CA2806254C

CA2806254C - Phase control switching device

Info

Publication number: CA2806254C
Application number: CA2806254A
Authority: CA
Inventors: Sho Tokoyoda; Sadayuki Kinoshita; Tomohito Mori; Kenji Kamei; Hiroki Ito
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2010-07-27
Filing date: 2010-07-27
Publication date: 2016-01-26
Anticipated expiration: 2030-07-27
Also published as: JP4717158B1; CA2806254A1; WO2012014282A1; CN102959669A; CN102959669B; JPWO2012014282A1

Abstract

Disclosed is phase control switchgear inhibiting generation of transient voltages and currents during breaker closing. Switchgear comprises residual voltage polarity estimating unit which determines, for each phase, that last detected zero point of the load voltage is zero point of the load voltage immediately before breaker opening when subsequent zero point of the load voltage cannot be detected within a predetermined time period after previous zero point of the load voltage was detected and which estimates that the polarity of the time differential value of the load voltage in the zero point of the load voltage immediately before breaker opening is the polarity of the residual voltage of each phase after breaker opening; and closing phase control unit to control breaker closing at the zero point of the load voltage at which the polarity of the residual voltage of each phase is inverted to a reverse polarity after breaker opening.

Description

DESCRIPTION
PHASE CONTROL SWITCHING DEVICE
Field [0001] The present invention relates to a phase control switching device that controls switching timing for a breaker.
Background

[0002] In the past, there is a phase control switching device that inhibits generation of transient voltages and electric currents by, when a power supply is applied to a phase-advancing load circuit such as a capacitor bank, a neutral point of which is grounded, or a no-load power transmission line, measuring power supply voltages of respective phases, detecting power supply voltage zero points of each of the phases, and separately turning on breakers in the phases near the power supply voltage zero points (e.g., Patent Literature 1).
Citation List Patent Literature

[0003] Patent Literature 1: International Patent Publication WO 00/04564 Summary Technical Problem

[0004] In general, during breaking of a phase-advancing load circuit, it is difficult to measure a voltage having direct-current properties (hereinafter, "residual voltage") due to residual charges remaining on a capacitor or a power transmission line. Therefore, the phase control switching =
DocketNo.PMAA-12124-PCT

device in the past controls an energization phase of the breaker focusing only on power supply voltages in the respective phases when the power supply is applied to the phase-advancing load circuit. However, when a residual voltage is generated on the capacitor or the power transmission line during the breaking, a direct-current voltage due to residual charges is superimposed between breaker electrodes in addition to a power supply voltage.
Therefore, there is a problem in that, when dielectric strength between the breaker electrodes in a breaker closing process is taken into account, even if the breaker is closed at a zero point of the power supply voltage, depending on the polarity of the power supply voltage zero point for closing the breaker, the breaker is electrically energized in a high phase of an inter-electrode voltage and an over voltage and an over current may not be able to be sufficiently inhibited.

[0005] The present invention has been devised in view of the above and it is an object of the present invention to provide a phase control switching device that can inhibit generation of transient voltages and electric currents involved in a closing action of a phase-advancing load circuit.
Solution to Problem

[0006] In order to solve the above problem and in order to attain the above object, in a phase control switching device that controls a closing phase of a three-phase switching device connected between a power supply and a phase-advancing load, the phase control switching device of the present invention, includes: a power-supply-side-voltage detecting unit configured to detect phase power supply side voltages on the power supply side; a load-side-DocketNo.PMAA-12124-PCT

voltage detecting unit configured to detect phase load side voltages on the phase-advancing load side; a residual-voltage-polarity estimating unit configured to estimate, at a point when zero points of the phase load side voltages cannot be periodically detected, polarities of time differential values of the phase load side voltages at zero points of the phase load side voltages detected last as polarities of phase residual voltages on the phase-advancing load side after opening of the three-phase switching device; and a closing-phase control unit configured to detect a period of the phase power supply side voltages and control the closing phase of the three-phase switching device such that the three-phase switching device is closed at a point where the phase power supply side voltages change from the polarities of the phase residual voltages to reverse polarities thereof.
Advantageous Effects of Invention

[0007] According to the present invention, there is an effect that it is possible to inhibit a phase control switching device that can inhibit generation of transient voltages and electric currents involved in a closing action of a phase-advancing load circuit.
Brief Description of Drawings

[0008] FIG. 1 is a diagram of a configuration example of a phase control switching device according to a first embodiment.
FIG. 2 is a waveform chart for explaining a method of estimating the polarity of a residual voltage remaining in a phase-advancing load after breaker opening.
FIG. 3 is a diagram for explaining a method of controlling a closing phase of the breaker based on the =
DocketNo.PMAA-12124-PCT

estimated polarity of the residual voltage.
Description of Embodiments

[0009] Phase control switching devices according to embodiments of the present invention are explained below with reference to the accompanying drawings. The present invention is not limited by the embodiments explained below.

