Abstract: A multimeter instrument for measuring variables, such as electrical current, voltage, or resistance includes touch-sensitive zones for selection of the variable to be measured. The measurement circuit associated with the variable selected with the aid of touch-sensitive selection zones is activated by the zone selected.

Abstract: In a device for the investigation of components of a generator which border on a machine air gap (29) between stator and rotor (22), with the rotor (22) built in, by means of at least one moveable inspection probe (35), a simple, flexible and rapid mounting is ensured in that the device comprises a base unit (31) which can be secured to the rotor (22) on both sides, and which permits at least one inspection probe (35) to move in the machine air gap (29), both in an axial direction with respect to the generator axis and also in the circumferential direction of the machine air gap (29) over the whole circumference of the rotor.

Abstract: A ground detection apparatus for electric automobile having a high-voltage DC power supply (31) which is electrically insulated from a body and a three-phase AC motor (33) which is driven by a DC voltage from the high-voltage DC power supply. A ground detection signal consisting of a square waveform is supplied to the DC power supply circuit through a detection resistor and a coupling capacitor, a voltage amplitude of a ground detection point serving as a connection point between the detection resistor (3) and the coupling capacitor (4) is detected, the detected voltage amplitude is converted into an insulation resistance on the basis of the relationship between a preset voltage amplitude and a preset insulation resistance, and levels of insulation resistance deterioration of the high-voltage DC power supply are detected by comparing the converted insulation resistance with a preset ground decision threshold value.

Abstract: A method and device for insulation monitoring of an electrically insulated DC network by measuring of the insulation resistance using galvanic isolation between a measuring resistor which is connected to ground, and a measuring pulse generator, and a measurement-data acquisition device, which eliminates some of the effect that noise in the DC network would otherwise have on the measurement.

Abstract: The invention relates to a method for monitoring a capacitor bushing (1) to which an electrical operating voltage (UB) is applied and in which a voltage divider is formed with an electrically conductive insert (4), whereby at least one measured value (UM1) of an electrical measured quantity (UM) is recorded and stored by using a measuring tap (7), which is connected to the insert (4), and by using each potential. The aim of the invention is to improve the method so that it is only slightly influenced by changes in the operating voltage. To this end, the impedance (ZE) between the measuring tap (7) and the earth potential is modified after recording the at least one measured value (UM1), and at least one signal value (US1) of a measurement signal (US) subsequently formed is recorded and stored using the measuring tap (7) and the earth potential.

Abstract: A preferred method for identifying a type of abnormality in an insulation system of a power transformer comprises measuring dielectric losses in a section of the insulation system, calculating theoretical dielectric losses for the section based on the material properties, geometry, and temperature of the section, and generating a graphical representation of a percent difference between the measured and calculated dielectric losses. The preferred method also comprises comparing a shape of the graphical representation with a shape of one or more graphical representations of a percent difference between measured and theoretical dielectric losses in one or more other sections of insulation each known to have a specific type of abnormality.

Abstract: Insulation monitoring of an electrical network such as a DC network which is electrically insulated with respect to the ground of a device, includes at least two insulation monitoring devices that monitor different network sections, which can be isolated by one or more switches. Non-contacting switches are used to alternatingly connect and isolate respective measuring resistors of the monitoring devices to, and from, ground, as a result of which the insulation monitoring devices can not negatively affect each other's measurements.

Abstract: A semiconductor device evaluation method includes the steps of measuring a total injected electron quantity before an insulating film causes a dielectric breakdown and obtaining the ratio between the total injected electron quantity and a total injected electron quantity before retention degradation is caused. In this method, using the ratio and the total injected electron quantity, the total injected electron quantity before the retention degradation is caused is calculated.

Abstract: The present invention relates to a method for testing a conductor element (20) applicable to locating a continuity defect of the conductor element, the conductor element having, relative to a reference conductor, an insulation resistance and a leak capacitance. According to the present invention, the method comprises a step of injecting into the conductor element at least two currents (i1, i2) of different frequencies by means of a current or voltage generator (23), one terminal of which is connected to the reference conductor, at least one step of measuring the amplitudes of currents at one measuring point (Pi) chosen along the conductor element, and a step of calculating the imaginary part of currents and/or calculating the leak capacitance of the conductor element downstream from the measuring point (P1).

