EMTP USA User Conference 2019
The validation of field measured switching overvoltages, inclusion of statistical prestrike and corona modeling
This presentation is on the simulation of switching overvoltages on transmission lines with trapped charge, validation of EMTP line models, modeling of prestrike in statistical simulation studies and discussion of necessary simulation practices by means of validations with field tests. On transmission lines where switching surges are not mitigated with closing resistors and/or surge arresters, high-speed reclosing on a line with trapped charge will produce high overvoltages that have been measured above 3 pu. Careful simulations of these switching events using available Electromagnetic Transient (EMT) programs consistently produce significantly higher voltages than the measurements. It is demonstrated that the transient voltage waveforms can be reproduced very well using frequency-dependent line models, but the magnitude of the maximum overvoltage is significantly overestimated unless the effect of corona is considered. In principle, once a line model is validated, it is possible to proceed with statistical simulation phase to identify the worst-case overvoltage, which is of utmost importance for transmission line and substation related issues such as the evaluation of minimum approach distance and clearance practices. However, before proceeding with statistical simulation phase, it is also necessary to tune the prestrike model in EMTP. In this presentation, we also discuss how to benefit from field tests to fine tune the generic prestrike model in EMTP and then how to proceed with statistical simulation studies while taking corona into account in an efficient manner.
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