Maintenance planning in compliance with new NERC reliability standard PRC 005-6

Author: Rodney Fickler

08/11/2016

Introduction

 

The North American Electric Reliability Council (NERC) Reliability Standards dealing with protection and control (Series PRC 005-X(XX)) are the most prescriptive standards adopted by the NERC regulatory authority. The group of NERC Reliability Standards most likely to be found non-compliant during an audit with operations and planning are shown below.

Part of the difficulty is the detail to which a generator or transmission owner must understand and interpret the sometimes vague and confusing language of the standard into actionable and well documented maintenance plans. Most transmission and generator owners know how to maintain the protection and control devices; however, demonstrating compliance requires extensive documentation and statistics that show that maintenance has been performed and provides the justification for the maintenance plans.

 

In January of 2016, the Federal Energy Regulatory Commission (FERC) approved the new PRC 005-6 standard, so it is important to revisit how to develop a PRC compliant maintenance program in light of recent changes in the standard.

 

PRC 005-6 and the standards it supersedes

 

The NERC Reliability Standard PRC 005-6 deals with protection systems, automatic reclosing, and sudden pressure relay system maintenance. The standard outlines the requirements of a “Protection System Maintenance Program“ (PSMP) – a program that shall be adopted by the registered entity (asset owner) and is applicable to generator owners (GO), transmission owners (TO), and distribution providers (DP). It is important to note that the PSMP is to cover those assets which are connected to the Bulk Electric System (BES). This article discusses the protections systems that will actuate circuit breakers or other switching apparatuses that disconnects or reconnects transmission and distribution equipment to and from the transmission system.  A good reference document to correctly identify the assets and related protection systems to be considered in the maintenance program is the NERC document “Supplementary Reference and FAQ, PRC-005-6 Protection System, Automatic Reclosing and Sudden Pressure Relaying Maintenance and Testing,” available at www.nerc.com.

 

The equipment listed in this document is the same as the equipment referenced in the older versions of the PRC 005-2 standard but now incorporates auto reclosing equipment, supervisory, alarm systems, and sudden pressure relays. Like the previous PRC 005-2, the standard incorporates tables stating mandatory time based maintenance intervals depending upon the level or existence of monitoring of the protection equipment. The standard defines what constitutes a performance based maintenance program, which is an option for the asset owner to consider as a basis for the maintenance program. Although this affords the opportunity for the asset owner to extend maintenance intervals based upon historical repair rates or corrective maintenance events, it requires an extensive amount of statistics based upon samples of comparable asset types to allow or to justify extension of maintenance intervals.

 

One of the problems that NERC faced with the implementation of the new standard was how to phase out the old and phase in the new without creating gaps in compliance. To achieve this, NERC elected to go with a phased-in approach. At first glance, this approach looks a little daunting, but after closer scrutiny, it does make sense. The following standards will be replaced by PRC 005-6:

  • PRC-005-5 – Protection System, Automatic Reclosing, and Sudden Pressure Relaying Maintenance 
  • PRC-005-4 Protection System, Automatic Reclosing, and Sudden Pressure Relaying Maintenance 
  • PRC-005-3 (ii) Protection System and Automatic Reclosing Maintenance 
  • PRC-005-3 (i) Protection System and Automatic Reclosing Maintenance 
  • PRC-005-3 Protection System and Automatic Reclosing Maintenance 
  • PRC-005-2 (ii) Protection System Maintenance 
  • PRC-005-2 (i) Protection System Maintenance 
  • PRC-005-2 Protection System Maintenance 
  • PRC-005-1b – Transmission and Generation Protection System Maintenance and Testing 
  • PRC-008-0 – Implementation and Documentation of Underfrequency Load Shedding Equipment Maintenance Program 
  • PRC-011-0 – Undervoltage Load Shedding System Maintenance and Testing 
  • PRC-017-0 – Special Protection System Maintenance and Testing.

Some of the standards being replaced, although approved, have not been put into effect yet. Part of the NERC’s reasoning was to consolidate some of the forthcoming standards into one comprehensive standard to simplify the implementation and administration of compliance. Although standards 005-5.-4.-3 had been developed, the standards that are currently in effect are PRC 005-2,011-0, 017-0. Since the PRC 011-0 and 017-0 call for the same maintenance plan strategy, the NERC elected to incorporate them into the new standard PRC 005-6. To summarize, PRC 005-2 will remain in effect until March 2027 when the new standard PRC 005-6 becomes fully enforced.

