JPH0515990B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical field to which the invention pertains] The present invention relates to locating the position of the ground fault point when a ground fault occurs in a three-phase power transmission/distribution line, for example, to identify the position of the power transmission/distribution line where the ground fault has occurred from a certain measurement point. This invention relates to a method for estimating the distance to a fault point in a vehicle. [Prior art and its problems] The simplest conventional means of locating the fault location is to measure the impedance of the power transmission and distribution line from a certain measurement point to the ground fault point, and to compare this with the characteristics of the power transmission and distribution line. This method estimates the distance to the fault point based on the impedance, but while the device can be constructed relatively easily, the distance can be estimated based on the impedance between the power transmission and distribution line at the fault point and the ground, that is, the value of the so-called fault point impedance. It is generally known that errors are likely to occur in the estimated value of . The impedance at the fault point is mainly resistive, and with this in mind, there is also a known method for locating the fault point by measuring the reactance component of the power transmission and distribution line with emphasis. However, in a measurement example in an ungrounded power transmission and distribution system, when the cross section of the overhead line is ^60mm2 , the resistance component of the fault point impedance at the ground fault fault point is 0 ~
It is known that it can vary widely between 20 kilohms. On the other hand, the error in the orientation distance is set to 100
In order to be within this range, it is necessary to measure impedance changes due to ground faults in transmission and distribution lines with an accuracy of 0.03 ohm for resistance and 0.03 ohm for reactance (value for 50 hertz). Therefore, if the impedance at the fault point is high and is about 10 kilohms, the impedance at the fault point is 10 ^-5 ~
10 ^-6 , that is, measurement with an accuracy of at least 1/1000 percent is required, and such measurement is practically impossible. For this reason, the present applicant has proposed the invention of Japanese Patent Application No. 56-22423 as a means to precisely measure the impedance up to the fault point of a power transmission and distribution line or the amount of electricity related thereto without being affected by the impedance at the fault point. has been applied for. However, in this invention, it is necessary to keep the frequency of the power supply for measurement relatively low, and it is difficult to economically manufacture a coupler such as a transformer for coupling the power supply for measurement to high voltage or ultra-high voltage transmission and distribution lines. It is desirable to increase the frequency of the measurement power supply, but if the frequency is increased to about several hundred hertz, the influence of distributed capacitance of power transmission and distribution lines cannot be ignored. [Object of the Invention] The present invention is based on the recognition of the drawbacks or problems of the prior art described above, and provides an AC power source that is less affected by fluctuations in fault point impedance at a ground fault fault point, and that is The purpose of this invention is to realize a method for locating the ground fault point of a power transmission/distribution line that is less affected by the distributed capacitance of the power transmission/distribution line even if the frequency of the test power supply is set high so that voltage can be easily injected. . [Summary of the Invention] According to the present invention, in order to achieve the above object,
Current source circuits that inject alternating current for locating into the transmission and distribution line where a ground fault has occurred are installed at both ends of the transmission and distribution line section where the fault point should be located, and when a ground fault occurs, the current at both ends is Same frequency from the source circuit,
Location currents with the same amplitude and opposite phases are injected into the ground fault transmission line. The locating currents injected from these two current source circuits will superimpose and flow in the fault point impedance at the point where the ground fault occurs, but as mentioned above, since the two measuring currents are in opposite phases, they are essentially As a result, no measuring current flows through the impedance at the fault point, or even if it does, only a very small current flows as compared to the conventional means. This is a major reason why the method of the present invention is essentially less affected by fault point impedance. Now, when a ground fault occurs, the impedance of the power transmission and distribution line for the locating current naturally changes from its normal state, and therefore the characteristic electrical values, such as the reactive power value, in the current source circuit that supplies the locating current also change accordingly. Therefore, in the orientation according to the present invention, such characteristic electric value is measured and used as the first measurement value. This first measurement value is a function of the location of the ground fault point, but is also a function of the fault point impedance, so the location of the ground fault point cannot be determined unless the value of the fault impedance is determined. Therefore, in the present invention, the zero-sequence voltage of the three-phase power transmission and distribution line at the time of a ground fault is measured as the second measurement value. Although this zero-sequence voltage is a function of the fault point impedance, it is not related to the location of the ground fault point.
