JP2009058234A - Leak current measuring instrument and measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure leak current owing to ground insulation resistance and leak current owing to ground capacitance, thereby determining a phase with a leak current value increasing therein. <P>SOLUTION: Tertiary harmonic voltage E<SB>3</SB>is calculated from capacitance of a measurement capacitor 10 connected to a three-phase power supply of a three-phase three-wire or three-phase four-wire distribution system and from tertiary harmonic current Ic<SB>3</SB>flowing through a grounding wire of the measurement capacitor 10. Besides, this leak current measuring instrument is equipped with: a high-frequency wave processing part 13 for measuring the value of total leakage current of three phases R, S, and T caused by the ground capacitance from the ground capacitance and phase voltages of three phases, which are calculated from the harmonic current Ic<SB>3</SB>included in zero-phase current I<SB>0</SB>and the harmonic voltage E<SB>3</SB>; and an operation part 14 for determining leakage current classified by phase and caused by the ground capacitance, a value found by minimizing an error in a leak current Igr caused by the ground insulation resistance, and a phase with the leak current Igr increasing, from output values of two processing parts of a fundamental wave processing part 3 for outputting an active component, a reactive component, and the zero-phase current I<SB>0</SB>of commercial frequency zero-phase current I<SB>0</SB>. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a leakage current measuring apparatus and a measuring method for measuring a leakage current from a voltage application portion to a ground portion of an electric circuit and an electric device.

  2. Description of the Related Art Conventionally, as a method for examining the insulation state of an electric circuit and an electric device, a method of measuring with an insulation resistance meter after causing a power failure of an electric circuit or electric device to be measured has been widely used. Such a method cannot be applied to distribution lines where continuous blackouts are not allowed, continuous operation factories, and the like.

In view of this, a technique for examining the insulation state of the electric circuit and the electric device while maintaining the live line without causing a power failure of the electric circuit to be measured and the electric device has been proposed and used. As this type of technology, there is a technique that detects a zero-phase current (hereinafter referred to as I ₀ ) that is a current flowing from a voltage application portion to a ground portion of an electric circuit and electrical equipment detected by a zero-phase current transformer. This zero-phase current (leakage current) I ₀ is usually a leakage current (hereinafter referred to as Igr) flowing through the insulation resistance between the voltage application portion and the ground portion of the electric circuit and electrical equipment, and between this voltage application portion and the ground portion. It consists of a vector sum with a leakage current (hereinafter referred to as Igc) flowing through the existing ground capacitance.

  In recent years, devices that generate high frequencies, such as inverters using power semiconductor elements, have been widely used. In 400V class distribution lines, leakage current Igc that flows through the capacitance is affected by the increase in installation length and line length. The increase is remarkable.

Therefore, only the detection of only the zero-phase current I _0, it is impossible to distinguish between the leakage currents Igr flowing originally detected through ground insulation resistance is a measure of the object of the leakage, by detecting an increase in the zero-phase current I ₀ The malfunction of the operating earth leakage circuit breaker is caused.

In recent years, 400V class 3 powered by a star-connected power source with three-phase windings on the low-voltage side of a transformer, which has been increasingly adopted by large-scale electric power consumers and has become the standard for overseas power distribution systems. As a method for measuring the insulation state of the circuit and electrical equipment insulation of the phase 4-wire distribution system (hereinafter referred to as 3-phase 4-wire distribution), the zero-phase current I ₀ flowing from the voltage application portion to the ground portion is measured, and this value Is used as a value of the leakage current Igr flowing through the insulation resistance.

In this method, when the ground capacitance values of the three phases are equal (hereinafter, this state is referred to as a balanced state), the value of the leakage current Igr matches the value of the zero-phase current I ₀ . not equal (below this state, that imbalance.), since the values resulting from the unbalanced state is output applied to the value of the zero-phase current I _0, leakage current value of the zero-phase current I ₀ When the value of Igr is included, a large error is included. Above all, the reliability of the measurement itself is lost because it is impossible to measure whether or not the ground capacitance of each phase is balanced at this point.

  Another method, the measurement method of the distribution system that grounds one of the 200V three-phase three wires fed from the power source that connects the three-phase windings on the low voltage side of the transformer in an equilateral triangle, is caused by the unbalanced state. Although the leakage current Igr including the error can be measured, it cannot be applied to the three-phase four-wire distribution system. As another method, there is a technique disclosed in JP-A-2002-125313 (Patent Document 1) and JP-A-3-179271 (Patent Document 2). The technologies disclosed in these publications are not suitable for measuring the leakage current Igr in a three-phase four-wire distribution system circuit because the configuration is complicated and the measurement program has a large capacity. As described in Patent Document 2, a method of feeding a low-frequency low voltage to a distribution line can be applied to all circuits, but the equipment is complicated and it is difficult to provide it at low cost.

In recent years, the system scale of the three-phase four-wire distribution system has become widespread, the value of the leakage current Igc flowing through the ground capacitance that causes malfunction of the earth leakage circuit breaker has increased, and measures to reduce these have become necessary. Yes. Further, in the three-phase four-wire distribution system, three-phase loads such as large-capacity power and single-phase loads such as lighting and large-capacity welders are mixed to increase the number of unbalanced systems. For this reason, the distribution system state is grasped by measuring the Igc for each phase, the leakage current Igr related to the failure with reduced errors due to the unbalanced state is measured, and the leakage current Igr is further increased. The demand for detecting the phase and grasping the insulation deterioration location and the degree of deterioration is increasing, but the conventional method cannot detect and measure these.
JP 2002-125313 A JP-A-3-179271

  The present invention has been proposed as a technical problem to solve the above-described problems, and each of the three-phase three-wire or three-phase four-wire distribution system flows through the ground capacitance. It is possible to grasp the current Igc value for each phase, further grasp the leakage current Igr value with reduced error due to the unbalanced state, and further determine the phase in which the leakage current Igr value is increasing. It is an object of the present invention to provide a leakage current measuring device and a measuring method.

In order to solve the technical problems as described above, the leakage current measuring apparatus according to the present invention is a three-phase three-wire type or three-phase four-wire type distribution circuit in which a power source is connected in a star shape or an electric circuit of an electric device. This is a leakage current measuring device that measures leakage current Igr caused by ground insulation resistance and leakage current Igc caused by ground capacitance. In this leakage current measuring device, three sets of capacitors are connected in a star shape, and the neutral point is grounded via a grounding wire and a three-phase three-wire type or a three-phase four-wire type. Due to the _third harmonic phase voltage E ₃ , which is three times the commercial power frequency included in the three-phase voltage of the three-phase power supply of the distribution system, the value of the _third harmonic current Ic ₃ flowing through the ground line and The value of the third-order harmonic phase voltage E ₃ is calculated from the capacitance values of the three sets of capacitors, and the third-order included in the zero-phase current I ₀ that is the vector sum of the currents flowing in the three-wire or four-wire. From the value of the harmonic current and the value of the third harmonic phase voltage E ₃ , the capacitance of the earth at the commercial frequency of the power supply is calculated from the value of the total capacitance of the three phases and the value of the three-phase voltage. R-phase, and harmonic processing means for measuring the value of the total leakage current of the three phases of the S-phase and T-phase _{(Igc R + Igc S + Igc} T) caused by Power commercial 3-phase phase voltage frequency is input, the zero-phase current I _0, and component I _0A of any one phase of the input voltage in phase with the direction of the three-phase input voltage and perpendicular components I _0B The leakage current Igc for each phase caused by the capacitance to the ground based on the current value obtained by decomposing the current, the zero-phase current I _0, and the total leakage current (Igc _R + Igc _S + Igc _T ) _R , Igc _S , Igc _T values, a value in which the error of the leakage current Igr caused by the ground insulation resistance is minimized, and a calculation means for calculating a phase in which the value of the leakage current Igr is maximized. .