 

Implementation of PRC 005-6

 

Starting January 1, 2017, PRC 005-6 requirements R1, R2, and R3 will become effective and registered entities will be expected to be 100% compliant by that date. Since these requirements are very similar to 005-2, this was not seen as an additional burden. However Requirements R3 and R4 will be phased in as shown below.

PRC 005-6 R3 and R4 compliance dates

Table reference
Maintenance interval
% compliant
Date
Tbl 1-1 to 1-5

>1 year

<2 year

100%
April 1 2017
Tbl 1-1 to 1-5
=3 year
30%
April 1 2016 or subsequent outage for GO interval >2 years
Tbl 1-1 to 1-5
=3 year
60%
April 1 2017
Tbl 1-1 to 1-5
=3 year
100%
April 1 2018
Tbl 1-1 to 1.-5 and 3
=6 year
30%
April 1 2016 or subsequent outage for GO interval >2 years
Tbl 1-1 to 1.-5 and 3
=6 year
60%
April 1 2019
Tbl 1-1 to 1.-5 and 3
=6 year
100%
April 1 2021

Tbl 1-1 to 1.-5

Tbl 2 & 3

=12 year
30%
April 1 2019

Tbl 1-1 to 1.-5

Tbl 2 & 3

=12 year
60%
April 1 2023

Tbl 1-1 to 1.-5

Tbl 2 & 3

=12 year
100%
April 1 2027

For Automatic Reclosing Components, Sudden Pressure Relaying Components, and Dispersed Generation Resources maintenance activities:

PRC 005-6 R3 and R4 compliance dates

Table reference
Maintenance interval
% compliant
Date
Tbl 4-1, 4-2(a), and 4.2(b)
=6 year
30%
April 1 2019
Tbl 4-1, 4-2(a), and 4.2(b)
=6 year
60%
April 1 2021
Tbl 4-1, 4-2(a), and 4.2(b)
=6 year
100%
April 1 2023

For Automatic Reclosing Components, Sudden Pressure Relaying Components, and Dispersed Generation Resources maintenance activities:

PRC 005-6 R3 and R4 compliance dates

Table reference
Maintenance interval
% compliant
Date
Tbl 4-1, 4-2(a), and 4-2(b)
=12 year
30%
April 1 2021
Tbl 4-1, 4-2(a), and 4-2(b)
=12 year
60%
April 1 2025
Tbl 4-1, 4-2(a), and 4-2(b)
=12 year
100%
April 1 2029

Part of the reason for the protracted dates for compliance is the expanded scope of the standards, including reclosing and sudden pressure devices as well as the option of the asset owner to implement a performance based maintenance program (PBMP). A PBMP allows the asset owner to extend the maintenance intervals beyond those stated in the PRC 005-6 tables. However, to achieve this requires the asset owner to have the data and statistics to warrant the extension. Another reason for the protracted dates for compliance is to allow asset owners time to gather data (corrective maintenance events) and perform the statistical analysis to justify the extension. If the data and analysis suggest that maintenance interval should be shorter than are stated in the tables of the NERC standard, then you are required to perform maintenance to that shorter interval. You cannot go back to the time based maintenance intervals outlined in the tables of the standard if your failure rates or corrective maintenance events dictates shorter intervals are necessary. This would result in non-compliance.

 

Methods of maintenance planning

 

Time Based Maintenance

 

The basic tables in both the older standard PRC 005-2 and the new standard PRC 005-6 are based upon time based maintenance. These intervals were arrived at based upon NERC solicitation of industry experts. One approach is to base your maintenance plan on these intervals stated in the reliability standard and stagger the maintenance resources such that the entire fleet of device types outlined in the tables receive their respective maintenance service within the prescribed interval stated in the tables.