Abstract: A motor drive including an input for alternating current, a rectifier circuit, an inverter, an output which provides the controlled alternating current to drive a motor; and an active EMI filter for eliminating common mode noise in the motor drive which employs a magneto-resistive sensor. In the filter, a pair of lead frame bars which are connectable to the current path of the motor drive and an MR sensor in the form of a Wheatstone bridge are fabricated on a semiconductor die, with the bridge in contact with and straddling the lead frame bars. The bridge elements are so oriented that opposed elements in the bridge are responsive to changes in magnetic flux in a first sense to exhibit an increase in resistance, and adjacent elements in the bridge are responsive to changes in magnetic flux in a second sense opposite to the first sense to exhibit an increase in resistance.

Abstract: A method of reliability testing is disclosed. A critical breakdown resistance of a device is determined. The test structure is subjected to stress conditions and electrically tested. The critical breakdown time of the test structure is recorded when the operating resistance of the test structure is equal or smaller than the critical breakdown resistance.

Abstract: A method and system for determining the resistance of a winding insulation. The method includes applying a pulsed voltage having a maximum value and a minimum value to the winding insulation. The maximum and minimum values of the pulsed voltage are both negative values in certain exemplary implementations. The values of the maximum and minimum current flowing through the winding insulation are determined, and the winding insulation resistance is calculated based on the difference between the maximum and minimum current. A ground fault may be detected based on the calculated winding insulation resistance. The winding insulation monitoring system includes a sense resistor connected to the winding insulation and a pulsed voltage source is coupled to the sense resistor to apply the pulsed voltage to the winding insulation via the sense resistor.

Abstract: A Time Dependent Dielectric Breakdown (TDDB) test pattern circuit, which can reduce testing time and statistically improve a precision of measurement as well as a method for testing the test pattern circuit are discussed. Typically, a test pattern circuit includes in plurality of unit test patterns. Each unit test pattern includes a capacitor connected to a stress voltage. The stress voltage is applied to the capacitor and the current flowing from the capacitor is measured over time. The dielectric in the capacitor breaks down over time and at a certain point, the current from the capacitor changes suddenly. Unfortunately, the convention test pattern circuit requires serial testing of each unit cell, and therefore, the measuring time is significant when there are many unit cells involved. The circuit allows for the measurements to take place simultaneously for all unit cells within the test pattern circuit.

Abstract: A tester for verifying the integrity of insulation in a branch circuit of a power distribution system. Two test circuits are included; the first providing an insulation test; and a second, a shared/grounded neutral test. In the insulation test, a 500-volt ac output limited to 5 milliamps is selectively applied to the pairs of wires of the branch circuit. If an output current of greater than 3 milliamps is recorded, an insulation failure is noted and the operator proceeds to the second test which applies a pulsed 3 volt, 1 ampere current-limited voltage across the suspected leads. One of the suspected leads is monitored with a portable ammeter to detect any pulse current.

Abstract: Provided is an inspection method for a multilayer gas sensing device, capable of certainly and easily detecting a defective product originating from faults such as gaps or cracks. For the inspection of the gas sensing device including a sensor cell in which a measured gas side electrode is coated with a porous diffusion resistance layer in a stacked condition and the diffusion resistance layer is further coated with a dense protective layer in a stacked condition, in a state where the gas sensing device is immersed in a conductive inspection solution and a reference electrode of the sensor cell is placed into a non-contact with the solution, a voltage is applied between the solution and the reference electrode to measure a current flowing therebetween. On the basis of the measured current value, a decision is made as to whether or not the insulation is kept between the solution and the reference electrode.

Abstract: A manufacturing method for manufacturing a solar panel including a solar cell and an outer housing and an inspection method for inspecting a solar panel generating system, include a step of performing one of a withstand voltage test and an insulation resistance test between a live electrical section electrically connected to the solar cell and a conductor section of the outer housing, and thereafter a step of applying a voltage between the live electrical section and the conductor section. In this way, a residual charge left subsequent to the withstand voltage test or the insulation resistance test is reliably removed within a short period of time.

Abstract: A method of reliability testing is disclosed. A critical breakdown resistance of a device is determined. The test structure is subjected to stress conditions and electrically tested. The critical breakdown time of the test structure is recorded when the operating resistance of the test structure is equal or smaller than the critical breakdown resistance.

