JP2011153913A - Leak current measuring device and measurement method in electric apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To precisely detect a leak current Igr flowing through a switching power supply and insulation resistance between a voltage application part of a load device connected to the switching power supply to a grounding part. <P>SOLUTION: A processing calculation part 16 is equipped with: a signal processing part 3; and a calculation part 14. The signal processing part 3 performs signal processing of one of line voltages E<SB>VU</SB>, E<SB>WV</SB>, E<SB>UW</SB>generated between power supply outputs U, V, W of a switching power supply or one of line voltages E<SB>SR</SB>, E<SB>TS</SB>, E<SB>RT</SB>of a distribution power supply or a line voltage of single-phase distribution line, and a zero-phase current I<SB>0</SB>detected by a zero-phase current transformer 9 as a vector sum of currents flowing from the distribution power supply to a load device 5 through the switching power supply, and also performs the signal processing by measuring a phase difference between an input voltage and the zero-phase current I<SB>0</SB>. The calculation part 14 calculates a phase angle θ relative to the input voltage of the zero-phase current I<SB>0</SB>, calculates active and reactive components A and B to the input voltage on the basis of the phase angle θ and the value of the zero-phase current I<SB>0</SB>, and calculates the value of the leak current Igr of the sum of respective phases excluding the sound one phase flowing through the ground leak resistances ru, rv, rw on the basis of the effective value. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a switching power supply such as an inverter connected to a distribution power supply and a leakage current measuring apparatus and a measuring method for measuring a leakage current flowing from a voltage application portion to a ground portion of a load device connected to the switching power supply.

  2. Description of the Related Art Conventionally, as a method for examining the insulation state of an electric circuit and an electrical device, a method in which a part to be measured is cut off and measured with an insulation resistance meter 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 particular, when measuring leakage current in load devices such as electric motors and fluorescent lamps driven by switching power supplies such as inverters, switching power supplies such as inverters composed of electronic elements are protected from high voltages applied during insulation resistance measurement. Therefore, it is necessary to measure only the load device, and much time and effort are required for the power failure procedure, the opening of the connection, and the reconnection. As a result, the line stop time is limited in a continuous operation factory or the like, and there is a problem that application of the insulation resistance meter is limited.

Therefore, a technique for examining the insulation state of the electric circuit and the load device without changing the power supply connected to the power source without causing a power failure has been proposed and used. As this type of technology, there is a technique in which a zero-phase current transformer is used to detect a zero-phase current I ₀ that is a current flowing from the voltage application portion of the electric circuit and the load device to the ground portion. The zero-phase current I ₀ detected by the zero-phase current transformer is a leakage current Igr that flows through an insulation resistance between the voltage application portion and the ground portion of the circuit and load device, and between the voltage application portion and the ground portion. It consists of a vector sum with a leakage current Igc that flows through a ground capacitance that normally exists.

Among these technologies, the technology for measuring the leakage current Igr that has been put into practical use in the power distribution system in which one of the 200 V class three-phase three wires currently in practical use is grounded is a common power distribution system. Although measurement is possible, measurement in a switching power supply and its load device is impossible. Further, the method of detecting only the zero-phase current I ₀ is excessive with respect to the actual value of Igr when the leakage current Igc that flows through the ground capacitance that normally exists between the voltage application portion and the ground portion is large. The measured value is shown.

This is because in a load device driven by a switching power supply such as an inverter, the voltage applied to the device and its frequency change, and three sets of windings on the distribution power supply side of the three-phase distribution transformer are triangular. Or, two sets of windings are connected in a V shape and the ends or middle points of the windings are grounded, and the ground voltage of each distribution line is not equal. In addition to the voltage of the change frequency, the voltage becomes a complex voltage waveform including the voltage of the distribution line frequency and the harmonic component voltage generated due to the state where the ground voltage of each distribution line is not equal. The zero-phase current I ₀ resulting from the voltage has a complicated waveform. In addition, the leakage current Igr flowing through the ground insulation resistance of these switching power supplies and load devices is often less than several mA because, for example, many robots and dedicated motors used in production sites have relatively small capacities. It makes measurement of leakage current of switching power supply and its load device difficult.

  As another method of measuring the insulation state, there is a method of measuring the leakage current Igr by supplying a low voltage with a low frequency to the distribution line. Also in this method, the supplied low frequency low voltage is absorbed by the rectification portion of the switching power supply, and the switching power supply and its load device cannot be measured.

  In addition, there exist some which are described in Unexamined-Japanese-Patent No. 3-179271 (patent document 1) and Unexamined-Japanese-Patent No. 2002-125313 (patent document 2) as a prior art of this kind of leakage current measurement.

JP-A-3-179271 JP 2002-125313 A

  The present invention provides a switching power source such as an inverter connected to a distribution power source in which a secondary winding of a transformer is connected in a star shape and a load device fed from the switching power source to a grounding portion through a ground insulation resistance. It is an object of the present invention to provide a leakage current measuring device and a method for measuring the leakage current that can detect a flowing leakage current Igr in an operating state.

By the way, the switching power supply generates a changing voltage and frequency (hereinafter referred to as an operation frequency) for operating the load device. The line voltage between the terminals of the switching power supply is substantially sinusoidal, but the ground voltage includes many harmonics, and in particular, the ground voltage of the distribution line supplying power to the switching power supply is not the same, for example, neutral The voltage to the ground of the switching power supply connected to the single-phase two-wire distribution line fed from either the point or the three-phase terminal includes the voltage of the distribution power supply frequency (hereinafter referred to as the commercial frequency) and harmonics in addition to the voltage of the operating frequency The voltage of the ground leakage current I ₀ caused by these ground voltages also shows a complicated shape. In the conventional method, the switching power supply and the load device are connected via the insulation resistance between the voltage application portion and the ground portion. It is considered impossible to measure the leakage current Igr that flows through.

Therefore, the technical problem of the present invention is to clarify the behaviors of these complicated various voltages and leakage currents I ₀ , and to make the measuring apparatus and measuring method concrete and put them into practical use.

  In addition, the technical problem of the present invention is to adopt a complicated method in which the ground voltage of each phase including a large amount of harmonics output from the switching power source is sequentially switched and input by a switch when inputting voltage elements for measurement. Adopting a method of inputting only one line voltage of the line voltage on the input side or output side of the switching power supply whose waveform is almost sine wave, from the distribution power supply to the switching power supply and its load device, grounding It is an object of the present invention to provide a leakage current measuring device and a measuring method capable of measuring a leakage current flowing through a wire at any portion flowing through the wire.

More specifically, the technical problem of the present invention will be described. In a leakage current measuring apparatus such as a leakage breaker conventionally used connected to a three-phase distribution line in which the ground voltage is equal in three phases and the ground capacitance is equal, When the leakage current Igr flowing through the ground insulation resistance exists only in one phase of the load device, the value of the zero-phase current I ₀ can be used as the value of the leakage current Igr. When Igr is generated in two phases, the leakage currents of the two phases are 120 degrees different from each other, so the value is not doubled and only the value of the leakage current Igr for one phase synthesized by the vector is shown. . Also, when the electrical equipment connected to this electrical system is connected across three wires, for example, when the center point between the two phases of the winding of the motor is grounded, the ground voltage at this center point is the three-phase terminal U , V and W are half of the ground voltage, and the leakage current Igr is also half of the ground fault at the three-phase terminal through the same ground leakage resistance. In the leakage current measuring apparatus, it was evaluated that the insulation state was good against the ground leakage resistance. As a result, the determination of the insulation state is wrong, and failure to take measures against insulation can lead to a serious failure.

  Therefore, the technical problem of the present invention is that the leakage current measuring device such as a leakage breaker that has been used in the past, which underestimates the value of the leakage current Igr generated between the two phases of the load device or the phase, has a problem. It is an object of the present invention to provide a leakage current measuring apparatus and a measuring method capable of accurately measuring the value of ground leakage resistance Igr as an actual value.

The present invention proposed to solve the above technical problem is that the secondary side winding of the transformer is connected in a star shape, the three-phase voltage terminals are R, S, T, and the star connection A three-phase four-wire system or a three-phase three-wire distribution line fed from a power source having a grounded neutral point N or a single unit fed from either the neutral point N and the terminals R, S, and T In the leakage current measuring device for measuring the leakage current Igr caused by the ground insulation resistance of the switching power supply connected to the phase 2-wire distribution line and the load device connected to the switching power supply, each terminal R of the secondary winding , S, T, line voltages E _SR , E _TS , E _RT or neutral point N and single-phase voltages E _R , E _S , E _T generated between the terminals R, S, _T and the above switching each output terminal U of the power supply, V, line voltage generated between W E _VU, E _WV, voltage measure either E _UW And detecting means, a zero-phase current detecting means for detecting a zero-phase current I ₀ is the vector sum of the currents flowing through the distribution line and the load connected to the switching power supply and the switching power supply, detected by said voltage detecting means The line voltages E _SR , E _TS , E _RT or the single-phase voltages E _R , E _S , E _T and the line voltages E _VU , E _WV , E generated between the switching power supply terminals U, V, W Any one of _UW is input, and any of the input line voltages E _SR , E _TS , E _RT or single-phase voltages E _R , E _S , E _T and between the switching power supply terminals U, V, W The phase comparison means for comparing any of the line voltages E _VU , E _WV , E _UW generated at the reference voltage and comparing the phase of the reference voltage with the zero-phase current I ₀ , The above zero-phase current I0 is calculated as follows: Reactive component B to determine the separate measured values, the respective terminals R, S, line voltage generated between _{T E SR, E TS, E} RT or single-phase voltage E _R, E _S, E _T and the switching to The effective component A of the zero-phase current I ₀ obtained when any of the line voltages E _VU , E _WV , E _UW generated between the power terminals U, V, W is used as a reference voltage and Based on the reactive component B having a phase difference, the total value of the leakage current Igr generated in two phases of the U phase, the V phase, and the W phase, and one phase of the U phase, the V phase, and the W phase Computation means for computing the value of the leakage current Igr generated and the value of the leakage current Igr generated inside the load device connected between two or three phases of the U phase, V phase and W phase. .