 

Performance Based Maintenance

 

If you elect to adopt PBMP as your maintenance strategy, the standard allows the asset owner to use a sampling technique to determine the appropriate maintenance interval. This has the potential to significantly reduce your maintenance work. To successfully adopt a sample based approach to establish your maintenance intervals you must:

  1. Obtain a statistically significant sample of an asset type relative to the entire population of the asset type you own.
  2. The asset types must be categorized in homogeneous groups with the same attribute data such as; manufacture, vintage or technology, working environment etc. To carry on the example in (1), if out of the 1000 current differential relays, you have 25% from one manufacture and 75% from another manufacture this would constitute two asset types, one being 250 population size and the other being a size of 750. If we further assume that within the 250 relays from one manufacturer 50% are electro-mechanical, 20% are solid state, and 30% are micro processor based, you must split the 250 in three more groups of 125 electro mechanical, 50 solid state, and 75 are micro processor based. Since a statistically significant sample would be in the range of 30 to 60 devices, you can quickly see that the sampling technique does not really save a lot of expense for the solid state and micro processor based relays compared to doing maintenance on all of the relays in their respective groups.
  3. After you have collected and analyzed the data, you can use the following recommended repair rate to determine your maintenance interval as shown in the table in the table below.

The math is actually quite simple. Assume there is a statistical rationale for a 4% annual failure rate, and the asset owner wants to increase the interval of maintenance. For this example, there are 1000 devices having like attributes that have an estimate failure rate of 4%. If  maintenance was performed on all of the devices every year, there would be an expected 4% of 1000 failures or 40 failures. If maintenance was performed every twenty years, failures would be expected to equal 1000/20 x 4%, or two failures each year inspections or preventative maintenance were performed on 50 devices.

 

Hence, it is strongly suggested you perform some preliminary analysis of your fleet, breaking down the quantity of devices into their respective attribute groups, and see if you gain a lot through adopting a sample based PBMP.

Testing interval example of 1000 units having common attributes.

Source:  NERC Document; Supplementary Reference and FAQ PRC-00506 Protection System, Automatic Reclosing, and Sudden Pressure Relaying Maintenance and Testing

Testing intervals (years)
Units per year
Acceptable number of countable events per year
Yearly failure rate based on 1000 unites in segment
1
1000.00
40.00
4.00%
2
500.00
20.00
2.00%
4
250.00
20.00
2.00%
6
166.67
6.67
0.67%
8
125.00
5.00
0.50%
10
100.00
4.00
0.40%
12
83.33
3.33
0.33%
14
71.43
2.86
0.29%
16
62.50
2.50
0.25%
18
55.56
2.22
0.22%
20
50.00
2.00
0.20%

Condition Based Maintenance

 

In this scenario, you apply monitoring to devices such that condition parameters are continuously monitored that provide advance notice of deterioration of performance or failure. The standard already has incorporated a typical six year increase in maintenance interval between devices that are monitored versus unmonitored. The increased cost of adding the monitoring versus performing the increased frequency of maintenance drives the value proposition in the business case, but there are usually additional benefits of avoiding catastrophic failure of major assets that could also help with cost justification. An example would be station battery systems. If your substation battery system is coming up for replacement, consider adding battery and battery charging equipment monitoring and integrating both alarm and monitoring data into your SCADA systems. This may prove to be a very cost effective solution from a maintenance budget perspective since the PRC standard calls for fairly high frequency maintenance intervals for this type of asset.

 

How Siemens complies with PRC standards

 

Siemens typically performs maintenance on merchant-owned generation and transmission assets, especially during initial warranty periods or when availability guarantees are contractually required. Since the maintenance services are contracted on a per transmission or generation station basis, the fleet size of a particular asset type is not sufficient large to allow a sampling strategy to be viable in for analysis of PRC compliance. Therefore, we elect to perform a time based approach. However, we do incorporate monitoring as much as is economically practical to extend maintenance intervals while allowing both local and remote monitoring of critical parameters to avoid forced outages.

 

For utility-owned assets with similar warranty and availability contractual commitments, Siemens plans on offering options to our customers that allow the customer to perform the NERC scheduled maintenance using a PBMP statistical approach, provided that equipment monitoring is incorporated to allow Siemens to remotely monitor the substation. If corrective maintenance is required, Siemens will share with the customer the maintenance actions taken, including root cause data to allow their maintenance statistical data to be updated accordingly. This allows Siemens to reduce its costs while allowing the customer to incorporate new asset types into their PBMP, which should generally improve overall statistical performance and allow longer maintenance intervals to be justified.