JP3532182B2 - Ground fault detection device for ungrounded electric circuit, ground fault protection relay using the same, and ground fault detection method - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to, for example, 6.6 kV.
A ground fault detection device that detects a ground fault accident that occurs in a high-voltage ungrounded electric circuit and determines whether the location of the ground fault accident is on the premises or outside the premises, and a ground fault protective relay and a ground fault protection relay using the ground fault detection device. A method for detecting a fault.

[0002]

2. Description of the Related Art For example, when a ground fault, such as a resistance ground fault or an intermittent ground fault, occurs in an ungrounded electric circuit composed of a 6.6 kV high-voltage distribution line, the ground fault is detected and the ground fault is detected. It is necessary to protect the electrical equipment on the premises by providing a ground fault protection relay that determines whether the location of the accident is on the premises or outside the premises.

FIG. 9 shows an ungrounded electric circuit 1 made of, for example, a 6.6 kV high-voltage distribution line. In this non-grounded electric circuit 1, various loads 3 are connected to a high-voltage distribution line (system bus) via a switch 2, and the electric circuit on the load side from the switch 2 which is the power receiving point is called the premises. It is common to set the protection range, and the electric circuit on the system side is referred to as "outside the building" and is outside the protection range. In the ground of this non-grounded electric circuit 1, a ground fault detection device 5 that detects a ground fault and determines whether the location of the ground fault is on the premises or outside the ground, and from the ground fault detection device 5. A ground fault protection relay 10 for protecting the load equipment that receives power is installed, which is composed of a relay 4 that selectively opens and closes the switch 2 based on the output determination result.

An instrument transformer (ZPC) for detecting the zero-phase voltage Vo appearing in the ungrounded electric circuit 1 due to the occurrence of a ground fault accident.
6 and a zero-phase current transformer (ZCT) 7 that detects the zero-phase current Io flowing in the non-grounded electric circuit 1 due to the occurrence of the ground fault, are connected to the ground fault detection device 5. This ground fault detection device 5
Is a phase difference detection circuit 8 that monitors the magnitudes of the zero-phase voltage Vo and the zero-phase current Io and the phase difference of the zero-phase current Io with respect to the zero-phase voltage Vo, and the location of the ground fault accident based on the detection result. The main part is composed of a decision circuit 9 for deciding whether it is inside or outside the premises. In the phase difference detection circuit 8, the zero phase current I with respect to the zero phase voltage Vo is
It is customary to use a waveform shaping circuit for both the zero-phase voltage Vo and the zero-phase current Io in order to facilitate monitoring of the phase difference of o.

In this ground fault protection relay 10, when a ground fault occurs in the non-grounded electric circuit 1, the zero-phase voltage Vo appearing in the non-grounded electric circuit 1 is detected by the instrument transformer 6 and The zero-phase current Io flowing in the non-grounded electric circuit 1 due to the occurrence of the ground fault is detected by the zero-phase current transformer 7. In the phase difference detection circuit 8, the detected zero phase voltage V
o by a predetermined angle, and the zero-phase voltage Vo after the phase shift
And the zero-phase current Io are waveform-shaped, the zero-phase voltage Vo and the zero-phase current Io after the waveform shaping are input to the AND circuit, and the output of the AND circuit is converted into a phase angle. The phase difference of the zero-phase current Io with respect to Vo is monitored. In the determination circuit 9, in addition to the condition that both the zero-phase voltage Vo and the zero-phase current Io exceed a predetermined magnitude, the zero-phase current Io is delayed by 3 with respect to the zero-phase voltage Vo, for example.
If it goes from 0 degree and is within the range of 120 degrees, it is determined that the location of the ground fault accident is on the premises, and at other phase differences,
It is determined that the location of the ground fault is off-site.

Based on the judgment output from the judgment circuit 9, when the location of the ground fault accident is on the premises, the relay 4 is operated to open the switch 2 to disconnect the load side from the grid. Protect the load equipment on the premises and also perform ground fault recovery work on the premises. on the other hand,
When the location of the ground fault is outside the building, unlike the case of the ground fault inside the building, it is not necessary to operate the relay 4, so it is possible to disconnect from the system without opening the switch 2. Absent.

[0007]

By the way, in the ground fault detection device 5 described above, when a ground fault occurs, in addition to the magnitudes of the zero phase voltage Vo and the zero phase current Io, the zero phase current with respect to the zero phase voltage Vo. There is the following problem because it is determined whether the location of the ground fault accident is inside or outside the building by monitoring the phase difference of Io.

When the above-mentioned ground fault accident is a resistance ground fault, the zero-phase voltage Vo and the zero-phase current Io have sinusoidal waveforms. Therefore, it is not possible to monitor the phase difference of the zero-phase current Io with respect to the zero-phase voltage Vo. It is easy, but if the ground fault is an intermittent ground fault, the phenomenon in which the electric charge charged to the ground capacitance formed between the ungrounded electric circuit 1 and the ground is instantaneously discharged due to the intermittent ground fault is repeated. Therefore, the zero-phase voltage Vo and the zero-phase current Io do not have a sinusoidal waveform but a steep pulse waveform.

