Method for locating short circuit in an overhead power transmission line by unsynchronized measurements at both ends thereof
The claimed invention relates to the power industry and can be used for locating short circuits in power transmission lines by measuring the instantaneous current and voltage values when unsynchronized measurements are taken at both ends of the line. It is a technological object of the invention to improve the accuracy of damage location. The technical result of the invention is achieved by accurately synchronizing the current and voltage values measured at the ends of the line and unsynchronized in time on measurement. Synchronization is effected by aligning the oscillograms at both ends of the line with the short circuit start section.
1. A method for locating a short circuit point in an overhead power transmission line by taking unsynchronized measurements at both ends thereof, said line having a length l, a real resistance R, and an inductive resistance X L and connecting two supply systems, said method comprising measuring the phase currents and voltages unsynchronized in time at both ends of the line during a short circuit; identifying the damaged phases; and determining the relative distance n to the short circuit point at the end of the line marked by ′ from the formula l′=n*l, where l′ represents when a short circuit occurs in the line; wherein the instantaneous values of phase currents (i′ A ,i′ B ,i′ C ) and (i″ A ,i″ B ,i″ C ) and voltages (u′ A ,u′ B ,u′ C ) and (u″ A ,u″ B ,i″ C ) are measured at both ends of the line (′ designates one end of the line and ″ marks the other end of the line) during a short circuit; oscillograms are constructed for currents and voltages; the oscillograms at both ends of the line are aligned in the short circuit start section; a section in the oscillograms of damaged phase current and voltage is chosen within the interval of two to ten periods from the start of the short circuit; the instantaneous values of currents i′ and i″ and voltages u′ and u″ are read off in the section and at neighboring points; time-specific current derivatives di′/dt and di″/dt are calculated; and the relative distance n to the short circuit point is determined from the formula:
n
=
(
u
′
-
u
″
)
+
R
·
i
″
+
X
L
·
ⅆ
i
″
ⅆ
t
R
·
(
i
′
+
i
″
)
+
X
L
·
(
ⅆ
i
′
ⅆ
t
+
ⅆ
i
″
ⅆ
t
)
,
wherein:
u′ and u″ are instantaneous voltage values obtained in the section of the damaged phase voltage oscillograms at one and the other ends of the line (V);
i′ and i″ are instantaneous current values obtained in the section of the damaged phase current oscillograms at one and the other ends of the line (A);
di′/dt and d″/dt are time-specific current derivatives (A/C); and
R and X L are the real and inductive phase resistances of the line (Ohms).