The output of the switching power supply The line voltages E _VU , E _WV , E _UW generated between the terminals U, V, W or the three-phase power supply lines R, S, T connecting the distribution power supply and the switching power supply When any one of the line voltages E _SR , E _TS , E _RT or the line voltage of the single-phase distribution line is used as a reference voltage, a phase comparison between the reference voltage and the zero-phase current I ₀ is performed, and the leakage Calculation of the current Igr is performed.

More specifically, the calculation means is more specifically a line voltage E _VU , E _WV , E _UW generated between the terminals U, V, W or a line between the feed lines R, S, T. When one of the voltages E _SR , E _TS , E _RT or the line voltage of the single-phase distribution line is used as a reference voltage, the value of the formula (B−√3A), the value of the formula (B + √3A), the formula (−2B ) Is calculated as the leakage current Igr caused by the ground insulation resistance of the load device connected to the U, V, and W terminals including the switching power supply. .

  The leakage current measuring apparatus according to the present invention preferably includes display means and displays the result calculated by the calculation means on the display means for notification.

  Furthermore, the leakage current measuring apparatus according to the present invention includes an alarm unit, and when the value of the leakage current Igr obtained by the calculation unit exceeds a predetermined value, an alarm is issued from the alarm unit, whereby the leakage current It can be notified that the value of Igr has exceeded a predetermined value.

  Furthermore, the leakage current measuring apparatus according to the present invention further includes a breaking means, and when the value of the leakage current Igr calculated by the computing means exceeds a predetermined value, the breaking circuit cuts off the electric circuit. Make it possible.

The present invention also provides a power supply in which the secondary winding of the transformer is connected in a star shape, the three-phase voltage terminals are R, S, T, and the neutral point of the star connection is N. A switching power supply connected to a three-phase four-wire distribution line or a three-phase three-wire distribution line to be fed or a single-phase two-line distribution line fed from one of the neutral points N and terminals R, S, and T In the leakage current measuring method for measuring the leakage current Igr caused by the ground insulation resistance of the load device connected to the switching power supply, a line voltage E generated between the terminals R, S, and T of the secondary winding is described. _SR , E _TS , E _RT or neutral point N and the single-phase voltages E _R , E _S , E _T generated between the terminals R, S, _T and the output terminals U, V, W of the switching power supply line voltage E _VU generated, E _WV, a voltage detection step for detecting either the E _UW, and the distribution line and the switching power supply Serial switching and zero-phase current detection step power is the connection for detecting a zero-phase current I ₀ is the vector sum of the currents flowing through the load device, the voltage detected by the detecting means the above line voltage E _SR, E _{TS, ERT} or single-phase voltages E _R , E _S , E _T and any of line voltages E _VU , E _WV , E _UW generated between the switching power supply terminals U, V, W are input and input as described above. One of the line voltages E _SR , E _TS , E _RT or the single-phase voltages E _R , E _S , E _T and the line voltages E _VU , E _WV generated between the switching power supply terminals U, V, W , _EUW as a reference voltage, a phase comparison step of comparing the phase of this reference voltage with the zero-phase current I _0, and the zero-phase current I ₀ with respect to the reference voltage And the measurement value separated into the reactive component B having a phase difference perpendicular to this, Each terminal R, S, line voltage generated between T E _SR, E _TS, the line generated E _RT or single-phase voltage E _R, E _S, E _T and the switching power supply the terminals U, V, between W Based on the effective component A of the zero-phase current I ₀ obtained when any of the inter-voltages E _VU , E _WV , and E _UW is used as a reference voltage, and the reactive component B having a phase difference perpendicular thereto, U The total value of the leakage current Igr generated in two of the phase, V phase, and W phase, the value of the leakage current Igr generated in one of the U phase, V phase, and W phase, U phase, V And a calculation step of calculating the value of the leakage current Igr generated in the load device connected between two or three phases of the W phase and the W phase.

The output of the switching power supply The line voltages E _VU , E _WV , E _UW generated between the terminals U, V, W or the three-phase power supply lines R, S, T connecting the distribution power supply and the switching power supply When any one of the line voltages E _SR , E _TS , E _RT or the line voltage of the single-phase distribution line is used as a reference voltage, a phase comparison between the reference voltage and the zero-phase current I ₀ is performed, and the leakage Calculation of the current Igr is performed.

In this case, the calculation step more specifically includes line voltages E _VU , E _WV , E _UW generated between the terminals U, V, W, or between the power supply lines R, S, T. When one of the voltages E _SR , E _TS , E _RT or the line voltage of the single-phase distribution line is used as a reference voltage, the value of the formula (B−√3A), the value of the formula (B + √3A), the formula (−2B ) Is calculated as the leakage current Igr caused by the ground insulation resistance of the load device connected to the U, V, and W terminals including the switching power supply. .

  As described above, the present invention makes it possible to measure the leakage current Igr flowing through the insulation resistance between the voltage application portion and the ground portion of the load device connected to the switching power supply and the switching power supply, which has been impossible in the past, Moreover, it is possible to monitor the insulation of the switching power supply and its load device connected to the three-phase and single-phase distribution lines of the three-phase four-wire star distribution system, which is an internationally standard distribution system.

Furthermore, in the interruption device that detects the leakage current Igr value that has been conventionally used as the value of the zero-phase current I ₀ and interrupts the electric circuit, it exists between the voltage application part and the grounding part of the electric circuit or load device. In anticipation of an increase in leakage current Io due to an increase in non-uniform capacitance to ground and an increase in harmonic components contained in the zero-phase current I ₀ due to an increase in the capacity of the switching power supply, the zero-phase current I The fault operating current of the earth leakage circuit breaker that operates by detecting ₀ is set to an excessive value, for example, several hundred mA. However, in the present invention, the leakage current Igr as described above can be detected, and the fault operation is performed. Reflecting this value when setting the current value, for example, by setting it to several mA, the earth leakage breaker can be operated before the accident expands due to an excessive failure current in the non-operation range. Safely, power system and Allowing protection of the load is, it is possible to reduce the accidental leakage accident.

  In addition, the present invention measures the leakage current Igr caused by the grounding resistance of the switching power supply and its load device connected to the distribution power supply or the single-phase distribution power supply in which the secondary winding of the transformer is connected in a star shape. At this time, since it is possible to measure the leakage current Igr by inputting a line voltage that does not require a ground terminal for voltage input, it is possible to reliably measure even the end portion of the distribution system lacking the ground terminal. is there.

  Further, by adopting the leakage current measuring device or method according to the present invention, the leakage current of the switching power supply and its load device can be input by inputting the zero-phase current and the line voltage of the distribution line supplying power to the switching power supply. Igr can be measured, and multiple switching power supplies connected in parallel to the terminal side from the place where the zero-phase current and line voltage of the distribution line supplying power to the switching power supply are input, and the collective monitoring of the load devices Is possible.

  In particular, the leakage current measuring apparatus and method according to the present invention includes a collective monitoring of weak leakage of an entire automatic device such as a robot driven by a plurality of servo motors, a collective monitoring of a load device such as an inverter air conditioner in a building, The present invention is suitable for applications such as batch monitoring of a plurality of inverter-lit fluorescent lamps.

  And, among the load devices of the switching power supply described above, the measured value of the ground fault current that occurs in the case of a leakage failure inside the load connected between two or three phases has been measured as an excessively small value in the past. Since this is measured as an appropriate value corresponding to the value of the leakage current Igr caused by the ground insulation resistance, the leakage current Igr caused by the ground insulation resistance can be measured with high reliability, and a leakage accident can be prevented with high reliability. It becomes possible to do.

  Furthermore, according to the present invention, since the result calculated by the calculation means is displayed on the display means, the load state of the switching power supply can be constantly monitored.

  Furthermore, according to the present invention, since the alarm means is provided, the fact that the leakage current Igr is in an abnormal state can be notified by an alarm such as a sound, so that an accident can be prevented.

