JPH0435968B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a fault point locating device, and particularly to a fault point locating device capable of locating the distance to a fault point when an accident occurs in an electric power system.

[Technical background of the invention]

As a fault point locating device for power transmission lines, there is a surge reception method in which the surge generated at the fault point is received at both terminals of the transmission line and the fault point is located based on the time difference, and a pulse is immediately sent to the power transmission line after the fault is detected. sending out,
Pulse radar methods and the like that measure the reflection time have been put into practical use. However, these systems are not inexpensive because they require a transmission device to connect both terminals of the power transmission line, or a blocking coil to prevent pulses from escaping.

However, in recent years, with the development of microcomputers, research has been actively conducted on methods for locating fault points at low cost by calculating the distance to the fault point using system voltage and current data.

FIG. 1 shows a general configuration diagram of a digital fault point locating device using a microcomputer. In FIG. 1, reference numerals 1a and 1b are input converters into which each phase voltage and each phase current of the power system are introduced, respectively, and convert the input electrical quantity into a voltage signal of an appropriate magnitude. Filters 2a and 2b remove harmonic components contained in the outputs of the input converters 1a and 1b. 3 is a sample and hold circuit which samples the output from each filter 2a, 2b at predetermined intervals. 4 is an A/D conversion circuit to which the output from the sample/hold circuit 3 is added via a multiplexer 5 and converted into digital data. 6 is a direct memory access (DMA) circuit to which the input of the A/D conversion circuit 4 is applied. 7 is a memory circuit and DMA circuit 6
As a result, the output of the A/D conversion circuit 4 is written to a predetermined address. 8 is a read-only memory (ROM) in which a program is built-in.
Reference numeral 9 denotes a central processing unit (CPU) which executes calculations for locating fault points using the voltage and current data of the electric power system written in the memory circuit 7 according to the program written in the ROM 8. Reference numeral 10 denotes an output circuit that displays the failure point location results on a printer or lamp (not shown) based on the calculation results of the (CPU) 9.
Many studies have been conducted on calculation methods executed by the (CPU) 9, and as an example, a method has already been proposed that uses the following equation to determine the distance to the accident point.

x=lin{Vs・I″s ^* }／lin{ZIs・I″s ^* }…
...(1) However, x: Distance to the accident point v: Voltage at the location device installation point I: Current at the location device installation point I'': Difference current Z before and after the accident at the location device installation point: Impedance per unit of the transmission line lin: Indicates imaginary part ^* : Indicates conjugate complex number.

Generally, the voltage and current of a system when a failure occurs often contains harmonic components. This trend is particularly strong today when the number of phase modifiers and underground cable lines in the power system is increasing. Therefore, when calculating equation (1), it is necessary to remove the harmonic components contained in the input using a filter and extract only the fundamental wave component.

This filter effect can be expected from the analog type filters 2a and 2b shown in FIG. However, in normal digital devices, the purpose of the analog filter placed before A/D conversion of the input AC quantity is to remove the so-called "aliasing error" that accompanies A/D conversion. In many cases, it mainly removes harmonic components of 1/2 or more of the sampling frequency. Therefore, it is preferable that the filter function for the input AC quantity of electricity, which is necessary for the calculation of the original failure point location, be processed in the form of a digital filter by software by the CPU 9 after A/D conversion.

Let's now consider a simple digital filter. Suppose that the voltages sampled every 30 degrees of electrical angle at the fundamental frequency are v _n1 , v _n-1 , v _n-2 . . .
etc. FIG. 2a shows v _n , v _n-1 . . . expressed as instantaneous values, and FIG. 2 b shows them expressed on a vector plane. Now, consider a filter as shown in the following equation.

v _Fn = (v _n − v _n-6 )/2 …(2) If the input current is a DC component, v _n = v _n-6 , so (2)
It is clear that the result of the expression is zero. When the input current is at the fundamental frequency, as can be seen from Figure 2b,
Since v _n and v _n-6 have a phase of 180° and are equal in magnitude, v _Fn = v _n . Furthermore, when the input current is a second harmonic, the phase of v _n and v _n-6 is 360°, so the result of equation (2) becomes zero again. In this way, it can be seen that the filter effect of equation (2), as shown in FIG. 3, has a filter effect that removes the DC component and even harmonics and allows odd harmonics to pass. The effect of equation (2) is expressed by the so-called Z transformation as shown in the following equation.

F=(1-Z ^-N )/2...(3) However, N=6 Generally, by appropriately selecting the value of N in equation (3), the attenuation pole can be arbitrarily selected. A simple example of a digital filter is as follows.

F=(1−Z ^-N ′)/2 ...(4) According to equation (4), the DC component is the passband,
By appropriately selecting the value of N', the attenuation pole can be arbitrarily selected.

