JPH104623A - Ground fault detection circuit and ground fault detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ground fault detection circuit, where the influence of capacitance to the ground of a cable, to detect ground fault in a non-grounded circuit by injecting a signal between the ground and an electric path, and measuring the leakage of the signal. SOLUTION: This circuit has a signal injection circuit 13 which injects the signals of multiple frequency component f1 and f2 into a non-grounded current path 12, through an injection filter 14 to check the power frequency of a current path, and the ratio between these injection frequency components is five or higher. This circuit is equipped with an earth resistance level detecting circuit 16 which measures and computes the earth resistance, by detecting the leak current of the injected frequency components by a zero-phase current sensor 15, provided at the current path 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground fault detecting circuit and a ground fault detecting method for detecting a leakage current of an ungrounded electric circuit.

[0002]

2. Description of the Related Art FIG. 8 shows, for example, Japanese Patent Publication No. 55-24331.
FIG. In the figure, 1 is a power distribution transformer, 2 is an electric circuit connected to the power distribution transformer 1, 3 is a grounding capacity of the electric circuit 2, 4 is a grounding device including a grounding resistor, and 5 is an unbalanced current of the electric circuit 2. It is a zero-phase current transformer. Reference numeral 6 denotes a coupling device connected to the electric circuit 2, which is a series resonance circuit including, for example, a capacitor and a reactor. For example, a commercial alternating current of 60 Hz is blocked, and only a signal current for ground fault detection is passed.

[0003] 7 is an oscillator which is connected to the coupling device 5, 2 times the frequency of the predetermined frequency f ₁ by a signal from the controller 101, for example, oscillating a frequency twice as f ₂ = 2f ₁ is satisfied Then, it is injected into the electric circuit 2 through the coupling device 6. Reference numeral 9 denotes an amplifying circuit. The amplifying circuit 9 amplifies a leakage current of the ground fault impedance Z (parallel impedance of the ground capacitance 3 and the ground fault resistor 8) detected by the zero-phase current transformer 5, and a processing circuit 10 Output to

The processing circuit 10 has OR gates 102 and 104 having one end commonly connected to the amplifier circuit 9 and the other end connected to the controller 101, an amplifier circuit 103 for amplifying the output of the OR gate 102, and an amplifier circuit. It comprises a comparator 105 for comparing the output of 103 with the output of OR gate 104. Reference numeral 20 denotes a switching element which performs a switching operation when the output of the comparator 105 reaches a predetermined set value, and operates a display circuit (not shown).

Next, the operation of the conventional circuit will be described.
Oscillator 7 oscillates a signal of twice the frequency such that f ₂ = 2f ₁ is established by a command from controller 101, and this signal is applied to electric circuit 2 via coupling device 6. since there is a ground capacitor 3 as the earth current ics ₁ flows through each ground capacitor 3 constitute a closed loop current flows through the electric branch number becomes nic ₁ to n Tosureba grounding device 4.

The current nic ₁ passing through the grounding device 4 is detected by the zero-phase current transformer 5 and is supplied to the OR gate 102 by the amplifier 9.
104 at each end. On the other hand, OR gate 104
Since the input signal for the gate is applied from the controller 101 to the other end, only the output signal of the OR gate 102 is amplified approximately twice by the amplifier 103 and input to the comparator 105.

The comparator 105 calculates the ratio between the output of the amplifier 103 and the output current of the OR gate 104, and outputs the leakage detection signal to the switching element 2 when the ratio becomes a value other than a predetermined value.
Output to 0. Upon receiving the leakage detection signal, the switching element 20 turns on, and activates a display circuit (not shown) to display the leakage detection.

[0008]

As described above, the conventional ground fault detection circuit uses the injection frequency having a small frequency ratio (double), so that the zero-phase current transformer is detected when the ground capacity is large. The variation has a large effect on the ground fault resistance calculation (this effect will be described later). The applicable ground capacity range is limited, that is, it is difficult to apply to a large ground capacity, that is, an electric circuit having a long wire length. There was a problem.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a ground fault detecting circuit and a ground fault detecting method which can be applied to a long electric wire having a large ground capacity. I do.