A switching power source connected to a three-phase star power source in which the secondary winding of the transformer is connected in a star shape, and a leakage current measuring device according to the present invention for measuring a leakage current Igr of a load device connected to the power source. It is a schematic system diagram which shows the applied structural example. Leakage current measurement according to the present invention for measuring leakage current Igr of a switching power supply for a three-phase distribution line connected to a three-phase four-wire star power supply, a switching power supply for a single-phase distribution line, and a load device connected to these power supplies It is a schematic system diagram which shows the structural example to which an apparatus is applied. When the ground voltage E _R , E _S , E _T , line voltage E _SR , E _TS , E _RT and neutral point N, ground voltage E _R of the three-phase star power source system are used as a single-phase distribution power source FIG. 4 is a vector diagram showing a relationship between an electrical neutral point Ns, its ground voltage E _Ns , and a ground pole G. Operating phase voltages E _U , E _V , E _W generated by the switching power supply connected to the single-phase distribution line N, R phase of the star-shaped power supply system, the electrical neutral point Ne, the grounding pole G, and the electrical neutral point FIG. 6 is a vector diagram showing the relationship between a ground point G of Ne and a potential E _Ns from a neutral point N of the same potential. The operating phase voltages E _U , E _V , E _W generated by the switching power supply, the line voltages E _VU , E _WV , E _UW with respect to their electrical neutral point Ne, and the potential with respect to the ground electrode G of the electrical neutral point Ne. It is an equivalent circuit diagram which shows the relationship between En and a load apparatus. Phase voltages E _U , E _V , E _W , line voltages E _VU , E _WV , E _UW , electric potential En with respect to the ground pole G of the electric neutral point Ne, and load it is a vector diagram showing the relationship between the voltage E _NM for electrically neutral Ne of the central point M. FIG. 6 is a diagram illustrating an example of a ground voltage waveform of a switching power supply output terminal, in which a commercial frequency is 60 Hz and an operation frequency is 20 to 50 Hz. Zero-phase current I ₀ , line voltages E _SR , E _TS , E _RT input as reference voltages, line voltages E _VU , E _WV , E _UW , and single-phase voltages E _R , E _S , E _T , phase angle theta, the active ingredient a of the zero-phase current I _0, is a vector diagram showing the relationship between the reactive component B of the zero-phase current I _0. The waveform of the input voltage E and the zero-phase current I ₀ of the phase difference θ at some point, is a diagram showing the relationship between the output waveform of the zero crossing circuit for phase determination. It is a block diagram which shows the detail of the signal processing part which comprises the leakage current measuring apparatus which concerns on this invention. FIG. 2 is a configuration diagram showing a leakage current measuring device according to the present invention having a configuration in which a plurality of switching power supplies and their load devices are monitored by one leakage current measuring device according to the present invention and a circuit breaker and an alarm device are controlled. .

  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 shows a star shape in which the low-voltage three-phase winding 1 of the distribution transformer is connected in a star shape, and the neutral point N, which is the center point of the star shape, is grounded by the grounding pole G via the grounding wire 8 It is a schematic system diagram which shows the example which applied the leakage current measuring apparatus which concerns on this invention to the power distribution system which employ | adopted the power distribution system.

  The star distribution system is a 400V class three-phase three-wire system as shown in Fig. 1, or a neutral wire connected to the neutral point N of the star winding is added as one line of the distribution line. There is also a three-phase four-wire system that can distribute power even to a single-phase load connected between the neutral point N and each of the three-phase terminals, and is widely spread as an international standard distribution system.

  A leakage current measuring apparatus according to the present invention is a main element constituting the star-shaped three-phase three-wire or three-phase four-wire distribution system, and is a three-phase distribution line (hereinafter referred to as a three-phase distribution line and a three-phase distribution line). Single-phase 2 in which the ground voltage of one line derived from either a grounded neutral point of a three-phase four-wire distribution system or a three-phase terminal is 0 and the ground voltage of the other line is a phase voltage. The leakage power Igr caused by the ground insulation resistance of the switching power supply connected to the line distribution line (hereinafter referred to as single-phase distribution line) and the load device 5 of the switching power supply is measured.

The leakage current measuring apparatus according to the present invention is applied to a distribution system employing a three-phase three-wire or three-phase four-wire star distribution system. In the three-phase three-wire power distribution system shown in FIG. 1, a winding 1 connected in a star shape is provided on the low-voltage side (secondary side) of the three-phase transformer for power distribution. A switching power supply 2 is connected to the star winding 1 via three-phase distribution lines 4 _R , 4 _S , 4 _T. Further, in the power distribution system of the three-phase four-wire as shown in FIG. 2, three-phase distribution lines 4 _R, 4 _S, 4 _T other neutral N ground line 4 _N derived from that shown in FIG. 1 is installed together, the three-phase distribution One of the wires 4 _R , 4 _S , and 4 _T , for example, the single-phase distribution wires 4 _N and 4 _R are configured together with the distribution wire 4 _R , and the switching power supply 2 s is connected thereto.

The star winding 1 on the low-voltage side of the three-phase transformer adopting the three-phase three-wire distribution system shown in FIG. 1 will be described in more detail. The star winding 1 is connected to form a star shape. The three-phase terminals R, S, and T, which are one terminals of the windings 1a, 1b, and 1c, are connected to the three-phase distribution lines 4 _R , 4 _S , 4 It is connected to the switching power supply 2 via _T. Further, the other ends of the windings 1a, 1b, and 1c are connected in common to form a neutral point N. In the winding 1a, a phase voltage E _R that is a potential of the terminal R with respect to the neutral point N is generated. A phase voltage E _S that is the potential of the terminal S with respect to the neutral point N is generated on the line 1b, and a phase voltage E _T that is a potential of the terminal T with respect to the neutral point N is generated on the winding 1c. , S, and T generate line voltages _ESR , _ETS , and _ERT .

  The relationship between these voltages is represented by the vector diagram of FIG. 3, where the electrical neutral point, which is the neutral point of the potential of the terminals R, S, and T, is the center of gravity of the triangle RST. Matches the neutral point N that is commonly connected. The neutral point N is connected to the ground electrode G through the ground wire 8.

Further, the line voltage of the single-phase distribution line shown in FIG. 2 is the phase voltage E _R , and its electric neutral point is an intermediate point Ns between the neutral point N and the terminal R, and this electric neutral point The potential of _Ns with respect to the ground point N is represented by a vector E _Ns , whose magnitude is 1/2 of the phase voltage E _R and has a commercial frequency.

In the power distribution system shown in FIG. 2, the line voltages E _SR , E _TS , E _RT or phase voltages E _R , E _S , E _{T applied} to the switching power supply 2 or 2 s are temporarily generated inside the switching power supply 2 or 2 s. An alternating current waveform that is converted to direct current, and that has a pulse-like waveform that is cut at a high cycle by a switching element such as a transistor, and this is combined to generate an operating frequency and voltage suitable for the operation of the load device connected to it. Is converted to If the load device is a device that requires magnetic flux, such as an electric motor, for example, a switching power supply having a so-called variable voltage variable frequency characteristic (hereinafter referred to as a VVVF characteristic) having a characteristic that the generated voltage also decreases as the operating frequency decreases. It becomes. The generated voltage of the switching power supply is a combination of pulse-like waveforms and includes harmonics of various frequencies. The line voltages E _VU , E _VW , E _UW generated between the terminals U, V, W of the switching power supply 2 or 2 s are applied to the load device 5.

Next, the state of the voltage generated in the switching power supply 2 or 2s is shown in FIG. 5, and the relationship between these voltages is shown in the vector diagram of FIG. Since the internal circuit of the switching power supply 2 or 2s is not grounded, the grounding pole G shown in FIG. 5 is handled as the grounding pole G connected to the grounded S-phase or midpoint N of the distribution transformer terminal. In the vector diagram of FIG. 6 showing the relationship between the voltages generated in the switching power supply 2 or 2s, the electrical neutral point Ne of the potential at the terminals U, V, W is the center of gravity of the triangle UVW, and the terminals U, The potentials at V and W are the phase voltages E _U , E _V and E _W , and their magnitudes are 1/3 of the line voltages E _VU , E _WV and E _UW between the terminals U, V and W, Symmetric power supplies with VVVF characteristics, each having a phase difference of 120 degrees.

In FIG. 5 and FIG. 6, if the electrical neutral point of the terminals U, V, W of the switching power supply 2 connected to the three-phase distribution line is Ne, the potential of the neutral point N of the star winding 1 shown in FIG. Is the electrical neutral point of the terminals R, S, T and the same potential as the neutral point N of the star winding, and the neutral point N is grounded by the ground electrode G. The electrical neutral point Ne of the terminals U, V, and W is also 0 potential, which is the same potential as the ground electrode G, and the potential En of the electrical neutral point Ne with respect to the ground electrode G shown in FIG. However, since the voltage En exists with respect to the harmonic voltage associated with the switching operation of the switching power supply 2, the ground voltage at the terminals U, V, and W becomes a composite voltage of the harmonic and the operating frequency, and this complex waveform ground Measurement is difficult if voltage is input, but the line voltages E _VU , E _WV , and E _UW of the terminals U, V, and W are sine waves having VVVF characteristics, and the leakage measuring apparatus and method according to the present invention are described below. Since these voltages are input, measurement is possible.

The electrical neutral point of the single-phase distribution line shown in FIG. 2 is an intermediate point Ns between the neutral point N and the terminal R, and the potential E _{Ns of the} electrical neutral point Ns with respect to the ground point N has a commercial frequency. The voltage En shown in FIG. 5 and FIG. 6 is obtained, and its magnitude is ½ of the phase voltage E _R. Therefore, the ground voltage of the switching power source connected to the single-phase distribution line is a voltage obtained by superimposing the operation frequency phase voltages E _U , E _V , E _{W on the} commercial frequency potential E _Ns , and this ground voltage is applied to the load device 5. The ground leakage current I ₀ is generated.

By the way, the ground capacitances C _U , C _V , and C _W exist in each phase of the load device 5. A three-phase winding such as an electric motor with a relatively large earth capacitance in a normal load device driven by a three-phase power supply or a single-phase power supply has a symmetrical structure with respect to the grounding part. The ground capacitance is negligible. Therefore, since the ground capacitances C _U , C _V , and C _W of each phase are almost the same, this is set to C, and the ground currents Igcu, Igcv, Igcw are always included in each of the three-phase capacitances C. Is flowing. Further, the load device 5 may have ground leakage resistances ru, rv, rw. Leakage currents Igru, Igrv, Igrw flow through these ground leakage resistances ru, rv, rw.

The leakage current measuring apparatus according to the present invention for measuring the leakage current Igr caused by the ground insulation resistance of the switching power supply connected to the three-phase distribution line or the single-phase distribution line as described above and the load device connected to the switching power supply, As shown in FIG. 1, a processing calculation unit 16 having a signal processing unit 3, a calculation unit 14, and a display unit 15 is provided. When measuring the leakage current Igr caused by the ground insulation resistance of the load device 5, the zero-phase current I which is the vector sum of the current flowing through the distribution line 4 is sent to the signal processing unit 3 constituting the processing calculation unit 16. ₀ is input via the current transformer 9 that detects this. Further, the vector sum of the currents flowing in the respective power supply lines connecting the output terminals U, V, W of the switching power supply 2 and the load device 5 may be inputted as the zero-phase current I ₀ .

