CA1159522A - System for coupling a capacitance to an ac voltage network - Google Patents
System for coupling a capacitance to an ac voltage networkInfo
- Publication number
- CA1159522A CA1159522A CA000374211A CA374211A CA1159522A CA 1159522 A CA1159522 A CA 1159522A CA 000374211 A CA000374211 A CA 000374211A CA 374211 A CA374211 A CA 374211A CA 1159522 A CA1159522 A CA 1159522A
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- CA
- Canada
- Prior art keywords
- capacitor
- voltage
- switch
- network
- conductors
- 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.)
- Expired
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Classifications
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03K—PULSE TECHNIQUE
- H03K17/00—Electronic switching or gating, i.e. not by contact-making and –breaking
- H03K17/13—Modifications for switching at zero crossing
- H03K17/136—Modifications for switching at zero crossing in thyristor switches
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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
- H02J3/18—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
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- 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]
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Control Of Electrical Variables (AREA)
- Supply And Distribution Of Alternating Current (AREA)
Abstract
Abstract A series combination of a capacitor, a choke, and a switch is connected across two conductors of an AC voltage network to compensate for inductive reactive loads placed on the network by consumers. The capacitor is advantageous-ly coupled to and decoupled from the conductors in the AC voltage network by closing and opening the series switch. During the time that the switch is opened and the capacitor is decoupled from the network, the capacitor is discharged in accordance with a predetermined discharge characteristic. Prior to coupling the capacitor to the network, the switch is briefly closed at a predetermined phase angle of the voltage of the network, the phase angle being selected in response to the magnitude of the residual voltage present on the capacitor. In this manner, the capacitor can be coupled to the network without causing transients therein. In some embodiments, a plurality of capacitors forming a capacitor battery are each provided with an associated switch so that the capacitors in the capacitor battery can be individually coupled to the network. The phase angle at which each of the capacitors in the capacitor battery is coupled to the network is determined in response to the number of capacitors already coupled to the net-work, and the number of capacitors which remain to be coupled.
Description
9~
Background of the Invention This invention relates generally to systems for connecting and discon-necting a capacitor across two conductors of an AC transmission network, and more particularly, to a method and arrangement whereby the capacitor is coupled to the network at a point in time responsive to the charge on the capacitor.
Consumers which draw electrical energy from an AC transmission network frequently appear to the network as inductive loads with fluctuating levels of reactive power drain. Such fluctuations in the reactive energy components sub-stantially interfere with the operation of the AC network. Generally, the reactive component of the load is compensated by a battery of capacitors which is arranged between the phases of the AC network. Predetermined sections of the capacitor battery are switched onto the line by switches which are in series with the battery, depending upon the magnitude of the required reactive cornpen-sation power. Thus, some or all of the capacitor sections in a battery may be connected between the conductors of the AC network by the switches in series with the capacitor sections. In such systems, the capacitor sections are disconnected from the network by opening the switches at the particular points in time where the network currents cross a zero current value. The disconnected capacitors remain initially charged at the peak value of the voltage between the conductors, and no switching-off transients occur. When the capacitors are reconnected to the AC network by closing the series switches, switching currents and transients can be substantially avoided if the capacitors are charged to the peak value of the-network voltage across the respective conductors~ and the series switches are closed exactly at the instant when the conductor voltage reaches the corre-sponding peak value. This corresponds to a zero voltage level across the series switch just prior to its closing. In order to improve the safety of the AC net-work, circuitry is generally provided for discharging the capacitor during the -1- ~
Z
period that it is disconnected from the line, thereby causing capacitor voltage to decay. In such a system, therefore, the capacitor must again be charged to the peak network voltage before it is reconnected to the AC network.
A known system which utilizes a parallel arrangement of thyristors which are poled for conduction in opposite directions is shown in German reference DE-OS 23 03 939. The system described therein is provided with a choke coil in series with the thyristor switching arrangement for limiting the rate of rise of current. The system further provides a series circuit consisting of an auxiliary thyristor switch and a voltage source connected by an inductance in parallel with the capacitor, for charging and discharging the capacitor. Within the first quarter-period after the capacitor is disconnected from the network, the capacitor is discharged to zero voltage by closing the auxiliary switch, and within a quarter-period before the capacitor is reconnected to the network, it is recharged to the peak network voltage by operating the auxiliary thyristor switch again. Since, in this known system, the capacitor is completely dis-charged and must be recharged to the peak voltage prior to being reconnected to the network, the phase angle at which the auxiliary thyristor switch is closed to recharge the capacitor (hereinafter "charging closing angle") is fixed.
Figure 1 of the German reference describes a circuit in which the capacitor is charged and discharged by the operation of a single thyristor switch. In that known system, the capacitor is charged and discharged by the AC voltage of the network itself. In addition, the phase angles at which the thyristor switch operates to charge and discharge the capacitor, and the phase angle at which the capacitor is connected to the network, are fixed. Thus, the control system for the thyristor switch provides switching-on pulses to the thyristor switch only if the capacitor is charged and the network voltage has reached the appropriate peak value, as determined by a minimum voltage across the thyristor switch. In this known circuit, therefore, the capacitor is completely discharged after the thyristor switch is opened so as to disconnect the capacitor from the network, by a brief, second firing of the thyristor switch.
The series choke which is provided in the known arrangement forrns an inductive storage device which is initially not charged when the capacitor is connected to the network, thereby permitting transients to occur when the capacitor is charged to the peak of the network conductor voltage. The German reference proposes an increase in the charging bias of the capacitor by shifting the charging firing point so as to be closer to the network voltage peak. This arrangement is supposed to achieve connection of the capacitor to the network without producing equalization currents. However, in this known system, current pulses having a magnitude corresponding to the maximum capacitor charge are always generated during charging and discharging, such current pulses correspond-ing to a maximum harmonic stress on the network.
It is, therefore, an object of this invention to maintain the current pulses required for charging the capacitor as small as possible.
Summary of the Invention The foregoing and other objects are achieved by this invention which provide a system for connecting and disconnecting a capacitor from an AC trans-mission network. The capacitor is discharged in accordance with a predetermined discharge characteristic, such discharge of the capacitor being performed without control and in accordance with a predetermined time constant which is a multiple of the AC voltage period. The moment of time at which the capacitor is connected to the network with respect to the phase angle of the network AC voltage is deter-mined as a function of the voltage on the capacitor.
