JPH11142465A - Ground-fault point detecting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect a distance to ground-fault point in a ground-fault distance relay. SOLUTION: A ground-fault point detecting method includes, for temporary ground-fault points in the noted sections of transmission line, a processing to calculate a temporary polarity current using a load impedance, a back impedance, a positive phase impedance, and a negative phase current, a processing to obtain a temporary reactance to the fault point using the temporary polarity current and a transmission line impedance constant, and a processing to identify the temporary reactance as a reactance to the ground-fault point when an error between the temporary reactance and a reactance calculated for the temporary fault point is within specified area and, when it is out of the specified area, obtain a new temporary fault point using a ratio of the temporary reactance to the amount of reactance of the positive phase impedance. Then the above processing is performed repeatedly for new temporary fault points until the fault points are converged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground fault distance relay such as a digital relay for protecting and controlling a ground fault in an electric power system.
The present invention relates to a method for calculating an impedance from one end of a transmission line having a positive-phase power supply to a fault point to detect a ground fault point.

[0002]

2. Description of the Related Art Conventionally, when a one-line ground fault of a transmission line occurs,
The following equation 1 is known as a means for calculating the impedance (resistance R, reactance X) from one end of the transmission line where the positive-phase power source exists to the failure point.

[0003]

[Number 1] _{R = Re {V a · I} p *} / Re {(I a + K 1 I 01 + K
^{_{2 I 02) I p *}}} X = Im {V a · I p *} / Im {(I a + K 1 I 01 + K 2 I 02) I
_p ^* }

In equation (1), I _p is called a polar current or a polar quantity, and is generally zero-phase current I ₀₁ , phase current I _a , α−
An α circuit current (I _a −I ₀₁ ) or the like known in the β-0 circuit method is used. Also, an asterisk ( ^* ) attached to I _p
Means a conjugate amount of I _p generally expressed as a complex vector amount. This I _p ^* is an amount used for a vector phase rotation process that sets the vector phase reference of Equation 1 to I _p , and R, in Equation 1 depends on what electric quantity is used for I _p . This will cause a difference in the calculation accuracy of X. In Equation 1, K ₁ and K ₂ are constants. Generally, K ₁ is a ratio (Z ₀ / Z ₁ ) between the positive-phase impedance Z ₁ and the zero-phase impedance Z _0, and K ₂ is a line between Z ₁ and the line. ratio of between mutual impedance _{Z mm (Z mm / Z 1} ) is used. I ₀₁ is a zero-phase current of the own line in the parallel two-line transmission line, and I ₀₂ is a zero-phase current of the adjacent line. If the transmission line is one line operation, the total current = 0 of the next line, I ₀₂ is zero.

[0005]

The impedance obtained by equation (1) is a combination of the transmission line impedance Z from one end of the transmission line to the failure point, the failure point resistance _Rg, and the load (resistance) _RL through which the load current flows. Quantity (complex vector). Of these, assuming that _Rg and _RL are almost pure resistance,
The reactance amounts obtained by the expression of X in Equation 1 are all amounts due to the impedance of the transmission line, and by obtaining this reactance amount, the reactance amount can be used for distance measurement in a distance relay or a fault location device. it can.

Here, the calculation accuracy of R and X is I_pBy
Depends greatly. Because, in Equation 1, Re
｛｛Is the complex I in ｛Ｉ_pAnd in-phase component (=
Toll I_pAnd this is the true R component
Contains I_pIs the pure resistance_g, R _LSame as the current flowing through
It is necessary to be a phase. Ideally, I_pIs late
The fault current flowing through the fault point is an unknown current
Therefore, the current at the fault point is simulated by some arithmetic processing.
Simulate or have different magnitudes as vectors
Will be replaced by other currents that are in phase.
You.

[0007] Next, as can be seen from the expression Im ｛in Equation 1, the X component is calculated by taking the component orthogonal to I _p , so that I _p is R _g , R _L If the current does not have the same phase, the value of X calculated by the equation 1 includes an error corresponding to R. This error is shown in FIG. 4A described later.

In any case, the accuracy of Equation 1 depends on the selection of the polarity current _Ip . In this regard, each of the _Ip candidates described above has the following problem. (1) When a phase current / α circuit current is used as I _{p In} this case, since a positive-phase current is included, it is easily affected by a load current (most of which is a positive-phase component). (2) When a zero-sequence current is used as I _{p Since} an influence is caused by a zero-sequence voltage and a zero-sequence charging current caused by a capacitance component of the transmission line to the ground, an error occurs particularly in a ground fault of a high-resistance grounding system.

