1. Field of the Invention
The present invention relates to a controlled switching device controlling opening and closing timing of a power switchgear such as a circuit breaker, and more particularly to a controlled switching device, which suppresses an overvoltage generated in time of making of a transmission line.
2. Description of the Related Art
In a conventional controlled switching device, the device finds frequencies, phases, and amplitudes from a power source voltage of a breaker and from measured waveforms of a load voltage for functional approximation; synthesizes an interpole voltage from the current time on using these approximation functions; executes a signal conversion based on a pre-arc characteristic of the breaker and a signal conversion based on variations of a mechanical action of the breaker; and determines a target closing time thereof (for example, see Patent Document 1). Then, the breaker is closed at this target closing time, thus suppressing the overvoltage generated at the time of making of a transmission line.
Patent Document 1: JP-A2003-168335
In general, sometimes a controlled switching device is used for a high-speed reclosing path in the event of a breakdown of a transmission line. In such a usage, it is required that within the limited time of about 500 milliseconds from the occurrence of a failure of the transmission line, a target closing time, at which the overvoltage is suppressed in time of making of the transmission line, and then the breaker is closed. In the above-described conventional controlled switching device, a lot of calculations have to be made to determine the target closing time during working of the device. Consequently, there has been demand for a high-performance arithmetic unit, with increased the cost of the device.
The present invention has been made to solve the above-mentioned problem, and an object of the present invention is to provide a controlled switching device able to offer a simple calculation during working of the device, and high-speed control even with an inexpensive arithmetic unit.
The controlled switching device according to the present invention includes a target-closing phase-map generating section generating a target closing phase map beforehand in consideration of a pre-arc characteristic and variations of a mechanical action of a power switchgear, and amplitude fluctuations of a load voltage; a target-closing time calculating section calculating a target closing time string from a frequency and a phase of each of power source voltages and a load voltage in the power switchgear referring to the target closing phase map; and a closing control section, when a close command is inputted to the power switchgear, controlling, based on a preset predicted closing time and the target closing time string, the timing of outputting a closing control signal for instructing the power switchgear to start its closing operation.
The controlled switching device according to the present invention is arranged such that the target-closing phase-map generating section generates in advance a target closing phase map, and the target-closing time calculating section calculates a target closing time string based on the target closing phase map, thus providing a simple calculation during working of the device, and high-speed control even with an inexpensive arithmetic unit.
Referring to the figure, the controlled switching device includes a voltage measuring section 1, a frequency-phase calculating section 2, a target-closing phase-map generating section 3, a target-closing time calculating section 4, and a closing control section 5.
The voltage measuring section 1 is a section measuring a power source voltage and a load voltage of a breaker 6, which is a power switchgear, and storing these voltages for a fixed period of time. Further, the breaker 6 is a device that is provided between a power supply 7 and a transmission line 8 located on the load side, and performs making of a power from the power supply 7 to the transmission line 8.
The frequency-phase calculating section 2 is a section calculating a frequency and a phase of each of a power source voltage 1a and a load voltage 1b, measured by the voltage measuring section 1. The target-closing phase-map generating section 3 is a section previously generating a target closing phase map 3a in consideration of a pre-arc characteristic 9 and variations of a mechanical action 10 of the breaker 6, and amplitude fluctuations of the load voltage prior to working of the device. The target-closing time calculating section 4 is a section for calculating a target closing time string, referring to the target closing phase map 3a, from the frequency and the phase of each of the power source voltage and the load voltage, calculated by the frequency-phase calculating section 2. The closing control section 5 is a section, upon input of a close command 11 thereto, controls, the timing of outputting a closing control signal 5a for instructing the breaker 6 to start its closing operation, based on a predicted closing time 12, and the target closing time string 4a outputted from the target-closing time calculating section 4.
Then, the operation of the controlled switching device thus configured as above will be explained below.