Upon being disconnected from the network, the capacitor is discharged by leakage currents, or by a high-resistance discharge resistor arranged parallel A~ f,:~
to the capacitor. The time constant of the discharge may be advantageously selected to be a long period of time, unless a rapid discharge of the capacitor is desired for safety and other reasons. Thus, the capacitor is not discharged in response to a controlled operation of a switch. If a considerable residual capacitor charge is present on the capacitor when the capacitor is next recon-nected to the AC network, and advantageously small charging current is required to recharge the capacitor to the peak network voltage. The charge current is controlled by operating the switch at a phase angle whic-n is correlated to the residual capacitor charge. Thus, the phase angle at which the switch is operated is not fixed, as in known systems. The charging process may be controlled by merely determining the voltage on the capacitor prior to its being reconnected, and determining in a switch control unit the phase angle of the network AC volt-age at which the capacitor will be connected to the AC network. Since the net-work AC voltage can be determined from the voltage across the switch if the capacitor voltage is known, the closing of the switch for initiating charging can be synchronized with the voltage across the switch, instead of with the network AC voltage.
In embodiments of the invention wherein the capacitor is formed of a plurality of individual capacitors in a capacitor battery, the individual capaci-tors may be connected in steps by respective switches between phases of the AC
voltage network. Such a plurality of individual capacitors may be provided for compensating a variable reactive power, the choice of the appropriate phase angle at which respective capacitors are coupled to the network being dependent upon the number of capacitors in the capacitor battery which are already connected to the network~ and the number of capacitors remalning unconnected. Such informa-tion could be stored in a switch control unit so as to permit the switch control unit to determine the optimum phase angle at which the capaci~ors are charged~
z in response to the numbers of connected and unconnected capacitors.
Thus, in accordance with one broad aspect of the invention, there is provided a method for connecting and disconnecting a capacitor between two conductors of an AC voltage network, the capacitor being arranged in series with a switch, the method comprising the steps of: determining a phase angle of the AC voltage across the two conductors in response to the voltage across the two conductors of the AC voltage network and a voltage across the capacitor, at which phase angle the swi~ch is temporarily closed so as to charge the capacitor from said voltage across the capacitor to a voltage which corresponds to a peak voltage value of the AC voltage across the conductors; connecting the capacitor to the conductors of the AC voltage network when a voltage across the switch reaches a predetermined minimum voltage value; disconnecting the capacitor from the conductors of the AC voltage network by opening the switch at a moment of time when a current flowing through the switch reaches a zero value; and discharging the capacitor during the time that the switch is open, said discharging being performed in accordance with a predetermined discharge characteristic having a predetermined time constant which corresponds to a multiple of a period of an AC voltage across the conductors of the AC voltage network.
In accordance with another broad aspect of the invention there is provided a circuit arrangement for connecting and disconnecting a capacitor between two conductors of an AC voltage network, the circuit arrangement com-prising: choke means connected in series with the capacitor; switch means having at least first and second thyristors connected in parallel with one another and poled for conduction in opposite directions, said switch means being connected in series with the capacitor and said choke ~eans; capacitor voltage measurement means for producing a first signal corresponding to a vol-: -5-.
` ` ~, :
35'~2 tage across the capacitor; phase sensor means for producing a second signal corresponding to the phase of the AC voltage network; and s~lcch control means for controlling the conductive state o~ said switch means in response to said first and second signals for momentarily closing said switch means so as to charge the capacitor to a voltage which corresponds to a peak voltage value of the AC voltage across the conductors, said momentary closing occurring at a selectable moment of time corresponding to a selected phase angle of said vol-tage across the conductors of the AC voltage network, said phase angle being selected in response to the magnitude of a voltage across the capacitor.
Brief Description of the Drawing Comprehension of the invention is facilitated by reading the fol-lowing detailed description în which:
Figure 1 illustrates, partly in schematic and partly in block and line form, an illustrative circuit for coupling a capacitor to a single-phase AC voltage network, in accordance wi-th the principles of the invention, Figure 2 shows a plurality of waveforms on correspondingly matched time scales which are useful in explaining the operation of the circuit of Figure l;
Figure 3 shows a plurality of superimposed waveforms which are use-ful in explaining the charging of the capacitor for different residual capacitor charges;
Figure 4 illustrates an arrangement, partly in schematic form and partly in block and line representation, for switching capacitors between con-ductors of a three-phase voltage network; and Figure 5 shows a plurality of waveforms which are useful for ex-plaining the operation of the embodiment of Figure 4.
Detailed Description Figure 1 shows a capacitor 3 which is coupled to the serial combina--5a-~.
,, ., ~ ~ ' .
~lS~S'~
tion of a choke 4 and a swltch 5~ Capacitor 3, choke 4, and switch 5 are arranged hetween conducto~s 1 and 2 of an AC voltage network. At such time as a consumer ~not shown) draws a level of reactive power from the network which exceeds a predetermined value, a capacitor is connected to the network at con-ductors 1 and 2 to achieve compensation. In this embodiment, switch 5 consists of the advantageous combination of two thyristor valves 5a and 5b which are arranged so as to conduct current in opposite directions from one another.
Thyristor valves 5a and -5b-' :- :, , . :
, ' ' ',', ' ~ , 5b are operated by a control unit 6. Control unit 6 provides firing pulses to the thyristor valves at firing phase angles which are determined in a switch control 7. Switch control 7 receives at an input a signal corresponding to a voltage Vc across capacitor 3, the voltage Vc being sensed by a pick-up device 8.
A phase measuring unit 9 senses the phase of the network AC voltage Vw across conductors 1 and 2, and provides a signal to control unit 6 which permits the firing pulses supplied to thyristor valves 5a and 5b to be synchronized with a predetermined firing angle of the network AC voltage.
During the time that the thyristor valves in switch 5 are opened, the voltage Vc across capacitor 3 will decay slowly. Such a discharge of the capacitor may occur naturally through leakage currents, or by a separate high resistance 10 arranged in shunt with the capacitor which insures that the capacitor will be safely discharged if the system is shut down. The decay of voltage Vc is exponential in accordance with a time constant which is a multiple of the period of one cycle of the network AC voltage. In one embodiment, the time constant may be in the order of several minutes. Thus, the rate of decay of capacitor voltage Vc is, in this embodiment, governed by the combination of capacitor 3 and resistor 10 so as to be exponential and not controlled by either switch 5 or its control circuitry.
