What is load encroachment?

Abstract - Cascaded tripping of power lines due to mal-operation

of zone 3 distance relays was one of the main causes of many

previous blackouts worldwide. Encroachment of load into the

zone 3 characteristics is one of the main cause for the maloperation

of the relays. By improving the operation of zone 3 of

distance relays it is possible to prevent such mal-operations so

that cascaded line tripping can be avoided.

A new algorithm that utilizes

Synchronized Phasor Measurements (SPM) to control the

operation of distance protection zone 3. Based on the proposed

algorithm, several improvements in operation of zone 3 can be

achieved. For instance, the relay can differentiate between actual

system faults and load encroachment.