[0010]

According to a first aspect of the present invention, there is provided a ground fault detection circuit comprising a signal of a first frequency component serving as a reference and at least a signal of the first frequency component between an ungrounded electric circuit and the ground. Signal injecting means for injecting a signal of a second frequency component having a frequency ratio of 5 times, and passing the signals of the first and second frequency components in the injected signal and blocking the signal of a power supply frequency component Injection filter, and a zero-phase current sensor that is installed on the non-grounded circuit and that combines the currents of the respective frequency components flowing through the non-grounded system with respective vectors to detect a zero-phase current, are detected by the zero-phase current sensor. Ground-fault resistance detecting means for calculating a ground-fault resistance value based on two levels of the zero-phase current of the first frequency component and the zero-phase current of the second frequency component; Is less than the specified value, an alarm Or those with an alarm output means for outputting a blocking signal of the path.

A ground fault detecting circuit according to a second aspect of the present invention provides a signal of a first frequency component serving as a reference, and a frequency ratio at least five times that of the first frequency component between an ungrounded electric circuit and the ground. Signal injecting means for injecting a signal of a second frequency component and a signal of a third frequency component lower than the first frequency component, and the first, second, and third signals in the injected signal. An injection filter that passes the signal of the frequency component and blocks the signal of the power supply frequency component, and is installed in the non-grounded circuit, and the current of each of the frequency components flowing in the non-grounded circuit is vector-synthesized to generate a zero-phase current. A zero-phase current sensor for detecting, a signal frequency extracting means corresponding to each frequency component for extracting a zero-phase current of each frequency component among the zero-phase currents detected by the zero-phase current sensor, and the first frequency component or Third frequency A changeover switch for switching the signal frequency extraction means corresponding to the component to transmit a zero-phase current of the corresponding frequency component, and a zero-phase current of the second frequency component extracted by the signal frequency extraction means and transmitted from the changeover switch. Ground-fault resistance detecting means for calculating a ground-fault resistance value based on two levels of the zero-phase current of the frequency component and
When the calculated ground fault resistance value is equal to or less than a predetermined value, an alarm output means for outputting an alarm output or a signal to cut off the electric circuit is provided.

A ground fault detecting circuit according to a third aspect of the present invention provides a signal of a first frequency component serving as a reference, and a frequency ratio at least five times that of the first frequency component between an ungrounded electric circuit and the ground. Signal frequency selection for selecting one of the first frequency component signal and the third frequency component signal from the second frequency component signal and the third frequency component signal lower than the first frequency component Means, signal injection means for injecting the signal of the second frequency component and the signal of the frequency component selected by the signal frequency selection means between the non-grounded electric circuit and the ground; And an injection filter that passes a signal of a selected frequency component and blocks a signal of a power supply frequency component, and is installed on the non-grounded electric circuit. A zero-phase current sensor for detecting a current; a zero-phase current of a second frequency component detected by the zero-phase current sensor; and a zero-phase current of a frequency component selected by the injection signal frequency selection means. Ground fault resistance detecting means for calculating a ground fault resistance value based on the ground fault resistance value, and when the calculated ground fault resistance value is equal to or less than a predetermined value, an alarm output or an alarm output means for outputting a cutoff signal of the electric circuit. is there.

According to a fourth aspect of the present invention, there is provided a ground fault detection circuit according to any one of the first to third aspects, wherein the injection filter is a band elimination filter, and a signal of a power supply frequency component among the injected frequency component signals. It is to be removed.

According to a fifth aspect of the present invention, there is provided a ground fault detecting method, wherein a signal of a first frequency component as a reference and a frequency ratio at least five times higher than the first frequency component are provided between the ungrounded electric circuit and the ground. And a vector of the current of each frequency component flowing through the ungrounded electric circuit is synthesized to detect a zero-phase current, and then the first phase detected by the zero-phase current sensor is detected. After calculating the ground fault resistance based on the two levels of the zero-phase current of the frequency component and the zero-phase current of the second frequency component, if the calculated ground fault resistance is equal to or less than a predetermined value, It outputs an alarm output or a signal to cut off the electric circuit.