If a command signal for either connecting or disconnecting capacitor 3 is provided by a reactive power control (not shown) at a command signal input 11 of switch control 7, the processes which are illustrated in the waveforms of Figure 2 will be initiated. The following process phases are distinguishable ; from the waveforms of Figure 2:
charging capacitor 3 by closing switch 5, illustratively because thyristor valve Sa is fired during the time period between tl and t2;
a switching readiness phase when switch 5 is opened during the time ' period between t2 and t3;
operation with the capacitor connected, switch 5 being closed during the time period between t3 and t4 by alternately firing thyristor valves 5a and 5b; and operation with the capacitors disconnected, switch 5 being open beginning at a time t4.
In Figure 2, Figure 2a shows the waveform of network AC voltage Vw;
Figure 2b shows the waveform of current i which flows through capacitor 3, choke 4 and switch 5, in series; Figure 2c shows the waveform of voltage Vc across capacitor 3; Figure 2d shows the waveform of a voltage Vs across switch 5.
As stated, it is an object of this invention that capacitor 3 be con-nected to the network in a manner which avoids the occurrence of transients.
Thus, capacitor 3 must be charged to an appropriate maximum voltage V and the instant t3, at which capacitor 3 is connected to the network, must be selected so that current i is sinusoidal. Since the series circuit consisting of capacitor 3, choke 4, and switch 5 has practically no ohmic resistance, voltages VW and Vc are in phase during the period between t3 and t4, while corresponding current i leads by 90 relative thereto. The instant in time t3 at which capacitor 3 is connected to the network occurs at a peak of the sinusoldal volt-age Vw.
The disconnecting of capacitor 3 from the network occurs at time t4 which, in order to avoid transients, occurs at a zero crossing of the waveform of current i. This may be achieved by suppressing a firing pulse for thyristor valve 5b while thyristor valve 5a is simultaneously extinguished as a result of the zero crossing of the current. At this point, the high-resistance discharge of capacitor 3 through resistor 10 causes an exponential decay in capacitor volt~
age Vc which decreases slowly for time beyond t~. Simultaneously, switch voltage : -' 5~
VS = VC ~ VW increases across switch 5.
Capacitor 3 is therefore disconnected from the network by blocking firing pulses to thyristor valves 5a and 5b upon the occurrence of an appropriate disconnect command from the compensation control. As previously stated~ distor-tion of the network AC voltage is prevented by first charging capacitor 3 to a voltage V , prior to its being connected to the network. Such charging is accomplished by closing switch 5 briefly at time tl. The current pulse generated thereby can be considered as the first half-period of a transient, the duration of which determines the closing duration of switch 5. If, for example, thyristor valve 5a is fired at time tl it will extinguish itself at time t2. Thus, the charging of the capacitor depends upon the resonant frequency of the series cir-cuit consisting of capacitor 3, choke 4 and switch 5; the residual capacitor voltage present across capacitor 3 prior to the charging; and the phase of the network voltage. For a given capacitance value of capacitor 3 and inductance value of choke 4, the instant at which switch 5 closes relative to the phase of the network AC voltage, i.e., the charging closing angle, can therefore be deter-mined for each possible value of the residual capacitor voltage, in such a manner that the capacitor is charged to the voltage V . The solid waveform lines in Figures 2b and 2d relate to the case wherein a considerable residual capacitor voltage is still present. The waveforms shown by dashed curves represent the case wherein the residual capacitor voltage has decayed practically to zero since the last opening of the switch. By shifting the charging-closing instant by a time period ~t, the capacitor can be charged to the voltage V in this case.
For most values of the residual capacitor voltage, charging-closing instant tl, in this embodiment, occurs shortly after the positive-going zero crossing of net-work AC voltage Vw. Switch 5 must therefore remain open for approximately three-quarters of a network voltage period after time t2, until the network AC voltage : ' , ' ' ' kas again reached the peak value of the same polarity and the capacitor can be connected without producing a transient. In this embodiment, switch 5 remains open until time t3. It should be understood, that persons skilled in the art can configure circuitry, in light of this teaching, which operates in a polarity opposite to that of the specific illustrative embodiment described herein.
With switch 5 in an open state, the phase of network voltage Vw can be determined from the waveform of voltage Vs across switch 5, by subtracting there-from capacitor voltage Vc. It is therefore possible, and in many cases more advantageous from a circuit design standpoint, to determine the closing times of the thyristor valves from switch voltage Vs instead of the network voltage Vw which, in this embodiment, is monitored by phase measuring unit 9.
Figure 3 shows the waveforms of the voltage across capacitor 3 for two levels of residual capacitor voltage, Vcl and Vc2, respectively, superimposed on the same voltage-time coordinates so as to be comparable with network AC volt-age Vw. Capacitor voltage waveform Vcl illustrates the case where the capacitor voltage has decayed to 0.6 V a ; and capacitor voltage waveform Vc2 illustrates the case where the capacitor is completely discharged. In Figure 2c it had been assumed that the voltage V corresponds to the peak value V0 of network AC
voltage Vw. However, in order to connect the capacitor to the network without producing transients, a voltage must be present across the capacitor such that, in the steady-state condition wherein the capacitor is connected to the network, the capacitor peak voltage Vmax is greater than V0. Vmax equals to V0 only in the case of a series circuit wherein the inductances connected between the con-ductors can be ignored. However, if thyristor valves are used as the switch, choke 4 must have a minimum inductance value such that when the swltch is closed during the period between times t3 and t4, the sinusoidal voltage waveform Vc across the capacitor consists of the network AC vo]tage Vw and a voltage VL which , : ~
` . , is induced by the choke and is of an opposite phase with respect to capacitor voltage Vc. The voltage Vmax to which t'ne capacitor is charged must represent an increase over peak value V0 of the network AC voltage by an amount corres-ponding to VL9 as shown in Figure 3. A special case applies if the capacitor is only slightly discharged and must be charged up to V from a residual capacitor voltage which is greater than the peak value of the network voltage V0. In such a case, a partial discharge of the capacitor must first occur in a transient, and subsequently the capacitor is charged to V by reversal of the direction of flow of the current.
In addition to a measured instantaneous capacitor voltage value, the determination of the correct closing angle must also take into consideration the value of the impedance of the circuit, or the resonant frequency of the series circuit. In embodiments wherein several series circuits consisting of capacitors, coils, and switches are connected between the two network phases, the determination of the correct charging-closing angle and the correct voltage V must take into consideration the number of capacitors which are already connected to the network phases and the number of capacitors which are to be additionally connected at the next connecting instant.