[0010] Principal part of an embodiment of the present invention A phase control switching device according to an embodiment of the present invention has a function of capable of inhibiting transient voltages and electric currents due to energization of a breaker to a phase-advancing load. In a process for closing the breaker using the phase control switching device, dielectric strength between electrodes decreases according to a decrease in an inter-electrode distance of a contact. At a point when the dielectric strength decreases to be equal to or lower than an electric field value due to a system voltage applied between the electrodes of the contact, a leading arc involved in dielectric breakdown between the electrodes of the contact is generated and electrically energized.
Because a change in the inter-electrode distance of the contact depends on an opening and closing action time of the breaker, the change can be evaluated by a mechanical characteristic test. Because the dielectric strength between the electrodes of the contact depends on a voltage applied between the electrodes of the contact and the inter-electrode distance of the contact, the dielectric strength can be evaluated by an electrical characteristic test. Therefore, a rate of decrease of dielectric strength (RDDS) characteristic line between the breaker electrodes in a breaker closing process is obtained from the =
DocketNo.PMAA-12124-PCT
mechanical characteristic test and the electrical characteristic test. However, when a residual voltage is generated in a phase-advancing load after the breaker opening, the breaker inter-electrode voltage is a voltage 5 on which the residual voltage is superimposed in addition to a power supply voltage. Therefore, the phase control switching device according to this embodiment is added with a function of estimating a residual voltage after the breaker opening and enabling, taking into account the rate of decrease of dielectric strength characteristic line between breaker electrodes in the breaker closing process, energization of the breaker at timing when the breaker inter-electrode voltage drops.

[0011] First Embodiment.
FIG. 1 is a diagram of a configuration example of a phase control switching device according to a first embodiment. In FIG. 1, a breaker 50, which is a three-phase switching device, is connected between a power supply side circuit including an R phase, an S phase, and a T
phase shown on the right side of the figure and phase-advancing loads (e.g., a capacitor bank, a neutral point of which is grounded or a no-load power transmission line is equivalent) 10a, 10b, and 10c shown on the left side of the figure. The breaker 50 includes arc-extinguishing chambers 52a, 52b, and 52c and includes operation units 54a, 54b, and 54c, which are independent from one another, such that contacts in the arc-extinguishing chambers 52a, 52b, and 52c can independently open and close. On a power supply side of the breaker 50, power-supply-side-voltage measuring units 72a, 72b, and 72c that measure phase power supply side voltages and current measuring units 74a, 74b, and 74c that measure phase currents flowing from a power supply side circuit to the phase-advancing loads side are provided.

= =
DocketNo.PMAA-12124-PCT

On the other hand, on the phase-advancing loads side of the breaker 50, load-side-voltage measuring units 73a, 73b, and 73c that measure phase load side voltages are provided.

[0012] A phase control switching device 80 according to the first embodiment is configured by, for example, a computer. The phase control switching device 80 includes a power-supply-side voltage detecting unit 82 that detects phase power supply side voltages based on signals from the power-supply-side-voltage measuring units 72a, 72b, and 72c, a load-side-voltage detecting unit 83 that detects phase load side voltages based on signals from the load-side-voltage measuring units 73a, 73b, and 73c, a current detecting unit 84 that detects phase currents based on signals from the current measuring units 74a, 74b, and 74c, and a control unit 81. The control unit 81 includes a residual-voltage-polarity estimating unit 81a and a closing-phase control unit 81b that operate based on outputs from the detecting units (the power-supply-side-voltage detecting unit 82, the load-side-voltage detecting unit 83, and the current detecting unit 84) and an opening and closing command 31 input to the phase control switching device 80.

[0013] The residual-voltage-polarity estimating unit 81a starts an operation at a point when an opening command for the breaker 50 is input, continuously detects zero points of phase load side voltages, and calculates time differential values at the zero points of the phase load side voltages. When the next zero points of phase load side voltages cannot be detected within a predetermined period from detection times of the last zero points of phase load side voltages, the residual-voltage-polarity estimating unit 81a estimates the polarities of time differential values of phase load side voltages at zero DocketNo.PMAA-12124-PCT

points of phase load side voltages detected last as the polarities of phase residual voltages after the opening of the breaker 50.

[0014] In other words, at a point when zero points of phase load side voltages cannot be periodically detected, the residual-voltage-polarity estimating unit 81a estimates the polarities of the time differential values of the phase load side voltages at the zero points of the phase load side voltages detected last as the polarities of the phase residual voltages after the opening of the breaker 50.

[0015] The closing-phase control unit 81b detects periods of the phase power supply side voltages and controls the breaker 50 to be closed at points when the phase power supply side voltages change from the polarities of the phase residual voltages estimated by the residual-voltage-polarity estimating unit 81a to reverse polarities thereof.