Therefore, the value of the fault point impedance can be uniquely determined from the measured value of this zero-sequence voltage, and then the position of the ground fault fault point can be easily determined from the first measured value using this fault point impedance value. can be located. [Embodiments of the Invention] Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory diagram of the principle of the present invention, and L
schematically represents one power transmission/distribution line, and its length l represents the section in which a ground fault should be located by the method of the present invention. Current source circuits 1 and 2 are installed at both ends of the section.
are provided respectively to inject the locating current into the high-voltage power transmission/distribution line L through appropriate coupling means, but in this figure, for the sake of simplicity, the locating current I1,
I2 is depicted as being directly injected from the current source circuits 1 and 2 into the power transmission/distribution line L. These measuring currents are controlled to have the same frequency f and the same amplitude _IS , but their phases are chosen to be opposite to each other. In order to indicate this opposite phase, an arrow is attached in FIG. 1 in the direction in which the measuring current I2 of the current source circuit 2 is drawn out from the power transmission/distribution line L. The ground fault point is indicated by F, the fault point impedance between this point and the ground, that is, the ground fault resistance, is Rg, and the distance from the left end of the transmission/distribution line section L to the ground fault point F is χ
Suppose that Now, if the ground fault fault point F is located at the center point of the transmission and distribution line section L, and therefore x = l/2, then the fault point impedance Rg has a current proportional to the measurement current I1 from the current source circuit 1. I1' and a current I2' proportional to the measurement current I2 from the current source circuit 2 flow in opposite directions, and as is easily understood, the magnitudes of I1' and I2' are equal, so both currents I
1' and I2' cancel each other out, and the current flowing through the fault point impedance Rg becomes zero. However, when the ground fault point F is located other than the center point, the power transmission and distribution line L
Since the impedance Z1 from the left end to the fault point F and the impedance Z2 from the right end to the fault point F are proportional to the lengths x and l-x of the transmission and distribution lines between them, the values of impedances Z1 and Z2 are different. , the magnitudes of the two currents I1' and I2' at the fault point F also differ, and the two currents do not cancel each other out completely. In such a general case, the following equation holds. V1 I1=A1 B1 C1 D11 1/Rg 0 1A2 B2 C2 D2V2 I2 ...(1) All signs in the above formula are vector quantities, and V
1. V2 is the voltage at the left end and right end of the power transmission and distribution line L as shown in Figure 1, but these are the voltages of the measurement current circuit of frequency f and are different from the commercial frequency voltage of the power transmission and distribution line. Please note that. The contents of other symbols are as follows. Rω=(YZ) ^1/2 (Propagation constant) Zω=(Z/Y) ^1/2 (Characteristic impedance) Y: Equivalent ground admittance/unit length Z: Equivalent impedance/unit length A1=cosh(Rω・x) C1 = (1/Zω) sinh (Rωx) B1 = Zωsinh (Rωx) D1 = cosh (Rωx) A2 = cosh {Rω (l-x)} C2 = (1/Zω) sinh {Rω (l-x)} B2 =Zωsinh{Rω(l-x)} D2=cosh{Rω(l-x)} Now, as mentioned above, since I ₁ = I ₂ = I _S , we can put this condition into equation (1) and do the same thing. The value of V1 on the left side of the equation can be determined using the fault point impedance Rg as a parameter and x as a variable. Here, when V ₁ is expressed by a general formula of functions f ₁ and f ₂ of the fault point impedance Rg and the distance x, it can be expressed as follows. V〓1=f ₁ (Rg, x) + jf ₂ (Rg, x) ... (1A) (however, expressed as a vector based on Is) Note that V〓1 can be obtained by decomposing equation (1) ( 1B)
It can be expressed in detail by the fault point impedance Rg and the distance x as shown in the equation. V〓1=ZωIs(B/A) ……(1B) However, B=cosh(Rωl)−1+Zω{sinh(Rωl)+sinh(Rω
(2x−l))}/2Rg A=sinh(Rωl)+Zω{cosh(Rωl)+cosh(Rω(
2x−l))}/2Rg On the other hand, the reactive power Q on the left end side of the power transmission and distribution line can be expressed as follows. Q=V1・Is・sinθ...(1C) (where θ is the phase angle between V1 and _Is ) Therefore, equation (1C) can be written as follows using equations (1A) and (1B). Can be rewritten. Q=Im{V〓1・Is} =Is ²・Im(Is・D/C) ...(1D) However, Im: Imaginary part of the vector D=cosh(Rωl)−1+Zω{sinh(Rωl)+sinh( Rω
(2x−l))}/2Rg C=sinh(Rωl)+Zω{cosh(Rωl)+cosh(Rω(
2x−l))}/2Rg In the expansion in Im, Rω and Zω are each complex numbers, so it is difficult to express a larger expansion formula, and it is easier to analyze numerically. . However, if the equivalent admittance Y and equivalent impedance Z are expressed only by the imaginary part under the following assumptions, Rω and Zω can be rewritten as shown in the following equation, so the reactive power Q is expressed as shown in equation (1E). Become.

