METHOD DETERMINING CONDUCTANCE OF PHASE INSULATION WITH REFERENCE TO GROUND IN NETWORKS WITH INSULATED NEUTRAL

摘要

FIELD: electrical measurement technology, phase-by-phase determination of conductance and admittance in networks with insulated neutral and symmetric capacitive conductance of insulation. SUBSTANCE: in accordance with method of determination of conductance of phase insulation with reference to ground in networks with insulated neutral voltages relative to ground, single-phase short- circuit currents to ground are measured per each phase. Then additional conductance is placed between each phase and ground and voltages with regard to ground are measured anew. Values of equivalent admittance of insulation, its active and capacitive components are computed by results of these measurements. Characteristic feature of method lies in additional measurement of voltage of zero point of transformer relative to ground and of phase emf of transformer under no-load condition. Then scaled topographic diagram of emf of transformer in rectangular coordinates with center in point of their crossing is plotted with laying one vector as abscissa. After this coordinate center is used to circumscribe circle with radius equal by scale to voltage U₀ of zero point of transformer with regard to ground and to construct three arcs with centers from ends of vectors of emf of transformer and radii equal by scale to corresponding voltages of phases relative to ground. Common point " 3 " of crossing of circle and three arcs is found by results of graphic construction. Further on found point is projected on to the abscissa and on to coordinate axis and values " Y " of reactive component of voltage of zero point of transformer relative to ground and " X " of active component of this voltage are found, they are multiplied by scale factor and conductance and admittance of insulation of corresponding phases are determined by proper formula. EFFECT: increased informativity of method thanks to phase-by- phase determination of conductance and admittance. 2 dwg