2019 Misoperation Report
Relay Work Group
Introduction ...3
Background ...3
Purpose ...3
Data…. ...3
2019 Misoperation Analysis ...4
Misoperation by Cause Category...4
Misoperation by Category ...6
Misoperation by Voltage Class ...7
Misoperation by Relay Technology ...9
Subgroup Analysis and Observations for Misoperations by Cause ...10
AC and DC Systems Cause Analysis ...10
Incorrect Setting/Logic/Design Errors Cause Analysis ...14
Communication Failure Cause Analysis ...18
Relay Failures/Malfunctions Cause Analysis ...20
As-left/Personnel Error Cause Analysis ...22
Unknown/Unexplainable Cause Analysis ...24
Conclusions ...26
Introduction
Background
The NERC has identified Protection System Misoperations as a major area of concern to reliability because they significantly increase the severity of an event. The NERC tracks annual Misoperation rates for each region to evaluate the performance of Protection Systems—both generator and transmission. The metric is the ratio of Protection System Misoperations to total system Protection System operations. Higher numbers indicated a greater probability for any particular Protection System operation to have been a Misoperation.
Purpose
The Relay Work Group (RWG) reviews the quarterly Misoperation data for registered entities in the Western Interconnection. This data is reported under NERC Section 1600 request. The RWG performs a yearly detailed analysis and multiyear trending to:
• Provide trend analysis of Protection System Misoperation data and possible root cause identification;
• Form conclusions/recommendations from the analysis to reduce the likelihood of future Misoperations;
• Develop guidance and best practices to industry through technical documents and webinars pertaining to Protection System Misoperation trends, conclusions, and recommendations; • Publish the analysis results to WECC’s Event and Performance Analysis Subcommittee (EPAS)
and the WECC membership.
The RWG focus is on Misoperations by cause to potentially identify ways to reduce future Misoperations. Each of the eight Misoperation cause categories was individually evaluated and analyzed by a subgroup of RWG members.
The impact of a Misoperation on the BES was not considered in the evaluation. The impact of a Misoperation on the BES is captured through the Event Analysis Process if the Misoperation is involved in a reportable event.
Data
The Misoperation data used for a one-year analysis is from the period January 1, 2019 through December 31, 2019. Trending data was from January 1, 2016 to December 31, 2019.
• The dataset was obtained by WECC from the NERC 1600 reporting template with defined categories and causes.
• The 2019 data was compared to data collected since 2016 for trending and analysis. The NERC 1600 data reporting has only been in effect since 2016.
• The reported corrective actions, event description and cause of the Misoperation were used to assist in root cause identification.
• The 2019 Misoperation data was reviewed quarterly by the RWG with resubmittals of clarification and correction.
2019 Misoperation Analysis
An analysis of the WECC 2019 data reported and the comparison to the 2016 through 2019 datasets for trending analysis is provided. The subgroup analyses, conclusions, and recommendations for
Misoperations by the eight causes are also included.
Misoperation by Cause Category
Evaluation of Misoperations by cause category shows key indicators of Misoperations attributed to human performance or a Protection System component. Figure 1 shows the distribution of
Misoperations as reported by cause category. The “Incorrect setting/logic/design errors” combined into one cause category was the largest, comprising 42% of all Misoperations, followed by
“Unknown/unexplainable” with 12% of all reported Misoperations. Over half of all Misoperations fall into these two categories.
The “Incorrect setting/logic/design errors” cause category, along with the “As-left personnel error” primarily consist of human performance. The other four cause categories (excluding the
“Unknown/unexplainable” and “Other/explainable” categories) consist of equipment or material problems and represent Protection System component type problems (see Figure 1). Evaluating the two groupings shows—
1. 48% of all Misoperations can be attributed to one of the cause categories related to human performance:
a. Incorrect setting/logic/design errors b. As-left personnel error
2. 33% of all Misoperations can be attributed to a Protection System component type category: a. AC system
b. Communication failure c. DC system
Figure 1: 2019 Misoperations by Cause
The trend in Figure 2 shows that the top two cause categories for Misoperations in WECC are “Incorrect setting/logic/design errors,” with an average of 113 Misoperations per year, and “Relay failures/malfunctions,” with an average of 41 Misoperations a year.
