JPH0139301B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for detecting a ground fault phase in an ungrounded power distribution line.

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, and 2a, 2b, 2c are a, _b , _c -phase distribution lines connected to power supplies 1a, 1b, 1c with voltages e _a , e b , e c. , 3a, 3b, 3c are distribution lines 2a, 2
Capacitance existing between b, 2c and the ground, 4 is resistance
Switches 5a, 5b, and 5c that equivalently indicate the occurrence of a grounding fault along with Rg are capacitors, and voltage dividers that divide the voltages of the distribution lines 2a, 2b, and 2c;
6a, 6b, 6c are adders that add the two voltages v _a , v _b , v _c of the voltage dividers 5 a, 5 b, 5 c;
7 is a resistor with a resistance value R _M that grounds the neutral points of the power supplies 1a, 1b, and 1c.

Next, the operation will be explained. Voltage divider 5a, 5
The voltages v _a , v _b , v _c of b, 5 c are applied to the adders 6 _a , 6 _b , 6 _c
are input in pairs, and voltages v ₁ , v ₂ , and v ₃ as shown in the following equations are generated at their output terminals.

v ₁ = v _a + v _b /2, v ₂ = v _b + v _c /2, v ₃ = v _c + v _a /2 Switch 1 is turned on, and the a-phase distribution line 2a is
When a ground fault occurs, the capacitance 3a, 3b, 3c and resistance
As the value of Rg changes, the center of the vector moves to 0' along the circle 8, as shown in the vector diagram in Figure 2, and the voltage v ₁ of the fault phase becomes smaller than the voltages v ₂ and v ₃ . becomes smaller, and becomes |v ₁ |<|e _a |<|v ₂ | or |v ₃ |.
This relationship is detected by a logic circuit (not shown), and a response is taken if an accident occurs.

As described above, the conventional ground fault phase detection device detects changes in the absolute value of the ground voltage of each phase before and after an accident occurs, and determines a ground fault phase from the magnitude relationship between them. However, if both the capacitance and the ground fault resistance of the power distribution line are large at the time of an accident, the difference between the line and the line when it is healthy is not significant, and the detection accuracy decreases. To increase detection sensitivity,
It is necessary that the voltage divider ratio and the operation of the adder be highly stable. Even if such stabilization could be achieved, it would not be possible to determine that an open phase has occurred due to poor contact or the like in the connected portion.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and it detects the zero-sequence voltage generated in proportion to the fault current due to a ground fault, and compares this zero-sequence voltage with each phase of the AC system. It is an object of the present invention to provide a ground fault phase detection device that can discriminate a ground fault phase by performing a logical product with a signal based on the voltage of , further integrating, and finally comparing with a reference voltage.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 3 is a block diagram of the ground fault phase detection device of the present invention. In the figure, 9 is the distribution line 2a, 2b, 2c
Connect one end of capacitors 9a, 9b, 9c to
A voltage divider (zero-phase voltage detector) whose other end is grounded via a capacitor 9d and obtains a zero-phase voltage v ₀ from the connection point of the capacitors 9a to 9d, 10 is a power distribution line 2a, 2
The windings 10a are connected in delta to windings 10a and 2c, and the voltages u a0 , _{u b0} , u _c0 are connected in a star pattern and are reference voltages leading by an angle α ₀ than the voltages e _a , e _b , e _c . A transformer (reference voltage generator) having a winding 10b and a function of a phase shifter, 11a, 11b, and 11c are voltages u _a0 , u _b0 , u _c0 of the transformer 10 multiplied by an angle α _1. Phase shift circuit that generates phase shifted voltages u _a1 , u _b1 , u _c1 12
a, 12b, 12c are voltages u _a0 , u _b0 , u _c0 at angle α ₂
The phase shift circuits 13a to 13f generate voltages u _a2 , u _b2 , u _c2 phase-shifted by the voltage v ₀ and the voltages u _a1 , u _b1 ,
Take the product of u _c1 , u _a2 , u _b2 , u _c2 and get the signals w _a1 , w _b1 ,
Multiplier for generating w _c1 , w _a2 , w _b2 , w _c2 14a
~14f is the signal w _a1 of the multipliers 13a~13f ~
By integrating w _c1 , w _a2 ~ w _c2 , the signals W _a1 , W _b1 , W _c1 ,
Integrators that generate W _a2 , W _b2 , W _c2 , 15a-1
5f is the signal W _a1 to W _c1 of the integrators 14a to 14f,
This comparator outputs signals a to c and a' to c' indicating a ground fault when W _a2 to W _c2 reach the reference voltage -W _t .