[0016] A method of estimating the polarities of residual voltages remaining in the phase-advancing loads 10a, 10b, and 10c after the opening of the breaker 50 is explained with reference to FIG. 2. FIG. 2 is a waveform chart for explaining a method of estimating the polarities of residual voltages remaining in the phase-advancing loads after breaker closing.

[0017] FIGS. 2(a) to (e) are diagrams of examples of waveforms obtained when contacts of the breaker 50 are electrically broken at phase breaking points shown in FIG.
2. More specifically, phase power supply side voltage waveforms are shown in FIG. 2(a), waveforms of phase currents flowing from a power supply to the phase-advancing loads 10a, 10b, and 10c via the breaker 50 are shown in FIG.
2(b), phase load side voltage waveforms are shown in FIG.
2(c), waveforms of gradients of phase load side voltages, DocketNo.PMAA-12124-PCT

which are time differential values of the phase load side voltages, are shown in FIG. 2(d), and inter-breaker electrode voltage waveforms obtained by subtracting the phase load side voltages from the phase power supply side voltages are shown in FIG. 2(e).

[0018] The waveforms of the phase currents (FIG. 2(b)) flowing from the power supply to the phase-advancing loads 10a, 10b, and 10c are waveforms phase-advanced by 1/4 cycle in respective power supply frequencies with respect to the phase power supply side voltage waveforms (FIG. 2(a)). In general, when the breaker 50 is opened, an opening phase is controlled such that the breaker 50 is electrically broken at zero points of phase currents. Therefore, breaking points of the phases are present near maximum values or near minimum values of the phase power supply side voltages.
In the phase load side voltage waveforms (FIG. 2(c)), direct-current residual voltages having direct-current properties of positive or negative polarity are generated after the phase breaking points. The polarities of the residual voltages at this point coincide with the polarities of the gradients (time differential values) of phase load side voltages at zero points of phase load side voltages immediately before the phase braking points (FIG.
2(d)).

[0019] For example, when focused on the R phase, the polarity of the gradient of an R phase load side voltage at a zero point at time A immediately before R phase breaking coincides with the polarity of an R phase residual voltage and is negative polarity. Similarly, for example, when focused on the T phase, the polarity of the gradient of a T
phase load side voltage at a zero point at time B
immediately before T phase breaking coincides with the polarity of a T phase residual voltage and is positive *
DocketNo.PMAA-12124-PCT

polarity. Similarly, for example, when focused on the S
phase, the polarity of the gradient of an S phase load side voltage at a zero point at time C immediately before S
phase breaking coincides with the polarity of an S phase residual voltage and is negative polarity.

[0020] In other words, when the next zero points of phase load side voltages cannot be detected within a predetermined period after the last zero points of phase load side voltages, zero points of phase load side voltages detected last can be determined as zero points of phase load side voltages immediately before the phase breakings.
The polarities of the gradients (time differential values) of the phase load side voltages at the zero points can be estimated as the polarities of phase residual voltages after the phase breaking points. It is determined whether zero points of phase load side voltages that periodically comes at each 1/2 cycle of a power supply frequency before the phase breakings are detected. Therefore, the predetermined period only has to be an arbitrary predetermined period longer than the 1/2 cycle of the power supply frequency. However, if the predetermined period is long, time for deciding the polarities of residual voltages is delayed. Therefore, it is not desirable to set the predetermined period too long. For example, when the power supply frequency is 50 Hz, the predetermined period only has to be set to about 12 milliseconds and, when the power supply frequency is 60 Hz, the predetermined period only has to be set to about 10 milliseconds.

[0021] A method of controlling a closing phase of the breaker 50 based on the estimated polarities of residual voltages is explained with reference to FIG. 3. FIG. 3 is a diagram for explaining a method of controlling a closing phase of the breaker 50 based on the estimated polarities DocketNo.PMAA-12124-PCT
of residual voltages.

[0022] In FIG. 3(a), waveform charts of the R phase after phase breaking points are shown as an example. In FIG. 3(b), waveform charts of the T phase after phase 5 breaking points are shown as an example. As shown in FIG.
3, as zero points of phase power supply voltages, two kinds of zero points are present: zero points inverted from the negative polarity to the positive polarity (a Ti point in FIG. 3(a) and a Ti' point in FIG. 3(b)) and zero points 10 inverted from the positive polarity to the negative polarity (a T2 point in FIG. 3(a) and a T2' point in FIG.
3(b)).

[0023] In FIG. 3(a), straight lines extending to the upper left respectively from the two zero points of the R
phase power supply side voltage of the Ti point and the T2 point respectively indicate rates of decrease of dielectric strength characteristic lines between the breaker electrodes in the breaker closing process obtained when the breaker 50 is controlled to be closed at the Ti point and the T2 point. In FIG. 3(b), straight lines extending to the upper left respectively from the two zero points of the T phase power supply side voltage of the Ti' point and the T2' point respectively indicate rates of decrease of dielectric strength characteristic lines between the breaker electrodes in the breaker closing process obtained when the breaker 50 is controlled to be closed at the Ti' point and the T2' point.