According to a sixth aspect of the present invention, in the ground fault detecting method according to the fifth aspect, the first frequency component and the third frequency component lower than the first frequency component are set.
And a signal of a second frequency component having a frequency ratio at least five times that of the first frequency are simultaneously injected into an ungrounded electric circuit, and the zero-phase current component detected by the zero-phase current sensor is And the zero-phase current of the second frequency component and the first
The ground fault resistance value is calculated on the basis of the two levels of the frequency component and the zero-phase current component of the third frequency component.

According to a seventh aspect of the present invention, there is provided a ground fault detecting method according to the fifth aspect, wherein the first frequency component and the third frequency component lower than the first frequency component are provided.
And a second frequency component signal having a frequency ratio of at least 5 times that of the first frequency, together with the second frequency component signal, one of the first or second frequency component signals. The vector of the current of each frequency component that flows between the ungrounded circuit and the ground and flows through the ungrounded circuit is vector-combined to detect the zero-phase current, and then the second frequency detected by the zero-phase current sensor is detected. Component zero-sequence current and the first
Alternatively, after calculating the ground fault resistance value based on the two levels of the zero-phase current of the third frequency component and the ground fault resistance value, if the calculated ground fault resistance value is equal to or less than a predetermined value, an alarm output or a cutoff signal of the electric circuit is provided. Is output.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a configuration of a ground fault detection circuit according to the first embodiment. In the figure, reference numeral 11 denotes a power distribution transformer in which a commercial AC power supply is connected to the primary side. For example, the voltages V1 and V2 on the secondary side are 100 V at a frequency of 60 Hz. Reference numeral 12 denotes an ungrounded AC circuit to which the secondary voltage of the power distribution transformer 11 is applied, and 13 denotes a signal injection unit that injects a signal voltage for ground fault detection into the ungrounded AC line 12. For example, the injection signal generators 13a and 13b
A plurality of frequency signals having a voltage E of 10 V AC and a first injection frequency f ₁ and a second injection frequency f ₂ (hereinafter, injection signal voltage ES) are injected.

Reference numeral 14 denotes an injection filter. The injection filter 14 blocks the power supply frequency 60 Hz of the frequency components of the injection signal voltage ES injected from the signal injection means 13 and conducts the signals of the injection frequencies f1 and f2. .

Reference numeral 15 denotes a zero-phase current sensor (ZCT) for detecting a zero-phase current (leakage current) Ig flowing due to a ground fault in the ungrounded AC circuit 12, and 16 denotes a ground-fault resistance level detecting circuit, which is a zero-phase current sensor. of 15 detection current, the leakage current Ig ₁ of the first injection frequency f ₁ and the second injection frequency f _2, Ig ₂
And ground fault resistance Rg is calculated from the detection level.
Reference numeral 17 denotes an alarm output circuit. The alarm output circuit 17 outputs an alarm output to the outside or a cutoff signal to a cutoff device (not shown) of the non-grounded AC power line 12 when the calculated ground fault resistance Rg is equal to or less than a predetermined value. .

FIG. 2 shows an ungrounded AC circuit 1 for an injection signal.
2 is an equivalent circuit diagram of FIG. In the figure, Rg is the ground fault resistance,
C ₀ is the ground capacity C ₁ of each of the electric wires 12R to 12T shown in FIG.
It is the sum of C ₂ and C ₃ .

Next, the operation of this embodiment will be described. Consider a case in which one line of the ungrounded AC electric circuit 12 has a ground fault at a position where the ground fault resistance Rg is present. As shown in the equivalent circuit diagram of FIG. 2, the injected signal voltage ES by the leakage current Ig flows to the ground fault resistance Rg and earth capacitance C _0, which zero-phase current sensor 15 detects. Here, the leakage current of the frequency f ₁ component in the injection signal voltage ES is Ig ₁ , the current flowing through the ground fault resistor Rg is Ir ₁ , and the current flowing through the total ground capacitance C ₀ is Ic ₁ .

