JPS6251057B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a ground fault phase detection device for ungrounded power distribution lines. Conventionally, various types of protective relays have been installed on ungrounded distribution lines, but their operating speed is slow, so they are
It had no effect. The present invention has been made in view of this point, and it is an object of the present invention to provide a ground fault phase detection device that is easily realizable and has high speed. First, before going into the explanation of the ground fault phase detection device, the basic ground fault phenomenon and its vector relationship will be explained. Figure 1 is an equivalent circuit diagram of a well-known one-line ground fault in an ungrounded distribution line, and 1 in the figure indicates the system phase voltage E/
√3, 2 is the fault point resistance Rg3 is the 3-phase active ground capacitance 3C4 is the limiting resistance. If the resistance value of limiting resistor 4 is r/3 and the angular frequency of the system is ω, then the voltage Vg applied to fault point resistance Bg in 2 and the voltage _V0 applied to ground capacitance 3C in 3 are as follows. Become a relationship. FIG. 2 illustrates this using vectors. This means that the trajectory of point P is a vector with respect to the change in resistance Rg at the fault point.

[Formula] is a string, and this string is shown to be drawn on the circumference at an angle of (π-θ). Now limiting resistance (including line leakage resistance) r/3
Considering that is a negligibly large value (r → ∞), θ = π/2 from equations (1) and (2) above, so the locus of point P in Figure 2 is on a semicircle with diameter OA. I will be drawing. In other words, zero-sequence voltage V ₀ = OP is phase voltage

It becomes a semicircle whose diameter is [formula]. Also, the zero-sequence voltage V ₀ is In this equation, if we consider the limiting resistance (including leakage resistance) r/3 to be infinite as shown above, Here, if the fault point resistance Rg → ∞, V ₀ = 0V, that is, point O in Figure 2, and if Rg → 0, then

[Formula] That is, it corresponds to point A. The third diagram illustrates the above relationship for three phases.
The relationship is the same for each phase. Therefore, the relationship between the fault phase voltage Vg and the zero-sequence voltage V ₀ at the time of a one-line ground fault on an ungrounded distribution line is
Considering Vg as the standard, the zero-sequence voltage V ₀ is the fault phase voltage
It exists between the in-phase with Vg and the phase delayed by π/2. Next, if we assume that the leakage resistance r/3 including the limiting resistance is not infinite but a finite value, the vector relationship will be as shown in Figure 2 from equations (1) and (2) above, but we can write it in more detail. For example, it will be as shown in Figure 4. i.e. circumferential OPA
is the phase voltage