In particular, in the current situation, in the ungrounded electric circuit 1 composed of a 6.6 kV high-voltage distribution line, an intermittent ground fault often occurs. On the other hand, in the conventional ground fault detection device 5, the waveform shaping circuit of the phase difference detection circuit 8 outputs a waveform shaped corresponding to the fundamental frequency, and a waveform including an irregular and high frequency component. That is, with the zero-phase voltage Vo and the zero-phase current Io having a steep pulse-like waveform in the intermittent ground fault, the zero-phase current I with respect to the zero-phase voltage Vo is
By monitoring the phase difference of o, it is difficult to determine whether the location of the ground fault accident is on the premises or outside the premises.

The zero-phase current Io may flow intermittently in a short time not only in the case of the intermittent ground fault described above but also in the case of the resistance ground fault. Also in this case, the waveform including the irregular and high frequency components is also present. Since the zero-phase voltage Vo and the zero-phase current Io have the following, the phase difference of the zero-phase current Io with respect to the zero-phase voltage Vo is monitored to determine whether the location of the ground fault accident is on the premises or outside the premises. It was difficult to do.

There is also means for determining whether the location of the ground fault is on the premises or outside the premises based on the polarities of the high frequency components of the zero phase voltage Vo and the zero phase current Io. That is, if the rising or falling of the high-frequency components of the zero-phase voltage Vo and the zero-phase current Io is in the same direction, the location of the ground fault is on the premises, and if the rising or falling is in different directions, the ground It is decided that the location of the accident is off-site.

However, in the determination based on the polarities of the high frequency components of the zero phase voltage Vo and the zero phase current Io, the zero phase current Io is large in the high frequency components,
The zero-phase voltage Vo is often small. That is, in the zero-phase circuit formed in the high-voltage ungrounded electric circuit 1, the ground capacitance is formed by the high-voltage cable in addition to the ground fault resistance. Therefore, a high-frequency component of the zero-phase voltage Vo due to a ground fault occurs. Occurs, the zero-phase current Io flows to the ground capacitance, and the higher the frequency of the zero-phase current Io, the better the flow. Therefore, even if the zero-phase current Io is large, the zero-phase voltage Vo is large. Is small.

On the other hand, the ground fault protection relay 10 has a zero phase voltage V
Since the operable range of o and the zero-phase current Io is defined, when the zero-phase voltage Vo becomes small as described above, the range of the ground fault protection relay 10 is deviated, and a ground fault accident occurs. It becomes difficult to determine whether the occurrence location is inside or outside the premises. Especially in recent distribution systems, the scale tends to increase,
There is also a problem that the zero-phase voltage Vo is unlikely to be generated at the time of a ground fault, and there is also a problem that it is difficult to set the threshold value of the zero-phase voltage Vo for the accident determination.

Therefore, the present invention has been proposed in view of the above problems, and an object of the present invention is to determine whether or not the ground fault occurrence location is on the premises based on the sinusoidal zero-phase voltage and zero-phase current. It is not only possible to determine whether or not it is also possible to easily and reliably determine whether the ground fault occurrence location is on the premises based on the steep pulse or intermittent zero-phase voltage and zero-phase current,
In addition, even if the scale of the distribution system is large and it is difficult to generate zero-phase voltage, it is possible to reliably determine whether or not a ground fault has occurred on the premises and a ground fault detection device for an ungrounded electric circuit. An object of the present invention is to provide a ground fault protection relay and a ground fault detection method using the same.

[0015]

As a technical means for achieving the above object, the device of the present invention provides a zero-phase voltage developed in a non-grounded electric circuit due to a ground fault occurring in the non-grounded electric circuit. In the ground fault detecting device, the zero phase voltage detecting means for detecting and the zero phase current detecting means for detecting the zero phase current flowing in the non-grounded electric circuit at the time of occurrence of the ground fault are connected. The zero-phase voltage differentiating means for differentiating the instantaneous value of the zero-phase voltage obtained by the above, and the differential value calculated by the zero-phase voltage differentiating means are calculated with respect to the zero-phase current by a predetermined calculation formula. It is characterized by comprising a computing means and a determining means for deciding whether the location of the ground fault accident is on-premises or off-site based on the computation result.

A ground fault protection relay can be constructed by adding a relay for operating the switch provided in the non-grounded electric circuit to the ground fault detection device by the output of the ground fault detection device. It is possible.

Further, the method of the present invention detects the zero-phase voltage and the zero-phase current appearing in the non-grounded electric circuit due to a ground fault occurring in the non-grounded electric circuit, and detects the detected zero-phase voltage instantaneously. A differential value obtained by differentiating the value with respect to time is calculated by a predetermined calculation formula with respect to the zero-phase current, and it is determined whether the location of the ground fault accident is on-premises or off-site based on the calculation result. It is characterized by

It is desirable that the calculation in the apparatus and method of the present invention is performed based on an arithmetic expression for dividing the zero-phase current by a differential value obtained by differentiating the instantaneous value of the zero-phase voltage with time. It is also possible to perform processing based on an arithmetic expression that multiplies the zero-phase current and the differential value obtained by differentiating the instantaneous value of the zero-phase voltage with time.