[Assumption]

Let g≒0 at Y=g+jωC and r≒0 at Z=r+jωL. Rω = (YZ) ^1/2 = (jωC・jωL) ^1/2 = jω(L・C)
^1/2 Zω=(Z/Y) ^1/2 =(jωL/jωC) ^1/2 =(L/C
) ^1/
2 Q=Is ²・(H/G) ……(1E) However, H=2・Rg ²・L/C・[{cos(ω(LC) ^1/2 l)−
1}・cos {ω(LC) ^1/2 (l−2x)}+cos ² (ω
(LC) ^1/2 l)−cos(ω(LC) ^1/2 l)−sin{ω
(LC) ^1/2 (l−2x)}×sin(ω(LC) ^1/2 l)+
sin ² (ω(LC) ^1/2 l)] G=(L/C) [cos {ω(LC) ^1/2 (l-2x)}+cos
(ω(LC) ^1/2 l)] ² + {2Rg (ω(LC) ^1/2 l)}
^2In addition, the above formulas (1B), (1D) and (1E)
The equation is an equation for the voltage V〓1 on the left end side of the power transmission/distribution line and the reactive power Q on the left end side of the power transmission/distribution line expressed as a distributed constant. However, the voltage
As is well known, V〓1 and reactive power Q can also be expressed by equivalent lumped constants. Since the reactive power Q can be determined by measurement, equation (1D) is drawn in FIG. 2 with the failure point impedance Rg as a parameter and the distance x as a variable. The horizontal axis of Fig. 2 is the distance x from the left end of the power transmission/distribution line to the ground fault point F, and the vertical axis is the aforementioned reactive power Q. The curve Ro in the figure shows the case where the fault point impedance Rg is zero, that is, when the fault point F is completely grounded. In this case, the curves R5 and R10 correspond to the case where the impedance at the fault point is 5 and 10 kilohms, respectively, and the curve R corresponds to the case where the impedance at the fault point is infinite, that is, there is no ground fault. However, in this numerical calculation, the transmission and distribution line is 60 mm, the distributed inductance of the overhead steel wire with ² cross sections is 0.001 mH/m, the distributed capacitance is 0.01 nF/m, and the frequency of the measurement current f =
300Hz, injection current value I _S =IA, transmission and distribution line length l = 5Km
The reactive power Q was calculated as follows, and is a typical value for 6.6kV class distribution lines. The following can be seen from the results shown in FIG. When a ground fault occurs at the center point of a transmission/distribution line, the reactive power Q at the end of the line is equal to the reactive power Q ₀ when there is no ground fault, regardless of the impedance Rg at the fault point. This is the fault point impedance when the fault is at the central store as mentioned above.
This was easily predicted from the fact that no measurement current flows through Rg. Next, when the distance x to the ground fault point deviates from the center point, the value of the reactive power value Q changes according to the value of the fault point impedance Rg according to a substantially linear function of the distance x. Therefore, as long as the value of the fault point impedance Rg is known, the distance x can be very easily determined from the measured value of the reactive power Q, which is the first measured value, using the relationship shown in FIG. In order to obtain the value of this fault point impedance Rg, in the present invention, the zero-sequence voltage with respect to the commercial frequency of the three-phase power transmission and distribution line at the time of a ground fault is measured as a second measurement value. This zero-sequence voltage V ₀ is expressed by the following equation. V ₀ =E/(1+Rg/Rn)+jωCbRg...(2) However, in equation (2), E: Phase voltage of three-phase transmission and distribution line Rn: Neutral point grounding resistance Cb: Ground capacitance (three-phase portion) ) ω=2πf, f: frequency (commercial frequency). In equation (2), E=6.6/√3kV, Rn=
When 10 kiloohm, Cb=3μF, f=50Hz
The relationship between V ₀ and Rg is shown in FIG. Note that the ground capacitance C _b in Equation (2) above is the value of the entire three-phase transmission and distribution line, and this value as seen from the fault point is constant regardless of the location of the fault point, so it is zero. It can be seen that the phase voltage V ₀ is not related to the position of the fault point, but only to the value of the fault point impedance once the line is determined. As described above, when the above-mentioned characteristic electric value, such as the reactive power Q, which is the first measurement value, and the zero-sequence voltage V ₀ , which is the second measurement value, is measured, the third measurement value is calculated from the value of the zero-sequence voltage V ₀ . The value of the fault point impedance Rg is known from the relationship shown in the figure, and from the value of the fault point impedance Rg and the value of the reactive power Q, the distance to the ground fault fault point can be calculated from the relationship shown in Figure 2. The distance x can be found. Next, a method for locating a ground fault point in a power transmission/distribution line using the above-mentioned principle will be explained with reference to FIG. In Figure 4, the power transmission and distribution lines L are three-phase high voltage overhead lines L1 and L2.
