Protection System Redundancy Criteria For Nerc Tpl-001.5 Footnote 13

NERC Standard TPL-001.5.1 is not a Protection and Control standard, however it’s footnote 13 is about redundancy of four of the five elements of the NERC defined Protection System. Most protection engineers are not familiar with the nuances of the defined requirements for redundancy or monitoring exemptions for elements such as DC supply and control circuitry. Some Protection engineers assume that compliance groups or planning groups, (Planning Coordinator or Transmission Planner), have this responsibility but in many cases those groups lack the detailed knowledge of control circuits and battery monitoring systems to understand where designs are deficient in meeting the requirements. The standard does not require redundancy in all cases but requires utilities to identify BES locations where any of the four redundancy tests are not met and to provide backup fault clearing times, breakers and thevenin impedances for sequentially clearing three phase and single line to ground faults. The authors have made presentations to WECC and NERC Relay Working Groups on some of the issues regarding footnote 13. Footnote 13 is a follow on effort based on the earlier FERC Order No. 754.

This paper and presentation will focus on identifying the NERC redundancy requirements for TPL-001.5.1 footnote 13 a, b, c and d. The most common redundancy failures for WECC utilities will be discussed. Data management and best practices will be addressed. These will focus on battery monitoring requirements and control circuit issues. In many cases non redundancy is allowed if the element is monitored and reported to a Control Center. Authors will discuss problems encountered while trying to provide evidence of compliance for the monitored and reported option. New databases or data repositories typically need to be created for some of the elements covered by footnote 13. Some common incorrect assumptions by planning groups will also be discussed as well as some approaches to streamline the simulation of backup clearing times.

The author’s employer has submitted a NERC standards authorization request (SAR) to modify requirement 13d that has been accepted and assigned to a Standard Drafting Team.