In order to further increase the attenuation pole and enhance the filter effect, it is conceivable to use filters of formula (3) or (4) in multiple stages. For example, it is a digital function such as the following equation.

F=(1-Z ^N1 )・(1-Z ^N2 )/4 ...(5) Or F=(1-Z ^N1 )・(1-Z ^N2 )・(1-Z ^N3 )/
8...(6) etc. Here, we assume that N1 = 6 and N2 = 4 in equation (5).
An example of the case is shown in FIG.

Now, when considering the response time of the filter in equations (3), (5), and (6), in the case of equation (3), the latest data and data N samples ago are used, but in the case of equation (5), In the case of equation (6), data from the past (N1+N2) samples are used, and in the case of equation (6), data from the past (N1+N2+N3) samples are used. From this, it can be said that in general, when it is desired to improve the attenuation characteristics of a filter, the response time of the filter becomes slower.

[Problems with background technology]

The purpose of a failure point locating device is to locate the distance to a failure point with high accuracy. Therefore, the digital filter described above needs to have a higher attenuation effect. However, on the other hand, a filter with a high damping effect has a slow response and requires a longer time to obtain a correct calculation result. Generally, a power system failure phenomenon often disappears in about 50 to 80 ms as long as the protection device operates normally. Considering this, it is not realistic to use a filter that has a very slow response.

Furthermore, the duration of a system fault can vary depending on the phase of fault occurrence, the state of the breakers, and the like. Therefore, it is necessary to determine the filter function by taking various points into consideration.

[Purpose of the invention]

The present invention was made in view of the above problems, and an object of the present invention is to provide a failure point locating device that can measure the distance to a failure point with high accuracy.

[Summary of the invention]

The present invention provides a digital fault point locating device that calculates the distance to a fault point using digital data of voltage and current of an electric power system to achieve the above object, which includes a memory section that stores the digital data, and a memory section that stores the digital data; It is equipped with a digital filter having a plurality of different filter functions into which data is input, and the distance to the fault point can be measured by utilizing the outputs of the plurality of digital films according to the elapsed time from the detection of a system fault. It is characterized by high precision.

[Embodiments of the invention]

FIG. 5 is a functional block diagram of a failure point locating device according to an embodiment of the present invention. In the figure, 51
52a, 52b, 53c are digital filters, and the filter function 52a is (3).
Equation 52b is based on equation (5), and equation 52c is based on equation (6). Therefore, the response times are 52a, 52b, 53c
The filter effect becomes more advanced in the same order. 53 is a switching control circuit which issues an output permission signal to 52a until T ₁ hour after the detection of a system failure, to 52b until T ₂ hours, and to 52c after T ₂ hours. 54a, 54b, and 54c are AND gates that control the output signals of the filters 52a, 52b, and 52c according to the signal from the switching control circuit 53. Reference numeral 55 denotes a distance measurement calculation unit that calculates the distance to the failure point using the system voltage and current signals that have passed through the filter controlled by the switching control circuit 53.

FIG. 6 explains the effect of the calculation according to FIG. 5. In the figure, curve a represents filter 5
2a is used to calculate the distance to the failure point. At first, the calculation results are unstable because transient data is used for calculation, but after T ₀ time, it reaches an almost steady state. However, even in a steady state, the calculation results fluctuate somewhat because the filter effect is insufficient.

Curve b is obtained by calculating the distance to the failure point using the filter 52b, and reaches a steady state for the first time after T ₁ hour, but the fluctuation in the steady state is smaller than that of curve a. In curve c, the time to reach the steady state is delayed further, after T ₂ hours,
The calculation results in steady state hardly change. In the present invention, up to T ₁ hour, curve a, and from T ₁
By adopting the results of curve b up to T ₂ hours and the results of curve c after T ₂ hours, the optimal result can be obtained depending on the duration of the system failure, regardless of whether the duration of the system failure is long or short. Therefore, the accuracy of distance measurement calculation can be significantly improved compared to the conventional calculation using a single filter.

FIG. 7 shows another embodiment of the invention. 55
a, 55b, and 55c are distance measurement calculation units, respectively;
It has exactly the same function as 55, but filters 52a,
The difference is that 52b and 52c are provided individually.
The results of these individual calculations are sent to the switching control circuit 53 and the AND gates 54a, 54b, 54c.
Even if the switching is performed using , exactly the same effect as that shown in FIG. 5 can be obtained.

FIG. 8 shows yet another embodiment. In the figure, reference numeral 56 denotes a selection section, which reads all the outputs of distance measurement calculation sections 55a, 55b, and 55c provided individually for each filter, and selects and outputs the calculation result that has the least variation before and after. In other words, to understand the fluctuation state of the calculation results, select the maximum Xmax and the minimum Xmin among the past N calculation results, and calculate the difference D.
The calculation result where =Xmax−Xmin is the smallest is
It is sufficient to select from the outputs of the distance measurement calculation units 55a, 55b, and 55c.

