JPS5950719A - Ground-fault phase detector - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ground fault phase detection device used in systems such as ungrounded distribution lines.

Conventionally, there has been a device of this type as shown in FIG.

In the figure, 1a, 1b, 1c are three-phase balanced power supplies, 2a s
2 b v 2c is the three-phase distribution line connected to this three-phase balanced power supply, 3a, 3b, and 3c are the ground capacitances each of these three-phase distribution lines have, and 4 is present in any one phase in the above distribution line. Possible ground fault points, 5a, 5b, 5c are voltage dividers that detect the ground voltage of each phase of the distribution line, 6a, 6b
, 6c is an operational amplifier that performs addition, and 7 is a grounding resistor at the neutral point of the power supply.

Next, the operation will be explained. As shown in Figure 1, if the a-phase has a ground fault across all resistors Rg at ground fault point 4, the ground potential changes from 0 to O' as shown in the vector diagram in Figure 2, and after the ground fault The ground voltages of each phase are Va, Vb, and Vc. When the capacitance and ground fault resistance of the line change at the time of an accident, the point o1 moves on the circle diagram 8. Voltage Va, Vb, VcY adder 6a detected by voltage dividers 5a, 5b, 5c in FIG.

By passing 6b v 6CY, the following output is obtained.

V, = va+Vb/2, v, = vb+”7
'2, v, = Vc+''/2 These voltages are shown in the vector diagram in Figure 2, but as can be seen from Figure 2, the magnitude of the vector synthesized in this way is The one corresponding to the phase is the smallest.Specifically, when a ground fault occurs in the a phase, between the amplitudes of the vectors lVl 1 < 1eal < lv, I ? lV
A relationship like l 1 holds true. Similar relationships hold when accidents occur in other phases. Therefore, by using an appropriate logic circuit Z, the fault phase can be determined.

As mentioned above, the conventional ground fault phase detection device detects all the fluctuations in the absolute value of each relative ground torpedo pressure before and after an accident, and distinguishes the ground fault phase by magnitude between them. If the ground capacitance Co and ground fault resistance Rg of the line are both large, the difference in voltage between normal and faulty conditions will be extremely small, making detection difficult, or if you try to improve the sensitivity Z. It is necessary that the voltage division ratio of the voltage divider and the amplification factor of the operational amplifier are highly balanced between each phase, and even if this were achieved, malfunctions due to noise are likely to occur, and furthermore, high voltage There was a drawback that it was not possible to determine whether an open phase occurred due to poor cable contact or the like.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and it is possible to directly detect the zero-sequence voltage generated in proportion to the fault current and to identify the ground fault phase 2 from the entire waveform. It is an object of the present invention to provide a phase interference detection device.

An embodiment of this invention will be described below. In FIG. 3, where the same parts and the same symbols as in FIG.
b, 3-phase phase shift transformer (reference voltage generator) that generates Lie f, 10 is a capacitive voltage divider (zero-phase voltage detector), [fa,
11b and 11c are ea, eb, and ea'4f full-wave rectifier circuits that perform full-wave rectification; 12 is an integration circuit that integrates the rectified voltage output from the rectifier circuit 11; 13a;
13b and 13c are voltage comparisons that output a signal when the integrated output exceeds the threshold voltage v1, that is, when each phase is normally connected to the high voltage line, compared with the output sound threshold voltage of the integrating circuit 12. and 14 are three voltage comparators 13a and 13b.
, 13° is an AND circuit that outputs a gate signal only when a signal is output from all of them, and 15 is a gate that allows the instantaneous value of the input signal (zero-sequence voltage ve) to pass only during the period when this gate signal is input. circuit, 16a, 1<Sb
, 1<SC is the zero-sequence voltage v0 and the reference voltages Lla, Llb,
uc'v multiplier, 17IL, 17b, 17
G is an integrator for integrating the output of the multiplier, 181
L, 18b, and 18c are comparators that compare the output t1 of the integrator with a predetermined threshold value -Wth.

Next, the operation and principle of the apparatus shown in FIG. 3 according to the present invention will be explained. Three-phase balanced power supply 1a of the system under consideration.

The phase voltages of 1b and 1c can be expressed as follows.

ea == B @ s plow ωt eb=B @5in(ωt −−π) ec==E*5in(ωt −−x) By the phase shift transformer 9i), these phase voltages and I) are also the angle If reference voltages ua, Llb, and UCV corresponding to vectors delayed by α are generated, these can be expressed as follows.

ua = E-sin (ωt-a) ub=E-s
in (ωt-a −-r ) uc=R@s sum (ω is one α
−−π) Since these reference voltages are related to the line voltage, the third
There is no change even when there is an unbalanced grounding accident of only hue as shown in FIG. However, the neutral point potential of this three-phase circuit fluctuates, and a zero-phase voltage is generated.