The circuit described for a single phase AC network can be applied to a polyphase AC network. A suitable series circuit consisting of a capacitor, a switch, and an optional choke can be used between any two of the current-carrying phases of the network. Additionally, such series circuits may be arranged between a respective phase and a neutral conductor.
Figure 4 shows a three-phase AC network having network conductors R, S, and T, the voltage waveforms on each such conductors being shown in Figure 5a.
A three-phase transformer 20 in Figure ~ is shown to have three primary windings (not specifically ident:Lfied) in a Y-circuit configuration, and three secondary z windings, also in a Y-circuit configuration, each such secondary winding having a respective one of conductors 22, 32, and 42 connected thereto. A conductor 21 is connected to the central junction of the secondary windings so as to form an artificial neutral terminal. Each of the conductors 22, 32, and 42 is coupled to the artificial neutral by a respective one of capacitors 23, 339 and 43; a respective one of chokes 24, 34, and 44; and a respective one of thyristor valve arrangements 25, 35, and 45. The voltage across each of capacitors 23, 33, and 43; and the voltage across each of thyristor valve arrangements 25, 35, and 45;
are conducted to a central switching control 26. Central switching control 26 determines the times for opening and closing each of the thyristor valves and delivers corresponding switching pulses to thyristor valve arrangements 25, 35, and 45, in accordance with the phase of the individual conductor voltages and the capacitor voltages. In this embodiment, the switching instants for each of the thyristor valve arrangements are determined independently of one another.
However, in embodiments wherein a plurality of capacitors in the form of a capacitor battery are used for each phase, each such capacitor in the capacitor battery is provided with a separate switch and the charging-closing angles or each of the capacitors in a capacitor battery is determined in accordance with the switching state of the other capacitors in the same capacitor battery, as described hereinabove with respect to the illustrative single phase embodiment.
Capacitors 23, 33, and 43 are all disconnected by the simultaneous removal of all firing pulses to thyristor valve arrangements 25, 35, and 45.
Thus, the thyristor valves are each always extinguished so as to be nonconductive at the zero crossing of the respective current. Accordingly, two of the capaci-tors are always disconnected at the maximum capacitor voltage of the same polarity with a phase shift corresponding to 120, while the third capacitor is already disconnected at the maximum voltage of opposite polarity with a phase "~
3~
shift corresponding to 60 relative to the first capacitor. Figure Sb illus-trates the situation wherein capacitors having vanishing residual capacitor charges are reconnected. The capacitors are connected by briefly closing their respective thyristor valves so that they may be charged to the maximum value of the prevailing polarity of the respective p~lase. Figures 5c and 5d illustrate the voltages across the capacitors and thyristor valves, respectively, in a manner corresponding to Figures 2c and 2d.
The charging-closing angles corresponding to the respective residual capacitor voltages are determined according to mathematical functions which can be determined empirically or by computing the solution of the differential equations of the system. Control unit 6 in Figure 1 and central switching con-trol 26 in Figure 4, which determine the charging-closing angles of their respec-tive systems, may each be formed of a function generator which is programmed with appropriate characteristic curves. Switch control 7 in Figure l may be a micro-processor which is used advantageously to determine the firing angles and the phase of the network voltage, or of the voltage across the thyristor valves, from stored measurement values.
It should be noted that only a few circuit components, arranged in a relatively simple circuit, are required to practice the invention. In parti-cular, in embodiments of the invention wherein only two thyristor valves are used in a switch, no further circuitry for quenching the thyristor valves is required because the thyristor valves always extinguish themselves at a ~ero crossing of their respective current waveforms.
It is to be remembered that, although the inventive concept disclosed herein is described in terms of specific embodiments and particular applications, persons skilled in the pertinent art can generate additional embodiments without departing from the spirit or exceeding the scope of the invention. The drawings and descriptions in this disclosure are merely illustrative embodiments proffered to facilitate comprehension of the invention, and should not be construed to limit the scope thereof.
Background of the Invention This invention relates generally to systems for connecting and discon-necting a capacitor across two conductors of an AC transmission network, and more particularly, to a method and arrangement whereby the capacitor is coupled to the network at a point in time responsive to the charge on the capacitor.
Consumers which draw electrical energy from an AC transmission network frequently appear to the network as inductive loads with fluctuating levels of reactive power drain. Such fluctuations in the reactive energy components sub-stantially interfere with the operation of the AC network. Generally, the reactive component of the load is compensated by a battery of capacitors which is arranged between the phases of the AC network. Predetermined sections of the capacitor battery are switched onto the line by switches which are in series with the battery, depending upon the magnitude of the required reactive cornpen-sation power. Thus, some or all of the capacitor sections in a battery may be connected between the conductors of the AC network by the switches in series with the capacitor sections. In such systems, the capacitor sections are disconnected from the network by opening the switches at the particular points in time where the network currents cross a zero current value. The disconnected capacitors remain initially charged at the peak value of the voltage between the conductors, and no switching-off transients occur. When the capacitors are reconnected to the AC network by closing the series switches, switching currents and transients can be substantially avoided if the capacitors are charged to the peak value of the-network voltage across the respective conductors~ and the series switches are closed exactly at the instant when the conductor voltage reaches the corre-sponding peak value. This corresponds to a zero voltage level across the series switch just prior to its closing. In order to improve the safety of the AC net-work, circuitry is generally provided for discharging the capacitor during the -1- ~
Z
period that it is disconnected from the line, thereby causing capacitor voltage to decay. In such a system, therefore, the capacitor must again be charged to the peak network voltage before it is reconnected to the AC network.
A known system which utilizes a parallel arrangement of thyristors which are poled for conduction in opposite directions is shown in German reference DE-OS 23 03 939. The system described therein is provided with a choke coil in series with the thyristor switching arrangement for limiting the rate of rise of current. The system further provides a series circuit consisting of an auxiliary thyristor switch and a voltage source connected by an inductance in parallel with the capacitor, for charging and discharging the capacitor. Within the first quarter-period after the capacitor is disconnected from the network, the capacitor is discharged to zero voltage by closing the auxiliary switch, and within a quarter-period before the capacitor is reconnected to the network, it is recharged to the peak network voltage by operating the auxiliary thyristor switch again. Since, in this known system, the capacitor is completely dis-charged and must be recharged to the peak voltage prior to being reconnected to the network, the phase angle at which the auxiliary thyristor switch is closed to recharge the capacitor (hereinafter "charging closing angle") is fixed.
