JP5679480B2 - Indirect AC megger measuring instrument and insulation resistance measuring method - Google Patents

Description

  The present invention relates to an indirect AC megger measuring device and an insulation resistance measuring method, and more particularly to an indirect AC megger measuring device and an insulation resistance measuring method suitable for use in measuring an insulation resistance of an extra high voltage transformer.

  Insulation resistance measurement (Megger measurement), which is one of the regular inspection items for extra high voltage transformers in the power generation and substation departments of electric power companies, is a grounded instrument transformer (hereinafter referred to as "GPT"), which is a grounding device. Is directly connected, since the transformer circuit is in the grounded state through the GPT, the insulation resistance measurement cannot be performed as it is, so the insulation resistance measurement is performed by separating the GPT main circuit. Further, in the case of an equipment configuration in which the GPT main circuit cannot be disconnected, the insulation resistance measurement is performed by removing the GPT primary side ground terminal.

  In Patent Document 1 below, in order to eliminate the need to remove and attach the ground wire of the primary side ground terminal of the GPT at the time of measuring the insulation resistance of the high piezoelectric path, the primary side ground terminal of the GPT is set to a predetermined By grounding via a capacitor with a capacitance value, the capacitor does not pass direct current, so when measuring insulation resistance, the high-voltage winding of the GPT is in the same state as disconnected from the ground, so insulation is performed with the capacitor connected. A grounded instrument transformer is disclosed which allows resistance measurements.

JP-A-6-84670

However, the conventional insulation resistance measuring method has the following problems.
(1) In the method of measuring the insulation resistance by separating the GPT main circuit, the removal and attachment of the three lead wires of the GPT main circuit (see the _{first to third} lead wires 51 to 53 shown in FIG. 1) Work is necessary.
(2) It takes time to measure the insulation resistance because it is necessary to remove the lead wire of the GPT main circuit or the primary ground terminal of the GPT along with the insulation resistance measurement.
(3) Since the work for removing the lead wire of the GPT main circuit is often performed at a high place where the GPT is installed, it may be dangerous.
(4) In the method of removing the primary side ground terminal of the GPT, since the insulator for the primary side ground terminal is small, there is a possibility that the insulator may be damaged at the time of removing the terminal. In some cases, the protective relay cannot be used or cannot be restored.
(5) GPT main circuit lead wire and GPT primary side grounding terminal are required to be removed and attached, which may lead to poor tightening or forgetting connection. An abnormal voltage with the same potential as that of the main circuit is generated at the terminal, resulting in damage to the equipment.

  An object of the present invention is to provide an indirect AC megger measuring device and an insulation resistance measuring method capable of improving workability and safety and preventing damage to insulators and equipment.

