JP2011217588A - Ground fault detection apparatus for electric circuit of non-grounded system and ground fault protective relay using the apparatus, and method of detecting ground fault - Google Patents

Abstract

PROBLEM TO BE SOLVED: To calculate a ground fault current caused to flow in an electric circuit of a non-grounded system electric path by a ground fault accident in premises of the electric circuit of the non-grounded system by simple arithmetic processing.SOLUTION: A ground fault detection apparatus 2 is connected to a potential transformer 7 which detects a zero-phase voltage Vo caused to appear in the electric circuit 1 of the non-grounded system by a ground fault accident in premises of the electric circuit 1 of the non-grounded system, and a zero-phase current transformer 8 which detects a zero-phase current Io caused to flow in the electric circuit 1 of the non-grounded system on the occurrence of the ground fault accident in the premises are connected. The apparatus includes a differential circuit 9 which differentiates the zero-phase voltage Vo obtained by the potential transformer 7 with respect to time, an arithmetic circuit 10 which sets ground static capacitance C of the premises of the electric circuit 1 of the non-grounded system, a multiplication circuit 11 which multiplies a differentiated value dVo/dt calculated by the differential circuit 9 by the ground static capacitance C calculated by the arithmetic circuit 10, and a subtraction circuit 12 which obtains a ground fault current Ig by subtracting a multiplication value C×(dVo/dt) calculated by multiplying the ground static capacitance C by the differentiated value dVo/dt from the zero-phase current Io.

Description

  The present invention monitors, for example, a ground fault accident occurring in a 6.6 kV high-voltage ungrounded electric circuit premises, and detects a ground fault current at the time of the premises ground fault, and a ground fault protection using the same. The present invention relates to a relay and a ground fault detection method.

  For example, in a non-grounded electric circuit consisting of a 6.6 kV high-voltage power receiving facility, various loads are connected to the high-voltage power receiving facility (system bus) via a switch. Is generally referred to as a premise and is defined as a protection range, and an electric circuit on the system side is generally referred to as a premise and is outside the protection range. Conventionally, various types of ground fault detection devices have been proposed for monitoring a ground fault occurring on the premises of this non-grounded electric circuit and detecting a zero phase current flowing at the time of the ground fault with a zero phase current transformer. (For example, refer to Patent Document 1).

  This Patent Document 1 is based on a line constant measuring device that measures the line constant of an ungrounded electric circuit in a live line state and accurately grasps the insulation state of the electric circuit from the line constant, and the line constant measured thereby. This discloses a ground fault monitoring device for a non-grounded electric circuit capable of obtaining a ground fault current with high accuracy from the zero-phase current calculated as described above.

  That is, the line constant measuring device disclosed in Patent Document 1 includes a zero-phase current detection unit that detects a zero-phase current flowing in a non-grounded circuit, and a zero-phase voltage detection unit that detects a zero-phase voltage of the non-grounded circuit. And a reference voltage generating means for detecting a partial voltage of the electric circuit and generating a reference voltage excluding the zero phase, and storing and detecting the zero phase current and the zero phase voltage at the start of the line constant measurement. When the zero-phase voltage fluctuates by more than a predetermined value from this stored value, the electric line change detecting means for storing the detected zero-phase current and zero-phase voltage, and the vector sum of the ground admittance of each phase as the first line constant When the ground admittance in the equation representing the zero phase current flowing due to the unbalanced portion of the ground admittance of each phase as a reference voltage is the second line constant, the zero phase voltage and the zero phase current stored by the circuit change detecting means are Based on binary By solving the vector equation, in which a line constant computing means for calculating a first line constant and a second line constants.

  Moreover, the ground fault monitoring apparatus disclosed in Patent Document 1 has the above-described line constant measurement device, and uses the first line constant and the second line constant calculated by this device, and the zero-phase current, zero-phase A ground fault current calculating means for inputting a voltage and a reference voltage as a vector quantity and performing a vector calculation based on a predetermined calculation formula to calculate a ground fault current is provided.

