status listed.)
Ceased
Application number
PCT/GB1996/001935
Other languages
English (en)
Inventor
David John Young
Bjarne Reinholdt Andersen
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
GE Power UK
Original Assignee
GEC Alsthom Ltd
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.)
Filing date
Publication date
Application filed by GEC Alsthom Ltd filed Critical GEC Alsthom Ltd
Priority to AU67459/96A priority Critical patent/AU6745996A/en
Publication of WO1997007581A1 publication Critical patent/WO1997007581A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

Links

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
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
    • H02J3/1821—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators
    • H02J3/1835—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control
    • H02J3/1864—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control wherein the stepless control of reactive power is obtained by at least one reactive element connected in series with a semiconductor switch
    • 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
    • Y02E40/10—Flexible AC transmission systems [FACTS]

Definitions

  • Static var compensators for use in controlling vars and regulating the supply voltage in, for example, high-voltage supply systems.
  • Static var compensators are known in which a series circuit comprising a capacitor bank, a switch and a current limiting reactor is connected across the supply system, the switch being controlled to switch the capacitor bank into or out of circuit according to the demands of the system. In a typical three-phase system three such series circuits may be connected in a delta arrangement.
  • the switch comprises a thyristor valve assembly consisting of a number of thyristors in series (each series device or parallel group of devices being known as a 'level') and, in certain cases, a number of paths in parallel.
  • Thyristors of the type in question are expensive and it is desirable to limit the numbers as far as possible.
  • An object of the present invention is to control the switch in such a manner as to limit the voltage to which the switch may be subjected in a blocking (turn-off) operation.
  • a static var compensator for connection to an AC supply
  • the compensator including at least one series circuit comprising capacitor means, inductive reactor means and switching means, the switching means being provided to switch the capacitor means and inductive reactor means into or out of circuit
  • the compensator including control means for performing a turn-off operation on said switching means, said control means being to this end arranged to perform a sequence of switching operations on said switching means thereby to cause an at least partly discharged condition of the capacitor means to coincide with a zero-current state of the series circuit.
  • the control means may be arranged to open the switching means at or near to a zero-current state ofthe series circuit, close the switching means after a delay, and re-open the switching means at said coincidence condition.
  • the control means may be arranged to close the switching means after a delay of less than a half-cycle at the AC system frequency, and preferably after a delay of less than a quarter-cycle.
  • control means When the switching means is closed, current flow in the series circuit being subject to resonance ofthe series circuit components, the control means may be arranged to permit one or more pulses of resonant current of alternating polarity to occur before the switching means is reopened.
  • the resonant frequency ofthe series circuit taking into account inductive reactance associated with the AC system to which the compensator is connected, may be greater than the AC system frequency, the delay period may be approximately 0.2 times the period of the
  • AC system frequency and the control means may be arranged to permit two pulses of resonant current of alternating polarity to occur before the switching means is reopened.
  • the electronic switching means may comprise thyristors.
  • the compensator may comprise a three-phase delta-connected arrangement of said series circuits.
  • it may comprise a three-phase star-connected arrangement of said series circuits having a star-point connected to the star-point of a three-phase supply system.
  • the control means may be arranged to open and, following a delay period, close the switching means more than once during said turn-off operation.
  • a method of controlling a static var compensator comprising at least one series circuit of capacitor means, inductive reactor means and switching means, the switching means being provided to switch the capacitor means and inductive reactor means into or out of circuit, in which method the capacitor means Ls switched out of circuit by opening the switching means at or near to a zero-current state of the series circuit, the switching means is closed after a delay period, and the switching means is re-opened at or near to a zero-current state of the series circuit, the delay period being such as to cause an at least partly discharged condition ofthe capacitor means to coincide with a zero-current state of the series circuit.
  • a method of controlling the switching means of a static var compensator including capacitor means, inductive reactor means and switching means in a series resonant circuit connected across an AC supply system and having a resonant frequency higher than the AC system frequency, the method comprising the steps of: - opening the switching means at a zero-current or near-zero-current state of the series circuit, thereby leaving the capacitor means charged;
  • the delay period being selected such that said zero-current transition coincides with a low value of the voltage across the capacitor means.
  • the said zero-current transition may be the second or later such transition after the closing of the switching means.
  • FIG. 1 is a diagram ofthe basic elements of a series circuit comprising a capacitor
  • Figure 2 is a graph ofthe voltages and currents in the circuit of Figure 1 on blocking the thyristor valve from a steady state in a conventional manner;
  • Figure 3 is a similar graph of the effect of temporarily blocking the thyristor valve for a period of 4 ms
  • Figure 4 is a graph of a blocking operation according to the invention using a preferred delay period of 4 ms;
  • Figures 5 and 6 are similar graphs showing the blocking operation with delay periods of 3 ms and 5 ms, respectively;
  • Figures 7(a) and 7(b) are diagrams of delta and star arrangements of the series circuits of Figure 1;
  • Figures 8(a) and (c) are vector diagrams ofthe voltages arising when switching off the three phases in a star arrangement with floating star-point, and
  • Hgure 9 is a diagram of the two-valve star-connected TSC resulting from the analysis of Figures 8(a), (b) and (c).
  • the series circuit shown known as a thyristor switched capacitor (TSC) circuit, may be connected between one phase (V 0 ) of a three phase system and star-point/neutral (N), as shown, or may be one arm of a delta arrangement.
