METHOD OF DETERMINING DOUBLE GROUND FAULTS IN NETWORK WITH INSULATED NEUTRAL Russian patent published in 2020 - IPC G01R31/08 

FIELD: electric power engineering.

SUBSTANCE: invention relates to power industry, namely to distribution networks relay protection and automatics, operating in mode with insulated neutral. Method involves measurement of phase currents and voltages at the beginning of the controlled power transmission line in the previous mode and in the mode of double earth fault. First, the damaged phases are set. Then, the load of the controlled power transmission line is determined from the measured phase currents and voltages in the previous mode. Next pure emergency current for each phase is determined as the difference between the measured phase current and the current of the corresponding phase of the model of the undamaged network for the monitored section when the measured phase voltages in the double-closing mode are acted on at its inputs. For each of the damaged phases, the corresponding difference current is determined by subtracting the undamaged phase of the pure fault current of the faulty phase from the purely fault current to the left of the first assumed closure point. Closure current is determined taking it proportional to difference current. For damaged phases, target functions are formed, which depend on the coordinate of the point on the power transmission line and the point on one of the damaged phases is taken as the first closing point, in which the target function passes through zero and the coordinate of which is closer to the measurement point. To determine the second closing point, the phase current is calculated to the right of the first closing point as the difference between the corresponding phase current to the left of the first fault and the short-circuit current. Finding pure emergency current for each phase to the right from the first closing point as difference of phase current to the right from the first closing point and current of the corresponding phase at the input of the new intact network model, which originates at the first closure point, when phase voltages of the first closing point act on its inputs. Intermediate component is selected in the form of non-zero component or component of zero sequence of pure emergency current of damaged phase to the left of current source. Second fault current is determined taking it proportional to said intermediate component. Target function is formed for second damaged phase, which depends on coordinate of point on power transmission line, and consider point of transition of this target function through zero by second closing point.

EFFECT: technical result: simple method by reducing the number of iterations in calculation by determining double ground faults by eliminating the need to re-model an undamaged network.

10 cl, 22 dwg