Simulation Of Overvoltages Research Articles

An efficient recursive scheme for the simulation of overvoltages on multiphase systems under corona

In the present work, an efficient recursive scheme that was previously described and tested in single-phase transmission lines is extended for multiphase power transmission systems. The scheme uses frequency domain modal theory techniques to obtain an independent solution for each multiphase line segment with frequency dependent parameters. The compensation method is then applied for a combined solution of the voltage profile at each section and its associated "corona branch". The entire multiphase line is treated as a single nonlinear element by the EMTP. Simulations of field tests on an actual line under corona are presented and comparisons are made with the previous implementations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A statistical vacuum circuit breaker model for simulation of transient overvoltages

A statistical model of a medium voltage vacuum circuit breaker was developed in EMTP by using new powerful TACS MODELS. The model includes the arc voltage characteristic, calculation of mean chopping current value with known di/dt, the dielectric breakdown voltage characteristic, contacts separation dynamics, probability of high frequency arc quenching capability and probability of high frequency (HF) zero current passings. The influence of a switching-off time is studied and a statistical estimation is given of the transient overvoltages expected for a specific network configuration. The relation between the switching-off times and the overvoltages is also presented. In addition to these results the paper includes explanation of the modeling technique in the EMTP for all elements constituting the distribution network and validation of the vacuum breaker model behavior. This approach provides valuable information to engineers constructing metal-enclosed switchgear, electric utilities and other users who are going to install vacuum breakers in medium voltage networks. >

Generator models for overvoltage simulations

Generator winding models were developed for simulating dielectric stresses arising from 5-50 kHz oscillatory transients and from steep-fronted surges. For oscillatory transients, field tests were used to build a distributed parameter line model, which was then simplified to a second-order R, L, C network. For steep-fronted surges, a new empirical formula for the winding surge impedance was developed and validated. Simulations based on these models show that the inductive transfer of lightning may be larger than previously reported. Also, power frequency bias is larger on an adjacent phase than transfer within one phase. Higher stresses may arise for distant lightning surges having an initial phase-to-phase component and for fault-generated transients resonating within the generator winding. Reflections at the end of the first slot can amplify steep-fronted surges. A novel model for capacitive transfer in the step-up transformer may replace expensive factory surge tests.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>