Current integral value measuring device

Abstract

This invention provides a current integral value measuring device that suppresses the discharge rate under long-term storage conditions while using small-capacity capacitors, leading to accurate evaluation of insulation performance. [Solution] The current integral value measuring device (20) is a measuring circuit (23) having a measuring input terminal (21) and a ground terminal (22), and comprises a charge storage capacitor (24) connected in series with an insulating sample (S), a surge absorber (27) connected in parallel with the charge storage capacitor, a buffer amplifier (25) connected from the connection point of the surge absorber towards the measuring input terminal, and a surge current protection resistor (26) connected before the buffer amplifier. The charge storage capacitor, the surge absorber, and the surge current protection resistor are potted, and the charge storage capacitor, the surge absorber, the surge current protection resistor, and the buffer amplifier are connected to the measuring circuit by point-to-point wiring.

Description

Technical Field

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[0001] The present invention relates to a current integral value measuring device.

Background Art

[0002] In recent years, it has been required to accurately grasp the deterioration state of the insulating layer of a high-voltage power cable. As one method for evaluating the performance of an insulator, a measurement system 1 based on the Qt method shown in FIG. 8 is known. The measurement system 1 based on the Qt method includes an insulating sample S to be evaluated, a current integral value measuring device 10, and a DC power supply 3 for applying a DC voltage. The current integral value measuring device 10 includes a charge storage capacitor 4 connected in series to the insulating sample S, a buffer amplifier 5 for measuring the voltage applied to the charge storage capacitor 4, and a voltmeter 6. In the measurement system 1 based on the Qt method, since the charge storage capacitor 4 is connected in series to the insulating sample S, the amount of charge accumulated in the charge storage capacitor 4 is equal to the amount of charge accumulated in the insulating sample S. By measuring the amount of charge (current integral value) of the charge storage capacitor 4 from the value of the voltmeter 6, the insulation performance of the insulating sample S is evaluated. For this basic configuration, for example, in Patent Document 1, a configuration for preparing for insulation breakdown by further including a protection capacitor is disclosed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In such current integral value measuring devices, there is a demand to use small capacitance capacitors (e.g., 0.1 μF) to improve responsiveness and measurement accuracy. However, reducing the capacitance of the capacitor increases the discharge rate during long-term measurements (e.g., 12 hours), making it difficult to accurately evaluate the insulation performance. Therefore, using small capacitance capacitors has been considered difficult. Furthermore, while it is desirable to add components to prepare for dielectric breakdown, etc., it has been considered difficult to easily add components because leakage current is generated around those components.

[0005] This invention has been made in view of these circumstances, and aims to provide a current integral value measuring device that suppresses the discharge rate under long-term storage conditions while using a small-capacity capacitor, leading to accurate evaluation of insulation performance. [Means for solving the problem]

[0006] To solve the above problems, a current integral value measuring device according to a first aspect of the present invention is a current integral value measuring device that applies a DC voltage to an insulating sample to evaluate the insulating performance of the insulating sample, and comprises a measurement circuit having a measurement input terminal and a ground terminal, a charge storage capacitor connected in series with the insulating sample, a surge absorber connected in parallel with the charge storage capacitor, a buffer amplifier connected from the connection point of the surge absorber towards the measurement input terminal, and a surge current protection resistor connected before the buffer amplifier, wherein the charge storage capacitor, the surge absorber, and the surge current protection resistor are potted, and the charge storage capacitor, the surge absorber, the surge current protection resistor, and the buffer amplifier are connected to the measurement circuit by point-to-point wiring.

[0007] In the current integral value measuring device of the second embodiment, it is also preferable that, in the first embodiment, the charge storage capacitor, the surge current protection resistor, and the buffer amplifier each include a first guard ring, a second guard ring, and a third guard ring, which operate at the same potential as the point-to-point wiring circuit.

[0008] In the current integral value measuring device of the third embodiment, in the second embodiment, it is also preferable that the first guard ring of the charge storage capacitor and the second guard ring of the surge current protection resistor are formed by connecting the charge storage capacitor and the surge current protection resistor to the same potential pattern formed by routing the output pattern of the buffer amplifier.

[0009] In the current integral value measuring device of the fourth embodiment, in the second or third embodiment, it is also preferable that the third guard ring of the buffer amplifier includes a high-impedance area that surrounds the high-impedance pattern of the buffer amplifier module at the same potential.