Figure 2: Misoperation by Cause, 2016 to 2019 Trending
9% 6% 11% 4% 42% 6% 9% 12%
AC System As-left personnel error Communication failure DC System
Incorrect setting/Logic/Design errors Other/Explainable Relay failures/malfunctions Unknown/unexplainable
13 24 23 7 128 19 54 33 25 25 17 10 128 19 43 17 27 29 19 3 95 26 45 23 23 14 26 10 103 15 23 30 0 20 40 60 80 100 120 140 2016 2017 2018 2019
Averaging the rest of the cause categories over the four-year period gives the following: Table 1: Four-Year Average Misoperations by Category
Cause Category Number of Misoperations
AC system 22
As-left personnel error 23
Communication failure 21
DC system 7.5
Other/explainable 20
Unknown/unexplainable 26
Misoperation by Cause Category Conclusions and Recommendations:
RWG recommends utilities develop a strategy to reduce Misoperations for “Incorrect setting/logic/design error” and “As-left personnel error" by internal controls and processes.
Implementation of PRC-027 will require entities to develop a process for new and revised Protection System settings plus review implemented settings within a period or based on fault level. Trending over the next few years may indicate whether PRC-027 has an impact.
Misoperation by Category
Misoperations can be grouped by security (unnecessary trip) or dependability (failure to trip or slow trip) categories. Unnecessary trips dominate the number of Misoperations as compared to failures to trip or slow trips. Figure 3 shows the distribution of Misoperations reported by category.
Figure 3: 2019 Misoperations by Category
2% 1%
48% 48%
Failure to trip—during fault Failure to trip—other than fault Unnecessary trip—other than fault Unnecessary trip—during fault
A review shows 48% of Misoperations were “Unnecessary trip—other than fault” and 48% were “Unnecessary trip—during fault.” The “Incorrect setting/logic/design errors” has a large impact on the “Unnecessary trip—during fault” category at 57%.
Figure 4 compares the Misoperations from 2016 through 2019 by category. Figure 4: Misoperations by Category, 2016–2019 Trending
Misoperation Category Conclusions and Recommendations:
The “Unnecessary trip—during fault” reduces the reliability of the BES due to unexpected loss of several BES facilities. The “Incorrect setting/logic/design errors” category dominates the unnecessary trips. Reducing “Incorrect setting/logic/design errors” will add reliability to the BES by decreasing multi-facility loss.
Misoperation by Voltage Class
Generally, voltage class is considered to be the operating voltage level of the equipment where the Protection System is applied. For Misoperations involving equipment at multiple voltages (i.e., transformers) or Misoperations impacting equipment at different voltage levels (e.g., breaker failure), the highest voltage class involved is reported.
Figure 5 shows the distribution of Misoperations as reported by voltage class. Misoperations involving 100-199 kV equipment made up 39% of reported Misoperations, while another 39% of Misoperations were reported as involving 200-399 kV equipment. These two voltage classes accounted for about 78% of all Misoperations. The result was as expected, since most of the Western Interconnection is
composed of Elements operated from 100-299 kV. 0 20 40 60 80 100 120 140 160 Failure to trip—during
fault Failure to trip—other than fault Slow trip Unnecessary trip—other than fault Unnecessary trip—during fault 2016 2017 2018 2019
Figure 5: 2019 Misoperations by Voltage Class
Figure 6 shows the trending of the 2016 through 2019 data by voltage class. The number of
Misoperations by voltage class has remained relatively the same throughout the trending period for 100-199 kV and 200-399 kV.
Figure 6: Misoperations by Voltage Class, 2016–2019 Trending
An indicator of reliability can be attained by knowing the number of Elements in each voltage class. The number of Misoperations per number of Elements provides a better trend of what is happening within each voltage class. The number of Transmission Availability Data System (TADS) Elements active in 2019 in the Western Interconnection was used to determine the number of Elements at a voltage class. The results are the Misoperation ratios shown in Table 2. The ratio will normalize the numbers as facilities are added or removed from the Western Interconnection.