This zero-phase voltage v0 is detected by the capacitive voltage divider 10.

This zero-phase voltage v0 is related to the ground fault resistance Rg, the capacitance C0 of the three-phase line, and the ground resistance RN at the neutral point, and is expressed as follows.

v, = -V, -sin (ω = 10) Figure 4 shows the above voltages ea, eb, ec, ua, ub
, Llc, and vo are shown in a vector diagram. When the value of Rg changes, the foot of the vector v0 moves on the circle diagram 8.

On the other hand, ea, eb are detected by the three-phase phase shift transformer 9 at the same time as the reference voltages Lla, LJb, Lie.
, ec can always obtain a positive voltage by passing through the full-wave rectifiers 11a, 11b, and 11cg unless there is an open phase due to a poor connection of the high-voltage lead wire. Conversely, if there is a missing phase, the phase is zero. Therefore, when compared with the positive voltage V formed by the comparators 13a, 13b, and 13cY, a signal is output from the healthy phase, and no signal is output from the phase corresponding to the open phase. Therefore, when signals are input from all three phases by inputting the outputs of these comparators to the YAND circuit, that is, only when all three phases are connected properly, the gate signal is input from the AND circuit 14 to the gate circuit 15. be done. Then, only when a gate signal is input to the gate circuit 15, the instantaneous value of the zero-phase voltage V0 is allowed to pass through as it is, and furthermore, the voltage of the gate signal is used to light up a well-connected lamp, etc. , the circuit without knowing that an open phase has occurred! You can avoid situations where you might make a misjudgment while driving.

Next, consider a state in which there is no open phase and the connection is good.

In this case, the electric phase voltage V. is the multiplier 16a.

16b, 16C and the gate circuit 15. When this zero-sequence voltage v0 and the reference voltages ua, Ub, uc are multiplied by the multiplier 16at16b16c in FIG. 3, first-order integrals Wag, Wbx, Wc1 are obtained.
is obtained.

2 wb=v, −ub= −−■. −E(ctJs(θ−a
−−π) −cm (2ω is 103 1α−−π)) 4 we = v 0・uc=7HV, −E(cos (θ
-a-:i) -cog (2ωt -6-α--π)
) The DC component of the first term on the right side is an amount proportional to each reference voltage direction component of the zero-sequence voltage in the vector diagram. As can be seen from the vector diagram in Figure 4, if a ground fault occurs in the hue, the foot of the vector of zero-phase voltage v0 will be somewhere on the circle diagram 8, so that αZO° ~ 900 If you choose an appropriate angle between them, the zero-sequence voltage V. and the reference voltage Ua is
In almost the opposite direction, the DC component of Wa is negative, but the DC components of Wb and We, which are not ground fault phases, are positive or have small negative values.

Therefore, the ground fault phase can be detected from this DC component. However, the second term in the above equation is a term that oscillates over time, and the influence of this term! In order to remove these quantities, these quantities may be integrated over time using integrators 17a, 17b, and 17c shown in FIG. Wa, Wb obtained in this way
, WC becomes zero if no accident occurs, but if an accident occurs, the following 1α)-s sum (2ωt'θ-
α)]) However, tg is the time when the accident occurred.

FIG. 5 shows how these integral quantities Wa, Wb, and We change over time. According to this, the accident phase component (Wa in this case) continues to increase in the negative direction with time while oscillating at 2ω, whereas the component of the phase without an accident increases in the positive direction1). , or almost no change. This is a phenomenon that can also be seen when accidents occur in other phases.

Therefore, if a certain negative threshold value -wth Y is set in advance and placed in the comparators shown in Fig. 83, 18a, 18b, and 18c, when the integral of any phase reaches this threshold value, the ground fault phase will be detected. Corresponding signals a t b t aw can all be generated. Although other suitable logic circuits may be considered, using a method that uses a fixed threshold value for the integral quantity will allow the integral quantity to rapidly increase in the event of a ground fault that generates a large zero-sequence voltage. Since the condition changes, the time to judgment is fast, but
It is common that small zero-sequence voltage accidents take a long time to some extent.

In the above case, we considered the case where the integrators 17a, 17b, 17c perform complete time integration, but the multipliers 16a, 16
If there is even a slight DC component due to the calculation accuracy of b, 16c, etc., this will accumulate.

In order to avoid this, it is necessary to set the characteristics of the integrators 17a, 17b, and 17c so that the integration has an appropriate time constant, that is, the transfer function of the first-order lag element is 1+ST. The above-mentioned function can be maintained as long as the integration time constant T is set to be appropriately long compared to the ground fault phenomenon to be detected.