  • the capacitor C and thyristor valve T are the basic components, the reactor L being provided to limit the current and also the rate of change of current in normal turn-on and under fault conditions.
  • FIG. 1 shows a switching means in the form of a simple thyristor valve T comprising a pair of thyristors back-to-back to provide conduction in both directions.
  • a control means (not shown) provides gating pulses at 90° after the zero voltage crossings, so mamtaining the thyristor valve in an unblocked condition.
  • the invention exploits the fact that since the series circuit - the TSC circuit in the particular case - is a resonant circuit having a resonant frequency different from and higher than the system frequency, it is possible to activate the resonance by charging the capacitor (by normal operation), and 'unloading' the charged capacitor at a suitable instant so as to produce charging/discharging oscillations with current zeros at least one or more of which are at instants which do not coincide with maxima in the applied supply voltage. It thus becomes possible to obtain a current zero coincidentally with a zero value, or at least a low value, of capacitor voltage. Opening the switch, i.e. blocking the thyristor valve, at such an instant results in a subsequent valve voltage which may be no more than the applied, supply voltage.
  • Figure 3 shows an intermediate stage in achieving this result.
  • the left-hand sides ofthe graphs show the steady condition with the capacitor in circuit.
  • the switch is opened at a current zero, leaving the capacitor fully charged.
  • the voltage across the valve now begins to rise as it did in Figure 2.
  • the switch is reclosed by deblocking the valve after a short delay period, in Figure 3 four milliseconds, the valve voltage drop will return to zero as shown.
  • the charged capacitor can now discharge, the capacitor current, as shown in the lower graph, being a composite current comprising a transient component due to the resonant circuit and the steady state fundamental current.
  • the resonant component produces zero current transitions at instants which do not correspond on a regular basis to maxima in the capacitor voltage graph.
  • the phase of the resonant transient is determined by the instant T 2 at which the switch is re-closed.
  • the current zeros, or rather, a selected one of them can be shifted to coincide with a zero value ofthe capacitor voltage, or at least a very low value. Blocking of the valve at such a point, e.g. T 3 , would then cause very little or no increase in the subsequent valve voltage over and above the supply voltage.
  • the system frequency is 50 Hz and the delay period is four milliseconds, i.e. one-fifth of the cycle period. Comparing the current and capacitor voltage graphs of Figure 3 it may be seen that the first current zero transition Z, coincides with a high value of capacitor voltage (which occurs shortly before the peak of the applied system voltage). The next current zero transition Z-, however, coincides with a zero value of the capacitor voltage as described above and would give an appropriate time to block the valve. The third current zero transition Z j coincides with a moderately low value of capacitor voltage and could be acceptable in some circumstances.
  • Figure 4 illustrates a blocking operation derived from Figure 3 in which the delay period is four milliseconds and the resonant period extends to the second current zero transition Z-,. Two pulses of resonant current of alternating polarity are permitted to flow before the valve is again blocked. The subsequent peak voltage across the valve is almost exactly equal to the applied system voltage because the voltage trapped on the capacitor is almost zero.
  • Figures 5 and 6 The effect of shortening and lengthening the delay period in particular circumstances is illustrated in Figures 5 and 6.
  • the delay period is reduced to three milliseconds, which has the effect of advancing the cycle of resonant current oscillation and making the second current zero, previously Z j , coincide with a significant value of capacitor voltage.
  • the result is an increase of about 35% in the maximum voltage to which the valve is subjected, compared with the condition of Figure 4.
  • a delay period of 5 milliseconds is used, which delays the cycle of resonant current and allows the capacitor voltage to overshoot its zero value in the opposite direction before the current zero transition occurs; this produces an increase in the valve voltage of about 45% compared with the condition of Figure 4.
  • valve voltage peak is significantly less than it is in the absence of the invention, i.e. in Figure 2, where the valve voltage peak exceeds the supply voltage peak by more than 100%.
  • the resonant frequency in Figures 2-6 is approximately 2.5 times the system frequency (i.e. 125 Hz instead of 50 Hz), this despite the fact that, as mentioned earlier, the reactor employed as component L in the TSC circuit (see Figure 1) is selected to give a resonant frequency of between three and five times the system frequency.
  • the inductance of the supply as a whole has to be taken into account. This takes the form of system reactances and coupling transformer reactances which appear in series with the ciirrent-limiting reactor L, increasing the effective value of L and lowering the resonant frequency.
  • the TSC circuit is connected to the high voltage transmission system by a star-delta transformer TF.
  • Star connection of TSC circuits would normally only be considered if the transformer and TSC star points were solidly linked, as shown in Figure 7(b), in which case the thyristor valves could have fewer series 'levels' but would have to be rated for a higher current.
  • the total valve rating of the star connected TSC of Figure 7(b) would be exactly the same as for the delta connected circuit If the line to line voltage of the transformer in Figure 7(a) is V L and the line current is I L then the total valve rating is:
  • any static var compensator employing series circuits of electronic switching means, capacitor and damping reactor will benefit from application of the invention, irrespective of the overall configuration of the compensator.
  • any electronic switching means may be employed in a particular application, or indeed, in some cases, even a very fast acting mechanical switch.
  • the blocking operation comprises the steps of first opening the switching means, waiting for a period, closing the switching means then, at a suitable zero-current point, re-opening the switching means, it may also be advantageous to have an arrangement in which more than one closing operation and more than one delay occurs during the blocking operation.
  • the reactor L in the series circuit has been described as being of such a value as will provide a resonant frequency of between about 150 and 250 Hz, in practice other values are possible also.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Control Of Electrical Variables (AREA)

