US5402058A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Method and apparatus for controlling discharge of a thyristor-switched capacitor
Assignee: General Electric Co
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Filing: 1992-12-09
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Granted: 1995-03-28
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Expires: 2012-12-09
Abstract
Abstract A static VAR compensator (11) is connected across a power transmission line (10) and includes a capacitor (12) connected to transmission line (10). The static VAR compensator (11) includes a capacitor (12) connected to the AC transmission line (10) and thyristor switches (18, 22) for controllably switching the capacitor (12) across the transmission line (10). The thyristors (18, 22) are fired based on signals generated by control circuitry (26, 28, 30). A substantially constant or DC voltage exists across the capacitor (12) after the thyristor switches have been turned-off. Discharge control circuitry (30) generates firing pulses to activate the thyristor switches (18, 22) in order to discharge the capacitor (12) and reduce the voltage across the capacitor (12) to zero. In one embodiment, the capacitor (12) is discharged gradually using a series of discharge pulses. In another embodiment, the capacitor (12) is rapidly discharged by gating the thyristor (16) for a period sufficient to accomplish complete discharge. The capacitor (12) and thyristor switches (18, 22) may be shunted by nonlinear clamping devices (26, 28), and a potential transformer (52) and resistor (50) may be connected in shunt across capacitor (12).
Inventors
- 👤 Einar V. Larsen
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-01 05:21
CPC Classifications
H; H02; H02J; H02J3/00; H02J3/18; H02J3/1821; H02J3/1835; H02J3/1864; Y; Y02; Y02E; Y02E40/00; Y02E40/10
Claims Analysis
Total Claims: 31
Claim 1
Independent Claim
80 words
A method of discharging a static VAR compensator connected to an AC electrical system including a capacitor connected in series between the AC electrical system and a thyristor switch of two antiparallel thyristors which are selectively controlled by external control signals comprising: determining whether voltage across the thyristors is within a predetermined voltage threshold range, firing the thyristors using one or more pulses to discharge energy stored in the capacitor, and returning the discharged energy to the AC electrical system.
Claim 2
Independent Claim
80 words
A method of discharging a static VAR compensator connected to an AC electrical system including a capacitor connected in series between the AC electrical system and a thyristor switch of two antiparallel thyristors which are selectively controlled by external control signals comprising: determining whether voltage across the thyristors is within a predetermined voltage threshold range, firing the thyristors using one or more pulses to discharge energy stored in the capacitor, and returning the discharged energy to the AC electrical system.
Claim 3
Independent Claim
90 words
A method of discharging a static VAR compensator connected to an AC electrical system including a capacitor connected in series between the AC electrical system and two antiparallel thyristors which are selectively controlled by external control signals, comprising: determining when the magnitude of the voltage across the thyristors is within a predetermined voltage threshold range when the thyristors are turned-off, applying a control pulse to activate one of the thyristors for a time period sufficient to substantially discharge the capacitor, and returning the discharged energy to the AC electrical system.
Claim 4
Independent Claim
90 words
A method of discharging a static VAR compensator connected to an AC electrical system including a capacitor connected in series between the AC electrical system and two antiparallel thyristors which are selectively controlled by external control signals, comprising: determining when the magnitude of the voltage across the thyristors is within a predetermined voltage threshold range when the thyristors are turned-off, applying a control pulse to activate one of the thyristors for a time period sufficient to substantially discharge the capacitor, and returning the discharged energy to the AC electrical system.
Claim 5
Dependent Claim
51 words
The method according to claim 2, further comprising: detecting the polarity of the supply voltage generated by the AC electrical system; comparing the polarity of the supply voltage with the polarity of the thyristor voltage; proceeding to the determining step (a) if the polarities of the supply and thyristor voltage differ.
Claim 6
Dependent Claim
33 words
The method according to claim 2, further comprising: determining if the voltage supplied to the static VAR compensator leads the voltage across the thyristor, and if so, proceeding to the determining step (a).
Claim 7
Dependent Claim
22 words
The method according to claim 2, further comprising: discharging the capacitor through a resistor and transformer connected in shunt across the capacitor.
Claim 8
Independent Claim
99 words
A method of discharging a static VAR compensator connected to a AC electrical system including a capacitor connected in series between the AC electrical system and two anti-parallel thyristor switches which are selectively controlled by external control signals comprising the steps off determining when a substantially constant voltage exists across the capacitor; applying a periodic series of firing pulses to one of the thyristors to gradually discharge the capacitor thereby relieving stress on and minimizing ratings for the capacitor and the thyristors; and determining when the magnitude of the voltage across the thyristor is within a predetermined threshold range.
Claim 9
Independent Claim
99 words
A method of discharging a static VAR compensator connected to a AC electrical system including a capacitor connected in series between the AC electrical system and two anti-parallel thyristor switches which are selectively controlled by external control signals comprising the steps off determining when a substantially constant voltage exists across the capacitor; applying a periodic series of firing pulses to one of the thyristors to gradually discharge the capacitor thereby relieving stress on and minimizing ratings for the capacitor and the thyristors; and determining when the magnitude of the voltage across the thyristor is within a predetermined threshold range.
Claim 10
Dependent Claim
51 words
The method according to claim 4, further comprising: detecting the polarity of the supply voltage supplied from the AC electrical system; comparing the polarity of the supply voltage with the polarity of the thyristor voltage; proceeding to the applying step (b) if the polarities of the supply and thyristor voltages differ.