In the above embodiment, the reference voltages Ua, Ub, uc
Although a sine wave is used, a rectangular wave voltage having the same phase and constant amplitude as the sine wave can also be used to obtain a device having the same function as the above embodiment. This is shown in FIG. 786 as a waveform. FIG. 6 shows the waveforms of various parts before and after the ground fault occurred in the a phase (t=tg), where (a) is the reference voltage Lla and (b) is the zero-sequence voltage v. , 4 is the product Wa of vo and ua, ni) is Wa(
7) Integral Wa. In the above example, the reference voltage is a rectangular wave, but even if the zero-phase voltage is shaped into a constant amplitude rectangular wave that has information only about the phase of the Z zero-phase voltage and input to the multiplier, the result will be the same as in the above embodiment. A device with multiple functions can be obtained.

Also, zero-phase voltage sensitivity! If you try to detect a ground fault phase by increasing the voltage, saturation may occur for large zero-sequence voltage signals due to the dynamic range constraints of the arithmetic circuit, but this extreme case is the rectangle shown above. Considering that this corresponds to the case where the zero-sequence voltage of the wave is used, even if saturation occurs in the arithmetic circuit, the phase information of the zero-sequence voltage remains, so it can be seen that the ground fault phase can be detected without any problem.

In the above embodiment, a malfunction occurs due to a slight zero-sequence voltage that occurs even during normal operation due to a slight unbalance in the system or unbalance in the detector! To prevent this, the integration circuit has a time constant. Therefore, Wa, Wb, which appear due to imbalance,
Although the small DC component of We is not rapidly integrated by the integrator, this DC component causes the integrator output Wa,
Since DC bases having different values are generated in Wb and Wc before the ground fault occurs, this may have an adverse effect on the ground fault phase detection using the threshold value. In order to eliminate this, it is sufficient to pass the output capacitor C7 of the integrator (first-order delay element with time constant T) as shown in FIG.

The resistor R placed after the capacitor C is used to make the output pace zero at all times, and the value of the time constant CR is determined based on the expected ground fault phenomenon and the constant system flow, as well as the integration time constant T. Make sure to consider the degree of turbulence when choosing.

Furthermore, even if the position 7 of the CR circuit and the integrating circuit are interchanged, the operation will not change.

In the above embodiment, the reference voltages Ua, ub, uc
Although a three-phase phase shift transformer is used to calculate f, the reference voltage can also be calculated using a capacitance voltage divider without being limited to this. Figure 8 shows the phase difference α=300
In the case of a capacitive voltage divider! An example of using this to calculate reference voltage Z! This is the circuit shown.