Abstract

L'invention porte sur un dispositif et un procédé pour réduire les tensions causées à un mécanisme de commutation utilisé pour interrompre le courant capacitif dans un compensateur VAR statique servant à des montages électriques. Au cours de l'ouverture normale d'un commutateur en présence d'un courant nul, une charge élevée reste captive du condensateur en série placé dans le condensateur. Après un autre demi-cycle, la tension appliquée et la tension du condensateur s'ajoutent, imposant ainsi une tension deux fois supérieure à la tension maximale au mécanisme de commutation. L'invention prévoit d'inclure dans le compensateur une bobine d'inductance limitant le courant et un dispositif de commande conçu pour accomplir une séquence d'opérations de commutation sur the thyristor, de façon à faire coïncider un état au moins partiellement déchargé du condensateur avec un état de courant nul du circuit série. De préférence, le thyristor est mis à l'état bloqué si le courant est nul, puis est mis à l'état passant après une pause, après quoi le condensateur résonne avec la bobine d'inductance limitant le courant. Lorsque la tension du condensateur est proche de zéro et que le courant l'est également, le thyristor est remis à l'état bloqué, ne laissant que peu ou pas de décalage sur la tension du dispositif bloqué. La séquence de blocage peut inclure plus d'une ouverture et d'une fermeture avant l'ouverture finale au point de coïncidence.
PCT/GB1996/001935 1995-08-11 1996-08-09 Compensateur var statique Ceased WO1997007581A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU67459/96A AU6745996A (en) 1995-08-11 1996-08-09 Static var compensator