Japanese Patent No. 2999615

  By the way, in the line constant measuring device and the ground fault monitoring device disclosed in Patent Document 1, the line constant of the non-grounded electric circuit is measured in a live line state, and the insulation state of the electric circuit is accurately grasped from the line constant, Thus, the ground fault current can be obtained with high accuracy from the zero-phase current calculated based on the measured line constant.

  However, since the line constant measuring device and the ground fault monitoring device disclosed in Patent Document 1 detect the ground fault current with high accuracy, the calculation processing for calculating the ground fault current becomes complicated. . In order to realize this device, high-precision analog parts and complicated digital processing are required, which makes the device expensive.

  Therefore, the present invention has been proposed in view of the above-mentioned improvements, and the object of the present invention is to simplify the ground fault current flowing in the non-grounded circuit due to the ground fault in the premises of the non-grounded circuit. An object of the present invention is to provide a ground fault detection device for a non-grounded circuit that can be calculated by arithmetic processing, a ground fault protection relay using the ground fault detection device, and a ground fault detection method.

  As a technical means for achieving the above-mentioned object, the device of the present invention is a zero-phase voltage detection for detecting a zero-phase voltage Vo that appears in an ungrounded circuit due to a ground fault in the premises of the ungrounded circuit. And a zero-phase current detecting means for detecting a zero-phase current Io that detects a zero-phase current Io flowing in an ungrounded circuit when a ground fault occurs on the premises, and obtained by the zero-phase voltage detecting means. Zero-phase voltage differentiating means for differentiating the obtained zero-phase voltage Vo with respect to time, capacitance setting means for setting the ground capacitance in the premises of the ungrounded circuit, and the differential value calculated by the zero-phase voltage differentiating means Multiplying means for multiplying dVo / dt by the ground capacitance C calculated by the capacitance setting means, and multiplying value C × (dVo / dt) by multiplying the differential value dVo / dt by the ground capacitance C is zero. Subtracting means for subtracting from the phase current Io to obtain the ground fault current Ig Characterized by comprising a. Each arithmetic processing described above is based on vector calculation. Here, “setting the ground capacitance C” means that the ground capacitance C is calculated by arithmetic processing, or the value is obtained by measuring the ground capacitance C with a measuring instrument. To do.

  In the present invention, a dividing unit that divides the zero-phase voltage Vo obtained by the zero-phase voltage detecting unit by the ground fault current Ig obtained by the subtracting unit may be added after the subtracting unit. In this way, it is possible to obtain the division value Vo / Ig calculated by the dividing means as the ground fault resistance Rg. The arithmetic processing in this case is also based on vector calculation.

  In the present invention, if a relay for operating a switch provided in the non-grounded electrical circuit is added to the ground fault detection device with the output of the ground fault detection device, a ground fault protection relay is configured. Is possible.

  Further, the method of the present invention is a ground fault detection for detecting the ground fault current Ig based on the zero phase voltage Vo and the zero phase current Io appearing in the non-ground system circuit due to the ground fault in the premises of the non-ground system circuit. In this method, a differential value dVo / dt obtained by differentiating the detected zero-phase voltage Vo with respect to time is multiplied by a ground capacitance C in the premises of the non-grounded circuit, and the differential value dVo / dt is multiplied by the electrostatic capacitance. A ground fault current Ig is obtained by subtracting a multiplied value C × (dVo / dt) multiplied by the capacitance C from the zero-phase current Io. Each arithmetic processing described above is based on vector calculation.

  In the method of the present invention, the zero-phase voltage Vo may be divided by the ground fault current Ig. In this way, the calculated division value Vo / Ig can be obtained as the ground fault resistance Rg. The arithmetic processing in this case is also based on vector calculation.

  In the present invention, the differential value dVo / dt obtained by differentiating the zero-phase voltage Vo appearing in the non-grounded circuit due to a ground fault in the ground of the non-grounded circuit with respect to time is obtained from the differential value dVo / dt. The multiplication value C × (dVo / dt) obtained by multiplying the capacitance C and multiplying the differential value dVo / dt by the ground capacitance C is a zero-phase current that flows in the ungrounded electric circuit when a ground fault occurs on the premises. By subtracting from Io to obtain the ground fault current Ig, the ground fault current Ig flowing in the non-grounded electrical circuit due to the ground fault in the premises of the non-grounded electrical circuit can be calculated by simple arithmetic processing.