As described above, according to the present invention, information from the entire waveform of the zero-sequence voltage of the grid is processed by the Z multiplier, and time information is integrated by the integrator to determine the fault phase. Even if it exists, there is an effect of stably and accurately detecting the ground fault phase.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing the structure of a conventional ground fault phase detection device, Fig. 2 is a vector diagram showing the vector relationship Z of each phase voltage and zero-phase voltage when a ground fault occurs in Fig. Fig. 3 is a circuit diagram showing the structure of the ground fault phase detection device based on the present invention, Fig. 4 is a vector diagram showing the vector relationship between the reference voltage, each phase voltage, and zero phase voltage in Fig. 3, and Fig. 5 is a vector diagram showing the vector relationship between the reference voltage, each phase voltage, and zero phase voltage in Fig. A characteristic diagram showing how the integral amount of each reference voltage direction component of the phase voltage changes over time. Figure 6 is a waveform diagram when the reference voltage is used as a rectangular wave. 9) is the reference voltage Lla, ( crl is the zero-sequence voltage V., 9 is the product of Ua and Vo, and b) is the product of Ua and v.
A waveform diagram showing an example of how the product bi-integrated value of o changes over time. Figure 7 is a circuit diagram that removes the influence 7 caused by the zero-sequence voltage v0 that occurs during normal operation. Figure 8 is a diagram showing how FIG. 2 is a circuit diagram for calculating a reference voltage using a voltage generator. 1a, 1b, Ic---3-phase balanced power supply, 2a, 2b, 2
0...3-phase distribution line, 3a, 3b, 3c...ground capacitance, 4...ground fault point, 7...power supply neutral point grounding resistance, 8...circle diagram, 9 ...3-phase phase shift transformer, 10.
...capacitance voltage divider, 11a, 11b, 11c...full wave rectifier, 12...integrator circuit, 13a, 13b, 13c...
=Voltage comparator, 14...AND circuit, 15...gate circuit, 16a, 16b, 16cm multiplier, 17a,
17b. 17 c --- Integrator, 18a, 18b, 18c ---
Comparator. In the drawings, the same reference numerals indicate the same or corresponding parts Z. Agent Makoto Kuzuno (and 1 other person) Figure 6 Wa=Swadt (d) tg -11------Wth Figure 7 Commissioner of the Japan Patent Office 1. Display of incident Patent application No. 57-162804 2
, Title of the invention Earth fault phase detection device 3, Relationship to the amended person's case Patent applicant address 2-2-3 Marunouchi, Chiyoda-ku, Tokyo Name (601) Mitsubishi Electric Corporation Representative Jinhachibe Katayama 4. Agent 5, Subject of amendment (1) Claims section of the specification (2) Detailed explanation of the invention section of the specification (3) Drawing 6, Contents of amendment (1) Patent as attached Amend the scope of claims. (2) On page 4, line 6 of the specification, the phrase "these voltages" is corrected to "the vector relationship of these voltages." (3) On page 5, line 16 of the specification, the phrase "with the same parts" is amended to read "with the same parts." (4) On page 9, line 17 of the specification, replace the word “integral” with “
Each component” is corrected. (5) Correct Figure 3 as shown in the attached sheet. 7. List of attached documents (1) One document containing the amended Figure 3 (2)
A document stating the scope of the amended claims (1 or more documents) Claims after the amendment (1) A power system whose neutral point is not effectively grounded for supplying balanced three-phase power, and each power system a zero-sequence voltage detector that detects a zero-sequence voltage from the ground voltage of each phase; an output of a path that generates a star-shaped phase voltage of each phase and a reference voltage that lags the star-shaped voltage of each phase by a predetermined angle; A multiplier group that multiplies the reference voltage, and a second comparator that receives the output of the multiplier through an integrator that is supplied with the second threshold voltage and makes a comparison decision. Ground fault phase detection device. (2) As a reference voltage, a predetermined value between 0° and 90° from the star-shaped phase voltage of each phase! ! 3, which corresponds to a vector delayed by 2 degrees
2. The ground fault phase detection device according to claim 1, wherein the earth fault phase detection device uses a rectangular wave voltage having the same phase as the sine wave voltage. (3) By using a voltage comparator etc. in the part that detects the zero-sequence voltage from the ground voltage of each phase, the amplitude is constant,
3. The earth fault phase detection device according to claim 1 or 2, wherein a rectangular wave voltage having the same phase as the zero-sequence voltage is generated and used as the zero-sequence voltage. (4) The sensitivity of the amplifier in the section that detects the zero-sequence voltage from the ground voltage of each phase is increased so that the output of the detection section is saturated for inputs above a predetermined level. A ground fault phase detection device according to scope 1 or 2. (5) A capacitor is inserted before or after the integrating circuit that integrates the product of the reference voltage and the zero-sequence voltage, and the ground fault phase can be detected by the constantly occurring DC component included in these integrals. The ground fault phase detection device according to claim 1.2.3 or 4, characterized in that it is not disturbed.

Claims (1)

[Claims] (11) A power system whose neutral point is not effectively grounded for supplying balanced three-phase power, and a zero-sequence voltage detector that detects zero-sequence voltage from the ground voltage of each phase of this power system. and a reference voltage generator that generates the star-shaped phase voltage of each phase and a reference voltage delayed by a predetermined angle from the star-shaped voltage of each phase, and the star-shaped phase voltage output of each of the reference voltage generators is connected through a rectifier. a group of voltage comparators to which a first threshold voltage is supplied and a first threshold voltage is supplied; an output circuit of the zero-phase voltage detector; A group of multipliers for multiplying the output of the gate circuit by each of the reference voltages, and an integrator to which the outputs of the multipliers are respectively supplied are inputted, and a second threshold voltage is inputted for comparison and judgment. (2) As reference voltages, three sine wave voltages corresponding to vectors delayed by a predetermined angular velocity between θ° and 90° from the star-shaped phase voltage of each phase. The ground fault phase detection device according to claim 1, characterized in that a rectangular wave voltage Z having the same phase is used. By using a voltage comparator etc., the amplitude is constant,
3. The earth fault phase detection device according to claim 1, wherein a rectangular wave voltage having the same phase as the zero-sequence voltage is generated and used as the zero-sequence voltage. (4) The sensitivity of the amplifier in the section that detects the zero-phase voltage from the ground voltage of each phase is increased so that the output of the detection section is saturated for inputs above a predetermined level. A ground fault phase detection device according to scope 1 or 2. (5) A capacitor is inserted before or after the integrating circuit that integrates the product of the reference voltage and the zero-sequence voltage, and the constantly occurring DC component included in these integrals is used to detect ground fault phases. 5. The ground fault phase detection device according to claim 1.2.3 or 4, wherein