JP5421538B2 - Insulation withstand voltage test method and apparatus - Google Patents

Description

  The present invention relates to an insulation withstand voltage test method and apparatus. The present invention is suitable for application to an insulation withstand voltage test method and apparatus for non-destructively inspecting the insulation characteristics of a thin film layered product such as a lithium ion secondary battery.

  In this type of thin film layered product, there is a problem of electric discharge generated at a defective portion (pinhole, metal piece, etc.) latent in the insulating layer. Discharge refers to a phenomenon in which an insulator loses its insulating properties under a strong electric field. The magnitude of the electric field at which discharge occurs is about 30,000 V per cm in the case of gas (spark discharge), and is solid or liquid. In this case, it becomes 50,000 V or more per 1 mm. In general, the discharge process is extremely complicated, but it is generally known that it occurs in the following manner.

  When positive and negative electrodes are placed in a gas and the voltage between them is gradually increased, a weak current (dark current) flows due to a small number of electrons and ions generated by the natural ionization. Further, when the voltage is increased, the ionization action due to the collision of the electrons accelerated by the electric field is repeated, and the increased electrons are absorbed by the positive electrode (anode). Further, when the voltage is increased, the positive ions generated by the ionization action are accelerated and reach the negative electrode (cathode), and a large number of secondary electrons are knocked out from the cathode. Flowing.

  As a transient phenomenon from the dark current to the sustained discharge, spark discharge and corona discharge (local breakdown discharge) may occur, and if there is an insulator between the electrodes, along the surface Dendritic corona discharge (creeping discharge) may occur. Thus, when the discharge further proceeds, an arc discharge finally occurs, and a large current flows to damage the device.

Conventionally, insulation failure such as pinholes has been detected by applying a single high voltage impulse to the device under test and observing the voltage waveform applied to the device under test (Patent Document 1).
JP-A-6-230071

  However, the method of applying a single high voltage impulse to the object to be measured not only makes it difficult to control a high voltage (crest value), but also can detect the presence / absence of defects only in an extreme state. Moreover, there are many cases where the insulation characteristics of the object to be measured are deteriorated by applying a large high-voltage impulse.

In addition, when detecting defects (pinholes, scratches, etc.) present in the insulating sheet attached to the metal plate, the electrostatic capacity is very small on the order of pF, so a high voltage impulse can be generated relatively easily. However, for example, a separator of a lithium ion secondary battery originally has a porous film structure for transmitting lithium ions (Li ⁺ ) and has a large capacitance on the order of nF. It was necessary to store a large amount of energy in the transformer), and there was a problem that the apparatus was enlarged.

  The present invention has been made in view of the above-mentioned problems of the prior art, and its purpose is to detect defects (pinholes, metal pieces, etc.) latent in a thin film layered product such as a lithium ion secondary battery with high reliability. It is an object of the present invention to provide a method and apparatus for testing a dielectric withstand voltage.

The dielectric withstand voltage test method according to the first aspect of the present invention changes stepwise by rectifying a high-voltage impulse generated at a predetermined cycle and repeatedly charging the capacitance of the apparatus and the device under test. A stepped high voltage is generated and applied to the device under test, and the insulation withstand voltage characteristic of the device under test is inspected by observing the transition of the applied stepped high voltage.

   In the present invention, since the insulation characteristics under various discharge conditions (voltages) can be observed by increasing the test voltage in small increments, it is easy to detect defects in the object to be measured. That is, even a slight discharge phenomenon that does not cause dielectric breakdown can be found accurately, and thus various defects can be found.

  In the second aspect of the present invention, a positive stepped high voltage and a negative stepped high voltage are alternately generated and applied to the object to be measured.

  In the present invention, by alternately applying positive and negative step-like high electric fields to the object to be measured, it becomes possible to easily find defects that are unevenly distributed according to the direction of the electric field. In other words, it is possible to easily find a type of defect that hardly appears in an electric field in one direction but tends to appear in an electric field in the opposite direction.

In the third aspect of the present invention, the generated stepped high voltage polarity terminals are interchanged and applied to the object to be measured.

  In the present invention, since the stepped high voltage terminals (for example, the high voltage side terminal and the GND side terminal) are switched and applied to the object to be measured, an electric field that is geometrically symmetrical with respect to the object to be measured. Can be applied.

