GB1486965A - Method of and apparatus for measuring impedances of a distribution network - Google Patents

Abstract

1486965 Measuring supply network impedances ELECTRICITE DE FRANCE (SERVICE NATIONAL) 14 May 1975 [24 June 1974] 20358/75 Heading G1U In a system for measuring the zero sequence and the positive and negative sequence impedances (these latter two being assumed to be equal) of a three-phase power supply network at a point known to be supplying a non-linear passive load and at a frequency which is any harmonic up to the thirtieth of the supply frequency, the following operations are performed:- (a) signals 2 1 , 22, 23, Fig. 3, representing the phase currents and signals 2 4 , 2 5 , 2 6 , representing the phase voltages are low pass filtered 81, 82, 8 3 , 91, 92, 93, up to the thirtieth harmonic, (b) the resulting signals are averaged 10, 10a, to give the zero-sequence current and voltage 33, 34, and combined linearly 11, 11a to give signals 3 1 and 3 2 representing the sums of the positive and negative sequence currents and voltages, (c) the resulting pairs of currents and voltages, 3 1 , 32 and 3 3 , 3 4 are each narrow-band filtered 34, 35, Fig. 8, the pass bands including two or three harmonics around the one of interest, and passed to circuits 36, 37 which_compute the quantities R = v#/#<SP>2</SP> and L = v ##d1/dt<SP>2</SP>, from which the desired impedances, using Z = R + jwL, may be derived. Conventional circuits for filters 8, 9, Fig. 3, are outlined, Figs. 5 and 4 respectively (not shown), as are circuits for filters 34, 35, Fig. 8, Figs. 12 or 13 (not shown), and appropriate operational amplifier circuits, Figs. 6 and 7 (not shown) are outlined for the circuits 10, 11, Fig. 3.