The indirect AC megger measuring device of the present invention is an indirect AC megger measuring device (10, 10 ') for measuring a transformer insulation resistance (R) which is an insulation resistance of an extra high voltage transformer (1). First to third grounded-type instrument transformers (2 ₁ to 2 _{3) in which the first} to _third primary terminals are connected to the first to third phases of the secondary transmission lines of the transformer, respectively. ) the first to the third secondary voltage applying means for applying an applied voltage (V) is to terminals, the first of the applied voltage of the first to third grounding type instrument transformer Through the _{first to third} primary ground terminals (2a _{1 to} 2a ₃ ) of the first to third earthing-type instrument transformers when applied to the second to third secondary terminals, respectively . 1st to 3rd primary side current (i _{1 to} i ₃ ) or current for detecting the current flowing through the output line of the voltage applying means Detection means, provided with a transformer insulation resistance measuring means for measuring a pre-Symbol transformer insulation resistance, the voltage applying means, said first through said first to third grounding type instrument transformer The applied voltage for inducing an AC voltage having a predetermined effective value between the third primary side terminal and the ground is calculated based on the voltage class of the high voltage system in which the transformer is installed, and the calculated An applied voltage is applied to each of the first to third secondary terminals of the first to third grounded-type instrument transformers, and the transformer insulation resistance measuring means includes the applied voltage and the predetermined voltage The transformer insulation resistance is measured on the basis of an effective value and a current flowing through the first to third primary currents or an output line of the voltage applying means .
Here, the applied voltage, respectively an alternating voltage of an effective value = 2,000 V between the first to third above the earth type instrument transformer first through the third primary-side terminal and the ground An alternating voltage to be induced may be used.
The first indirect AC megger measuring device of the present invention is an AC power source (11) for the indirect AC megger measuring device (10) to output the applied voltage, and for the first to third grounding type meters. First to third clamp current transformers (21 _{1 to} 21 ₃ ) respectively attached to first to third ground lines for grounding the first to third primary side ground terminals of the transformer, respectively. ), A microprocessor (14) for calculating the transformer insulation resistance based on the first to third primary currents respectively input from the memory, and a memory (15) connected to the microprocessor; A display (16) for displaying various data and an operation panel (17) for inputting an insulation resistance start command and the voltage class are provided.
Here, the microprocessor calculates an effective value (ie) of a primary side current (i) that is a vector sum of the first to third primary side currents, and the primary side current and the applied voltage. And the transformer insulation resistance may be calculated using the following equation.
R = {2000 / ie} × cos θ
Where ie = effective value of the primary side current
θ = phase difference between the primary side current and the applied voltage The second indirect AC megger measuring device of the present invention is an AC power source for the indirect AC megger measuring device (10 ′) to output the applied voltage. (11), a current transformer (18) installed on the output line of the AC power supply, and a microprocessor (14) for calculating the transformer insulation resistance based on the current input from the current transformer And a memory (15) connected to the microprocessor;
A display (16) for displaying various data and an operation panel (17) for inputting an insulation resistance start command and the voltage class are provided.
Here, the microprocessor position between the applied voltage and the secondary current and calculates the effective value of the secondary-side current (I) to (Ie) based on the current that will be input from the current transformer You may obtain | require a phase difference ((theta)) and may calculate the said transformer insulation resistance using following Formula.
R = {2000 / (Ie / transformation ratio)} × cos θ
Where Ie = effective value of the secondary current
θ = phase difference between the secondary current and the applied voltage The first insulation resistance measuring method of the present invention uses the first indirect AC megger measuring device of the present invention to The first to third grounded-type instrument transformers when the applied voltage is applied from the AC power source to the first to third secondary terminals of the topographic instrument transformer, respectively . The first to third clamp current transformers detect the first to third primary currents respectively flowing through the three primary ground terminals, respectively, and the first to third clamp current transformers are detected. The transformer insulation resistance is measured by the microprocessor on the basis of the first to third primary side currents detected respectively by the microprocessor.
The second insulation resistance measuring method of the present invention uses the second indirect AC megger measuring device of the present invention to perform the first to third secondary of the first to third earthing-type instrument transformers. the current flowing through the output line of the AC power when applying the application voltage from the AC power supply to the positive terminal respectively detected by the current transformer, the transformer on the basis of the current detected by the displacement current transformer The insulation resistance is measured by the microprocessor.

The indirect AC megger measuring device and the insulation resistance measuring method of the present invention have the following effects.
(1) Since it is not necessary to remove the lead wire of the GPT main circuit or the primary side ground terminal of the GPT, the insulation resistance measurement time can be greatly shortened compared to the conventional method. It is possible to eliminate the risk of equipment damage due to breakage of the insulator for the side ground terminal or forgetting connection, etc., and it is possible to eliminate the incidental costs associated with inspection.
(2) Since it is possible to eliminate the work of removing the lead wire of the GPT main circuit which is dangerous at high places, safety can be improved.

It is a figure for demonstrating the indirect alternating current megar measuring device 10 by one Example of this invention. It is a block diagram which shows the structure of the indirect alternating current megger measuring device 10 shown in FIG. 3 is a flowchart for explaining the operation of the MPU 14 shown in FIG. 2. It is a block diagram which shows the structure of the indirect alternating current megger measuring device 10 'which is a modification of the indirect alternating current megger measuring device 10 shown in FIG. It is a figure for demonstrating the test circuit used in the verification test of the insulation resistance measuring method of this invention. It is a figure which shows an example of the verification test result of the insulation resistance measuring method of this invention.

  For the above purpose, when an applied voltage is applied from the AC power source to the secondary side terminals of the first to third GPTs, the first to third primary side ground terminals of the first to third GPTs flow respectively. This was realized by measuring the transformer insulation resistance based on the first to third primary side currents or the current flowing through the output line of the AC power supply.