Further, the leakage current at the second frequency f ₂ in the injection signal voltage ES is Ig ₂ , the current flowing through the ground fault resistor Rg is Ir ₂ , the current flowing through the total ground capacitance C ₀ is Ic ₂ ,
Assuming that the frequency ratio f ₂ / f ₁ of each injection signal voltage ES is N,
From the vector diagram of FIG. 3, Ic ₂ = N · Ic ₁ , Ir ₂ = Ir ₁
The following equation holds.

[0023] _{^{Ig 1 2 = Ic 1 2 +}} Ir 1 2 Ig 2 2 = (N · Ic 1) 2 + Ir 1 2

From the above equations, the following equation (1) is obtained. ^{_{Ir 1 2 = {(N ·}} Ig 1) 2 -Ig 2 2} / (N 2 -1) ···· (1)

Here, the influence of the detection variation of the zero-phase current sensor 15 will be described. Assuming that the detection variation is α and the upper and lower limits of the variation are assumed, Ig ₁ is Ig ₁ · (1 + α),
Leakage current I when the ig ₂ is detected and Ig ₂ · (1-α)
The calculation error of g is β.

Ir ₁ = ES / Rg Ic ₁ = 2πf ₁ · C ₀ · E = A · Ir ₁ (where A = 2π
f ₁ · C ₀ · Rg).

[0027] Therefore, from equation (1) ^{(1 + β) 2 · Ir} 1 2
^{= [N 2 {(A ·} Ir 1) 2 + Ir 1 2} (1 + α) 2 -
_{{(N · A · Ir 1} ) 2 + Ir 1 2} (1-α) 2] / (N 2
-1) and the following equation (2) is obtained.

(1 + β) ² = (N ² · A ² · 4α + N ² (1 + α) ^2- (1-α) ² ) / (N ² -1) (2)

FIG. 4 is a graph showing the equation (2) when the frequency ratios N = 2 and N = 5. The vertical axis represents the error variance (1 + β) ² , the horizontal axis represents A, and the ground fault. Resistance Rg (= ES
/ Ir ₁ ) assuming an allowable calculation error of 20%, (1+
β) ² = (1 + 0.2) ² = 1.41, so N = 2
In this case, it can be tolerated up to about A = 0.3.

Similarly, when N = 5, (1 + β) ² =
1.41 is about A = 0.7. A = 2π
f ₁ · C ₀ · Rg, and if the ground fault resistance Rg is the same,
Since A is proportional to the ground capacity C ₀ , the error is substantially the same for N = 5 up to about twice the ground capacity, that is, about twice as long as N = 2, when N = 2.

FIG. 5 is a graph showing the equation (2) when A = 0.7. The vertical axis is error variance (1 + β) ² ,
The horizontal axis indicates the frequency ratio N. As can be seen from the figure, (1 + β) ² decreases rapidly from N = 2 to N = 3, and β becomes almost constant from about N = 5. By setting the frequency ratio N to 5 or more, the error can be reduced and the ground fault resistance Rg can be detected.

When the allowable calculation error range of the ground fault resistance Rg is set, A (A = 2 · π · f1 · C ₀ · R) is obtained from the equation (2).
g), the first injection frequency f ₁ and the ground capacitance C
_{Since 0} is inversely proportional, the smaller the first injection frequency f _{1, the} larger the ground capacitance C ₀ may be, and the ground fault detection circuit according to the present embodiment can be applied to an electric circuit having a longer wire length.

The frequency of the signal injected into the ungrounded AC power line 12 near the commercial power frequency is blocked by the injection filter 14 composed of a band elimination filter. Therefore, the first injection frequency f ₁ is lower than the commercial power supply frequency, for example, 2
By setting 0 Hz and the second injection frequency f ₂ to a value higher than the commercial power frequency, for example, 100 Hz, the ground fault resistance Rg can be detected within a predetermined error range without being affected by the injection filter 14. As described above, by setting the first injection frequency f ₁ and the second injection frequency f ₂ with the commercial power supply frequency of the ungrounded AC power line 12 interposed therebetween, it becomes easy to set the frequency ratio to 5 or more.