From [Formula], it can be seen that it is a part of a circle that has the diameter of a circle in phase advanced by (π/2-θ). Therefore, the phase of V ₀ in this case exists between the in-phase with the fault voltage and the θ-lag phase. As is clear from the above, if θ = tan ^-1 rωC takes any value between θ and π/2 and the fault point resistance Rg is considered from 0 to ∞, then the existence range of the zero-sequence voltage V ₀ is As shown in FIG. 3, it exists on or inside a semicircle (shaded area) having a diameter equal to the phase voltage. Figure 3 is finally derived from the ground fault phenomenon and vector relationship described above, and no matter what kind of ground fault is considered, the zero-sequence voltage V ₀ will range from the in-phase to the delayed phase π/2 with the fault phase voltage as the reference. It was found that there is a between. Taking advantage of this fact, we are trying to create a ground fault phase detection device, but if the reference voltage is taken as the phase voltage as described above, the phase voltage at the time of a complete ground fault will be:
Since it becomes completely zero and is not desirable as a reference voltage, it is easy to detect a faulty phase if the line voltage is used as a reference. For example, in the case of an A-phase ground fault, the zero-sequence voltage V ₀
is for line voltage V _AB V _BC V _CA It has a phase difference angle of Here ( ₀ − _AB ) is V _AB
represents the phase difference angle between the phase angle _AB of and the phase angle ₀ of V ₀ . Rewriting condition (5) results in the following equation (6). Now, if we calculate formula (6), that is, the sine of the phase difference angle, we can get the formula
The faulty phase can be determined from the positive and negative signs of the first and second equations (6). Here, it will be explained that a determination equivalent to Equation (6) can be made using the sampling values of the zero-sequence voltage and the line voltage. The phases of the zero-sequence voltage and line voltage are not fixed, but actually rotate with the system angular frequency ω. Therefore, the zero-phase voltage V ₀ and the line voltage V _K (K=AB, BC, CA) are expressed by the following equations. Here, V _OM and V _KM are the peak values of V ₀ and V _K. If the sampling interval of V ₀ and V _K is △t, then
The sampling values of t=t ₀ and t=t ₀ −Δt are as follows. Furthermore, the function f _K (V ₀ , V _K ) is defined as shown below. f _K (V ₀ , V _K )=V _K (t ₀ )・V ₀ (t ₀ −△t)−V _K (t ₀ −△t)・V ₀ (t ₀ )……(9) Equation ( 8) and (9), f _K (V ₀ , V _K ) is transformed as follows. f _K (V ₀ , V _K ) = V _KM sin (ωt ₀ +)・V _OM sin (ωt ₀ −ω・△t+ ₀ ) −V _KM sin (ωt ₀ −ω・△t+)・V _OM sin ( ωt ₀ + ₀ ) =V _KM V _OM sin(ωt ₀ +) {sin(ωt ₀ + ₀ ) cos(ω・△t) −cos(ωt ₀ + ₀ ) sin(ω・△t)−V _KM V _OM sin (ωt ₀ + ₀ ) {sin (ωt ₀ +) cos (ω・△t) − cos (ωt ₀ +) sin (ω・△t)} =V _OM V _KM {−sin (ωt ₀ +) cos (ωt ₀ + ₀ ) + sin (ωt ₀ + ₀ ) cos (ωt ₀ +)} sin (ω・△t) = V _OM V _KM sin (ω・△t) sin (ωt ₀ + ₀ −ωt ₀ − ) =V _OM V _KM sin (ω・△t) sin ( ₀ −) ...(10) If V _AB is chosen as the line voltage V _K , equation (10) can be rewritten as follows. f _AB (V ₀ , V _AB )=V _OM・V _ABM sin (ω・△t) sin ( ₀ − _AB ) ……(11) Comparing equation (11) with equation (6) and the first equation, V _OM , V _AB
Since _M is positive and sin(ω·Δt) is positive if the sampling interval ω·Δt is within 180°, the positive and negative values of both equations match. Therefore, the sampling values of the zero-sequence voltage and line voltage at time t ₀ -△t, t ₀ are V ₀ (t ₀ -△t), V ₀
(t), V _K (t ₀ −△t), and V _K (t ₀ ) into equation (9) and determine whether it is positive or negative, the same judgment as equation (6) has been made. . That is, f _AB (V ₀ , V _AB )=V _AB (t ₀ )・V ₀ (t ₀ −△t)−V _AB (t ₀ −△t)・V ₀ (t ₀ )<0 f _BC ( V ₀ , V _BC )=V _BC (t ₀ )・V ₀ (t ₀ −△t)−V _BC (t ₀ −△t)・V ₀ (t ₀ )≧0 (12) f _CA (V ₀ , V _CA )=V _CA (t ₀ )・V ₀ (t ₀ −△t)−V _CA (t ₀ −△t)・V ₀ (t ₀ )=0 can be determined using equation (6). This is equivalent to the determination of Similarly, ground faults in the B and C phases can also be detected. In other words, the sine of the phase difference angle between the line voltage and the zero-sequence voltage of the other two phases that are not the grounded phase is positive or zero, and the sine of the phase difference angle between the line-to-line voltage and the zero-sequence voltage between the grounded phase and the delayed phase is positive or zero. is negative. To summarize the above, f _AB (V ₀ , V _AB )<0 and f _BC (V ₀ , V _BC )≧
A phase ground fault at 0 f _BC (V ₀ , V _BC ) < 0 and f _CA (V ₀ , V _CA ) ≧
B phase ground fault at 0 f _CA (V ₀ , V _CA ) < 0 and f _AB (V ₀ , V _AB ) ≧
