AC Voltage Stress Research Articles

Numerically established correlation in electrical responses of polymer film capacitors to ac and pulsed voltages

In this paper, an equivalent circuit model is used to simulate electrical responses of metalized polymer film capacitors to either ac voltage or pulsed voltage stresses, in particular electric field induced on the electrode coating surface and power dissipation within the film capacitor. Electrode segmentation patterns are taken into consideration by means of arrays of interconnected lumped surface resistors, and the film capacitance is modeled by a set of shunt capacitors distributed across the length of the capacitor film. Voltage magnitude and waveform characteristics are studied in great detail for their effects on surface electric field and power dissipation. Through numerical examples, surface electric field and dissipated power induced by one type of external stress (ac or pulsed) at one frequency are shown to correlate with those at a different frequency. Further correlation is also established to relate surface field and dissipated power induced by one type stress (e.g. ac) to those by the other (pulsed), provided the waveform. characteristics of the two different stresses are specifically related. These numerically established correlations can permit significant reduction in development time of metalized film capacitors.

Comparison between direct current and sinusoidal current stressing of gate oxides and oxide/silicon interfaces in metal–oxide–silicon field-effect transistors

It was recently reported that plasma process-induced damage to metal–oxide–silicon field-effect transistors (MOSFETs) comprises a damage mechanism that involves alternating-current (ac) stressing of the oxide and the oxide/silicon interface. The study reported herein is aimed at establishing signatures of MOSFET damage induced by ac stressing applied at conditions that emulate plasma processing environment. We apply sinusoidal ac voltage stress signals to 0.5 μm n-channel or p-channel MOSFETs with 90-Å-thick gate oxides. We assess damage on MOSFETs by measuring transconductance, threshold voltage, and subthreshold swing. We find that the onset of damage to devices subjected to ac stressing occurs at voltage amplitudes as low as 4 V, whereas in dc stressing, applied for the same time, damage becomes significant only at dc voltages larger than 10 V. We also show that damage from ac stressing attains a maximum at frequencies in the range 1–100 kHz and decreases at frequencies above 5 MHz. It is proposed that carrier hopping is primarily responsible for oxide current and, hence, device damage observed following the ac stress. This hopping current is insignificant during high-field dc stress when Fowler–Nordheim tunneling becomes the dominant conduction mechanism.

インバータ装置における単極性矩形波電圧印加時の部分放電特性

For high voltage induction motors of large ratings, new driving systems such as inverters using Pulse Width Moduration (PWM) are becoming popular in industrial plants using mill motors and traction motors. Understanding of the partial discharge characteristics under inverter voltage stress is very important to achieve reliable insulation design for these apparatus. A model sample with a single void in insulation and IEC (b) electrode system for surface discharge on insulation were used. Partial discharge inception voltages under ac voltage stress, unipolar rectified ac voltage stress and unipolar rectangular step pulses were investigated by varying the applied voltage. As a result, it was found that the zero-to-peak value of partial discharge inception voltage under unipolar voltage stress was 1.5 to 2 times higher than that under ac voltage stress. This reason can be attributed to the behaviour of the residual voltage after discharge at the void since the occurrence of the partial discharge inception voltage under unipolar stress is considered to be higher than under ac stress.

Ferroelectric Pb(Zr, Ti)O3 thin films prepared by Gas Jet Deposition

Lead-zirconate-titanate thin films were successfully codeposited in a modest vacuum environment using a novel Gas Jet Deposition (GJD) process. The GJD process utilizes supersonic carrier gas jets to efficiently transfer the depositing species to substrates. High throughput, large coating area, and easy control of film stoichiometry make the GJD unique among various deposition techniques. GJD deposited PZT films exhibit excellent ferroelectric properties. Unlike other films reported in the literature, only one preferred orientation ([110]) was found in our films grown on Pt electrode. Fatigue tests show that the films are quite stable under ac voltage stress.

