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.
Limitation of transmission line switching overvoltages using switchsync relays
When an overhead transmission line is energized by closing the line circuit breaker, some switching transients are generated in the power system including the line and the supply network. A traditional method for limiting switching overvoltages to acceptable levels is use of circuit breakers equipped with pre-insertion resistors. These resistors provide efficient limitation of the switching overvoltages. However, they make the circuit breakers more complex and costly. Controlled closing and re-closing of line circuit breakers using switchsync controllers eliminates the need for pre-insertion resistors. The mitigation of the switching overvoltages especially when used in conjunction with surge arresters could provide acceptable results. Calculation of transmission line switching overvoltages for the case that line circuit breakers are equipped with appropriately designed switchsync controllers is performed in this paper. The transient based EMTP software is used to model an appropriate power system and various simulations are performed. Statistical studies have been investigated to determine the maximum switching overvoltages when a switchsync relay for an uncompensated transmission lines is used. Effectiveness of the new line energization method is evaluated in the paper as well.
Comparison of statistical switching results using Gaussian, uniform and systematic switching approaches
The three phase circuit breaker closing produces significant transient overvoltages depending on the angle on the voltage waveform, circuit breaker closing span and standard deviation. The Gaussian distribution, uniform distribution and the systematic switching methods are used to calculate the overvoltage distribution. These statistical approaches are assessed in this paper.