Note: Descriptions are shown in the official language in which they were submitted.
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DESCRIPTION
POWER SWITCHING CONTROL DEVICE AND CLOSING CONTROL METHOD
THEREOF
Field
[0001] The present invention relates to a power
switching control device and a closing control method
thereof.
Background
[0002] It is known that an electric charge remains in
sound phases after a current is interrupted in an
accidental power interruption on a power transmission line.
In this case, various voltages are generated on a load side
(a transmission line side) of a circuit breaker depending
on transmission line conditions. For example, in a case of
the circuit breaker connected to a shunt-reactor-
compensated power transmission line, an AC voltage having a
constant frequency due to a reactor and the capacitive load
of the power transmission line is generated on the load
side of the circuit breaker, and in a case of the circuit
breaker connected to a shunt-reactor-uncompensated power
transmission line, a DC voltage in proportion to the power-
supply side voltage of the circuit breaker during the
interruption is generated on the load side of the circuit
breaker.
[0003] A conventional power switching control device
estimates a gap voltage at and after the present time as
the difference between the power-supply side voltage at and
after the present time that is obtained from the measured
value of the power-supply side voltage and the load-side
voltage at and after the present time that is obtained from
the measured value of the load-side voltage. Furthermore,
the conventional power switching control device controls
the timing of closing the circuit breaker so that the
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circuit breaker can be closed at the timing when a gap-
voltage estimate value is equal to a minimum value, thereby
suppressing an overvoltage at the time of closing the
circuit breaker (for example, Patent Literature 1).
Citation List
Patent Literature
[0004] Patent Literature 1: Japanese Patent No. 3986810
Summary
Technical Problem
[0005] The above conventional technique is adopted on
the premise that the behavior of the load-side voltage does
not change after interrupting a current. However, in a
case where the power transmission line connected to the
load side of the circuit breaker is the shunt-reactor-
uncompensated power transmission line and the load-side
voltage is measured by using a voltage measuring instrument
such as a voltage transformer (VT) that discharges an
electric charge, the electric charge remaining on the load
side is discharged via the voltage measuring instrument.
As a result, the load-side voltage rapidly attenuates to
zero. Furthermore, whether the power transmission line
connected to the load side of the circuit breaker is the
shunt-reactor-compensated power transmission line or the
shunt-reactor-uncompensated power transmission line, the
electric charge remaining on the load side is discharged by
the leakage resistance or the like of an insulator
supporting the power transmission line as long as a
sufficient time interval is secured from a previous
interruption to the next closing similarly to a case, for
example, of executing slow re-closing for which the time
from the interruption to the closing is longer than a time
specified in advance. Accordingly, the load-side voltage
at the next closing attenuates over time and eventually
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becomes zero. Therefore, the conventional technique has
the following problems. The gap-voltage estimate value
does possibly not match an actual gap voltage, and it is
impossible to suppress generation of a transient voltage or
current at the time of closing the circuit breaker to a
minimum.
[0006] The present invention has been achieved in view
of the above problems, and an object of the present
invention is to provide a power switching control device
that can suppress generation of a transient voltage or
current that is possibly caused by a mismatch between a
gap-voltage estimate value after interrupting a current and
an actual gap voltage.
Solution to Problem
[0007] In order to solve above-mentioned problems and
achieve the object of the present invention, there is
provided a power switching control device applied to a
configuration of connecting a circuit breaker to a power
transmission line between a power supply and a load,
comprising: a voltage measurement unit that measures a
power-supply side voltage and a load-side voltage of the
circuit breaker; a gap-voltage estimation unit that
estimates a power-supply-side voltage estimate value at and
after a time when the circuit breaker interrupts a current
based on the power-supply side voltage, that estimates a
load-side voltage estimate value at and after the time when
the circuit breaker interrupts the current based on the
load-side voltage and a passage of time since the circuit
breaker interrupts the current, and that calculates a
circuit-breaker-gap-voltage estimate value at and after the
time when the circuit breaker interrupts the current based
on the power-supply-side voltage estimate value and the
load-side voltage estimate value; a target closing-time
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detection unit that detects an optimum timing of closing
the circuit breaker and outputs a target closing time based
on the circuit-breaker-gap-voltage estimate value; and a
closing control unit that controls the circuit breaker to
be closed at the target closing time.