In the present invention, the differential value obtained by differentiating the instantaneous value of the zero-phase voltage with respect to time is subjected to a predetermined arithmetic expression with respect to the zero-phase current, that is, the zero-phase current is differentiated with respect to the instantaneous value of the zero-phase voltage with respect to time. The operation result is divided by the calculated differential value, or the calculation result is calculated by multiplying the zero-phase current and the differential value obtained by differentiating the instantaneous value of the zero-phase voltage with time. If the location of the accident is on the premises, it will always be a positive value, and if the location of the ground fault is off-site, it will always be a negative value. This is because the zero-phase voltage and zero-phase current are satisfied not only at the commercial frequency but also at any frequency, so even if a zero-phase voltage and zero-phase current with steep pulse or intermittent waveforms appear, the ground fault occurs. It is possible to easily and reliably determine whether the location of the accident is inside or outside the premises.

Further, in this non-grounded circuit, there may be a residual zero-phase current even when the ground fault current is zero and there is no zero-phase voltage. This is caused by the imbalance of the ground capacitance (ground admittance) in the premises of the ungrounded electric circuit. This unbalance is caused by, for example, electrical equipment connected to the ungrounded electric circuit, and by this connection or disconnection. Zero-phase current fluctuates. Therefore, even if the zero-phase current is detected, the ground-fault current itself is not detected, and an error occurs by the magnitude of the residual zero-phase current generated in the state where there is no ground fault. Therefore, in the present invention, an unbalanced element that is connected to the zero-phase current detection means and the zero-phase voltage detection means and detects the unbalanced component of the zero-phase current that flows due to the unbalanced capacitance to ground in the ground of the ungrounded electric circuit. It is preferable to include a component detecting means and a subtracting means for calculating a value obtained by subtracting the unbalanced component detected by the unbalanced component detecting means from the zero-phase current.

As described above, the unbalanced component of the zero-phase current flowing due to the unbalanced capacitance to ground in the ground of the ungrounded electric circuit is detected, and the value obtained by subtracting the unbalanced component from the zero-phase current is zero. By calculating the differential value of the phase voltage with a predetermined calculation formula, it is possible to exclude the unbalanced component of the zero-phase current due to the unbalanced capacitance to ground. It is possible to detect an accident.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the present invention. For example, a ground fault protection relay 21 having a ground fault detection device 20 provided in an ungrounded electric circuit 1 made of a 6.6 kV high voltage distribution line.
Indicates. In the non-grounded electric circuit 1, various loads 3 are connected to a high-voltage distribution line (system busbar) via a switch 2, and the electric circuit on the load side from the switch 2 which is the power receiving point is called a premises. On the other hand, the electric circuit on the system side is called off-site and out of the protection range. The ground fault detection device 20 installed on the premises of the non-grounded electric circuit 1 detects a ground fault and determines whether the location of the ground fault is on the premises or outside the premises. The ground fault protection relay 21 installed in the non-grounded electric circuit 1 in order to protect the load facility that receives the power is a switch based on the ground fault detection device 20 and a determination result output from the ground fault detection device 20. And a relay 4 for selectively opening and closing 2. The ground fault detection device 20 is
It can also be applied to other non-grounded electric circuits that include special high-voltage distribution lines and low-voltage distribution lines other than the above-mentioned high-voltage distribution lines.

As shown in the hardware configuration of FIG. 1, the zero-phase voltage V appearing in the ungrounded electric circuit 1 due to the occurrence of a ground fault.
A transformer for an instrument (Z
PC) 6 and zero-phase current Io flowing due to occurrence of ground fault
Zero phase current transformer (ZC
T) 7 is connected to the ground fault detection device 20.

This ground fault detection device 20 includes a transformer 6 for instruments.
And a zero-phase current transformer 7, which is a zero-phase voltage differentiating means for differentiating the instantaneous value of the zero-phase voltage Vo output from
The zero-phase current Io output from the division circuit 12 that is a calculation unit that divides the zero-phase current Io by the differential value calculated by the differentiation circuit 11.
And a determination circuit 14 that is a determination means for determining whether the location of the ground fault accident is on the premises or on the outside based on the division value. In the ground fault detection device 20 of this embodiment, an integration circuit 13 that integrates the division value output from the division circuit 12 within a predetermined time is inserted between the division circuit 12 and the determination circuit 14. .

FIG. 2 shows a control algorithm when the ground fault detection device 20 of this embodiment is realized by digital processing. In the ground fault detection device 20, when a ground fault occurs in the non-grounded electric line 1, the zero-phase voltage Vo appearing in the non-grounded electric line 1 is detected by the instrument transformer 6, and the zero phase is detected. The zero-phase current Io flowing in the non-grounded electric circuit 1 due to the generation of the voltage Vo is detected by the zero-phase current transformer 7 (ST
EP1). The detected zero-phase voltage Vo and zero-phase current I
A is A / D converted (STEP2) and then stored in the memory (STEP3).