Embodiments of an indirect AC megger measuring device and an insulation resistance measuring method according to the present invention will be described below with reference to the drawings.
As shown in FIG. 1, the indirect AC megger measuring device 10 according to one embodiment of the present invention has a primary terminal connected to the first to third phases of the secondary transmission line of the extra high voltage transformer 1. the first to the effective value between the third GPT2 ₁ to 2 ₃ of the applied voltage V 2 primary terminals (first to third GPT2 ₁ to 2 ₃ of the primary-side terminal and the ground was = 2,000 V Are applied to the _first to _third primary side ground terminals 2a _{1 to} 2a ₃ of the first to _third GPTs 2 ₁ to 2 ₃ , respectively. Primary side currents i _{1 to} i ₃ are detected, and based on the detected first to third primary side currents i _{1 to} i ₃ , the insulation resistance R (hereinafter referred to as “transformer insulation resistance”) of the transformer 1 is detected. R ”)).

Therefore, when measuring the transformer insulation resistance R, the GPT secondary side knife switch installed between the secondary side terminals and the secondary side common terminals of the _first to _third GPTs 21 to 23 and the switchboard 3 and at the same time, the GPT tertiary knife switch 4 installed between the tertiary side terminals of the _first to _third GPTs 2 ₁ to 2 ₃ and the switchboard is turned off, so that the first to third GPTs 2 ₁ to 2 are turned off. _The secondary side common terminals of the _first to _third secondary wirings L _{1 to} L ₃ and the _first to _third GPTs 2 ₁ to 2 _{3 that} connect the secondary side terminals of ₃ to the GPT secondary side knife switch 3, respectively. Is applied to the secondary common wiring L _C connected to the GPT secondary knife switch 3 from the indirect AC megameter 10.
The first to third GPT2 ₁ to 2 ₃ of the primary-side ground terminal 2a ₁ first, to 2A region ₃ to the first to third ground line is grounded third clamp current transformer 21 ₁ - 21 ₃ , and the first to third primary currents i _{1 to} i ₃ detected by the first to _third clamp current transformers 21 _{1 to} 21 ₃ , respectively, to the indirect AC megger measuring device 10. input.
In the indirect AC megger measuring device 10, the transformer insulation resistance R is measured based on the _{first to third} primary currents i _{1 to} i ₃ .

As shown in FIG. 2, the indirect AC megger measuring device 10 includes a variable insulated AC power supply 11 for outputting an applied voltage V, an applied voltage V input from the variable insulated AC power supply 11 and first to third clamps. An analog / digital converter 12 (hereinafter referred to as “A / D converter 12”) for converting the primary currents i _{1 to} i ₃ input from the current transformers 21 _{1 to} 21 ₃ into digital data. And a microprocessor for calculating the transformer insulation resistance R based on the input / output interface 13 (hereinafter referred to as “I / O 13”) and the first to third primary currents i _{1 to} i _3. 14 (hereinafter referred to as “MPU 14”), a memory 15 connected to the MPU 14, a display 16 for displaying various data, an insulation resistance start command, a voltage class of a circuit under test, and the like. Operation panel ; And a 7.
The variable insulation AC power supply 11, the A / D converter 12, the MPU 14, the display 16 and the operation panel 17 are connected to the I / O 13.

One of the two output lines of the variable insulated AC power supply 11 (hereinafter referred to as “first output line”) is branched into three branches and then first to third secondary. The other output lines (hereinafter referred to as “second output lines”) are connected to the side wirings L _{1 to} L ₃ , respectively, and are connected to the secondary side common wiring L _C.

Next, the operation of the MPU 14 will be described with reference to the flowchart shown in FIG.
When the MPU 14 receives the insulation resistance start command and the voltage class of the circuit under test from the operation panel 17 via the I / O 13 (step S11), the primary side terminals of the _first to _third GPTs 2 ₁ to 23 ₃ After calculating the applied voltage V (effective value Ve = 2000 / transformation ratio) induced by an alternating voltage of effective value = 2,000 V between the ground and the ground based on the voltage class, the calculated applied voltage V is output. To the variable insulated AC power supply 11 via the I / O 13 (step S12).
For example, the effective value Ve of the applied voltage V is 20.0 V for the 11 kV system, 10.0 V for the 22 kV system, 3.3 V for the 66 kV system, and 2.0 V for the 110 kV system.
As a result, the applied voltage V is applied between the first to third secondary wirings L _{1 to} L ₃ and the secondary common wiring L _C , respectively, and the first to third GPTs 2 ₁ to 2 are applied. ₃ of the primary-side ground terminal 2a ₁ to 2A region ₃ through the first to third primary-side current i ₁ through i _3, respectively.
The applied voltage V and the first to third primary currents i _{1 to} i ₃ detected by the first to _third clamp current transformers 21 _{1 to} 21 ₃ are digitally converted by the A / D converter 12. After being converted to data, it is input to the MPU 14 via the I / O 13.