  When the present invention and the invention according to claim 1 are combined, a stepped high voltage and GND are applied from one direction of the object to be measured, and then the stepped high voltage and GND are reversed from the opposite direction of the object to be measured. Will be applied. Therefore, an electric field that is geometrically symmetrical to the object to be measured can be applied, and the possibility that a defect can be detected is improved.

  When the present invention and the invention according to claim 2 are combined, positive and negative stepped high voltages and GND voltages are applied from one direction of the object to be measured, and then the reverse of the object to be measured. From the direction, positive and negative stepped high voltages and GND are applied. Therefore, an electric field that is geometrically symmetrical with respect to the object to be measured can be applied, and the possibility of detecting a defect is further improved.

An insulation withstand voltage test apparatus according to a fourth aspect of the present invention includes an impulse generating means for generating a high voltage impulse at a predetermined period, and a static voltage possessed by the apparatus and / or the device under test by rectifying the generated high voltage impulse. generating a stepped high voltage changes stepwise by charging repeatedly capacitance, the steps like high voltage generating means for applying to the object to be measured, the changes in step-like high voltage is applied to the object to be measured And observing means for inspecting the dielectric strength characteristics of the object to be measured.

  In the present invention, since the electrostatic capacity of the device and / or the device under test can be charged in a plurality of times, the charging energy per time can be reduced, and the impulse generating means has a relatively small inductance. Coils and transformers can be used. Therefore, this type of device can be realized in a small size and at a low cost.

  In the fifth aspect of the present invention, the stepped high voltage generating means alternately generates a positive stepped high voltage and a negative stepped high voltage.

In the sixth aspect of the present invention, the stepped high voltage generating means replaces the generated stepped high voltage polarity terminals with each other and applies them to the object to be measured.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the same reference numerals denote the same or corresponding parts throughout the drawings.

  FIG. 1 is a diagram showing the configuration of an insulation withstand voltage test apparatus according to the first embodiment. In the figure, Q1 is a semiconductor switch made of a MOSFET or the like, T1 is a step-up transformer, SW1 to SW3 are relays, semiconductor elements, etc. D1, D2 are rectifying diodes, 11 is a reset (discharge) circuit for residual applied voltage, and 12 is charged by itself or repeatedly with an impulse-like high voltage together with the capacitance of the device under test 20. Capacitance (stepped high voltage generator) for generating a stepped high voltage that changes stepwise by dividing the high voltage by C1, C2, R3, and R4 (Vm) , A circuit to be sent to the measurement unit. P1 and P2 are electrodes (probes) for applying a high voltage to the object 20 to be measured, 20 is an object to be measured (for example, a lithium ion secondary battery), 15 is a control unit for controlling an insulation withstand voltage test, 16 Is a measuring unit for applied voltage (divided voltage Vm).

  Here, the circuit comprising the semiconductor switch Q1 and the transformer T1 corresponds to the impulse generating means of the present invention, and the circuit comprising the diodes D1, D2 and the capacitances C1, C2 etc. corresponds to the stepped high voltage generating means of the present invention. To do.

  FIG. 2 shows a circuit diagram of the semiconductor switch according to the embodiment. In the figure, the switch circuit SW2 is composed of FETs Q2 and Q3. When a positive high voltage is generated, the FET Q2 is turned on and the FET Q3 is turned off. Conversely, when a negative high voltage is generated, the FET Q3 is turned on and the FET Q2 is kept off. For example, a bias resistor is connected between the gate and source of the FET Q2, and a photodiode (solar cell) is connected in parallel with the resistor. With this configuration, when light is incident on the photodiode, the anode side is positively biased with respect to the cathode side, so that the FET Q2 becomes conductive. When no light is incident, the FET Q2 is turned off because the gate side is not positively biased. The same applies to the FET Q3. Thus, the control unit 15 on the low voltage side is isolated from the high voltage circuit on the secondary side of the transformer. In the switch circuit SW3, the FET Q4 and the FET Q5 are connected in anti-series (a circuit in which the sources are connected), so that both the FET Q4 and the FET Q5 are conductive when conducting. At the time of blocking, the FET on the side where the drain-source voltage is in the reverse direction is conducted by the internal parasitic diode, but the FET on the side taking the forward direction is blocked. Therefore, the switch circuit SW3 can switch both positive and negative voltages, and resets (discharges) the residual charge via the resistor R2.