Advantageous Effects of Invention
[0008] According to the present invention, it is
possible to suppress generation of a transient voltage or
current that is possibly caused by a mismatch between a
gap-voltage estimate value after interrupting a current and
an actual gap voltage.
Brief Description of Drawings
[0009] FIG. 1 is a configuration example of a power
switching control device according to a first embodiment.
FIGS. 2 depict an example of a behavior of voltages
and a current of respective parts before and after
interrupting the current on a shunt-reactor-compensated
power transmission line.
FIGS. 3 depict an example of a behavior of voltages
and a current of respective parts before and after
interrupting the current on a shunt-reactor-uncompensated
power transmission line.
FIG. 4 is a flowchart of an example of processes
performed by the power switching control device according
to the first embodiment.
FIG. 5 is a flowchart of an example of processes
performed by a power switching control device according to
a second embodiment.
Description of Embodiments
[0010] A power switching control device and a closing
control method thereof according to embodiments of the
present invention will be explained below in detail with
reference to the accompanying drawings. The present
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invention is not limited to the embodiments.
[0011] First embodiment.
FIG. 1 is a configuration example of a power switching
control device according to a first embodiment. In FIG. 1,
5 a circuit breaker 2 is connected between a power-supply-
side main circuit 1 on a left-side of Fig. 1 and a no-load
power transmission line 3 on a right-side thereof. A
voltage measurement unit 6 that includes a power-supply-
side voltage measurement unit 4 measuring a power-supply
side voltage of the circuit breaker 2 and a load-side
voltage measurement unit 5 measuring a load-side voltage of
the circuit breaker 2 is connected to both ends of the
circuit breaker 2. An auxiliary switch 7 interlocking with
movable contacts of the circuit breaker 2 is connected to
the circuit breaker 2. An open/closed-state detection unit
10 detecting whether the auxiliary switch 7 is in an open
state or a closed state is connected to the auxiliary
switch 7. In the example shown in FIG. 1, only one phase
among phases R, S, and T is shown for the brevity of
explanations.
[0012] In the example shown in FIG. 1, the power
transmission line 3 is a shunt-reactor-compensated power
transmission line or a shunt-reactor-uncompensated power
transmission line. If the power transmission line 3 is the
shunt-reactor-compensated power transmission line, an AC
voltage having a constant frequency due to a reactor on a
load side of the circuit breaker 2 and an electrostatic
capacity of the power transmission line 3 is generated. If
the power transmission line is the shunt-reactor-
uncompensated power transmission line, a DC voltage in
proportion to a power-supply side voltage at a time of
interrupting a current is generated on the load side of the
circuit breaker 2.
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[0013] For example, the power switching control device
according to the first embodiment is constituted by a
computer and the like, and includes a gap-voltage
estimation unit 11, a target-closing-time detection unit 12,
and a closing control unit 13. In the example shown in FIG.
1, it is described that the power switching control device
does not include the voltage measurement unit 6, the
auxiliary switch 7, and the open/closed-state detection
unit 10. Alternatively, the power switching control device
can be configured to include these constituent elements.
[0014] The gap-voltage estimation unit 11 continuously
estimates instantaneous values of a gap voltage based on
the power-supply side voltage output from the power-supply-
side voltage measurement unit 4, the load-side voltage
output from the load-side voltage measurement unit 5, and
an open/closed-state detection signal output from the
open/closed-state detection unit 10, and outputs the
instantaneous values of the gap voltage to the target-
closing-time detection unit 12.
[0015] The target-closing-time detection unit 12 detects
an optimum closing timing when the circuit breaker 2 can be
closed next time based on a circuit-breaker-gap-voltage
estimate value, and outputs a target closing time.
[0016] When a closing command is input, the closing
control unit 13 controls the circuit breaker 2 to be closed
at the target closing time output from the target-closing-
time detection unit 12.
