JPS649815B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method and apparatus for detecting disconnection of an electric line that can reliably distinguish between a disconnection of an electric line supplying power to a three-phase load and an open load on the power source side. Distribution lines are generally ungrounded at the neutral point, and the system is dendritic. Accidents such as ground faults and overcurrents on distribution lines are detected using ground relays, overcurrent relays, etc., but in order to improve the reliability of power distribution lines and ensure safety, The use of insulated wires for railway lines is progressing. However, even if the insulated wire breaks and falls to the ground, the insulated wire has a covering, so
Since the internal conductor does not come into contact with the ground, zero-sequence current does not flow, and there are cases where the ground fault cannot be detected at the substation, posing a problem in terms of safety and power supply. Therefore, the present inventor developed a method that can detect a disconnection in a distribution line even if no zero-sequence current flows first. Detection that determines the disconnected phase by utilizing the fact that the line current of the disconnected phase is larger than the sum of the line currents of other healthy phases when the effective value (scalar amount) of the line current of each phase changes from immediately afterward. proposed a method. Another method for detecting disconnection is to check that the ratio of the change in line current (vector amount) before and after the disconnection of the distribution line is within a certain range, and that the phase angle of the change in line current before and after the disconnection is within a certain range. A method has been proposed for detecting the presence of However, the above-described method has a problem in that when the load is a single-phase load or a V load, it is difficult to distinguish between a load open and a disconnection. The inventor of this invention discovered that there is a constant relationship between the amount of change in the symmetrical component of the line current before and after the wire is disconnected. It is an object of the present invention to provide a wire breakage detection method that can detect a wire breakage with high accuracy, regardless of the state of load equilibrium, by utilizing the above-mentioned relationship. Hereinafter, the disconnection detection method of the present invention will be explained with reference to the drawings. FIG. 1 is a diagram showing a line in which a load L ₁ and a load L ₂ are connected to a substation T ₁ , and the line current I _L in the substation is in a loaded state or in a line connected only to that load. is the vector sum of the line current I _L of load L ₁ which does not change and the line current I _L2 of load L ₂ whose load state or line condition changes, but the line impedance between the substation and each load is Line impedance is ignored as it is small compared to the load impedance. Furthermore, each line voltage has a phase difference of 120°, and the load
It is assumed that even if the line condition of _L2 changes, the phase difference between each line voltage and each line current at point P shown in FIG. 1 does not change. Therefore, the change in the line current at the substation △I _L depends only on the change △I _L2 due to the change in the line condition of the load L ₂ , and the change in the load L ₁ △I _L1 = 0. Therefore, in the following explanation, the load L ₁ will not be considered. Therefore, the change in the line state of the load _L2 can be shown by the equivalent circuits shown in FIGS. 2A to 2D. However, Figure 2 A is an equivalent circuit when one wire of A phase is disconnected, Figure 2 B is an equivalent circuit when AB phase single-phase load is opened, and Figure 2 C is an equivalent circuit when 3-phase load is opened. , and D in the same figure is an equivalent circuit when the V load is released and there is no load between the BC phases. In FIGS. 2A to 2D, A in the steady state
Ia, Ib and Ic for each line current of phase, B phase and C phase
Let the voltage between each line be Vab, Vbc and Vca, and the current of the load connected between each line Iab, Ibc and Ica,
Their absolute values are |Ia|, |Ib|, |Ic|, |Vab
|, |Vbc|, |Vca|, |Iab|, |Ibc| and |
Ica|, and the power factor angles of each load are α, β, and γ, each line current is Ia=Iab−Ica=|Iab|e ^j 〓−|Ica|e ^j 〓・a...(1) Ib= Ibc−Iab＝｜Ibc｜e ^j 〓・a ² −｜Iab｜e ^j 〓 ……(2) Ic＝Ica−Ibc＝｜Ica｜e ^j 〓・a−｜Ibc｜e ^j 〓・a ² … ...(3) However, a=e ^j2/3 〓, a ² = e ^j4/3 〓. Also,
Calculate each line impedance of the load with Zab and Zbc.
If Zca is ignored, the line impedance is ignored, so the line voltage maintains the original three-phase equilibrium.