[0024] In the breaker closing process, a crossing point of the rate of decrease of dielectric strength characteristic line and an absolute value of the breaker inter-electrode voltage is an electrical energization point.
In the example shown in FIG. 3, in the R phase, when the breaker 50 is controlled to be closed at the Ti point, an A

=
DocketNo.PMAA-12124-PCT

point is the electrical energization point. When the breaker 50 is controlled to be closed at the T2 point, a B
point is the electrical energization point. In the T phase, when the breaker 50 is controlled to be closed at the Ti' point, an A' point is the electrical energization point.
When the breaker 50 is controlled to be closed at the T2' point, a B' point is the electrical energization point. A
position on the abscissa of the electrical energization point is an energization phase. A position on the ordinate of the electrical energization point is the magnitude of an inter-electrode applied voltage applied when inter-electrode insulation is broken. The magnitude of the inter-electrode applied voltage is an initial value of a transient phenomenon started by the energization of the breaker 50. Therefore, the influence on power transmission and transformation apparatuses and the like connected to a power system is larger as the inter-electrode applied voltage is larger. Therefore, it is necessary to control the breaker 50 to be closed at zero points of phase power supply side voltage at which the inter-electrode applied voltage further decreases.

[0025] In the example shown in FIG. 3, in the R phase, when the breaker 50 is controlled to be closed at a zero point of the R phase power supply side voltage that changes from the negative polarity, which is the polarity of the R
phase residual voltage, to the positive polarity, i.e., the T2 point, the breaker 50 is electrically energized at the B
point where the absolute value of the breaker inter-electrode voltage is a lower voltage. The inter-electrode applied voltage further decreases. In the T phase, when the breaker 50 is controlled to be closed at a zero point of the T phase power supply side voltage that changes from the polarity polarity, which is the polarity of the T phase DocketNo.PMAA-12124-PCT

residual voltage, to the negative polarity, i.e., the Ti' point, the breaker 50 is electrically energized at the A' point where the absolute value of the breaker inter-electrode voltage is a lower voltage. The inter-electrode applied voltage further decreases.

[0026] In other words, the breaker 50 is controlled to be closed at the zero points of the phase power supply side voltages that change from the polarities of the phase residual voltages to the reverse polarities thereof.
Consequently, it is possible to electrically energize the breaker 50 at timing when the absolute value of the breaker inter-electrode voltage is lower and further reduce the inter-electrode applied voltage.

[0027] When the beaker 50 is opened, if an accident such as an earth fault or short-circuit occurs in any one phase or plurality of phases, a residual voltage after the opening of the breaker 50 is sometimes zero. In such a case, the closing-phase control unit 81b only has to control the breaker 50 to be closed at an arbitrary zero point of a power supply side voltage of the accident phase.
As a method of determining the accident phase, for example, a phase in which the residual-voltage-polarity estimating unit 81a detects at least one or more zero points of phase load side voltages within a period shorter than a 1/2 cycle period of the power supply frequency from detection times of the last zero points of phase load side voltages can be determined as the accident phase. A phase in which the magnitude of phase currents input from the current detecting unit 84 before the breaking of the breaker 50 is equal to or larger than a predetermined current threshold (e.g., about a double of a rated current) can be determined as the accident phase. Alternatively, the accident phase can be determined using both of these methods as well.

DocketNo.PMAA-12124-PCT

Even if such control is performed, it is possible to attain the object of the present invention to inhibit transient voltages and electric currents during the energization of the breaker.

[0028] As explained above, with the phase control switching device according to the first embodiment, if the next zero points of phase load side voltages cannot be detected within the predetermined period from the last zero points of phase load side voltages, zero points of phase load side voltages detected last are determined as zero points of phase load side voltages immediately before phase breakings. The polarities of time differential values of load side voltages at the zero points of the phase load side voltages immediately before the phase breakings are estimated as the polarities of phase residual voltages after breaker opening. The breaker is controlled to be closed at points where phase power supply side voltages change from the polarities of the phase residual voltages to the reverse polarities thereof after the breaker opening.
Therefore, it is possible to electrically energize the breaker at timing when the breaker inter-electrode voltage decreases. An effect is obtained that it is possible to inhibit generation of transient voltages and electric currents involved in the closing action of the phase-advancing load circuit.

[0029] Second Embodiment.
In the first embodiment, the method of estimating the polarities of time differential values of load side voltages at zero points of phase load side voltages immediately before phase breakings as the polarities of phase residual voltages after breaker opening is explained.
In a second embodiment, a method of estimating reverse polarities of instantaneous values or integrated values of DocketNo.PMAA-12124-PCT

phase breaker inter-electrode voltages after phase breakings as the polarities of phase residual values after breaker opening is explained. The configuration of a phase control switching device according to the second embodiment is the same as the configuration explained in the first embodiment in the components other than the residual-voltage-polarity estimating unit. Therefore, detailed explanation of the components is omitted.