Therefore, the present invention does not have the above-mentioned problem caused by the candidate for _Ip , and as a result, a ground fault detecting method capable of calculating the impedance to the fault with high accuracy by the following equation (1). It is intended to provide.

[0010]

The characteristics of I _p that are not easily affected by the load current and the ground capacity in the case of a single-line ground fault in a transmission line are as follows: (1) The component is hardly included in the load current. Good reverse phase current and zero phase current. (2) Since the charging current is the product of the ground capacity and the voltage,
It is sufficient that no voltage is generated as much as possible during a ground fault. Therefore, in general, the zero-phase voltage> negative-phase voltage is satisfied for a one-line ground fault, so that the negative-phase component is good. For example, 1 of high resistance grounding system
In the case of a line ground fault, since zero-phase voltage> negative-phase voltage and positive-phase voltage> negative-phase voltage, it is understood that a negative-phase current is appropriate as _Ip . However, it should be noted that the load current may also include a negative phase component, although it is smaller than the positive phase component, and simply using the negative phase current for _Ip may cause a distance measurement error.

In view of these points, in the present invention, based on the reverse phase current at the time of the ground fault, the fault point current (a single-line ground fault has almost three times the magnitude of the reverse phase current in phase with the reverse phase current). ) And the impedance calculation are performed as one set, and the calculation is repeatedly performed, and the convergence value is calculated to correctly calculate the current amount at the fault point, and thus to accurately calculate the impedance up to the fault point. .

That is, the present invention provides a method for detecting a ground fault point by calculating the impedance from one end of the transmission line where the positive-phase power source exists to the fault point when a single-line ground fault of the transmission line occurs. First, a three-phase voltage / current at one end of the transmission line when the system is healthy is detected by a voltage / current detector, and a load impedance connected to the transmission line is calculated by using a positive phase component of the voltage / current. And calculating the impedance behind the system as viewed from the installation point of the voltage / current detector using the opposite phase components of the voltage / current detected by the voltage / current detector at the time of the one-line ground fault. Processing and
For the provisional fault point set in the section of interest, the load impedance, the back impedance, the known positive-phase impedance and the negative-phase current of the transmission line section of interest, using the provisional failure point current as a provisional polarity current Third to calculate
, A fourth process of obtaining a tentative reactance up to the failure point using the tentative polarity current calculated by the third process and the known transmission line impedance constant, and a tentative reactance obtained by the fourth process. If the error between the reactance and the reactance calculated for the tentative fault point is within a predetermined range, the tentative reactance is determined as a reactance up to the ground fault point, and the fifth process and the fourth process are used. When an error between the tentative reactance and the reactance calculated for the tentative failure point is outside a predetermined range, a new tentative failure point is determined by a ratio of the tentative reactance and the reactance of the positive-phase impedance. And the third to sixth processes are repeatedly executed on the new temporary fault point obtained by the sixth process until the fault point converges. It is intended.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. First, FIG. 1 is a system configuration diagram to which this embodiment is applied. In the figure, reference numeral 10 denotes a system power supply, 2
Reference numerals 1 and 22 are transmission lines, 30 is a transformer, NGR is a neutral point ground resistance, 40 is a load (impedance is Z _L ), 5
0 indicates a voltage / current detector such as PT and CT. Further, the positive phase component of the impedance behind the transmission line 21 including the transformer 30 is defined as Z _b , and the positive phase impedance of all the lines (interest section) on the transmission line 22 side is defined as Z ₁ . Note that aZ ₁ , (1-
a) Z ₁ is a longitudinal impedance of the ground fault point F, the ratio a is in the range of 0 ≦ a ≦ 1. Here,
The three-phase voltage at one end of the transmission line detected by the current detector 50
Based on the current, the line impedance (particularly the reactance X) from the installation point of the voltage / current detector 50 to the fault point F
Is determined.