The voltage measuring section 1 measures the power source voltage and the load voltage of the breaker 6, stores these voltages for a fixed period of time, and outputs these voltages to the frequency-phase calculating section 2 as the power source voltage 1a and the load voltage 1b.
The frequency-phase calculating section 2 calculates a frequency and a phase 2a of the power source voltage and a frequency and a phase 2b of the load voltage, respectively, from the power source voltage 1a and the load voltage 1b corresponding to those for a past fixed period of time, outputted from the voltage measuring section 1. To be more specific, the frequency-phase calculating section detects, and stores a plurality of certain zero-cross point times at which the obtained voltage signal changes its sign, from negative to positive, vice versa. When the voltage signal is a sine wave signal, the zero-cross point is obtained every half-cycle and therefore, the value, which is obtained by averaging a reciprocal number of the mean value in the time interval between each of the plurality of stored zero-cross point times, and by doubling the reciprocal number, may be taken as a frequency f (Hz). Concerning a frequency of the power source voltage, it is fixed to a frequency of 50 Hz or of 60 Hz according to a system condition and therefore, the value, which has been preset, is used.
Regarding the phase, letting the time, which is closest to the current time in the plurality of stored zero-cross point times, be t1 (sec) and the current time be t2 (sec), the phase is calculated from the following equations.
Where the voltage signal changes from negative to positive at the zero-cross point of the time t1,
the phase (degree)=(t2−t1)×f×360, and
where the signal changes from positive to negative at the zero-cross point of the time t1,
the phase (degree)=(t2−t1)×f×360+180.
The above-mentioned calculations give a frequency and a phase 2a of the power source voltage, and a frequency and a phase 2b of the load voltage.
Then, the operation of generating a target closing phase map in the target-closing phase-map generating section will be explained below.
First of all, a characteristic of the breaker 6 will be taken up here. When a closing control signal 5a is outputted from the closing control section 5, contacts of the breaker 6 come in mechanically contact with each other after a certain mechanical operation time lapsed. A moment at which the contacts come in mechanically contact is referred to as “closing,” and the time elapsed from an output of the closing control signal 5a to “closing” of the contacts are “closed” is referred to as “closing time.” Further, it is known that the main circuit current begins to flow by a pre-discharge prior to closing. This pre-discharge is referred to as a “pre-arc,” and a moment at which the main circuit current begins to flow is referred to as “making.” The moment of making depends on the voltage applied between the contacts of the breaker 6, i.e., on the absolute value of the interpole voltage, which is a difference value between the power source voltage 1a and the load voltage 1b.
An withstand voltage line 101 shown in
In order to suppress the overvoltage generated at the time of the making, it should make the breaker 6 at a moment when the absolute value of the interpole voltage becomes minimum. Therefore, it should determine the target closing time, after consideration of the pre-arc characteristic, such that a moment when the absolute value of the interpole voltage becomes minimum is a making point, and that the closing control signal 5a should output so that the breaker 6 is closed at the target closing time.
However, the predicted closing time 12, which is a predicted value of the next closing time, does not necessarily coincide with the actual closing time, as the breaker 6 does entail mechanical variations in operation. In other words, the output of the closing control signal 5a at the time going back from the target closing time by the predicted closing time 12 results in the actual closing times being normally distributed with the actual closing time as the target closing time.
In
Further, in case of failure of the transmission line, the power source voltage 1a can be considered to have a rated amplitude. However, the load voltage 1b fluctuates its amplitude according to the conditions in failure, leading to a change of the magnitude of the interpole voltage, which is a difference value between the power source voltage 1a and the load voltage 1b.
The method of generating the target closing phase map will be explained referring to
At the first, a slant of the withstand voltage line 204 is set in advance based on the pre-arc characteristic of the breaker 6. Further, a closing time variation 205 is set beforehand based on the variations of the mechanical action of the breaker 6. An explanation will be forwarded hereinafter on condition that the frequency of the power source voltage is 60 (Hz).