[0017] A method of suppressing the generation of a
transient voltage or current by the power switching control
device according to the first embodiment is explained next
with reference to FIGS. 2 and 3.
[0018] FIGS. 2 depict an example of a behavior of
voltages and a current of respective parts before and after
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interrupting the current on the shunt-reactor-compensated
power transmission line. FIG. 2(a) depicts a waveform of a
main circuit current in one phase. FIG. 2(b) depicts a
waveform of the power-supply side voltage in the phase and
FIG. 2(c) depicts a waveform of the load-side voltage in
the phase. FIG. 2(d) depicts a waveform of the circuit-
breaker gap voltage in the phase obtained by subtracting
the load-side voltage shown in FIG. 2(c) from the power-
supply side voltage shown in FIG. 2(b).
[0019] FIGS. 3 depict an
example of a behavior of
voltages and a current of respective parts before and after
interrupting the current on the shunt-reactor-uncompensated
power transmission line. FIG. 3(a) depicts a waveform of
the main circuit current in each phase. FIG. 3(b) depicts
a waveform of the power-supply side voltage in each phase
and FIG. 3(c) depicts a waveform of the load-side voltage
in each phase. FIG. 3(d) depicts a waveform of the
circuit-breaker gap voltage in each phase obtained by
subtracting the load-side voltage shown in FIG. 3(c) from
the power-supply side voltage shown in FIG. 3(b). FIG.
3(e) depicts a waveform of the load-side voltage when a
voltage measuring instrument such as a voltage transformer
(hereinafter, "VT") that discharges an electric charge is
used as the load-side voltage measurement unit 5.
[0020] As shown in FIG.
2(c), when the current is
interrupted at a time T on the shunt-reactor-compensated
power transmission line, the waveform of the load-side
voltage changes to a waveform of the AC voltage having the
constant frequency due to the reactor and the capacitive
load of the power transmission line.
[0021] As shown
in FIG. 3(c), when the current is
interrupted at the time T on the shunt-reactor-
uncompensated power transmission line, the waveform of the
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load-side voltage changes to a waveform of the DC voltage
in proportion to the power-supply side voltage at the time
of an interruption.
[0022] As
shown in FIG. 2(c), for example, when timings
when the load-side voltage is equal to or higher than a
predetermined positive-electrode-side threshold (80% of a
maximum value of the power-supply side voltage, for
example) and timings when the load-side voltage is equal to
or lower than a negative-electrode-side threshold equal to
the positive-electrode-side threshold are respectively
detected at least once within a certain time (100
milliseconds, for example) at and after a current
interruption time T, it is possible to determine that the
load-side voltage is an AC wave signal. In this case, it
is possible to determine that the power transmission line 3
------------------------------------------------------------------------- ted
to the load side of the circuit breaker 9 is the
shunt-reactor-compensated power transmission line. In
other cases, the load-side voltage is determined to be a DC
signal. In this case, it is determined that the power
transmission line 3 connected to the load side of the
circuit breaker 2 is the shunt-reactor-uncompensated power
transmission line. Alternatively, it is possible to
determine that the load-side voltage is an AC waveform
signal and that the power transmission line 3 connected to
the load side of the circuit breaker 2 is the shunt-
reactor-compensated power transmission line when, for
example, zero points in a constant cycle are generated on
the load-side voltage within the certain time at and after
the circuit interruption time T.
[0023] As in a case of executing slow re-closing for
which a time from the current interruption of the circuit
breaker 2 to the closing of the circuit breaker 2 is longer
than a time specified in advance (by 3 or more seconds, for
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example), when a sufficient time interval is secured from
the current interruption time T to the next closing, the
load-side voltage (that is, a residual voltage) attenuates
by a time constant or the like that is determined by the
electrostatic capacity of the power transmission line 3 and
a leakage resistance of an insulator supporting the power
transmission line 3 and eventually converges into zero over
time. Therefore, when a time from the current interruption
time is counted and a predetermined time determined, for
example, based on an attenuation time constant of the
residual voltage on the power transmission line 3 estimated
by a prior calculation or the like, then it is determined
that the slow re-closing is executed, and it is estimated
that the load-side voltage estimate value at the time of
closing the circuit breaker 2 is zero. On the other hand,
if the predetermined time does not pass since the current
interruption time T, it is determined that fast re-closing
is executed and the load-side voltage estimate value at and
after the present time is calculated using data by as much
as the certain time since the current interruption time T.