As in the conventional case, when determining whether the location of the ground fault accident is on the premises or outside the premises, these zero-phase voltage Vo and zero are applied prior to proceeding to a predetermined calculation process. It is also possible to take into consideration the condition that both of the phase currents Io exceed a predetermined magnitude.

Next, the instantaneous value of the zero-phase voltage Vo is differentiated by the differentiating circuit 1.
Differentiate time by 1. The differentiating circuit 11 calculates the difference between the instantaneous value Vo (t) of the zero-phase voltage Vo at a certain time t and the instantaneous value Vo (t ') of the zero-phase voltage Vo at t ′ after the elapse of a predetermined number of sampling times. By doing so, the differential value dVo / dt of the zero-phase voltage Vo is obtained (STEP 4). Note that the zero-phase voltage Vo can be differentiated with time by performing a Freeer conversion of the zero-phase voltage Vo, then performing an inverse Freeer conversion, and differentiating the function.

Then, in the division circuit 12, the zero-phase current Io
Is divided by the differential value dVo / dt of the zero-phase voltage Vo (STEP
5). Here, when the differential value dVo / dt of the zero-phase voltage Vo, which is the denominator of the division value Io / (dVo / dt), becomes zero, the division process becomes impossible. In that case, exceptional processing is required so that the division value Io / (dVo / dt), which is the result of the division processing, becomes zero.

Based on this division value Io / (dVo / dt), it is determined whether the location of the ground fault accident is on-premises or off-premises. That is, when the location of the ground fault accident is on the premises, the zero-phase current Io is 90 with respect to the zero-phase voltage Vo.
° Leading phase. Therefore, assuming that the zero-phase voltage Vo detected by the instrument transformer 6 is Vsinωt, the zero-phase current Io detected by the zero-phase current transformer 7 is Isin.
(Ωt + 90 °) = Icosωt.

On the other hand, as described above, the differential value dVo / dt obtained by time-differentiating the instantaneous value of the zero-phase voltage Vo detected by the instrument transformer 6 by the differentiating circuit 11 is d (Vsinω
t) / dt = ωVcosωt and Do Ri, the above-described zero-phase current I
It becomes the same function (cosωt) as o and the difference between the two is the coefficient
Ru ω Dakedea. Therefore, when the above-mentioned zero-phase current Io is divided by the differential value dVo / dt by the division circuit 12, the divided value Io / (dVo / dt) becomes I / ωV, which is always a positive value.

In this way, the division value Io / (dVo / d
If t) is a positive value, the determination circuit 14 determines that the location of the ground fault accident is on the premises, and operates the relay 4 based on the determination output to open the switch 2 and load. The side will be disconnected from the grid to protect the load equipment on the premises and to perform the ground fault accident recovery work on the premises.

FIG. 3 exemplifies a case where the ground fault occurs in the high voltage cable in the premises, and the upper stage shows the zero phase current Io.
The middle stage is the zero-phase voltage Vo, and the lower stage is the measured waveform and the determination output indicating the determination output, respectively. As shown in the figure, the zero-phase current Io and the zero-phase voltage Vo having a steep pulse-like waveform are shown.
Even when the current appears, as described above, the zero-phase current I
Since the result of dividing o by the differential value dVo / dt of the zero-phase voltage Vo is a positive value, it can be easily and reliably determined that the location of the ground fault accident is on the premises.

FIG. 4 exemplifies the measured waveforms of the zero-phase current Io, the zero-phase voltage Vo, and the judgment output and the judgment output when the ground fault due to the contact with a small animal (rat) is on the premises. As shown in the figure, even when the zero-phase current Io and the zero-phase voltage Vo having a sinusoidal waveform appear, as in the case of the steep pulse-shaped waveform,
Since the result of dividing the zero-phase current Io by the differential value dVo / dt of the zero-phase voltage Vo is a positive value, it is determined that the location of the ground fault accident is on the premises even in the case of a sinusoidal waveform. Easy and certain to be.

Further, when the location of the ground fault accident is outside the building, the zero-phase current Io is delayed by 90 ° with respect to the zero-phase voltage Vo. Therefore, assuming that the zero-phase voltage Vo detected by the instrument transformer 6 is Vsinωt, the zero-phase current Io detected by the zero-phase current transformer 7 is Isin (ωt-
90 °) = − Icosωt.

On the other hand, the zero detected by the instrument transformer 6
The instantaneous value of the phase voltage Vo is time differentiated by the differentiating circuit 11.
The differential value dVo / dt is d (Vsinωt) / dt = ω
VcosωtThe same function as the zero-phase current Io described above.
(Cosωt), and the only difference between the two is the coefficient ω.
It Therefore, the zero-phase current Io described above is divided by the dividing circuit 12.
When divided by the differential value dVo / dt, the divided value Io /
(DVo / dt) becomes -I / ωV, which is always a negative value.
Become.

In this way, the divided value Io / (dVo / d
If t) is a negative value, the determination circuit 13 determines that the location of the ground fault accident is outside the building, and based on the determination output, unlike the case where the ground fault accident occurs on the premises, the relay 4 is turned on. Since it is not necessary to operate it, there is no disconnection from the system without opening the switch 2.