Vab｜=｜Vbc｜=｜Vca｜=｜V｜ as Zab=Vab/Iab=｜V｜/｜Iab｜・e ^j 〓 …(4) Zbc=Vbc/Ibc=｜V｜・a ² /( |Ibc|・e ^j 〓・a ² ) …(5) Zca = Vca/Ica = |V|・a/(|Ica|・e ^jr・a) …(6) However, in Figure 2b, Zbc and Zca
is infinite, Ibc and Ica are zero, and in Figure 2D, Zbc is infinite and
Ibc becomes zero. Incidentally, a vector diagram of the line voltage and each load current is shown in FIG. Disconnection coefficient In the present invention, the ratio between the amount of change △I ₁ for the positive phase component of the line current and the amount of change △I ₂ for the negative phase component before and after disconnection, K = △I ₂ / △I ₁ ... (7) A disconnection is detected. Hereinafter, this K will be referred to as the disconnection coefficient. Next, in the equivalent circuits shown in Figures 2A to D, if one wire is disconnected or the single-phase load is opened,
The disconnection coefficient K will be studied in the case of 3-phase load opening and also in the case of V load opening. (1) Disconnection of one wire in phase A As shown in Figure 2A, if the line currents in each line when the A phase line is disconnected are I'a, I'b, and I'c,
If I′a=0 and each load current is I′ab, I′bc, and I′ca, I′ab=I′ca, and I′bc=Ibc, so I′ab=I′ca =-Vbc/Zab+Zca =-1/1/|Iab|・e ^j 〓+1/|Ica|・e ^j 〓・a ² ...(1-1) I'b=-I'c=I'bc-I ′ab=I′bc−I′ca=｜Ibc｜
・e ^j 〓・a ₂ +1/1/｜Iab｜e ^j 〓+1/｜Ica｜e ^j 〓 …(1-2), and the changes in each line current △Ia, △Ib, and △
Ic is △Ia=I′a−Ia =−(|Iab|e ^j 〓−|Ica｜e ^j 〓・a) …(1-3) △Ib=I′b−Ib=|Iab|e ^j 〓／｜Iab｜e ^j 〓＋｜Ic
a｜e ^j 〓・(｜Iab｜e ^j 〓−｜Ica｜e ^j 〓・a) =−｜Iab｜e ^j 〓／｜Iab｜e ^j 〓＋｜Ica｜e ^j 〓
・△Ia…(1-4) △Ic＝I′c−Ic＝｜Ica｜e ^j 〓／｜Iab｜e ^j 〓＋｜Ic
a｜e ^j 〓・(｜Iab｜e ^j 〓−｜Ica｜e ^j 〓・a) =−｜Ica｜e ^j 〓／｜Iab｜e ^j 〓＋｜Ica｜e ^j 〓
・△Ia...(1-5) From the above formulas, the changes in each line current before and after disconnection △Ia, △Ib, △Ic are the phase voltage Va of phase A
Based on △Ia＝−{｜Iab｜e ^j( 〓 ^-30゜⁾ −｜Ica｜e ^j( 〓 ^-30゜⁾
a} …(1-6) △Ib＝｜Iab｜e ^j 〓／｜Iab｜e ^j 〓＋｜Ica｜e ^j 〓｜｜I
ab｜e ^j( 〓 ^-30゜⁾ −｜Ica｜e ^j( 〓 ^-30゜⁾ a}…(1-7
) △Ic＝｜Ica｜e ^j 〓／｜Iab｜e ^j 〓＋｜Ica｜e ^j 〓｜｜I
ab｜e ^j( 〓 ^-30゜⁾ −｜Ica｜e ^j( 〓 ^-30゜⁾ a}…(1-8
) △I ₀ = 1/3 (△Ia + △Ib + △Ic) = 0 ... (1-9) △I ₁ = 1/3 (△Ia + a△Ib + a ² △Ic) = 1/3・｜Iab｜e ^j 〓・(a-1)+｜Ica｜e ^j 〓・
(a ² −1)／｜Iab｜e ^j 〓＋｜Ica｜e ^j 〓｛｜Iab｜e ^j( 〓
^-30゜⁾ −｜Ica｜e ^j( 〓 ^-30゜⁾ a} …(1-10) △I ₂ = 1/3 (△Ia+a ² △Ib+a△Ic) = 1/3・｜Iab｜e ^j 〓・(a ² −1)＋｜Ica｜e ^j 〓・
(a-1)／｜Iab｜e ^j 〓＋｜Ica｜e ^j 〓{｜Iab｜e ^j( 〓
^-30゜⁾ −｜Ica｜e ^j( 〓 ^-30゜⁾ a} …(1-11) From formulas (1-10) and (1-11), the disconnection coefficient K is K=△I ₂ /△I ₁ ＝｜Iab｜e ^j 〓(a ² −1)＋｜Ica
｜e ^j 〓(a-1)／｜Iab｜e ^j 〓(a-1)+｜Ica｜e ^j
It is expressed as 〓(a ² −1)…(1−12). Here, |Ica|/|Iab| and |Iab|/|Ica
By setting the smaller of ｜ as Y It is transformed into Furthermore, from equation (1-12), find the real part Re(K) and the imaginary part 1m(K), If Y is eliminated from the above formula, Also, if we eliminate (α−γ), we get (2) Single-wire disconnection in phase B (or phase C) Considering the symmetry of the power supply, α
is read as β, γ is read as α, and Y is |Iab
It may be the smaller of |/|Ibc| and |Ibc|/|Iab|. Regarding phase C, ｜Ica