The present invention is not limited to the method of
calculating the load-side voltage estimate value adopted in
this case.
[0024] Furthermore, in a case where the power
transmission line 3 is the shunt-reactor-uncompensated
power transmission line and where the voltage measuring
instrument such as the VT that discharges an electric
charge is used as the load-side voltage measurement unit 5,
as shown in FIG. 3(e), the electric charge remaining on the
load side is rapidly discharged because of saturation of an
iron core of the VT after interrupting the current.
Accordingly, the load-side voltage actually output from a
secondary side of the load-side voltage measurement unit 5
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converges into zero in several hundreds of milliseconds
after the current interruption. Generally, a time interval
since the circuit breaker 2 interrupts the current until
the circuit breaker 2 is closed next time is about 0.3
5 second to about 1.0 second even in the case of the fast re-
closing. Therefore, the load-side voltage attenuates to
nearly zero by the time of closing the circuit breaker 2
next time as a result of discharging the electric current
by the VT. Therefore, when the power transmission line 3
10 is the shunt-reactor-uncompensated power transmission line
and the load-side voltage shows a behavior of converging
into zero at a speed equal to or higher than a constant
speed (100 milliseconds, for example) after the current
interruption time T, then it is determined that the load-
side voltage measurement unit 5 is the voltage measuring
instrument such as the VT that discharges
charge, and the load-side voltage estimate value at the
time of closing the circuit breaker 2 next time is
estimated as zero. On the other hand, when the load-side
voltage does not show the behavior of converging into zero
at the speed equal to or higher than the constant speed
after the current interruption time T, then it is
determined that the load-side voltage measurement unit 5 is
not the voltage measuring instrument such as the VT (such
as a capacitive voltage transformer) that discharges an
electric charge, and the load-side voltage estimate value
at and after the present time is calculated using the data
by as much as the certain time since the current
interruption time T. The present invention is not limited
to the method of calculating the load-side voltage estimate
value adopted in this case.
[0025] That is, the power switching control device
according to the first embodiment estimates that the load-
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side voltage estimate value at the next closing is zero
when the predetermined time determined based on the
attenuation time constant of a residual voltage on the
power transmission line 3 in advance passes since the
current interruption time T, and when the load-side voltage
at and after the current interruption time T is a DC signal
and the load-side voltage shows the behavior of converging
into zero at the speed equal to or higher than the constant
speed at and after the current interruption time T. The
power switching control device according to the first
embodiment can thereby more accurately estimate the gap
voltage at and after the present time and suppress
generation of a transient voltage or current that is
possibly caused by a mismatch between the gap-voltage
estimate value and the actual gap voltage in a case of a
slow re-closing operation or even in a case where the power
transmission line 3 is the shunt-reactor-uncompensated
power transmission line and where the load-side voltage
measurement unit 5 is the voltage measuring instrument such
as the VT that discharges an electric charge.
[0026] An operation performed by the power switching
control device according to the first embodiment is
explained next with reference to FIGS. 1 to 4. FIG. 4 is a
flowchart of an example of processes performed by the power
switching control device according to the first embodiment.
[0027] First, the gap-voltage estimation unit 11
converts an analog signal of the power-supply side voltage
input from the power-supply-side voltage measurement unit 4
into a digital signal, discretizes the digital signal at a
predetermined sampling interval, and stores therein the
power-supply-side voltage signal by as much as a certain
time (Step ST101). In addition, the gap-voltage estimation
unit 11 converts an analog signal of the load-side voltage
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input from the load-side voltage measurement unit 5 into a
digital signal, discretizes the digital signal at a
predetermined sampling interval, and stores therein the
load-side voltage signal by as much as the certain time
(Step ST201).