Embodiment 2 FIG. 6 is a diagram showing a configuration of a ground fault detection circuit according to Embodiment 2 of the present invention. In the figure, reference numerals 11 to 17 are the same as those in the first embodiment. 13c is injected signal generating unit for emitting a third injection signal voltage ES of the injection frequency f ₃ of the frequency lower than the first injection frequency f _1, the relationship between the injection frequency of the injected signal voltage ES f ₃ <f ₁ <a f _2.

Numeral 18 denotes frequency selection means for selecting an injection signal voltage of the first injection frequency f ₁ or an injection signal voltage of the third injection frequency f ₃ to the signal injection means 13. If the third injection frequency f ₃ is smaller than the first injection frequency f ₁ , the longer the period, the longer the detection time is required to detect the leakage current Ig ₃ in the third injection frequency f ₃ band. .

For example, when the injection frequency is 5 Hz, 1
Since the cycle period is 200 ms, it is not suitable for high-speed detection (usually, high-speed ground fault detection is 100 ms or less,
In the case of the delay type, it is performed in about 300 ms to 2 seconds). Therefore, depending on the permissible detection time, the third injection frequency f
_By selecting ₃ at a lower injection frequency, the ground capacitance C ₀ can be increased in inverse proportion to the frequency reduction. This is because if A is the same, that is, if the frequency × C ₀ is constant, the error becomes larger and smaller than that in FIG.

Embodiment 3 FIG. 7 is a diagram showing a configuration of a ground fault detection circuit according to Embodiment 3 of the present invention. In the figure, 11 to 17 and 13a to 13c are the same as those described in the second embodiment. 16e is an operation detection unit, 16a, 16
b, 16c are the first, second, and third injection frequencies f ₁ , f ₂ ,
leakage current Ig _1, Ig _2, Ig ₃ selective extraction injecting signal frequency extraction circuit constituted by filter f _3, 16d is a changeover switch, the first injection frequency f ₁ or the third injection frequency f ₃ leakage current Ig _1, one of the Ig ₃ selects and transmitted to computing detection unit 16e.

Next, the operation will be described. Signal injection means 13
The injection signal voltage ES of the first, second, and third injection frequency components f ₁ , f ₂ , and f ₃ is injected into the AC electric circuit 12 from. The zero-phase current sensor 15 detects leakage currents Ig ₁ , Ig ₂ , and Ig ₃ at the respective injection frequencies f ₁ , f ₂ , and f _3. According to the allowable detection time, the changeover switch 16 d is set to the first injection frequency. by selecting f1 and one of the leakage current Ig _1, Ig ₃ of the third injection frequency f3, path from one of the distribution transformer 11 has different earth capacitance C ₀ of the respective branch paths are branched When the allowable detection time is different, the reference frequency ratio is selected in accordance with the length (the magnitude of the ground capacity) of the AC circuit 12 after the zero-phase current sensor 15 inserted in each branch circuit. The detection of the ground fault resistance Rg for each branch electric circuit can be performed accurately within the allowable detection time range.

For convenience of explanation, the first injection frequency f
₁ has been described as being equal to the injection signal voltage ES of the second injection frequency f2. Even if the injection signal voltage ES is different, this voltage ratio is determined in advance by the ground fault resistance level detection circuit 16. , It is possible to calculate the ground fault resistance Rg in consideration of the voltage ratio in the above formula. Further, although the electric circuit has been described using the frequency of a general commercial power supply, it is apparent that the electric circuit can be used for an electric circuit of another frequency (for example, a 400 Hz circuit) without being limited to this.