Y may be the smaller of |/|Ibc| and |Ibc|/|Ica|. ^{( 3 ) Value of K} when switching ^load 〓 ^-30゜⁾ a ² −｜Iab｜e ^j( 〓 ^-30゜⁾ Ic＝｜Ica｜e ^j( 〓 ^-30゜⁾ a−｜Ibc｜e ^j( 〓 ^-30゜⁾ a ² Like this When the load is opened, the line currents I′a, I′b, and I′c after the release are 0, so △Ia＝I′a−Ia＝−｛｜Iab｜e ^j( 〓 ^-30゜⁾ −｜Ica
｜e ^j( 〓 ^-30゜⁾ a｝ △Ib＝I′b−Ib＝−｛｜Ibc｜e ^j( 〓 ^-30゜⁾ a ² −｜Ia
b｜e ^j( 〓 ^-30゜⁾ a｝ △Ic＝I′c−Ic＝−｜｜Ica｜e ^j( 〓 ^-30゜⁾ a−｜Ib
c｜e ^j( 〓 ^-30゜⁾ a ² }...(3-0) Therefore, the change in the symmetrical current before and after the load is released is △I ₀ = 1/3 (△Ia + △Ib + △Ic) = 0 …(3-1) △I ₁ = 1/3 (△Ia+a△Ib+a ² △Ic) = a-1/3 {｜Iab｜e ^j( 〓 ^-30゜⁾ +｜Ibc｜e ^j( 〓
^-30゜⁾ +｜Ica｜e ^j( 〓 ^-30゜⁾ }...(3-2) △I ₂ = 1/3 (△Ia+a ² △Ib+a△Ic) = a ² -1/3｜｜Iab｜ e ^j( 〓 ^-30゜⁾ ＋｜Ibc｜e ^j( 〓
^-30゜⁾ a+｜Ica｜e ^j( 〓 ^-30゜⁾ a ² }...(3-3). Therefore, the disconnection coefficient K is: K=△I ₂ /△I ₁ = −a ²・｜Iab｜e ^j 〓+｜Ibc｜e ^j 〓・a
＋｜Ica｜e ^j 〓・a ² /｜Iab｜e ^j 〓＋｜Ibc｜e ^j 〓＋｜Ica
|e ^j 〓 …(3-4), and |K| ² is From the above equation, the real part of K is Re(K) = m and the imaginary part Im(K) = n is Re(K) = m1/2 |Iab| ² -2 | Ibc| ² + | Ica | ² +2
｜Iab｜｜Ibc｜cos (β−α−120゜)／｜Iab｜ ² +｜Ib
c｜ ² +｜Ica｜ ² +2｜Iab｜｜Ibc｜cos (β−α) +2｜Ibc｜｜Ica｜cos (γ−β−120°) −4｜Ica
｜｜Iab｜cos (α−γ−120°)／+2｜Ibc｜｜Ica｜c
os (γ − β) + 2 | Ica | | Iab | cos (α − β)… (3
-6) In equations (3-4) to (3-7) |
Iab｜, ｜Ibc｜, ｜Ica｜ in descending order
As Imax, Imid, and Imin, Imid/Imax=P,
Imin/Imax=Q, and (β-α), (γ-
β), and (α-γ) in random order A, B, C
Then, A+B+C=0 and C can be erased. By substituting the above terms, |K| ² = 1 + P ² + Q ² + 2PQcos (A + B - 120°) + 2Pco
s(A+120°)+2Qcos(B+120°)/1+P ² +Q ² +2P
Qcos(A+B)+2PcosA+2QcosB...(3-8) When |Ibc| is not the maximum, the real part and imaginary part of K are Re(K)=1/2・1+2P ² +Q ² +2PQcos(A+B-120°)+2Pcos( A-120゜) + 4Q (B-120゜) / 1 + P ² +Q
² +2PQcos(A+B)+2PcosA+2QcosB...(3-9) Also, when |Ibc| is maximum, Re(K)=1/2・-2+P ² +Q ² −4PQcos(A+B+120°)+2Pcos(A-120°)+2Qcos(B-120°)/1+P ²
+Q ² +2PQcos(A+B)+2PcosA+2QcosB...(3-11) becomes. However, 0P, Q1, -180°A,
B is 180°. Next, using the above formula, the possible ranges of K when opening and closing various loads are determined with reference to FIG. Note that the vertical axis in the same figure represents the imaginary axis, and the horizontal axis represents the real axis. (i) Three-phase balanced load For three-phase balanced load, α=β=γ, |Iab=
|Ibc|=|Ica|, so A=0,
B=0, P=Q=1. Yotsute expression (3-
9) Or from equation (3-11) Re(K)=0 Also from equation (3-10) or equation (3-12)
Im(K)=0. Therefore, K is at the center of the coordinates as shown in Figure 4A. (ii) In the case of a three-phase unbalanced load Assuming that the power factor angle of the load on the actual distribution line is within a certain range, calculate A, B, and C in 30° increments.
Value between 30° and 30°, and 0.5P, Q
1.0 using equation (3-9) or (3-11) and (3-10) or equation (3-12), K is found within and around the curve shown in Figure 4 (b). exists above. (iii) Three-phase unbalanced load A, B, and C are the same conditions as (ii), 0.0<P, Q
When set to 1.0, formula (3-9) or (3-11)