Abstract: A safety compliance test instrument includes a display capable of displaying prompts, a menu display program, software for displaying a plurality of instrument verification menus, prompts, and messages concerning results of the verification tests, and software for enabling or preventing safety compliance tests from being performed depending on results of the verification. The safety compliance instrument includes at least two different safety compliance tests involving different connections to a device under test. The tests may be selected from the group consisting of a continuity test, a ground test, a dielectric withstand test, and an insulation resistance test, and more specifically from the group consisting of a continuity test, a ground bond test, AC and DC dielectric withstand tests, and an insulation test.

Abstract: A procedure and a system for the evaluation of the quality and/or efficiency of a cable or a cable segment by a current measurement is disclosed. This is achieved by supplying between the core and the screen of a cable a voltage with alternating polarity and rectangular shape. The periodic duration' of this voltage is selected in a way so as to permit the current measurement of the charge current shortly before a polarity reversal, providing a current value equal to the leakage current.

Abstract: Detecting failed integrated circuit among integrated circuits by (a) assuming that all integrated circuits under test define under-test set, and testing each one of the integrated circuits in under-test set, (b) removing integrated circuits judged to be in failure in step (a) from the under-test set, (c) measuring spectrum of a current supplied from power source into each one of integrated circuits in under-test set, (d) calculating both mean value and standard deviation of spectrum for under-test set, (e) judging whether an integrated circuit is in failure or not, based on both the mean value and the standard deviation of the spectrum, (f) removing integrated circuits having been judged to be in failure in step (e) from under-test set, and (g) judging under-test set to be in no failure. Thus, it is possible to find failed integrated circuits without preparing data of integrated circuit in no failure, as a reference.

Abstract: Detecting failed integrated circuit among integrated circuits, by (a) assuming that all integrated circuits under test define under-test set, and testing each one of the integrated circuits in the under-test set, (b) removing integrated circuits judged to be in failure in step (a) from the under-test set, (c) measuring spectrum of a current supplied from a power source into each one of integrated circuits in under-test set, (d) calculating both mean value and standard deviation of spectrum for under-test set, (e) judging whether an integrated circuit is in failure or not, based on both the mean value and the standard deviation of the spectrum, (f) removing integrated circuits having been judged to be in failure in step (e), from the under-test set, and (g) judging under-test set to be in no failure. Thus, it possible to find failed integrated circuits without preparing data of integrated circuit in no failure, as a reference.

Abstract: There is provided a method of detecting an integrated circuit in failure among integrated circuits, based on spectrum which is a result of analyzing a frequency of a current running through an integrated circuit when a test signal is applied to the integrated circuit, comprising the steps of (a) assuming that all integrated circuits under test define a under-test integrated circuit set, and testing each one of the integrated circuits in the under-test integrated circuit set in a conventional manner, (b) removing integrated circuits having been judged to be in failure in the step (a), from the under-test integrated circuit set, (c) measuring spectrum of a current supplied from a power source into each one of the integrated circuits in the under-test integrated circuit set, (d) calculating both a mean value and standard deviation of the spectrum for the under-test integrated circuit set, (e) judging whether an integrated circuit is in failure or in no failure, based on both the mean value and the standard devia

Abstract: A method and device for insulation monitoring of an electrically insulated DC network by measuring of the insulation resistance using galvanic isolation between a measuring resistor which is connected to ground, and a measuring pulse generator, and a measurement-data acquisition device, which eliminates some of the effect that noise in the DC network would otherwise have on the measurement.

Abstract: A safety compliance test instrument includes a display capable of displaying prompts, a menu display program, software for displaying a plurality of instrument verification menus, prompts, and messages concerning results of the verification tests, and software for enabling or preventing safety compliance tests from being performed depending on results of the verification. The safety compliance instrument includes at least two different safety compliance tests involving different connections to a device under test. The tests may be selected from the group consisting of a continuity test, a ground test, a dielectric withstand test, and an insulation resistance test, and more specifically from the group consisting of a continuity test, a ground bond test, AC and DC dielectric withstand tests, and an insulation test.

Abstract: The present invention provides a method and device for detecting a discharge in an electrical device comprising, providing a bushing having a bottom lower flange and a top upper flange, providing a shield inside the bushing extending from the bottom lower flange to a position at least below the top upper flange and providing an antenna outside the bushing at least above the position for measuring an output signal from the device for detecting the discharge.