The computing means used here is a component in the same phase direction as the input voltage for two phases of the three-phase voltage of the three-phase power supply, and a component in a direction perpendicular to the input voltage for two phases of the three-phase voltage. When the value of is zero or almost zero, the value of the commercial power frequency component included in the zero-phase current I ₀ is output as the leakage current Igr caused by the ground insulation resistance.

  The leakage current measuring apparatus according to the present invention further includes a display unit, and the display unit displays a result calculated by the calculation unit.

  The leakage current measuring apparatus according to the present invention further includes alarm means for issuing an alarm when any of the values obtained by the arithmetic means exceeds a predetermined value.

In addition, the present invention provides a leakage current Igr caused by a ground insulation resistance of an electric circuit or an electric device of a three-phase three-wire system or a three-phase four-wire distribution system connected in a star shape and a ground capacitance. A leakage current measuring method for measuring a current Igc, comprising a measurement circuit in which three sets of capacitors are connected in a star shape and the neutral point thereof is grounded via a grounding wire. 3 flowing through the ground line due to the _third harmonic phase voltage E3, which is three times the commercial power frequency included in the three-phase voltage of the three-phase power supply of the three-phase four-wire power distribution system The value of the _third harmonic phase voltage E ₃ is calculated from the value Ic ₃ of the second harmonic current and the capacitance values of the three sets of capacitors, and is the vector sum of the currents flowing in the three or four lines. tertiary harmonic current value and a three-phase sum of the ground calculated from the value of the third harmonic phase voltage E ₃ included in the zero-phase current I ₀ From the value of the value and 3 phase phase voltage of capacitance, R-phase due to the earth capacitance of the power supply line frequency, the value of the total leakage current of the three phases of the S-phase and T-phase _{(Igc R + Igc S + Igc} T) A three-phase voltage of a commercial power frequency and a zero-phase current I ₀ , a component I _{0A in the} same phase direction as the input voltage of any one of the three phases, Based on the current value obtained by decomposing the input voltage and the component I _{0B in the} perpendicular direction, the zero-phase current I _0, and the total leakage current (Igc _R + Igc _S + Igc _T ), Phases in which the values of the leakage currents Igc _R , Igc _S , Igc _T due to each phase, the value of the leakage current Igr caused by the ground insulation resistance is minimized, and the value of the leakage current Igr is maximized And a calculation step for calculating.

In the leakage current measuring method according to the present invention, the calculation step includes a component I _{0A in the} same phase direction as the input voltage for two phases of the three-phase voltages of the three-phase power supply, and two of the three-phase voltages. When the value of the component I _{0B in} the direction perpendicular to the input voltage of the phase is zero or almost zero, the value of the commercial power frequency component included in the zero-phase current I ₀ is output as the leakage current Igr caused by the ground insulation resistance .

  Here, the center point of the star winding that is the power source of the three-phase four-wire distribution circuit connected in a star shape to which the leakage current measuring apparatus and the measuring method according to the present invention are applied is directly grounded. In a commercial power supply of 50 Hz or 60 Hz (hereinafter referred to as a fundamental frequency), a three-phase voltage having a magnitude equal to and different in phase by 120 degrees with respect to the potential at the ground point 0 is transferred from the three-phase terminal at the other end of the winding to the distribution line Supplied.

By the way, an electric circuit or an electric device is connected to the three-phase terminal, and a ground capacitance exists between the voltage application portion and the ground portion. When each relative ground capacitance is the same value, the leakage current Igc flowing through the ground capacitance in each phase is equal in magnitude and the phase is different by 120 degrees. Therefore, the Igc of each phase is added in a vector form. The value becomes 0, and the value of Igc of each phase is unknown in the measurement of the zero-phase current I ₀ that is the vector sum of the currents flowing through the three wires including this value. In addition, even in an unbalanced state, the total Igc value of each phase is different from the sum of these in a vector manner. In the method of detecting the zero-phase current I ₀ including these vector sum values, It is impossible to detect the value of Igc.

In the leakage current measuring apparatus and measuring method according to the present invention, measurement is performed at a normal fundamental frequency in order to determine the balance state of whether or not the values of the ground capacitances of the three phases are equal. First, the three-phase voltage of the star winding sharing the grounding point of the three-phase three-wire system or the three-phase four-wire distribution system is sequentially input, and the zero-phase current I ₀ is input to each input voltage. The component I _0A and the component I _0B having a phase difference of 90 degrees are decomposed into components, and the balance state is determined according to the mutual tendency of the values of these components I _0A and I _0B. The value of the leakage current Igr in which the error due to is reduced is calculated, and the phase in which the value of the leakage current Igr is increasing is also determined.

At the fundamental frequency as described above, the phase angle of the current flowing through each phase differs by 120 degrees. Therefore, if the value of the leakage current Igc flowing through the ground capacitance is equal to each phase, the vector sum of the three phases becomes 0. The leakage current Igc cannot be measured. Therefore, in the present invention, the value of the leakage current Igc of the total of each phase is measured using a third harmonic voltage contained in a small amount in the power supply voltage, and this measured value, the zero-phase current I ₀ , The leakage current Igc for each phase is calculated together with the component I _{0A in} phase with the input voltage obtained by decomposing the zero-phase current I ₀ and the value of the component I _0B having a phase difference of 90 degrees from this component I _0A . Based on the calculated value, the value of the leakage current Igr caused by the ground insulation resistance is corrected, the leakage current Igr with a small error is calculated, and the failure phase is determined based on the relationship between these values.

  By the way, the phase angle between the three phase voltages is 120 degrees at the fundamental frequency, but the third harmonic phase voltage is three times the frequency, and the phase angle is the same phase of 360 degrees, which is three times 120 degrees. A third harmonic voltage of the same phase exists at each terminal to the ground point, which is the center point of the star winding of the three-phase four-wire distribution circuit connected in a star shape, and is connected to each phase The third-order harmonic currents flowing through the ground capacitance of the load such as distribution lines and electrical equipment to be made have the same phase, and their values are summed up without being canceled like the fundamental frequency. Using the third harmonic voltage, the value of the third harmonic current of each phase is measured.

  In the present invention, the value of the leakage current Igc flowing through the ground capacitance for each phase and the state of error due to the unbalanced state are calculated from the values obtained by the two types of measurements different in the above method. Then, the value of the leakage current Igr caused by the ground insulation resistance that minimizes this error is calculated, and the phase in which the value of the leakage current Igr is increased is determined.