[0040]

According to the first aspect of the present invention, a signal of a first frequency component serving as a reference and a frequency ratio at least five times that of the first frequency component are provided between an ungrounded electric circuit and the ground. Signal injecting means for injecting the signal of the frequency component 2;
In the injected signal, an injection filter that passes the signals of the first and second frequency components and blocks a signal of a power supply frequency component, and each of the injection filters that are installed on the non-grounded electric circuit and flow through the non-grounded electric circuit. A zero-phase current sensor for vector-synthesizing the currents of the frequency components to detect a zero-phase current, a zero-phase current of a first frequency component detected by the zero-phase current sensor, and a zero-phase current of a second frequency component Ground fault resistance detecting means for calculating a ground fault resistance value based on the two levels, and an alarm output means for outputting an alarm output or a cutoff signal for the electric circuit when the calculated ground fault resistance value is equal to or less than a predetermined value. With
By setting the ratio of the frequency components of the two signals to 5 times or more, 2
There is an effect that the measurement error due to the ground fault resistance calculation from the vector calculation of the leakage current of two frequency components can be reduced.

According to the second aspect of the present invention, a signal of a first frequency component serving as a reference, and a second signal having a frequency ratio at least five times that of the first frequency component are provided between the ungrounded electric circuit and the ground. Signal injecting means for injecting a signal of a frequency component and a signal of a third frequency component lower than the first frequency component; and wherein the first, second, and third signals are included in the injected signal.
An injection filter that passes the signal of the frequency component and blocks the signal of the power supply frequency component, and is installed on the ungrounded electric circuit,
A zero-phase current sensor for vector-synthesizing the current of each of the frequency components flowing through the ungrounded electric circuit to detect a zero-phase current; and a zero-phase current of each of the frequency components in the zero-phase current detected by the zero-phase current sensor. A signal frequency extracting means corresponding to each frequency component for extracting a current, and a changeover switch for switching the signal frequency extracting means corresponding to the first frequency component or the third frequency component and transmitting a zero-phase current of the corresponding frequency component; A ground fault resistance calculating a ground fault resistance value based on two levels of a zero-phase current of the second frequency component extracted by the signal frequency extracting means and a zero-phase current of the frequency component transmitted from the changeover switch; Detecting means, and an alarm output means for outputting an alarm output or a signal to cut off the electric circuit when the calculated ground fault resistance value is equal to or less than a predetermined value. There is an effect that can be precisely ground fault resistance detected with the wiring length long path in.

According to the third aspect of the present invention, a signal of a first frequency component serving as a reference, and a second signal having a frequency ratio at least five times that of the first frequency component, between the ungrounded electric circuit and the ground. Signal frequency selecting means for selecting one of the first frequency component signal and the third frequency component signal from the frequency component signal and the third frequency component signal lower than the first frequency component; Signal injecting means for injecting the signal of the second frequency component and the signal of the frequency component selected by the signal frequency selecting means between the ungrounded electric circuit and the ground; An injection filter that passes a signal of a frequency component and blocks a signal of a power supply frequency component, and is installed in the ungrounded circuit, and a vector synthesis of the current of each frequency component flowing in the ungrounded circuit is performed to detect a zero-phase current. A zero-phase current sensor based on two levels of a zero-phase current of a second frequency component detected by the zero-phase current sensor and a zero-phase current of a frequency component selected by the injection signal frequency selection means. A ground-fault resistance detecting means for calculating a ground-fault resistance value, and an alarm output means for outputting an alarm output or a signal for cutting off the electric circuit when the calculated ground-fault resistance value is equal to or less than a predetermined value. By setting the ground fault detection allowable time limit according to the wiring length after the sensor,
There is an effect that the ground fault resistance can be detected with high accuracy.

According to the fourth aspect of the present invention, the injection filter is a band elimination filter, and the power supply frequency component signal is removed from the injected frequency component signals.
There is an effect that the injection frequency can be set freely.

According to the fifth aspect of the present invention, the signal of the first frequency component serving as a reference and the second signal having a frequency ratio at least five times that of the first frequency component are provided between the ungrounded electric circuit and the ground. The signal of the frequency component is injected, and the current of each frequency component flowing in the ungrounded electric circuit is vector-synthesized to detect the zero-phase current, and then the first frequency component of the first frequency component detected by the zero-phase current sensor is detected. After calculating the ground fault resistance based on the two levels of the zero-phase current and the zero-phase current of the second frequency component, if the calculated ground fault resistance is equal to or less than a predetermined value, an alarm output or Since the cutoff signal of the electric circuit is output, the ratio of the frequency components of the two signals is made five times or more, and the measurement error due to the calculation of the ground fault resistance from the vector calculation of the leakage current of the two frequency components can be reduced. The effect of being able to do That.