[0028] Next, the gap-voltage estimation unit 11 detects
and stores therein a plurality of zero-point times when a
sign of the power-supply-side voltage signal changes from
minus to plus or from plus to minus (Step ST102). In
addition, the gap-voltage estimation unit 11 detects and
stores therein a plurality of zero-point times when a sign
of the load-side voltage signal changes from minus to plus
or from plus to minus (Step ST202).
[0029] The gap-voltage estimation unit 11 always stores
therein the power-supply-side voltage signal before the
certain time since the present time, the load-side voltage
signal before the certain time since the present time, the
zero-point times of the power-supply-side voltage signal,
and the zero-point times of the load-side voltage signal as
data. When detecting that the auxiliary switch 7 changes
from the closed state to the open state, the gap-voltage
estimation unit 11 determines that the circuit breaker 2
interrupts the current and stops storing therein the above
data at a time point when the certain time passes since the
current interruption time T. That is, the gap-voltage
estimation unit 11 calculates the power-supply-side voltage
estimate value and the load-side voltage estimate value at
and after the present time using the data by as much as the
certain time since the current interruption in subsequent
processing steps.
[0030] Next, the gap-voltage estimation unit 11
determines whether the power-supply-side voltage signal is
an AC waveform signal (Step ST103). In addition, the gap-
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voltage estimation unit 11 determines whether the load-side
voltage signal is the AC waveform signal (Step ST203). A
process of calculating the load-side voltage estimate value
is explained first.
[0031] When the load-side voltage signal is the AC
waveform signal (YES at Step ST203), the gap-voltage
estimation unit 11 determines that the power transmission
line 3 is the shunt-reactor-compensated power transmission
line, and determines whether the predetermined time passes
since the current interruption time T (Step S204). When
the predetermined time does not pass since the current
interruption time T (NO at Step S204), the gap-voltage
estimation unit 11 determines that the fast re-closing is
executed, determines that an attenuation due to the leakage
resistance or the like does not occur to the load-side
voltage, obtains a frequency, a phase, and an amplitude of
the load-side voltage, and calculates the load-side voltage
estimate value at and after the present time (Step S205).
When the predetermined time passes since the current
interruption time T (YES at Step ST204), the gap-voltage
estimation unit 11 determines that the slow re-closing is
executed and estimates the load-side voltage estimate value
as zero (Step ST206).
[0032] An example of a method of calculating the load-
side voltage estimate value at and after the present time
at Step S205 is explained. As for the frequency of the
load-side voltage signal, for example, it suffices to
obtain an average value of a plurality of zero-point time
intervals of the load-side voltage signal stored at Step
ST202, to multiply a reciprocal of the average value of the
zero-point time intervals by 1/2, and to set a resultant
value as the frequency of the load-side voltage signal. As
for the phase of the load-side voltage signal, a value of
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the latest zero-point time when the load-side voltage
changes from the minus sign to the plus sign among a
plurality of zero-point times stored at Step ST202 is
stored as the time of a phase of 0 degree. In addition, a
value of the latest zero-point time when the load-side
voltage signal changes from the plus sign to the minus sign
is stored as a phase of 180 degrees. As for the amplitude
of the load-side voltage signal, a maximum value and a
minimum value of a plurality of load-side voltage signals
obtained for a period, for example, from the current
interruption time T to the present time are stored, and an
average of absolute values of the stored maximum and
minimum values is set as the amplitude of the load-side
voltage signal. Alternatively, the amplitude of the load-
side voltage signal can be obtained by integrating the
load-side voltage signals by a cycle to obtain an effective
value and by multiplying the effective value by *V2. If the
above calculated values are used, the load-side voltage
signal can be approximated as expressed by "voltage value =
amplitude x sin(2n x frequency xt)", with t=0 as the time
corresponding to the phase of 0 degree. This value obtained
by the equation is assumed as the load-side-voltage
estimate value at and after the present time at step STP205.
