High Voltage Transients Research Articles

Laser-Induced Voltages at Room Temperature in YBa2Cu3O7 and PrxY1-xBa2Cu3O7 Thin Films

ABSTRACTRecent reports on high transient transverse voltages at room temperature in YBa2Cu3O7 and PrxYl-xBa2Cu3O7 thin films grown on SrTiO3 single crystal substrates, with a tilt angle between the [ 001 ] cubic axis and the substrate surface plane, have been interpreted by thermoelectric fields transverse to a laser-induced temperature gradient which are caused by the non-zero off diagonal elements of the Seebeck tensor. We have studied this effect in epitaxially grown Pr- doped, as well as undoped YBa2Cu3O7, thin films and observed for a 2 mm long YBa2Cu3O7 strip exposed to a UV photon fluence of 100 mJ/cm2 signals as large as 30 V. The unexpected high values for the signals and their doping dependence are discussed within the frame of a model based on a thermopile arrangement, the growth induced defect structure and the doping induced modifications of the material properties.

The high level chopping phenomena of sink-in type triggered vacuum gaps

In the positive mode of the main gap with both triggering modes, it was found that the discharge is quite unstable. This instability has a strong influence on the precise control of the triggered vacuum gap (TVG) and gives rise to high transient voltage across the main gap. This unstable phenomenon is investigated in detail. The influence of triggering pulse type, residual pressure, contamination and main gap polarity on the chopping phenomena is described. The experimental setup is described, and results are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A surge-free intelligent power device specific to automotive high side switches

A novel type of intelligent power device (IPD), which is suitable for automotive monolithic high side switch with high current capability, is presented. An integration of a vertical-power DMOSFET and planar MOS IC devices is performed by the newly developed junction-isolation technique using only one epitaxial growth. The isolation voltage of 80 V has been obtained, which is large enough for automotive IPDs if they are protected against high voltage transients on the battery line. A rugged vertical DMOSFET (VDMOS) has also been developed for this IPD. It has a cellular Zener diode between its source and drain, which prevents the secondary breakdown of parasitic bipolar transistor, and the resulting avalanche capability enhancement is more than an order of magnitude. This VDMOS is used for both output power device and protection device for low-voltage MOS circuitry, which makes the IPD free from any transients in the automobile without the need for external protection.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Characterizing transient measurements by use of the step response and the convolution integral

A method of determining the suitability of a divider system for making measurements of high-voltage transients is described. This method involves the convolution of the experimentally determined step response of the divider with various analytic waveforms which represent ideal waveforms expected in the experimental arrangement. The result of the convolution is compared, both graphically and in terms of relevant parameters such as peak amplitude and front time, with the original waveform. This procedure allows the distortion introduced by the convolution calculation to be seen clearly. The numerical implementation of the method is easily run on a personal computer. >

A serial bus transceiver for the automotive environment

A custom monolithic integrated circuit used as a direct interface between a single-wire data link and microcomputer assemblies in the harsh automotive environment is described. Unusual circuitry allows operation from a single 5-V supply with a grounded substrate despite 6-V ground differences between the nodes. The IC features a 10-mA tristate output with a voltage swing to within 1/2 V of each rail. In addition, the output maintains the high-impedance state during loss of ground and through shorts to -16 and +16 V, remains stable for unlimited capacitive loads, and provides protection from short circuits and high-voltage transients. On-chip waveshaping referenced to an external RC time constant approximates a third-order filter for precise control of rise times and radiated noise in transmitted data. The differential receiver accepts voltage levels from -6 to +12 V and filters input signals for noise immunity. Bit rates to 9600 baud are possible in the described application.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Digital Simulations and Field Measurement of Transients Associated with Large Capactior Bank Switching on Distribution Systems

Several unexplained and unusual arrester failures have been noted on some Canadian power systems. Data collected from one SCADA system has correlated these failures with the deenergizing of large shunt capacitor banks at the next higher voltage level. Laboratory experiments on a typical capacitor switch, digital transient simulations of a typical system where failures had occurred, and staged transient field tests on that system were undertaken to resolve the problem. The laboratory experiments showed that voltage escalation due to multiple restrikes and high frequency current clearing is unlikely for the air magnetic breaker involved. However, the simulations and field tests illustrated the possibility of high transient voltages being coupled through a delta-wye transformer following a single severe restrike. These high frequency and low frequency transients could have caused the arrester failures. It was found that surge arresters placed at the capacitor bank location would not effectively reduce the transferred surge. A solution being pursued by one Canadian utility is replacement of the air magnetic breakers with restrike-free circuit breakers for improved capacitor switching performance.

Transient Ground Potential Rise in Gas Insulated Substations - Experimental Studies

The very rapid dielectric breakdown of SF6 (eg, during the operation of disconnect switches in gas-insulated substations) generates steep-fronted travelling waves which couple to the exterior enclosure surface at the air/SF6 bushings and cause transient ground potential rise. These high voltage transients, which can be in the 100 kV range, propagate from the air/SF6 termination, along a transmission line defined by the bus enclosure and the ground plane, toward the switchgear. This paper presents a theoretical and experimental investigation of the phenomenon, from which the basic mechanisms have been identified.