FIG. 2 is a flowchart of a process for obtaining the reactance X up to the failure point F in the present embodiment, the contents of which will be described later. FIG. 3 is an equivalent circuit diagram based on the symmetric coordinate method of FIG. 1 and partially overlaps with the description of FIG. 1, but Z ₁ is a section of interest (from the installation point of the voltage / current detector 50 in FIG. The positive-phase impedance of the section up to 40), Z ₀ is the zero-phase impedance of the same section, Z _b is the positive-phase part of the back impedance, Z _b ′ is the same zero-phase part, and V ₁ is the voltage / current detector 50 installation. The positive-phase voltage at the point, V ₂ is the negative-phase voltage, V _2F is the negative-phase voltage at the fault point F, I ₁ is the positive-phase current flowing into the fault point F, I ₂ and I ₂ ′ are the same-phase current and R _g is the fault point resistance.

FIGS. 4 (a) and 4 (b) show the voltages V and V related to the failure phase when a single-line ground fault occurs at the failure point F in FIG.
It is a vector diagram of the current I, FIG. 4 (a) when the phase current I _a as a phase reference, FIG. 4 (b) phase reference polarity current I _p of the fault point current I _F and phase are unknown amount Is the case. In these figures, V _g is fault point voltage is unknown amount, V _a is the phase voltage is measured quantity, is I _a is the phase current is measured quantity.

In the prior art equation 1, I _{p in} FIG.
It can be satisfactorily calculated impedance to fault point F (the reactance) without being influenced by the exact calculated Rarere if fault point voltage V _g. However, the phase current and the zero-phase current measured by the main CT of the system cannot be accurate _{Ip as} it is as described above. Further, even from a simple reverse-phase current, an accurate I _p cannot be obtained due to the influence of the load current. However, if the reverse-phase current (I _F = I ₂ + I ₂ ′ in FIG. 3) that actually flows to the fault point F can be calculated, I _p
Can be determined as an accurate value. Of the negative phase currents, I ₂ can be easily calculated from the phase currents, so how to handle the unknown I ₂ ′ is a problem.

The procedure for calculating the reactance X up to the fault point F will be described below with reference to the flowchart of FIG.
The load impedance Z _L shown in FIG. 3 is the system voltage / current (for the positive phase) and the positive phase impedance Z ₁ when the system is healthy.
Can be obtained based on the equation (2) (S1 in FIG. 2).

[0018]

## EQU2 ## Z _L = V ₁ / I ₁ -Z ₁

Next, it is determined by a known means whether or not a one-line ground fault has occurred in the system (step S2). If it has not occurred, the process returns to step S1, and if it has been confirmed, the process returns to step S3. Move to Here, Equation 3 holds for the negative-phase voltage V _2F at the failure point F. In addition, Equation 4 is obtained from Equation 3.

[0020]

## EQU3 ## V _2F = (Z _b + aZ ₁ ) I ₂ = {(1-a) Z ₁ +
Z _L ｝ I ₂ '

[0021]

## EQU4 ## I ₂ ′ = {(Z _b + aZ ₁ ) I ₂ } / ｛(1-a)
Z ₁ + Z _L ｝

From this, equation 5 can be obtained for the polarity current _Ip .

[0023]

## EQU5 ## I _p = I ₂ + I ₂ ′ = ｛(Z _b + Z _L + aZ ₁ )
I ₂ ｝ / {(1-a) Z ₁ + Z _L ｝

In Equation 5, the back impedance Z _b
Uses the voltage-current detector reverse-phase voltage V ₂ is calculated from the phase voltages and current of the installation point 50 and the negative phase current I _2, can be calculated by Equation 6 (step S3).

[0025]

## EQU6 ## Z _b = −V ₂ / I ₂

Further, Z ₁ in Equation 5 is the positive impedance of all lines in the section of interest, which is a known quantity.
Therefore, the only unknown quantity in Equation 5 is the ratio a that determines the distance to the fault point F.

In the present embodiment, a temporary value is substituted for a in equation (5), and a temporary I _p is calculated from equation (5). And
The temporary reactance up to the failure point F is calculated by substituting the temporary _Ip into Expression 1. Now, the value of the temporary a a ', a temporary reactance calculated by Equation 1 X', when the reactance of Z ₁ and X _1, if a 'is equal to true ratio a, Formula 7 is satisfied Should do it.

[0028]

X ′ = a′X ₁

That is, when a 'is not equal to the true ratio a, Equation 7 does not hold, and a certain error ε shown in Equation 8 occurs.

