High Voltage Insulation Systems Research Articles

Active high voltage insulation

This paper presents a new concept for an active high voltage insulation system with dynamic and adaptive features. The governing principle is based on surface charge accumulation on dielectrically covered electrodes in air under atmospheric pressure. This accumulation results in a charge-induced electric field component which steers the field distribution within the system advantageously. At equilibrium, the electric field component in the air gap normal to the dielectric surface will be zero, except for the field component needed to balance charge losses. Consequently, in the ideal case, the electrical breakdown strength of the electrode coatings determines the breakdown strength of the entire system. Nevertheless, in order to reach equilibrium, a dynamic phase with changing electric field distribution in the insulation system has to be passed. The dynamic system aspects of the concept are demonstrated in numerical simulations.

Discharge measurements using a HTS-SQUID based amplifier system

In the design and development of high voltage insulation systems, partial discharge measurements are often used for system characterization and evaluation. The aim of this work was to investigate the SQUID sensor as an amplifier in a high voltage environment. An HTS SQUID amplifier has been developed and tested under laboratory conditions. Different SQUIDs and a number of different input configurations have been investigated. Preliminary data indicate that the system has a performance similar to a commercial system used as reference. However, calculations and simulations show that the new method has potential for further improvement.

High strain insulation systems for compulsator rotors

As the power density requirement for new compulsator (CPA) designs increases, designers are driven to use more composites to reduce mass, spin the rotors faster to store more energy, and operate the machine at higher voltages to increase machine power output. In any particular compulsator design, the rotor windings are subjected to high strain levels as the rotor is spun and experiences radial growth. A critical component in the rotor winding design is the high voltage insulation. As the rotor is spun, the induced strains are applied to the insulation system on the coil conductors. This implies that over the operating life of a compulsator, the coil structure and the high voltage insulation must remain structurally intact, while undergoing repeated cyclic loading. This paper presents the design and testing of a compulsator rotor winding that has been recently fabricated at the Center for Electromechanics at The University of Texas at Austin. The paper focuses on the testing done both at room and elevated temperature to evaluate the winding structure and high voltage insulation system under both tensile and transverse strain conditions. Data presented suggests a factor of safety of at least five for strain to failure values and high voltage insulation good for at least twice line voltage after testing to strain failure.

Numerical modelling of inhibited electrical discharges in air

The inhibited discharge is a discharge in which the input of energy into the discharge channel is limited by the presence of a large series resistance in the external circuit supplying the discharge current. One situation in which such a discharge occurs is in outdoor high-voltage insulation systems when the system is subjected to rain. The inhibiting resistance is caused by layers or runnels of water on the insulator's surface. This paper concentrates upon the numerical modelling of the inhibited discharge. The core of the modelling is the interaction between the discharge itself and the external circuit which supplies the discharge current. Physical models of the corona streamer development, the propagation of the streamer-leader system and the final jump were used for the calculation of the discharge current. The calculations show that propagation of the streamer is not influenced by a large series resistance, whereas the propagation of the streamer-leader system and the final jump may be significantly inhibited.

An experimental study of inhibited electrical discharges in air

Modern society demands a stable electricity supply, the reliability of which is partly determined by the dielectric strength of the outdoor high-voltage insulation systems. This paper concentrates upon the experimental study of one particular discharge phenomenon that occurs when such a system is subjected to rain, namely the inhibited discharge. This is a discharge whereby the energy input into the discharge channel is limited by the presence of a large series resistance in the discharge circuit; in practice water drops or runnels can act as this resistance. The experimental arrangement was a rod-to-plane electrode gap of up to 1 m subjected to a switching impulse. A water resistor (up to ) was placed in series with the rod electrode. The experimental results reveal the negative feedback characteristics of such an inhibited discharge; that is, as the discharge propagates, the discharge current charges the rod electrode and lowers the gap voltage. This negative feedback gives an increase in disruptive discharge voltage, a low discharge current and a prolongation of the final jump phase.

On-line monitoring of partial discharges on stator windings of large rotating machines in the petrochemical environment

This paper describes a joint collaboration program between a major large electric machine manufacturer and a petrochemical manufacturer to investigate the effectiveness of time- and frequency-domain techniques for the online monitoring of the health of high-voltage machine stator insulation systems. Information is given on the factory and site testing carried out, as well as on the analysis and discussion of the results. It is concluded that both techniques can be used in the petrochemical environment for general assessments, but the time domain technique is required if identification of specific locations of discharge sites is needed.