If it is 0, it can be determined that there is a C-phase ground fault. This invention is based on this principle, but in the case of power distribution lines, there are other requirements to consider when making a determination. When considering a power distribution system, the load condition is not balanced among the three phases, and a certain amount of zero-sequence voltage is always generated. In order to prevent erroneous determination due to this zero-sequence voltage, operation determination becomes more reliable by adding zero-sequence overvoltage detection, which indicates a ground fault when the zero-sequence voltage exceeds a certain level, to the ground fault phase judgment conditions. Now, regarding the calculation of the magnitude of this zero-sequence voltage,
Let the zero-sequence voltage be V ₀ =V _OM sin(ωt+ ₀ ), and the sampling value at t=t ₀ −△t t=t ₀ t=t ₀ +△t is V ₀ (t ₀ −△t)=V _OM sin(ωt ₀ −ω・△t+
₀ ) V ₀ (t ₀ )=V _OM sin (ωt ₀ + ₀ ) V ₀ (t ₀ +△t)=V _OM sin (ωt ₀ +ω・△t+
₀ ), then V ₀ (t ₀ −△t)・V ₀ (t ₀ +△t)=V ² _OM・{sin ² (ωt ₀ + ₀ )−sin ² (ω・△t)} = { V ₀ (t ₀ )} ² −V _OM ²・sin ² (ω・△t). Therefore, as V ² _OM = 1/sin ² (ω・△t) {(V ₀ (t ₀ )) ² −V ₀ (t ₀ −△t)・V ₀ (t ₀ +△t)}, the time The square value of the peak value of the zero-phase voltage can be calculated from the sampling values of t ₀ -Δt, t ₀ , and t ₀ +Δt. Therefore, if we set g(V ₀ )=1/sin(ω・△t)・√{ ₀ ( ₀ )} ² − ₀ ( ₀ −△)・₀ ( ₀ +△), then g(V ₀ )≧c ₁ or {g(V ₀ )} ² ≧ (c ₁ ) ² , the presence or absence of a ground fault can be detected. Here, c ₁ is a constant and has a value larger than the peak value of the zero-sequence voltage that occurs when the system is healthy. In particular, in a power distribution system, the load is rarely balanced among the three phases, and is always in an unbalanced state, resulting in zero-sequence voltage. For this reason, if a judgment is made only based on the phase relationship, there is a possibility of making a false judgment due to the zero-sequence voltage due to this unbalanced load, so the condition that the zero-sequence voltage is greater than a certain value is generated g (V ₀ ) ≧ c ₁ is necessary. Furthermore, in order to reduce supply disturbances, especially in distribution lines, slight ground faults (for example, instantaneous contact with leaves) are often not treated as accidents. For this reason as well, the above conditions are necessary. As described above, when this invention is applied to a digital relay, the determination formula is g (V ₀ ) = 1/sin (ω・△t)√{ ₀ ( ₀ )} ² − ₀ ( ₀ −△)・₀ ( ₀ +△) (13) f _AB (V ₀ , V _AB )=V _AB (t ₀ )・V ₀ (t ₀ −△t)−V _AB (t ₀ −△t)・V ₀ (t ₀ ) (14) f _BC (V ₀ , V _BC )=V _BC (t ₀ )・V ₀ (t ₀ −△t)−V _BC (t ₀ −△t)・V ₀ (t ₀ ) (15 ) f _CA (V ₀ , V _CA )=V _CA (t ₀ )・V ₀ (t−△t)−V _CA (t ₀ −△t)・V ₀ (t ₀ ) (16) Using g (V ₀ )≧c ₁ or {g(V ₀ )} ² ≧(c ₁ ) ² and f _B
C (V ₀ , V _BC )≧0f _AB (V ₀ , V _AB )<0 and A phase ground fault g(V ₀ )≧c ₁ or {g(V ₀ )} ² ≧(c ₁ ) ² and f _B
C (V ₀ , V _BC )<0f _CA (V ₀ , V _CA )≧0 and B phase ground fault g(V ₀ )≧c ₁ or {g(V ₀ )} ² ≧(c ₁ ) ² and f _C
By detecting a C-phase ground fault when _A (V ₀ , V _CA )<0f _AB (V ₀ ·V _AB )≧0, a faulty ground fault phase can be detected at high speed. Here, ω=2πf (f is the system frequency) and Δt is the sampling interval time. For this reason, if the ability of arithmetic processing units improves, △
By reducing t, the detection speed can be increased as much as possible. As an example of the configuration of the ground fault phase detection device according to the above invention, an embodiment in which a digital processing device is used is shown in FIG. In FIG. 5, reference numeral 51 denotes an analog-to-digital converter, which mainly consists of a filter 51, a sample-and-hold circuit 52, and an analog-to-digital converter 53, and converts the line (or phase) voltage detected by the voltage transformer and Extra frequency components are removed from the zero-sequence voltage by a filter 51, sampled at a certain time interval (Δt) by a sample-and-hold circuit 52, and converted into a digital quantity by an analog-to-digital converter 53. It can be done. The voltage information converted into a digital quantity is stored in the data memory 61 of the arithmetic processing unit 6.
The arithmetic processing unit 63 performs arithmetic processing based on the voltage data stored in the data area of the data memory 61 and based on the determination procedure stored in the program memory 62 . If there is an accident in the system, the output section 7 outputs a command to disconnect the shingle breaker or an alarm/display signal to notify the occurrence of the accident. As described above, the present invention focuses on the voltage vector phases in FIGS. 3 and 4, and determines whether the sine of the phase difference between the zero-sequence voltage and the line voltage and the zero-sequence voltage are greater than a predetermined value. This has the effect of being able to quickly identify a faulty ground-fault phase under certain conditions. The invention is also easily applicable to digital relays. That is, by calculating equations (13) to (16) based on the sampled values of the zero-sequence voltage and line voltage, the faulty phase can be identified at high speed.