FIG. 5 exemplifies a case where the ground fault occurs in the high voltage cable outside the building, and the upper part shows the zero-phase current Io.
The middle stage is the zero-phase voltage Vo, and the lower stage is the measured waveform and the determination output indicating the determination output, respectively. As shown in the figure, the zero-phase current Io and the zero-phase voltage Vo having a steep pulse-like waveform are shown.
Even when the current appears, as described above, the zero-phase current I
Since the result of dividing o by the differential value dVo / dt of the zero-phase voltage Vo has a negative value, it can be easily and reliably determined that the location of the ground fault accident is outside the building.

FIG. 6 exemplifies the measured waveforms of the zero-phase current Io, the zero-phase voltage Vo, and the judgment output and the judgment output when the ground fault accident due to the air discharge is outside the building. As shown in the figure, even when the zero-phase current Io and the zero-phase voltage Vo having a sinusoidal waveform appear, as in the case of the steep pulse-shaped waveform, the zero-phase current Io.
Since the result of dividing o by the differential value dVo / dt of the zero-phase voltage Vo is a negative value, it is easy to determine that the location of the ground fault accident is outside the building even in the case of a sinusoidal waveform. And certain.

Regardless of whether the ground fault occurs on the premises or outside the premises, a subharmonic having a lower amplitude than the fundamental frequency and a large amplitude appears immediately after the occurrence of the ground fault. This subharmonic is difficult to appear in the zero-phase current Io, and easily appears in the zero-phase voltage Vo (see, for example, FIG. 6). In the conventional case, since the ground fault was detected based on the phase difference of the zero-phase current with respect to the zero-phase voltage, the ground fault detection device was in the locked state while the subharmonic was appearing, Although there was a delay in the detection of the ground fault, in the case of the ground fault detection device according to the present invention, since the ground fault is detected based on the above-described arithmetic expression, the occurrence of the subharmonic causes the occurrence of the ground fault. Without delay in detection,
The ground fault can be detected quickly.

As described above, the differential value dVo / dt obtained by time-differentiating the instantaneous value of the zero-phase voltage Vo is a value with ω as a coefficient as represented by ωVcosωt. Since the coefficient ω is related to the fundamental frequency, the value obtained by dividing the differential value dVo / dt of the zero-phase voltage Vo by ω is replaced with the differential value dVo / dt in the subsequent arithmetic processing, that is, the processing in the division circuit 12. May be used for. By doing so, even if the fundamental frequency is different, it is not affected by the difference, and the ground fault detection device 20 is provided in the area where the fundamental frequency is different.
Is easy to use. In addition to the above-mentioned ω related to the fundamental frequency, even if there is ω related to the harmonic component, by removing this, high-precision arithmetic processing becomes possible, and more accurate determination can be realized easily. Becomes

The determination circuit 14 is based on the division value Io / (dVo / dt) calculated by the division circuit 12 as described above.
Then, it is determined whether the location of the ground fault accident is on the premises or outside the premises. In this embodiment, as shown in FIG. 1, the integration circuit 13 is provided between the division circuit 12 and the determination circuit 14.
Is inserted.

In the integrating circuit 13, as shown in FIG. 2, the divided value Io / (dVo / dt) within a predetermined time is integrated (STEP 6), and the integrated value Σ [Io / (dVo / dt)].
It is determined whether or not the absolute value of is larger than a predetermined set value (STEP 7). If the absolute value of the integrated value Σ [Io / (dVo / dt)] is smaller than the set value, it is considered that the judgment error is within the allowable range, and there is no ground fault, and the integrated value Σ [Io / (d
If the absolute value of Vo / dt)] is larger than the set value, it is determined that there is a ground fault.

Then, the above-mentioned division value Io / (dVo)
/ Dt) integrated value Σ [Io / (dVo / dt)]
Is a positive value (STEP8), if it is a positive value, the judgment that the location of the ground fault accident is on the premises is output, and if it is a negative value, the location of the ground fault accident is on the premises. Is output (STEP 9). The integrating circuit 13 is not always necessary, and the integrating circuit 13 can be omitted if it is not necessary to consider the determination error. Therefore, the determination output of the determination circuit 14 is basically the zero-phase current Io.
Is divided by a differential value dVo / dt of the zero-phase voltage Vo, based on a division value Io / (dVo / dt). As described above, after the determination output, the data of the zero-phase voltage Vo and the zero-phase current Io is stored in the abnormal waveform storage memory (STEP
10).

In the above embodiment, the ground fault detection device 20 is incorporated in the ground fault protection relay 21, but the ground fault detection device 20 can be used in the embodiment shown in FIG. In other words, if the ground fault detection device 20 is installed on site and the output of the ground fault detection device 20 can be taken out,
The worker can take the output of the ground fault detection device 20 obtained at the site as the determination data from the site, or transmit it through a communication line and input it to an analysis device installed at another place to make the determination at the site. Judgment processing based on data can be performed by an analysis device provided in another place.

