Distance protection of unsymmetrical lines

✍ Scribed by H. Hupfauer; P. Schegner; R. Simon

• Publisher: John Wiley and Sons
• Year: 2007
• Tongue: English
• Weight: 628 KB
• Volume: 6
• Category: Article
• ISSN: 1430-144X
• DOI: 10.1002/etep.4450060203

✦ Synopsis

Technical, economical and ecological aspects lead to untransposed power lines. Full transposition schemes are often to expensive and not applicable to short poly-circuit lines. Therefore line unsymmetry is of importance with respect to the impedance calculation and the setting of distance-protection relays. As a consequence of line unsymmetry the short-circuit impedance depends on the fault type and the measuring loop. As conventional distance protection is based on the model of a symmetrical line, this causes an unsharpness of the tripping area in the complex impedance plane. To avoid wrong tripping, distance-protection relays must be set with reduced ranges. consequently, the fault clearing time increases for extended sections at both line ends.

Furthermore fault localization -an additional feature of increasing importancewill be as inaccurate as the measured impedance. Improvement of distance measurement by new current-compensation methods are discussed in this paper. Extensions of the methods to mutual coupled double-circuit lines are outlined.