From equation (3-10) or (3-12), the value of K is as follows, where m is the real part and n is the imaginary part. Exists within the curve of (iv) At V load By setting Q to 0, the value of K becomes the curve d,
It exists on the circumference of curves N' and N. (v) Single-phase load Since both P and Q are 0, the value of K is at the intersections E, H, and G of curves N, N', and N. Its coordinates are

[Formula] (-1, 0),

[Formula] becomes. Considering (i) to (v) above, if the value of K is outside the range surrounded by curves ni, ni', ni'',
Can detect wire breakage. In addition, since it may not be possible to clearly detect the proximity of the intersections H, H, and G due to measurement errors, etc., the tangent lines H, CH', and
If K exists outside the range of the triangle surrounded by ``chi'', it may be determined that the line is broken. Note that the curves ``chi'', ``chi'', and It is expressed as Next, an apparatus for carrying out the method for detecting disconnection of an electric line according to the present invention will be explained with reference to FIG. FIG. 5 shows a block diagram of a disconnection detection device in a substation for carrying out the method for detecting disconnection in electrical lines according to the present invention. In the figure, CT ₁ to CT ₃ are current transformers that measure line currents Ia, Ib, and Ic in the substation, and each measured current is converted to voltage by current-voltage conversion circuit 1, and bandpass Only the components near the commercial frequency are extracted by the filter 2, and the extracted first signals S _1a to S _1c
are each converted into a DC voltage proportional to the AC effective value by an effective value conversion circuit 3, ripples are removed by a low-pass filter 4, and then settled by a DC amplifier 5, resulting in three elements of current. On the other hand, PT ₁ is the phase voltage Va, Vb and
This is a transformer that measures Vc, and from each measured phase voltage, only the components near the commercial frequency are extracted by a bandpass filter 2, and the extracted signals are each passed through a square wave forming circuit 6 to The sine wave is converted into a square wave, and the second signals S _2a to S _2c
becomes. Further, the first signals S _1a to S _1c measured by the current transformers Ch ₁ to CT ₃ and passed through the bandpass filter 2 are respectively converted into square waves by the square wave forming circuit 6, The signals S _3a to S _3c are obtained. Second signals S _2a to S 2c corresponding to these phase voltages and third signals _{S 3a to} S _3c corresponding to the line currents.
is input to the phase discrimination circuit 7 for each phase, converted into a DC voltage proportional to each phase, ripples are removed by the low-pass filter 4, and then settled by the DC amplifier 5 to determine the phase. The signals representing the currents |Ia|, |Ib|, |Ic| and the signals representing the phases φa, φb, and φc, which are signals representing the three elements φa, φb, and φc, are processed by the microprocessor 1.