In the distribution system shown in FIG. 2, when the leakage current Igr caused by the ground insulation resistance of the load device 5s is measured, the current flowing through the distribution line 4 is transmitted to the signal processing unit 3 that constitutes the processing calculation unit 16s. A zero-phase current I ₀ that is a vector sum is input via a zero-phase current transformer 9s that detects this.

Here, the current flows Igcu, Igcv, Igcw flowing through the ground capacitance C of each phase generated in the load device 5 or 5 s and the ground leakage resistance ru, rv, rw of each phase generated in the load device 5 or 5 s. The zero-phase current I ₀ , which is the vector sum of the leakage currents Igru, Igrv, Igrw, passes from the ground via the grounding pole G and the grounding line 8 of the distribution power supply transformer to the switching power supply 2 or 2s. Since it circulates, the zero-phase current I ₀ can be measured at any point on the power supply side or load side of the switching power supply 2 or 2s in the middle of the circulation path.

  Further, by adopting the present invention, as shown in FIG. 11 described later, the leakage current of a system in which load devices 5a and 5b are connected to a plurality of switching power supplies 2a and 2b, respectively, is monitored by a single leakage current measuring device. Is possible.

  Here, due to the ground insulation resistance of the switching power supply connected to the three-phase distribution line or single-phase distribution line in which the constant-voltage side winding of the distribution transformer described above is connected in a star shape and the load device connected to the switching power supply A method for measuring the leakage current Igr and its principle will be described.

First, the three-phase terminals R, S, and three-phase terminals of the three-phase three-wire or three-phase four-wire distribution system in which the low-voltage side winding (secondary side winding) of the distribution transformer as shown in FIG. Line voltages E _SR , E _TS , E _RT generated between T and ground voltages E _R , E generated with respect to neutral point N where terminals R, S, T are ground points of the star winding The relationship between _S and E _T can be expressed as a vector diagram shown in FIG. At this time, the neutral point N coincides with the electrical neutral points of the R, S, and T phases, and in the three-phase four-wire distribution system, one of the ground wires from the neutral point N connected to the ground electrode G. Is added to the three-phase distribution line.

Line voltages E _VU , E _WV , E _UW and U, V, W generated between the output terminals U, V, W of the switching power supply 2 connected to the three-phase distribution lines 4 _R , 4 _S , 4 _T described above. The relationship between the electrical neutral point Ne of the phase and the phase voltages E _U , E _V , E _W generated between the terminals U, V, _W and the voltage En applied to the neutral point Ne with respect to the ground electrode G is as follows: This is represented by an equivalent circuit diagram shown in FIG. However, if each voltage and current is handled as having a commercial frequency, an operating frequency, and their combined frequency by removing the harmonic components contained therein by a filter, the three-phase three-wire or three-wire shown in FIG. The potential of the neutral point N connected to the ground pole G of the phase 4 wire distribution system and the electrical neutral point Ne of each terminal U, V, W of the switching power source 2 shown in FIGS. Since the potentials match, in the switching power supply 2 connected to the three-phase distribution line, the voltage En shown in FIG. 5 is 0, and the potential of the electrical neutral point Ne is the ground potential (0).

Here, when measuring the leakage current Igr and the like of the switching power supply 2 and the load device 5 connected to the three-phase distribution line, first, as the reference voltage E serving as a measurement reference input to the leakage current measuring device, The case where any one of the line voltages E _VU , E _WV , E _UW generated between the terminals U, V, W of the switching power supply 2 having the operation frequency is described.

Here, the frequency of the zero-phase current I ₀ generated in the load device 5 is the operating frequency, and the commercial frequency is not superimposed, and as shown in FIG. 8, the input voltage is a reference vector on the real axis that is the horizontal axis. On the other hand, it is represented as a vector I ₀ of phase angle θ.

Therefore, in FIG. 6, when the line voltage E _VU generated by the terminal U with respect to the terminal V is used as a reference voltage, the value is the phase voltage E _U , E _V , It is shown as √3E with respect to the value E of E _W , and each phase voltage E _U , E _V , E _W can be expressed by the vector symbol method as in the following formulas (1) to (3).

E _U = 0.5√3E−j0.5E (1)
E _V = −0.5√3E−j0.5E (2)
E _W = jE (3)
Then, U of the load device 5, V, approximately equal earth capacitance C is large enough to present in each phase of W is always ground current Igcu, Igcv, but Igcw is flowing, the phase voltage E _U , E _V and E _W are balanced three-phase voltages, and the vector sum of the ground currents Igcu, Igcv and Igcw is almost zero.

  Further, leakage currents Igru, Igrv, Igrw flowing in the ground leakage resistances ru, rv, rw of the respective phases generated in the load device 5 can be expressed by the following vector symbol expressions (4) to (6).

Igru = Eu / ru = 0.5√3E / ru−j0.5E / ru (4)
Igrv = Ev / rv = −0.5√3E / rv−j0.5E / rv (5)
Igrw = Ew / rw = jE / rw (6)
From the above, grounding is performed via the grounding wire 8 that connects the middle point N of the winding 1 and the grounding pole G, the distribution line 4 (4 _R , 4 _S , 4 _T ), the switching power supply 2, and the load device 5. The zero-phase current I ₀ , which is the current flowing back to the pole G, is obtained by adding the above formulas (4) to (6) and can be represented by the following vector symbol formula (7).

I ₀ = 0.5√3 (E / ru−E / rv)
+ J (E / rw-0.5E / ru-0.5E / rv) (7)
Here, when measuring the leakage current Igr, when the line voltage E _VU input to the leakage current measuring apparatus is used as the reference voltage E, the zero-phase current I ₀ expressed by the above equation (7) and the reference The relationship between the effective component A of the zero-phase current I ₀ having the same phase as the voltage E and the reactive component B of the zero-phase current I ₀ advanced in phase by 90 degrees from the reference voltage E is expressed as in the vector diagram of FIG. Since the effective component A is the effective component A of the zero-phase current I _{0 in} the vector diagram shown in FIG. 8 and the real part of the above equation (7), it can be expressed by the following equation (8). However, the following Igru, Igrv, and Igrw represent the magnitudes of the respective vectors, where Igru is Ev / rv and Igrw is Ew / rw.

A = 0.5√3 (Igru-Igrv) (8)
The invalid component B of the zero-phase current I ₀ whose phase is advanced by 90 degrees from the line voltage E _VU input as the reference voltage is the invalid component B of I _{0 in} the vector diagram shown in FIG. 8 and the imaginary number of Expression (7). Since it is a part, it can be shown by the following formula (9).

B = Igrw−0.5 Igru−0.5 Igrv (9)
Here, if the phase angle between the zero-phase current I ₀ and the reference voltage E is θ, the effective component A is represented by I ₀ cos θ and the ineffective component B is I ₀ , as can be seen from FIG. It is represented by sin θ.

Meanwhile, the active ingredient A of the zero-phase current I _0, when the determined by measuring the value of the reactive component B actually, the reference voltage E and the zero-phase current I ₀ that is inputted to the signal processing section 3 of the processing operation section 16 From the waveform, as shown in FIG. 9 to be described later, the phase difference between the reference voltage E and the zero-phase current I ₀ is measured, and the zero-phase current I ₀ is effective in the same phase as the reference voltage E by the calculation unit 14. The component A and the invalid component B whose phase is advanced by 90 degrees from the reference voltage E are decomposed and output. That is, the calculation unit 14 detects the effective component A and the ineffective component B based on the phase angle θ between the reference voltage E and the zero-phase current I ₀ .

  Next, X, Y, and Z are set as shown in the following formulas (10), (11), and (12).

X = B−√3A (10)
Y = B + √3A (11)
Z = -2B (12)
Then, by substituting A and B in the above equations (8) and (9) into the above equations (10) to (12), the following equations (13) to (15) are obtained.

X = Igrv + Igrw−2Igru (13)
Y = Igrw + Igru-2Igrv (14)
Z = Igru + Igrv-2Igrw (15)
Here, in the switching power supply 2 and the load device 5, it is assumed that the leakage current Igr does not flow simultaneously in each of the three phases, and the above equation (13) is obtained when the leakage current Igru does not flow, and the above equation (13) when the leakage current Iggr does not flow. If the equation (14) is adopted when the equation (14) is used when the leakage current Igrw does not flow, the maximum value among the above X, Y, and Z values is the leakage current Igr flowing in one phase. The measured value of the leakage current Igr in the case of two phases, and when the leakage current Igr flows in two phases, the value of the total leakage current Igr for two phases is shown, and further, the ground leakage resistance generated during the line load described later Is output as a value close to the measured value of the ground leakage current Igr corresponding to.

As described above, in the description of the part including the equations (1) to (15), the line voltage E _VU generated between the terminal V and the terminal U is used as the reference voltage E, but other line voltages E _WV , The above formulas (13) to (15) can be applied in the same manner even when E _UW is used as the reference voltage E. The combination of X, Y, Z in the formulas (13) to (15) and the formula on the right side thereof is Since the values of the leakage current Igr are the same value, the maximum value of which is the measured value of the leakage current Igr, so that the same measurement result can be obtained regardless of which phase voltage of the three-phase line voltage is input. Therefore, the selection error of the input voltage at the time of measurement does not occur.