  According to the present invention, the differential value dVo / dt obtained by differentiating the zero-phase voltage Vo appearing in the non-grounded circuit due to a ground fault in the ground of the non-grounded circuit with respect to the ground of the non-grounded circuit is shown. A multiplication value C × (dVo / dt) obtained by multiplying the capacitance C and multiplying the differential value dVo / dt by the ground capacitance C is zero flowing in the ungrounded circuit when a ground fault occurs on the premises. By subtracting from the phase current Io to obtain the ground fault current Ig, the ground fault current Ig flowing in the non-grounded circuit due to the ground fault in the premises of the non-grounded circuit can be calculated by a simple calculation process. . Since the ground fault current Ig is calculated by such a simple calculation process, a ground fault detection device for an ungrounded electrical circuit that detects the occurrence of a ground fault by simple digital processing, a ground fault protection relay using the ground fault detection device, and A ground fault detection method can be provided.

In the embodiment of the present invention, it is a schematic configuration block diagram showing a ground fault detection device installed in a non-grounded electrical circuit. In embodiment of this invention, it is a schematic block diagram which shows the ground fault protection relay which has the ground fault detection apparatus installed in the non-ground system electric circuit. In other embodiment of this invention, it is a schematic block diagram which shows the ground fault detection apparatus installed in the branch electric circuit of a non-ground system electric circuit. In other embodiment of this invention, it is a schematic block diagram which shows the ground fault protection relay which has the ground fault detection apparatus installed in the branch circuit of a non-ground system circuit. FIG. 3 is a circuit diagram showing an equivalent circuit in the case where a ground fault has occurred in the ungrounded electrical circuit of FIGS. 1 and 2. In the case of a healthy state in which no ground fault has occurred, (A) is a waveform diagram showing zero-phase voltage and zero-phase current, and (B) is a waveform diagram showing differential values of zero-phase voltage and zero-phase current. . When a local ground fault occurs, (A) is a waveform diagram showing zero phase voltage and zero phase current, and (B) is a waveform diagram showing differential values of zero phase voltage and zero phase current. It is for explaining instantaneous value calculation of ground fault resistance and ground capacitance based on singular point of zero phase voltage waveform, and shows current flowing in zero phase voltage, zero phase current, ground fault current and ground capacitance It is a waveform diagram. It is a schematic block diagram showing a ground fault detection device for obtaining ground fault resistance by instantaneous value calculation using a singular point of a zero phase voltage waveform. It is a schematic block diagram showing a ground fault detection device for obtaining ground capacitance by instantaneous value calculation using a singular point of a zero phase voltage waveform.

  FIG. 1 shows an embodiment of the present invention, and shows a ground fault detection device 2 provided in a non-grounded electric circuit 1 composed of, for example, a 6.6 kV high-voltage power receiving facility. The ground fault detection device 2 monitors a ground fault that has occurred on the premises of the ungrounded electrical circuit 1 and detects a ground fault current that flows when the ground fault occurs. FIG. 2 shows another embodiment of the present invention, which shows a ground fault protection relay 3 incorporating the above-described ground fault detection device 2 in order to protect a load facility to receive power. The ground fault protection relay 3 includes the above-described ground fault detection device 2 and a relay 6 that selectively opens and closes the switch 4 based on the detection result output from the ground fault detection device 2.

  In this non-grounded electric circuit 1, various loads 5 are connected to a high-voltage power receiving facility (system bus) via a switch 4, and the load-side electric circuit from the switch 4 that is the power receiving point is referred to as a premises and is zero. In contrast to the protection range in which the phase current transformer 8 can detect the zero-phase current Io, the electric circuit on the system side is referred to as off-premise and out of the protection range. The ground fault detection device 2 can also be applied to other non-grounded electric circuits including special high voltage power receiving equipment other than the above-described high voltage power receiving equipment, high voltage power receiving equipment receiving special high voltage, and low voltage power receiving equipment.