[0030] The residual-voltage-polarity estimating unit 81a in the second embodiment starts operation at a point when an opening command for the breaker 50 is input and subtracts phase load side voltages from phase power supply side voltages to calculate phase breaker inter-electrode voltages. When absolute values of the phase breaker inter-electrode voltages are equal to or larger than a predetermined voltage threshold, i.e., when the phase breaker inter-electrode voltages are equal to or larger than a predetermined positive voltage threshold or equal to or smaller than a predetermined negative voltage threshold, the residual-voltage-polarity estimating unit 81a estimates reverse polarities of instantaneous values of the phase breaker inter-electrode voltages at this point as polarities of the phase residual voltages after the opening of the breaker 50.

[0031] A method of estimating the polarities of phase residual voltages in the second embodiment is explained with reference to FIG. 2.

[0032] As explained in the first embodiment, the breaker inter-electrode voltage waveforms shown in FIG. 2(e) is a waveform obtained by subtracting the phase load side voltages shown in FIG. 2(c) from the phase power supply side voltages shown in FIG. 2(a). In general, when the breaker 50 is opened, an opening phase is controlled such DocketNo.PMAA-12124-PCT
that the breaker 50 is electrically broken at zero points of phase currents. Therefore, the breaker 50 is broken near maximum values or near minimum values of phase power supply side voltages. A breaker inter-electrode voltage 5 having positive or negative polarity is generated after the phase breaking points. The breaker inter-electrode voltage has reverse polarity of the polarity of a residual voltage.
The breaker inter-electrode voltage has a waveform that changes in synchronization with the phase power supply side 10 voltages in ranges from zero to voltage values about twice as large as the minimum values of the phase power supply side voltages when the phase breaking points are present near the maximum values of the phase power supply side voltages and changes in synchronization with the phase 15 power supply side voltages in ranges from zero to voltage values about twice as large as the maximum values of the phase power supply side voltages when the phase breaking points are present near the minimum values of the phase power supply side voltages (FIG. 2(e)).

[0033] For example, when focused on the R phase, an R
phase beaker inter-electrode voltage after R phase breaking has positive polarity, which is reverse polarity of the polarity of an R phase residual voltage, and changes in synchronization with an R phase power supply side voltage in a range from zero to a voltage value about twice as large as a maximum value of the R phase power supply side voltage. Similarly, for example, when focused on the T
phase, a T phase beaker inter-electrode voltage after T
phase breaking has negative polarity, which is reverse polarity of the polarity of a T phase residual voltage, and changes in synchronization with a T phase power supply side voltage in a range from zero to a voltage value about twice as large as a maximum value of the T phase power supply DocketNo.PMAA-12124-PCT

side voltage. Similarly, for example, when focused on the S phase, a S phase beaker inter-electrode voltage after S
phase breaking has positive polarity, which is reverse polarity of the polarity of an S phase residual voltage, and changes in synchronization with an S phase power supply side voltage in a range from zero to a voltage value about twice as large as a maximum value of the S phase power supply side voltage.

[0034] In other words, it is possible to detect that time is after the phase breaking points by detecting that the phase breaker inter-electrode voltages increase to be equal to or larger than a predetermined positive voltage threshold or decrease to be equal to or smaller than a predetermined negative voltage threshold from immediately after the phase breakings. It is possible to estimate, as the polarities of the phase residual voltages, reverse polarities of instantaneous values of the phase breaker inter-electrode voltages at that detection point. The positive voltage threshold only has to be set to about a quarter of a maximum value that can be taken as a breaker inter-electrode voltage value (i.e., a double of the maximum values of the phase power supply side voltages).
Similarly, the negative voltage threshold only has to be set to about a quarter of a minimum value that can be taken as a breaker inter-electrode voltage value (i.e., a double of the minimum values of the phase power supply side voltages). If the voltage thresholds are set in this way, it is possible to prevent a peak value of an arc voltage, which is generated in a period from the opening of the breaker 50 to phase breaking points when phase currents are electrically broken, from being misdetected as a breaker inter-electrode voltage.

[0035] As another operation form of the residual-Docket No. PMAA-12124-PCT

voltage-polarity estimating unit 81a in the second embodiment, it is also possible to estimate, as the polarities of the phase residual voltages after the opening of the breaker 50, reverse polarities of integrated values of phase breaker inter-electrode voltages before and after a point when the phase breaker inter-electrode voltages increase to be equal to or larger than the predetermined positive voltage threshold or decrease to be equal to or smaller than the predetermined negative voltage threshold.
If such an operation form is adopted, for example, even if transient oscillation occurs in a breaker inter-electrode voltage after the opening of the breaker 50, it is possible to accurately estimate the polarities of the phase residual voltages.