[0030]

Ε = | X′−a′X ₁ |

Therefore, this error ε is equal to the operation convergence judgment constant ε
_{If the value} is smaller than ₀ , the provisional reactance X ′ is set as a solution (reactance to the failure point F) as a calculation result under good accuracy.

The processing up to this point will be described below with reference to FIG. That is, the value A of the operation discontinuation counter is set to 0 (initial value) (step S4), and as described above, the temporary a 'is set to, for example, 0.5 (assuming that the fault point F is an intermediate point in the section of interest). (Step S5). Next, a '
Is determined to be a value in the section of interest (steps S6, S
7) If the value is within the focused section, the process proceeds to the next step S8.

In step S8, the temporary I
_p (the value is defined as I _p ′), and the next step S9
Then, a temporary X (the value is X ') is calculated by Expression 1. Then, as described above, the error ε = | X′−a′X ₁
| And the constant ε ₀ are used to determine the operation convergence (step S
10) If the error ε is smaller than ε ₀ , the process is terminated with the provisional reactance X ′ as a solution (step S11), and the relay operation is determined based on the fault point F measured based on the reactance X ′ (within the protection range).・ External judgment), failure point evaluation, etc.

Now, even if the error ε is larger than the constant ε ₀ due to the inaccuracy of X ′ calculated in step S9, the error factor of X ′ is only the calculation error of I ₂ ′. 'is accurate than X _1. Accordingly, once determined the calculated X 'and the new provisional a with the X ₁ a' as = X '/ X ₁ (step S12), the after incrementing the value A of the counter (step S1
3) The process after step S8 is repeated again. If the value A of the counter exceeds the predetermined value K, the operation is terminated (step S14), and the process is terminated by solving X 'at that time (step S15). in this way,
If the calculation convergence determination condition in step S10 is not satisfied, a ′ is reset and the calculation of I _p ′ and the calculation of X ′ are performed again, and a series of processing is repeatedly performed until the error ε becomes smaller than the constant ε _0. By the convergence calculation method described above, the reactance X up to the failure point F can be favorably calculated.

[0035]

As described above, according to the present invention, the estimation of the fault point current and the reactance calculation are repeatedly performed as a set based on the reverse-phase current at the time of the one-line ground fault, and the convergence is obtained. Since the value is calculated to enable the fault point current and, therefore, the accurate impedance to be calculated, it is possible to accurately detect and measure a ground fault point in a ground fault distance relay or a fault point locating device.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram to which an embodiment of the present invention is applied.

FIG. 2 is a flowchart showing the operation of the embodiment of the present invention.

FIG. 3 is an equivalent circuit diagram when a one-line ground fault occurs in FIG.

FIG. 4 is a voltage / current vector diagram relating to a failure phase at the time of a one-line ground fault.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Power supply 21,22 Transmission line 30 Transformer 40 Load 50 Voltage / current detector

Claims (1)

[Claims] 1. A method for detecting a ground fault point by calculating an impedance from one end of a transmission line having a positive-phase power supply to a fault point when a one-line ground fault of the transmission line occurs, comprising the steps of: A first process of detecting a three-phase voltage / current at one end of the transmission line with a voltage / current detector, and calculating a load impedance connected to the transmission line using a positive phase component of the voltage / current; At the time of a line ground fault, a second process of calculating the impedance behind the system as viewed from the installation point of the voltage / current detector using the negative phase component of the voltage / current detected by the voltage / current detector, For the temporary fault point set in the target section, the load impedance, the back impedance, the known positive-phase impedance and the negative-phase current of the transmission line target section are used, and the temporary fault point current is set as the temporary polarity current. The third calculated
A fourth process of obtaining a temporary reactance up to the failure point using the temporary polarity current calculated by the third process and the known transmission line impedance constant; and a temporary process of obtaining the temporary reactance up to the failure point. If the error between the reactance and the reactance calculated for the tentative failure point is within a predetermined range, the tentative reactance is identified as the reactance up to the ground fault point, and the fifth process is used to determine the reactance. When an error between the tentative reactance and the reactance calculated for the tentative fault point is outside a predetermined range, a new tentative fault point is obtained by a ratio of the tentative reactance and the reactance of the positive-phase impedance. And repeatedly executing the third to sixth processes for the new temporary fault point obtained by the sixth process until the fault point converges. A ground fault point detection method.