Next, the operation of this invention will be explained. Power supply 1
The voltages e _a , e b , and e c of a, 1 _b , and 1 _c are expressed by the following equations.

Therefore, transformer 1 whose phase is shifted by angle α ₀
The zero voltages u _a0 , u _b0 , and u _c0 are expressed as follows.

Since the voltages u _a0 to u _c0 are related to the line voltage, there is no change even if an unbalanced ground fault point occurs only in the a phase as shown by turning on the switch 4. Therefore, using the voltages u _a0 to u _c0 , the voltages u _a1 , _{u b1} , u _c1 having a phase delayed by the angle α ₁ from the voltages e a , e _b , e _c are as follows.

Similarly, the voltages u _a2 , u _b2 , u _c2 that are delayed by the angle α ₂ from _the voltages e a , e _b , e _c are given by the following equations.

Since these voltages u _a2 to _{u c2} are also related as line voltages, they do not change even if a ground fault occurs.
If a ground fault occurs in resistor Rg on phase a, these three
The potential at the neutral point of the phase circuit changes, and a zero-sequence voltage v ₀ appears at the output of the voltage divider 9. The voltage v ₀ has a relationship with the capacitance C ₀ and the resistance R _N as shown in the following equation.

v ₀ = −V ₀・sin(ωt−θ) However, Figure 4 shows the voltages la,
FIG. 2 is a vector diagram showing the vector relationship among u _a0 , u _a1 and u _a2 . When the value of the resistance R _g changes, the voltage v ₀ moves on the circle 8.

The multipliers 13a to 13f to which the voltages v ₀ , u _a1 , u _b1 , u _c1 , u _a2 , u _b2 , and u _c2 are input, generate a signal expressed by the following equation.
Output w _a1 , w _b1 , w _c1 , w _a2 , w _b2 , w _c2 .

w _a1 =v ₀・u _a1 =−1/2V ₀・E{cos(θ−α ₁
)−cos(2ωt−θ−α ₁ )} w _b1 =v ₀・u _b1 =−1/2V ₀・E{cos(θ−α ₁
−2/3π)−cos(2ωt−θ−α ₁ −2/3π)} w _c1 =v ₀・u _c1 =−1/2V・E{cos(θ−α ₁
−4/3π)−cos(2ωt−θ−α ₁ −4/3π)} In the above equation, the first term on the right side is the DC component, and the second term is the AC component that changes at twice the frequency of the power source e _a . However, information regarding the fault phase is included in the DC component, and the AC component in the second term should be deleted in order to determine the fault phase.

As is clear from the vector diagram in Figure 4, if a ground fault occurs in phase a, the foot of the vector of voltage v ₀ will be on circle 8, so the angles α ₁ and α ₂ can be changed from 0° to 90°. If an appropriate value is selected between them, the voltages v ₀ and u _a1 (u _a2 ) will be in almost opposite directions, the DC components of the signals w _a1 and w _a2 will be negative, and the signals w _b1 , which are not ground fault phases will be negative. w _c1 , w _b2 ,
The DC component of w _c2 is a positive or small negative value.

Integrators 14a to 14f handle such signals.
Signals w _a1 , w _b1 , w _c1 , w _a2 , w _b2 , w _c2 are obtained by integrating w _a1 , w _b1 , w _c1 , w _a2 , w _b2 , w _c2 as shown in the following equation.

Note that t=t _g is the time when the accident occurred.