[0010] In the current integral value measuring device of the fifth embodiment, it is also preferable that, in the fourth embodiment, a solid is formed in the second layer below the first layer on which the third guard ring is formed, the third guard ring is connected to the solid of the second layer, and a plurality of through holes are formed around the high impedance pattern of the third guard ring.

[0011] In the current integral value measuring device of the sixth embodiment, in any of the first to fifth embodiments, the surge current protection resistor is housed in a surge current protection resistor case, the case legs of the surge current protection resistor case are connected to the ground of the measuring circuit, and it is also preferable that a slit is formed in the circuit board below the surge current protection resistor case.

[0012] In the current integral value measuring device of the seventh embodiment, it is also preferable that the area between the measurement input terminal and the surge absorber be a non-guard ring region, in any of the first to sixth embodiments. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a current integral value measuring device that suppresses the discharge rate under long-term storage conditions while using a small-capacity capacitor, leading to accurate evaluation of insulation performance.

Brief Description of the Drawings

[0014] [Figure 1] This is an example of the evaluation circuit configuration of the current integration value measuring device 20 according to an embodiment of the present invention. [Figure 2] This is a schematic circuit diagram of the main part of the current integration value measuring device 20. [Figure 3] This is an example of the configuration of the charge storage capacitor 24 and its mounting area. [Figure 4] This is an example of the configuration of the surge absorber 27 and its mounting area. [Figure 5] This is an example of the configuration of the surge current protection resistor 26 and its mounting area. [Figure 6] This is an example of the configuration of the buffer amplifier 25 and its mounting area. [Figure 7] This is an equivalent circuit diagram of the current integration value measuring device 20. [Figure 8] This is a schematic circuit diagram of the current integration value measuring device according to the prior art.

Modes for Carrying Out the Invention

[0015] Next, a preferred embodiment of the present invention will be described based on the drawings.

[0016] (Overall Configuration) FIG. 1 is an example of the evaluation circuit configuration of the current integration value measuring device 20 according to an embodiment of the present invention during measurement. The current integration value measuring device 20 is used in a system for measuring insulation performance by the Qt method, and is attached to an insulation sample S to be evaluated via electrodes 10A and 10B. The current integration value measuring device 20 is connected to the insulation sample S via a damping resistor 10C for reducing the inrush current, and is also connected to a DC power supply 10D for applying a DC voltage to the insulation sample S. A high voltage (for example, 10 kV, etc.) is applied from the DC power supply 10D, and the insulation performance of the insulation sample S is evaluated.

[0017] The current integral value measuring device 20 includes a measurement input terminal 21 and a ground terminal 22. The measurement circuit 23 between the measurement input terminal 21 and the ground terminal 22 includes a charge storage capacitor 24 connected in series to the insulation sample S, a surge absorber 27 connected in parallel to the charge storage capacitor 24, a buffer amplifier 25 connected on the measurement input terminal 21 side from the connection point of the surge absorber 27, and a surge current protection resistor 26 connected in front of the buffer amplifier 25. The signal detected by the buffer amplifier 25 is digitally converted by the A / D converter 28 and sent to the receiving device 10E via the wireless module 29. The receiving device 10E is, for example, a personal computer equipped with a wireless receiver, and the communication is performed, for example, in the Wi-SUN (Wireless Smart Utility Network) wireless standard in the 920 MHz band. The receiving device 10E includes a CPU, measures the voltage value applied to the charge storage capacitor 24 from the signal detected by the buffer amplifier 25, calculates the charge amount (current integral value) of the charge storage capacitor 24, and obtains the accumulated charge amount. The current integral value and the like are displayed on a display unit (not shown) provided in the receiving device 10E, and measurement and evaluation over time are possible via the receiving device 10E. Since the resistance value of the surge current protection resistor 26 is significantly smaller than the resistance value of the input resistance of the buffer amplifier 25, the surge current protection resistor 26 does not affect the measurement of the current integral value of the charge storage capacitor 24.

[0018] Here, the current integral value measuring device 20 may be arranged on the upstream side or the downstream side of the insulation sample S. When the insulation sample S is an object that can be measured indoors, such as a film, the current integral value measuring device 20 may be arranged on the downstream side of the insulation sample S. On the other hand, when the insulation sample S is an object that is difficult to measure indoors, particularly when it is a power cable buried in the ground at the site, as shown in this embodiment, the current integral value measuring device 20 is arranged on the upstream side of the insulation sample S, and it is also possible to use the current integral value measuring device 20 in a manner that electrically floats it from the ground.