Further, as shown in FIGS. 3 and 4, the non-grounded electric circuit 1 may have branch electric circuits 1 ₁ to 1 _n that are branched into a plurality from the power receiving point of the main electric circuit on the inner side. In this branch circuit 1 ₁ to 1 _n , a ground fault detection device 2 ₁ to 2 _n that monitors a ground fault occurring in the branch circuit 1 ₁ to 1 _n and detects a ground fault current that flows at the time of the ground fault of the campus is provided. It is possible to install. Incidentally, FIG. 3, illustrate case of installing the ground fault sensing device 2 ₁ to 2 _n to the respective branch paths 1 ₁ to 1 _n, 4, land incorporating the grounding detector 2 ₁ to 2 _n The case where the fault protection relays 3 _{1 to} 3 _n are installed in the branch electric circuits 1 ₁ to 1 _n is illustrated.

  As shown in FIGS. 1 and 2, an instrument transformer 7 which is a zero-phase voltage detecting means for detecting a zero-phase voltage Vo appearing in the non-grounded electric circuit 1 due to the occurrence of a ground fault on the premises, A zero-phase current transformer 8, which is a zero-phase current detection means for detecting the zero-phase current Io flowing due to the generation, is connected to the ground fault detection device 2. The zero-phase voltage Vo and the zero-phase current Io described above represent vector quantities, and the differential value dVo / dt of the zero-phase voltage Vo, the ground fault current Ig, and the current Ic flowing through the ground capacitance C described below are also vectors. Represents an amount. Each calculation process is based on vector calculation.

When the ungrounded circuit 1 has a plurality of branch circuits 1 ₁ to 1 _n , as shown in FIGS. 3 and 4, the switches 4 ₁ to 4 are connected to the main circuit as in FIGS. Various loads 5 _{1 to} 5 _n are connected via _n, and zero phase current transformers 8 ₁ to 8 _{n which} are zero phase current detecting means for detecting the zero phase current Io flowing due to the occurrence of a ground fault are ground faults. It is connected to the detection devices 2 _{1 to} 2 _n .

Note that FIG. 3 and ground fault detecting in the embodiment shown in FIG. 4 device 2 ₁ to 2 _n of the structure and operation (calculation of the ground fault resistance Rg ₁ ~Rg _n in each branch path 1 ₁ to 1 _n) are 1 and FIG. 2 are the same as the configuration and operation of the ground fault detection device 2 in the embodiment shown in FIG. 1 (calculation of the ground fault resistance Rg in the non-grounded electric circuit 1). The embodiment will be described in detail, and redundant description in the embodiment of FIGS. 3 and 4 will be omitted.

  The ground fault detection device 2 includes a differentiating circuit 9 which is a zero-phase voltage differentiating means for differentiating the zero-phase voltage Vo output from the instrument transformer 7 with respect to time, and a ground capacitance in the premises of the ungrounded electric circuit 1. For example, the arithmetic circuit 10 which is a capacitance setting means for setting C by calculating the arithmetic processing and the differential value dVo / dt of the zero-phase voltage Vo calculated by the differentiating circuit 9 is calculated by the arithmetic circuit 10. A multiplication circuit 11 which is a multiplication means for multiplying the ground capacitance C, and a multiplication value C × (dVo / dt) obtained by multiplying the differential value dVo / dt by the ground capacitance C by the multiplication circuit 11 is a zero-phase current transformation. The subtracting circuit 12 which is a subtracting means for subtracting from the zero phase current Io detected by the calculator 8 and the zero phase voltage Vo obtained by the instrument transformer 7 are divided by the ground fault current Ig obtained by the subtracting circuit 12. Mainly with division circuit 13 Part is configured, the division value Vo / Ig calculated by the division circuit 13 is obtained as the ground fault resistance Rg. In this embodiment, the ground fault resistance Rg is obtained by providing the division circuit 13. However, if the division circuit 13 is omitted, the subtraction value Io-C × (dVo / dt) calculated by the subtraction circuit 12 is grounded. You may make it obtain | require as electric current Ig. The ground capacitance C in the premises of the non-grounded electric circuit 1 is calculated by the arithmetic circuit 10, but may be measured by a measuring instrument.

