US 5,956,220 AGranted

Adaptive distance protection system

AssigneesABB Power T&D Company Inc., ABB Network Partner AB

InventorsDamir Novosel, Yi Hu, Murari M. Saha

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Abstract

An adaptive distance relaying system provides improved performance for parallel circuit distance protection. The system utilizes the parallel circuit's current, when available, in conjunction with measurements of voltage and current on the protected line to compensate for the zero sequence current mutual coupling effect. The sequence current ratio (zero or negative sequence) is used to avoid incorrect compensation for relays on the healthy circuit. If the parallel circuit current is not available and the line operating status is, the best zero sequence current compensation factors are selected accordingly as a next level adaptation. If both the parallel circuit current and line operating status are unavailable, a fallback scheme that offers better results than classical distance protection schemes is employed.

Claims12

Dependent claims

An adaptive distance protection method for use with an underreaching relay in a power system comprising a protected circuit and a parallel circuit, wherein said protected and parallel circuits are connected in parallel between a first bus (G) and a second bus (H), and wherein said underreaching relay comprises current and voltage measuring devices for measuring currents and voltages on said protected circuit, comprising the steps of:

(A) determining whether a measurement of current in said parallel circuit is available and, if so:
(A1) calculating a blocking criterion (.alpha..sub.0 or .alpha..sub.2);
(A2) determining whether said blocking criterion (.alpha..sub.0 or .alpha..sub.2) is less than a predefined default value;
(A3) if said blocking criterion is less than said default value, computing a compensated fault current using the zero sequence current (I.sub.Psf0) in said parallel circuit;
(A4) if said blocking criterion is not less than said default value, computing the compensated fault current using a first zero sequence current compensation factor;
(B) if said current measurement is unavailable:
(B1) determining whether an operating status of said parallel circuit is available and, if so, whether said protected and parallel circuits are in operation;
(B2) if the parallel circuit's operating status is available and both circuits are in operation, calculating a compensated fault current using a second zero sequence current compensation factor;
(B3) if the parallel circuit's operating status is unavailable, calculating the compensated fault current using a third zero sequence compensation factor;
(B4) if the parallel circuit's operating status is available and one line is not in operation, calculating the compensated fault current using a fourth zero sequence compensation factor;
and
(C) calculating an apparent impedance value Z.sub.apparent.

9 more elements

An adaptive distance protection method for use with an overreaching relay in a power system comprising a protected circuit and a parallel circuit, wherein said protected and parallel circuits are connected in parallel between a first bus (G) and a second bus (H), and wherein said overreaching relay comprises current and voltage measuring devices for measuring currents and voltages on said protected circuit, comprising the steps of:

(A) determining whether a measurement of current in said parallel circuit is available and, if so:
(A1) calculating a blocking criterion (.alpha..sub.0 or .alpha..sub.2);
(A2) determining whether said blocking criterion (.alpha..sub.0 or .alpha..sub.2) is less than a predefined default value;
(A3) if said blocking criterion is less than said predefined default value, computing a compensated fault current using the zero sequence current (I.sub.Psf0) in said parallel circuit;
(A4) if said blocking criterion is not less than said predefined default value, calculating a compensated fault current using a first zero sequence current compensation factor;
(B) if said current measurement is unavailable:
(B1) determining whether an operating status of said parallel circuit is available and, if so, whether the protected and parallel circuits are in operation;
(B2) if the parallel circuit's operating status is available and both circuits are in operation, calculating a compensated fault current using a second zero sequence current compensation factor;
(B3) if the parallel circuit's operating status is unavailable, calculating the compensated fault current using a third zero sequence compensation factor;
(B4) if the parallel circuit's operating status is available and at least one line is not in operation, calculating the compensated fault current using a fourth zero sequence compensation factor;
and
(C) calculating an apparent impedance value Z.sub.apparent.

9 more elements

Dependencies are inferred from the claim text.