[Brief explanation of the drawing]

Figure 1 is an equivalent circuit diagram when a ground fault occurs in an ungrounded distribution line, Figure 2 is a vector diagram of zero-sequence voltage when a phase A ground fault occurs, and Figure 3 is a vector diagram of Figure 2 for three phases. FIG. 4 is a vector diagram taking leakage resistance into consideration, and FIG. 5 is an example of the configuration of a ground fault phase detection device according to the present invention. In the figure, 5 is an analog-to-digital converter for deriving the input electrical quantity, and 6 is an arithmetic processing section.

Claims (1)

[Claims] 1. The first phase between the first phase and the second phase of a three-phase AC system.
, the second line voltage between the second and third phases of the system, and the zero-sequence voltage of the system, and calculate the difference between the first line voltage and the zero-sequence voltage. When the sine of the phase difference is negative, the sine of the phase difference between the second line voltage and the zero-sequence voltage is positive or zero, and the zero-sequence voltage is greater than or equal to a predetermined value, A ground fault phase detection device characterized by determining that there is a fault. 2 With a predetermined time interval Δt, the first line voltage V between the first phase A and the second phase B of the three-phase AC system
_AB , the second line voltage V _BC between the second phase B and the third phase C of the system, and the zero-sequence voltage V ₀ of the system
The sampling value derived by sampling V ₀
(t-Δt), V ₀ (t), V _AB (t-Δt), V _AB
(t), V _BC (t-△t), and V _BC (t), f _BC (V ₀ , V _BC ) = V _BC (t)・V ₀ (t-△t) − V _BC ( t-△
t)・V ₀ (t)≧0 f _AB (V ₀ , V _AB ) =V _AB (t)・V ₀ (t−△t)−V _AB (t−Δ
t)·V ₀ (t)<0 and when the zero-sequence voltage is equal to or higher than a predetermined value, it is determined that there is a ground fault in the first phase.