FIG. 3 is a diagram for explaining the operation of the dielectric strength test apparatus according to the embodiment. When the control unit 15 turns ON the power supply control signal TG at the time t0, the current _{I 1} in the primary winding of the transformer T1,

Where R ₁ : current limiting resistor
r: Internal resistance of power supply
L ₁ : Flows in the form of inductance of the transformer T1, and this current reaches a predetermined value Ic, for example, at time t1. Since the transformer T1 operates by flyback, no current flows on the secondary side from t0 to t1.

Next, when the control unit 15 turns off the power supply control signal TG at time t1, the FET switch Q1 is turned off and the predetermined current Ic is cut off. By this current interruption, a high voltage V ₂ is induced in the transformer T 1 (secondary side), and this is applied to the DUT 20 via the diode D 1 and the stepped high voltage generator 12.

  When the device under test 20 is normal, the insulation resistance Rs is sufficiently large, so that the current Is flowing through the device under test is almost on the capacity Cs side of the device under test 20.

Where L ₂ : inductance of the transformer T1 (secondary side)
I ₂ : flows in the form of a secondary current. However, it is assumed that C ₁ and C ₂ do not exist or are sufficiently smaller than Cs. As a result, the capacitor Cs is charged, and the voltage Vs applied to both ends of the DUT 20 is

Stand up in the form of.

In this state, when the time t2 when I ₂ = 0 first elapses, the diode D1 turns to cut-off, so that the electrostatic energy injected into the capacitor Cs does not return to the transformer T1 side, so that the resistance (R ₃ + R ₄ ) and the resistor Rs is gradually discharged. Then, when the high voltage impulse is generated again, the battery is further charged from the discharge voltage at that time, and finally charged to the vicinity of the peak value of the high voltage impulse.

  In such a configuration, if the insulation characteristics (Rs, Cs) of the DUT 20 are normal (standard), a predetermined rising characteristic (for example, characteristic b in the figure) can be obtained for the charging voltage Vs of the capacitor Cs. However, if the insulation characteristics are degraded, such as Cs is larger than standard or Rs is small, the rise characteristic of Vs will be as shown in c in the figure. If dielectric breakdown occurs in the middle, at that time Suddenly descend. On the other hand, when Cs is smaller than the standard or Rs is larger than the standard, the rising characteristic of Vs is as shown in FIG. In any case, if it is out of the normal (standard) range, it can be determined that the insulation is abnormal. The measurement unit 16 comprehensively evaluates the insulation characteristics of the DUT 20 by measuring and plotting the divided voltage Vm of the applied voltage. At the end of measurement, a reset signal RS is applied to the switch circuit SW3, and the residual charge of the device under test 20 is discharged to zero.

  The above describes the case where the positive step-like high voltage Vs is applied to the object to be measured 20, but the same applies to the case where the negative step-like high voltage Vs is applied. Switching to the negative polarity is performed by a control signal P / N applied to the switch circuits SW1 and SW2.

FIG. 4 shows a structure of an example lithium ion secondary battery. Separators 23 a and 23 b made of a polyolefin microporous film such as polyethylene or polypropylene are sandwiched between a negative electrode 22 made of graphite or the like and a positive electrode 21 made of lithium cobalt oxide (LiCoO ₂ ) or the like. Further, the positive electrode tab 21t and the negative electrode tab 22t are welded to the positive electrode 21 and the negative electrode 22, respectively, and these films are wound up in a spiral shape to obtain a battery body.

  The positive and negative electrodes 21 and 22 have a thickness of about a few tens of μm, the separator 23 has a thickness of about 25 μm, and a thin film structure in which the reaction area of the positive and negative electrodes is increased can provide a large output. Yes. The separators 23a and 23b are used as spacers that separate the positive and negative electrodes to prevent an internal short circuit, hold the electrolytic solution sealed when the battery is mounted, and pass ions between the positive and negative electrodes.