Figure 1 of the German reference describes a circuit in which the capacitor is charged and discharged by the operation of a single thyristor switch. In that known system, the capacitor is charged and discharged by the AC voltage of the network itself. In addition, the phase angles at which the thyristor switch operates to charge and discharge the capacitor, and the phase angle at which the capacitor is connected to the network, are fixed. Thus, the control system for the thyristor switch provides switching-on pulses to the thyristor switch only if the capacitor is charged and the network voltage has reached the appropriate peak value, as determined by a minimum voltage across the thyristor switch. In this known circuit, therefore, the capacitor is completely discharged after the thyristor switch is opened so as to disconnect the capacitor from the network, by a brief, second firing of the thyristor switch.
The series choke which is provided in the known arrangement forrns an inductive storage device which is initially not charged when the capacitor is connected to the network, thereby permitting transients to occur when the capacitor is charged to the peak of the network conductor voltage. The German reference proposes an increase in the charging bias of the capacitor by shifting the charging firing point so as to be closer to the network voltage peak. This arrangement is supposed to achieve connection of the capacitor to the network without producing equalization currents. However, in this known system, current pulses having a magnitude corresponding to the maximum capacitor charge are always generated during charging and discharging, such current pulses correspond-ing to a maximum harmonic stress on the network.
It is, therefore, an object of this invention to maintain the current pulses required for charging the capacitor as small as possible.
Summary of the Invention The foregoing and other objects are achieved by this invention which provide a system for connecting and disconnecting a capacitor from an AC trans-mission network. The capacitor is discharged in accordance with a predetermined discharge characteristic, such discharge of the capacitor being performed without control and in accordance with a predetermined time constant which is a multiple of the AC voltage period. The moment of time at which the capacitor is connected to the network with respect to the phase angle of the network AC voltage is deter-mined as a function of the voltage on the capacitor.
Upon being disconnected from the network, the capacitor is discharged by leakage currents, or by a high-resistance discharge resistor arranged parallel A~ f,:~
to the capacitor. The time constant of the discharge may be advantageously selected to be a long period of time, unless a rapid discharge of the capacitor is desired for safety and other reasons. Thus, the capacitor is not discharged in response to a controlled operation of a switch. If a considerable residual capacitor charge is present on the capacitor when the capacitor is next recon-nected to the AC network, and advantageously small charging current is required to recharge the capacitor to the peak network voltage. The charge current is controlled by operating the switch at a phase angle whic-n is correlated to the residual capacitor charge. Thus, the phase angle at which the switch is operated is not fixed, as in known systems. The charging process may be controlled by merely determining the voltage on the capacitor prior to its being reconnected, and determining in a switch control unit the phase angle of the network AC volt-age at which the capacitor will be connected to the AC network. Since the net-work AC voltage can be determined from the voltage across the switch if the capacitor voltage is known, the closing of the switch for initiating charging can be synchronized with the voltage across the switch, instead of with the network AC voltage.
In embodiments of the invention wherein the capacitor is formed of a plurality of individual capacitors in a capacitor battery, the individual capaci-tors may be connected in steps by respective switches between phases of the AC
voltage network. Such a plurality of individual capacitors may be provided for compensating a variable reactive power, the choice of the appropriate phase angle at which respective capacitors are coupled to the network being dependent upon the number of capacitors in the capacitor battery which are already connected to the network~ and the number of capacitors remalning unconnected. Such informa-tion could be stored in a switch control unit so as to permit the switch control unit to determine the optimum phase angle at which the capaci~ors are charged~
z in response to the numbers of connected and unconnected capacitors.
Thus, in accordance with one broad aspect of the invention, there is provided a method for connecting and disconnecting a capacitor between two conductors of an AC voltage network, the capacitor being arranged in series with a switch, the method comprising the steps of: determining a phase angle of the AC voltage across the two conductors in response to the voltage across the two conductors of the AC voltage network and a voltage across the capacitor, at which phase angle the swi~ch is temporarily closed so as to charge the capacitor from said voltage across the capacitor to a voltage which corresponds to a peak voltage value of the AC voltage across the conductors; connecting the capacitor to the conductors of the AC voltage network when a voltage across the switch reaches a predetermined minimum voltage value; disconnecting the capacitor from the conductors of the AC voltage network by opening the switch at a moment of time when a current flowing through the switch reaches a zero value; and discharging the capacitor during the time that the switch is open, said discharging being performed in accordance with a predetermined discharge characteristic having a predetermined time constant which corresponds to a multiple of a period of an AC voltage across the conductors of the AC voltage network.
In accordance with another broad aspect of the invention there is provided a circuit arrangement for connecting and disconnecting a capacitor between two conductors of an AC voltage network, the circuit arrangement com-prising: choke means connected in series with the capacitor; switch means having at least first and second thyristors connected in parallel with one another and poled for conduction in opposite directions, said switch means being connected in series with the capacitor and said choke ~eans; capacitor voltage measurement means for producing a first signal corresponding to a vol-: -5-.
` ` ~, :
35'~2 tage across the capacitor; phase sensor means for producing a second signal corresponding to the phase of the AC voltage network; and s~lcch control means for controlling the conductive state o~ said switch means in response to said first and second signals for momentarily closing said switch means so as to charge the capacitor to a voltage which corresponds to a peak voltage value of the AC voltage across the conductors, said momentary closing occurring at a selectable moment of time corresponding to a selected phase angle of said vol-tage across the conductors of the AC voltage network, said phase angle being selected in response to the magnitude of a voltage across the capacitor.
Brief Description of the Drawing Comprehension of the invention is facilitated by reading the fol-lowing detailed description în which:
Figure 1 illustrates, partly in schematic and partly in block and line form, an illustrative circuit for coupling a capacitor to a single-phase AC voltage network, in accordance wi-th the principles of the invention, Figure 2 shows a plurality of waveforms on correspondingly matched time scales which are useful in explaining the operation of the circuit of Figure l;
Figure 3 shows a plurality of superimposed waveforms which are use-ful in explaining the charging of the capacitor for different residual capacitor charges;
Figure 4 illustrates an arrangement, partly in schematic form and partly in block and line representation, for switching capacitors between con-ductors of a three-phase voltage network; and Figure 5 shows a plurality of waveforms which are useful for ex-plaining the operation of the embodiment of Figure 4.