7% 39% 39% 7% 8% < 100 kV 100-199 kV 200-299 kV 300-399 kV > 400 kV HVDC 9 121 101 22 47 1 11 121 110 19 23 0 12 125 89 23 14 4 16 96 95 18 19 0 0 20 40 60 80 100 120 140 < 100 kV 100–199 kV 200–299 kV 300–399 kV > 400 kV HVDC 2016 2017 2018 2019
Table 2: 2019 Misoperation Ratio by TADS Voltage Class Element
Voltage Class AC Circuit Converter DC Circuit Transformer Misops Ratio
0-99 kV 500 0 0 42 2.77
100-199 kV 3089 0 0 178 2.94
200-299 kV 1835 5 3 694 3.74
300-399 kV 171 2 0 179 5.11
400-599 kV 294 0 5 238 3.54
Misoperation by Relay Technology
Relay technology refers to one of three broad types of relays—
1. Electromechanical, representing the earliest generation of relay technology using basic electrical circuits together with moving parts;
2. Solid-state, representing a second generation of relay technology using transistorized components; and
3. Microprocessor, representing the third and latest generation of relay technology using integrated circuit components.
Figure 7 shows the distribution of reported Misoperations by relay technology. Microprocessor technology was involved in 77% of Misoperations, far out-pacing the other two types.
Figure 7: 2019 Misoperation by Relay Technology
13%
77% 3% 7%
A further analysis of Misoperations by relay technology showed the two major causes are “Incorrect settings/Logic/Design errors” and “Relay failures/malfunctions.” Additional analysis, conclusions and recommendations are provided in the “Incorrect setting/logic/design errors” and “Relay
failures/malfunctions” sections of the report.
Figure 8 provides the trending of Misoperation by relay technology for 2016 through 2019. The trend shows Misoperations for solid-state and electromechanical relays have little influence on the
Misoperation rate. Entities are continuing to replace electromechanical and solid-state relays with microprocessor relays.
Figure 8: Misoperation by Relay Technology, 2016 through 2019 Trending
Subgroup Analysis and Observations for Misoperations by Cause
AC and DC Systems Cause Analysis
There were 33 Misoperations attributed to “AC systems” and “DC systems” for 2019. For analysis, the Misoperations due to AC and DC systems were combined into one cause. The following discussion identifies the drivers of the Misoperations in AC and DC systems cause.
The number of AC and DC failures has been relatively flat, with a reduced number in 2016 (see Figure 9. 53 212 21 15 26 218 21 19 36 200 12 19 31 189 7 17 0 50 100 150 200 250
Electromechanical Microprocessor Solid State Other 2016 2017 2018 2019
Figure 9: AC and DC Systems Misoperation Totals, 2016 through 2019
Through the entity’s reported descriptions of the Misoperations and the corrective action plans, the RWG was able to break AC and DC systems into various triggers. The largest sources of Misoperations in 2019 were wiring problems/damage at 37%, followed by equipment failures (see Figure 10). The data from the 2016–2019 trending indicates wiring problems/damage is the leading cause (see Figure 11).
Figure 10: 2019 AC and DC Systems Misoperations
17 30 29 33 0 5 10 15 20 25 30 35 2016 2017 2018 2019 N um ber of M is op s 15% 3% 37% 9% 30% 6% Equipment Failure Relay Settings/Misapplication Wiring problem/damage CT Saturation Loss of Potential Unknown PT Transient Response DC Noise
Figure 11: AC and DC Systems Misoperations by Triggers, 2016 through 2019 Trending
Most triggers result in “Unnecessary trip—other than fault” as shown in Figure 12 and the trending data in Figure 13.
Figure 12: AC and DC Systems Misoperations by Category, 2019 Data
7 3 7 0 0 0 0 0 8 1 14 0 4 3 0 0 11 0 10 4 0 0 2 2 5 1 12 3 10 0 0 2 0 2 4 6 8 10 12 14 16 2016 2017 2018 2019 6% 9% 24% 61%
Failure to trip—during fault Failure to trip—other than fault Unnecessary trip—during fault Unnecessary trip—other then fault
Figure 13: AC and DC Systems Misoperations by Category, 2016–2019 Trending
A small change in the overall number of AC and DC system Misoperations can result in large percentage differences. However, the AC and DC systems Misoperation category is dominated by triggers that result in “Unnecessary trip—other than fault” for the four years of data trending.
The number of TADS elements within WECC identify the number of elements in a voltage class. Figure 14 is in line with what is expected with the largest numbers of terminals within the 100-199kV and 200-299kV voltage classes.