FIG. 9 is a flowchart for performing calculations according to the embodiment of FIG. 5. In 91, the time from the occurrence of a system failure is measured, and if it is within T ₁ hour, it is in 92a, and if it is within T ₁ to T ₂ hours, it is in 92b,
T If more than ₂ hours have passed, control is transferred to 92c.
92a, 92b, 92c are filters 52, respectively.
The voltage and current signals from the grid are processed using digital filters corresponding to a, 52b, and 52c.
In step 93, calculation of equation (1) is executed using the filtered voltage and current data.

FIG. 10 is a flowchart for performing calculations according to the embodiments of FIGS. 7 and 8. 92a, 92
b, 92c are filters 52a, 52b, respectively.
52c is used to process the voltage and current signals from the grid. 101a, 102b,
101c uses the voltage and current data processed by 92a, 92b, and 92c to calculate the equation (1). In 102, 101a, 101b, 10
If the result of 1c is selected, a flowchart corresponding to FIG. 7 will be obtained. Furthermore, by comparing the fluctuation states of the results and selecting the result with the smallest fluctuation width, a flowchart corresponding to FIG. 8 will be obtained.

In the above embodiment, the principle equation for locating the failure point was explained as equation (1), but it is not limited to this.
Of course, there is no problem as long as it is proportional to the distance to the failure point.

Further, in the above embodiment, the digital filters are of three types, but it goes without saying that any number of filters may be used as long as there are two types in order to carry out the present invention.
Also, regarding the filter function, in the above embodiment, filter functions based on equations (3), (5), and (6) were shown as examples, but the present invention can be applied to digital filters of any function form. can do.

There are two possible methods for detecting a system failure: (1) obtaining failure detection conditions from an external device, and (2) making a judgment based on system voltage and current information captured by the system itself. In the case of method (2), it can be easily implemented by, for example, undervoltage detection.

Although it is possible to configure the present invention described above using an analog filter, it is especially advantageous to configure it using a digital filter, considering that processing can be performed using only software without adding extra hardware. It is.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to locate the fault point with high accuracy according to the duration of the system fault.

[Brief explanation of drawings]

Figure 1 is a general configuration diagram of a digital fault location device, Figure 2 is an explanatory diagram of data obtained by sampling normal system voltage every 30 degrees, and Figure 3 is (1-Z ^-6 ).
Figure 4 shows the attenuation characteristics of digital filters of (1-Z ^-6 ) type, (1-Z ^-4 ) type, and their composite (1-Z ^-6 ) (1-Z ^-4 ) type digital filters. FIG. 5 is a functional block diagram illustrating one embodiment of the present invention; FIG. 6 is a diagram illustrating the effects of the present invention; FIGS. 7 and 8 are diagrams showing other embodiments of the present invention. The functional block diagrams of FIGS. 9 and 10 according to the example are shown in FIG.
FIG. 8 is a flowchart for executing each embodiment of the present invention according to FIGS. 7 and 8 in a calculation unit. 51...Memory section, 56...Selection section, 52a,
52b, 52c...Digital filter, 53...
...Switching control circuit, 55, 55a, 55b, 55c
... Distance calculation unit.

Claims (1)

[Claims] 1. A digital fault location device that calculates a distance to a fault point using digital data of voltage and current of a power system, comprising: a memory unit that stores the digital data; and a memory unit that stores the digital data; a digital filter having a plurality of different filter functions; a distance measurement calculation section that calculates the distance to a failure point by calculating the outputs of the plurality of digital filters; and the plurality of digital filters input to the distance measurement calculation section. A digital failure point locating device comprising a switching control circuit that switches the output of a filter according to the elapsed time after a system failure is detected. 2. In a fault point locating device that calculates the distance to a fault point using digital data of voltage and current from an electric power system, there is a memory section that stores data converted into digital quantities, and a plurality of memory sections into which the digital data is input. a digital filter having different filter functions; a distance measurement calculation section into which the outputs of the plurality of digital filters are respectively input; A digital failure point locating device comprising a switching control circuit for outputting. 3. In a fault point locating device that calculates the distance to a fault point using digital data of voltage and current from an electric power system, a memory section stores data converted into digital quantities, and a plurality of different A digital filter having a filter function, a distance measurement calculation section into which the outputs of the plurality of digital filters are respectively input, and a distance measurement calculation section that selects the most temporal fluctuation range from among the plurality of calculation results sequentially output from the distance measurement calculation section. A selection unit that selects and outputs a small one.