[0019] Figure 2 is a schematic circuit diagram of the main part of the current integral value measuring device 20 (the part indicated by symbol C in Figure 1). As shown in Figure 2, the charge storage capacitor 24, surge absorber 27, and surge current protection resistor 26 are "potted" (in Figure 2, the potted areas are indicated by symbol P). The charge storage capacitor 24, surge absorber 27, surge current protection resistor 26, and buffer amplifier 25 are connected to the measuring circuit 23 by "point-to-point wiring" (in Figure 2, the point-to-point wiring areas are indicated by symbol aw). The charge storage capacitor 24, surge current protection resistor 26, and buffer amplifier 27 are each fitted with "guard rings" (in Figure 2, the guard ring areas are indicated by symbol G).

[0020] The configurations of the charge storage capacitor 24, surge absorber 27, surge current protection resistor 26, and buffer amplifier 25 will be described below.

[0021] (Configuration of a charge storage capacitor) The charge storage capacitor 24 is subjected to potting, point-to-point wiring, and a guard ring. Figure 3 shows an example of the configuration of the charge storage capacitor 24 and its mounting area, where (A) is a perspective view of the capacitor module 240, (B) is a plan view of the mounting area of ​​the charge storage capacitor 24, (C) is a front view of (B), and (D) is a right side view of (B).

[0022] As shown in Figure 3(A), the capacitor module 240 of the charge storage capacitor 24 has a film capacitor 241 housed in a capacitor case 242, with only mounting hardware 243 exposed from the bottom of the case. The film capacitor 241 is, for example, made of polypropylene and is a low-leakage, minute-capacitance film capacitor with a capacitance of 0.1 μF. It is soldered to the mounting hardware 243, cured and dried while embedded in silicon inside the capacitor case 242, and sealed inside the case 242 (potting process). This prevents deterioration of the surface insulation resistance of the film capacitor 241.

[0023] Each capacitor module 240 cannot be mounted on the circuit board 230 of the measurement circuit 23 in order to suppress leakage current between terminals. The terminals of each capacitor module 240 need to be wired away from the circuit board 230. For this reason, the mounting area of ​​the charge storage capacitors 24 is electrically isolated from the circuit board 230 by placing a fluororesin insulating plate 244 therein. As shown in Figures 3(C) and (D), a space is secured between the insulating plate 244 and the circuit board 230 by interposing fluororesin aerial wiring terminals 231 with board mounting bracket feet and spacers 232 of the required length. As shown in Figures 3(B) to (D), terminal fittings 245 are fixed to the insulating plate 244 corresponding to the positions of the mounting fittings 243 of each capacitor module 240. The capacitor module 240 is mounted by screwing the mounting bracket 243 to the terminal bracket 245, and each capacitor module 240 is connected by lead wires 234 soldered to the lug holes of the point-to-point wiring terminals 231 (point-to-point wiring).

[0024] Since the charge storage capacitor 24 operates at a different potential than the circuit board 230, there is a possibility of leakage current from the charge storage capacitor 24 to the circuit board 230. For this reason, in the mounting area of ​​the charge storage capacitor 24, each capacitor module 240 is connected to a potential pattern 233 (first guard ring) formed by routing from the output pattern connected to the output terminal 253 (described later) of the buffer amplifier 25. As shown in Figures 3(C) and (D), the potential pattern 233 is located under the board mounting bracket feet of the aerial wiring terminals 231 of each capacitor module 240, and the aerial wiring terminals 231 are soldered to the potential pattern 233.

[0025] (Surge absorber configuration) The surge absorber 27 is potted and has point-to-point wiring. Figure 4 shows an example of the configuration of the surge absorber 27 and its mounting area, where (A) is a perspective view of the surge absorber module 270 and (B) is a side view of the mounting area of ​​the surge absorber module 270. The surge absorber module 270 of the surge absorber 27 has a voltage protection element 271 housed in a surge absorber case 272. The surge absorber case 272 is made of fluororesin, and mounting feet 273 are integrally formed with the case at the bottom of the case, and the case is screwed to the circuit board 230 using the mounting feet 273.