Abstract: An object of the present invention is to easily, quickly and precisely measure an insulation resistance of an capacitor. An insulation resistance measurement apparatus of the present invention includes a variable/constant-voltage power source, voltmeter, intermittent circuit and constant-current supply circuit, constant-current sink circuit, test capacitor, current amplifier, and A/D converter and calculation processor. The intermittent circuit and constant-current supply circuit intermittently output a current based on a voltage supplied from variable/constant-voltage power source. When a constant voltage is intermittently applied to the test capacitor, the current flowing through the test capacitor is amplified by the current amplifier, and subsequently inputted to the A/D converter and calculation processor.

Abstract: Monitoring a leakage current from an isolator for a high voltage conductor to ground includes directing the leakage current through a primary wire inductively coupled to a secondary winding energizing an amplifier.

Abstract: A dielectric test structure formed over a dielectric layer. The test structure includes a first structure and a second structure. The first structure comprises a first liner pad, a second liner pad and a first conductive layer for connecting the first and the second liner pad. The second structure comprises a first section and a second section positioned symmetrically on each side of the first conductive layer but detached from the first conductive layer. The first section includes a second conductive layer parallel to the first conductive layer, a third liner pad and a third conductive layer for connecting the second conductive layer and the third liner pad. The second section includes a fourth conductive layer parallel to the first conductive layer, a fourth liner pad and a fifth conductive layer for connecting the fourth conductive layer and the fourth liner pad.

Abstract: An insulation tester and oscillator circuit for use in same includes a transformer including a primary winding and at least one secondary winding to be coupled across an external load such as an electrode. First and second bipolar junction transistors are connected in a “push-pull” operating mode and coupled to the primary winding of the transformer for producing a high frequency voltage. The primary winding has two ends each respective one of which is coupled to a respective one of the collectors of the first and second bipolar junction transistors. First and second field effect transistors are respectively coupled in parallel with the first and second bipolar junction transistors. An actuator for activating the first and second field effect transistors to respectively conduct substantially synchronously with the first and second bipolar junction transistors shortly after start-up is provided, whereby the majority of current is shunted through the field effect transistors.

Abstract: Disclosed is a method of testing a dielectric, comprising setting a reference current below a breakdown current of the dielectric, applying a stress voltage to the dielectric below a breakdown voltage of the dielectric and measuring a stress current resulting therefrom, incrementally increasing said stress voltage until said measured stress current exceeds said reference current.

Abstract: A semiconductor wafer test system for carrying out a burn-in test on a semiconductor wafer including multiple semiconductor devices thereon. A metal interconnect is connected to the gate electrode of each of those devices. A power supply applies an ac voltage of predetermined amplitude to a conductive plate, which creates an ac electric field to be placed on the devices. The ac field should have an intensity at least equal to a minimum value required for the burn-in test and less than a critical value, below which no breakdown occurs in the gate oxide film of each device. By changing the amount of time for which the devices are exposed to the ac field, the burn-in period can be changed freely. In addition, forward and reverse fields are both placed on the gate oxide film of each device. Thus, failures can be screened out very effectively.

Abstract: In one aspect, the invention includes an apparatus having a semiconductor substrate receiving device with at least one extension configured to hold a semiconductor substrate within a liquid bath. The device is configured to have at least a portion of the extension at least periodically placed within the liquid bath. The extension includes a conductive material at least partially coated with an insulative protective material. The insulative protective material is configured to protect the portion of the conductive material which is in the bath from physically contacting the liquid of the bath. The apparatus also includes an electrode within the bath, and an electrical connection between the electrode and the conductive material of the extension. Additionally, the apparatus has a monitor configured to monitor a current flow state of a circuit that includes the electrode, conductive material of the extension, and liquid bath to determine if the circuit is in a closed state or in an open state.

Abstract: Motor insulation degradation is determined using circuitry to sense the common mode leakage current from the ground wire cable. In a preferred embodiment of the invention, a small current transformer detects the common mode leakage current flowing in the ground wire cable of the motor controller circuit. A single pole low pass filter generates an average leakage current signal from the sensed current. The average leakage current signal is converted to a PWM signal. A pulse generator receives the PWM signal and generates pulse signals at the rising and falling edges of the PWM signal. A pair of level shifters receive the rising edge and falling edge pulse signals and transpose those signals from a floating high voltage to a voltage referenced to ground. A pulse reconstruction circuit receives the level shifted pulse signals and reconstructs a pulse width modulated signal having a duty cycle which varies with respect to the magnitude of the common mode leakage current.