[0036] An integration period for the phase breaker inter-electrode voltages can be set to an arbitrary predetermined period before and after the point when the phase breaker inter-electrode voltages increase to be equal to or larger than the predetermined positive voltage threshold or decrease to be equal to or smaller than the predetermined negative voltage threshold. However, the integration period only has to be set to, for example, a 1/2 cycle period of a power supply frequency (when the power supply frequency is 50 Hz, about 10 milliseconds and, when the power supply frequency is 60 Hz, about 8.33 milliseconds) to prevent time for deciding the polarity of a residual voltage from being delayed.

[0037] As explained above, with the phase control switching device according to the second embodiment, reverse polarities of instantaneous values of phase breaker inter-electrode voltages at a point when phase breaker inter-electrode voltages obtained by subtracting phase load side voltages from phase power supply side voltages Docket No. PMAA-12124-PCT

increase to be equal to or larger than the predetermined positive voltage threshold or decrease to be equal to or smaller than the predetermined negative voltage threshold or reverse polarities of integrated values of phase breaker inter-electrode voltages before and after a point when the phase breaker inter-electrode voltages increase to be equal to or larger than the predetermined positive voltage threshold or decrease to be equal to or smaller than the predetermined negative voltage threshold are estimated as the polarities of phase residual voltages after the breaker opening. The breaker is controlled to be closed at a point when the phase-power supply side voltages change from the polarities of the phase residual voltage after the breaker opening to reverse polarities thereof. Therefore, as in the first embodiment, it is possible to electrically energize the breaker at timing when the breaker inter-electrode voltage decreases. An effect is obtained that it is possible to inhibit generation of transient voltages and electric currents involved in the closing action of the phase-advancing load circuit.

[0038] In the second embodiment, the phase breaker inter-electrode voltages are obtained by subtracting the phase load side voltages from the phase power supply side voltages. However, the phase breaker inter-electrode voltages can be obtained by subtracting the phase power supply side voltages from the phase load side voltages. In this case, the polarities of the instantaneous values or the polarities of the integrated values of the phase breaker inter-electrode voltages only have to be estimated as the polarities of the phase residual voltages after the breaker opening.

[0039] Third Embodiment.
In the first embodiment, the method of estimating the Docket No. PMAA-12124-PCT

polarities of time differential values of load side voltages at zero points of phase load side voltages immediately before phase breakings as the polarities of phase residual voltages after breaker opening is explained.
In the second embodiment, the method of estimating reverse polarities of instantaneous values or integrated values of phase breaker inter-electrode voltages after phase breakings as the polarities of phase residual values after breaker opening is explained. In a third embodiment, a method of estimating the polarities of integrated values of phase load side voltages after phase breakings as the polarities of phase residual voltages after breaker opening is explained. The configuration of a phase control switching device according to the third embodiment is the same as the configuration explained in the first and second embodiments in the components other than the residual-voltage-polarity estimating unit. Therefore, detailed explanation of the components is omitted.

[0040] The residual-voltage-polarity estimating unit 81a in the third embodiment starts operation at a point when an opening command for the breaker 50 is input and continuously detects zero points of phase load side voltages. When the next zero points of phase load side voltages cannot be detected within a predetermined period from detection times of the last zero points of phase load side voltages, the residual-voltage-polarity estimating unit 81a estimates times a 1/4 cycle of a power supply frequency after detection times of zero points of the phase load side voltages detected last as phase breaking times, calculates integrated values of phase load side voltages after the phase breaking times, and estimates the polarities of the integrated values as the polarities of phase residual voltages after the opening of the breaker 50.

Docket No. PMAA-12124-PCT

[0041] In other words, at a point when zero points of phase load side voltages cannot be periodically detected, the residual-voltage-polarity estimating unit 81a in the third embodiment estimates, as phase breaking times, times 5 a 1/4 cycle of the power supply frequency after the detection times of the zero points of the phase load side voltages detected last and estimates, as the polarities phase residual voltages after the opening of the breaker 50, the polarities of integrated values of the phase load side 10 voltages after the phase breaking times.

[0042] A method of estimating the polarities of phase residual voltages in the third embodiment is explained with reference to FIG. 2.

[0043] As explained in the first embodiment, the 15 waveforms of the phase currents (FIG. 2(b)) flowing from the power supply to the phase-advancing loads 10a, 10b, and 10c are waveforms phase-advanced by 1/4 cycle in respective power supply frequencies with respect to the phase power supply side voltage waveforms (FIG. 2(a)). Therefore, zero 20 points of the phase current waveforms and the phase power supply side voltage waveforms come at times shifted by a 1/4 cycle from each other. On the other hand, when the breaker 50 is opened, an opening phase is controlled such that the breaker 50 is electrically broken at zero points of phase currents. Therefore, times of zero points of the phase load side voltage waveforms (FIG. 2(c)) immediately before the phase breakings are times a 1/4 cycle period before the phase breaking times. In other words, the phase breaking times are times a 1/4 cycle period of the power supply frequency after the times of the zero points the phase load side voltages immediately before the phase breakings.