Development of modern high-voltage insulation systems for large motors and generators

Many advances have been made in the development of insulation materials and processes over the past 100 years. Here, the author describes how this has enabled corresponding improvements in performance calculations to be used with complete confidence so that machines can utilise the full thermal, mechanical and electrical capabilities of present-day insulation materials.

Application of the thermal analysis for detection of the resinoid bond influence on quality of the compositions

The hardening process of bond compositions is very important technological operation from the point of view of quality and reliability of high-voltage insulation systems. The thermal analysis TMA, DTMA and DTA were used and compared for detection of the bond compositions.

Pulse-sequence analysis: a new method for investigating the physics of PD-induced ageing

A new method is presented of partial discharge data analysis for the investigation of space charge and degradation phenomena in high-voltage insulation systems. The basic principles of the pulse-sequence-analysis (PSA) are illustrated and the characteristic differences with regard to standard procedures that have been established during the past few years are outlined. A description is given of an electronic partial discharge acquisition system, which is designed on a plug-in interface board for a standard PC to perform long-term measurements of all the discharge parameters required for the succeeding analysis. Electrical treeing in polyethylene is used to demonstrate the usefulness of the method. It is shown that information on the physics of treeing phenomena especially with regard to the influence of local space charges and their build-up and decrease over time as well as the development of the local degradation can be obtained by considering correlations between consecutive discharge pulses. Some experimental results from different stages of the electrical tree growth are analysed and their meaning with regard to the local microscopic phenomena inside the tree or in the vicinity of the tree tips discussed. This paper is based on an oral presentation at a conference on Partial discharge, September 1993, Canterbury, titled 'Pulse-sequence analysis, a way to get a better insight into the physics of discharges'.

Mathematical formulation of 2D and 3D finite and boundary element model for transient electric fields in high performance capacitors

Capacitors and their pulse-forming networks deliver very high currents in the millisecond time frame to electromagnetic and electrothermal chemical guns. The authors outline the principles of 2-D and 3-D finite and boundary element method codes for calculating electric field strength distribution in high-voltage capacitor insulation systems in arrangements with complex boundaries. A very accurate representation of the space distribution of electric fields, varying in time during the discharge as the combined effect of the circuit parameters, modulated by diffusion and time-changing parameters as properties of the dielectric materials, corona effects, and accelerated aging, can be the basis for a global performance criterion for the system. This criterion should be large enough to represent the complexity of the phenomena in heavy-duty capacitors but still simple enough to be meaningful.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Specific fabrication techniques of the Polo model coil and its components

Poloidal field coils of Tokamak machines are characterized by their pulsed operation needed for plasma ramp up and control. They have to sustain operation faults such as plasma disruptions in their superconducting state. A low-loss conductor, low-loss structural reinforcement and a high-voltage insulation system are needed for fulfilling these requirements. The basis for this technology has been developed for a superconducting model coil. The fabrication technique applied for the coil and some high-voltage related components are described. >

The Potential Use of Optical Sensors for the Measurement of Electric Field Distribution

An optical sensor using the Pockels effect can be a useful measurement tool in electrical applications where mapping distributed E-fields is required. In this paper, results from E-field tests with a 2 m sphere and the voltage distribution of an 1100 kV cascaded test transformer are presented to demonstrate its utility. These results show that the optical sensor, owing to its inherent dielectric link to the data acquisition electronics can be employed as a research tool in the measurement of the voltage distribution on high voltage insulation systems.

The potential use of optical sensors for the measurement of electric field distribution

An optical sensor using the Pockels effect can be a useful measurement tool in electrical applications where mapping distributed E-fields is required. Results from electric field tests with a 2 m sphere, and the voltage distribution of a 1100 kV cascaded test transformer are presented to demonstrate its utilisation. These results show that the optical sensor, due to its inherent dielectric link to the data acquisition electronics, can be utilized as a research tool in the measurement of the voltage distribution on high-voltage insulation systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A system for the measurement of the loss tangent and capacitance of high-voltage insulation over a wide range of frequency and voltage

There is no need to determine the high-voltage characteristics of high-voltage insulation systems used in high-powered electrical machines in order to evaluate the relevance of 0.1 Hz measurements to those taken at power frequency and to investigate their value for diagnostic purposes. A computer-controlled system for the generation of test voltages and the measurement of loss tangent and capacitance in the range 1 mHz to 1 kHz and 100 V to 22 kV RMS is described. The high voltage generator is basically a class B amplifier with an output rating of 30 kV (peak) and 100 mA (peak). The measurement system is based on the analysis of the out-of-balance signal of a modified capacitance bridge. The accuracy of the system is discussed and measurements from samples of high-voltage conductor bar insulation used in turbo-generators are presented.