Detailed Description Figure 1 shows a capacitor 3 which is coupled to the serial combina--5a-~.
,, ., ~ ~ ' .
~lS~S'~
tion of a choke 4 and a swltch 5~ Capacitor 3, choke 4, and switch 5 are arranged hetween conducto~s 1 and 2 of an AC voltage network. At such time as a consumer ~not shown) draws a level of reactive power from the network which exceeds a predetermined value, a capacitor is connected to the network at con-ductors 1 and 2 to achieve compensation. In this embodiment, switch 5 consists of the advantageous combination of two thyristor valves 5a and 5b which are arranged so as to conduct current in opposite directions from one another.
Thyristor valves 5a and -5b-' :- :, , . :
, ' ' ',', ' ~ , 5b are operated by a control unit 6. Control unit 6 provides firing pulses to the thyristor valves at firing phase angles which are determined in a switch control 7. Switch control 7 receives at an input a signal corresponding to a voltage Vc across capacitor 3, the voltage Vc being sensed by a pick-up device 8.
A phase measuring unit 9 senses the phase of the network AC voltage Vw across conductors 1 and 2, and provides a signal to control unit 6 which permits the firing pulses supplied to thyristor valves 5a and 5b to be synchronized with a predetermined firing angle of the network AC voltage.
During the time that the thyristor valves in switch 5 are opened, the voltage Vc across capacitor 3 will decay slowly. Such a discharge of the capacitor may occur naturally through leakage currents, or by a separate high resistance 10 arranged in shunt with the capacitor which insures that the capacitor will be safely discharged if the system is shut down. The decay of voltage Vc is exponential in accordance with a time constant which is a multiple of the period of one cycle of the network AC voltage. In one embodiment, the time constant may be in the order of several minutes. Thus, the rate of decay of capacitor voltage Vc is, in this embodiment, governed by the combination of capacitor 3 and resistor 10 so as to be exponential and not controlled by either switch 5 or its control circuitry.
If a command signal for either connecting or disconnecting capacitor 3 is provided by a reactive power control (not shown) at a command signal input 11 of switch control 7, the processes which are illustrated in the waveforms of Figure 2 will be initiated. The following process phases are distinguishable ; from the waveforms of Figure 2:
charging capacitor 3 by closing switch 5, illustratively because thyristor valve Sa is fired during the time period between tl and t2;
a switching readiness phase when switch 5 is opened during the time ' period between t2 and t3;
operation with the capacitor connected, switch 5 being closed during the time period between t3 and t4 by alternately firing thyristor valves 5a and 5b; and operation with the capacitors disconnected, switch 5 being open beginning at a time t4.
In Figure 2, Figure 2a shows the waveform of network AC voltage Vw;
Figure 2b shows the waveform of current i which flows through capacitor 3, choke 4 and switch 5, in series; Figure 2c shows the waveform of voltage Vc across capacitor 3; Figure 2d shows the waveform of a voltage Vs across switch 5.
As stated, it is an object of this invention that capacitor 3 be con-nected to the network in a manner which avoids the occurrence of transients.
Thus, capacitor 3 must be charged to an appropriate maximum voltage V and the instant t3, at which capacitor 3 is connected to the network, must be selected so that current i is sinusoidal. Since the series circuit consisting of capacitor 3, choke 4, and switch 5 has practically no ohmic resistance, voltages VW and Vc are in phase during the period between t3 and t4, while corresponding current i leads by 90 relative thereto. The instant in time t3 at which capacitor 3 is connected to the network occurs at a peak of the sinusoldal volt-age Vw.
The disconnecting of capacitor 3 from the network occurs at time t4 which, in order to avoid transients, occurs at a zero crossing of the waveform of current i. This may be achieved by suppressing a firing pulse for thyristor valve 5b while thyristor valve 5a is simultaneously extinguished as a result of the zero crossing of the current. At this point, the high-resistance discharge of capacitor 3 through resistor 10 causes an exponential decay in capacitor volt~
age Vc which decreases slowly for time beyond t~. Simultaneously, switch voltage : -' 5~
VS = VC ~ VW increases across switch 5.
Capacitor 3 is therefore disconnected from the network by blocking firing pulses to thyristor valves 5a and 5b upon the occurrence of an appropriate disconnect command from the compensation control. As previously stated~ distor-tion of the network AC voltage is prevented by first charging capacitor 3 to a voltage V , prior to its being connected to the network. Such charging is accomplished by closing switch 5 briefly at time tl. The current pulse generated thereby can be considered as the first half-period of a transient, the duration of which determines the closing duration of switch 5. If, for example, thyristor valve 5a is fired at time tl it will extinguish itself at time t2. Thus, the charging of the capacitor depends upon the resonant frequency of the series cir-cuit consisting of capacitor 3, choke 4 and switch 5; the residual capacitor voltage present across capacitor 3 prior to the charging; and the phase of the network voltage. For a given capacitance value of capacitor 3 and inductance value of choke 4, the instant at which switch 5 closes relative to the phase of the network AC voltage, i.e., the charging closing angle, can therefore be deter-mined for each possible value of the residual capacitor voltage, in such a manner that the capacitor is charged to the voltage V . The solid waveform lines in Figures 2b and 2d relate to the case wherein a considerable residual capacitor voltage is still present. The waveforms shown by dashed curves represent the case wherein the residual capacitor voltage has decayed practically to zero since the last opening of the switch. By shifting the charging-closing instant by a time period ~t, the capacitor can be charged to the voltage V in this case.
For most values of the residual capacitor voltage, charging-closing instant tl, in this embodiment, occurs shortly after the positive-going zero crossing of net-work AC voltage Vw. Switch 5 must therefore remain open for approximately three-quarters of a network voltage period after time t2, until the network AC voltage : ' , ' ' ' kas again reached the peak value of the same polarity and the capacitor can be connected without producing a transient. In this embodiment, switch 5 remains open until time t3. It should be understood, that persons skilled in the art can configure circuitry, in light of this teaching, which operates in a polarity opposite to that of the specific illustrative embodiment described herein.
With switch 5 in an open state, the phase of network voltage Vw can be determined from the waveform of voltage Vs across switch 5, by subtracting there-from capacitor voltage Vc. It is therefore possible, and in many cases more advantageous from a circuit design standpoint, to determine the closing times of the thyristor valves from switch voltage Vs instead of the network voltage Vw which, in this embodiment, is monitored by phase measuring unit 9.