The leakage current measuring apparatus and the measuring method according to the present invention are, for example, a three-phase four-wire distribution system connected in a star shape, and a zero-phase value as a leakage current Igr caused by a ground insulation resistance representing the insulation state. This solves the problem caused by the determination by measuring the value of the current I ₀ . In the conventional technique for measuring the leakage current Igr based on the value of the zero-phase current I ₀ , there is a measurement error due to the unbalanced state of the ground capacitance, and the determination of the unbalanced state itself is impossible. Therefore, the reliability of the measured value was extremely low and lacked in reliability. In order to elucidate the state of these errors, the present invention obtains the ground capacitance for each phase, which has conventionally been impossible to measure, and uses this ground capacitance to determine the value of the leakage current Igr that represents the insulation state. In addition, it is possible to measure the capacitance to ground for each phase necessary for elucidating the cause of the malfunction of the earth leakage relay, by accurately measuring the phase and determining the phase in which the insulation has deteriorated. As a result, by adopting the present invention, it is possible to continuously measure the insulation state caused by failure of power distribution equipment and electrical equipment while it is energized, greatly improving the accuracy of preventive maintenance, and preventing the occurrence of power outage accidents In addition, the maintenance cost has been reduced and the reliability of the entire equipment has been significantly improved.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of a leakage current measuring apparatus and a measuring method to which the present invention is applied will be described with reference to the drawings.

  FIG. 1 is a schematic system diagram showing an example in which the leakage current measuring apparatus according to the present invention is applied to a three-phase four-wire power distribution system. The three-phase four-wire distribution system is used for a 400 V class three-phase four-wire electric circuit and electrical equipment fed from a power source in which a three-phase winding on the low voltage side of the transformer is connected in a star shape.

  The leakage current measuring apparatus according to the present invention uses the leakage current Igr caused by the ground insulation resistance and the leakage current Igc caused by the earth insulation resistance of the electric circuit of the distribution system or the electric equipment using the three-phase four-wire distribution method. taking measurement.

  As shown in FIG. 1, a distribution system using a three-phase four-wire distribution system to which a leakage current measuring apparatus according to the present invention is applied is wound around a star on the low voltage side of a three-phase transformer for distribution. The star-shaped winding 1 and the load facility 5 are connected by a distribution line 4 including three-phase R, S, T connection lines 4R, 4S, 4T and a ground line 4G.

The star-shaped winding 1 on the low voltage side of the three-phase transformer for power distribution has three coils connected at a neutral point N and three-phase terminals R, S, and T connected to a three-phase line, respectively. . The star winding 1 is grounded at the neutral point N at the point G and is also connected to the load facility 5. However, in the three-phase three-wire system, the connection to the load facility 5 is omitted. Three-phase phase voltages E _R , E _S , and E _T are generated at the three-phase terminals R, S, and T. The three-phase phase voltages E _R , E _S , and E _T are equal in magnitude to the neutral point N and the ground point G, which are ground potentials, and differ in phase by 120 degrees at the fundamental frequency.

The neutral point N of the transformer and the ground point G are connected via a ground line 8. A vector sum current I ₀ of leakage currents of R, S, and T phases flows from the neutral point N to the ground point G through the connection line 8. The combined current I ₀ of the leakage current is detected as a zero-phase current I ₀ by the zero-phase current transformer 9 as will be described later.

In addition, ground capacitances C _R , C _S , and C _T exist in each phase of the distribution line 4 (4 _R , 4 _S , 4 _T ). Specifically, a ground capacitance C _R is generated in the distribution line 4 _R that connects the terminal R and the load facility 5 among the three phases. A ground capacitance C _S is also generated in the distribution line 4 _S connecting the terminal S and the load facility 5, and a ground capacitance C _T is also generated in the distribution line 4 _T connecting the terminal T and the load facility 5. The ground currents Igc _R , Igc _S , and Igc _T always flow through these ground capacitances C _R , C _S , and C _T. In addition, a leakage resistance r may occur in the distribution line 4 or the load facility 5 that connects any of the terminals and the load facility 5. A leakage current Igr flows through the leakage resistance r.

  In addition, since the ground voltage 4G in the distribution line 4 is almost zero, ground leakage current shall not flow.

The leakage current measuring apparatus according to the present invention includes a zero-phase current transformer 9 that detects a zero-phase current I ₀ that is a combined current of leakage currents of R, S, and T phases, and three-phase terminals R, S, A switching switch 2 is provided that switches the three-phase voltages E _R , E _S , E _T generated at T and supplies them to the processing operation unit 16 to be described later. The leakage current measuring device further includes a measuring capacitor 10. In addition, the leakage current measuring device controls the measurement opening / closing of the measurement capacitor current Ic ₃ measured by the measurement capacitor 10 and the third harmonic current I ₀₃ included in the zero-phase current I ₀ to control the input to the processing arithmetic unit 16. A shunt 12 composed of a resistor 11 and a resistor 12 that converts the measured capacitor current Ic ₃ into a voltage amount and supplies it to the processing arithmetic unit 16, the zero-phase current I ₀ , the measured capacitor current Ic ₃ , and the third order Processing the harmonic current I _O3 to determine the value of the leakage current Igr caused by the ground insulation resistance and the value of the leakage current Igc for each phase caused by the ground capacitance and the phase in which the leakage current Igr is generated And a processing operation unit 16 for displaying the determination result and each value on the display unit 15.

The processing calculation unit 16 compares the voltage of any of the three-phase voltages E _R , E _S , E _T switched by the switching switch 2 with the zero-phase current I ₀ from the zero-phase current transformer 9. Using the fundamental wave processing unit 3 for measuring the phase difference, the third harmonic current I ₀₃ included in the zero phase current I ₀ and the measurement capacitor current Ic ₃ , and the third harmonic current. Then, the value of the leakage current Igc for each phase, the value of the leakage current Igc for each phase, and the value of the leakage current Igr caused by the ground insulation resistance are measured and calculated, and the phase where the leakage current Igr is increased is calculated. The calculation unit 14 for determination, the value of the leakage current Igr with reduced error, the leakage current Igc for each phase, and a display unit 15 for displaying the determination result and the like are provided.

  Here, the operation | movement with respect to the fundamental wave performed in the fundamental process part 3 of the leakage current measuring apparatus applied to the power distribution system shown in FIG. 1 is demonstrated.

In FIG. 1, the switching switch 2 switches three-phase phase voltages E _R , E _S , E _T generated at the three-phase terminals R, S, T, respectively, and inputs them to the fundamental wave processing unit 3.

FIG. 2 illustrates vectors of the three-phase phase voltages E _R , E _S , E _T by the vector symbol method. For example, when the phase voltage E _R of the R phase is switched by the switching switch 2 and input to the fundamental wave processing unit 3, the input phase voltage E _R is a reference vector on the real axis in the effective component direction which is the horizontal axis. E. As shown in FIG. 2, when the other phase voltages E _S and E _T are decomposed into an effective component and a portion with a symbol j representing an ineffective component in the vertical axis direction, each phase R, S, T The phase voltages E _R , E _S and E _T are expressed by the following formulas (1) to (3).

E _R = E (1)
E _S = −0.5E−j 0.5√3E (2)
E _T = −0.5E + j0.5√3E (3)
FIG. 3 is a diagram in which the zero-phase current I ₀ is decomposed into an effective component I _0A having the same direction component as that of the reference voltage E and an ineffective voltage I _0B having a component perpendicular to the reference voltage. At this time, the zero-phase current I ₀ is expressed by the following equation (4).

I ₀ = I _0A + jI _0B (4)
Note that an angle between the reference voltage E and the zero-phase current I ₀ is a phase angle θ.

FIG. 4 shows that when the reference voltage E is a ground voltage which is an input voltage, the leakage current (zero phase current) I ₀ of the actual distribution system is represented by the leakage current Igr caused by the ground insulation resistance and the leakage caused by the ground capacitance. It is the figure decomposed | disassembled into the current Igc.

Incidentally, as described above, the distribution line 4 and the load facility 5 have ground capacitances C _R , C _S , and C _T in their respective phases, and these ground capacitances always have a ground leakage current Igc. _R , Igc _S , and Igc _T are flowing.