Measurement of nanosecond HV transients with the Kerr effect

A technique for measuring the high-voltage transients associated with low inductance, pulsed gas discharges is described. Measurements are made directly at the 10-kV level with a transmission line Kerr cell and narrow-width, pulsed dye laser, synchronized with the test discharge. The data indicates a temporal resolution of 2 ns.

Computer recognition of generalized spike-wave discharges

Twelve 12 h daytime telemetered EEGs were read for generalized spike-wave (S-W) bursts by a computer and independently by three experienced electroencephalographers. The computer system was a hybrid of analog devices (tape-recorder, voltage summator, and high-pass filters) and a multipurpose laboratory digital device (PDP-12). The computer was programmed to identify only the location on the record and the duration of the generalized S-W paroxysms. From 1,462 discharges identified by both the readers and the computer, a consensus list of 609 was derived by selecting only those bursts identified by all three readers. The computer recognized 516 (85%) of those bursts on the consensus list; the computer's accuracy, as compared with the consensus, rose to 92% when portions of the EEG containing sleep were discounted. The computer also recognized as generalized S-W paroxysms 15 high-voltage transients, which none of the three readers selected. Ten of these, however, occurred during sleep. When the computer results were added to those of the three readers to permit a fourway inter-reader comparison, the computer was found to have had about as many isolated decisions as any of the three readers. In the number of bursts recognized, the computer tended to be about as conservative as the reader under whose guidance it was originally programmed. The computer's accuracy in measuring burst duration was not evaluated statistically.

Low Voltage Initiation of Damaging Arcs Between Electrical Contacts

Metallic arcs were found to precede the firm contacting of electrical contacts which were closed without bounce. When the open-circuit voltages were below the ionization potential, the initiation of these arcs was found to depend on the presence of asperities on the .surfaces and on asperity contacting, melting, and pinching off by magnetic forces. The arc is thought to be initiated inductively when the molten metallic asperity contact is pinched off, and the electrode damage is similar to that produced by the arcing of opening contacts. Arcing could not be produced for exceptionally Smooth surfaces, or, for rough surfaces when the open-circuit potential was below the melting voltage of the electrode metals. In order to prevent damage to contact surfaces by melting or arcing, it is suggested that test potentials be limited to below the melting voltages, that the current be limited, the test circuits be designed to prevent inductively generated high voltage transients, and the contact surfaces be very smooth. In order to facilitate arc initiation in arc welding applications, it is suggested that the surfaces of electrodes and work pieces be roughened.

A New Technique for Recording High-Voltage Transients in Telephone Networks

Some basic difficulties in the protection of telephone networks against dangerous overvoltage disturbances such as lightning are discussed, and a new method for measuring and recording such transients is presented. The method essentially consists of measuring the analog disturbance signals, converting and coding their temporal values into digital numbers easily available to shift register memories and subsequently recording the results either with a teleprinter for computer analysis and statistical abstracts or with a xy -recorder for a human observer. The instrument is capable of recording disturbance amplitudes of 0.1-MHz spectral content linearly with an 300-V interval up to voltages of 5 kV, the sampling rate of the A/D converter used for the recording being adjustable to values of 500 kHz, 1 MHz or 2 MHz. The digital circuits of the instrument use positive logic and are realized for the most part by TTL and MOS technologies.

High voltage probe for liquid immersion

A capacitive voltage divider for the measurement of very high voltage transients in liquid-filled transmission lines has been developed. The probe is suitable for pulse lengths in the range 10 nsec to 1 μsec, and peak voltages between 50 kV and 10 MV. The divider automatically compensates for changes in dielectric constant and loss.

Pulsed Laser Kerr System Polarimeter for Electro-Optical Fringe Pattern Measurement of Transient Electrical Parameters

Novel electro-optical fringe pattern methods are developed for measurement of transient high voltages and electric fields. Several techniques employing the Kerr effect, a pulsed laser source, and high speed photographic recording equipment are described. Typical fringe pattern results are compared with conventional resistive divider measurements.

Maintenance of Substation Insulators Without Power Shutdown

IT is essential to maintain the integrity of electrical substation apparatus and associated equipment to ensure the availability of uninterrupted power. Cement plants must maintain continuous production and avoid the high cost of unscheduled interruptions. Periodic substation surveys will determine the integrity of the equipment. Where the condition of apparatus and porcelain insulators are less than satisfactory, service can usually be accomplished without power interruption. The integrity of porcelain insulators is of special importance because of the nature of contamination prevailing in the area of a cement plant. Metal oxides and sulphides adhere to the insulator and become an electrolyte in water, thereby increasing leakage currents to dangerous levels where flashover can occur in the event of high voltage transients. Flashover of the insulator can cause damage to the insulator, damage to apparatus, and interruption to service.

