JPH0136330B2 - - Google Patents

Description

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

A conventional device of this type is shown in FIG. In the figure, 1a, 1b, 1c are three-phase balanced power supplies, 2a, 2b, 2c are three-phase distribution lines connected to the three-phase balanced power supplies, and 3a, 3b, 3c are the three-phase balanced power supplies.
4 is a ground fault point that may exist in any one phase of the distribution line; 5a, 5b, and 5c are voltage dividers that detect the ground voltage of each phase of the distribution line; , 6a, 6b, and 6c are adders, 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,
For example, if phase a is grounded at ground fault point 4 through resistor R _g , the ground potential changes from 0 to O' as shown in the vector diagram in Figure 2, and each phase after the ground fault occurs. The voltage to ground of is v _a , v _b , v _c .

When the capacitance and ground fault resistance of the line change at the time of an accident, point 0' moves on the circle diagram 8. By passing the voltages v _a , v _b , v _c detected by the voltage dividers 5 a , 5 b , 5 c in FIG. 1 through adders 6 a , 6 b , 6 c , the following outputs are obtained.

v ₁ = v _a + v _b /2, v ₂ = v _b + v _c /2 v ₃ = v _c + v _a /2 These voltages are shown in the vector diagram in Figure 2, and as can be seen from this figure, The magnitude of the vectors synthesized in this way is the smallest corresponding to the accident phase. In other words, when a ground fault occurs in phase a, the relationship |v ₁ |<|e _a |<|v ₂ |, |v ₃ | holds true between the vector amplitudes, and if a ground fault occurs in other phases, A similar relationship holds true when .

Therefore, the accident phase can be determined using the above relational expression.

As mentioned above, conventional ground fault phase detection devices essentially detect fluctuations in the absolute value of each relative ground voltage before and after an accident, and determine the ground fault phase from the magnitude of these voltages. If the ground capacitance C ₀ and ground fault resistance R _g of the line are both large, the difference between the voltages in normal condition and in fault condition is extremely small, making detection difficult, and if you try to improve sensitivity, ,
It is necessary that the voltage division ratio of the voltage divider and the precision of the adder be highly balanced among the phases, and even if this were achieved, there was a drawback that malfunctions due to noise were likely to occur.

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 from the entire waveform. The purpose is to provide a phase interaction detection method.

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 3, where the same parts as in FIG. 1 are represented by the same symbols, 9 is a capacitive voltage divider (zero-sequence voltage detector) that detects the zero-sequence voltage _v0 , and 10 is a vector delayed by a certain angle from the star-shaped phase voltage of the power supply. reference voltage equivalent to
A three-phase phase shift transformer (reference voltage generator) that generates u _a , u _b , u _c , 11a, 11b, 11c is the zero-phase voltage v ₀
and a multiplier for multiplying reference voltages u _a , u _b , u _c , 12
a, 12b, 12c are integrators that integrate the output of the multiplier; 13a, 13b, 13c are differentiating circuits with long time constants that remove DC components superimposed on the outputs of the integrators; 14a, 14b, 14c are A comparator that compares the output of the differentiating circuit with a threshold value.
15 is a peak value detection circuit for determining the amplitude of the AC component included in the output of the differentiating circuit; 16 is an amplifier; 17
a and 17b are diodes.

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 1 of the system currently being considered
The phase voltages e _a , e _b , and e _c of a, 1 b, and 1 c can be expressed as follows.

e _a = E sin ω _t e _b = E sin (ω _t -2/3π) e _c = E sin (ω _t -4/3π) Due to the phase transformer 10, the phase voltages are each delayed by an angle α from the above phase voltages. Phase reference voltages u _a , u _b , u _c
are generated, they are expressed by the following equation.

u _a = E・sin (ω _t −α) u _b = E・sin (ω _t −α−2/3π) u _c = E・sin (ω _t −α−4/3π) These voltages are between the lines Since it is related to voltage,
There is no change even if there is an unbalanced ground fault only in the a phase as shown in FIG.

However, when a fault occurs in the ground fault resistance R _g in the a phase, the neutral point potential of this three-phase circuit fluctuates, and a zero-sequence voltage v ₀ is generated, which appears at the output of the capacitive voltage divider. The above zero-phase voltage v ₀ is expressed as follows in relation to the ground fault resistance R _g , the capacitance C ₀ of the three-phase line, and the ground resistance R _N of the power supply neutral point.

v ₀ = −v ₀・sin(ω _t −θ) However, Figure 4 shows the above voltages e _a , e _b , e _a0 , u _b0 , u _c0 , u _a ,
This is a vector diagram showing the relationship between u _b , u _c and v ₀ . When the value of R _g changes, the foot of vector v ₀ moves on the circle diagram 8.