According to the sixth aspect of the present invention, the signal of the first frequency component, the third frequency component lower than the first frequency component, and the signal of the second frequency component having a frequency ratio at least five times as high as the first frequency are generated. The zero-phase current of the second frequency component and the zero-phase current of the first frequency component or the third frequency component among the zero-phase current components detected by the zero-phase current sensor simultaneously injected into the ungrounded electric circuit. Since the ground fault resistance value is calculated based on the two levels of the component and the ground fault resistance, there is an effect that the ground fault resistance can be accurately detected even on an electric circuit having a longer wiring length within the ground fault detection allowable time limit.

According to the seventh aspect of the present invention, in the signal of the first frequency component, the third frequency component lower than the first frequency component, and the second frequency component having a frequency ratio at least five times that of the first frequency component , One of the first and second frequency component signals is injected between the ungrounded electric circuit and the ground together with the second frequency component signal, and the current of each frequency component flowing through the ungrounded electric circuit is vector-combined. A zero-phase current, and subsequently based on two levels of the zero-phase current of the second frequency component and the zero-phase current of the first or third frequency component detected by the zero-phase current sensor. After calculating the ground fault resistance value, if the calculated ground fault resistance value is equal to or less than a predetermined value, an alarm output or a signal to cut off the electric circuit is output, so that it is determined according to the wiring length after the zero-phase current sensor. To set the allowable time limit for ground fault detection. In, there is an effect that it is precisely the ground fault resistance detection.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a ground fault detection circuit according to a first embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram of an injection signal of the ground fault detection circuit according to the first embodiment.

FIG. 3 is a vector diagram for explaining the invention of calculating a ground fault resistance leakage current in the first embodiment.

FIG. 4 is a graph showing error dispersion characteristics of ground fault resistance leakage current calculation using a frequency ratio of an injection signal as a parameter in the first embodiment.

FIG. 5 is a graph showing an error dispersion characteristic of a ground fault resistance leakage current calculation when the frequency ratio of an injection signal is changed in the first embodiment.

FIG. 6 is a diagram showing a configuration of a ground fault detection circuit according to a second embodiment of the present invention.

FIG. 7 is a diagram showing a configuration of a ground fault detection circuit according to a third embodiment of the present invention.

FIG. 8 is a diagram of a conventional ground fault detection circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 Distribution transformer, 12 AC circuit, 13 Signal injection means, 14 Injection filter, 15 Zero-phase current sensor, 16 Ground fault resistance level detection circuit, 16a-16c
Injection signal frequency extraction circuit, 16d changeover switch,
16e Operation detection section, 17 alarm output circuit, 18 frequency selection means.

Claims (7)

