Applying Distance Protection To Comply With Prc-026-1 Without Implementing Power Swing Blocking

PRC-026-1 requires that identified protection functions on the bulk electric system do not trip for stable power swings during non-fault conditions. For distance protection elements, PRC-026-1 Attachment B Criterion A defines an unstable power swing region. Any distance protection element subject to the standard (as defined in Attachment A) that has the tripping (operate) region of its characteristic not fully contained within this defined unstable power swing region requires action to be taken to meet, or become excluded from, the requirements of the standard.

Tripping (operation) of any distance protection element (as defined in Attachment A) for a power swing that remains outside the unstable power swing region is not permitted. The standard applies to distance protection elements with instantaneous tripping or intentional trip delays less than 15 cycles, or that are used in high-speed communication-aided tripping schemes. A distance protection element subject to the standard is inherently compliant if the tripping (operate) region of its characteristic is completely contained within the unstable power swing region.

To comply with the standard, a distance protection element must meet Attachment B Criterion A, or it must be excluded under an Attachment A criterion (which states that any non-compliant distance protection element can be excluded if it is supervised by power swing blocking).

This paper is part 2 to the paper that was presented in 2025. That paper covered the supervision of non-compliant distance elements by power swing blocking, and also proposed a method that does not use power swing blocking. The proposed method required two dedicated distance zone elements (say zone X and zone Y that are readily available in multi-zone distance protection functions). Applying power swing blocking has some challenges. This was the core motivation for proposing another method that does not require the use of power swing blocking, hence alleviating the challenges associated with power swing blocking.

This paper will focus predominantly on the proposed method, and will include the results of verification testing that was performed. Here are some details of the tests performed: - Three-phase faults were placed at 10%, 40%, 70% and 100% along the line. Faults were simulated at 0° and 90° fault inception angles (with respect to phase A). The reason for performing these three-phase faults was to determine the maximum operating time difference between zone X (that must surround the non-compliant zones) and zone Y (that must be completely within the PRC-026-1 unstable power swing region). This maximum time difference is a critical component in the logic of the proposed method. The tests were performed with both maximum permitted and minimum required zone X R-axis reach (as this changed the R-axis distance between zone X and zone Y elements). - Power swings to ensure correct PRC-026-1 performance, i.e. that non-compliant distance zones extending outside the unstable power swing region can be excluded from meeting the requirements of the standard by supervising them with the proposed method. The two source voltages start at 60° apart (remote source ER lagging local source ES), move to 180° apart at the applied swing frequency, hold there for 3 cycles, then return back to 60° apart following same path, i.e. not an out-of-step pole slip. Swing frequencies evaluated were 2.5Hz, 5Hz, 7.5Hz and 10Hz (based on a 60Hz nominal system frequency). The tests were performed with both maximum permitted and minimum required zone X R-axis reach (as this changed the R-axis distance between zone X and zone Y). - Power swings, then during the power swing add a fault (zero-sequence current) – performed for 2.5Hz, 5Hz and 10Hz power swings. - Compare functional performance of the proposed method with traditional power swing blocking.