JP2006038604A - Leakage current measuring instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problems wherein, though a method wherein a leakage current is measured at a wiring service entrance of a residence and the amount thereof is specified to be kept below 1 mA when insulation measurement in the residence is difficult is utilized widely because the insulation state in the residence is known from the outside without service interruption in this method, the leakage current sometimes exceeds 1 mA because it includes a current caused by a capacitance between a circuit in the residence and the ground, and in this case, a method for measuring circuit insulation by an insulation-resistance meter after applying service interruption of the circuit by a distribution board in the residence is adopted, and consequently a long time and much labor are required because re-measurement is necessary though the insulation state of the circuit is in a good state. <P>SOLUTION: Two or more electrodes are installed in a window of a split current transformer of a leakage current meter, and the magnitude and the phase of an electric potential induced between the electrodes and the ground are detected through a space or an insulator of an electric wire, and a reference phase is determined, and a zero-phase current is synchronously detected by the phase, and a current caused by an insulation resistance included in the leakage current is displayed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a measurement of an insulation state of an electric circuit, and relates to a leakage current measuring instrument that measures a leakage current caused by an insulation resistance of the electric circuit without directly touching the electric circuit in a live line state.

According to the technical standards based on the Electricity Business Law (electrical equipment technical standards, hereinafter referred to as electrical engineering), as a principle of safety, electricity is required to be insulated from the earth. In the measurement with an insulation resistance meter, the reference value is 1 mA in terms of the circuit voltage used. Insulation resistance in ordinary houses is carried out once every four years. However, there are cases where the present situation is absence during the day, problems due to power outage work, and measurement in a house are not preferable. In order to meet these requirements, it has been stipulated that the leakage current be kept at 1 mA or less when the working voltage is in a low voltage circuit and insulation measurement is difficult. This method is widely used in order not to cause a power outage and to understand the insulation state in the house from the outside. There is a method of measuring the leakage current with a clamp-type leakage ammeter with high accuracy (Patent Document 1).

When the leakage current exceeds 1 mA, it is unclear whether the leakage current is due to the capacitance between the electric circuit and the ground or the insulation of the electric circuit is lowered. Therefore, measure the insulation resistance with an insulation resistance tester after a power failure, or input the circuit voltage and zero-phase current while keeping the live line state in the distribution board in a general house, and the resistance included in the leakage current A method of measuring the partial current has been performed.

The method is shown in FIG. In FIG. 1, the circuit voltage is taken into the leakage current resistance measuring device 6 by the voltage detection clip 4 at the load side terminal 2 of the breaker 1. The split-type ZCT 5 is inserted into the electric wire 3 through which the load current flows, and the zero-phase current is detected, and the current in the same phase as the circuit voltage included in the zero-phase current is measured. This current is a resistance component current included in the leakage current (Patent Document 2).
Japanese Patent No. 2802993 JP 2002-125313 A

In the measurement of leakage current at the outdoor entrance, the stray capacitance (capacitance) between the wiring in the entire house and the ground appears as leakage current. The size is around 1 mA. This is an unnecessary current in response to a requirement that the standard of the measured value of the insulation of the electric circuit is 1 mA or less. If the measured current exceeds 1 mA, enter the house, cut off the distribution board, and measure the insulation resistance meter for each feeder. Alternatively, the voltage is measured from the secondary side of the breaker of the distribution board to measure the resistance divided current included in the leakage current, and it is confirmed that the insulation of the electric circuit is good. In such a case, it takes a lot of time and effort.

Two or more electrodes are installed in the current transformer window, the magnitude and phase of the potential induced between this electrode and the ground are detected, the reference phase is obtained, and the zero-phase current is synchronously detected by this phase. Let

The voltage induced in this electrode is the voltage of the primary conductor in the CT window. The phase is detected simultaneously with the voltage. The phase of the live conductor phase of the primary conductor is calculated from the detected phase and voltage magnitude. Thereby, it is possible to measure the resistance leakage current in the leakage current flowing in the electric circuit only by clamping the divided CT to the primary conductor.