  From the above formulas (13) to (15), the measured value of the leakage current Igr represents the measured value when one phase or two phases are grounded at the wiring of the load device 5 or its terminal. Even when a ground leakage current is generated in a load, for example, a winding of an electric motor, the above equations (13) to (15) can be applied as they are to measure the leakage current. This will be described below.

For example, as is apparent from FIG. 6, the ground voltage of the terminals U, V, W of the switching power supply 2 connected to the star distribution power supply shown in FIG. Therefore, when the phase voltages E _U , E _V , E _W with respect to the electrical neutral point Ne are the phase voltages E of the operating voltage, for example, the motor winding of the load device 5 connected between the V phase and the U phase When the line load center point M, which is the center point of the line, causes a ground fault through the leakage resistance r, the magnitude of the ground voltage E _NM with respect to the electrical neutral point Ne of the line load center point M Since the voltage En is 0, it is 0.5E as apparent from the vector diagram shown in FIG. 6, the ground leakage current is 0.5 E / r, and the value of the zero-phase current I _{0 is} the value of the leakage current Igr. The conventional leakage current measuring instrument measures this value.

However, if the ground fault occurs not at the line load center point M but near the terminal R or S where the ground voltage is E, the ground leakage current becomes E / r, and the line load is equal to the same leakage resistance r. The measured value of the ground leakage current due to the ground fault at the center point M is half of this value. Therefore, in a leakage current measuring apparatus that evaluates the degree of electric leakage failure with the ground leakage current value at the rated voltage, the degree of failure is underestimated. As a result, it is difficult to accurately find a leakage failure, and it may be impossible to find an accident due to leakage while measuring the leakage current I ₀ .

In the present invention, the measured value of the leakage current Igr obtained by dividing the ground voltage E by the value of the ground leakage resistance r is not the measured value of the leakage current Igr that shows an excessively small value as described above. It is verified by using the above-described equations (1) to (15) that the measured value is doubled when entangled. Note that the value of the line voltage E _VU generated between the terminal U and the terminal V of the motor winding is √3E when the value of the ground voltage is E, and exists in the load device 5 including the motor. The ground capacitances C _U , C _V , and C _W are verified as being equal.

First, in the vector diagram shown in FIG. 6, when the ground leakage resistance r exists only at the line load center point M, the ground voltage E _{NM with} respect to the electrical neutral point Ne which is the ground potential of the line load center point M is Therefore, −j0.5E with respect to the input voltage vector E _VU having the magnitude √3E, the ground leakage current I _NM passing through the ground leakage resistance r from the motor winding center point M is −j0.5E / r. , Igru, Igrv, and Igrw are all zero.

If this is substituted into the above-mentioned formulas (7) to (9), the effective component A of the zero-phase current I ₀ is 0 and the ineffective component B is −0.5 E / r. By substituting A and B into the above formulas (10) to (12), X and Y are both -0.5 E / r, Z is E / r, and the maximum value E of X, Y, and Z is E. / R is displayed as a measured value of the leakage current Igr, that is, a ground leakage current value at the rated voltage. In the leakage current measuring apparatus according to the present invention, the measured ground leakage current value is displayed on the display unit 15 of the processing calculation unit 16.

  Next, when the ground leakage resistance r exists in the U phase and the V phase, the effective component A is 0 and the ineffective component B is -E / r. When A and B are substituted into equations (10) to (12), X and Y are both -E / r, Z is 2E / r, and the maximum value 2E / r of X, Y, and Z is R It is displayed as a measured value of the total leakage current Igr of the phase and S phase. This display is also performed on the display unit 15 of the processing calculation unit 16.

Next, when measuring the leakage current Igr and the like, a line voltage E generated between terminals R, S, and T of the distribution system, which is a commercial frequency, is used as a reference voltage E that is a measurement reference input to the leakage current measuring device. A case where any one of _SR , _ETS , and _ERT is input will be described.

The commercial frequency is 50 Hz or 60 Hz, with special exceptions, while the operating frequency is mostly changed or at least elapses in the 60 Hz to 20 Hz band. Zero-phase current I ₀ of the switching power supply 2 and the load device 5 connected to a three-phase distribution line as described above has the operation frequency, because different from the commercial frequency of the reference voltage E, the zero-phase to the reference voltage E current I ₀ The phase angle θ varies from 0 degree to 360 degrees in the frequency cycle of the difference between the two frequencies.

In this case, in order to obtain the change of X, Y, Z in the above-described equations (10) to (12), and hence the change of the leakage current Igr which is the maximum value of X, Y, Z, from the vector diagram shown in FIG. Substituting A = I ₀ × cos θ and B = I ₀ × sin θ into the equations (10) to (12), the following equations (16) to (18) are obtained.

X = 2I ₀ × sin (θ−60 degrees) (16)
Y = 2I ₀ × sin (θ + 60 degrees) (17)
Z = -2I ₀ × sin θ (18)
Here, when the phase angle θ changes, each of the equations (16) to (18) changes between + 2I ₀ and −2I ₀ , making measurement difficult. However, the present invention has the maximum of X, Y, and Z. Since the value is the value of the leakage current Igr, θ is 30 degrees, the Y value is 2I ₀ , θ is 150 degrees, the X value is 2I ₀ , θ is 270 degrees, the Z value is 2I ₀ , and θ is 90 At two degrees, 210 degrees and 330 degrees, any two of X, Y, and Z become I _0, and the maximum value of X, Y, and Z is a value between I ₀ and 2I ₀ of the operating frequency 3 It fluctuates with a period of double frequency.

Here, the relationship between the zero-phase current I ₀ and the leakage current Igr is examined. From FIG. 8, I ₀ ² = A ² + B ² , and when A and B in the above formulas (8) and (9) are substituted into this formula, I ₀ is represented by the following formula (19).
I ₀ ² = Igru ² + Igrv ² + Igrw ² −Igru · Igrv−Igrv · Igrw
-Igrw · Igru (19)
When any one of the leakage currents Igru, Igrv, and Iggrw occurs, I ₀ = Igr, but when two phases, for example, Igru and Igrv occur simultaneously,
I ₀ ² = (Igru + Igrv) ² −3 (Igru × Igrv)
Thus, the value of I ₀ is smaller than the total value of Igru and Igrv.

Next, at 2I ₀ which is the upper limit value of the fluctuations of the equations (16) to (18),
4I ₀ ² = (Igru + Igrv) ² +3 (Igru-Igrv) ²
The value of 2I ₀ is larger than the total value of Igru and Igrv, and when the values of Igru and Igrv are equal, they are the total value of both.

Therefore, the maximum value 2I _{0 of} the equations (16) to (18), and hence the maximum value among X, Y, and Z of the equations (10) to (12) can be set as the value of the leakage current Igr.

Further, the values of the zero-phase current I ₀ and the leakage current Igr are proportional to the values of the ground voltages E _U , E _V , E _W of the respective phases U, V, W, and these ground voltages E _U , E The values of _V and E _W are constant due to the characteristics of the switching power supply when the operating frequency is 60 Hz or more, and the maximum value is obtained at this time. The value measured at this time is the value of the rated leakage current Igr. As the operating frequency decreases below 60 Hz, the operating voltage also decreases. For example, the operating frequency is about half at 30 Hz. Since the above calculation is based on the premise that the operating frequency reaches around 60 Hz, when the operating frequency is lower than this, the value of the leakage current Igr measured as described above according to the maximum frequency reached is as follows. Correction is performed by the equation (19a) shown. However, the error increases when the operating frequency falls below 30 Hz.

Correction Igr = Measurement Igr × (60 ÷ maximum operating frequency) (19a)
Next, a state in which the switching power supply 2s is connected between the single-phase distribution lines 4 _N and 4 _R as shown in FIG. 2 will be described.

As described above, of the single-phase distribution lines 4 _N and 4 _R , the potential of the distribution line 4 _R with respect to the distribution line 4 _N having zero potential is the phase voltage E _R , and this value is the line voltage of the single-phase distribution line. Yes, this voltage is input as the reference voltage E. The line voltage used as the reference voltage E is rectified in the switching power source 2s, converted into a DC voltage having the maximum value of the line voltage, and further converted into a three-phase operation voltage having a VVVF characteristic. The magnitudes of the voltages E _U , E _V , and E _W become lower as the frequency decreases at an operating frequency of about 60 Hz or more and about E / √3. The electrical neutral point of the single-phase distribution lines 4 _N and 4 _R is a midpoint Ns between the terminals R and N. The potential E _NS of the midpoint Ns with respect to the zero potential point N is a vector shown in FIG. It can be expressed as shown in the figure.

Electrical neutral point of each phase of line voltages E _VU , E _WV , E _UW and U, V, W generated between terminals U, V, W of switching power supply 2s connected to the above single-phase distribution line The relationship between the phase voltages E _U , E _V , E _W generated between Ne and the terminals U, V, W and the voltage En applied to the electrical neutral point Ne with respect to the ground pole G is equivalent to that shown in FIG. It can be expressed as a circuit, and when expressed as a vector diagram, it can be expressed as shown in FIGS.

However, since the electrical neutral point Ns shown in FIG. 3 of the single-phase distribution line and the electrical neutral point Ne of each terminal U, V, W of the switching power supply 2s shown in FIG. The voltage En of FIG. 4 representing the relationship of the above corresponds to the potential E _Ns of the electrical neutral point Ne with respect to the N terminal grounded by the ground pole G in FIG. However, if the commercial frequency vector En shown in FIG. 4 is fixed, the operating frequency vectors E _U , E _V , E _W rotate around the neutral point Ne while maintaining a phase difference of 120 degrees and are displayed in FIG. At this time, the state where the ground voltage of the terminal U is maximized is displayed.

