Man-made faults - line protection operation for an unintended phase cross-connect condition

For a temporary operating condition, a utility installed a new switch to tie together two subtransmission lines. During the installation, operating personnel inadvertently crossed two phases. When the operators closed the line switch, it created an unusual fault, cross-connecting two phases between the sources and causing the line protection to operate on one end of the line. Another relay protecting a line connected to a common bus also tripped for this condition.