Charge transfer and tree initiation in polyethylene subjected to AC voltage stress

An electrical tree is grown in the region of a dielectric subjected to an intensified local electric field. It can be artificially generated in a specimen by using a needle-to-plane electrode configuration. It is characterized by an incubation period which usually tends to decrease with applied voltage. During this period, charge carriers (electrons and positive holes) move back and forth repeatedly between the electrode and the dielectric. This repeated charge transfer is believed to be mainly responsible for tree initiation. Two main contributions can be conceived: the space charge buildup and the attack on the polymer chains by high-energy charge carriers. A space-charge distortion model is proposed for the initiation of an electric tree in polyethylene. This model can also include material aging processes initiated by injected carriers. It can explain ultraviolet light emission and morphological effects which are experimentally observed in association with tree initiation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A time-dependent parameter acquisition system for the characterization of MOS transistors and SONOS memory devices

An inexpensive and fully automated test station is described for the dynamic characterization of MOS and SONOS devices. The system incorporates a novel circuit which monitors the extrapolated threshold, transconductance, and subthreshold slope over time; onboard circuitry to place the system into one of several different modes of operation; an IEEE-488 interface to a controlling desktop computer; and a control program which performs several different measurement functions. Nonvolatile memory transistors are evaluated by the use of memory retention, programming, and endurance measurements, while short-channel MOS transistor reliability under DC and AC voltage stress is evaluated by monitoring the degradation in threshold and transconductance over time. >

A study of short-term partial discharge aging of polypropylene film

Polypropylene film has been subjected to surface discharge of known initial maximum magnitude for different periods of time (2 to 12 h) at subatmospheric pressures ranging from 10 to 66.50 kPa, using uniform field electrodes with AC voltage stress of 625 kV/cm. By measuring the residual breakdown voltage of the aged samples, a degradation rate curve is obtained and an estimate of the life of the films under experimental conditions is attempted. These estimates are compared with results from life tests in which the samples are stressed to failure. The estimates are extended to normal service conditions. The erosion of the films is studied from microphotographs of the aged samples.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Field Testing of Cables: Theory and Practice

Testing cables in the field requires a specialized knowledge of dielectric behavior, electrical stress phenomena, safe and proper use of test equipment, and interpretation of test results. Theoretical and practical aspects of high-potential field testing of medium- and high-voltage extruded cables are discussed. The fundamental theory of ac and dc voltage stresses is reviewed along with the behavior of the cable insulation under dc stress. It is concluded that a dc test is preferred over an ac test for field applications. However, for a dc test the cable should be cooled to ambient temperature so that the voltage stress distribution is the same as for an ac voltage. A program for field testing is suggested along with the voltage levels to use for the test. Finally, guidance on performing the test in the field is given along with examples on interpreting the test results.

Metal Oxide Surge Arrester

The MOSA (Metal Oxide Surge Arrestor) comprising ZnO non-linear elements has been taking the place of the conventional gapped arresters on a world-wide scale. The ZnO non-linear element was developed in Japan and the application for the surge arrester was also established in Japan for the first time. Since the first completion of MOSA in 1975, many improvements have been made in the characteristics of the ZnO element, such as life characteristics, nonlinearity, and energy absorption capability. Especially the improvement of life characteristics against continuous ac voltage stress has been significant. In the design of MOSA, thermal stability should be studied carefully in addition to the characteristics of the ZnO element itself. This paper outlines the development of MOSA, the basic characteristics of the ZnO element, and its application as MOSA.

Detection of Non-Destructive Pulse Currents in Polyethylene Prior to its Dielectric Breakdown

Prebreakdown, non-destructive current pulses were observed in a solid dielectric under ac voltage stress for the first time. They were detected in polyethylene using a needle-plane configuration. The needle electrode was made of carbon-filled polyethylene, to improve contact with bulk polyethylene. The observed charge pulses were less than 1 pC in magnitude, and appeared well in advance of dielectric failure or tree formation.

Barrier voltage and its effect on stability of ZnO varistor

The major voltage drop in ZnO varistors occurs across the grain boundaries, which behave generally as Schottky barriers supporting a barrier voltage Vg. This voltage is proportional to the device voltage. Experimental evidence shows that there is a time-dependent reduction in the barrier voltage combined with an increase in resistive current iR when the varistor is subjected to a continuous ac voltage stress. The phenomena is reversed when the applied voltage is removed, showing nearly complete recovery. Instabilities of the resistive current and of the barrier voltage are shown to be manifestations of the same phenomenon and are attributed to a metastable component in the Schottky barriers. It is proposed that this metastable component is due to interstitial zinc ions that are capable of migration under thermal and electrical driving forces. When these ions are removed or stabilized by a suitable heat treatment, the instability of the device is reduced. This paper presents experimental data and analysis to support this hypothesis.