[0026] Surge absorbers have traditionally been used to protect charge storage capacitors from surge voltages in the event of dielectric breakdown. However, when introduced into a measurement circuit in a conventional manner, a problem arose: during normal operation (measurement), the charge stored in the charge storage capacitor would leak from the surface of the surge absorber component.

[0027] Therefore, in this embodiment, the voltage protection element 271 is cured and dried embedded in silicon within the surge absorber case 272 and sealed inside the case 272 (potting process). In addition, two or more voltage protection elements 271 are provided in series to ensure the insulation performance of the voltage protection elements 271, the lead wires 234 at both ends of the voltage protection element 271 are soldered to aerial wiring terminals 231 located outside the case, and the lead wires 234 between voltage protection elements 271 are supported and wired with another aerial wiring terminal 231 (aerial wiring). Through these measures, the surge voltage protection element can be introduced into the measurement circuit 23 while preventing leakage current from the component surface during normal operation (measurement). Note that the aerial wiring terminals 231 between voltage protection elements 271 may be potted together with the voltage protection elements 271.

[0028] (Configuration of surge current protection resistors) The surge current protection resistor 26 is potted, has point-to-point wiring, and a guard ring. Figure 5 shows an example of the configuration of the surge current protection resistor 26 and its mounting area, where (A) is a perspective view of the surge current protection resistor module 260, (B) is a plan view of the mounting area of ​​the surge current protection resistor 26, and (C) is a front view of (B). The surge current protection resistor module 260 of the surge current protection resistor 26 has a resistive element 261 housed in a surge current protection resistor case 262. The surge current protection resistor case 262 is made of fluororesin, and case feet 263 are integrally formed with the case at the bottom of the case, and the case feet 263 are screwed to the circuit board 230 in the configuration described later in Figure 5 (B). It is also preferable to use the same surge current protection resistor case 262 as the surge absorber case 272 to reduce costs.

[0029] Surge current protection resistors have traditionally been considered for use in buffer amplifiers to protect against surge currents in the event of dielectric breakdown. However, it was believed that simply introducing them into a measurement circuit in the usual manner would render them ineffective because, when a voltage large enough to cause a surge current is applied, the surge current would still flow through the surface of the resistor to the buffer amplifier.

[0030] Therefore, in this embodiment, the resistive element 261 is cured and dried embedded in silicon within the surge current protection resistor case 262 and sealed inside the case 262 (potting process). The lead wires 234 at both ends of the resistive element 261 are soldered to fluororesin terminals 231 for aerial wiring located outside the case (aerial wiring). Furthermore, as shown in Figure 5(B), a ground plane 236 of the measurement circuit 23 is positioned at the location of the case feet 263 of the surge current protection resistor module 260, and a slit (board hole) 264 for cutting the leakage path is formed in the circuit board 230 in the lower region of the surge current protection resistor case 262. Through these measures, a surge current protection element can be introduced into the measurement circuit 23.

[0031] In other words, when dielectric breakdown occurs, surge current flows into the surface of the resistive element 261 and the surge current protection resistor case 262. Since the inside of the case is potted, the surge current flowing on the surface of the resistive element 261 is suppressed. The surge current flowing on the surface of the case can be discharged to ground along its path because the case body is physically separated from the circuit board 230 by the slit 264 and the case feet 263 are connected to the ground plane 236. In addition, during normal operation (during measurement), the potential difference between the two terminals of the surge current protection resistor module 260 is only a few volts, so the path to ground is sufficiently secured by the slit 264, and therefore no leakage current is generated from the terminals.

[0032] Furthermore, the surge current protection resistor 26 needs to operate at the same potential as the charge storage capacitor 24 and the buffer amplifier 25 in order to suppress leakage current to the circuit board 230 during normal operation (measurement). For this reason, as shown in Figure 5(C), in the mounting area of ​​the surge current protection resistor 26, the point-to-point wiring terminal 231 located on the output side of the surge current protection resistor module 260 is soldered to the same-potential pattern 233 of the buffer amplifier 25 (second guard ring).