By multiplying this zero-sequence voltage v ₀ and each reference voltage u _a , u _b , u _c using multipliers shown in 11a, 11b, and 11c in FIG. 3, the following voltages wa , w _{b ,}
w _c is obtained.

w _a =v ₀・u _a =−1/2V ₀・E {cos(θ−α) −cos(2ω _t −θ−α)} w _b =v ₀・u _b =−1/2V ₀・E {cos(θ−α−2/3π) −cos(2ω _t −θ−α−2/3π)} w _c =V ₀・u _c =−1/2V ₀・E{cos(θ−α−4 /3π) −cos(2ω _t −θ−α−4/3)} The DC component of the first term on the right side is an amount proportional to each reference voltage of the zero-phase voltage in the vector diagram. As can be seen from the vector diagram in Figure 4, a
If a ground fault occurs in the phase, the foot of the vector of v ₀ will be somewhere on the circle diagram 8, so change α from 0°.
If the angle is selected and placed at an appropriate angle between 90°, v ₀ and u _a
are almost in the opposite direction, and the DC component of the above-mentioned w _a is negative, but the DC components of w _b and w _c , 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 in order to remove the influence of this term, these quantities may be integrated over time using integrators 12a, 12b, and 12c. The values w _a , w _b , and w _c obtained in this way are zero when no accident occurs, but when an accident occurs, the following signals are generated.

w _a0 =∫ ^t _tg w _adt =-1/2V ₀・E[cos(θ-α) ・(tt _g )-1/2ω{sin(2ω _t -θ-α) −sin(2ωt _g −θ− α)}] w _b0 =∫ ^t _tg w _bdt = -1/2V ₀・E [cos (θ−α−2/3π)・(t−t _g ) −1/2ω{sin (2ω _t −θ− α−2/3π) −sin(2ωt _g −θ−α−2/3π)}] w _c0 =∫ ^t _tg w _cdt =−1/2V ₀・E[cos(θ−α−2/3π)・(t-t _g ) -1/2ω{sin (2ω _t -θ-α-2/3π) -sin (2ωt _g -θ-α-2/3π)}] However, t _g is the time of the accident occurrence. be.

When such integral quantities w _a0 , w _b0 , w _c0 are passed through differentiating circuits 13a, 13b, 13c with long time constants, calculation errors in the multipliers 11a, 11b, 11c or integrators 12a, 12b, 12c, etc. If DC components are included in w _a0 , w _b0 , w _c0 , the amount from which these DC components are removed is w _a ,
w _b and w _c are output.

FIG. 5 shows how these integral quantities W _a , W _b , and W _c change over time. according to this,
The accident phase component (W _a in this case) continues to increase in the negative direction with time while oscillating at 2ω, whereas the component of the accident-free phase increases in the positive direction or , almost unchanged.

This phenomenon also occurs when an accident occurs in other phases. Therefore, by setting a certain negative threshold value -w _th , FIG.
14c, it is possible to generate signals a, b, and c corresponding to the ground fault phase when the integral value of any phase reaches this threshold value.

However, as can be seen from Fig. 5, the integral quantity w _a ,
w _b and w _c include a 2ω AC component. If this alternating current component is large and -w _th0 in FIG. 5 is set as the threshold, w _b also exceeds the threshold -w _th0 and there is a risk of malfunction. In order to prevent this, the threshold value should be changed depending on the size of the AC vibration component, and when the AC vibration is large,
The threshold value may be set high.

This function is provided by the peak value detection circuit 15, amplifier 16, and diodes 17a and 17 shown in FIG.
This circuit consists of b. According to this circuit,
The threshold value _-wth input to the comparators 14a, 14b, and 14c is the peak value _Ep of the AC vibration component detected by the peak value detection circuit 15 and the amplifier 16.
The amplification factor A can be set as follows.

−w _th = −w _th0 −A・E _p w _th0 ≧A・E _p w _th0 <A・E _p Therefore, the threshold value −w _th is the AC vibration component of the integral quantities w _a , w _b , w _c Since it can be automatically set depending on the size, malfunctions can be prevented.

In the above case, the case where the integrators 12a, 12b, 12c perform complete time integration has been considered, but if there is even a slight DC component due to the calculation precision of the multipliers 11a, 11b, 11c, this will accumulate.

To avoid this, integrators 12a, 12b, 1
It is necessary to set the characteristic of 2c to be an integral with an appropriate time constant, that is, the transfer function of the first-order lag element: 1/1+ST. If the integration time constant T is selected to be appropriately long compared to the ground fault phenomenon to be detected, the above-described function can be maintained as is.