[0044] For example, when focused on the R phase, R phase Docket No. PMAA-12124-PCT

breaking time is time the 1/4 cycle period after time A of a zero point of an R phase load side voltage immediately before R phase breaking. Similarly, for example, when focused on the T phase, T phase breaking time is time the 1/4 cycle period after time B of a zero point of a T phase load side voltage immediately before T phase breaking.
Similarly, for example, when focused on the S phase, S
phase breaking time is time the 1/4 cycle period after time C of a zero point of an S phase load side voltage immediately before S phase breaking.

[0045] In other words, by detecting zero points of phase load side voltages immediately before phase breakings in the same manner as in the first embodiment, it is possible to estimate times the 1/4 cycle period after the power supply frequency from the zero points as phase breaking times and estimate the polarities of integrated values of phase load side voltages after the phase breaking times as the polarities of phase residual voltages after the opening of the breaker 50. An integration period for the phase load side voltages can be set to an arbitrary predetermined period from the phase breaking times. However, the integration period only has to be set to, for example, the 1/2 cycle period of the power supply frequency to prevent time for deciding the polarity of a residual voltage from being delayed.

[0046] As explained above, with the phase control switching device according to the third embodiment, if the next zero points of phase load side voltages cannot be detected within the predetermined period of the last zero points of phase load side voltages, times after the 1/4 cycle period of the power supply frequency from detection times of zero points of phase load side voltages detected last are estimated as phase breaking times, integrated values of phase load side voltages after the phase breaking times are calculated, and the polarities of the integrated values are estimated as the polarities of phase residual voltages after the breaker opening. The breaker is controlled to be closed at points where phase power supply side voltages change from the polarities of the phase residual voltages after the breaker opening to reverse polarities thereof. Therefore, as in the first and second embodiments, it is possible to electrically energize the breaker at timing when the breaker inter-electrode voltage decreases. An effect is obtained that it is possible to inhibit generation of transient voltages and electric currents involved in the closing action of the phase-advancing load circuit.

[0047] The configurations explained in the embodiments are examples of the configuration of the present invention.
It goes without saying that the configurations can be combined with other publicly-known technologies and can be changed by, for example, omitting a part of the configurations without departing from the scope of the present invention.
Industrial Applicability

[0048] As explained above, the phase control switching device according to the present invention is useful as an invention that can inhibit generation of transient voltages and electric currents involved in a closing action of a phase-advancing load circuit.
Reference Signs List

[0049] 10a, 10b, 10c phase-advancing loads 31 opening and closing command

50 breaker Docket No. PMAA-12124-PCT

52a, 52b, 52c arc-extinguishing chambers 54a, 54b, 54c operation units 72a 72b, 72c power-supply-side-voltage measuring units 73a, 73b, 73c load-side-voltage measuring unit 74a, 74b, 74c current measuring units 80 phase control switching device 81 control unit 81a residual-voltage-polarity estimating unit 81b closing-phase control unit 82 power-supply-side-voltage detecting unit 83 load-side-voltage detecting unit 84 current detecting unit

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A phase control switching device that controls a closing phase of a three-phase switching device connected between a power supply and a phase-advancing load, the phase control switching device comprising:
a power-supply-side-voltage detecting unit configured to detect phase power supply side voltages on a power supply side;
a load-side-voltage detecting unit configured to detect phase load side voltages on a phase-advancing load side;
a residual-voltage-polarity estimating unit configured to estimate, at a point when zero points of the phase load side voltages cannot be periodically detected, polarities of time differential values of the phase load side voltages at zero points of the phase load side voltages detected last as polarities of phase residual voltages on the phase-advancing load side after opening of the three-phase switching device; and a closing-phase control unit configured to detect a period of the phase power supply side voltages and control the closing phase of the three-phase switching device such that the three-phase switching device is closed at a point where the phase power supply side voltages change from the polarities of the phase residual voltages to reverse polarities thereof.

2. A phase control switching device that controls a closing phase of a three-phase switching device connected between a power supply and a phase-advancing load, the phase control switching device comprising:

a power-supply-side-voltage detecting unit configured to detect phase power supply side voltages on a power supply side;
a load-side-voltage detecting unit configured to detect phase load side voltages on a phase-advancing load side;
a residual-voltage-polarity estimating unit configured to calculate phase breaker inter-electrode voltages based on the phase power supply side voltages and the phase load side voltages and estimate polarities of phase residual voltages on the phase-advancing load side after opening of the three-phase switching device based on polarities of instantaneous values of the phase breaker inter-electrode voltages at a point when the phase breaker inter-electrode voltages increase to be equal to or larger than a predetermined positive voltage threshold or decrease to be equal to or smaller than a predetermined negative voltage threshold; and a closing-phase control unit configured to detect a period of the phase power supply side voltages and control the closing phase of the three-phase switching device such that the three-phase switching device is closed at a point where the phase power supply side voltages change from the polarities of the phase residual voltages to reverse polarities thereof.