In FIG. 5 showing the voltage state of the switching power supply 2s connected to the single-phase distribution lines 4 _N and 4 _R , the zero-phase current I ₀ flowing into the load device 5 is obtained. The ground voltage applied to the U, V, and W phases of the load device 5 is obtained by superposing the commercial frequency voltage En on the operation frequency phase voltages E _U , E _V , and E _W , and the potential E shown in FIG. _Ns is the voltage En of the commercial frequency, and the magnitude of the voltage En is constant at 1/2 of the single-phase distribution line voltage E _R that is the reference voltage E, whereas the phase voltage E _U , Since E _V and E _W are VVVF characteristics, when the operating frequency is 60 Hz, the value is approximately 1 / √3 of the reference voltage E, which is approximately 2 / √3 times the value of the commercial frequency voltage En. As the voltage decreases, the voltage decreases.

_Let p be the ratio of the phase voltages E _U , E _V , E _{W to} the commercial frequency voltage En. However, when p is 2 / √3 or less, the operating frequency and the commercial frequency are f and fn, respectively, and the time is t, the instantaneous ground voltage eo of the U, V, and W phases is expressed by the following equation (20). expressed.

eo = √2En (sin2πfnt + psinπft) (20)
When formula (20) is rewritten, it can be expressed as the following formula (20a).

eo = √2En {(1 + p) sin αcos β + (1-p) cos αsin β)}
... (20a)
In equation (20a), α = 2π {(fn + f) / 2} t and β = 2π {(fn−f) / 2} t.

  In the above formula (20), when the operating frequency f is 60 Hz to 40 Hz close to the commercial frequency fn, p is 1.2 to 0.8, so that the formula (20a) (1 + p) is 2.2 to 1.8. On the other hand, (1-p) is -0.2 to 0.2, and the term (1-p) can be ignored when considering the waveform of the instantaneous ground voltage eo. Therefore, the frequency of the waveform of the instantaneous ground voltage eo is the average value of the operating frequency f and the commercial frequency fn from α in the equation (20a), and the waveform of this frequency is represented by the equation (20a). Waveform modulated at half of the difference between the operating frequency f and the commercial frequency fn of β, and the instantaneous ground voltage eo shows the highest value in the modulation period, and the vicinity of this highest value is measured and leaked. The value of the current Igr is calculated.

Next, in the equation (20), when the operating frequency f is 40 Hz to 20 Hz, p becomes 0.8 to 0.4, so that (1 + p) 1.8 to 1.4 in the above equation (20a), (1-P) is 0.2 to -0.6. Similarly, the (1-p) term is ignored, and the average values of the operating frequency f and the commercial frequency fn of the waveform of the instantaneous ground voltage eo are 50 Hz and 45 Hz. , 40 Hz, and the waveform of this frequency is a waveform modulated by β of the equation (20a), which is half the difference between the operating frequency f and the commercial frequency fn, and the instantaneous ground voltage eo is the highest value in this modulation period. Indicates. FIG. 7 shows the waveform of the instantaneous ground voltage eo of the switching power supply U, V, W phase connected to the three-phase four-wire system 220V, 50 Hz single-phase power supply in the equation (20) having such characteristics. A zero-phase current I ₀ which is a leakage current having the same waveform as the instantaneous ground voltage eo flows. Since the waveform in the vicinity of the maximum value of the waveform of the current I ₀ substantially coincides with the waveform of the commercial frequency voltage En, the phase angle θ as shown in FIG. 9 while corresponding to the waveform of the input commercial frequency reference voltage E. Is measured to calculate the value of the leakage current Igr. Thus, even when the operating frequency f is 60 to 20 Hz, the frequency of the zero-phase current I ₀ to be measured is 60 to 40 Hz as described above, and there is little difference from the commercial frequency fn with the frequency being 50 Hz or 60 Hz, and the terminal R The ground voltage E _R of the commercial frequency fn generated between the ground terminal N and the ground terminal N is input as the reference voltage E, and the phase angle θ between the above-mentioned instantaneous ground voltage eo and the zero-phase current I ₀ having the same waveform is measured. Contains a little measurement error, but is practically possible.

In FIG. 2, a switching power supply 2s is connected to a commercial frequency terminal R and a neutral point N which is a ground potential, and a voltage E _R shown in FIG. In FIG. 3, the middle point of the voltage E _R is the electric neutral point Ns of the applied voltage, and the ground voltage of the electric neutral point Ns is represented by E _Ns in FIG. Since the electrical neutral point Ns of the commercial frequency power supply coincides with the electrical neutral point Ne of the switching power supply 2s shown in FIG. 4 and FIG. 5, the commercial frequency voltage En of FIG. 4 and FIG. E _Ns , the magnitude of which is half of the R-phase ground voltage E _R.

In FIGS. 4 and 6, the phase of the operation phase voltages E _U , E _V , and E _W is constantly changing with respect to the phase of the commercial frequency voltage En, so that, for example, the U-phase ground voltage is maximized. At this point, the vector Eu coincides with the direction of the commercial frequency voltage En, and the vector diagram shown in FIG. 4 represents this state.

  Since the two vectors En and Eu shown in FIG. 4 have different frequencies, they cannot be expressed by vectors. However, here, the two frequencies are close to each other, and the analysis is performed when the phases of the two are almost the same. Are treated as equal.

When the operating phase voltage E _U in FIG. 4, E _V, the value of E _W and Ed, the voltage En shown in voltage E _Ns and 4 shown in FIG. 3 are the same, the reference voltage shown in FIG. 4 When the voltage E _Ns ½ of E and the voltage En have the same phase, the ground voltage of the U phase becomes the maximum, so the ground voltages E _GU , E _GV , E _GW of the U, V, W terminals at this time are It can be shown by the vector symbol method as the following formulas (21) to (23).

E _GU = En + Ed (21)
E _GV = En−0.5Ed−j0.5 √3Ed (22)
E _GW = En-0.5Ed + j0.5√3Ed (23)
Then, when the ground currents flowing through the ground capacitances C having substantially the same magnitude in the U, V, and W phases of the load device 5 are Igcu, Igcv, and Igcw and the angular frequency ω = 2πfn, The currents Igcu, Igcv, and Igcw can be expressed by the following formulas (24) to (26).

Igcu = jωCE _GU = jωC (En + Ed) (24)
Igcv = jωCE _GV = jωC (En−0.5Ed) + ωC · 0.5√3Ed
... (25)
Igcw = jωCE _GW = jωC (En−0.5Ed) −ωC · 0.5√3Ed
... (26)
Further, assuming that the leakage currents flowing to the ground leakage resistance ru, rv, rw of each phase generated in the load device 5 are Igru, Igrv, Igrw, each leakage current can be expressed by the following equations (27) to (29). it can.

Igru = E _GU / ru = (En + Ed) / ru (27)
Igrv = E _GV /rv=(En−0.5Ed)/rv−j0.5√3Ed/rv
... (28)
Igrw = E _GW /rw=(En−0.5Ed)/rw+j0.5√3Ed/rw
... (29)
From the above, the ground electrode G is connected via the ground wire 8, the distribution lines 4 _N and 4 _R , the switching power supply 2s, and the load device 5s that connect the neutral point N of the winding 1a and the ground electrode G in FIG. The zero-phase current I _{0 that} is the current flowing through the circuit is the sum of the above formulas (24) to (29). If 1 / ru = gu, 1 / rv = gv, 1 / rw = gw, (30).

I ₀ = (gu + gv + gw) En + (gu−0.5 gv−0.5 gw) Ed
+ J {3ωCEn + 0.5√3 (gw−gv) Ed} (30)
Here, when measuring the leakage current Igr, when the ground voltage E _R inputted to the leakage current measuring device and the reference voltage E, the zero-phase current I ₀ of the formula (30), the reference voltage The relationship between the effective component A of the zero-phase current I ₀ in phase with E and the ineffective component B of the zero-phase current I ₀ advanced in phase by 90 degrees from the reference voltage E is expressed as in the vector diagram of FIG. Since the effective component A is I _{0 in the} vector diagram shown in FIG. 8 and the real part of the equation (30), it can be expressed by the following equation (31).

A = (gu + gv + gw) En + (gu−0.5 gv−05 gw) Ed (31)
The reactive component B of the zero-phase current I ₀ has advanced 90 degrees phase from ground voltages E _R which is also the line voltage E of the single-phase distribution line input as the reference voltage, I ₀ of the vector diagram shown in FIG. 8 Since it is the imaginary part of the equation (30), it can be expressed by the following equation (32).

B = 3ωCEn + 0.5√3 (gw−gv) Ed (32)
Next, when the equations (31) and (32) are substituted into the equations (10), (11), and (12), the following equations (33), (34), and (35) are obtained.
X = B-√3A
= {3ωC−√3 (gu + gv + gw)} En + √3 (gw−gu) Ed
... (33)
Y = B + √3A
= {3ωC + √3 (gu + gv + gw)} En + √3 (gu−gv) Ed
... (34)
Z = −2B = −6ωCEn−√3 (gw−gv) Ed (35)
Of the expressions (33) to (35), the expression indicating the maximum value is the expression (34).

In the equation (34), the normal operation phase voltage Ed is the maximum value when the operation frequency f is 60 Hz from the characteristics of the switching power supply, and this value is the phase voltage E _R of the distribution power supply in FIG. 3, that is, the reference voltage that is the input voltage. approximately equal to 1 / √3, En is half of the input voltage E _R, i.e. since the En = 0.5√3Ed, substituting this relationship in equation (34), the following equation (34a) is obtained.

