Reducing air clearance requirements for voltage uprating of overhead line by use of line surge arresters
While uprating an overhead line to a higher voltage level, it is often difficult to achieve the required clearance level for the uprated structure. Use of Transmission Line Arresters (TLAs) is an effective technique in controlling overvoltages and thereby, achieving the required clearance margin. In this paper, suitability of this technique in reducing the clearance margin is discussed. A case study on uprating an existing 275 kV overhead line to 400 kV is investigated here.
Significance of switching impulse breakdown voltage characteristics in voltage uprating
The voltage rating of overhead lines is determined by a combined consideration of the stress applied to the line and its electrical strength. In this investigation, the voltage uprating of an existing `L3' 275 kV transmission line to 400 kV is explored. Minimum air clearances for 275 kV and 400 kV lines are first reviewed and the IEC recommendations for insulation coordination were considered. The importance of switching impulse breakdown voltage characteristics in determining the required electrical clearance has been highlighted through a detailed review of published literature of breakdown characteristics of long air gaps. Based on the data obtained, a new simplified empirical equation is derived which allows determination of air clearances to suit switching and lightning breakdown voltage characteristics of lines.
Progress Report on Impulse Testing of Commercial Transformers
The transformer subcommittee of the A.I.E.E. electrical machinery committee presents herewith a progress report covering its work to date on the impulse voltage testing of commercial electric power transformers. A tentative test procedure has been agreed upon, although complete agreement has not yet been reached on all details. It is hoped that this report will stimulate among members of the Institute discussion that will be helpful to the committee in completing a formal test code during the coming year.