  FIG. 5 shows an equivalent circuit in the case where a ground fault has occurred in the ungrounded circuit 1 of FIGS. 1 and 2. As shown in FIG. 5, when a ground fault (resistance ground fault) occurs in the premises of the ungrounded circuit 1, a zero-phase voltage Vo composed of the power supply voltage Eg and the power supply side impedance Zo appears on the ungrounded circuit 1. The zero-phase current Io that can be detected by the zero-phase current transformer 8 flows in the ungrounded electric circuit 1. Here, the zero-phase current Io is the sum of the current Ic flowing through the ground capacitance C on the campus and the current flowing through the ground fault resistance Rg at the time of the ground fault, that is, the ground fault current Ig [Io = Ic + Ig (1)]. Since Ic = jωCVo, Ic = C × (dVo / dt) (2). Therefore, the zero phase current Io is expressed by the following equation (3) from the above equations (1) and (2).

  Io = C × (dVo / dt) + Ig (3)

  In this embodiment, the zero-phase voltage Vo appearing in the non-grounded electric circuit 1 due to the ground fault of the non-grounded electric circuit 1 is detected by the instrument transformer 7, and the zero-phase voltage Vo is detected by the differentiation circuit 9 in time. The differential value dVo / dt differentiated by is calculated. On the other hand, the ground capacitance C on the premises is calculated by the arithmetic circuit 10. The multiplication circuit 11 multiplies the ground capacitance C calculated by the arithmetic circuit 10 by the differential value dVo / dt of the zero-phase voltage Vo calculated by the differentiation circuit 9. The multiplication value C × (dVo / dt) obtained by multiplying the differential value dVo / dt of the zero-phase voltage Vo by the ground capacitance C is subtracted from the zero-phase current Io detected by the zero-phase current transformer 8 by the subtracting circuit 12. Subtract. That is, the ground fault current Ig is obtained as the subtraction value Io−C × (dVo / dt) calculated by the subtraction circuit 12 as shown in the following expression (4) from the above expression (3).

  Ig = Io−C × (dVo / dt) (4)

  Here, in the case of a healthy state where no ground fault has occurred on the premises, as shown in FIG. 6A, the zero-phase current Io is 90 ° behind the zero-phase voltage Vo. The differential value dVo / dt of the zero-phase voltage Vo has an opposite phase (180 °) to the zero-phase current Io as shown in FIG. The multiplication value C × (dVo / dt) obtained by multiplying the differential value dVo / dt of the zero-phase voltage Vo by the ground capacitance C on the premises is the current Ic flowing through the ground capacitance C according to the above equation (2). Therefore, when the current Ic flowing through the ground capacitance C is subtracted from the zero-phase current Io, the ground fault current Ig becomes zero.

  On the other hand, in the case of occurrence of a ground fault on the premises, as shown in FIG. 7A, the zero-phase current Io has a 90 ° advance phase with respect to the zero-phase voltage Vo. The value dVo / dt is in phase with the zero-phase current Io as shown in FIG. As described above, the multiplication value C × (dVo / dt) obtained by multiplying the differential value dVo / dt of the zero-phase voltage Vo by the ground capacitance C on the premises becomes the current Ic flowing through the ground capacitance C. [Refer to equation (2)], the ground fault current Ig is obtained by subtracting the current Ic flowing through the ground capacitance C from the zero-phase current Io.

