Introduction

Utilities have managed relay performance with periodic testing and calibration programs, using intervals and testing activities based on failure experience.  Many also use testing as the final confirmation of whether relays are set correctly.  However, a relay may fail at any time following a test, posing a hidden system performance risk.  Also, maintenance errors sometimes disable the relay. The utility is lucky if a fault does not expose the problem before the next test. 

Manufacturers have promoted the ability of modern microprocessor relays to monitor internal functions and alarm for failures.  The monitoring coverage even extends to some of the application circuits connected to the relay. Ac input circuits connect to A/D conversion subsystems that don’t drift and have no calibration adjustments.  As manufacturers have refined successive relay generations, users have experienced improving reliability, and have also experienced the usefulness of the failure alarms.  Users have extended maintenance intervals and trimmed the testing activities for these relays.

The next technical wave to impact maintenance is the use of multiplexed data communications paths between microprocessor relays in place of dedicated control wires.  With serial or Ethernet connections, background heartbeat messaging monitors the entire communications path, and can alarm for failures in a way that wires cannot do.

Relay manufacturers promote these legitimate advances as keys to better and easier maintenance programs.  But note these challenges to the full realization of this benefit:

• Manufacturers and users have not joined efforts to create a clear picture of exactly what is and is not covered by monitoring in a particular system design.  There are gaps in the overall design for reporting failures in protection systems
• Field maintenance technicians sometimes apply familiar old techniques to new equipment, losing the benefit.  Working procedures have not kept up with technical advances
• The industry is just beginning a concerted effort to analyze and document these monitoring and maintenance practices so that all users can benefit from guidance by the industry experts and leaders
• Many utilities lack enterprise database systems that could support effective analysis of relay reliability, maintenance issues, operating experience, and system configuration  (the huge arrays of interacting parameters in systems of relays)

Major Action in N. America

The North American Electric Reliability Corporation (NERC) has been appointed by the US Federal Energy Regulatory Commission (FERC) and Canadian provincial government authorities to develop and enforce a broad range of standards for reliability of the bulk electric system (BES) - generally transmission above 100 kV plus key generating facilities.  NERC and its eight component regional reliability organizations (RROs) are charged with auditing BES owners for compliance, and can levy fines of up to 1 MUSD per violation per day.  It is no surprise that utilities are paying close attention, with massive investments in organizational compliance, documentation, and internal systems for monitoring compliance.  Of interest to PACworld readers are the protective relaying and control (PRC) series of standards available under the Standards/Reliability Standards selections on the home page www.nerc.com/.  NERC is revising many of these standards, as well as writing new standards for previously missed issues.

This article focuses on the technical concepts behind the updating of PRC-005-1, Protection System Maintenance and Testing.  The existing standard requires only that an owner of a protection system have a documented maintenance program, with a documented basis for the maintenance intervals.  The owner must also have full documentation proving that the stated program is being carried out without gaps or exceptions.  When FERC ordered NERC to update PRC-005-1, it specified addition of firm maximum maintenance time intervals and activities appropriate to the type of protection.  The Standard Drafting Team (Project 2007-17 in the NERC web site list of Standards under Development) is now issuing a new draft of PRC-005-2, Protection System Maintenance, along with supporting explanatory documents.  PRC-005-2 is the most technically complex reliability standard from NERC to date.  The new standard implements FERC-ordered changes by adding specific requirements for maximum maintenance time intervals and activities. However, the drafting team has also opened doors to maintenance based on condition or performance monitoring that can reduce or eliminate hands-on maintenance testing of most components.  While this regulatory driver is unique to North America, the new technical approaches can benefit users and manufacturers around the world as they transition to new protection designs.