Multi-Stress Endurance Tests on High-Voltage Motor Insulations, With Equal Acceleration Of Each Stress

An ageing test was performed on two high-voltage motor insulation systems using three principal ageing stresses: temperature, electric field, and mechanical stress. An equal acceleration of each stress was used with the goal of an ageing process identical with that at service conditions. For the determination of the true acceleration factor a parallel ?ageing? test at service conditions was run, up to so long testing times that changes in characteristic properties (flexural modulus, tan?, and capacitance) could be determined. Humidity tests and high-voltage withstand tests were also performed after each ageing cycle. The observed acceleration factor for both systems was lower than predicted. In one of the systems the changes in characteristic properties were measurable and of the same type at both test conditions, so that the test acceleration could be evaluated reliably. Both systems show good class F performance connected with appropriately defined severe service conditions.

Stochastic Models for Simulating The Breaddown Probability of High-Voltage Insulation Systems

Stochastic Models for Simulating The Breaddown Probability of High-Voltage Insulation Systems

A 2.5-MVA High-Voltage Lightweight Generator

The design and development of a 2.5-MVA, 13,600 rpm, air-cooled, 2887/5000-V, 680-Hz, lightweight generator for helicopter application is discussed. The generator is a brushless machine designed to have a maximum weight of 1500 Ib. The high-voltage insulation system, the mechanical design of the high-speed rotor, the electromagnetic design, the thermal analyses, and the squeeze-film damper system which facilitates operation above the first and second critical speeds are discussed. High-voltage insulation endurance test and rotor spin test results are also presented.

Partial Discharge Characteristics of Silicone Liquids

New safety and environmental considerations in the design and operation of modern public transportation systems exclude the use of materials that can cause fire and ecological hazards. Therefore, the power transformers in trains and subway stations require new safer insulating liquids. The askarels or polychlorinated biphenyl (PCB) liquids have been classified as nonflammable, but recent investigations have indicated that spills of these chlorinated liquids may have adverse ecological effects. The manufacture and use of PCB's in Japan have been prohibited by law. To meet environmental and toxicological requirements, new insulation systems for transformers were developed using silicone insulating liquids. In the evaluation of a high-voltage transformer insulation system, it is important to study partial discharge behavior in the insulating liquid. This paper describes measurements of partial discharge inception voltage and of discharge pulse amplitudes at higher test voltages in silicone liquids. The initial partial discharge inception phenomenon in both silicone liquids and mineral oils is the same and is probably related to the presence of contaminants such as water and particles in the liquids. But the further development and growth of the discharges in the liquids seem to be dependent on the chemical and physical properties of the insulating liquid. During the partial discharge measurements, it was observed that small amounts of solid material were formed on the electrode. Chemical analysis showed the material to be cross-linked polymeric siloxanes. The quantity of gelied material is a function of the partial discharge intensity and the duration of discharges.

A Solid Insulation System for Airborne High-Voltage Components and Systems

A method for the design of a high-voltage solid insulation system used in airborne or satellite high-voltage components and systems is presented, and illustrated with a successful system now used in these applications. The design is based on the elimination of corona in the solid, and principally involves making an insulation with a very high corona inception voltage and then controlling the electric field stress below that level. Examples of actual components and systems designed in this way are shown.

Accelerated-Frequency Hydrogen-Atmosphere Voltage-Endurance Testing of Micaceous Insulation Systems

Voltage-endurance testing of high-voltage micaceous insulation systems has traditionally been performed at normal power frequency. The test atmosphere has been air. The completion of tests in practical time periods has required the use of high dielectric stresses. Two series of voltage-endurance tests were conducted on micaceous insulation systems. These tests were designed to determine the effect on insulation life of accelerated frequency and of hydrogen atmosphere. The frequency of the test voltage was 412 Hz. From these tests two conclusions are drawn for voltage stress below 150 V/mil: 1) the voltage-endurance life-test rate was accelerated linearly with the increase of the frequency of the test voltage, and 2) the hydrogen atmosphere extended voltage-endurance life by a factor of at least 4.