Gate protection of MIS devices

Gate shorts caused by electrical breakdown of the gate dielectric are a major yield and reliability problem for MOS transistors and integrated circuits. Diodes or diffused resistors with breakdown voltages of about 40 V can be used to protect the gate from high voltage transients or static discharges. This paper provides a uniform approach to gate protection. It is shown theoretically that in order to obtain effective gate protection: the protecting device should have a low dynamic resistance in breakdown; the breakdown voltage of the protecting device should be above, but close to, the maximum gate operating voltage; and protection by a diffused resistor in series with the gate is much more effective than by a diode in parallel with the gate. It is shown experimentally that, compared to the widely used fieldplate-induced breakdown, breakdown due to reach-through to a highly doped substrate provides: a dynamic resistance that is almost two orders of magnitude lower; reasonable control of the breakdown voltage; much better protection against simulated static discharges. Since under pilot line conditions no adverse effects on performance or yield have been observed, reach-through breakdown devices seem to improve gate protection decisively without any coincident disadvantages.

A High-Reliability Solid-State Ignitron Replacement

The design approach, development, and application of a reliable and efficient silicon power diode ignition replacement assembly are presented. The module design provides for natural convection air cooling and a direct replacement capability in 300-kW ignitron power rectifier units not requiring phase control. The discussions include 1) a brief comparison of the economics favoring its use; 2) design philosophy and criteria, operation of silicon power diodes in parallel without paralleling reactors, protection from damaging high voltage and current transients or overloads, mechanical design and physical requirements for optimum cooling, electrical insulation, and package configuration; 3) dynamic operational test information from prototypes and production samples in the testing laboratory and from field installations; 4) history of a field installation (supervised by the author) with more than 4000 hours of satisfactory operation under rigorous load and environmental conditions.

Kerr cell system for the measurement of high voltage transient waveforms

A system is described in which use is made of the electro-optic Kerr effect, combined with modern de-ionization techniques, for the measurement of high voltage transients. The magnitude of the electro-optic effect in a Kerr cell is proportioned to the square of the applied voltage; hence, greater resolution is obtained as the voltage increases towards its peak value. To obtain maximum resolution the dielectric liquid must be purified to withstand a high voltage stress and for the stability of measurement maintained in this state. This is accomplished by ion-exchange membranes which de-ionize the liquid before its use as a dielectric in the cell.

Capacitance potential dividers for the investigation of transient overvoltages in crossbonded cables

The work outlined in the paper was initiated in order to ascertain the nature of transient overvoltages due to switching in a 132kV crossbonded-cable system. The instrumentation for recording high-voltage transients comprised high-ratio capacitance potential dividers capable of reproducing voltages at the cable terminals, cable midsections and cable joints, in conjunction with portable oscilloscopes. The theory and design of the types of potential divider used is given in detail. The design of a coaxial divider which may be built into a cable or cable joint is described. A hybrid-type potential divider has been devised for use at 33kV which employs capacitive and resistive potential division, to give a high division ratio and a flat response up to 2Mc/s, while using inexpensive components. The calibration of potential dividers is discussed, and a simple function generator devised for this purpose is described, Illustrations of calibration waveforms and oscillograms recorded in the field are reproduced.

Induced voltages in the sheaths of crossbonded a.c. cables

When groups of single-conductor concentric cables are used in power systems, it is necessary both to bond the sheaths together at the various joint shells and to earth them at intervals to ensure that there are no large potentials present on them. This arrangement leads to large circulating sheath currents and losses.Various arrangements have been devised to eliminate the sheath losses, the one which is probably most in favour in Britain being the Kirke-Searing scheme. In this scheme, the cable conductors are transposed at regular intervals along a run, and the sheaths are bonded and transposed at the same intervals. While the arrangement eliminates the circulating currents and losses under balanced conditions, it does not prevent relatively large potentials from being present at intermediate points, and it causes appreciable voltages to be present across the insulators inserted in the sheaths at the joints.It is of interest to know the magnitudes of the sheath voltages which are likely to be present in the absence of voltage limiting devices. Some analytical work has been done on this subject for both balanced and unbalanced steady-state conditions, and there are also some experimental results relating to transient conditions. There is, however, little analytical work available on the latter topic. This paper extends the analysis of steady-state conditions by the use of symmetrical-component techniques, and explains the underlying reasons for the high transient sheath voltages which have been detected in the past.

Brush Wear During Commutation

This paper compares the influence of the brush wear on commutators exerted by arcs with the influence of transient high contact voltages, here called flashes. The wear per kilometer travel is expressed as a function of the mechanical load on the brush, the current, the voltage flashes, and the charge transported by arcs. It is important to note that the flashes cause more wear than the arcs. However, strong arcing is accompanied by strong flashes and thus indicates general high brush wear.