Ya = {1.5√3ωC + (1.5 + √3) gu + (1.5−√3) gv
+1.5 gw} Ed (34a)
In the above formula (34a), the ground leakage current Igc due to the ground capacitance C is expressed by a term including ωCEd in the formula, but this value is usually as small as 1 mA or less at the operating frequency and commercial frequency band. Omitted, the phase of the operating frequency voltage Ed is rotationally changed with respect to the commercial frequency voltage En. Since the expression (34a) represents the point in time when the phases of the voltages En and Ed coincide with each other, it is not necessary to fix the subscripts u, v, and w of gu, gv, and gw in the expression. Since the leakage current Igr does not simultaneously flow in the phase, the minimum term is omitted.

  Further, from the vector diagram shown in FIG. 6, Igru = (En + Eu) gu = (0.5√3 + 1) Ed · gu. Therefore, when these relationships are substituted into the above equation (34a), the following equation (34b) is obtained. obtain.

Ya = √3 {Igru + √3 / (2 + √3) Igrw} (34b)
The leakage current in parentheses in this formula (34b) is Igru for one-phase grounding and 0.5 times the other one phase for two-phase grounding. Of the formulas (33) to (34), if the maximum measured value is Ym, the value of the leakage current Igr is given by the following formula (36).

Igr = Ym / √3) (36)
When the maximum operating frequency f is smaller than 60 Hz and does not pass 60 Hz, the value of the voltage Ed is also low, so the value is corrected by the operating frequency.

  Certainly, the error increases as the operating frequency decreases, but the measurement result is clearly different from the case where the leakage current Igr is zero. In general switching power supplies, the difference between the operation frequency and the commercial frequency is operated within 30 Hz or the operation frequency passes, and there is almost no chance of impeding practical use due to this error.

Next, a specific example of the signal processing unit 3 constituting the processing calculation unit 16 shown in FIGS. 1 and 2 will be described with reference to FIG. The signal processing unit 3 includes a voltage detector 21, a first amplifier 22, a first low-pass filter (LPF) 23, a first effective value converter 28, and a zero-phase current (I ₀ ) detector. 24, a second amplifier 25, a second low-pass filter (LPF) 26, a second effective value converter 29, and a phase difference measuring device 27.

In FIG. 10, the voltage detector 21 includes any of line voltages E _SR , E _TS , E _RT generated between terminals of each phase of the three-phase distribution lines R, S, T, or a terminal of the switching power supply 2. Switching between U, V and W line voltage E _VU , E _WV , E _UW , distribution line 4 _N and distribution lines 4 _R , 4 _S , 4 _T A single-phase line voltage in a state where the power source 2s is connected is input as the reference voltage E.

Incidentally, FIG. 1, the three-phase distribution line of the system diagram shown in Figure 2, is input line voltage E _SR, the line voltage E _R are input in the single-phase distribution line. Then, the first amplifier 22 amplifies the reference voltage E 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 a frequency component exceeding, for example, 60 Hz, which is the highest frequency of the voltage input as the reference voltage E, and extracts a reference voltage frequency waveform.

In the three-phase distribution line, the zero-phase current detector 24 includes a zero-phase current I that is a vector sum of currents flowing through the distribution lines 4 _R , 4 _S , and 4 _T of R, S, and T phases. ₀ is entered.

Further, in the three-phase four-wire distribution system, the distribution lines 4 _R , 4 _S , 4 _T and the neutral wire 4 _N of each phase of R, S, T and each of N phases as the ground phase The zero-phase current I _0, which is the vector sum of the currents flowing through the four wires, is input, and in the single-phase power source of any one of the neutral wire 4 _N and the distribution lines 4 _R , 4 _S , 4 _T , A zero-phase current I ₀ which is a vector sum of currents flowing through the line is input.

The second amplifier 25 amplifies the zero-phase current I ₀ output from the zero-phase current detector 24 according to the detection sensitivity of the zero-phase current detector 24 until it reaches an appropriate value. The second low-pass filter 26 attenuates frequency components exceeding the commercial frequency and the operating frequency of the zero-phase current I ₀ to extract the commercial frequency and the operating frequency and their combined frequency waveforms.

Then, the phase difference measuring instrument 27 is one of the line voltages E _SR , E _TS , E _RT generated between the terminals R, S, T of the distribution power supply input as the reference voltage, or the terminal U of the switching power supply 2. , V, W, or any one of the line voltages E _VU , E _WV , E _UW , or neutral wire 4 _N and distribution lines 4 _R , 4 _S , 4 _T The phase difference between any one of the single-phase line voltages and the zero-phase current I ₀ when the switching power supply 2s is connected is measured. Here, any of line voltages E _SR , E _TS , E _RT generated between terminals R, S, T input as reference voltage E, or a line generated between terminals U, V, W of switching power supply 2 Switching power supply 2s is connected to one-phase single-phase power supply of any one of interphase voltages E _VU , E _WV , E _UW , or neutral wire 4 _N and distribution lines 4 _R , 4 _S , 4 _T FIG. 8 and FIG. 9 show the relationship between the phase angle θ between one of the single-phase line voltages and the zero-phase current I ₀ . Although the phase angle θ changes with time, FIGS. 8 and 9 show typical examples.

In the signal processing unit 3, the first low-pass filter 23 outputs the waveform of the output 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. When input, their output waveforms are indicated by E _Z for the reference voltage E and indicated by I _Z for the zero-phase current I _{0 as} shown in FIG. The peak values of the output waveforms of the reference voltage E and the zero-phase current I ₀ are matched to obtain the difference between the output waveforms E _Z and I _Z. The absolute waveform of the difference is | E _Z −I _Z | waveform shown in FIG. If the areas of the protruding portions of the | E _Z −I _Z | waveform and the I _Z waveform shown in FIG. 9 are S ₁ and S ₂ , respectively, S ₁ is the phase difference angle θ between the reference voltage E and the zero-phase current I _0. 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 waveform of the reference voltage E in both waves to convert it into an analog value proportional to the effective value, and inputs it to the calculation unit 14. The second effective value converter 29 rectifies the fundamental frequency waveform of the zero-phase current I ₀ into two-wave rectified and converts it to an analog value proportional to the effective value, and inputs it to the computing unit 14.

The calculation unit 14 uses the phase difference angle θ between the reference voltage E and the zero-phase current I ₀ measured by the phase difference measuring device 27 to convert the zero-phase current I ₀ into an active component A having the same phase as the reference voltage E, and It is decomposed into an ineffective component B having a phase advanced by 90 degrees from the reference voltage E and output.

The phase difference angle θ between the reference voltage E detected by the phase difference measuring instrument 27 and the zero-phase current I ₀ is calculated from the following equation (37).

θ = (180S ₁ ) / S ₂ (37)
Here, the calculation unit 14 calculates and outputs the value of I ₀ cos θ as the value of the effective component A of the zero-phase current I ₀ and the value of I ₀ sin θ as the value of the invalid component B of the zero-phase current I ₀ . These zero-phase current I _0, the relationship of the active ingredient A and reactive component B of the zero-phase current I _0, as described above, is expressed as shown in the vector diagram of FIG.

  Then, the arithmetic unit 14 performs the arithmetic processing as described above, and the ground leakage resistances ru, rv, rw of the U, V, W phases of the load device 5 of the switching power supply 2 are one phase or two phases, or When the load exists between two phases, the value of the current flowing in them or the total current value of the two phases is measured as the value of the leakage current Igr, and the value is displayed on the display unit 15 as necessary. Display.

In the leakage current measuring apparatus and the measuring method using this measuring apparatus according to the present invention, the effective component A and the ineffective component B of the above-described zero-phase current I ₀ are expressed by the above-described equations (10) to (12) or (33). ) To (35) are performed by the calculation unit 14 so that the ground leakage resistance ru, rv, rw of each phase of U, V, W is one phase, two phases, or a load that spans between two phases. When present, measurement of the current value flowing in them or the total current value of two phases or a current value close to that value is realized.

  Further, as shown in FIG. 11, the leakage current measuring apparatus according to the present invention can monitor a plurality of switching power supplies 2a and 2b and their load devices 5a and 5b with a single leakage current measuring apparatus. Moreover, it is good also as a structure which provides the circuit breaker 19 in the middle of the distribution line 4, and controls the interruption | blocking operation | movement of the circuit breaker 19 with the result of the calculation of the calculating part 14. FIG. The leakage current measuring apparatus according to the present invention uses, as a control signal, the measurement result of the leakage current Igr flowing through the ground leakage resistances ru, rv, and rw calculated and measured by the calculation unit 14, and is distributed based on this control signal. By operating the circuit breaker 19 provided in the middle of the electric wire 4, the switching power supplies 2 a and 2 b and the load devices 5 a and 5 b are disconnected from the distribution power supply 1.

  In the leakage current measuring apparatus according to the present invention, by further providing a circuit breaker as described above, when the leakage current Igr exceeds a predetermined value, the switching power supply and the load device are removed from the distribution power supply together with the detection of the leakage current Igr. Since it can be made to cut off, the switching power supply connected to the power distribution power supply and its load device can be protected from a serious accident caused by an insulation failure.

  Furthermore, in the leakage current measuring apparatus according to the present invention, when it is determined that the value of the leakage current Igr caused by the ground insulation resistance is larger than a predetermined value based on the calculation result of the calculation unit 14, An alarm device such as sound or light emission may be operated using the determination signal as a control signal, and an alarm may be issued using sound or light emission. By providing such an alarm device, it is possible to reliably prevent an accident due to electric leakage. As shown in FIG. 11, the alarm device operates the alarm device 18 using the determination signal of the calculation unit 14 as a control signal. Therefore, the alarm signal is input so that the determination signal from the calculation unit 14 is input. Connected to the calculation unit 14.

  A leakage current measuring device and a measuring method according to the present invention include a servo motor incorporated in a load device such as an inverter and an electric motor driven by the inverter, an automatic machine robot, etc. It can be used for insulation measurement in a switching power supply for driving them.

