In this paper the authors suggest exact analytic formulations which al
low numerical characterization of the transient electromagnetic enviro
nment, during operation of circuit breakers or disconnectors, of an el
ectric power transmission network. In this work, an exact method for c
alculating the transient field radiated by an air insulation substatio
n (AIS) together with the strictest formalism which enables the same c
alculation to be made for a power transmission line are paid particula
r attention. Results of simulations for different examples together wi
th results of measurements complete the study.