  As described above, the differential value dVo / dt obtained by differentiating the zero-phase voltage Vo appearing in the non-grounded electric circuit 1 with respect to time due to a ground fault in the non-grounded electric circuit 1 is determined in the non-grounded electric circuit 1. Is multiplied by the differential value dVo / dt multiplied by the ground capacitance C, and a multiplied value C × (dVo / dt) is obtained when a ground fault occurs on the premises. By subtracting from the zero-phase current Io flowing to the ground, the ground fault current Ig is obtained, so that the ground fault current Ig flowing to the non-grounded circuit 1 due to the ground fault in the premises of the non-grounded circuit 1 can be obtained by simple arithmetic processing. Can be calculated. Further, the ground fault resistance Rg is calculated by the division circuit 13 by dividing the zero-phase voltage Vo obtained by the instrument transformer 7 by the ground fault current Ig obtained by the subtraction circuit 12 by the division circuit 13. The division value Vo / Ig is obtained as shown by the following equation (5).

  Rg = Vo / Ig (5)

  When the ground fault detection device 2 is used alone as in the embodiment of FIG. 1, an operator takes home from the site or communicates with the ground fault resistance Rg output from the division circuit 13 of the ground fault detection device 2 as detection data. By transmitting through a line and inputting to an analysis apparatus installed at another location, determination processing based on on-site detection data can be performed by the analysis apparatus provided at another location. It is also possible to use the output of the divider circuit 13 of the ground fault detection device 2 as an alarm signal. Moreover, when it is set as the structure which incorporated the ground fault detection apparatus 2 in the ground fault protection relay 3 like embodiment of FIG. 2, the relay 6 is operated based on the output of the division circuit 13 of the ground fault detection apparatus 2. It is possible to open and close the switch 4. When the output of the ground fault detection device 2 is used as an alarm signal or a relay operation signal, a predetermined threshold value may be set.

  As described above, the ground fault resistance Rg can be obtained by vector calculation based on the above-described equation (5). As described in detail below, the singular points A and 0 of the zero-phase voltage Vo shown in FIG. Based on B, the ground fault resistance Rg and the ground capacitance C can be obtained by instantaneous value calculation.

As shown in FIG. 8, when the differential value dVo / dt of the zero-phase voltage Vo is 0, the zero-phase current Io becomes the maximum value Ig _MAX of the ground fault current Ig. Thus, in the waveform of the zero-phase voltage Vo, when the differential value dVo / dt of the zero-phase voltage Vo is 0, the singular point A (black circle in the figure) is used, and the zero-phase voltage Vo at this time is the maximum value Vo _MAX. Thus, the zero-phase current Io detected by the zero-phase current transformer 8 becomes the maximum value Ig _MAX of the ground fault current Ig, so that the maximum value Vo of the zero-phase voltage Vo is expressed by the following equation (6). _By dividing _MAX by the maximum value Ig _MAX of the ground fault current Ig, the ground fault resistance Rg can be obtained by simple arithmetic processing.

Rg = Vo _MAX / Ig _MAX (6)

Thus, in order to obtain the ground fault resistance Rg by instantaneous value calculation, as shown in FIG. 9, the differentiation circuit 21 for differentiating the zero-phase voltage Vo with time, and the differential value dVo / dt of the zero-phase voltage Vo are A zero detection circuit 22 for detecting zero, a sampling circuit 23 for extracting the zero-phase voltage Vo when the differential value dVo / dt of the zero-phase voltage Vo is 0 as the maximum value Vo _MAX , and a differential value dVo / dt The sampling circuit 24 that extracts the zero-phase current Io when the value is 0 as the maximum value Ig _MAX of the ground fault current Ig, and the maximum value Vo _MAX of the zero-phase voltage Vo obtained by the sampling circuit 23 is obtained by the sampling circuit 24 This can be realized by a ground fault detection device including a division circuit 25 that obtains a ground fault resistance Rg by dividing by the maximum value Ig _MAX of the ground fault current Ig.

Further, as shown in FIG. 8, when the zero-phase voltage Vo is 0, the zero-phase current Io becomes the maximum value Ic _{MAX of the} current Ic flowing through the ground capacitance C. Thus, in the waveform of the zero-phase voltage Vo, when the zero-phase voltage Vo is 0, the singular point B (white circle in the figure) is used, and the differential value dVo / dt when the zero-phase voltage Vo at this time is 0 is When the maximum value (dVo / dt) _{MAX is} reached and the zero-phase current Io becomes the maximum value Ic _{MAX of the} current Ic flowing through the ground capacitance C, the ground capacitance C is expressed by the following equation (7). By dividing the maximum value Ic _MAX of the current Ic flowing through the current by the maximum value (dVo / dt) _MAX of the differential value dVo / dt, the ground capacitance C can be obtained by simple arithmetic processing.