  In addition, since the ground voltage N of the three windings of the star winding 1 and the distribution line 4G connected thereto is almost 0, the ground leakage current can be ignored.

Here, it is assumed that the fundamental frequency is fHz, the angular frequency is ω = 2πf (rad / s), and the phase voltages E _R , E _S , E _T of the phases R, S, T are input to the fundamental wave processing unit 3. Each current is calculated using E as the reference vector and the input voltage as the reference vector.

At this time, leakage currents Igc _R , Igc _S , and Igc _T due to the ground capacitances of the phases R, S, and T are expressed by the following equations (5), (6), and (7).

_{Igc R = jωC R E R =} jωC R E ··· (5)
_{Igc S = jωC S E S =} 0.5√3ωC S E-j0.5ωC S E ··· (6)
Igc _T = jωC _T E _T = −0.5√3ωC _T E−j0.5ωC _T E (7)
Here, the leakage current Igr in the R phase is a current when grounded via the ground resistance 7 of the electric resistance r. This leakage current Igr is expressed by the following equation (8), where 1 / r is g.

Igr = gE _R = gE (8)
Then, from the ground point G to the neutral point N of the star winding 1 on the low voltage side of the three-phase transformer for power distribution, as described above, each phase of R, S, T is connected via the ground wire 8. A zero-phase current I _0, which is a vector sum of leakage currents, flows. This zero-phase current I ₀ is detected by the zero-phase current transformer 9 and output to the fundamental wave processing unit 3.

By the way, the fundamental wave processing unit 3 compares the zero-phase current I ₀ , which is the vector sum of the leakage currents of the R, S, and T phases, with respect to the input voltage of each phase, as shown in FIG. Decompose. The zero-phase current I ₀ is expressed by an equation (9).

I ₀ = Igc _R + Igc _S + Igc _T
= JωC _R E + 0.5√3ωC _S E−j0.5ωC _S E + (− 0.5√3ωC _T E−
j0.5ωC _T E) + gE
= (0.5√3ω (C _S −C _T ) + g) E + jω (C _R −0.5C _S −0.5C _T ) E
... (9)
When the active ingredient of which is an input reference voltage E in phase zero-phase current I ₀ and I _0A, I _0A can be expressed by the following equation (10).

I _0A = (0.5√3ω (C _S −C _T ) + g) E
= 0.5√3 (Igc _S −Igc _T ) + Igr (10)
Further, if the invalid component of I ₀ that is the coefficient part of the symbol j advanced by 90 degrees from the input reference voltage E is I _OB , I _OB can be expressed by the following equation (11).

_{I OB = ω (C R -0.5C} S -0.5C T) E
= Igc _R -0.5 Igc _S -0.5 Igc _T (11)
From the above calculation results, the reference voltage E input from the star winding 1, the zero-phase current I ₀ which is the vector sum of the leakage current of each phase, its effective component I _0A , and its ineffective component I _0B. Is represented by a vector diagram as shown in FIG. The vector sum of the effective component I _0A and the ineffective component I _0B of the zero-phase current I ₀ is the total leakage current I ₀ . The reference voltage E is shown on the same reference axis as the effective component I _0A of the total current I ₀ .

In actual measurement, as shown in the leakage current measurement value vector diagram of FIG. 3, the reference voltage E and the zero-phase current I are calculated from the waveforms of the reference voltage E and the zero-phase current I ₀ input to the fundamental wave processing unit 3. reactive component as an active ingredient I _0A and 90 degrees advanced components than the reference voltage E of calculating the phase angle theta, the zero-phase current I ₀ in the calculating portion 14 as a component of the reference voltage E in phase between ₀ Disassembled into I _0B and output.

Next, the switching switch 2 switches from the R phase to the S phase, or from the R phase to the T phase, and the fundamental voltage processing is performed on the phase voltage E _S input to the S phase and the phase voltage E _T input to the T phase, respectively. When input to the unit 3 and the same measurement as in the case of the R phase described above is performed, the values of the effective component I _0A and the invalid component I _OB of the S phase and the R phase are obtained.

When measuring the states of the S phase and the T phase other than the R phase as described above, as in the case of the R phase, the effective component I _0A of the zero-phase current I ₀ obtained by the above formulas 10 and 11 is used. Then, the value of the reactive component I _OB of the zero-phase current I ₀ is obtained.

As described above, FIG. 5 shows expressions representing the effective component I _0A of the zero-phase current I _{0 and} the ineffective component I _OB of the zero-phase current I ₀ in the R, S, and T phases obtained by the expressions 10 and 11. .

Then, the switching switch 2 is switched to switch the phase voltages E _R , E _S , and E _T input to the fundamental wave processing unit 3, and two of the three phases R, S, and T, or three phases When the state of is measured, the value actually measured is 0 or a value close to 0 as judged from the equations of the effective component I _0A and the invalid component I _OB of the zero-phase current I ₀ obtained by the equations 10 and 11. In this case, each phase is in a balanced state, and the leakage current Igr caused by the ground insulation resistance is almost zero. This state is almost the case in small-scale power distribution systems that are widely used in general. In this state, the value of the zero-phase current I ₀ can be handled as the value of the leakage current Igr.

Next, a specific configuration of the fundamental wave processing unit 3 shown in FIG. 1 will be described with reference to FIG. The fundamental wave processing unit 3 includes a voltage detector 21, a first amplifier 22, a first low-pass filter (LPF) 23, a first RMS converter 28, an I ₀ detector 24, 2 amplifier 25, second low-pass filter (LPF) 26, second effective value converter 29, and phase difference measuring device 27.

In the fundamental wave processing unit 3, the phase voltage E _R , E _S , E _T applied to each phase of R, S, T, which is switched by the switching switch 2, is input to the voltage detector 21. . The first amplifier 22 amplifies each phase voltage E _R , E _S , E _T output from the voltage detector 21 according to the detection sensitivity of the voltage detector 21 until it reaches an appropriate value. The first low-pass filter 23 attenuates the frequency component exceeding the fundamental frequency of each phase voltage E _R , E _S , E _T and extracts the fundamental frequency waveform.

Next, the I ₀ detector 24 takes in the zero phase current I ₀ which is a leakage current flowing through the ground line 8 through the zero phase current transformer 9. The second amplifier 25 amplifies the zero-phase current I ₀ detected by the I ₀ detector 24 to an appropriate amount. The second low-pass filter 26 attenuates the frequency component exceeding the fundamental frequency of the zero-phase current I ₀ amplified by the second amplifier 25 and extracts the fundamental frequency waveform.

Then, the phase difference measuring device 27 measures the phase difference between the reference voltage E input from each phase and the zero phase current I ₀ . Here, FIG. 7 shows the phase difference between the reference voltage E input from each phase and the zero-phase current I ₀ . In the fundamental wave processing unit 3, the first low-pass filter 23 inputs the waveform of the input reference voltage E and the waveform of the zero-phase current I ₀ output from the second low-pass filter 26 to, for example, an operational amplifier zero crossing circuit. Then, as shown in FIG. 7, these output waveforms are Ez for the reference voltage E and Iz for the zero-phase current I ₀ . The peak values of the output waveforms Ez and Iz of the reference voltage E and the zero-phase current I ₀ are made to coincide with each other to obtain the difference. The waveform of the absolute value of the difference is the | Ez-Iz | waveform shown in FIG. As shown in FIG. 7, if the areas of the protruding portions of the | Ez−Iz | waveform and the Iz waveform are S ₁ and S ₂ , respectively, S ₁ is the phase difference angle between the reference voltage E and the zero-phase current I _0. It is proportional to θ, and S ₂ is proportional to the phase difference of 180 degrees. The voltage proportional to S ₁ and S ₂ is output to the calculation unit 14.