and L3, of which a case where a ground fault with fault point impedance Rg occurs at fault point F of overhead line L2 is shown. Current source circuits 1 and 2 are respectively arranged at both ends of the transmission and distribution line section L,
The locating currents of the same frequency and the same amplitude generated by the constant current generators 11 and 21 are injected into one of the high voltage transmission and distribution lines via the current transformers 12 and 22. Of course, locating currents with mutually opposite phases are injected from the left and right ends of the section. Ground fault determination device 1
Reference numerals 3 and 23 are shown in a simplified manner because they may be well-known devices, which detect the power transmission/distribution line where the ground fault has occurred and selectively close the contacts of the switches 14 and 24 corresponding to that line. Constant current device 11, 21 only for the corresponding current transformer among the three current transformers 12, 22
The measurement current is injected into the fault wire by passing a current from the The current transformers 15 and 25 are used to prevent the locating current from flowing out of the predetermined transmission and distribution line section, and are opened and closed in response to commands from the ground fault phase determination devices 13 and 23 described above. The contacts of the transformer 16 are selectively closed to connect only the circuit of the corresponding one of the three current transformers 15, 25 to the fault line. The filters 17 and 27 are used to remove commercial frequency signals that enter the current source circuits 1 and 2 via the current transformers 12 and 22. The measuring circuit 30 measures characteristic electrical values of the current source circuits 1 and 2, such as reactive power, voltage, and power factor. In the illustrated configuration of the current source circuits 1, 2, the constant current from the constant current device 11 or 21 flows through one of the three current transformers 12 or 22, respectively, and further flows through one of the three current transformers 15, respectively. or 25 and the switch 14 or 24 into the measuring device 30 and from there return to the constant current device 11 or 21, respectively. In addition, the measuring device 30
need only be provided at the measuring end of the line section L, for example, on the current source circuit 1 side on the left side of the figure. Now, the method of locating the fault point will be explained using the current source circuit 1 as the measurement end. As shown in the diagram, power transmission and distribution line L2
When a ground fault occurs at fault point F, a ground fault detection device (not shown) detects that a ground fault has occurred, and as a result, the ground fault phase discrimination devices 13 and 23 operate, and the transmission/distribution line L2 is It is determined that it is a faulty line, and switch 1 is switched on.
4, 24 and switches 16, 26 are selectively closed to connect current transformers 12, 22 and current transformers 15, 25 corresponding to the fault line to current source circuits 1, 2, respectively. In this state, the measuring device 30 measures a characteristic electrical value, such as reactive power Q, in the current source circuit 1. This becomes the first measurement value. At the same time, the zero-sequence voltage of the three-phase power transmission and distribution line is
Measure V ₀ . For example, by simply adding the outputs of the voltage transformers connected to each line of power transmission and distribution lines L1 to L3 and taking the average value, the zero-sequence voltage V ₀ at the time of a ground fault can be calculated as the second
can be easily read or recorded as a measured value. Note that this zero-phase voltage V ₀ does not need to be measured within section L, and may be measured anywhere on the three-phase power transmission and distribution line. As described above, if the first measured value (reactive power Q) and the second measured value (zero-sequence voltage V ₀ ) are known, the distance x to the failure point can be easily estimated. That is, first, from the value of the zero-sequence voltage V ₀ , which is the second measured value, the relationship between the zero-sequence voltage V ₀ and the fault point impedance Rg is expressed by equation (2) or based on this equation (2). According to Figure 3, the fault point impedance
Find the value of Rg. Next, from the reactive power Q which is the first measurement value and the value of the fault point impedance Rg obtained as above, the value of the distance x corresponding to the value of this fault point impedance Rg is calculated as (1C)
It can be determined by the equation or from FIG. 2, which shows the relationship between the reactive power Q and the distance x using the fault point impedance Rg as a parameter based on the equation (1C). In other words, first, the second measured value, the zero-sequence voltage
By substituting V ₀ into equation (2) and solving equation (2), or by using the relationship between the zero-sequence voltage V ₀ and the fault point impedance Rg in Figure 3, the fault point impedance Rg can be determined.