The MPU 14 calculates the effective value ie of the vector sum of the input first to third primary side currents i _{1 to} i ₃ (hereinafter referred to as the vector sum of the first to third primary side currents i _{1 to} i ₃ ). (Referred to as “primary side current i”) and a phase difference θ between the primary side current i and the applied voltage V is obtained (step S13).

Thereafter, the MPU 14 calculates the transformer insulation resistance R using the following equation (1) (step S14).
R = {2000 / ie} × cos θ (1)
Where ie = effective value of primary side current i
θ = phase difference between primary current i and applied voltage

  Thereafter, the MPU 14 determines that the transformer insulation resistance R obtained is “good” if the obtained transformer insulation resistance R is 500 MΩ or more (500 MΩ ≦ R), and the obtained transformer insulation resistance R is 100 MΩ or more and less than 500 MΩ (100 MΩ ≦ R <500 MΩ). If there is, it is determined as “Needs Attention”, and if the obtained transformer insulation resistance R is less than 100 MΩ, it is determined as “defective” and the determination result is displayed on the display 16 via the I / O 13 (steps S15 to S15). S18).

Thereafter, the MPU 14 stores the applied voltage V, the first to third primary side currents i _{1 to} i ₃ , the primary side current i, and the transformer insulation resistance R in the memory 15 in accordance with an instruction from the operation panel 17. The information is stored or displayed on the display 16 (step S19).

In the above description, the transformer insulation resistance R is measured based on the _{first to third} primary currents i _{1 to} i ₃ input from the first to _third clamp current transformers 21 _{1 to} 21 ₃ . However, as shown in FIG. 4, a current transformer 18 is installed in the first output line of the variable insulated AC power supply 11 as in the indirect AC megameter 10 ′, and the first output line of the variable insulated AC power supply 11 The flowing current may be detected by the current transformer 18, and the transformer insulation resistance R may be measured based on the detected current.
In this case, the MPU 14 calculates the effective value Ie of the secondary side current I based on the current input from the current transformer 18 via the A / D converter 12 and the I / O 13 and the secondary side current. The phase difference θ between I and the applied voltage V is obtained, and the transformer insulation resistance R is calculated using the following equation (2).
R = {2000 / (Ie / transformation ratio)} × cos θ (2)
Where Ie = effective value of secondary side current I
θ = phase difference between secondary current I and applied voltage Note that the current transformer 18 may be installed on the second output line of the variable insulated AC power supply 11.

Next, the result of the verification test for measuring the insulation resistance of the transformer 1 using the indirect AC megger measuring devices 10 and 10 ′ will be described with reference to FIGS. 5 and 6A and 6B.
As shown in FIG. 5, this demonstration test uses a variable AC power source 51 in place of the indirect AC megger measuring device 10 to apply the applied voltage V to the secondary terminals of the _first to _third GPTs 2 ₁ to 2 _3. applied to, as well as using the bonding wire 53 to the primary-side terminals of the simulated device 52 first to third GPT2 ₁ to 2 _3, first to the first to third GPT2 ₁ to 2 ₃ The third primary side ground terminals 2a _{1 to} 2a ₃ were connected to the ground line 54, and the process was performed as follows.
(1) The transformer insulation resistance R is measured based on the primary side current i (first to third primary side currents i _{1 to} i ₃ ) as in the indirect alternating current megger 10 shown in FIG. Regarding the method (hereinafter referred to as “first insulation resistance measuring method”), the applied voltage V from the variable AC power source 51 is measured by the voltmeter 55 and the _first to _third GPTs 21 to 23 are measured. A clamp current transformer 55 in which a primary current i, which is a vector sum of first to _third primary currents i _{1 to} i ₃ flowing in the primary ground terminals 2a _{1 to} 2a ₃ , is attached to the ground line 54, respectively. And by determining the insulation resistance r of the simulated device 52 (hereinafter referred to as “simulated device insulation resistance r”) using the above-described equation (1) based on the measured primary current i. .
(2) A method of measuring the transformer insulation resistance R based on the secondary current I as in the indirect AC megger measuring instrument 10 ′ shown in FIG. 4 (hereinafter referred to as “second insulation resistance measurement method”). ), The applied voltage V from the variable AC power supply 51 is measured by the voltmeter 55, and the secondary current I is connected to the common output line (secondary common wiring L _C) of the variable AC power supply 51. ) Was measured by using a clamp current transformer 57 attached to (), and based on the measured secondary current I, the above-described equation (2) was used to obtain the simulated device insulation resistance r.