In the above example, the reference voltages u _a , u _b , and u _c are used as sine waves, but even if these are made into rectangular waves with the same phase and constant amplitude as the sine wave, the same function as in the above example can be obtained. You can get the equipment. FIG. 6 shows a case in which this is represented by a waveform. This Fig. 6 shows the waveforms of various parts before _and after the ground _fault occurred in the a phase. Ha is the product of v ₀ and u _a
w _a and d are the product W _{a of w a .}

In the above example, the reference voltage is a rectangular wave, but even if the zero-sequence voltage v ₀ is shaped into a rectangular wave with a constant amplitude that has only phase information and is input to the multiplier, the above embodiment will still work. It is possible to obtain a device with similar functions.

In addition, when trying to detect a ground fault phase by increasing the zero-sequence voltage detection sensitivity, due to the dynamic range constraints of the arithmetic circuit, the circuit that calculates v ₀ for large zero-sequence voltage signals However, considering that this extreme case corresponds to the one using the zero-sequence voltage of the rectangular wave above, even if saturation occurs in the arithmetic circuit, the phase of the zero-sequence voltage Since the information remains, it is possible to detect the ground fault phase without any problem.

In the above embodiment, a three-phase phase shift transformer was used to calculate the reference voltages u _a , u _b , and u _c , but the reference voltages may be calculated using a capacitive voltage divider. is also possible.

FIG. 7 is an electrical circuit diagram showing an example when α=60°.

As described above, according to the present invention, the multiplier processes information from the entire zero-sequence voltage waveform of the grid, and the integrator integrates information for a certain period to determine the fault phase. This has the effect of providing a ground fault phase detection device that operates accurately and stably even in the presence of noise.

[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 between each phase voltage and zero-phase voltage when a ground fault occurs, and Fig. 3
The figure is a circuit diagram showing the structure of the ground fault phase detection device according to the present invention, FIG. 4 is a vector diagram showing the vector relationship between the reference voltage, each phase voltage, and the zero-sequence voltage, and FIG. A characteristic diagram showing how the integral amount of the directional component changes over time. Figure 6 is a waveform diagram showing the phenomenon when the reference voltage is converted into a rectangular wave and used, where A is the reference voltage u _a and B is zero. Phase voltage v ₀ , h is u _a and
A characteristic diagram showing an example of how the integral W _a of the product W _a of v ₀ changes over time. Figure 7 is a circuit diagram showing an example of calculating a reference voltage using a capacitive voltage divider. be. 1a, 1b, 1c...3-phase balanced power supply, 2a, 2
b, 2c... 3-phase distribution line, 3a, 3b, 3c...
Ground capacitance, 4... Ground fault point, 5a, 5b,
5c...capacitance voltage divider, 6a, 6b, 6c...adder, 7...power supply neutral point grounding resistance, 8...circle diagram,
9...Capacity voltage divider, 10...Phase shift transformer, 11
a, 11b, 11c...multiplier, 12a, 12
b, 12c... Integrator, 13a, 13b, 13c
...Differential circuit, 14a, 14b, 14c...Comparator, 15...Peak value detection circuit, 16...Amplifier, 17a, 17b...Diode. In addition, in the figure,
The same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] 1. 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. , a reference voltage generator that generates three reference voltages corresponding to vectors delayed by a predetermined angle between 0° and 90° from the star-shaped phase voltage of each phase, and multiplying the zero-phase voltage and the reference voltage, respectively. a plurality of multipliers for integrating the outputs of the multipliers, a differentiation circuit to which the outputs of the integrators are supplied;
a plurality of comparators that determine a fault phase by comparing the output of the differentiating circuit with a negative threshold value of a component corresponding to a ground fault phase of the power system; a peak value detection circuit that detects and automatically sets a negative threshold according to the amount of change in the amount of integration so that the absolute value of the negative threshold increases when the amount of change in the amount of integration of the integrator is large; Equipped with ground fault phase detection device. 2 As the above reference voltage, use the same phase as three sinusoidal voltages corresponding to vectors delayed by an angle determined by the amplitude of the zero-sequence voltage between 0° and 90° from the star-shaped phase voltage of each phase. 2. The ground fault phase detection device according to claim 1, wherein the ground fault phase detection device uses a rectangular wave voltage. 3 Detect the zero-sequence voltage, determine the delay angle α of the reference voltage, use a voltage comparator, etc., to generate a rectangular wave voltage with constant amplitude and the same phase as the zero-sequence voltage, and apply it to the multiplier. A ground fault phase detection device according to claim 1 or 2, characterized in that the ground fault phase detection device is provided with: 4 Detecting the zero-sequence voltage, determining the delay angle α of the reference voltage, and amplifying the zero-sequence voltage with an amplifier,
Claims 1 to 3, wherein the output of the amplifier is supplied to the multiplier in such a manner that the output of the amplifier is saturated for a zero-sequence voltage of a predetermined level or higher. Ground fault phase detection device.