Abstract: In a method for detecting a line-short between conductive layers, a potential (or temperature) distribution of the conductive layers is detected while applying a DC voltage thereto. The method is particularly applicable to interdigitated conductive layers. A potential distribution across a wide range perpendicular to the conductors is detected to determine a first location of the line short. Potential distributions between conductors at points parallel to the conductors near the first location are then examined to determine a second location where the potential between the conductors is minimal. Potential distribution at points along a conductor are then examined to determine a location where the potential is sharply changed.

Abstract: Method for locating an insulation fault (Rd) in the screen (SCR) of a cable relative to the ground, the screen being electrically accessible at least at one point of origin (Po) and at one terminal point (Pe). A current is injected between the point of origin (Po) and the terminal point (Pe) of the screen (SCR), by a current or voltage generator (21) that is insulated from the ground, a first electric voltage (U1) is measured at the point of origin (Po), in reference to the ground, and a second electric voltage (U, U2) is measured at the terminal point (Pe). The ratio between the first (U1) and the second (U, U2) voltages measured is representative of the relative position (Pdr) of the insulation fault between the point of origin (Po) and the terminal point (Pe).

Abstract: A total injected electron quantity QBD, which has reached a constant value against a variation in stress voltage applied to an insulating film for use in a semiconductor device, is obtained as a critical injected electron quantity QBDcrit. The total injected electron quantity QBD is a total quantity of electrons injected into the insulating film before the film causes a dielectric breakdown. Thereafter, a time it should take for a total quantity of electrons, injected into the insulating film under actual operating conditions of the device, to reach the critical injected electron quantity QBDcrit is estimated as the expected lifetime of the insulating film.

Abstract: By a test vessel, a test enclosure is created immediately surrounding the zone of the line or cable harness to be inspected by detection. This enclosure is sealed off before detection-inspection and an internal atmosphere is substituted by at least a partial gas substitution with a test gas or a test gas mixture with a lower disruptive discharge voltage than that of air. This test method permits detection of faulty lines with greater distances between the faulty line, the test electrode, and the corresponding counter-electrode. A corresponding pliers-type device for the sectional detection of a line or harness, or a stationary vacuum seal-tight testing chamber capable of performing the same detection may be used. The method is suitable also for a local detection when the test vessel is created and formed by the installation object itself (e.g., an aircraft fuselage).

Abstract: An electrical test instrument includes an improved operator interface capable of including the following features: (i) a pause/prompt feature enable prompts to be displayed during a pause, in order to facilitate operator reconfiguration of the instrument during testing; (ii) an autocalibration alert function to alert the operator that the instrument requires calibration; (iii) a security function that enables the operator to select from among a plurality of security level options; and (iv) a more flexible menu structure that enables set-up of additional tests performed by plug-in test instrument modules.

Abstract: The disclosure provides a two-output voltage test system, wherein the system includes a plurality of D/A converters, buffers, sinusoidal wave generators, power amplifiers, and a micro-processing controller. The two-output voltage test system provides for a number of processes including one group of the plurality of D/A converters, buffers, sinusoidal wave generators, and power amplifiers to perform the measurement of AC voltage durability (WAC), DC voltage durability (WDC), insulation resistance (IR), and leakage current (LK). The other group of the plurality of D/A converters, buffers, sinusoidal wave generators, and power amplifiers performs the measurement of ground resistance (GR). The micro-processing controller outputs the measurements simultaneously or with slight time delay in order to obtain the results measured at the same time.

Abstract: An electrical system and a sensor for on-line monitoring of the state of high-voltage insulation in the electrical system. In this arrangement, the signals associated with partial discharge activity are monitored and transmitted from the sensor to monitoring instrumentation. The sensor is interconnected with the potential stress shield of existing bushings. The capacitance in the bushing between the main conductor and the stress shield conducts partial discharge current which is available for being sensed.

Abstract: For an electrical system a sensor and associated circuits are provided for on-line monitoring of the state of the high-voltage insulation in the electrical system. In this arrangement, both the power frequency signal and of the radio frequency signals associated with partial discharge activity may be monitored and transmitted from the sensor to remote monitoring instrumentation. The sensor is disposed in a stand-off insulator which also may act to support the high voltage conductor system.