As shown in FIG. 6A, the result of the verification test for the first insulation resistance measurement method is the measurement of the simulated equipment insulation resistance r when the insulation resistance of the simulated equipment 52 is set to 10 MΩ, 5 MΩ, 2 MΩ, and 1 MΩ. The values were 7.52 MΩ (error = −25%), 4.34 MΩ (error = −13%), 1.94 MΩ (error = −3%) and 0.81 MΩ (error = −19%). In this test, the leakage current component flowing in the simulation device 52 used for the verification is mostly in-phase with the applied voltage V, and the influence of the phase difference θ between the applied voltage V and the leakage current is small. Correction by (cosθ) was omitted.
Here, the reason why the error is as large as −25% is that the clamp current transformer 56 cannot prepare a device capable of detecting a minute current and uses a device having a measurement range of 0 to 20 A. Conceivable. Therefore, it was confirmed that the transformer insulation resistance R can be measured with less error by the first insulation resistance measurement method by using the clamp current transformer capable of detecting a minute current.

As shown in FIG. 6B, the result of the verification test for the second insulation resistance measurement method is the measurement of the simulated equipment insulation resistance r when the insulation resistance of the simulated equipment 52 is set to 10 MΩ, 5 MΩ, 2 MΩ, and 1 MΩ. The values were 1.40 MΩ (error = −86%), 1.25 MΩ (error = −75%), 0.90 MΩ (error = −55%) and 0.55 MΩ (error = −45%).
As a result, among the current components flowing through the GPT, the component of the secondary current I in phase with the applied voltage V increases as the simulated device insulation resistance r decreases, but the component of the secondary current I delayed by 90 degrees greatly changes. However, it has been found that it is difficult to calculate the transformer insulation resistance R based on the secondary current I (this is because the GPT is compared with the simulated equipment insulation resistance r). This is probably because the resistance component of the excitation impedance is small).
However, the second insulation resistance measurement method is affected by the excitation current of the GPT, but the verification test result is an error in a direction that becomes smaller than the actual simulated equipment insulation resistance r, so that the safety direction is judged. Therefore, only when the measured transformer insulation resistance R is outside the allowable range, the lead wire of the GPT main circuit or the primary side ground terminal of the GPT is removed and the transformer insulation resistance R is measured as before. As a result, it proved effective in complementing the conventional insulation resistance measurement method.

1 Transformer 2 _{1 to} 2 _{3 1st} to _3rd GPT
2a _{1 to} 2a ₃ 1st to 3rd primary side ground terminal 3 GPT secondary side knife switch 4 GPT tertiary side knife switch 5 _{1 to} 5 ₃ 1st to 3rd lead wires 10, 10 'Indirect AC megger measuring device 11 Variable Insulation AC Power Supply 12 A / D Converter 13 I / O
14 MPU
15 Memory 16 Display 17 Operation Panel 18 Current Transformers 21 _{1 to} 21 ₃ First to Third Clamp Current Transformers 51 Variable AC Power Supply 52 Simulated Equipment 53 Connection Line 54 Grounding Line 55 Voltmeter 56, 57 Clamp Current Transformer L _{1 to} L ₃ First to third secondary side wirings L _C Secondary side common wiring R Transformer insulation resistance r Simulated equipment insulation resistance V Applied voltage Ve Effective value i of applied voltage V Primary side current ie Primary RMS values i _{1 to} i _{3 of} the side current i _{1st to 3rd} primary current I Secondary current Ie RMS values of the secondary current I S11 to S19

Claims (8)