[0033] (Buffer amplifier configuration) The buffer amplifier 25 is equipped with point-to-point wiring and a guard ring. Figure 6 shows an example of the configuration of the buffer amplifier 25 and its mounting area, and is a schematic perspective view of the mounting area of ​​the buffer amplifier 25. The buffer amplifier module 250 of the buffer amplifier 25 has an operational amplifier 251 housed in an amplifier case 252. The amplifier case 252 is mounted on an amplifier module board 254, which is connected to the measurement circuit 23 of the main circuit board 230 by four metal terminals 237 and one point-to-point wiring terminal 231. The input terminal 255 of the buffer amplifier module 250 is connected to the point-to-point wiring terminal 231, and the output terminal 253 of the buffer amplifier module 250 is connected to one of the metal terminals 237. The metal terminal 237 connected to the output terminal 253 is soldered to the aforementioned potential pattern 233. The other metal terminals 237 are the power supply terminals (positive / negative) and the buffer amplifier ground terminal of the buffer amplifier module 250, respectively.

[0034] The area surrounding the input terminal 255 of the buffer amplifier 25 is a high-impedance area 256 equipped with a high-impedance pattern (not shown). The connections from the charge storage capacitor 24 and surge current protection resistor 26 to the input terminal 255 are wired to the amplifier module board 254 using metal spacers, etc., with high insulation from the main circuit board 230 ensured by fluororesin point-to-point wiring terminals 231 (point-to-point wiring).

[0035] In the high-impedance area 256, a solid plane (not shown) is formed around the high-impedance pattern, which is at the same potential as the low-impedance output from the operational amplifier 251, creating a guard ring around the high-impedance pattern (third guard ring). This suppresses leakage current from the high-impedance area 256 to other areas.

[0036] More preferably, in the high-impedance area 256, the aforementioned high-impedance pattern and solid plane pattern are formed on the first layer of the amplifier module substrate 254, and a solid plane 257 is formed on the second layer of the amplifier module substrate 254, with the solid plane 257 of the second layer being formed to connect with the solid plane pattern of the first layer (guard plane). This provides a guard ring directly beneath the high-impedance area 256, suppressing leakage current through the glass epoxy material of the inner layer of the amplifier module substrate 254. In addition, in the high-impedance area 256, multiple through-holes 258 are mounted at predetermined intervals so as to surround the high-impedance pattern in the circumferential direction (via fence). This also suppresses leakage current from the laminate sides of the guard ring of the first layer and the guard ring of the second layer.

[0037] (Effects and Benefits) As described above, with the current integral value measuring device 20 of this embodiment, a surge absorber 27 for surge voltage protection and a surge current protection resistor 26 for surge current protection can be introduced by using potting and point-to-point wiring techniques, so as to prevent surges in the event of dielectric breakdown without reducing measurement performance during normal operation (during measurement).

[0038] As mentioned above, when surge absorbers and surge current protection resistors are introduced in a conventional manner, the surge absorber is thought to cause leakage during normal operation (measurement), and the surge current protection resistor is thought to not function during dielectric breakdown. However, by introducing them in a clever manner as in this embodiment, both elements can be made to function effectively both during normal operation and during dielectric breakdown.

[0039] Furthermore, with the current integral value measuring device 20 of this embodiment, the discharge rate in the measuring circuit 23 can be greatly reduced by applying potting treatment to the charge storage capacitor 24, surge absorber 27, and surge current protection resistor 26 to suppress leakage current flowing on the component surface, by using aerial wiring to suppress leakage current to the circuit board 230, and by further suppressing leakage current by using guard rings on the charge storage capacitor 24, surge current protection resistor 26, and buffer amplifier 25. In addition, by applying a triple guard of guard ring, guard plane, and via fence to the buffer amplifier 25, leakage current can be suppressed three-dimensionally.

[0040] Figure 7 shows the measurement circuit 23 of the current integral value measuring device 20 as an equivalent circuit. In the current integral value measuring device 20, after accumulating charge using a 0.1 μF charge storage capacitor 24, the discharge rate after disconnecting the charge input and leaving it for 12 hours is determined by measuring the output voltage of the buffer amplifier 25 and using the following equation (1). Discharge rate = (Voltage measured at the start of storage - Voltage measured after 12 hours) / Voltage measured at the start of storage × 100 ... (1) Under these conditions, the discharge rate of the current integral value measuring device 20 becomes 1% or less. According to the current integral value measuring device 20 of this embodiment, a discharge rate of 1% or less can be achieved with a charge storage capacitor 24 of minute capacitance (0.1 μF) under the condition of being left unattended for a long period of time (12 hours).

