Localizers, Suppressors, and Experiments

Generators on a loaded three-phase system maintain practically constant delta potential between phases. The generators themselves generate nearly constant and stable Y potentials. Any shifting of the neutral of the generator on a loaded system is transitory. The values of potential of the three phases to ground are determined by lines drawn from the corners of the delta triangle to a point on a semicircle drawn on the Y potential as diameter. This semicircle is drawn on the side of the Y potential next to the succeeding phase (see Fig. 35). For example, if phase 2 is grounded the semicircle is on the side of phase 3. In the oscillograms of the operation of the arcing ground suppressors, no dangerous potentials were observed. The suppressor operates in one-quarter of a second in accordance with the usual design of switch. Different harmonics were found on the system, namely: 11, 13 and 17, which were magnified more or less according to the conditions of capacity. In themselves, these harmonics have no baneful significance. The effects of an arcing ground on a cable are modified by movements of the melted metal of the lead sheath. On the under side the lead drops away and thus increases the arc length. On the upper side the molten metal runs down into the fault and shortens the arc.