An indirect AC megger measuring device (10, 10 ') for measuring a transformer insulation resistance (R) which is an insulation resistance of an extra high voltage transformer (1),
First to third grounded-type instrument transformers (2 ₁ to 2 _{3) in which the first} to _third primary terminals are connected to the first to third phases of the secondary transmission lines of the transformer, respectively. ) and the first to third secondary voltage applying means for applying each applied voltage (V) at the terminals of,
First of the first to third grounding type instrument transformer when applying respectively the applied voltage to the first to third secondary terminals of the first to third grounding type instrument transformer First to third primary side currents (i _{1 to} i ₃ ) flowing through the first to _third primary side ground terminals (2a _{1 to} 2a ₃ ), respectively, or a current flowing to the output line of the voltage applying means are detected. Current detection means for
A transformer insulation resistance measuring means for measuring the transformer insulation resistance ,
The voltage application means induces an AC voltage having a predetermined effective value between the first to third primary terminals of the first to third grounded-type instrument transformers and the ground, respectively. The voltage is calculated based on the voltage class of the high voltage system in which the transformer is installed, and the calculated applied voltage is used as the first to third secondary of the first to third grounded-type instrument transformers. Apply to each side terminal,
The transformer insulation resistance measuring means is configured to change the voltage based on the applied voltage, the predetermined effective value, and the first to third primary currents or the current flowing through the output line of the voltage applying means. Measuring the insulation resistance,
An indirect AC megger measuring device. The applied voltage induces an AC voltage having an effective value of 2,000 V between the first to third primary terminals of the first to third grounded-type instrument transformers and the ground, respectively. 2. The indirect AC megger measuring device according to claim 1, wherein the measuring device is a voltage. The indirect AC megger measuring device (10)
An AC power supply (11) for outputting the applied voltage;
First to third attached to first to third ground lines for grounding the first to third primary side ground terminals of the first to third grounded-type instrument transformers, respectively. and based clamp current transformer from (21 ₁ to 21 ₃₎ in the first to third primary current is inputted, the microprocessor for calculating the transformer insulation resistance (14),
A memory (15) connected to the microprocessor;
A display (16) for displaying various data;
An operation panel (17) for inputting an insulation resistance start command and the voltage class ;
The indirect AC megger measuring device according to claim 1 or 2, characterized by comprising: The microprocessor calculates an effective value (ie) of a primary side current (i) that is a vector sum of the first to third primary side currents, and calculates the level of the primary side current and the applied voltage. Obtain the phase difference (θ) and calculate the transformer insulation resistance using the following equation: R = {2000 / ie} × cos θ
Where ie = effective value of the primary side current
The indirect AC megameter according to claim 3, wherein θ is a phase difference between the primary side current and the applied voltage. The indirect AC megger measuring device (10 ′)
An AC power supply (11) for outputting the applied voltage;
A current transformer (18) installed on the output line of the AC power supply;
A microprocessor (14) for calculating the transformer insulation resistance based on the current input from the current transformer;
A memory (15) connected to the microprocessor;
A display (16) for displaying various data;
An operation panel (17) for inputting an insulation resistance start command, the voltage class, and the like;
The indirect AC megger measuring device according to claim 1 or 2, characterized by comprising: The microprocessor the phase difference between the applied voltage and the secondary current to calculate an effective value (Ie) of the based on the current that will be input from the current transformer secondary current (I) (theta ) And calculate the transformer insulation resistance using the following equation: R = {2000 / (Ie / transformation ratio)} × cos θ
Where Ie = effective value of the secondary current
The indirect AC megameter according to claim 5, wherein θ is a phase difference between the secondary current and the applied voltage. 5. The applied voltage from the AC power source to the first to third secondary terminals of the first to third earthing-type instrument transformers using the indirect AC megger measuring device according to claim 3 or 4. The first to third primary-side currents flowing through the first to third primary-side ground terminals of the first to third earthing-type instrument transformers when applied, respectively . The transformer insulation resistance is detected by the third clamp current transformer, and the transformer insulation resistance is determined based on the first to third primary currents respectively detected by the first to third clamp current transformers. An insulation resistance measuring method, comprising: measuring with a processor. The applied voltage from the AC power source to the first to third secondary terminals of the first to third earthing-type instrument transformers using the indirect AC megger measuring device according to claim 5 or 6. when applying respectively the current flowing through the output line of the AC power supply detected by the current transformer, the said transformer insulation resistance based on the current detected by the displacement current transformer can be measured by the microprocessor A method for measuring insulation resistance, which is characteristic.

Images