Then, the first effective value converter 28 rectifies the fundamental frequency waveform of the reference voltage E into both waves, converts it to an analog value proportional to the effective value, and inputs it to the calculation unit 14. The second effective value converter 29 converts the fundamental frequency waveform of the zero-phase current I ₀ into an analog value converted into an effective value by performing both-wave rectification, and inputs the analog value to the calculation unit 14.

The phase voltages E _R , E _S , and E _T input to the fundamental wave processing unit 3 are sequentially input by switching the switching switch 2 and are measured.

Incidentally, the basic frequency waveforms of the reference voltage E and the zero-phase current I ₀ inputted from each phase are shown in FIG. 7 as if the phase of the zero-phase current I ₀ is delayed from the phase of the reference voltage E. For the same zero-phase current I ₀ , the input reference voltage E is sequentially input to the R, S, and T phases, so that the phase difference changes from 0 degrees to 360 degrees. FIG. 7 shows a case where the phase difference θ from the time when both waveforms have passed through the zero point, that is, the so-called zero crossing is 0 to 180 degrees, and FIG. 8 shows a case where the phase difference θ is 180 to 360 degrees. . When the phase difference θ between the basic frequency of the reference voltage E and the zero-phase current I ₀ shown in FIG. 7 is in the range of 0 to 180 degrees, the phase difference θ is the value immediately after the basic frequency of the zero-phase current I ₀ is zero-crossed. It is determined whether the values of the zero crossing outputs Iz and Ez are “negative” or “positive”, and the phase difference pulse area S ₁ or time t ₁ , half-wave pulse area S ₂ or time t ₂ is input to the calculation unit 14 and calculated from the following formula (12) or formula (13).

θ = 180S ₁ / S ₂ (12)
θ = 180 t ₁ / t ₂ (13)
When the phase difference θ between the basic frequency of the reference voltage E and the zero phase current I ₀ shown in FIG. 8 is in the range of 180 to 360 degrees, the phase difference θ is zero crossing of the basic frequency of the zero phase current I ₀ . The value of the zero crossing outputs Iz and Ez immediately after is determined by being either “positive / negative” or “negative positive”, and the phase difference pulse area S ₃ or time t ₃ , half-wave pulse area S ₂ or time t ₂ is input to the calculation unit 14 and calculated from the following formula (14) or formula (15).

θ = 360−180S ₃ / S ₂ (14)
θ = 360−180t ₃ / t ₂ (15)
In addition, the calculation unit 14 performs calculations of Expressions (16) and (17) shown below using the input zero-phase current I ₀ of the fundamental frequency.

I _0A = I ₀ cos θ (16)
I _0B = I ₀ sin θ (17)
That is, the effective component I _0A and the invalid component I _0B of the zero-phase current I _{0 with} respect to the input reference voltage E of a certain phase are obtained. Then, the values of the effective component I _0A and the invalid component I _OB of the zero-phase current I ₀ for each phase input voltage are obtained from the measured values of the voltages input from the R, S, and T phases. This was R, S, and the measured value I _0RA ~I _0TA active ingredients I _0A in each phase of the input phase T shown in FIG. 5, further, the measured value I _0RB ~I _0TB the reactive component I _0B. These measured values I _{0RA to} I _0TA and measured values I _{0RB to} I _0TB are values corresponding to values obtained from the right side of the calculation formula shown in FIG.

In the leakage current measuring apparatus and measuring method according to the present invention, each of the distribution lines 4 (4 _R , 4 _S , 4 _T ) of the distribution system adopting a three-phase four-wire or three-phase three-wire distribution system. The total of leakage currents Igc _R , Igc _S , and Igc _T flowing in the ground capacitances C _R , C _S , and C _T existing in the phase is three times the commercial power frequency included in the three-phase voltage of the three-phase power source. Measurement is performed using the third-order harmonic phase voltage E ₃ which is the frequency.

In FIG. 1, a measurement capacitor 10 is formed by connecting _three capacitors C _{1 to} C ₃ in a star shape, and a neutral point M thereof is grounded via a measurement switch 11 and a shunt 12. The other terminals of the capacitors C _{1 to} C ₃ are connected to the three-phase terminals R, S, and T. If a three-phase voltage having a fundamental frequency of 50 Hz or 60 Hz is applied to the three capacitors C _{1 to} C ₃ of the measuring capacitor 10, when these capacitors C _{1 to} C ₃ have the same capacitance, the vector sum of their currents Becomes 0, and the current of the fundamental frequency flowing from the neutral point M of the measuring capacitor 10 to the ground point is 0.

The voltage applied to each of the three-phase terminals R, S, T of the measurement capacitor 10 has a phase difference of 120 degrees with respect to the fundamental frequency, but in the third harmonic, this phase difference is 360 times three times 120 degrees. The same phase voltage is applied to each terminal R, S, T. Therefore, the third harmonic current in the same direction flows through the three capacitors C _{1 to} C _3, and the _three capacitors are connected while being grounded from the neutral point M via the measurement switch 11 and the shunt 12. A third harmonic current I _{C3 that} is a sum of current values of C _{1 to} C ₃ flows.

Accordingly, the capacitances of the three capacitors C _{1 to} C ₃ may be different values as long as they are limited to the third harmonic current. If the third harmonic voltage E ₃ of each phase of R, S, T is the same value, and the total value of the capacitance of the measuring capacitor 10 is C ₀ , the total value of the third harmonic current is I _C3 . Therefore, the following equation (18) is obtained.

E ₃ = I _C3 / (2π3fC ₀ ) (18)
Then, the shunt 12 constituted by a resistor converts the third harmonic current I _C3 into a voltage amount, and the third harmonic voltage E ₃ included in the power supply voltages E _R , E _S , E _T of each phase. Is converted to an amount proportional to the input signal and input to the harmonic processing unit 13. Since the resistance value of the resistor constituting the shunt 12 is sufficiently smaller than the reactance value of the measurement capacitor 10, it hardly affects the measurement of the third harmonic current I _C3 .

Here, in order to measure the _third harmonic voltage E ₃ , when the measurement switch 11 is closed, ₃ proportional to the third harmonic voltage E ₃ included in the power supply voltages E _R , E _S and E _T of each phase. A second harmonic current I _C3 flows from the measuring capacitor 10 to the shunt 12.

When the measurement switch 11 is in the open circuit state, the zero-phase current I ₀ is input to the processing arithmetic unit 16 via the zero-phase current transformer 9, but the power supply voltage E supplied to each phase during the zero-phase current I _{0. The} total current I ₀₃ flowing into the ground capacitance 6 caused by the _third harmonic voltage E ₃ included in _{R 1} , E _S and E _T is included, and this current component is also input to the harmonic processing unit 13. The The fundamental wave processing unit 3 processes a fundamental wave that is a commercial frequency included in the zero-phase current I ₀ .

Next, details of the harmonic processing unit 13 in FIG. 1 will be described with reference to FIG. The harmonic processing unit 13 includes an I ₀₃ detector 31 that detects a total current I ₀₃ of the third harmonic current of each phase included in the zero phase current I ₀ , a first amplifier 32, and a first band. A pass filter (BPF) 33, a first effective value converter 34, an Ic ₃ detector 35 for detecting the _third harmonic current Ic ₃ , a second amplifier 36, and a second band pass filter (BPF) 37) and a second effective value converter 38.