The value of is known. Next, by substituting the value of the fault point impedance Rg found in this way and the reactive power Q, which is the first measured value, into equation (1C), we obtain (1C).
By solving the equation, or as shown in Figure 2 (assuming that the value of the found failure point impedance Rg is _R5 , for example, the value of reactive power Q on the vertical axis when a straight line is drawn on the horizontal axis The value of the horizontal axis x at the intersection of the straight line and the curve _R5 is the required distance x.)
From this, the distance x can be found. When locating the fault point as described above, the frequency of the measurement current can be selected in the range of several hundred to several thousand hertz. In addition, in the above explanation, we mainly explained reactive power as the characteristic electrical value to be measured, but it is not necessarily limited to this, and it may be reactive power factor, impedance value, or active power. . [Effects of the Invention] As explained above, in the present invention, current source circuits for injecting alternating current for evaluation into the transmission and distribution line in the section are provided at both ends of the transmission and distribution line section in which ground fault fault location is to be performed. When locating currents of the same frequency, same amplitude, and mutually opposite phases are injected into the power transmission and distribution line from both current source circuits, characteristic electrical values such as reactive power are measured as the first measurement value in the current source circuit serving as the measurement end. On the other hand, measure the zero-sequence voltage at the time of a ground fault on the three-phase power transmission and distribution line as a second measurement value, and calculate the distance from the measurement end of the ground fault point from the first and second measurement values. I tried to estimate it, so
The locating current flowing through the fault point impedance of the ground fault fault point is essentially small, so even when the fault point impedance is high, the error in evaluating the position or distance of the ground fault fault point is small compared to the conventional technology. There is. Furthermore, as can be seen from Fig. 2, in the case of the present invention, even if the frequency of the rating current is several hundred hertz (Fig. 2 is for 300 hertz),
There is a clear correlation between the distance x to the failure point and the first measured value, for example, the reactive power value Q, and therefore the distance x to be determined corresponding to the first measured value can be determined accurately. Furthermore, the correlation between Q and x described above is almost linear, which shows that the method of the present invention is not only convenient for estimating x, but can also be used even when the evaluation frequency becomes higher. Specifically, it is known that the method can be applied up to several thousand hertz, and therefore, the method of the present invention selects a higher frequency of the rated current compared to the conventional technology to inject the rated current into the transmission and distribution lines. This has the advantage of making the equipment more economical. This advantage is particularly significant when evaluation sections must be established at a large number of locations in order to evaluate ground fault points in a power distribution network.

[Brief explanation of the drawing]

All drawings are for explaining the contents of the present invention, and FIG. 1 is a circuit diagram for explaining the principle of the present invention.
FIG. 2 is a diagram showing changes in reactive power as an example of characteristic electrical values to be measured during evaluation according to the present invention, with the distance x from the measuring end to the ground fault point as a variable, and FIG. FIG. 4 is a circuit diagram illustrating a specific example of measuring characteristic electrical values during evaluation according to the present invention. In the figure, 1, 2: current source circuit, 1
1, 21: constant current device, 12, 22, 15, 2
5: Current transformer as a means for injecting current for evaluation into the transmission and distribution line, F: Ground fault point, L: Transmission and distribution line where the ground fault point should be evaluated, L2: Transmission and distribution line where the ground fault occurred Electric wire, l: power transmission and distribution line length, Q: reactive power as an example of characteristic electrical value of the current source circuit to be measured,
V ₀ : Zero-sequence voltage, x : Distance from the measuring end to the point of failure.

Claims (1)

[Scope of Claims] 1. Current source circuits are provided at both ends of a three-phase transmission/distribution line section, and locating currents of the same frequency, same amplitude, and mutually opposite phases are applied from both current source circuits to detect a ground fault within the section. is injected into the transmission and distribution line where the current source circuit occurred, and measure the reactive power Q of the current source circuit and the zero-sequence voltage V ₀ of the three-phase transmission and distribution line at the time of the ground fault, and from the zero-sequence voltage V ₀ , The fault point impedance Rg of the ground fault fault point is estimated based on the following formula, V ₀ = E / (1 + Rg / Rn) + jωCbRg [E: Phase voltage of three-phase transmission and distribution line Rn: Neutral point grounding resistance Cb: Grounding resistance Capacitance (three phases) ω=2πf, f: frequency] The fault point impedance Rg and the reactive power Q
A method for locating a ground fault point in a three-phase power transmission and distribution line, comprising: locating a position of a ground fault point in the section from .