[0041] (modified version) The surge current protection resistor 26 may be an optional component. Even without the surge current protection resistor 26, other measures may improve measurement performance by reducing leakage elements under low capacitance and long-term storage conditions. However, without the surge current protection resistor 26, if dielectric breakdown occurs, there is a risk that surge current will flow into the buffer amplifier 25 in the short time before current flows into the surge absorber 27, potentially damaging the buffer amplifier 25. With the surge current protection resistor 26 implemented, the surge current flowing into the buffer amplifier 25 during dielectric breakdown can be limited to about 10mA under conditions of surge voltage of 50kV or less.

[0042] Furthermore, it is preferable that the measurement circuit 23 from the measurement input terminal 21 to the surge absorber 27, indicated by reference numeral 238 in Figure 2, be a non-guard ring region 238 where no guard ring is applied. The non-guard ring region in the current integral value measuring device 20 is a region where peripheral circuits (guard rings) operating at the same potential as the output of the buffer amplifier 25 are not applied. If a guard ring is applied to the surge absorber 27, a surge current will flow to the output of the buffer amplifier 25 when dielectric breakdown occurs. By making the surge absorber 27 and its surroundings a non-guard ring region 238, when dielectric breakdown occurs, the surge current can be induced to the surge absorber 27, thus preventing damage to the buffer amplifier 25.

[0043] While preferred embodiments and variations of the present invention have been described above, these can be modified and combined based on the knowledge of those skilled in the art, and such forms are also included within the scope of the present invention. [Explanation of Symbols]

[0044] S…Insulated sample, 10D…DC power supply, 20…Current integral value measuring device, 21…Measurement input terminal, 22…Ground terminal, 23…Measurement circuit, 230…Circuit board, 233…Same potential pattern, 236…Ground pattern, 238…Non-guard ring area, 24…Charge storage capacitor, 25…Buffer amplifier, 250…Buffer amplifier module, 253…Buffer amplifier output terminal, 256…High impedance area, 257…Second layer solid, 26…Surge current protection resistor, 262…Surge current protection resistor case, 263…Case feet, 264…Slit, 27…Surge absorber

Claims

1. A current integral value measuring device for evaluating the insulating performance of an insulating sample by applying a DC voltage to the insulating sample, In a measurement circuit equipped with a measurement input terminal and a ground terminal, A charge storage capacitor connected in series with the insulating sample, A surge absorber connected in parallel to the charge storage capacitor, A buffer amplifier connected from the connection point of the surge absorber to the measurement input terminal side, A surge current protection resistor connected before the buffer amplifier, Equipped with, The charge storage capacitor, the surge absorber, and the surge current protection resistor are subjected to potting. The charge storage capacitor, surge absorber, surge current protection resistor, and buffer amplifier are connected to the measurement circuit by point-to-point wiring. A current integral value measuring device characterized by the following features.

2. The current integral value measuring device according to claim 1, characterized in that the charge storage capacitor, the surge current protection resistor, and the buffer amplifier each include a first guard ring, a second guard ring, and a third guard ring, which operate at the same potential as the circuit of the point-to-point wiring.

3. The current integral value measuring device according to claim 2, characterized in that the first guard ring of the charge storage capacitor and the second guard ring of the surge current protection resistor are formed by connecting the charge storage capacitor and the surge current protection resistor to the same potential pattern formed by routing the output pattern of the buffer amplifier.

4. The current integral value measuring device according to claim 2, characterized in that the third guard ring of the buffer amplifier has a high impedance area that surrounds the high impedance pattern of the buffer amplifier module at the same potential.

5. A solid layer is formed in the second layer below the first layer on which the third guard ring is formed, and the third guard ring is connected to the solid layer of the second layer. The current integral value measuring device according to claim 4, characterized in that a plurality of through holes are formed around the high impedance pattern of the third guard ring.

6. The current integral value measuring device according to claim 1, characterized in that the surge current protection resistor is housed in a surge current protection resistor case, the case legs of the surge current protection resistor case are connected to the ground of the measuring circuit, and a slit is formed in the circuit board below the surge current protection resistor case.

7. The current integral value measuring device according to claim 1, characterized in that the area between the measurement input terminal and the surge absorber is a non-guard ring region.

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