At least two copper tape or metal strip electrodes are attached to the inner periphery of the CT window. An electric field shield is attached to each electrode as a common ground potential surface on the side surface or side surface and outer peripheral side of the CT. As a result, the ground-to-ground potential of each phase voltage of a single-phase or three-phase power source arranged at an arbitrary position in the CT window is processed by the potential generated between the electrode and the electric field shield, and the primary side of the CT is processed. Calculate the phase of each phase. Based on the calculated phase, synchronous detection is performed with respect to the leakage current, and the resistance component current included in the leakage current is measured. For a single-phase circuit, the phase of the voltage induced in the electrode is used as a reference. For the three-phase circuit, the reference phase is obtained from the phase induced in each electrode or the phase including the magnitude of the induced voltage, and synchronous detection is performed on the zero-phase current to obtain the resistance leakage current.

As an example, FIG. 2 shows the CT window according to the present invention and the electrostatic coupling between the electrodes, shields and primary conductors attached around the periphery. A secondary winding 8 for detecting a zero-phase current is wound around the iron core 7. The periphery is covered with a resin outer case 9. Electrodes 10, 11, 12, and 13 made of a conductor are attached to the inner periphery of the CT window while being insulated from each other. In order to use the electric potential on the earth ground side as a reference, an electric field shield 14 connected to the earth via a human body or directly is attached around the inner periphery of the CT window. The primary conductor 15 is the R phase, and the conductor 16 is the ground phase S phase. As a result, capacitance is generated between the components. When the capacitance values near the conductors 15 and 16 are shown, the capacitance value between the electrode conductor 15 and the electrode 10 is C1, the gap between the electrode 10 and the shield 14 is C2, the gap between the conductor 15 and the shield C3, and the conductor 15 And the electrode 13 are C4, the conductors 15 and 16 are C5, the conductors 16 and 10 are C6, the conductors 16 and 13 are C7, and the electrodes 13 and the shield 14 are C8. An equivalent circuit for calculating the potential of each nearby electrode can be represented in FIG. In Figure 3, the voltage V _R of the voltage 17 is the voltage of the R phase to earth conductor 15. The conductor 16 is at the same potential as the ground. The potentials between the electrodes 10 and 13 and the shield 14 are indicated by voltages V1 and V2, respectively. Then V1, the output of V2 is manifested as a change in only while magnitude maintaining the phase of V _R. Therefore, if synchronous detection is performed on the zero-phase current using either V1 or V2 as a reference phase, the resistance leakage current can be measured. In a general three-phase electric circuit in which the delta connection is made and one terminal is B-type grounded, the phase range of the voltage between the primary active line phases is 60 degrees. At this time, a phase of 30 degrees that is an intermediate phase in the phase range of the primary voltage is calculated from the size and phase of each electrode, and this phase is set as a reference phase. FIG. 4 is a circuit block diagram of a clamp-type resistance leakage current meter according to the present invention. The CT section 18 is a split CT and has a secondary winding 8 for measuring leakage current, and details are as shown in FIG. Impedance conversion is performed by the buffers 19, 20, 21, and 22. The arithmetic circuit 23 detects the phase of the primary voltage in the CT 18 window. When the phases of the outputs of the buffers 19, 20, 21, and 22 are the same or include only a phase of 180 °, it is determined as a single phase power supply, and the phase of one electrode is set as a reference phase. When the output phase range of the buffers 19, 20, 21, and 22 is 10 ° to 60 °, the primary side voltage is determined to be a three-phase power source, which is 1/2 of the phase range of the primary side power source 30. Calculate ° as a reference. This 30 ° phase detection method that is ½ of the phase range of the primary power supply is obtained by a method of obtaining a solution from an equation that averages the outputs of the buffers 19, 20, 21, and 22, simultaneous equations, or the like. The output of the arithmetic circuit is converted to direct current by the rectifier circuit 24, compared with the reference voltage by the comparator 25, noise and signal level are selected, and the measurement state is indicated by the LED display 26. After confirming the good state of measurement, the calculation output is amplified by the amplifier 27 and then used as a reference signal for the synchronous detection 28. The zero-phase current is output from the CT secondary coil 8, amplified by the amplifier 29, adjusted in error phase by the phase variable circuit 30, and input as a signal to the synchronous detection 28. The output of the synchronous detection 28 becomes a DC level after passing through the filter 31, and the display unit 32 displays the resistance-divided current included in the zero-phase current.

