V-A Characteristic Measuring of Stress Grading Tapes in the End-winding of Synchronous Generators

Krpal, Ondrej; Mráz, Petr

doi:10.1016/j.proeng.2014.03.150

Cited by 4 publications

(4 citation statements)

References 9 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…They found an incredible increase in leakage current. A factor 12 was measured [50]. Therefore, even if stress-grading has a positive impact in the local mitigation of electrical field, investigations must be done by monitoring its own aging.…”

Section: Main Insulation In the End Winding Area Criteria And Issuementioning

confidence: 99%

The Insulation for Machines Having a High Lifespan Expectancy, Design, Tests and Acceptance Criteria Issues

Barré¹,

Napame²

2017

Machines

View full text Add to dashboard Cite

Abstract:The windings insulation of electrical machines will remain a topic that is updated frequently. The criteria severity requested by the electrical machine applications increases continuously. Manufacturers and designers are always confronted with new requirements or new criteria with enhanced performances. The most problematic requirements that will be investigated here are the extremely long lifespan coupled to critical operating conditions (overload, supply grid instabilities, and critical operating environments). Increasing lifespan does not have a considerable benefit because the purchasing price of usual machines has to be compared to the purchasing price and maintenance price of long lifespan machines. A machine having a 40-year lifespan will cost more than twice the usual price of a 20-year lifetime machine. Systems which need a long lifetime are systems which are crucial for a country, and those for which outage costs are exorbitant. Nuclear power stations are such systems. It is certain that the used technologies have evolved since the first nuclear power plant, but they cannot evolve as quickly as in other sectors of activities. No-one wants to use an immature technology in such power plants. Even if the electrical machines have exceeded 100 years of age, their improvements are linked to a patient and continuous work. Nowadays, the windings insulation systems have a well-established structure, especially high voltage windings. Unfortunately, a high life span is not only linked to this result. Several manufacturers' improvements induced by many years of experiment have led to the writing of standards that help the customers and the manufacturers to regularly enhance the insulation specifications or qualifications. Hence, in this publication, the authors will give a step by step exhaustive review of one insulation layout and will take time to give a detailed report on the standards that are linked to insulation systems. No standard can provide insurance about lifespan, nor do any insulation tests incorporate all of the operating conditions: thermal, mechanical, moisture and chemical. Even if one manufacturer uses the standards compliance to demonstrate the quality of its realization; in the end, the successful use in operation remains an objective test. Thereafter, both customer and manufacturers will use the standards while knowing that such documents cannot fully satisfy their wishes. In one 20-year historical review, the authors will highlight the duration in insulation improvements and small breakthroughs in standards writing. High lifespan machines are not the main interest of standards. A large part of this publication is dedicated to the improvements of the insulation wall to achieve the lifespan. Even if the choice of raw materials is fundamental, the understanding of ageing phenomena also leads to improvements.

show abstract

Section: Main Insulation In the End Winding Area Criteria And Issuementioning

confidence: 99%

The Insulation for Machines Having a High Lifespan Expectancy, Design, Tests and Acceptance Criteria Issues

Barré¹,

Napame²

2017

Machines

View full text Add to dashboard Cite

show abstract

“…The SGT is composed of resin containing silicon carbide (SiC) or zinc oxide (ZnO) varistor powder, and both types show nonlinear conductivity-field characteristics [11]. In [6], [12]- [17], the nonlinear conduction properties of the SGT were investigated for the stress grading of the overhang region; however, the VPI procedure was not addressed. In [18]- [20], the VPI procedure was considered in measuring the properties of the SGT, but the effect of heat shrinkage tape (HST) or the mica insulation layer was not considered.…”

Section: Introductionmentioning

confidence: 99%

Stress Grading Performance Analysis of Stator Coil Considering the Manufacturing Method and the Insulation Design

Kim

2022

IEEE Access

View full text Add to dashboard Cite

In rotating machines, the approach of applying nonlinear conductive stress grading tape (SGT) has been applied to reduce the electric field stress in the coil's overhang region. To characterize and verify the electric field grading effect of SGT in electric machines, electric field analysis using the nonlinear conductivity of SGT as a boundary condition must be considered. However, previous studies have shown limitations in the characterization and application of SGT materials in insulation system design for various reasons, such as lack of conductivity measurement standards for nonlinear materials or not considering possible changes in material properties during the manufacturing procedure. In this study, the nonlinear conductivity of SGT was measured by considering the rotating machine's manufacturing procedure. A finite element method (FEM) electric field analysis was performed using the measured nonlinear conductivity. Based on the improved conductivity measurement method of SGT and FEM analysis, the effects of changing several insulation design parameters in the field grading performance were studied on a 13.8 kV stator coil. Moreover, the effect of preheating on the SGT conductivity was also examined. Based on analysis results, we realized the possibility of more precise insulation design of the stator coil. Our findings supplement the insufficient insulation design guide on the SGT part and contribute to establishing a systematic approach for insulation design. Furthermore, the proposed methods enable design optimization and detection of the cause of insulation failure.

show abstract

“…Semi-conductive tapes are widely used in connection boxes of high voltage cables [1]. They are also used for getting a correct potential distribution in the end-winding connections of large big machines working in high voltages [2]. These two applications concern macroscopic objects, which sizes are more than 10 centimeters.…”

Section: Introductionmentioning

confidence: 99%

An enameled wire with a semi-conductive layer: A solution for a better distibution of the voltage stresses in motor windings

2019

View full text Add to dashboard Cite

The paper analyzes a possible improvement of Pulse Width Modulation (PWM) fed motor insulation according to a principle developed by the high voltages industry. The proposed principle consists in using a specific enameled wire made with an additional semi-conductive layer on its outer surface. Experimental study is realized in order to measure Partial Discharges (PDs) activity with three technologies: Classical enameled wire, enameled wire with an external conductive layer (silver paint) and enameled wire with an external semi-conductive layer (2% of carbon nanoparticles). Simulations are made in order to understand the behavior of the new semi-conductive wire.

show abstract

V-A Characteristic Measuring of Stress Grading Tapes in the End-winding of Synchronous Generators

Cited by 4 publications

References 9 publications

The Insulation for Machines Having a High Lifespan Expectancy, Design, Tests and Acceptance Criteria Issues

The Insulation for Machines Having a High Lifespan Expectancy, Design, Tests and Acceptance Criteria Issues

Stress Grading Performance Analysis of Stator Coil Considering the Manufacturing Method and the Insulation Design

An enameled wire with a semi-conductive layer: A solution for a better distibution of the voltage stresses in motor windings

Contact Info

Product

Resources

About