FIG. 8 shows a ground fault protection relay 21 'having a ground fault detection device 20' according to another embodiment. Ground fault detection device 2 incorporated in this ground fault protection relay 21 '
At 0 ', in order to remove the unbalanced component of the zero-phase current Io caused by the unbalance of the electrostatic capacitance (ground admittance) to the ground in the ground of the ungrounded electric circuit 1, the instrument transformer 6 and the zero-phase current transformer 7 are removed. In the subsequent stage, a detection circuit 1 which is an unbalanced component detection means for detecting an unbalanced component of the zero-phase current Io flowing due to an unbalanced capacitance to ground in the ground of the ungrounded electric circuit 1.
5 and a subtraction circuit 16 which is a subtraction means for calculating a value obtained by subtracting the unbalanced component from the zero-phase current Io. The detection circuit for detecting the unbalanced component of the zero-phase current Io is a known technique as disclosed in Japanese Patent Application Laid-Open No. 11-271384, and a detailed description thereof will be omitted.

According to the ground fault detection device 20 'of this embodiment, the unbalanced component of the zero-phase current Io flowing due to the unbalanced capacitance to ground in the ground of the ungrounded electric circuit 1 is detected.
5, the value obtained by subtracting the unbalanced component from the zero-phase current Io is calculated by the subtraction circuit 16 to generate an unbalanced component of the zero-phase current Io, that is, a state in which there is no ground fault. The error of the magnitude of the residual zero-phase current can be excluded, and the actual ground fault current itself can be obtained. By using the zero-phase current Io from which the unbalanced component is subtracted, the accuracy of the calculation is increased in the process of dividing the zero-phase current Io by the differential value dVo / dt of the zero-phase voltage Vo, and the determination circuit based on the divided value. The determination result in 14 becomes more accurate.

By the way, in the above-described embodiment, the zero-phase current Io is differentiated by the differential value dV of the zero-phase voltage Vo as a predetermined arithmetic expression of the differential value dVo / dt of the zero-phase voltage Vo and the zero-phase current Io.
The case of dividing by o / dt has been described, but the present invention is not limited to this, and the zero-phase current Io and the zero-phase voltage Vo.
The determination may be made based on an arithmetic expression that is multiplied by the differential value dVo / dt of o.

Similar to the above-described embodiment, when the ground fault accident is on the premises, and the zero-phase voltage Vo is Vsinωt, the zero-phase current Io is Isin (ωt + 90 °) = I
Since cosωt, the differential value dV of the zero-phase voltage Vo
o / dt is d (Vsinωt) / dt = ωVcosω
t and Do Ri, the same function as the zero-phase current Io of the above-mentioned (cosω
The difference between the two becomes t) is Ru coefficient ω Dakedea. Therefore,
Differential value dVo / d of the zero-phase current Io and the zero-phase voltage Vo described above.
When t is multiplied by a multiplication circuit (not shown), the multiplication value becomes ωVI (cosωt) ² , which is always a positive value. If this multiplication value is a positive value, the determination circuit 14 determines that the location of the ground fault accident is on the premises, and operates the relay 4 based on the determination output, as in the case of the division processing described above. Thus, the switch 2 is opened to disconnect the load side from the system to protect the load equipment on the premises and to perform the ground fault recovery work on the premises.

When the location of the ground fault accident is outside the building and the zero-phase voltage Vo is Vsinωt, the zero-phase current I
Since o becomes Isin (ωt−90 °) = − Icosωt, the differential value dVo / dt of the zero-phase voltage Vo is d
(Vsinωt) / dt = ωVcosωt and Do Ri, above
The same function (cosωt) as the zero-phase current Io of
Difference is Ru coefficient ω Dakedea. Therefore, the above-mentioned zero-phase current I
When o and the differential value dVo / dt of the zero-phase voltage Vo are multiplied by a multiplication circuit (not shown), the multiplication value is −ωV.
It becomes I (cosωt) ² , which is always a negative value. If this multiplication value is a negative value, as in the case of the division processing described above,
The judgment circuit 14 judges that the location of the ground fault accident is outside the building, and there is no need to operate the relay 4 based on the judgment output, so there is no disconnection from the system without opening the switch 2. .

In the above-described division processing or multiplication processing, a negative value may appear in part due to some cause at the time of sampling when a positive value should be output.
On the contrary, a positive value may partially appear due to some cause at the time of sampling when a negative value should be output, which may cause a malfunction of the ground fault detection device. Since the number of occurrences of such a phenomenon is extremely small with respect to the total number of samplings, in order to prevent a malfunction of the ground fault detection device in advance, by calculating an average value after division processing or multiplication processing, It is possible to prevent the calculation result from being inverted between positive and negative. If the average value is calculated at short time intervals, the determination accuracy can be improved, but if high determination accuracy is not required, the time interval for calculating the average value can be lengthened.

Differential value dVo / d of the zero-phase voltage Vo described above.
For the predetermined calculation of t and the zero-phase current Io, the division process is more effective than the multiplication process. In other words, when determining whether the location of the ground fault accident is on the premises or outside the premises, it is determined whether the operation result of the multiplication process or the division process is a positive value or a negative value. In this case, it is further possible to determine whether the location of the ground fault is on the premises or on the premises, depending on the magnitude of the absolute value of the division result.