W _a1 =∫ ^t _tg w _a1 dt=-1/2V ₀・E [cos(θ−α ₁ )(
t-tg)-1/2ω{sin2ωt-θ-α ₁ )-sin(2ωt _g
−θ−α ₁ )}] W _b1 =∫ ^t _tg w _b1 dt=−1/2V ₀・E[cos(θ−α
₁ −2/3π) (t−tg) −1/2ω{sin(2ωt−θ−α ₁ −2/3π)−s
in(ωt _g −θ−α ₁ −2/3π)}] W _c1 =∫ ^t _tg w _a1 dt=−1/2V ₀・E[cos(θ−α
₁ −4/3π) (t−tg) −1/2ω{sin(2ωt−θ−α ₁ −4/3π)−s
in(ωt _g −θ−α ₁ −4/3π)}] W _a2 =∫ ^t _tg w _a2 dt=−1/2V ₀・E[cos(θ−α
₂ ) (t−tg) −1/2ω{sin(2ωt−θ−α ₂ )−sin(2ωt _g
−θ−α ₂ )}] W _b2 =∫ ^t _tg w _b2 dt=−1/2V ₀・E[cos(θ−α
₂ −2/3π) (t−tg) −1/2ω{sin(2ωt−θ−α ₂ −2/3π)−s
in(2ωt _g −θ−α ₂ −2/3π)}] W _c2 =∫ ^t _tg w _c2 dt=−1/2V ₀・E[cos(θ−α
₂ −4/3π) (t−tg) −1/2ω{sin(2ωt−θ−α ₂ −4/3π)−s
in(2ωt _g −θ−α ₂ −4/3π)}] In the above equation, the signals W _a1 and W _a2 are from the accident phase and increase in the negative direction while oscillating at 2ω, but the slope is It is determined by the vertical components of the signals w _a1 and w _a2 . Therefore, the difference in slope between signals W _a1 and W _a2 is
It is determined by cos(θ−α ₁ ) and cos(θ−α ₂ ). Now, as shown in Fig. 4, by selecting angles α ₁ and α ₂ , the foot of the vector of voltage v ₀ caused by a ground fault is |θ−α ₁ |＞|θ−α ₂ | When reaching the position where , cos(θ−α ₁ )<cos(θ−α ₂ ), the signal W _a2 increases more rapidly in the negative direction than the signal W _a1 .

FIG. 5 is a waveform diagram of the signals W _a1 to W _c1 and W _a2 to W _c2 before _{and after the time t g} when the ground fault occurred.
As shown in the figure, signals W _a1 and W _a2 related to the accident phase
exceeds the reference voltage −Wt and increases in the negative direction, whereas the signals W _b1 , W _b2 , W _c1 , of the phases without faults
W _c2 increases in the positive direction or hardly changes.

Therefore, the comparators 15a to 15f output the signals W _a1 to
When W _c1 , W _a2 to W _c2 become less than the reference value -W _t , signals a to c and a' to c' indicating that a ground fault has occurred are output. In this case, the ground fault phase is the a phase, so the signals a,
a′ is output.

Note that in the above embodiment, the delay angle of the reference voltage is α ₁
and α ₂ , but if there are more than that, the legs of the zero-sequence voltage vector become |θ−α _i |, (i
=1, 2, .

Further, in the above embodiment, a case has been described in which the integrators 14a to 14f perform complete time integration. Due to the calculation precision of the multipliers 13a to 13f, if there is even a small amount of direct current, this will accumulate. For this reason, it is necessary to set the characteristics of the integrators 14a to 14f so that the integration has an appropriate time constant, that is, the transfer function of the first-order lag element is 1/1+ST. If the time constant T of this integration is made longer than the ground fault phenomenon to be detected, the same effect as in the above embodiment can be obtained.

In addition, in the above embodiment, the voltages u _a1 , u _b1 , u _c1 , u _a2 ,
Although u _b2 and u _c2 are used as sine waves, the same effect as in the above embodiment can be obtained even if these are converted into rectangular waves having the same phase and constant amplitude as the sine wave using a waveform conversion circuit. The waveforms of the operation in such a case are shown in FIGS. 6 and 7. In Figure 6, a is the voltage, e _a ,
b is a rectangular wave signal of voltage u _a1 , c is a rectangular wave signal of voltage u _a2 , d is zero-phase voltage v ₀ , e is signal w _a1 of the product of voltage v ₀ and u _a1 , f is voltage v ₀ , Indicates the signal w _a2 of the product of u _a2 .

Fig. 7 shows a signal w _a1 which is obtained by integrating the signal w _a1 shown in Fig. 6, and a signal which is obtained by integrating the signal w _a2 shown in Fig. 7.
It is a waveform diagram of w _a2 . The signals W _a1 and W _a2 have more vibration components than those in Fig. 5, but the reference value −W _t
The accident phase can be determined in the same manner as in the above embodiment by comparing with the above.

Further, in the above embodiment, the zero-phase voltage is a sine wave, but the same effect as in the above embodiment can be obtained even if the voltages v ₀ and v ₀ ' are shaped into a rectangular wave of constant amplitude and input to the multiplier. .