The I ₀₃ detector 31 takes in the leakage current I ₀₃ including the fundamental frequency and the third harmonic flowing through the ground line 8 through the zero-phase current transformer 9. The first amplifier 32 amplifies the leakage current I ₀₃ taken in by the I ₀₃ detector 31 to an appropriate amount. The first band pass filter 33 attenuates the frequency exceeding the fundamental frequency and the third harmonic of the leakage current I ₀₃ amplified by the first amplifier 32. The first effective value converter 34 rectifies the current waveform of the third harmonic current I ₀₃ included in the leakage current I ₀ filtered by the first bandpass filter 33, and is proportional to the effective value. An analog value is converted and input to the calculation unit 14.

The I ₀₃ detector 35 takes in the current Ic ₃ including the third harmonic flowing from the measurement capacitor 10 via the shunt 12 to the ground point and including the third harmonic. The second amplifier 36 amplifies the current Ic ₃ including the third harmonic captured by the Ic ₃ detector 35 to an appropriate amount. The second band-pass filter 37 attenuates the frequency exceeding the fundamental wave and the third harmonic of the current Ic ₃ including the third harmonic amplified by the second amplifier 36. The second effective value converter 38 rectifies the current waveform of the current Ic ₃ including the third harmonic filtered by the second bandpass filter 37, and converts it into an analog value proportional to the effective value. Input to the calculation unit 14. Further, the analog value is proportional to the third harmonic voltage E _3, are fed to the processing unit 14 as data for calculating the third harmonic voltage E _3.

The third harmonic voltage E ₃ obtained in the harmonic processing unit 13 having the above-described configuration and the total current I ₀₃ flowing into the ground capacitance 6 due to the _third harmonic voltage E ₃ and the measurement capacitor The total current Ic ₃ is input to the calculation unit 14 as data.

Here, assuming that the ground phase voltage of the fundamental frequency is E, the total current Igc _R + Igc _S + Igc _T flowing in the ground capacitance of each phase at this time is considered to be the fundamental frequency as follows. The calculation unit 14 calculates the value based on the equation (19).

Igc _R + Igc _S + Igc _T = I ₀₃ E / (3E ₃ ) (19)
By substituting the equation (18) into the equation (19), the following equation (20) is obtained.

Igc _R + Igc _S + Igc _T = I ₀₃ · 2πfC ₀ E / Ic ₃ (20)
Obtain the total value of leakage currents Igc _R , Igc _S , and Igc _T due to the ground capacitance of each phase from the total current I ₀₃ flowing into the zero-ground capacitance 6 and the measured capacitor total current Ic _3. Can do.

The effective component I _0A of the zero-phase current I ₀ that is in phase with the reference voltage E that is the commercial frequency input to the star winding 1 and the ineffective component I _0B that is 90 degrees out of phase with the reference voltage E 5 is represented by the formula shown in FIG.

For example, when the phase voltage E _R is applied to the R phase and a fault such as leakage occurs in the R phase, the measured value A of the effective component I _0A of the zero phase current I ₀ is the right side of the following equation (21) The measured value B of the invalid component I _0B corresponds to the value obtained from the right side of the following equation (22).

Measurement A = 0.5√3 (Igc _S −Igc _T ) + Igr (21)
Measurement B = Igc _R −0.5 (Igc _S −Igc _T ) (22)
When the total value of the leakage current flowing in the ground capacitance of each phase is represented by F, this is the same as the measured value obtained by the equations (19) and (20) and is represented by the following equation (23). The

Measurement value F = Igc _R + Igc _S + Igc _T (23)
Here, assuming that the leakage current Igr caused by the ground insulation resistance generated in the R phase is a certain value, the currents Igc _R , Igc _S , and Igc _T flowing in the ground capacitance of each phase are expressed by the above equation (21). ), Formula (22), and formula (23), the following formula (24), formula (25), and formula (26) are obtained.

Igc _R = F / 3 + 2B / 3 (24)
Igc _S = F / 3−B / 3 + A / √3−Igr / √3 (25)
Igc _T = F / 3−B / 3−A / √3 + Igr / √3 (26)
Although the handling of the leakage current Igr caused by the ground insulation resistance will be described later, the currents Igc _R , Igc _S and Igc _T flowing in the ground capacitance for each phase can be obtained in this way.

Similarly, the currents Igc _R , Igc _S , and Igc _T flowing in the ground capacitance for each phase when a fault such as a leakage current occurs in the S phase and the T phase should be obtained in consideration of the relationship shown in FIG. Can do. The equations for obtaining these are shown in FIG.

Then, a failure phase in which a failure such as an electric leakage occurs is determined from the equation shown in FIG. Here, when the unknown leakage current Igr is excluded to form a discriminant and the currents Igc _R , Igc _S , and Igc _T flowing in the ground capacitance for each phase are arranged in this order, F / 3 + 2B / 3, F / 3-B / 3 + A / √3, F / 3−B / 3−A / √3. This is calculated by substituting the actual measurement values, and listed in the order of the above discriminants. The position of the maximum value of the three values is the expression of FIG. 9, for example, when the expression of the input phase R is viewed from the upper line to the lower line direction, it substantially matches the position of the expression including −Igr / √3. It can be seen from the equation of FIG. 9 that the Igr value of the R phase is large at the center position, the S phase is at the right end, and the T phase is large at the left end, regardless of the input phase. If they do not match, an unnatural value is generated in the subsequent calculations. In this case, the position of the next value after the maximum value matches the position of the expression including -Igr / √3.

Next, the leakage current Igc resulting from the ground capacitance for each phase of R, S, and T is obtained. Here, assuming that Igc _R = R, Igc _S = S, and Igc _T = T, when a failure occurs in the R phase, the following formula is obtained from the relationship between the table in FIG. 5 and the following formula (27). (28) is obtained.

I _0A ² + I _OB ² = I ₀ ² ... (27)
I ₀ ² = R (R−S) + S (S−T) + T (T−R)
+ √3 (ST) Igr + Igr ² (28)
Since the equation (28) is a quadratic equation relating to Igr, the following equation (29) is obtained by solving this for Igr.

Igr = {I ₀ ² − ((S−T) (S + 3T) / 4 + R (R−S)
+ T (T−R))} ^1/2 −0.5√3 (S−T) (29)
In a normal power distribution system, it is empirically known that the degree of unbalance of the value of the leakage current Igc due to the ground capacitance of each phase has a maximum value within twice the minimum value. Under this condition, the value of ((S−T) (S + 3T) / 4 + R (R−S) + T (T−R))} ^{1/2 in} the above formula (29) is the electrostatic capacitance of each phase. This value is within 1/5 of the total current flowing in the capacitor (Igc _R + Igc _S + Igc _T ), and is even smaller for the zero-phase current I ₀ , so this value can be ignored. Therefore, Igr at the time of R-phase failure is as shown in the following equation (30).

Igr = I ₀ −0.5√3 (Igc _S −Igc _T ) (30)
Here, the value of Igc _S −Igc _T is within 0.2 times of the measured value F in the degree of the unbalance, and since this is the same for each phase, for example, Igr provisional value = I ₀ -0.17F, and the value obtained by subtracting the Igr provisional value / √3 from the value of the position including −Igr / √3 calculated by the discriminant formula as an Igc approximate value at that position, + Igr / √3 The value obtained by adding the provisional value of Igr / √3 to the value of the position of the expression including the value can be used as the Igc approximate value at that position, and the value without adjustment can be used as the Igc approximate value at that position.

