Note: Descriptions are shown in the official language in which they were submitted.
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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
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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-
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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
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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
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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.
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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
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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,
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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
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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
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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
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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
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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.
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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
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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
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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
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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-
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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
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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
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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.
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[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
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21
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
CA 02806254 2014-11-03
22
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
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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