In the zero-phase circuit formed in the non-grounded electric circuit 1, the ground capacitance is formed by the ground resistance and the high voltage cable. Generally, the ground capacitance outside the building is the ground capacitance inside the building. It is more than tens of times the capacity. Therefore, the ground admittance (zero-phase current Io to zero-phase voltage V
(divided by o) is proportional to the electrostatic capacitance to the ground, so it is possible to determine whether the location of the ground fault accident is on-premises or off-site from the magnitude of the ground admittance.

On the other hand, in the division processing in the ground fault detection device 20 described above, the zero-phase current Io is differentiated by the differential value dV of the zero-phase voltage Vo.
Dividing by o / dt, the numerator is the zero-phase current Io,
The denominator is the differential value dVo / dt of the zero-phase voltage Vo. Here, the differential value dVo / dt of the zero-phase voltage Vo is the zero-phase voltage Vo.
Therefore, instead of the ground admittance, the calculation result by the division process in the ground fault detection device 20, that is, the zero-phase current Io, is a differential value dVo of the zero-phase voltage Vo.
Based on the magnitude of the division value Io / (dVo / dt) divided by / dt, it is possible to determine whether the place where the ground fault accident occurs is on the premises or on the premises. In this way, by making a determination based on both the positive / negative of the division value Io / (dVo / dt) and the magnitude of its absolute value, a double check function can be exerted and the reliability is greatly improved. .

As described above, the differential value dV of the zero-phase voltage Vo
Since o / dt is proportional to the zero-phase voltage Vo, if the zero-phase voltage Vo becomes large, for example, the differential value dV of the zero-phase voltage Vo.
o / dt also becomes large. When the location of the ground fault accident is on the premises, the zero phase current Io detected by the zero phase current transformer 7 is detected even if the zero phase voltage Vo detected by the instrument transformer 6 of the ground fault detection device 20 is small. Therefore, the zero-phase current Io is equal to the zero-phase voltage Vo.
Divided value Io / (dVo
/ Dt) has a large value. From this, the divided value Io
If / (dVo / dt) becomes a value larger than a predetermined reference value, it can be determined that the location of the ground fault accident is on the premises.

If the location of the ground fault accident is outside the building,
Since the zero-phase current Io detected by the zero-phase current transformer 7 becomes smaller, the zero-phase current Io is differentiated from the zero-phase voltage Vo by the differential value dVo / dt.
The divided value Io / (dVo / dt) divided by is a small value. From this, if the divided value Io / (dVo / dt) becomes a value smaller than the predetermined reference value, it can be determined that the location of the ground fault accident is outside the building.

As described above, the differential value dV of the zero-phase voltage Vo
By using o / dt, the zero-phase voltage Vo and the zero-phase current Io have the same phase, and an accurate calculation result is obtained by dividing the instantaneous values of the zero-phase voltage Vo and the zero-phase current Io to improve the determination accuracy. Can be achieved. Here, the predetermined reference value for judging whether it is on-premises or off-premises based on the magnitude of the above-mentioned calculation result is defined by the ratio of the off-premises electrical path length to the on-premises electrical path length in the non-grounded electrical path 1. The ground fault detection device 20 is appropriately set according to the non-grounded electric circuit 1.

In the above-described embodiment, the differential value dVo / dt obtained by differentiating the zero-phase voltage Vo with time is used, but conversely, the differential value dIo / dt obtained by differentiating the zero-phase current Io with time is used.
The calculation process is possible in the case of a sinusoidal zero-phase current Io, but is not suitable in the case of a steep pulse-shaped zero-phase current Io. That is, when a ground fault occurs, the waveform disturbance in the zero-phase voltage Vo is relatively small, but since the zero-phase current Io contains many high-frequency components, the waveform disturbance is too large. Differential value dI of Io
This is because using o / dt for the arithmetic processing makes it difficult to make an accurate determination.

[0058]

According to the present invention, the differential value obtained by differentiating the instantaneous value of the zero-phase voltage with respect to time is used as a predetermined arithmetic expression for the zero-phase current,
That is, the zero-phase current is divided by the differential value obtained by differentiating the instantaneous value of the zero-phase voltage with time, or the zero-phase current and the differential value obtained by differentiating the instantaneous value of the zero-phase voltage with time are calculated. By calculating with the multiplication formula, if the location of the ground fault accident is on the premises, the calculation result will always be a positive value, and if the location of the ground fault accident is off-site, it will always be a negative value. Become. This is because the equations for calculating the zero-phase voltage and the zero-phase current according to the present invention are satisfied not only at the commercial frequency but also at any frequency, and therefore based on the zero-phase voltage and the zero-phase current having a steep pulse-like or intermittent waveform. As a result, it is possible to easily and surely determine whether the location of the ground fault accident is on the premises or outside the premises, and the reliability is greatly improved. Further, when a ground fault accident occurs, a large number of subharmonics are often involved. Even in such a case, it is possible to quickly determine whether the place where the ground fault accident occurs is on the premises or outside the premises.

[Brief description of drawings]

FIG. 1 is a schematic configuration block diagram showing a ground fault protection relay having a ground fault detection device installed in an ungrounded electric circuit according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a control algorithm when the ground fault detection device is realized by digital processing in the embodiment of the present invention.