Claim 11
Dependent Claim
24 words
The method according to claim 4, further comprising: determining if the voltage supplied to the static VAR compensator leads the voltage across the thyristor.
Claim 12
Independent Claim
66 words
A system for gradually discharging a static VAR compensator, comprising: a power transmission line for providing AC power; a capacitor connected to the transmission line; switching means for controllably switching the capacitor across the transmission line; a control circuit for periodically activating the switching means gradually reducing the capacitor voltage; and means for detecting when the voltage across the switching means is within a predetermined range.
Claim 13
Independent Claim
66 words
A system for gradually discharging a static VAR compensator, comprising: a power transmission line for providing AC power; a capacitor connected to the transmission line; switching means for controllably switching the capacitor across the transmission line; a control circuit for periodically activating the switching means gradually reducing the capacitor voltage; and means for detecting when the voltage across the switching means is within a predetermined range.
Claim 14
Dependent Claim
32 words
The system according to claim 9, wherein the control circuit periodically activates the switching means when a substantially constant voltage exists across the capacitor to gradually reduce the capacitor voltage to zero.
Claim 15
Dependent Claim
47 words
The system according to claim 9, wherein the control circuit includes: thyristor control circuitry; capacitor discharge control circuitry; and means for generating firing pulses for activating the switching means to conduct current based on signals received from the thyristor control circuitry and the capacitor discharge control circuitry.
Claim 16
Dependent Claim
28 words
The system according to claim 9, further comprising: a first varistor connected in shunt with the capacitor, and a second varistor connected in shunt with the thyristor switches.
Claim 17
Dependent Claim
19 words
The system according to claim 9, further comprising: a surge inductor connected between the capacitor and the switching means.
Claim 18
Dependent Claim
29 words
The system according to claim 9, wherein the control circuit includes: means for determining if voltage supplied to the static VAR compensator leads the voltage across the switching means.
Claim 19
Dependent Claim
61 words
The system according to claim 9, wherein the control circuit includes: means for detecting the polarity of supply voltage supplied via the transmission line, and means for comparing the polarity of the supply voltage with the polarity of the voltage across the switching means, wherein the switching means are activated when the voltage polarities of the supply and switching means differ.
Claim 20
Dependent Claim
55 words
The system according to claim 9, wherein the predetermined range is variable and includes: a positive voltage and a negative voltage whose magnitudes are less than the peak value of a supply voltage, wherein the values of the positive and negative voltages determine the timing of and extent to which the capacitor voltage is reduced.
Claim 21
Dependent Claim
24 words
The system according to claim 9, wherein varying the magnitude of the predetermined range changes the rate at which the capacitor voltage is reduced.
Claim 22
Dependent Claim
31 words
The system according to claim 9, further comprising: means connected to the capacitor for delaying the rate at which the capacitor voltage is reduced for dissipating energy discharged by the capacitor.
Claim 23
Independent Claim
81 words
A system for rapidly discharging a static VAR compensator, comprising: a power transmission line for delivering AC power; a capacitor connected to the transmission line; switching means for controllably switching the capacitor across the transmission line; control means for activating the switching means during a single time period when a substantially constant voltage exists across the capacitor to rapidly reduce the capacitor voltage to zero; and means for detecting when the voltage across the switching means is within a predetermined range.
Claim 24
Independent Claim
81 words
A system for rapidly discharging a static VAR compensator, comprising: a power transmission line for delivering AC power; a capacitor connected to the transmission line; switching means for controllably switching the capacitor across the transmission line; control means for activating the switching means during a single time period when a substantially constant voltage exists across the capacitor to rapidly reduce the capacitor voltage to zero; and means for detecting when the voltage across the switching means is within a predetermined range.
Claim 25
Dependent Claim
47 words
The system according to claim 11, wherein the control means includes: thyristor control circuitry; capacitor discharge control circuitry; and means for generating firing pulses for activating the switching means to conduct current based on signals received from the thyristor control circuitry and the capacitor discharge control circuitry.
Claim 26
Dependent Claim
28 words
The system according to claim 11, further comprising: a first varistor connected in shunt with the capacitor, and a second varistor connected in shunt with the switching means.
Claim 27
Dependent Claim
19 words
The system according to claim 11, further comprising: a surge inductor connected between the capacitor and the switching means.
Claim 28
Dependent Claim
29 words
The system according to claim 11, wherein the control means includes: means for determining if voltage supplied to the static VAR compensator leads the voltage across the switching means.
Claim 29
Dependent Claim
61 words
The system according to claim 11, wherein the control means includes: means for detecting the polarity of supply voltage generated by the transmission line, and means for comparing the polarity of the supply voltage with the polarity of the voltage across the switching means, wherein the switching means are activated when the voltage polarities of the supply and switching means differ.
Claim 30
Dependent Claim
55 words
The system according to claim 11, wherein the predetermined range is variable and includes: a positive voltage and a negative voltage whose magnitudes are less than the peak value of a supply voltage, wherein the values of the positive and negative voltages determine the timing of and extent to which the capacitor voltage is reduced.
Claim 31
Dependent Claim
31 words
The system according to claim 11, further comprising: means connected to the capacitor for delaying the rate at which the capacitor voltage is reduced for dissipating energy discharged by the capacitor.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1998-03-27 | 1998-09-26 | 1999-03-28 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2002-03-27 | 2002-09-26 | 2003-03-28 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2006-03-27 | 2006-09-26 | 2007-03-28 | $7700.00 | Window Closed / Lapsed |