Differential protection of multi-terminal lines without synchronization

Abstract

Differential protection is more appropriate for multi-terminal lines than distance protection, due to its selectivity. However, the sampling process at all terminals should be synchronized. The new methods presented don't need the sampled values for comparison and therefore no synchronization.Firstly, the positive-sequence component of currents and voltages is calculated from the sampled values. Then, using line parameters, currents and voltages as well the admittances or apparent powers at the tap poin~are calculated for each line section. The sum of the admittances, and also the sum of apparent powers are equal to zero for the sound line. Phase shifts between currents at all terminals in the prefank stage, caused by the not synchronized samp~mg can also be calculated. An appropriate sum of currents at the tap point is also eqnal to zero under sound line conditions. The proposed methods are especially suitable for deteetion of faults with considerable impedances. Keywords:digital algorithms, line proteetio% power transmission lines, differential protectio~symmetrical components.

Novel unit protective relaying techniques for teed circuit based on sequential overlapping derivative transform

“…However even for the differential protection such applications might pose special operating conditions which need to be investigated [1].Current differential relaying has long been an alternative to directional comparison relaying, especially for short line applications [4]. And also differential protection is more appropriate for multiterminal lines than distance protection, due to its selectivity [5]. Under reach for a distance relay-in feed from another source to a fault point at a multi terminal line makes a distance relay to see higher impedance.…”

“…However the restraint quantity used the vector difference between the largest incremental current and the vector sum of incremental currents of other terminals. In Reference [5], the positivesequence component of currents and voltages from the sampled values are calculated. Then, using line parameters, currents and voltages as well the admittances or apparent powers at the tap point, are calculated for each line section.…”