First of all, the power source voltage 201 is generated such that a phase of the power source voltage at the time of 0 second becomes 0 degree, and further, the load voltage 202 is generated such that a phase of the load voltage at the time of 0 second becomes 30 degrees. Then, the absolute value 203 of the interpole voltage is found, which is the absolute value of the difference value between the power source voltage 201 and the load voltage 202.
Subsequently, a withstand voltage line 204 having a slant based on the pre-arc characteristic of the breaker 6 is changed within the range of the closing time variation 205, with the time 0 second as the center, and thereby, an input voltage 206 is found, which is the maximum value of the intersection between the withstand voltage line and the absolute value 203 of the interpole voltage. Thereafter, as shown in
In the above-described operations, changing the phase of the power source voltage within the range of 0-360 degrees and the phase of the load voltage within the range of 0-360 degrees, and calculating the map point in each of the phases generates a target closing phase map in two-dimensional form.
Iteration of the above-described operation with the frequency of the load voltage changed generates the target closing phase map 3a of each of the frequencies of the load voltage. In parenthesis, the target closing phase map 3a shall be generated prior to working of the controlled switching device.
Then, the target-closing-time calculating section 4 determines the target closing time strings 4a, from the frequency and phase 2a of the power source voltage and the frequency and phase 2b of the load voltage, which are found by the frequency-phase calculating section 2, referring to the target closing phase map 3a.
A method of calculating the target closing time string 4a will be explained referring to
The slant of the straight line 209=the frequency of the load voltage/the frequency of the power source voltage.
Accordingly, a value of the maximum input voltage from the current time 208 on can be found immediately by reading out the target closing phase map 3a along the straight line 209. For example, an example in which the value of the time when the maximum input voltage is less than 0.8 PU is assumed to be 1 and a value of the time when the voltage is 0.8 PU or more is assumed to be 0, and the target closing time string 4a is generated is shown in the lower part of
In this connection, it is required that the target closing time string 4a be calculated in a time area of the future passed away the predicted closing time 12 from the current time.
After that, upon an input of a close command 11 to the closing control section 5, the target closing time string 4a and a closing control signal 5a instructing the breaker to start its closing operation based on the predicted closing time 12 are outputted after delaying the output by a time described hereinafter.
As shown in
Upon output of the closing control signal 5a, the breaker 6 is closed at the time 302 when the predicted closing time 12 has elapsed.
As mentioned above, according to the controlled switching device of the first embodiment, the device includes the voltage measuring section measuring the power source voltage and the load voltage of a power switchgear; the frequency-phase calculating section calculating the frequency and the phase of each of the power source voltage and the load voltage; the target-closing phase-map generating section previously generating a target closing phase map in consideration of the pre-arc characteristic and the variations of the mechanical action of the power switchgear, and the amplitude fluctuations of the load voltage; the target-closing time calculating section calculating a target closing time from the frequency and the phase of each of the power source voltage and the load voltage referring to the target closing phase map; and the closing control section, when a close command is inputted to the power switchgear, controlling, based on the preset predicted closing time and the target closing time string, the timing of outputting a closing control signal for instructing the power switchgear to start its closing operation. Thus, the device allows performing the making of the power switchgear at the optimum timing, which enables suppressing the overvoltage generated in time of the making of the transmission line. Further, the controlled switching device provides a simple calculation during working of the device, and enables high-speed control even with an inexpensive arithmetic unit.
Moreover, according to the controlled switching device of the first embodiment, the target closing phase map is designed to indicate the maximum value of the absolute value of the interpole voltage, corresponding to the power source voltage phase and the load voltage phase at the making point in time of the power switchgear, thus permitting determination of the optimum time in making the power switchgear by a simple calculation.
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2007-119429 | Apr 2007 | JP | national |
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Number | Date | Country |
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2003-168335 | Jun 2003 | JP |
Number | Date | Country | |
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20080269952 A1 | Oct 2008 | US |