  As described above, the separators 23a and 23b are very thin. However, the separators 23a and 23b are not easily broken as long as the metal pieces are sandwiched. However, when a metal piece is present, the electric field between the positive and negative electrodes via the separator 23 is locally affected. The inset (a) shows a case where a metal piece 25a exists between the positive electrode 21 and the separator 23a, and the local electric field in this case is positive with the separator 23a sandwiched between the upper surface of the plate-like negative electrode 22. It can be modeled as equivalent to a state in which the pin electrode 25a is approaching. Further, the inset (b) shows a case where a metal piece 25b exists between the negative electrode 22 and the separator 23a, and the local electric field in this case sandwiches the separator 23a on the lower surface of the plate-like positive electrode 21. Thus, it can be modeled as equivalent to a state in which the negative pin electrode 25b is approaching.

  FIG. 5 is a graph of the insulation withstand voltage test result according to the first embodiment. FIG. 5A shows the needle electrode connected to a high voltage through an air gap close to the grounded plate electrode and the needle. 2 shows a conceptual configuration in the case where a positive stepped high voltage and a negative stepped high voltage are alternately applied to an electrode (hereinafter referred to as test method A). FIG. 5B shows a measurement result when the needle electrode is driven to ± 600V. When the needle electrode is on the + side, Vs rises normally and then resets. When the needle electrode is on the-side, Vs once fell to -600 V, but it could not withstand the high voltage for a specified time, and a sharp discharge (short circuit) occurred midway. FIG. 5C shows the measurement result when the needle electrode is driven to ± 600V. Also in this case, the needle electrode is normal on the + side, but abnormal discharge occurs midway when the needle electrode is on the-side. In this embodiment, this type of transient error can be found without overlooking. 5D and 5E are both typical error patterns, and both occur when the needle electrode is on the negative side. In this way, by alternately driving the needle electrode to the + side and the − side, it is possible to detect even an abnormality that is difficult to find by the conventional method. FIG. 5F shows a case where the needle electrode is driven to ± 700V.

  FIG. 6 is a diagram showing a configuration of an insulation withstand voltage test apparatus according to the second embodiment, and shows a case where the generated stepped high voltage polarity terminals can be exchanged and applied to the object to be measured. In the figure, SW4 is a terminal changeover switch. When the SW4 is ON (test method A shown), the stepped high voltage is on the upper side of the device under test 20 and the GND is on the lower side of the device under test 20. When the SW4 is OFF (hereinafter referred to as test method B), GND is applied to the upper side of the device under test 20 and a stepped high voltage is applied to the lower side of the device under test 20. Thereby, a stepped high voltage can be applied symmetrically from both surfaces of the device under test 20, and the probability that an insulation error latent in a thin film layered product such as a lithium ion secondary battery can be detected is improved. About another structure, it may be the same as that of the said insulation withstand voltage test apparatus of the said FIG.

FIG. 7 is a graph of the insulation withstand voltage test result according to the second embodiment. FIG. 7A is a diagram illustrating a state in which a grounded needle electrode is brought close to a plate electrode connected to a high voltage via an air gap and the plate. 2 shows a conceptual configuration when a positive step-like high voltage and a negative step-like high voltage are alternately applied to the electrode (test method B). FIG. 7B shows a measurement result when the plate electrode is driven to ± 800V. When the plate electrode is on the + side, Vs once fell to +800 V, but it could not withstand the high voltage for a specified time, and a sharp discharge (short circuit) occurred midway. This is similar to the measurement conditions in FIG. 5F (plate electrode is on the high potential side), and the same measurement results as in FIG. 5F are obtained. In this example, since an error occurs in the positive half cycle of the plate electrode, the measurement of the negative half cycle of the plate electrode is not performed. FIG. 7C shows the measurement result when the plate electrode is driven to ± 600V. Also in this case, abnormal discharge occurs on the positive side of the plate electrode. Further, in each of FIGS. 7D to 7F, an insulation error occurs when the plate electrode is on the + side. In these cases, the plate electrode is continuously tested on the − side. The tests on the negative side of the plate electrode are in a state where no discharge occurs, and these are similar to the measurement conditions and measurement results of FIGS. 5 (d) to (f). In this way, by replacing the polarity terminal of the stepped high voltage and applying it to the device under test 20, it is possible to detect and reconfirm the error even if the abnormality is difficult to find by the conventional method.

