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Electric arc is a complex phenomenon occurring during the current interruption process in the power system. Therefore performing digital simulations is often necessary to analyse transient conditions in power system during switching operations. This paper deals with the electric arc modelling and its implementation in simulation software for transient analyses during switching conditions in power system. Cassie, Cassie-Mayr as well as Schwarz-Avdonin equations describing the behaviour of the electric arc during the current interruption process have been implemented in EMTP-ATP simulation software and presented in this paper. The models developed have been used for transient simulations to analyse impact of the particular model and its parameters on Transient Recovery Voltage in different switching scenarios: during shunt reactor switching-off as well as during capacitor bank current switching-off. The selected simulation cases represent typical practical scenarios for inductive and capacitive currents breaking, respectively.

The classical liquid drop theory for condensation was used in a computer solution to determine the effects of a carrier gas on homogeneous condensation. Zinc was used as the condensing vapor with helium, argon, or xenon as carrier gas in a nominal Mach 5 nozzle. It was found that the rate of accumulation of condensate is strongly dependent on the amount of carrier gas and can be rapidly increased by either increasing the mass fraction of carrier gas of low molecular weight or by decreasing the molecular weight of the carrier gas (for a given mass fraction). It was also found that for a change in nozzle angle of a factor of two, the area ratio at which the onset of condensation occurred changed very little. This was also true for a change in nozzle size (throat diameter) for a factor of two. Nomenclature A = nozzle area C p = specific heat of mixture in the stagnation chamber g = mass fraction of condensed liquid / = nucleation rate k = Boltzman's constant L = latent heat ra = mass rate of flow NA = Advogadro's number p = pressure of the mixture PD = pressure at drop surface p v = partial pressure of the vapor PV S = saturation pressure of the vapor corresponding to T p Zo = partial pressure of the vapor in the stagnation chamber p z = partial pressure of the zinc in the expanding mixture p 0 = pressure of the mixture in the stagnation chamber r = radius of a liquid drop r* -critical drop radius r' = the integrated value of dr/dx from the saturation point R u = universal gas constant R* = radius of the throat of the nozzle S = the sum in the equation for gr; denned in Eq. (24) T = the gas temperature TD = the temperature of the droplet T s = saturation temperature corresponding to p v To = gas temperature in the stagnation chamber u = gas velocity x = distance downstream from the throat Ax = increment in x used in S y = initial mass fraction of the vapor in the stagnation chamber dc = thermal accommodation coefficient of the carrier gas

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