Figure 3 shows the waveforms of the voltage across capacitor 3 for two levels of residual capacitor voltage, Vcl and Vc2, respectively, superimposed on the same voltage-time coordinates so as to be comparable with network AC volt-age Vw. Capacitor voltage waveform Vcl illustrates the case where the capacitor voltage has decayed to 0.6 V a ; and capacitor voltage waveform Vc2 illustrates the case where the capacitor is completely discharged. In Figure 2c it had been assumed that the voltage V corresponds to the peak value V0 of network AC
voltage Vw. However, in order to connect the capacitor to the network without producing transients, a voltage must be present across the capacitor such that, in the steady-state condition wherein the capacitor is connected to the network, the capacitor peak voltage Vmax is greater than V0. Vmax equals to V0 only in the case of a series circuit wherein the inductances connected between the con-ductors can be ignored. However, if thyristor valves are used as the switch, choke 4 must have a minimum inductance value such that when the swltch is closed during the period between times t3 and t4, the sinusoidal voltage waveform Vc across the capacitor consists of the network AC vo]tage Vw and a voltage VL which , : ~
` . , is induced by the choke and is of an opposite phase with respect to capacitor voltage Vc. The voltage Vmax to which t'ne capacitor is charged must represent an increase over peak value V0 of the network AC voltage by an amount corres-ponding to VL9 as shown in Figure 3. A special case applies if the capacitor is only slightly discharged and must be charged up to V from a residual capacitor voltage which is greater than the peak value of the network voltage V0. In such a case, a partial discharge of the capacitor must first occur in a transient, and subsequently the capacitor is charged to V by reversal of the direction of flow of the current.
In addition to a measured instantaneous capacitor voltage value, the determination of the correct closing angle must also take into consideration the value of the impedance of the circuit, or the resonant frequency of the series circuit. In embodiments wherein several series circuits consisting of capacitors, coils, and switches are connected between the two network phases, the determination of the correct charging-closing angle and the correct voltage V must take into consideration the number of capacitors which are already connected to the network phases and the number of capacitors which are to be additionally connected at the next connecting instant.
The circuit described for a single phase AC network can be applied to a polyphase AC network. A suitable series circuit consisting of a capacitor, a switch, and an optional choke can be used between any two of the current-carrying phases of the network. Additionally, such series circuits may be arranged between a respective phase and a neutral conductor.
Figure 4 shows a three-phase AC network having network conductors R, S, and T, the voltage waveforms on each such conductors being shown in Figure 5a.
A three-phase transformer 20 in Figure ~ is shown to have three primary windings (not specifically ident:Lfied) in a Y-circuit configuration, and three secondary z windings, also in a Y-circuit configuration, each such secondary winding having a respective one of conductors 22, 32, and 42 connected thereto. A conductor 21 is connected to the central junction of the secondary windings so as to form an artificial neutral terminal. Each of the conductors 22, 32, and 42 is coupled to the artificial neutral by a respective one of capacitors 23, 339 and 43; a respective one of chokes 24, 34, and 44; and a respective one of thyristor valve arrangements 25, 35, and 45. The voltage across each of capacitors 23, 33, and 43; and the voltage across each of thyristor valve arrangements 25, 35, and 45;
are conducted to a central switching control 26. Central switching control 26 determines the times for opening and closing each of the thyristor valves and delivers corresponding switching pulses to thyristor valve arrangements 25, 35, and 45, in accordance with the phase of the individual conductor voltages and the capacitor voltages. In this embodiment, the switching instants for each of the thyristor valve arrangements are determined independently of one another.
However, in embodiments wherein a plurality of capacitors in the form of a capacitor battery are used for each phase, each such capacitor in the capacitor battery is provided with a separate switch and the charging-closing angles or each of the capacitors in a capacitor battery is determined in accordance with the switching state of the other capacitors in the same capacitor battery, as described hereinabove with respect to the illustrative single phase embodiment.
Capacitors 23, 33, and 43 are all disconnected by the simultaneous removal of all firing pulses to thyristor valve arrangements 25, 35, and 45.
Thus, the thyristor valves are each always extinguished so as to be nonconductive at the zero crossing of the respective current. Accordingly, two of the capaci-tors are always disconnected at the maximum capacitor voltage of the same polarity with a phase shift corresponding to 120, while the third capacitor is already disconnected at the maximum voltage of opposite polarity with a phase "~
3~
shift corresponding to 60 relative to the first capacitor. Figure Sb illus-trates the situation wherein capacitors having vanishing residual capacitor charges are reconnected. The capacitors are connected by briefly closing their respective thyristor valves so that they may be charged to the maximum value of the prevailing polarity of the respective p~lase. Figures 5c and 5d illustrate the voltages across the capacitors and thyristor valves, respectively, in a manner corresponding to Figures 2c and 2d.
The charging-closing angles corresponding to the respective residual capacitor voltages are determined according to mathematical functions which can be determined empirically or by computing the solution of the differential equations of the system. Control unit 6 in Figure 1 and central switching con-trol 26 in Figure 4, which determine the charging-closing angles of their respec-tive systems, may each be formed of a function generator which is programmed with appropriate characteristic curves. Switch control 7 in Figure l may be a micro-processor which is used advantageously to determine the firing angles and the phase of the network voltage, or of the voltage across the thyristor valves, from stored measurement values.
It should be noted that only a few circuit components, arranged in a relatively simple circuit, are required to practice the invention. In parti-cular, in embodiments of the invention wherein only two thyristor valves are used in a switch, no further circuitry for quenching the thyristor valves is required because the thyristor valves always extinguish themselves at a ~ero crossing of their respective current waveforms.
It is to be remembered that, although the inventive concept disclosed herein is described in terms of specific embodiments and particular applications, persons skilled in the pertinent art can generate additional embodiments without departing from the spirit or exceeding the scope of the invention. The drawings and descriptions in this disclosure are merely illustrative embodiments proffered to facilitate comprehension of the invention, and should not be construed to limit the scope thereof.
Claims (5)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method for connecting and disconnecting a capacitor between two conductors of an AC voltage network, the capacitor being arranged in series with a switch, the method comprising the steps of: determining a phase angle of the AC voltage across the two conductors in response to the voltage across the two conductors of the AC voltage network and a voltage across the capacitor, at which phase angle the switch is temporarily closed so as to charge the capa-citor from said voltage across the capacitor to a voltage which corresponds to a peak voltage value of the AC voltage across the conductors; connecting the capacitor to the conductors of the AC voltage network when a voltage across the switch reaches a predetermined minimum voltage value; disconnecting the capacitor from the conductors of the AC voltage network by opening the switch at a moment of time when a current flowing through the switch reaches a zero value; and discharging the capacitor during the time that the switch is open, said discharging being performed in accordance with a predetermined discharge characteristic having a predetermined time constant which corresponds to a multiple of a period of an AC voltage across the conductors of the AC voltage network.