[Claims] 1. A signal of a first frequency component serving as a reference and a signal of a second frequency component having a frequency ratio at least five times that of the first frequency component are injected between an ungrounded electric circuit and the ground. A signal injecting means for transmitting a signal of the first and second frequency components in the injected signal and blocking a signal of a power supply frequency component; A zero-phase current sensor for vector-synthesizing the currents of the respective frequency components flowing through the grounding system electric circuit to detect a zero-phase current; a zero-phase current of a first frequency component detected by the zero-phase current sensor; 2 with the zero-phase current of the frequency component 2
Ground-fault resistance detecting means for calculating a ground-fault resistance value based on the two levels; and, when the calculated ground-fault resistance value is equal to or less than a predetermined value, an alarm output means for outputting an alarm output or a cutoff signal for the ungrounded electric circuit. And a ground fault detection circuit. 2. A signal of a first frequency component serving as a reference, a signal of a second frequency component having a frequency ratio at least 5 times that of the first frequency component, between the ungrounded electric circuit and ground,
And a signal injecting means for injecting a signal of a third frequency component lower than the first frequency component; and a power supply for passing the signals of the first, second, and third frequency components in the injected signal. An injection filter that blocks a signal of a frequency component, and a zero-phase current sensor that is installed in the non-grounded electric circuit, and that synthesizes a vector of the current of each of the frequency components flowing through the non-grounded electric circuit and detects a zero-phase current, Signal frequency extracting means corresponding to each frequency component for extracting a zero-phase current of each of the frequency components from the zero-phase current detected by the zero-phase current sensor. A changeover switch for switching the signal frequency extracting means corresponding to the first frequency component or the third frequency component and transmitting a zero-phase current of the corresponding frequency component; and the second frequency extracted by the signal frequency extracting means. Ground-fault resistance detecting means for calculating a ground-fault resistance value based on two levels of the zero-phase current of the component and the zero-phase current of the frequency component transmitted from the changeover switch; In the following case, an alarm output means for outputting an alarm output or an interruption signal of the electric circuit is provided. 3. A signal of a first frequency component serving as a reference, a signal of a second frequency component having a frequency ratio at least five times that of the first frequency component, and a third signal lower than the first frequency component. Signal frequency selecting means for selecting one of the signal of the first frequency component or the signal of the third frequency component, and the signal of the second frequency component and the signal frequency selecting means. Signal injecting means for injecting a signal of the selected frequency component between the ungrounded electric circuit and the ground, and passing the signal of the second and selected frequency components in the injected signal to block the signal of the power supply frequency component Injection filter, installed in the ungrounded circuit, a zero-phase current sensor that detects the zero-phase current by vector-combining the currents of the respective frequency components flowing in the ungrounded circuit, and the zero-phase current sensor Ground-fault resistance detecting means for calculating a ground-fault resistance value based on two levels of the zero-phase current of the second frequency component detected by the detection means and the zero-phase current of the frequency component selected by the injection signal frequency selecting means. And a warning output means for outputting a warning output or a cutoff signal of the electric circuit when the calculated ground fault resistance value is equal to or less than a predetermined value. 4. The injection filter is a band elimination filter,
4. The ground fault detection circuit according to claim 1, wherein a signal of a power supply frequency component is removed from the injected frequency component signals. 5. A signal of a first frequency component serving as a reference and a signal of a second frequency component having a frequency ratio at least five times that of the first frequency component are injected between an ungrounded electric circuit and the ground. Then, the current of each frequency component flowing in the ungrounded system electric circuit is vector-synthesized to detect a zero-phase current, and then the zero-phase current of the first frequency component detected by the zero-phase current sensor, and After calculating the ground fault resistance value based on the two levels with the zero-phase current of the second frequency component,
If the calculated ground fault resistance value is equal to or less than a predetermined value, an alarm output or a signal for shutting off the electric circuit is output. 6. A signal of a first frequency component, a third frequency component lower than the first frequency component, and a signal of a second frequency component having a frequency ratio at least five times that of the first frequency are simultaneously injected into an ungrounded electric circuit. Then, among the zero-phase current components detected by the zero-phase current sensor, two levels are obtained: a zero-phase current of the second frequency component and a zero-phase current component of the first frequency component or the third frequency component. The ground fault detection method according to claim 5, wherein the ground fault resistance value is calculated based on the ground fault resistance value. 7. The second frequency component in a signal of a first frequency component, a third frequency component lower than the first frequency component, and a second frequency component having a frequency ratio at least five times that of the first frequency component. And one of the signals of the first or second frequency component is injected between the non-grounded circuit and the ground, and the current of each frequency component flowing in the non-grounded circuit is vector-combined to generate a zero-phase current. Detecting and subsequently detecting the zero-phase current of the second frequency component and the first or third
After calculating the ground fault resistance value based on the two levels of the zero-phase current of the frequency component and the calculated ground fault resistance value, if the calculated ground fault resistance value is equal to or less than a predetermined value, an alarm output or a cutoff signal of the electric circuit is output. The ground fault detection method according to claim 5, wherein: