The metal oxide arrester can be built without series gaps and
its voltage–time behaviour for fast rising surges depends only
on the turn-on behaviour of the arrester material and the
construction. It is known that the turn over of the metal
oxide blocks from a capacitive behaviour to an ohmic
behaviour takes some time [6]. The capacitive effect of the
arrester block depends on the steepness of the applied
surge. The rate of rise of the incoming current surge plays
an important role in triggering the operation of the surge
arrester. In order to study the capacitive effect, the values of
residual voltage for 3 kV arrester block (height: 30 mm and
diameter: 60 mm) with different current surges are
computed. There is no variation in time at which Vr occurs.
However a perceptible drop in the rate of rise of residual
voltage is observed because of capacitive effect. Further
analysis is therefore performed based on initial peak value
(Vi) and the corresponding initial rise time (ti). Fig. 1 shows
Vi, ti, Vr and the time at which peak occurs (tr) for 8/20 ms,
10 kA current surge [18]. Fig. 1 is given to understand Vi
and Vr of the residual voltage.
For higher rated surge arresters, the stray capacitance effect
is more and thereby the drop in the rate of rise of residual
voltage is more. Therefore the dynamic characteristics
cannot be obtained under VFTO, causing delay in the initial
response (initial rise time of the residual voltage) of the
arrester. To include the stray capacitance effect and to meet
the needs of the dynamic characteristics of the arrester
under VFTOs, an innovative modelling study and
minimisation of delay between residual voltage and current
surge are very much essential. Owing to presence of this
delay, the computation of residual voltage waveform with