[0033] Referring back to the flowchart shown in FIG. 4,
when the load-side voltage signal is not the AC waveform
signal (that is, a DC signal) (NO at Step ST203), the gap-
voltage estimation unit 11 determines that the power
transmission line 3 is the shunt-reactor-uncompensated
power transmission line, and determines whether the load-
side voltage shows the behavior of converging into zero at
the speed equal to or higher than the constant speed at and
after the current interruption time T (Step ST207).
[0034] When the load-side voltage shows the behavior of
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converging into zero at the speed equal to or higher than
the constant speed at and after the current interruption
time T (YES at Step ST207), the gap-voltage estimation unit
11 determines that the load-side voltage measurement unit 5
5 is the voltage measuring instrument such as the VT that
discharges an electric charge, and estimates the load-side
voltage estimate value as zero (Step ST206). When the
load-side voltage does not show the behavior of converging
into zero at the speed equal to or higher than the constant
10 speed at and after the current interruption time T (NO at
Step ST207), the gap-voltage estimation unit 11 determines
that the load-side voltage measurement unit 5 is not the
voltage measuring instrument such as the VT (such as a
capacitive voltage transformer) that discharges an electric
15 charge, and determines whether the predetermined time
passed since the current intr11ption time T (Step ST208).
When the predetermined time does not pass since the current
interruption time T (NO at Step S208), the gap-voltage
estimation unit 11 determines that the fast re-closing is
executed, determines that the attenuation due to the
leakage resistance or the like does not occur to the load-
side voltage, calculates a time average value of the load-
side voltage signals, for example, as the amplitude of a DC
signal, and sets this value as the load-side voltage
estimate value at and after the present time (Step ST209).
When the predetermined time passes since the current
interruption time T (YES at Step ST208), the gap-voltage
estimation unit 11 determines that the slow re-closing is
executed and estimates the load-side voltage estimate value
as zero (Step ST206).
[0035] A process of calculating the power-supply-side
voltage estimate value is explained next. When the load-
side voltage signal is the AC waveform signal (YES at Step
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ST103), the gap-voltage estimation unit 11 obtains a
frequency, a phase, and an amplitude of the power-supply-
side voltage and calculates the power-supply-side voltage
estimate value at and after the present time (Step ST105).
Because a method of calculating the power-supply-side
voltage estimate value at Step ST105 is identical to the
method of calculating the load-side voltage estimate value
at Step ST205, the calculation method is not described
herein.
[0036] When the power-supply-side voltage signal is not
the AC waveform signal (that is, a DC signal) (NO at Step
ST103), the gap-voltage estimation unit 11 calculates a
time average value of the load-side voltage signals, for
example, as the amplitude of the DC signal, and sets this
value as the power-supply-side voltage estimate value at
and after the present time (Step ST109).
[0037] The gap-voltage estimation unit 11 calculates an
absolute value of the gap-voltage estimate value for the
certain time since the present time using the power-supply-
side voltage estimate value and the load-side voltage
estimate value (Step ST310).
[0038] The target-closing-time detection unit 12
estimates the target closing time for the certain time
since the present time so that the circuit breaker 2 can be
closed at a timing when the absolute value of the gap-
voltage estimate value becomes smaller based on the
absolute value of the gap-voltage estimate value input from
the gap-voltage estimation unit 11 (Step ST311). The
present invention is not limited to this method of
estimating the target closing time.
[0039] The target-closing-time detection unit 12 assumes
that a latest estimation result of the target closing time
is correct, deletes the target closing time estimated in a
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previous process, rewrites the target closing time
estimated in the previous process to the target closing
time estimated in the present process, and updates and
outputs the target closing time (Step ST312).
[0040] When a closing command 15 is input, the closing
control unit 13 controls the circuit breaker 2 to be closed
at the target closing time obtained by the target-closing-
time detection unit 12 (Step ST313).