  Next, Igr with minimum error is obtained.

As described above, when an R-phase fault occurs, Igr = I ₀ −0.5√3 (Igc _S −Igc _T ). The Igc approximate value obtained as described above is added to the Igc value of each phase of this equation. substitute.

  That is, when it is determined that the phase having the maximum leakage current Igr is the R phase, Igr with the smallest error is obtained from the following equation (31).

Igr = I ₀ −0.5√3 (Igc _S approximate value−Igc _T approximate value) (31)
When the phase having the maximum leakage current Igr is determined to be the S phase, Igr with the smallest error is obtained from the following equation (32).

Igr = I ₀ −0.5√3 (Igc _T approximate value−Igc _R approximate value) (32)
When the phase having the maximum leakage current Igr is determined to be the T phase, Igr with the minimum error is obtained from the following equation (33).

Igr = I ₀ −0.5√3 (Igc _R approximate value−Igc _S approximate value) (33)
As described above, in the present invention, the leakage current Igr caused by the ground insulation resistance of the electric circuit of the three-phase four-wire distribution system or the electrical equipment connected in a star shape and the leakage current Igc caused by the ground capacitance When measuring the basic measurement data of each phase using the formulas shown in FIGS. 5 and 9, each phase of the three-phase four-wire or three-phase three-wire distribution system and the total It is possible to grasp the value of Igr with reduced errors due to the value of Igc, the unbalanced state, and the ground capacitance, and to know the fault phase having a large value of Igr.

  In addition, as shown in FIG. 10, the leakage current measuring device according to the present invention is provided with a 4-wire circuit breaker 17 (CB) in the middle of the distribution line 4, and the circuit breaker 17 ( It is good also as a structure which controls interruption | blocking of CB). FIG. 10 is a schematic system diagram showing a configuration in which the leakage current measuring device of the present invention is applied to a three-phase four-wire distribution system. In particular, a breaker is provided in the distribution line 4, and the leakage current measuring device controls the breaker. It is a figure which shows a structure. In the case of a three-phase three-wire system, a three-wire circuit breaker is used.

  That is, in the leakage current measuring apparatus having the configuration shown in FIG. 10, when it is determined by control using the calculation unit 14 that the measurement results of Igr and Igc are interrupted, the circuit breaker 17 (CB) is used to connect the distribution line 4 and the load. Shut down facility 5. Thereby, the leakage current measuring apparatus shown in FIG. 8 can protect each phase of the three-phase four-wire distribution circuit and the load equipment from a serious accident due to an insulation failure.

  Furthermore, in the leakage current measuring apparatus according to the present invention, the values of the leakage current Igr caused by the ground insulation resistance and the leakage current Igc caused by the ground capacitance become larger than a predetermined value as a result of the calculation by the calculation unit 14. If it is determined that the alarm has occurred, an alarm may be issued using alarm means such as sound or light emission. By providing such alarm means, it is possible to reliably prevent accidents caused by leakage.

  The leakage current measuring apparatus and measuring method according to the present invention can be applied not only to the above-described three-phase four-wire or three-phase three-wire distribution system but also to any distribution system in which the three-phase voltage is substantially equal to the ground potential. is there. The present invention can also be applied to an apparatus and method for measuring a leakage current flowing from a voltage application portion to a ground portion of an electric device.

  For the purpose of preventing electrical disasters, insulation measurement of distribution systems and electrical equipment is required by law. Conventionally, insulation measurement has been performed in the state of power failure when the supply of power to the distribution system is stopped, but in recent years power failure has been limited, especially star-connected 3-phase 4-wire or 3-phase 3-wire system distribution The system is also a 400V system, which has many important and wide-range loads, and requires detailed and accurate data. The leakage current measuring apparatus and measuring method according to the present invention meet these requirements, and in particular, there are many factories, lighting power, and air conditioning equipment for large capacity power equipment adopting a three-phase four-wire or three-phase three-wire system. Expected to be used in large offices and buildings.

It is a schematic system diagram which shows the structure which applied the leakage current measuring apparatus of this invention to the three-phase four-wire power distribution system. It is a commercial frequency three-phase phase voltage vector diagram. It is a vector diagram of a leakage current calculation value. It is a vector diagram of a leakage current measurement value. Is a list showing the calculation formula for obtaining a value of the active ingredients I _0A and reactive component I _OB of the zero-phase current I ₀ in each phase. It is a figure which shows the specific structure of a basic process part. It is a figure explaining a state when the phase difference of a voltage and an electric current exists in 0-180 degree | times. It is a figure explaining a state when the phase difference of a voltage and an electric current exists in the range of 180-360 degree | times. It is a table | surface which shows the formula which calculates | requires Igc and Igr in each phase. It is a schematic system diagram which shows the structure which applied the leakage current measuring apparatus of this invention to the three-phase four-wire distribution system, and is a figure which shows the structure which provides a circuit breaker especially in a distribution line and a leakage current measuring apparatus controls a circuit breaker. is there.

Explanation of symbols

  1 Low voltage side star winding of 3-phase transformer for power distribution, 2 switching switch, 3 fundamental wave processing unit, 4 distribution line, 5 load equipment, 6 ground capacitance, 7 leakage resistance, 8 ground wire, 9 Zero-phase current transformer, 10 measuring capacitor, 11 measuring switch, 12 shunt, 13 harmonic processing unit, 14 computing unit, 15 display unit, 16 processing computing unit, 17 circuit breaker

Claims (10)