The signals are sequentially led from a multiplexer 11 controlled by a microprocessor 13 to an A/D converter 12, which is also controlled by a microprocessor 13, where they are A/D converted. The microprocessor 13, which operates according to a program stored in the memory 14, detects changes in the current of each phase from the digital signals representing the current and the signal representing the phase. That is, the phase current and phase of each phase of A, B, and C at a certain timing t ₀ are |Ia ₀ |, |Ib ₀ |, |Ic ₀ |,
Let φa ₀ , φb ₀ , φc ₀ be, and the current and phase of each phase at the timing (t ₀ + △t) after the sampling period △t are |Ia ₁ |, |Ib ₁ |, |Ic ₁ |, φa ₁ , Let φb ₁ and φc ₁ . However, φa is the phase angle of the A-phase current Ia with respect to the A-phase voltage Va, φb is the phase angle of the B-phase current Ib with respect to the B-phase voltage Vb, and φc is the C-phase current with respect to the C-phase phase voltage Vc. is the phase angle of Ic. First, the orthogonal components △I _1x , △I _1y , △I 2x , △I _2y of the change in the positive sequence current △I ₁ and the change in the negative sequence current △I ₂ with respect to the phase voltage Va of the A phase as a _reference. is calculated using the following formula. △I _1x = 1/3 {｜Ia ₁ ｜cosφa ₁ +｜Ib ₁ ｜cosφb ₁ +｜I
c ₁ | cosφc ₁ − ( | Ia ₀ | cosφa ₀ + | Ib ₀ | cosφb ₀ + | Ic ₀ | cosφc ₀ )} …(4-1) △I _1y = 1/3 {( | Ia ₁ | sinφa ₁ ＋｜Ib ₁ ｜sinφb ₁ ＋
|Ic ₁ |sinφc ₁ )−(|Ia ₀ |sinφa ₀ +|Ib ₀ |sinφb ₀ +|Ic ₀ |sinφc ₀ )} …(4-2) △I _2x = 1/3 [{|Ia ₁ | cosφa ₁ + | Ib ₁ | cos(φb ₁
＋120゜）＋｜Ic ₁ ｜cos(φc ₁ −120゜)｝ −｛(｜Ia ₀ ｜cosφa ₀ +｜Ib ₀ ｜cos(φb ₀ +120゜)
+ | Ic ₀ | cos (φc ₀ −120゜)]}…(4-3) △I _2y = 1/3 [{|Ia ₁ | sinφa ₁ + | Ib ₁ | sin(φb ₁
＋120゜）＋｜Ic ₁ ｜sin(φc ₁ −120゜)｝ −｛(｜Ia ₀ ｜sinφa ₀ +｜Ib ₀ ｜sin(φb ₀ +120゜)
+ | Ic ₀ | sin (φc ₀ −120°)}]...(4-4) Each of these values is applied to the disconnection coefficient calculation circuit 13, and the absolute value R of K and the argument angle θ are calculated by the following formula. be done. θ＝tan ^-1 △I _2y ／△I _2x −tan ^-1 △I _1y ／△I _1x …(4
-6) However, the value of tan ^-1 (a ₂ /a ₁ ) is the argument of the point whose rectangular coordinates are given by (a ₁ , a ₂ ). Therefore, −180°≦tan ⁻¹ (a ₂ /a ₁ )<180°. Next, by utilizing the symmetry of the disconnection determination diagram, the value of θ is limited to a range of 0°≦θ≦60° in order to facilitate the determination. As shown in the flowchart in Figure 6, first, |θ|−120x[|θ|/120]...(4-7) (where x is the largest integer that does not exceed |θ|/1200. ) is calculated and set as a new θ, and only if the value is larger than 60°, the value obtained by subtracting θ from 120° is used as the new θ.
