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The severe insulation breakdown on one medium-voltage (MV) switchgear led to a complete blackout of Taipower's 3rd nuclear power plant on March 18th, 2001. This has been one of the most serious incidents during the past 30 years of Taipower's nuclear generation and while the cause of the event was a combination of design, maintenance, and equipment aging issue, it is apparent that repeated switching operation on the extra-high-voltage (EHV) side eventually caused this severe insulation breakdown on MV switchgear. Very-fast transient overvoltage (VFTO) is the phenomenon of transient overvoltage generated during switching operation characterized by a very short rise time of 4 to 100 ns. Prior research on this topic focused on VFTO's impact on the EHV side of the transformer and this paper presents the field measurement result together with long-duration multiple-restrike simulation for the VFTO transferred from the EHV side to the MV system through the power transformers. It is shown that this VFTO can be as high as 7 times the rated line-to-ground peak voltage and the maximum VFTO often occusr neither at the first nor at the last strike due to the superposition of restriking voltage on top of oscillation voltage created by prior strikes. [ABSTRACT FROM AUTHOR]

The subject of this paper is to construct a current-transformer (CT) model based on the Jiles-Atherton (J-A) theory of ferromagnetic hysteresis using transient analysis of control systems (TACS) functions within the Electromagnetic Transients Program (EMTP) in a closed-loop manner. The J-A theory of ferromagnetic hysteresis is presented by the nonlinear first-order ordinary differential equations and inclusive of five parameters that can be found by measurements of hysteresis characteristic. We can use TACS functions within EMTP to describe the J-A theory of ferromagnetic hysteresis. The powerful advantage of this way is the interaction between the electrical network and TACS in EMTP. Compared with the CT model based on the type 96 nonlinear hysteresis inductor, the simulated result of the CT model based on the J-A theory of ferromagnetic hysteresis is almost the same in steady-state situations, but apparently different in a fault transient situation. The analysis and simulation of the actual measured fault profiles in the Taiwan power system is an example of the validation of this proposed model. Therefore, this proposed CT model based on the J-A theory of ferromagnetic hysteresis has the analysis capability of the transient response. The flexibility of TACS makes the simulation of any other situation easier and is another advantage. [ABSTRACT FROM AUTHOR]