C = Ic _MAX / (dVo / dt) _MAX (7)

Thus, in order to obtain the ground capacitance C by instantaneous value calculation, as shown in FIG. 10, a zero detection circuit 31 that detects that the zero-phase voltage Vo is zero, and the zero-phase voltage Vo is zero. Differential circuit 32 that calculates the differential value dVo / dt at the time as the maximum value (dVo / dt) _MAX , and the maximum value of the current Ic that flows through the ground capacitance C from the zero-phase current Io when the zero-phase voltage Vo is 0 The sampling circuit 33 that is extracted as Ic _MAX , and the maximum value Ic _MAX obtained by the sampling circuit 33 is divided by the maximum value (dVo / dt) _MAX of the differential value dVo / dt calculated by the differentiating circuit 32. This can be realized by a ground fault detection device including a division circuit 34 for obtaining the capacitance C.

  The present invention is not limited to the above-described embodiments, and can of course be implemented in various forms without departing from the gist of the present invention. It includes the equivalent meanings recited in the claims and the equivalents recited in the claims, and all modifications within the scope.

DESCRIPTION OF SYMBOLS 1 Non-ground system electric circuit 2 Ground fault detection device 3 Ground fault protection relay 4 Switch 6 Relay 7 Zero phase voltage detection means (instrument transformer)
8 Zero-phase current detection means (zero-phase current transformer)
9 Zero-phase voltage differentiation means (differential circuit)
10 Ground capacitance setting means (arithmetic circuit)
11 Multiplication means (multiplication circuit)
12 Subtraction means (subtraction circuit)

Claims (5)

Zero-phase voltage detecting means for detecting the zero-phase voltage V ₀ that appears in the non-grounded circuit due to a ground fault in the ground of the non-grounded circuit, and the non-grounded circuit in the event of a ground fault in the campus A ground fault detection device connected to zero phase current detection means for detecting zero phase current I ₀ flowing through
Zero-phase voltage differentiation means for differentiating the zero-phase voltage Vo obtained by the zero-phase voltage detection means with respect to time, capacitance setting means for setting a ground capacitance in the premises of the ungrounded circuit, and the zero Multiplication means for multiplying the differential capacitance dVo / dt calculated by the phase voltage differentiation means by the ground capacitance C calculated by the capacitance setting means; and the differential value dVo / dt multiplied by the ground capacitance C. And a subtracting means for subtracting the multiplied value C × (dVo / dt) from the zero-phase current Io to obtain a ground fault current Ig.   2. A division means for adding a ground fault resistance Rg by dividing the zero phase voltage Vo obtained by the zero phase voltage detection means by the ground fault current Ig obtained by the subtraction means is added to the subsequent stage of the subtraction means. A ground fault detection device for a non-grounded electrical circuit according to claim 1.   A ground fault protection relay comprising the ground fault detection device according to claim 1 and a relay for operating a switch provided in a non-grounded electrical circuit with an output of the ground fault detection device.   A ground fault detection method for detecting a ground fault based on a zero-phase voltage Vo and a zero-phase current Io that appear in the non-ground system circuit due to a ground fault in the premises of the non-ground system circuit. A differential value dVo / dt obtained by differentiating the zero-phase voltage Vo with respect to time is multiplied by a ground capacitance C in the premises of the non-grounded circuit, and a multiplication value C obtained by multiplying the differential value dVo / dt by the ground capacitance C. A ground fault detection method for a non-grounded electric circuit, wherein x (dVo / dt) is subtracted from the zero-phase current Io to obtain a ground fault current Ig.   The ground fault detection method for an ungrounded electrical circuit according to claim 4, wherein the zero-phase voltage Vo is divided by the ground fault current Ig to obtain a ground fault resistance Rg.

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