Abstract: A broadband test procedure detects the onset of stator winding insulation damage, identifies the failure mechanism, determines the winding's susceptibility to further damage, and predicts stator winding failure. This is accomplished by realizing that changes in the stator winding insulation and/or geometry are reflected as changes in the capacitance between the individual windings and, hence, as changes in the stator winding's broadband impedance response. In the currently preferred approach, the impedance response includes the frequency, magnitude, width, and phase of the resonant impedance.

Abstract: An insulated device diagnosing system capable of judging the deterioration, lifetime, defects and so on of a device highly sensitively and precisely.

Abstract: A sorting method of monolithic ceramic capacitors in which high reliable sorting can be efficiently achieved based on measuring an insulating resistance involves first performing a burn-in process, which applies not less than double of the rated voltage at the maximum working temperature to a monolithic ceramic capacitor. Thereafter, a high temperature insulation resistance measuring process, which involves measuring an insulation resistance while applying not less than the rated voltage at a temperature of not less than 70° C. to the monolithic ceramic capacitor, is performed so that monolithic ceramic capacitors having abnormal insulation resistances are eliminated. Preferably, the direction of applied voltage in the burn-in process agrees with the direction of applied voltage in the high temperature insulation resistance measuring process.

Abstract: In the temperature of 70-140 degrees C., the burn-in process of applying a voltage to monolithic ceramic capacitors so that the strength of the electric field applied between the internal electrodes opposing each other may be 7 30 kV/mm is performed. Subsequently, the insulation resistance of the monolithic ceramic capacitor is measured. The monolithic ceramic capacitors are sorted based on the insulation resistance measured during this insulation-resistance measurement process. In this case, it is sufficient to apply the burn-in process for 2-300 seconds.

Abstract: An electrical run test instrument having a connection to a device under test includes a line voltage input, a high voltage input, and a high voltage switching matrix that enables selective connections between the device under test and line voltage or high voltage inputs using the same test set-up. The high voltage input may be interconnected with a safety compliance test instrument, permitting both run tests and line tests to be performed in succession using the same basic connection to the device under test.

Abstract: A method for testing a cable for defective insulation. A user connects one end of each cable conductor to a numbered terminal block. The user measures the insulation resistance between the first and second conductors of the cable using an insulation resistance tester. Next, the user shorts conductors one and two at the terminal block. The user then measures the insulation resistance between the first and third conductors. Measuring the insulation resistance between conductors one and three also measures the insulation resistance between conductors two and three. The user continues these steps until the insulation resistance for all conductors is measured.

Abstract: A cathode-anode apparatus is constructed whereby the wafer under test, connected to a conducting wire, forms the cathode terminal and a copper plate, also connected to a conducting wire, forms the anode terminal. The wafer under test and the copper plate are immersed in a CuSO4—H2O solution. A positive dc voltage is applied to the copper plate; the dc current ionizes the CuSO4 solution and forms Cu2+ ions. These Cu2+ ions will diffuse to the wafer surface. Most of the Cu2+ ions will accumulate in and around defective contacts or vias in the semiconductor surface making these defective contacts or vias readily identifiable.

Abstract: A sensor and associated circuits are provided for on-line monitoring of the state of the high-voltage insulation in electrical equipment with capacitance tap. In this arrangement, both the power frequency signal and the radio frequency signals associated with partial discharge activity are sensed. These signals are transmitted from the sensor to remote monitoring instrumentation via one connecting cable. The sensor contains a surge arrester in parallel with a capacitor shunt, a radio frequency current transformer and a connecting circuit. The polarity terminal of the primary winding of the radio frequency current transformer is connected to the tap output. The non-polarity terminal is connected to the common connection point of the surge arrester and the capacitor shunt while the second terminals of these components are connected to the local ground.

Abstract: An insulated device diagnosing system is capable of judging the deterioration, lifetime, and defects of a device. The intensity at each voltage phase angle is measured at a plurality of specific frequencies, taking high voltage phase angles as the abscissas. The deterioration, lifetime, and the kind and extent of abnormality of the device are judged from the pattern and intensity of the spectral distribution, which is obtained by peak-holding the measured intensity for a defined time period. According to the present invention, partial discharge can be measured highly sensitively and precisely to diagnose the deterioration, lifetime and the extent of defect of the device. As a result, the insulation reliability of the device can be improved, and the part of the device that should be repaired/replaced can be grasped before disassembly of the device, thereby cutting the maintenance cost.