Symmetrical Components in Distance Protection

Application of Symmetrical Components in Distance Protection

Microprocessor relays use symmetrical components by converting 3-phase unbalanced systems into two sets of balanced phasors and one set of single-phase phasors, called positive, negative, and zero-sequence components. This method simplifies the fault analysis process and is applied in common protection schemes.

Assuming normal operating conditions, a balanced three-phase power system can be modeled based on the electrical characteristics of the current-flowing components which comprise the system. This also holds true during balanced three-phase faults, which are symmetrical in nature, but least common. Typical faults, such as line-to-ground, line-to-line, and double-line to ground, are unbalanced and asymmetrical. The method of symmetrical components was introduced to simplify the calculation and analysis of the fault characteristics by creating a balanced system made up of sequence components. These components are combined of positive-sequence phasors which share the original system sequence, negative-sequence phasors (opposite of original system sequence), and the three zero-sequence components which share a common phase angle. This concept is applied in protection schemes to increase sensitivity for specific fault types and provide supervision to improve security.

This presentation will introduce symmetrical components, and discuss the application of sequence elements to enhance protection for transmission, transformer, and generator/motor applications. Fault-type identification and location will be discussed, as well as implementing sequence elements for directional and differential protection, and distance element polarization. Creating test parameters for sequence element pickup and timing will also be discussed.

This is a free webinar

All webinar attendees are eligible to receive 1 NETA CTD and 1 PDH or 0.1 CEU. 


Michael Wilson

Applications Engineer