This can be done by After finding R and θ as described above, in order to know the position of K in the disconnection determination diagram, orthogonal components m and n
is calculated using the following formula. m=Rcosθ...(4-8) n=Rsinθ...(4-9) With these m and n, (m+1) ² +n ² >3...(4-10) (m-0.5) ² -(n-0.938) ² ＞0.130
...(4-11) Calculate. This result is applied to the determination circuit 15, and if m and n satisfy equations (4-10) and (4-11), it is determined that the wire is disconnected. In addition, equations (4-10) and (4-11) are (1-22),
In equation (1-23), α−γ=30°, and based on experimental results, Y=
Calculated as 0.2. The focus of FIG. 4 is the value of the coefficient K in an actual three-phase distribution line calculated using the above-mentioned apparatus and displayed on a CRT image. In Fig. 4, the coefficient K at the time of wire breakage is concentrated in the wire breakage detection areas (N), (L), and (O), and the coefficient K at the time of load switching is roughly concentrated within the curve B, and from now on, It can be seen that it is possible to distinguish between wire breakage and load switching. As detailed above, according to the present invention, a disconnection can be detected from the positive and negative phase components of the current in a three-phase distribution line, so disconnections can be detected even in systems where it is difficult to detect the zero-phase component. This method has the advantage of being able to accurately determine the difference between opening/closing and disconnection of a single-phase load or unbalanced load.

[Brief explanation of drawings]

Figure 1 is a diagram showing the lines where load L ₁ and load L ₂ are connected to substation T _1. Figure 2 A to D are equivalent circuits when one wire of A phase is disconnected, and when a single phase load of AB phase is opened. Figure 3 is a vector diagram of the line voltage of each load and the load current of each phase. be. FIG. 4 is a graph showing the boundary between the wire breakage region and the load switching region on a complex plane regarding the wire breakage coefficient K obtained by the present invention, and also shows the experimental results obtained by the present invention. FIG. 6 is a block circuit diagram showing one embodiment of the present invention, and FIG. 6 is a flowchart showing a program used in the embodiment of FIG. K = △I ₂ / △I ₁ ... wire breakage coefficient, △I ₁ ... change in positive sequence current, △I ₂ ... change in negative sequence current, m ... real number of K, n ... K Imaginary components of CT ₁ , CT ₂ , CT ₃ …
...Current transformer, 13...Microprocessor.

Claims (1)

[Claims] 1. The change in the positive and negative phase currents before and after time is extracted from the line current of the three-phase distribution line, and when the ratio of both changes is within a certain range, it is determined that the line is disconnected. A method for detecting disconnection in an electric line, characterized in that: 2. The disconnection detection method according to claim 1, wherein the ratio of the change in the positive phase component and the negative phase component is decomposed into a real part and an imaginary part and the value thereof is detected. 3 The real part of the ratio of the change in the positive phase component and the negative phase component is m,
When the imaginary part is n, the following formula A wire breakage detection method according to claim 1 or 2, wherein the wire breakage is determined to be a wire breakage when the ratio of both changes exists outside the range surrounded by the curve represented by . 4 The real part of the ratio of the change in the positive phase component and the negative phase component is m,
When the imaginary part is n, the following formula A wire breakage detection method according to claim 1 or 2, wherein the wire breakage is determined to be a wire breakage when the ratio of both changes exists outside the range surrounded by the curve represented by . 5 The real part of the ratio of the change in the positive phase component and the negative phase component is m,
Claim 1: When m and n are in the range of (m+1) ² +n ² >3 (m-0.5) ² + (n-0.938) ² >0.130, where n is the imaginary part, it is determined that the wire is disconnected. Disconnection detection method described. 6 A line current detection means for each phase of a three-phase distribution line, a means for extracting the detection value of the line current detection means at a predetermined sampling period, and a means for extracting the line current of each phase in one sampling period and each phase in the next sampling period. means for extracting a change in the line current from the line current, an arithmetic device for extracting a positive phase component and a negative phase component from the change in the line current extracted by the extracting means and calculating a ratio of the two; 1. A disconnection detection device for an electric line, comprising: determination means for detecting a disconnection when the ratio is within a certain range.