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9516495A GB2304240B (en) 1995-08-11 1995-08-11 Static var compensator
GB9516495.0 1995-08-11

Publications (1)

Publication Number Publication Date
WO1997007581A1 true WO1997007581A1 (fr) 1997-02-27

Family

ID=10779109

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1996/001935 Ceased WO1997007581A1 (fr) 1995-08-11 1996-08-09 Compensateur var statique

Country Status (3)

Country Link
AU (1) AU6745996A (fr)
GB (1) GB2304240B (fr)
WO (1) WO1997007581A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
TWI617109B (zh) * 2012-10-05 2018-03-01 史內德電子工業精簡股份有限公司 無效功率補償器

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FI116922B (fi) * 2004-05-25 2006-03-31 Nokian Capacitors Oy Menetelmä tyristorikytketyn kondensaattoripariston irtikytkemiseksi ja tyristorikytketty kondensaattoriparisto
GB2457709A (en) * 2008-02-25 2009-08-26 Elspec Engineering Ltd Reactive power compensation circuit
WO2010083639A1 (fr) * 2009-01-21 2010-07-29 北京馨容纵横科技发展有限公司 Circuit de commutation à phase commandée de précharge « deux commandent trois » pour commutation de banc de condensateurs
RU2446538C1 (ru) * 2011-01-24 2012-03-27 Олег Фёдорович Меньших Устройство конвертирования активной нагрузки

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2303939A1 (de) * 1973-01-24 1974-07-25 Licentia Gmbh Verfahren zum betrieb eines kondensators zur blindstromkompensation eines wechselstromnetzes
GB2031667A (en) * 1978-09-15 1980-04-23 Westinghouse Electric Corp Hybrid switched-capacitor controlled-inductor static var generaotr and control apparatus
WO1981000648A1 (fr) * 1979-08-28 1981-03-05 Ass Elect Ind Dispositifs d'amortissement de courant
US4571535A (en) * 1984-11-15 1986-02-18 Westinghouse Electric Corp. VAR Generator having controlled discharge of thyristor switched capacitors
US4638238A (en) * 1985-10-15 1987-01-20 Westinghouse Electric Corp Switching technique for thyristor-switched capacitors to achieve network damping
US4719402A (en) * 1986-12-18 1988-01-12 Westinghouse Electric Corp. VAR generator system with minimal standby losses

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2303939A1 (de) * 1973-01-24 1974-07-25 Licentia Gmbh Verfahren zum betrieb eines kondensators zur blindstromkompensation eines wechselstromnetzes
GB2031667A (en) * 1978-09-15 1980-04-23 Westinghouse Electric Corp Hybrid switched-capacitor controlled-inductor static var generaotr and control apparatus
WO1981000648A1 (fr) * 1979-08-28 1981-03-05 Ass Elect Ind Dispositifs d'amortissement de courant
US4571535A (en) * 1984-11-15 1986-02-18 Westinghouse Electric Corp. VAR Generator having controlled discharge of thyristor switched capacitors
US4638238A (en) * 1985-10-15 1987-01-20 Westinghouse Electric Corp Switching technique for thyristor-switched capacitors to achieve network damping
US4719402A (en) * 1986-12-18 1988-01-12 Westinghouse Electric Corp. VAR generator system with minimal standby losses

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
SALAMA M M A ET AL: "FAULT-CURRENT LIMITED WITH THYRISTOR-CONTROLLED IMPEDANCE (FCL-TCI)", IEEE TRANSACTIONS ON POWER DELIVERY, vol. 8, no. 3, 1 July 1993 (1993-07-01), pages 1518 - 1527, XP000403147 *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
TWI617109B (zh) * 2012-10-05 2018-03-01 史內德電子工業精簡股份有限公司 無效功率補償器

Also Published As

Publication number Publication date
GB9516495D0 (en) 1995-10-11
GB2304240B (en) 2000-05-24
GB2304240A (en) 1997-03-12
AU6745996A (en) 1997-03-12

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