2. The method of claim 1 wherein there is further provided a choke con-nected in series with the capacitor and the switch, said selected phase angle corresponding to said moment of time at which the switch is momentarily closed being selected in response to a predetermined resonant frequency of the series circuit, the capacitor being charged to a predetermined maximum voltage, said predetermined maximum voltage being greater than a peak value of said voltage across the two conductors of the AC voltage network.
3. The method of claim 1 or 2 wherein there are further provided a plurality of capacitors arranged in a capacitor battery for connecting between the two conductors of the AC voltage network, each of the capacitors in the capacitor battery having an associated switch, said step of selecting a moment of time corresponding to a selected phase angle of said voltage across the conductors of the AC voltage network being performed for each of the capacitors in the capacitor battery, each said selected phase angle for each of the capacitors in the capacitor battery being selected in response to the number of capacitors in the capacitor battery which are connected to the two conductors of the AC voltage network, and the number of capacitors in the capacitor battery which remain to be connected.
4. A circuit arrangement for connecting and disconnecting a capacitor between two conductors of an AC voltage network, the circuit arrangement com-prising: choke means connected in series with the capacitor; switch means hav-ing at least first and second thyristors connected in parallel with one another and poled for conduction in opposite directions, said switch means being con-nected in series with the capacitor and said choke means; capacitor voltage measurement means for producing a first signal corresponding to a voltage across the capacitor; phase sensor means for producing a second signal corresponding to the phase of the AC voltage network; and switch control means for controlling the conductive state of said switch means in response to said first and second signals for momentarily closing said switch means so as to charge the capacitor to a voltage which corresponds to a peak voltage value of the AC voltage across the conductors, said momentary closing occurring at a selectable moment of time corresponding to a selected phase angle of said voltage across the conductors of the AC voltage network, said phase angle being selected in response to the magnitude of a voltage across the capacitor.
5. The circuit arrangement of claim 4 wherein there is further provided a plurality of capacitors arranged in a capacitor battery, each of said capacitors in said capacitor battery having an associated choke means and switch means con-nected in series, said switch control means selecting a selected phase angle for each of said capacitors in said capacitor battery, said selected phase angles being responsive to the number of capacitors in said capacitor battery connected to the two conductors of the AC voltage network, and the number of capacitors which remain to be connected.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19803012511 DE3012511A1 (en) | 1980-03-31 | 1980-03-31 | METHOD AND DEVICE FOR Vibration-free switching on and off of a capacitor between two conductors of an alternating voltage network |
| DEP3012511.2 | 1980-03-31 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1159522A true CA1159522A (en) | 1983-12-27 |
Family
ID=6098905
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000374211A Expired CA1159522A (en) | 1980-03-31 | 1981-03-30 | System for coupling a capacitance to an ac voltage network |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0037087B1 (en) |
| JP (1) | JPS56150930A (en) |
| CA (1) | CA1159522A (en) |
| DE (2) | DE3012511A1 (en) |
| ZA (1) | ZA812096B (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5959023A (en) * | 1982-09-27 | 1984-04-04 | 株式会社 伸和技研 | Power factor regulating method and device |
| JPS59110335A (en) * | 1982-12-14 | 1984-06-26 | 富士電機株式会社 | Thyristor type condenser switching device |
| AT384502B (en) * | 1985-09-10 | 1987-11-25 | Sprecher & Schuh Ag | DEVICE FOR THE CONTROLLED SWITCHING ON AND / OR SWITCHING OFF OF INDUCTIVE AND CAPACITIVE ELEMENTS IN THE HIGH VOLTAGE NETWORK |
| EP0476917A3 (en) * | 1990-09-18 | 1993-07-28 | Black & Decker Inc. | Timed battery charger |
| DE4425247A1 (en) * | 1994-07-16 | 1996-01-18 | Fraunhofer Ges Forschung | Switching device for a capacitor-equipped reactive power compensation device |
| GB2307803B (en) * | 1995-11-28 | 2000-05-31 | Gec Alsthom Ltd | Three-phase static var compensator arrangement |
| GB2494770A (en) * | 2011-09-13 | 2013-03-20 | O M K Greenpower Uk Ltd | Reactive power compensation system having capacitors with parallel connected discharge resistors |
| CN115313412B (en) * | 2022-09-19 | 2023-09-29 | 广州华园智电科技有限公司 | Single-phase power capacitor rapid and safe switching method based on thyristor control strategy |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2303939C2 (en) * | 1973-01-24 | 1982-06-09 | Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt | Method for operating a reactive current compensation capacitor on an alternating current network |
| JPS602289B2 (en) * | 1976-07-07 | 1985-01-21 | 丸善石油株式会社 | Improved separation and purification method for vinylphenol |
| SE417472B (en) * | 1977-10-13 | 1981-03-16 | Asea Ab | CONDENSOR EQUIPMENT FOR CONNECTING TO AN AC POWER NETWORK |
| DE2816361A1 (en) * | 1978-04-13 | 1979-10-25 | Licentia Gmbh | METHOD FOR OPERATING A POWER CAPACITOR FOR BLIND CURRENT COMPENSATION |
-
1980
- 1980-03-31 DE DE19803012511 patent/DE3012511A1/en not_active Withdrawn
-
1981
- 1981-03-26 EP EP81102295A patent/EP0037087B1/en not_active Expired
- 1981-03-26 DE DE8181102295T patent/DE3162217D1/en not_active Expired
- 1981-03-30 CA CA000374211A patent/CA1159522A/en not_active Expired
- 1981-03-30 ZA ZA00812096A patent/ZA812096B/en unknown
- 1981-03-31 JP JP4829381A patent/JPS56150930A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| JPS56150930A (en) | 1981-11-21 |
| DE3012511A1 (en) | 1981-10-08 |
| ZA812096B (en) | 1982-04-28 |
| EP0037087B1 (en) | 1984-02-15 |
| EP0037087A1 (en) | 1981-10-07 |
| DE3162217D1 (en) | 1984-03-22 |
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