Measures leakage current Igr caused by ground insulation resistance and electrical current of the electrical circuit or electrical equipment of the three-phase three-wire system or three-phase four-wire power distribution system in which the power supply is connected in a star shape, and leakage current Igc caused by the ground capacitance In the leakage current measuring device,
A measurement circuit that connects three sets of capacitors in a star shape and grounds the neutral point via a ground wire;
Due to the _third harmonic phase voltage E3, which is three times the power commercial frequency included in the three-phase voltage of the three-phase power supply of the three-phase three-wire or three-phase four-wire distribution system, The value of the third harmonic phase voltage E ₃ is calculated from the value Ic ₃ of the third harmonic current flowing through the grounding wire and the capacitance value of the three sets of capacitors. The value of the ground capacitance of the total of the three phases calculated from the value of the _third harmonic current included in the zero phase current I ₀ which is the vector sum of the flowing currents and the value of the third harmonic phase voltage E ₃ From the value of the three-phase voltage, the value of the total leakage current (Igc _R + Igc _S + Igc _T ) of the R-phase, S-phase, and T-phase caused by the ground capacitance at the commercial power frequency is measured. Harmonic processing means;
A three-phase voltage of the commercial power frequency is input, and the zero-phase current I ₀ is converted into a component I _{0A in the} same phase direction as the input voltage of any one of the three phases, and a component perpendicular to the input voltage. Based on the current value obtained by decomposition into I _0B , the zero-phase current I _0, and the total leakage current (Igc _R + Igc _S + Igc _T ), Of calculating leakage currents Igc _R , Igc _S , and Igc _T, a value in which the error of leakage current Igr caused by ground insulation resistance is minimized, and a phase in which the value of leakage current Igr is maximized And a leakage current measuring device. The calculation means includes a component in the same phase direction as the input voltage for two phases of the three-phase voltage of the three-phase power supply, and a component in a direction perpendicular to the input voltage for two phases of the three-phase voltage. when the value is zero or substantially zero, the leakage current of claim 1, wherein the output value of the power supply the commercial frequency component included in the zero-phase current I ₀ as the leakage current Igr resulting from the ground insulation resistance Measuring device. The calculation means sets the measured value of the component I _{0A in} the same phase direction as the input voltage of any one of the three phases to A, and the component I _{0B in the} direction perpendicular to the input voltage of the phase where the measured value A is measured. If the measured value of the three-phase total leakage current (Igc _R + Igc _S + Igc _T ) caused by the capacitance to ground is F, the following formula (1) to formula (3) Substituting the actual measurement values, find the values by each formula,
F / 3 + 2B / 3 (1)
F / 3−B / 3 + A / √3 (2)
F / 3-B / 3-A / √3 (3)
From the measured value of the zero-phase current I ₀ and the measured value F, a provisional value Igr ′ of the leakage current Igr is calculated, and a value obtained by dividing the provisional value Igr ′ by √3 is a value x,
Of the values obtained from the equations (1) to (3), when the value of the equation (1) is the maximum, the value obtained by subtracting the value x from the value of the equation (1) is D11, The value obtained by adding the value x to the value of (2) is D22, the value of equation (3) is D3, and when the value of D11 is larger than the value of D22, the T-phase leakage current Igr is maximum. Determination, and the values of D11, D22, and D3 are approximate values of leakage currents Igc _R , Igc _S , and Igc _T caused by the R-phase, S-phase, and T-phase ground capacitances, respectively,
When the value of D11 is smaller than the value of D22, it is determined that the R-phase leakage current Igr is maximum, the value of the equation (1) is set to D1, and the value x from the value of the equation (2) is determined. The value obtained by subtracting D is D21, the value obtained by adding the value x to the value of Equation (3) is D32, and the values of D1, D21, and D32 are caused by the ground capacitance of the R phase, S phase, and T phase, respectively. Leakage currents Igc _R , Igc _S , and Igc _T approximate values and none,
Among the values obtained from the equations (1) to (3), when the value of the equation (2) is the maximum and the value of D21 is larger than the value of D32, the leakage current Igr of the R phase is It is determined that the value is maximum, and the values of D1, D21, and D32 are not approximate values of leakage currents Igc _R , Igc _S , and Igc _T caused by the R-phase, S-phase, and T-phase ground capacitances, respectively. ,
When the value of D21 is smaller than the value of D32, it is determined that the S-phase leakage current Igr is the maximum, and the value obtained by subtracting the value x from the value of the equation (3) is D31, and the equation (2) ) Is D2, the value obtained by adding the value x to the value of the equation (1) is D12, and the values of D12, D2, and D31 are caused by the ground capacitance of the R phase, S phase, and T phase, respectively. Leakage currents Igc _R , Igc _S , and Igc _T approximate values and none,
Among the values obtained from Equation (1) to Equation (3), when the value of Equation (3) is the maximum, and when the value of D31 is greater than the value of D12, the leakage current of the S phase It is determined that Igr is the maximum, and the values of D12, D2, and D31 are approximate values of leakage currents Igc _R , Igc _S , and Igc _T caused by the R-phase, S-phase, and T-phase ground capacitances, respectively. And none,
When the value of D31 is smaller than the value of D12, it is determined that the T-phase leakage current Igr is maximum, and the values of D11, D22, and D3 are set to R, S, and T, respectively. 2. The leakage current measuring device according to claim 1, wherein the leakage current measuring device is an approximate value of leakage currents Igc _R , Igc _S , and Igc _T caused by ground capacitance. The computing means is
When the phase in which the value of the leakage current Igr caused by the ground insulation resistance is maximum is determined as the R phase, the leakage current Igr with the smallest error is
Igr = I ₀ −0.5√3 (approximate value of leakage current Igc _S of S phase−approximate value of leakage current Igc _T of T phase)
When the phase in which the value of the leakage current Igr caused by the ground insulation resistance is the maximum is determined to be the S phase, the leakage current Igr with the smallest error is
Igr = I ₀ −0.5√3 (approximate value of T-phase leakage current Igc _T− approximate value of R-phase leakage current Igc _R )
When it is determined that the phase in which the value of the leakage current Igr caused by the ground insulation resistance is the maximum is the T phase, the leakage current Igr with the minimum error is
4. The leakage current measurement according to claim 3, wherein the output is Igr = I ₀ −0.5√3 (approximate value of R-phase leakage current Igc _R− approximate value of S-phase leakage current Igc _S ). apparatus.   The leakage current measuring apparatus further includes a display unit, and the display unit displays a result calculated by the calculation unit. Leakage current measuring device.   6. The leakage current measuring apparatus according to claim 5, wherein the display means displays a phase in which the leakage current Igr caused by the ground insulation resistance output from the arithmetic means is maximized.   7. The leakage current measuring apparatus according to claim 1, further comprising alarm means for issuing an alarm when any of the values obtained by the computing means exceeds a predetermined value. The leakage current measuring device described in 1.   8. The leakage current measuring apparatus according to claim 1, further comprising a blocking means for cutting off the electric circuit when any of the values obtained by the calculating means exceeds a predetermined value. The leakage current measuring apparatus according to 1. Measures leakage current Igr caused by ground insulation resistance and electrical current of the electrical circuit or electrical equipment of the three-phase three-wire system or three-phase four-wire power distribution system in which the power supply is connected in a star shape, and leakage current Igc caused by the ground capacitance A leakage current measuring method,
It has a measurement circuit that connects three sets of capacitors in a star shape and grounds the neutral point via a ground wire.
Due to the _third harmonic phase voltage E3, which is three times the power commercial frequency included in the three-phase voltage of the three-phase power supply of the three-phase three-wire or three-phase four-wire distribution system, The value of the third harmonic phase voltage E ₃ is calculated from the value Ic ₃ of the third harmonic current flowing through the grounding wire and the capacitance value of the three sets of capacitors. The value of the ground capacitance of the total of the three phases calculated from the value of the _third harmonic current included in the zero phase current I ₀ which is the vector sum of the flowing currents and the value of the third harmonic phase voltage E ₃ From the value of the three-phase voltage, the value of the total leakage current (Igc _R + Igc _S + Igc _T ) of the R-phase, S-phase, and T-phase caused by the ground capacitance at the commercial power frequency is measured. Harmonic processing step;
A three-phase voltage of the commercial power frequency is input, and the zero-phase current I ₀ is converted into a component I _{0A in the} same phase direction as the input voltage of any one of the three phases, and a component perpendicular to the input voltage. Based on the current value obtained by decomposition into I _0B , the zero-phase current I _0, and the total leakage current (Igc _R + Igc _S + Igc _T ), Of calculating leakage currents Igc _R , Igc _S , and Igc _T, a value in which the error of leakage current Igr caused by ground insulation resistance is minimized, and a phase in which the value of leakage current Igr is maximized And a step of measuring a leakage current. The calculation step includes a component in the same phase direction as the input voltage for two phases of the three-phase voltage of the three-phase power supply, and a component in a direction perpendicular to the input voltage for two phases of the three-phase voltage. when the value is zero or substantially zero, the leakage current of claim 1, wherein the output value of the power supply the commercial frequency component included in the zero-phase current I ₀ as the leakage current Igr resulting from the ground insulation resistance Measuring method.

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