The figure which shows the measurement example of the resistance leakage current measuring instrument which took in the conventional zero phase current and voltage The figure which shows the electrostatic coupling of the electrode pasted around the window and outer periphery of CT, a shield, and a primary conductor by this invention Equivalent circuit diagram between primary conductor and electrode and shield in close proximity to primary conductor Circuit block diagram of resistance measurement according to the present invention

Explanation of symbols

1 .... Breaker 2. Load terminal of breaker 3 .... Electric wire through which load current flows 4 .... Clip for voltage measurement 5 .... Split CT, 6 .... Measuring instrument for resistance measurement of leakage current Main body, 7 ... Iron core used for CT, 8 ... CT secondary winding, 9 ... Exterior case, 10 ... Electrode 1, 11 ... Electrode 2, 12 ... Electrode 3, 13 ... Electrode 4 , 14 .. Electric field shield, 15 .. R phase power supply, 16 .. S phase power supply, 17 .. Potential of R phase power supply with respect to ground, 18 .. CT section, 19, 20, 21, 22,. Buffer, 23 .... arithmetic circuit for measuring voltage magnitude and phase, 24..rectifier circuit, 25..comparator circuit, 26..LED display, 27..amplifier circuit, 28..synchronous detection circuit, 29. ..Amplifier 30 ..Phase adjustment circuit 31 ..Low pass filter 2 ··· Display unit, capacitance between C1 ·· R phase and electrode 1, C2 ··· Capacitance between electrode 1 and electric field shield, C3 ·· Capacitance between R phase and electric field shield, C4 · · Capacitance between R phase and electrode 2, C5 ·· Capacitance between R phase and S phase, C6 ·· Capacitance between S phase and electrode 1, C7 ·· S phase and electrode 2 , Capacitance between C8... Electrode 2 and electric field shield, C9... Capacitance between S phase and electric field shield, V1... Potential generated between electrode 1 and electric field shield 14, V2 .. Potential generated between electrode 2 and electric field shield 14

Claims (3)

  When measuring the insulation state of the circuit in the live line state by measuring leakage current using CT in the lead-in line or branch circuit of the single-phase two-wire type, single-phase three-wire type, three-phase three-wire type circuit , Provide two or more electrodes in the CT window, detect the phase of the voltage induced in the electrodes, compare the phase with the leakage current flowing in the electric circuit output to the secondary side of the CT, and insulate the electric circuit Leakage current measuring instrument that measures the leakage current caused by resistance.   When measuring the insulation state of the electric circuit in the live line state using CT in the lead-in line or branch circuit of the single-phase two-wire type, single-phase three-wire type, three-phase three-wire type electric circuit, the inner circumference of the CT Two or more electrodes are provided, and the phase of the voltage induced in the electrodes is detected, the harmonic component included in the detected voltage is detected, and the harmonic component included in the leakage current flowing through the circuit is compared. Leakage current measuring instrument that measures the leakage current caused by the insulation resistance of the electric circuit. Insulation of the electric circuit by using the electrode and the electric field shielding material used in the CT shown in claim 1 or 2 together with the magnetic shield for reducing the residual current and the external magnetic field attached to the CT. Leakage current measuring instrument that measures leakage current caused by resistance

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