[0041] As described above, the power switching control
device according to the first embodiment estimates that the
load-side voltage estimate value at the next closing is
zero when the predetermined time determined based on the
attenuation time constant of a residual voltage on the
power transmission line in advance passes since the current
interruption time, and when the load-side voltage at and
after the current interruption time is a DC signal and the
load-side voltage shows the behavior of converging into
zero at the speed equal to or higher than the constant
speed at and after the current interruption time. The
power switching control device according to the first
embodiment can thereby more accurately estimate the gap
voltage at and after the present time and suppress the
generation of the transient voltage or current that is
possibly caused by a mismatch between the gap-voltage
estimate value and the actual gap voltage after the current
interruption in the case of the slow re-closing operation
or even in the case where the power transmission line 3 is
the shunt-reactor-uncompensated power transmission line and
where the load-side voltage measurement unit 5 is the
voltage measuring instrument such as the VT that discharges
an electric charge.
[0042] Second embodiment.
FIG. 5 is a flowchart of an example of processes
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performed by a power switching control device according to
a second embodiment. Because configurations of a power
switching control device according to the second embodiment
are identical to those described in the first embodiment
and shown in FIG. 1, explanations thereof will be omitted.
In addition, in the flowchart of FIG. 5, processes
identical or equivalent to those shown in FIG. 4 and
described in the first embodiment are denoted by same step
numbers and detailed explanations thereof will be omitted.
[0043] In the flowchart of the first embodiment shown in
FIG. 4, the process of determining whether the
predetermined time passes since the current interruption
time T (that is, whether the slow re-closing is executed)
(Step ST204 or ST208) is carried out in each of the case
where the load-side voltage signal is an AC waveform signal
and the case where the load-side signal is a DC signal. In
the second embodiment, before the process of determining
whether the load-side voltage is the AC waveform signal
(Step ST203a), a process of determining whether the
predetermined time passes since the current interruption
time T is performed (Step ST204a), as shown in FIG. 5.
When the predetermined time passes since the current
interruption time T (that is, the slow re-closing is
executed) (YES at Step ST204a), the gap-voltage estimation
unit 11 estimates the load-side voltage estimate value as
zero (Step 3T206) whether the load-side voltage signal is
the AC waveform signal or the DC signal. Therefore, in the
second embodiment, the number of processing steps can be
decreased as compared with that in the first embodiment.
[0044] As described above, the power switching control
device according to the second embodiment performs the
process of determining whether the predetermined time
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passes since the circuit breaker is closed before the
process of determining whether the load-side voltage signal
is the AC waveform signal, and estimates the load-side
voltage estimate value as zero whether the load-side
voltage signal is the AC waveform signal or the DC signal.
Therefore, in addition to effects of the first embodiment,
it is possible to decrease the number of processing steps
as compared with that in the first embodiment.
[0045] In the embodiments described above, it has been
explained that it is determined whether the load-side
voltage signal is the AC waveform signal or the DC signal
and determined whether the power transmission line is the
shunt-reactor-compensated power transmission line or the
shunt-reactor-uncompensated power transmission line.
Alternatively, if it is already known that the power
transmission line is the shunt-reactor-compensated power
transmission line or the shunt-reactor-uncompensated power
transmission line, the power switching control device can
be configured to select one of these options using a switch
or the like.
[0046] Furthermore, it has been described that it is
determined whether the load-side voltage falls at the speed
equal to or higher than the constant speed at and after a
current interruption time and determined whether the load-
side voltage measurement unit is the voltage measuring
instrument that discharges an electric charge such as the
VT. Alternatively, if it is already known whether the
load-side voltage measurement unit is the voltage measuring
instrument that discharges an electric charge such as the
VT, the power switching control device can be configured to
select one of these options using a switch or the like.
[0047] The configuration described in the above
embodiments is only an example of the configuration of the
CA 02824435 2013-07-09
present invention, and it is possible to combine the
configuration with other publicly-known techniques, and it
is needless to mention that the present invention can be
configured while modifying it without departing from the
5 scope of the invention, such as omitting a part of the
configuration.
Reference Signs List
[0048] 1 main circuit
2 circuit breaker
10 3 power transmission line
4 power-supply-side voltage measurement unit
5 load-side voltage measurement unit
6 voltage measurement unit
7 auxiliary switch
15 10 open/closed-state detection unit
11 gap-voltage estimation unit
12 target-closing-time detection unit
13 closing control unit