Additionally, when detecting a ground fault phase by increasing the detection sensitivity of the zero-sequence voltage, saturation may occur in the zero-sequence voltage signal due to the dynamic range constraints of the arithmetic circuit. Since this information is retained, it is possible to detect a ground fault phase.

In the embodiment described above, the integrating circuit is provided with a time constant in order to prevent malfunctions caused by zero-sequence voltages that slightly occur even in normal conditions due to slight unbalance of the system or unbalance of the detector. Therefore, the slight DC component caused by unbalance is not integrated by the integrator, but because of this DC component, the output of the integrator has a DC base with a different value even before the ground fault occurs. This adversely affects ground fault phase detection using threshold values.

Figure 8 shows that in order to eliminate such adverse effects,
2 is a circuit diagram in which the output of an integrator (first-order lag element with time constant T) is taken out via a capacitor C. FIG. In this case, the value of the time constant CR, like the time constant for integration, is selected in consideration of the expected ground fault phenomenon and the degree of regular system disturbance. The operation is the same even if the positions of the CR circuit and the integrating circuit are swapped back and forth.

Further, in the above embodiment, a three-phase phase shift transformer is used to derive the voltages u _a0 , u _b0 , and u _c0 , but a capacitive voltage divider may be used to derive these. FIG. 9 is a circuit diagram of such another embodiment,
The case where the phase α=30° is shown. Voltage dividers 5a, 5b,
The output of 5c is input to adders 6a, 6b, and 6c, and voltages u _a0 , u _b0 , and u _c0 are derived.

As described above, according to the present invention, the product of the zero-sequence voltage signal of the system and the phase-shifted reference voltage of the system is taken, further integrated, and finally, the level is compared and determined with the reference voltage. Since the fault phase is determined based on the above, the influence of noise can be reduced and a device that operates stably can be obtained.

Further, the present invention provides a plurality of reference voltages by shifting a reference voltage that is a predetermined angle ahead of the star-shaped phase voltage of each phase by a predetermined phase, and an integral amount corresponding to a reference voltage having a small phase angle with the zero-phase voltage. Since the fault phase is detected by Even if the current situation changes (ground fault resistance, ground capacity of the distribution line), it is possible to detect the fault phase stably and quickly, resulting in a significant performance improvement.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a conventional ground fault phase detection device, Figure 2
The figure is a vector diagram of each phase and zero-sequence voltage when a ground fault occurs, Fig. 3 is a circuit diagram of a ground fault phase detection device according to an embodiment of the present invention, and Fig. 4 is an input to the device shown in Fig. 3. 5 is a waveform diagram of the operation of the device shown in FIG. 3, FIGS. 6 and 7 are waveform diagrams of the operation of the ground fault phase detection device according to other embodiments of the present invention, 8 and 9 are circuit diagrams of a ground fault phase detection device according to another embodiment of the present invention. 3a-3b, 9a-9d, c...capacitor,
4...Switch, 6a-6c...Adder, 9...
Voltage divider, 10...Transformer, 11a to 11c, 12
a to 12c...phase shift circuit, 13a to 13f...multiplier, 14a to 14c...integrator, 15a to 15
f... Comparator. In addition, in the figures, the same reference numerals indicate the same parts.

Claims (1)

[Scope of Claims] 1. A zero-phase voltage detector that detects a zero-phase voltage from the ground voltage of each phase of an AC system, and a reference voltage that generates a reference voltage that is advanced by a predetermined angle from the star-shaped phase voltage of each phase. a generator, a plurality of transfer circuits that shift the reference voltage by a predetermined phase, a plurality of multipliers that multiply the zero-sequence voltage and the output voltage of the transfer circuit, respectively, and an output signal of the converter that is integrated. A ground fault phase detection device comprising a plurality of integrators and a plurality of comparators that generate a signal indicating the detection of an accident when the output signal of the integrator falls below a predetermined negative reference voltage. 2. Claims characterized by comprising a waveform conversion circuit that converts the output signal of each transfer circuit into a rectangular wave of constant amplitude, and supplying the rectangular wave to a multiplier for multiplication by a zero-phase voltage. The ground fault phase detection device according to item 1. 3. Claim No. 3, comprising a waveform conversion circuit for converting zero voltage into a rectangular wave of constant amplitude, and supplying the rectangular wave to a multiplier to be multiplied by the output signal of the phase shift circuit. The ground fault phase detection device according to item 1. 4. The ground fault phase detection device according to any one of claims 1 to 3, characterized in that a DC interrupting capacitor is connected in series to the integrator.