  DESCRIPTION OF SYMBOLS 1 Star distribution power supply, 2 Three-phase distribution line switching power supply, 2s Single-phase distribution line switching power supply, 3 Signal processing part, 4 Distribution line, 5 Load device, 8 Ground line 9 Zero-phase current transformer, 14 Calculation part, 15 Display unit, 16 processing operation unit, 18 alarm, 19 circuit breaker,

Claims (13)

Three-phase 4 fed from a power source with the secondary winding of the transformer connected in a star shape, the three-phase voltage terminals R, S, T, and the neutral point grounded in the star connection N A switching power supply connected to a wire-type or three-phase three-wire distribution line or a single-phase two-wire distribution line fed from one of the neutral points N and terminals R, S, and T, and the switching power supply In the leakage current measuring device for measuring the leakage current Igr caused by the ground insulation resistance of the load device,
Line voltage E _SR , E _TS , E _RT generated between the terminals R, S, T of the secondary winding or a single phase voltage E generated between the neutral point N and the terminals R, S, T Voltage detecting means for measuring any of line voltages E _VU , E _WV , E _UW generated between _R , E _S , E _T and the output terminals U, V, W of the switching power supply;
Zero-phase current detection means for detecting zero-phase current I ₀ which is a vector sum of currents flowing through each distribution line and the switching power supply and the load device connected to the switching power supply;
The line voltages E _SR , E _TS , E _RT or the single-phase voltages E _R , E _S , E _T detected by the voltage detection means and the line voltages generated between the switching power supply terminals U, V, W Any of E _VU , E _WV , E _UW is input, and any of the input line voltages E _SR , E _TS , E _RT or single-phase voltages E _R , E _S , E _T and the switching power supply Phase comparison means for comparing any of the line voltages E _VU , E _WV , E _UW generated between the terminals U, V, W with the reference voltage and comparing the phase of the reference voltage with the zero-phase current I _0. ,
A measurement value obtained by separating the zero-phase current I0 into the active component A having the same phase and the reactive component B having a phase difference orthogonal to the zero-phase current I0 with respect to the reference voltage is obtained and generated between the terminals R, S, and T. Line voltages E _SR , E _TS , E _RT or single-phase voltages E _R , E _S , E _T and line voltages E _VU , E _WV , E _UW generated between the switching power supply terminals U, V, W Based on the effective component A of the zero-phase current I ₀ obtained when any one of the above is used as a reference voltage and the reactive component B having a phase difference perpendicular to the effective component A, of the U-phase, V-phase, and W-phase Total value of leakage current Igr generated in two phases, value of leakage current Igr generated in one of U phase, V phase, and W phase, between two phases of U phase, V phase, and W phase or Computing means for computing the value of the leakage current Igr generated in the load device connected between the three phases. Leakage current measurement apparatus according to symptoms. The calculation means is configured to detect line voltages E _SR , E _TS , E _RT generated between the terminals R, S, T or line voltages E _VU , E generated between the terminals U, V, W of the switching power supply. _WV, when a reference voltage of either voltage E _UW, the value of the formula (B-√3A), the value of the formula (B + √3A), the maximum of the values of the formula (-2B), 2. The leakage current measurement according to claim 1, wherein the leakage current measurement is performed as an approximate value of the leakage current Igr caused by ground insulation resistance of the switching power supply and a load device connected to each terminal U, V, W of the switching power supply. apparatus. The calculation means is configured to detect line voltages E _SR , E _TS , E _RT generated between the terminals R, S, T or line voltages E _VU , E generated between the terminals U, V, W of the switching power supply. _WV, when a reference voltage of either one of the voltage E _UW, the value of the formula (B-√3A), the value of the formula (B + √3A), the value of formula (-2B), the time of the respective values Several values near the maximum value among the fluctuating values are sampled, and the average value of these values is ground insulation resistance of the load device connected to each terminal U, V, W of the switching power supply and the switching power supply. The leakage current measuring device according to claim 1, wherein the leakage current measuring device is calculated as an approximate value of the leakage current Igr caused by. The calculation means has a value twice the zero-phase current I ₀ when any of the line voltages E _SR , E _TS , E _RT generated between the terminals R, S, T is used as a reference voltage. 2 is calculated as an approximate value of the leakage current Igr caused by the ground insulation resistance of the load device connected to each terminal U, V, W of the switching power supply and the switching power supply. measuring device.   When the voltage between the single-phase two-wire distribution lines is the reference voltage, the calculation means is a value of the formula (B−√3A), a value of the formula (B + √3A), and a value of the formula (−2B) Is calculated as an approximate value of the leakage current Igr caused by the ground insulation resistance of the load device connected to each terminal U, V, W of the switching power supply and the switching power supply. The leakage current measuring apparatus according to claim 1.   The leakage current measuring device according to claim 1, further comprising a display unit, wherein a result calculated by the calculating unit is displayed on the display unit. .   The leakage current measuring device further comprises an alarm means, and issues an alarm from the alarm means when the value of the leakage current Igr required by the arithmetic means exceeds a predetermined value. 6. The leakage current measuring device according to any one of 6.   2. The leakage current measuring apparatus further comprises a breaking means, and the electric circuit is cut off by the breaking means when a value of the leakage current Igr obtained by the computing means exceeds a predetermined value. The leakage current measuring device according to any one of? 7. Three-phase 4 fed from a power source with the secondary winding of the transformer connected in a star shape, the three-phase voltage terminals R, S, T, and the neutral point grounded in the star connection N A switching power supply connected to a wire-type or three-phase three-wire distribution line or a single-phase two-wire distribution line fed from one of the neutral points N and terminals R, S, and T, and the switching power supply In the leakage current measuring method for measuring the leakage current Igr caused by the ground insulation resistance of the load device,
Line voltage E _SR , E _TS , E _RT generated between the terminals R, S, T of the secondary winding or a single phase voltage E generated between the neutral point N and the terminals R, S, T A voltage detecting step for detecting any of line voltages E _VU , E _WV , E _UW generated between _R , E _S , E _T and the output terminals U, V, W of the switching power supply;
A zero-phase current detection step of detecting a zero-phase current I ₀ that is a vector sum of currents flowing through each distribution line and the switching power supply and a load device connected to the switching power supply;
The line voltages E _SR , E _TS , E _RT or the single-phase voltages E _R , E _S , E _T detected by the voltage detection means and the line voltages generated between the switching power supply terminals U, V, W Any of E _VU , E _WV , E _UW is input, and any of the input line voltages E _SR , E _TS , E _RT or single-phase voltages E _R , E _S , E _T and the switching power supply A phase comparison step in which any of the line voltages E _VU , E _WV , E _UW generated between the terminals U, V, W is used as a reference voltage, and the phase of the reference voltage and the zero-phase current I ₀ are compared. ,
A measurement value obtained by separating the zero-phase current I0 into the active component A having the same phase and the reactive component B having a phase difference orthogonal to the zero-phase current I0 with respect to the reference voltage is obtained and generated between the terminals R, S, and T. Line voltages E _SR , E _TS , E _RT or single-phase voltages E _R , E _S , E _T and line voltages E _VU , E _WV , E _UW generated between the switching power supply terminals U, V, W Based on the effective component A of the zero-phase current I ₀ obtained when any one of the above is used as a reference voltage and the reactive component B having a phase difference perpendicular to the effective component A, of the U-phase, V-phase, and W-phase Total value of leakage current Igr generated in two phases, value of leakage current Igr generated in one of U phase, V phase, and W phase, between two phases of U phase, V phase, and W phase or A calculation step of calculating the value of the leakage current Igr generated inside the load device connected between the three phases. Leakage current measurement method and butterflies. The calculation process includes line voltages E _SR , E _TS , E _RT generated between the terminals R, S, T or line voltages E _VU , E generated between the terminals U, V, W of the switching power supply. _WV, when a reference voltage of either voltage E _UW, the value of the formula (B-√3A), the value of the formula (B + √3A), the maximum of the values of the formula (-2B), The leakage current measurement according to claim 9, wherein the leakage current measurement is performed as an approximate value of the leakage current Igr caused by the ground insulation resistance of the switching power supply and a load device connected to each terminal U, V, W of the switching power supply. Method. The calculation means is configured to detect line voltages E _SR , E _TS , E _RT generated between the terminals R, S, T or line voltages E _VU , E generated between the terminals U, V, W of the switching power supply. _WV, when a reference voltage of either one of the voltage E _UW, the value of the formula (B-√3A), the value of the formula (B + √3A), the value of formula (-2B), the time of the respective values Several values near the maximum value among the fluctuating values are sampled, and the average value of these values is ground insulation resistance of the load device connected to each terminal U, V, W of the switching power supply and the switching power supply. The leakage current measuring method according to claim 9 or 10, wherein the leakage current is calculated as an approximate value of the leakage current Igr.
Method. The calculation step is a value that is twice the zero-phase current I ₀ when any of the line voltages E _SR , E _TS , E _RT generated between the terminals R, S, T is used as a reference voltage. The leakage current according to claim 9, wherein the leakage current Igr is calculated as an approximate value of the leakage current Igr caused by the ground insulation resistance of a load device connected to each terminal U, V, W of the switching power supply and the switching power supply. measuring device.   The calculation step includes a value of the formula (B−√3A), a value of the formula (B + √3A), and a value of the formula (−2B) when the voltage between the single-phase two-wire distribution lines is a reference voltage. Is calculated as an approximate value of the leakage current Igr caused by the ground insulation resistance of the load device connected to each terminal U, V, W of the switching power supply and the switching power supply. The leakage current measuring method according to claim 1.