3. The phase control switching device according to claim 2, wherein the phase breaker inter-electrode voltages are values obtained by subtracting the load side voltages from the power supply side voltages, and the residual-voltage-polarity estimating unit estimates reverse polarities of the instantaneous values as the polarities of the phase residual voltages.

4. The phase control switching device according to claim 2, wherein the phase breaker inter-electrode voltages are values obtained by subtracting the phase power supply side voltages from the phase load side voltages, and the residual-voltage-polarity estimating unit estimates the polarities of the instantaneous values as the polarities of the phase residual voltages.

5. A phase control switching device that controls a closing phase of a three-phase switching device connected between a power supply and a phase-advancing load, the phase control switching device comprising:
a power-supply-side-voltage detecting unit configured to detect phase power supply side voltages on a power supply side;
a load-side-voltage detecting unit configured to detect phase load side voltages on a phase-advancing load side;
a residual-voltage-polarity estimating unit configured to calculate phase breaker inter-electrode voltages based on the phase power supply side voltages and the phase load side voltages and estimate polarities of phase residual voltages on the phase-advancing load side after opening of the three-phase switching device based on polarities of integrated values of the phase breaker inter-electrode voltages before and after a point when the phase breaker inter-electrode voltages increase to be equal to or larger than a predetermined positive voltage threshold or decrease to be equal to or smaller than a predetermined negative voltage threshold; and a closing-phase control unit configured to detect a period of the phase power supply side voltages and control the closing phase of the three-phase switching device such that the three-phase switching device is closed at a point where the phase power supply side voltages change from the polarities of the phase residual voltages to reverse polarities thereof.

6. The phase control switching device according to claim 5, wherein the phase breaker inter-electrode voltages are values obtained by subtracting the phase load side voltages from the phase power supply side voltages, and the residual-voltage-polarity estimating unit estimates reverse polarities of the integrated values as polarities of the phase residual voltages.

7. The phase control switching device according to claim 5, wherein the phase breaker inter-electrode voltages are values obtained by subtracting the phase power supply side voltages from the phase load side voltages, and the residual-voltage-polarity estimating unit estimates the polarities of the integrated values as polarities of the phase residual voltages.

8. A phase control switching device that controls a closing phase of a three-phase switching device connected between a power supply and a phase-advancing load, the phase control switching device comprising:
a power-supply-side-voltage detecting unit configured to detect phase power supply side voltages on a power supply side;
a load-side-voltage detecting unit configured to detect phase load side voltages on a phase-advancing load side;

a residual-voltage-polarity estimating unit configured to estimate, at a point when zero points of the phase load side voltages cannot be periodically detected, phase breaking times based on detection times of zero points of the phase load side voltages detected last and estimate polarities of integrated values of the phase load side voltages after the phase breaking times as polarities of phase residual voltages on the phase-advancing load side after opening of the three-phase switching device; and a closing-phase control unit configured to detect a period of the phase power supply side voltages and control the closing phase of the three-phase switching device such that the three-phase switching device is closed at a point where the phase power supply side voltages change from the polarities of the phase residual voltages to reverse polarities thereof.

9. A phase control switching device according to any one of claims 1 to 8, wherein the residual-voltage-polarity estimating unit determines, as an accident phase, a phase in which at least one or more zero points of the phase load side voltages are detected within a period shorter than a 1/2 cycle period of a power supply frequency from detection times of last zero points of the phase load side voltages, and the closing-phase control unit controls the closing phase of the three-phase switching device such that the three-phase switching device is closed at an arbitrary zero point of a phase power supply side voltage of the accident phase.

10. The phase control switching device according to any one of claims 1 to 8, further comprising a current detecting unit configured to detect phase currents flowing from the power supply to the phase-advancing load, wherein the residual-voltage-polarity estimating unit determines, as the accident phase, a phase in which magnitude of the phase currents is equal to or larger than a predetermined current threshold, and the closing-phase control unit controls the closing phase of the three-phase switching device such that the three-phase switching device is closed at an arbitrary zero point of a phase power supply side voltage of the accident phase.

11. The phase control switching device according to any one of claims 1 to 8, further comprising a current detecting unit configured to detect phase currents flowing from the power supply to the phase-advancing load, wherein the residual-voltage-polarity estimating unit determines, as the accident phase, a phase in which at least one or more zero points of the phase load side voltages are detected within a period shorter than a 1/2 cycle period of a power supply frequency from detection times of last zero points of the phase load side voltages and a phase in which magnitude of the phase currents is equal to or larger than a predetermined current threshold, and the closing-phase control unit controls the closing phase of the three-phase switching device such that the three-phase switching device is closed at an arbitrary zero point of a phase power supply side voltage of the accident phase.