  In the second embodiment, positive and negative stepped high voltages are measured from the upper surface of the measured object 20, and then positive and negative stepped high voltages are measured from the lower surface of the measured object 20, respectively. Although applied, it is not restricted to this. In addition, a stepped high voltage having a positive polarity from the upper surface of the object to be measured 20 and then a positive polarity from the lower surface, or a negative step from the upper surface of the object to be measured 20, and a negative step from the lower surface is then applied. A high voltage may be applied to each. Also in this case, the stepped high voltage is applied symmetrically from both surfaces of the DUT 20. According to the second embodiment, even a defect hidden in the asymmetry of the physical property, shape, structure, etc. of the object to be measured 20 can be reliably detected.

  FIG. 8 is a diagram showing the configuration of an insulation withstand voltage test apparatus according to the third embodiment, and shows a case where a coil Ll is used in place of the transformer T1 of the impulse voltage generator of FIG. As a result, the measurement circuit can be reduced in size and weight.

  In each of the above embodiments, the high voltage is directly generated by the rectifier circuit connected to the secondary side of the transformer T1, but the present invention is not limited to this. By connecting a known voltage doubler rectifier circuit (Billard circuit), n voltage doubler rectifier circuit (Cockcroft-Walton circuit) or the like to the secondary side of the transformer T1, a higher voltage can be applied to the device under test 20. You may comprise as follows.

  In addition, although a plurality of embodiments suitable for the present invention have been described, it goes without saying that various changes in the configuration, control, processing, and combination of each part can be made without departing from the spirit of the present invention. No.

It is a figure which shows the structure of the insulation withstand voltage test apparatus by 1st Embodiment. It is a circuit diagram of the semiconductor switch by embodiment. It is operation | movement explanatory drawing of the insulation withstand voltage test apparatus by embodiment. It is a figure which shows the structure of an example lithium ion secondary battery. It is a graph of the insulation withstand voltage test result by 1st Embodiment. It is a figure which shows the structure of the insulation withstand voltage test apparatus by 2nd Embodiment. It is a graph of the insulation withstand voltage test result by 2nd Embodiment. It is a figure which shows the structure of the insulation withstand voltage test apparatus by 3rd Embodiment.

Explanation of symbols

Q1 Semiconductor switch T1 transformer SW1 to SW3 switch D1, D2 Diode 11 Reset circuit 12 Capacitance (stepped high voltage generator)
P1, P2 electrodes (probes)
15 Control Unit 16 Measurement Unit 20 Measured Object

Claims (6)

A stepped high voltage that changes stepwise is generated by rectifying the high-voltage impulse generated at a predetermined period and repeatedly charging the capacitance of the device and / or the device under test, and then applied to the device under test. An insulation withstand voltage test method for examining the insulation withstand voltage characteristics of the object to be measured by observing the transition of the applied stepped high voltage. 2. The insulation withstand voltage test method according to claim 1, wherein a positive stepped high voltage and a negative stepped high voltage are alternately generated and applied to the object to be measured. 3. The insulation withstand voltage test method according to claim 1, wherein the generated stepped high voltage polarity terminals are exchanged with each other and applied to the object to be measured. Impulse generating means for generating a high voltage impulse at a predetermined period;
Step of generating a stepped high voltage that changes stepwise by rectifying the generated high voltage impulse and repeatedly charging the capacitance of the device and / or the device under test, and applying the stepped high voltage to the device under test High voltage generating means,
An insulation withstand voltage test apparatus comprising: inspection means for inspecting the insulation withstand voltage characteristics of the object to be measured by observing the transition of the stepped high voltage applied to the object to be measured. 5. The insulation withstand voltage test apparatus according to claim 4, wherein the stepped high voltage generating means alternately generates a positive stepped high voltage and a negative stepped high voltage. 6. The insulation withstand voltage test apparatus according to claim 4 or 5, wherein the stepped high voltage generating means applies the generated stepped high voltage polarity terminals to the device under test while replacing the polarity terminals of the generated stepped high voltage.

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