Surge Modelling of Transformer Using Matlab-Simulink

Abstract

Abstract -This paper aims to validate the surge modelling of a transformer using Matlab-Simulink using an electromagnetic model and thereby ascertaining the model accuracy. The studies cover winding responses to both full and chopped standard lightning impulses with time to chop varying over a wide range. Modelling was carried out using the design data of a 3 MVA, 33/11 kV, 3-phase, 50 Hz, Dyn 11 Transformer whose 33 kV mesh connected winding was considered to be subjected to standard full wave (1.2/ 50 μs) and chopped impulses chopped at 3 μs, 8 μs and 15 μs. The mathematical model considered takes into account the series and shunt capacitances and inductances of the winding elements, including the effect of their mutual inductances. The Simulation compared with the experimental results shows the validity of the Surge modelling of the transformer. Keywords - Modelling, Lightning Surges, Transformer winding, Transients.I. INTRODUCTION n a power system a power transformer is the most important and expensive piece of equipment. The fundamental work on transients in a magnetic winding was done by Wagner [1] 1915. Great progress has been made since 1915 in understanding the physical phenomenon which govern the transient response in transformer. Required transformer insulation is determined to a great extent by the transient voltages and stresses which appear in the transformer winding. Varying impulse voltages with long wave shape and large magnitude may be due to switching fault, lightning surge or by commercial impulse voltage test in the laboratory [2]. To design the insulation it is necessary to know the voltage appearing across the insulation (as a function of time) and the strength of insulation against the particular voltage wave. The study of the behaviour of a transformer winding with one grounded end is done when stressed by standard impulse voltage wave (1.2/50 μs) and chopped impulse waves chopped at 3 μs, 8 μs and 15 μs [2]. II. MODEL PARAMETERS The Transformer winding is represented by a network with distributed parameters as shown in Fig. 1. C, K, L and M represent the capacitance to ground, series capacitance, self inductance and mutual inductance per unit winding length respectively. Magnetic losses have been ignored [2, 3, 4].