FIG. 3 is a waveform diagram showing a steep pulse-shaped zero-phase current and zero-phase voltage and a calculation result in the case where the place where the ground fault occurs is the premises in the embodiment of the present invention.

FIG. 4 is a waveform diagram showing a sinusoidal zero-phase current and zero-phase voltage and a calculation result in the case where the place where the ground fault occurs is the premises in the embodiment of the present invention.

FIG. 5 is a waveform diagram showing a steep pulse-shaped zero-phase current and zero-phase voltage and a calculation result in the case where the location of the ground fault is off-site in the embodiment of the present invention.

FIG. 6 is a waveform diagram showing a sinusoidal zero-phase current and zero-phase voltage and a calculation result in the case where the location of the ground fault is off-site in the embodiment of the present invention.

FIG. 7 is a schematic block diagram showing a ground fault detection device installed in a non-grounded electric line according to another embodiment of the present invention.

FIG. 8 is a schematic block diagram showing a ground fault relay having a ground fault detection device installed in a non-grounded electric circuit according to another embodiment of the present invention.

FIG. 9 is a schematic configuration block diagram showing a conventional example of a ground fault relay having a ground fault detection device installed in an ungrounded electric circuit.

[Explanation of symbols]

4 relays 6 Zero-phase voltage detection means (instrument transformer) 7 Zero-phase current detection means (zero-phase current transformer) 11 Zero-phase voltage differentiating means (differential circuit) 12 Operation means (division circuit) 14 Judgment means (judgment circuit) 15 Unbalanced component detection means (detection circuit) 16 Subtraction means (subtraction circuit) 20 Ground fault detector 21 Ground fault protection relay

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-262023 (JP, A) JP-A-5-76132 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H02H 3 / 38,3 / 44 H02H 7/26 G01R 31/08

Claims (9)

(57) [Claims] 1. A zero-phase voltage detecting means for detecting a zero-phase voltage appearing in a non-grounded electric circuit due to a ground fault occurring in the non-grounded electric circuit, and a non-grounded circuit in the non-grounded electric circuit when the ground fault occurs. In a ground fault detecting device connected to a zero-phase current detecting means for detecting a flowing zero-phase current, a zero-phase voltage differentiating means for differentiating an instantaneous value of the zero-phase voltage obtained by the zero-phase voltage detecting means with respect to time. Calculating means for calculating the differential value calculated by the zero-phase voltage differentiating means with a predetermined arithmetic expression with respect to the zero-phase current, and the place where the ground fault accident occurs on the premises or outside the premises based on the calculation result. A ground fault detection device for a non-grounded electric circuit, comprising: a determination unit that determines which of the two. 2. The calculation means processes the zero-phase current based on an arithmetic expression that divides the instantaneous value of the zero-phase voltage by a differential value obtained by differentiating with time. Ground fault detection device for non-grounded electric circuits. 3. The arithmetic unit according to claim 1, wherein the arithmetic unit performs processing based on an arithmetic expression that multiplies a zero-phase current and a differential value obtained by differentiating an instantaneous value of the zero-phase voltage with time. Ground fault detection device for non-grounded electric circuits. 4. An unbalanced component connected to the zero-phase current detecting means and the zero-phase voltage detecting means and detecting an unbalanced component of a zero-phase current flowing due to an unbalanced capacitance to ground in the ground of an ungrounded electric circuit. 4. The detecting means and the subtracting means for calculating a value obtained by subtracting the unbalanced component detected by the unbalanced component detecting means from the zero-phase current. Ground fault detection device for non-grounded electric circuits. 5. The ground fault detection device according to claim 1, and a relay for operating a switch provided in an ungrounded electric circuit by the output of the ground fault detection device. A ground fault protection relay that is characterized. 6. A zero-phase voltage and a zero-phase current appearing in the non-grounded electric circuit due to a ground fault occurring in the non-grounded electric circuit are detected, and the instantaneous value of the detected zero-phase voltage is differentiated with respect to time. It is characterized in that the differentiated value is calculated with respect to the zero-phase current by a predetermined calculation formula, and whether the location of the ground fault accident is on-premises or off-site is determined based on the operation result. Ground fault detection method for non-grounded circuits. 7. The non-operation according to claim 6, wherein the operation is performed based on an operation expression that divides the zero-phase current by a differential value obtained by differentiating the instantaneous value of the zero-phase voltage with time. Ground fault detection method for earthed circuits. 8. The calculation according to claim 6, wherein the calculation is performed based on a calculation formula for multiplying a zero-phase current by a differential value obtained by differentiating an instantaneous value of the zero-phase voltage with time. Ground fault detection method for non-grounded circuits. 9. An unbalanced component of a zero-phase current flowing due to an unbalanced capacitance to ground of the ungrounded electric circuit is detected, and a zero-phase voltage is calculated with respect to a value obtained by subtracting the unbalanced component from the zero-phase current. 9. The method for detecting a ground fault in an ungrounded electric circuit according to claim 6, wherein the differential value of is calculated by a predetermined arithmetic expression.