Tiebin Zhao

Calculation of single phase AC and monopolar DC hybrid corona effects

Operating a hybrid HVAC and HVDC power transmission line is an option for increasing the efficiency of power transmission and overcoming the difficulties in obtaining a new right-of-way. This paper proposes a new calculation method for the study of hybrid power line corona. The proposed method can be used to calculate DC corona losses and corona currents in DC or AC conductors for single phase AC and monopolar DC hybrid lines. Profiles of electric field strength and ion current density at ground level can be estimated. The effects of the presence of an energized AC conductor on DC conductor corona and DC voltage on AC conductor corona are included in the method. Full-scale and reduced-scale experiments were utilized to investigate the hybrid line corona effects. Verification of the proposed calculation method is given.

Review of features of fog chamber at the Ohio State University for polymer insulator evaluation

Non-ceramic (composite) insulators consist of a fiberglass core rod surrounded by a polymer weather-shed housing. The housing is generally manufactured from an elastomer material. Weathershed materials may be subject to degradation and aging in service due to harsh environmental conditions. Performance evaluation of polymer weathersheds can employ fog chambers. Design and operational features of a new fog chamber are reviewed in this paper. Specific characteristics reviewed are: size and main layout of the chamber, insulator arrangement, high voltage source; protection, water circulation and data acquisition systems. Test cycles and techniques are also discussed briefly.

Development of reduced-scale line modeling for the study of hybrid corona

A review of the reduced-scale hybrid line model development for the study of hybrid corona phenomena is presented. Techniques to model hybrid corona through the modeling of conductor size and conductor corona onset voltage have been developed. Instrumentation for the reduced-scale hybrid line model has been developed and physical facilities have been designed and constructed. Test series and parameters to be varied were selected for simple configurations with one AC and one DC bundle conductor. Measurements were performed and test data were evaluated and organized. Modeling techniques have been extended to full configurations with three phase AC and bipolar DC line models.<<ETX>>

Leakage current magnitudes and waveshapes along polymer insulators

In order to analyze the development of the leakage currents along polymer insulators during artificial pollution tests, a test series was developed. Contaminated polymer insulators were tested in a fog chamber according to a predetermined cycle. Leakage current progress, waveshapes and their frequency contents were recorded and analyzed.

Salt fog aging tests on non-ceramic insulators and fog chamber data acquisition system

Significant improvements in the quality and performance of non-ceramic insulators have been made in the 25 years since their introduction for use in high voltage transmission and distribution systems. However, the industry in general still has questions about the service life of such insulators. A combination of field service experience and laboratory aging tests can help answer these questions. One of the aging tests which is extensively applied to evaluate polymeric weathershed materials of non-ceramic insulators is the salt fog aging test. To obtain more information during the test periods and to have a better understanding of the performance of insulator samples during aging tests, a data acquisition system was developed to record the leakage current of insulators being tested. Salt fog aging tests in accordance with IEC Std. 1109 were performed on silicone rubber and EPDM/silicone alloy insulators. Test and leakage current measurement results are presented.

Corona tests on reduced-scale two-conductor hybrid lines

Tests were conducted to determine the effect of various parameters on DC fields due to the interaction between energized AC and DC conductors. A summary of observations and conclusions drawn from over 25,000 readings taken in the course of more than 40 series of tests is given. Quantities measured were the ground level DC electric field strength and ion current density, and conductor corona currents. Parameters were the hybrid line geometry, the conductor conditions, the magnitude of the applied AC and DC voltages, and the polarity of the applied DC voltage.<<ETX>>

Analysis of visual discharge activities along polymer insulators

A test program was designed to study the joint effects of fog salinity and pre-deposit contamination on polymer insulators in a fog chamber. The objective of the test program was to analyze and record the visual appearance of the discharge activities along the insulators and to correlate the results with the leakage currents observed in the course of the tests. The test setup that allows the joint view of the leakage current waveshapes and visual appearance of the discharges is also discussed.

Simultaneous electrical and visual measurements of leakage currents along polymer insulators in artificial pollution tests

Various discharge phenomena of polymer insulators tested in a fog chamber are analyzed and discussed. The insulators are tested inside the chamber for a 500 hour-long test period. During this test period, the magnitude of the current waveshapes together with the visual appearance of the leakage current discharge activities along the polymer insulators are investigated. By employing a rather simple technique, a joint view of the discharge activity and its corresponding waveshape is possible. The events are recorded on video tapes and later on, played back at a slower speed for analysis purposes. Events that are particularly of interest are paused and captured by using a video capture board installed in an IBM(R) compatible personal computer (PC).

Evaluation of polymer insulator performance in salt fog chamber

Polymer insulators made of different weathershed materials have been tested in a salt fog chamber at two different salinity (i.e., conductivity) levels for a 500 hour-long test period. The leakage currents flowing through the contamination layer on the surface of the insulators under test, the cumulative charge, and the magnitude and number of leakage current pulses have been monitored. This paper presents the results of salt fog tests performed on silicone rubber and EPDM insulators. In addition, a case study is reviewed. It shows the analysis of the cumulative charge daily profiles for some of the polymer insulators tested.

Polymer insulator test procedures and techniques followed during fog chamber test series

Non-ceramic (composite) insulators consist of a core fiberglass rod and a set of polymer weathersheds. The weathersheds may be subjected to degradation and aging due to various environmental stresses. Performance evaluation of polymer weathersheds can employ various techniques. First, this paper briefly summarizes the features of a new fog chamber at The Ohio State University. Then, details of the manysided procedures and techniques of a test series, a joint project of The Ohio State University and The Ohio Brass Company, involving a total of 50 polymer insulators of 5 different weathershed materials are reviewed in the paper.