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Frequency and impulse responses of cast resin transformer windings are presented. The stress arising during lightning impulse test is compared with that originated during switching operations, in case of oscillating transients.
Of late years, in densely housed megapolises 110-kV line circuits are used overhead and cable line sections. Most frequently occurring emergency states in such grids arise from line-to-ground faults with inflammation of electromagnetic voltage transformers. The causes of such accidents and developing efficient prevention measures are considered in this paper.
In this work a computer model for calculating surge distribution in transformer windings is presented. The transformer model is developed using transmission line theory. The capacitance, inductance, resistance and conductance are calculated with simple formulations. The electrical parameters are used for calculating modal parameters in order to represent the winding as a two port network. The model...
Calculation of over-voltage distribution of transformer windings under Very Fast Transient Over-voltage (VFTO) is very important to insulate design of transformers windings. In order to investigate over-voltage distribution under VFTOs, a proposed model using lumped-parameter components is presented in this paper. In the case of easily destroyed former several windings, each winding is modeled as...
Understanding the potential and electric field distribution in the insulation system of a transformer during transients is vital to its construction. Therefore, we have developed a method for electric field analysis inside a power transformer. The method consists of the following steps. (1) A lumped parameter equivalent model is constructed by dividing transformer windings into several blocks. (2)...
To calculate the very fast transient overvoltages in transformer windings, a novel model based on the modified multi-conductor transmission line (MTL) theory is proposed in this paper. In original MTL model, the lengths of all the conductors are considered to be equal and this approximation can cause inaccuracy. In fact, the lengths of the conductors are decreasing from the outside to the interior...
Calculation of over-voltage distribution of transformer windings under very fast transient over-voltage (VFTO) is very important to insulate design of transformer windings. In order to investigate over-voltage distribution of transformer windings under VFTOs, firstly in the case of easily destroyed former several windings, each winding is modeled as one unit, others are modeled using two windings...
The paper deals with the computation of very fast transient overvoltages (VFTOs) in transformer windings with frequency-dependent effect. For this purpose, a new technique that extends the idea of integrated congruence transform(ICT) is presented so that it can handle multiconductor transmission lines(MTLs) with frequency-dependent per-unit-length(FD-PUL) parameters. Based on it, a fast frequency...
To investigate the Very Fast Transient Over-voltage (VFTO) distribution in transformer windings in Gas Insulated Substation (GIS), a systematic methodology based on hybrid model is presented for establishing high-frequency model of transformer windings in this paper. Firstly, the voltages at the end of each coil are calculated by means of Single-Conductor Transmission Line Model (STLM). Secondly,...
This paper is concerned with the phenomena of very fast transient overvoltages (VFTO) invading the transformer windings. Some literatures have pointed out that the insulation breakdown usually locates near the entrance of the windings. So it is very important to study the voltage distribution along the coils near the entrance of the windings under VFTO. A new hybrid model is presented to simulate...
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