Figure 14: AC and DC Systems Misoperations by Voltage Class, 2019 Data
Figure 15 shows the number of Misoperations in the 100-199 kV voltage range remains flat, while the 200-399 kV voltage class average is relatively higher. 2019 data for 200-299kV and 300-399kV have been lumped together for comparison to prior years where these were all reported in one group of 200-399kV. 1 0 4 12 1 1 9 19 0 0 10 19 2 3 8 20 0 5 10 15 20 25 Failure to trip—
during default Slow trip—during default Unnecessary trip—during fault Unnecessary trip—other than fault 2016 2017 2018 2019 15% 33% 46% 6% <100kV 100-199kV 200-400kV >400kV
Figure 15: AC and DC Systems Misoperations by Voltage Class, 2016–2019 trending
AC and DC System Misoperation Subcategory Conclusions and Recommendations:
Based on TADS, the highest concentration of total system assets in the Western Interconnection is within the 100-199kV and 200-399kV groupings correlating to the highest number of total
Misoperations. In 2019, the numbers of Misoperations in both the AC and DC systems remained at the same level since 2017, which may be attributed to better identification and classification from the “Unknown/unexplainable” cause category.
The RWG maintains that routine maintenance and inspection of wiring and equipment will find most problems before a Misoperation. The RWG continues to recommend that regular maintenance practice extend beyond visual inspection.
Incorrect Setting/Logic/Design Errors Cause Analysis
There were 103 Misoperations attributed to “Incorrect setting/logic/design errors,” making it the largest of all cause categories in 2019. The following discusses the drivers for the Misoperations within this group.
Figure 16 shows Misoperations grouped by the relay technology involved. 89% of all 2019 Misoperations involved microprocessor relay technology. The large percentage of Misoperations suggests the widely adopted use of microprocessor technology, although enhancing system reliability through event analysis is also a leading contributor to Misoperations. However, without knowledge of the total populations of the relay technologies this may be misleading, e.g., eventually 100% of the Misoperations may be due to microprocessor-based relays when older technologies have been entirely
1 4 8 4 2 9 14 5 2 12 12 3 5 11 15 2 0 2 4 6 8 10 12 14 16 <100kV 100-199kV 200-400kV >400kV 2016 2017 2018 2019
Figure 16: 2019 Misoperations by Relay Technology Subgroup
The four-year trend in Figure 16 indicates microprocessor relays continue to be the leading technology associated with Misoperations, and it is leveling off at around 90% of all Misoperations in the
“Incorrect setting/logic/design errors” cause category. If extrapolated into the future, the trend is toward 100% of Misoperations attributable to microprocessor relays. As shown, the trend will be related directly to the continued installation of microprocessor relays for new installations and as replacements for older relay technologies. Microprocessor relays will eventually account for nearly all the installed fleet.
Misoperations have decreased in 2018 and 2019 compared to 2016 and 2017, although 2019 had about a 10% increase in the total number of Misoperations in this cause category compared to 2018. While it is premature to consider this improvement a trend, it may be reflective of the concerted effort that WECC and the RWG have put into reviewing reported Misoperations, engaging member utilities on potential areas of improvement, and developing strategies for improvement.
89%
2% 9%
Figure 17: Misoperations by Relay Type, 2016–2019 Trending
Figure 18 further subdivides the “Incorrect setting/logic/design errors” cause into setting, logic, and design errors. The chart shows setting errors make up 77% of the Misoperations, while logic and design errors account for 23%. This balance is similar to that of 2019. The percentages suggest most
Misoperations are attributed to setting errors, and when considered in conjunction with statistics on relay type, may be indicative of the complexity of microprocessor relays and their applications.
Figure 18: 2019 Misoperations by Subgroup
The trend shown in Figure 19 indicates setting errors continue to be the primary cause of
Misoperations. However, the trend shows a gradual decrease in the percentage attributed to settings errors, with a corresponding increase in the percentage attributed to logic and design errors. While the
91 2 5 1 92 3 2 2 94 1 5 0 88 2 9 1 0 20 40 60 80 100
Microprocessor Solid State Electromechanical Other
Perc en tg ae of M is op era tio ns 2016 2017 2018 2019 79% 13% 11%
Figure 19: Misoperations subdivided into Setting and Logic/Design Errors, 2016–2019 Trending
When the settings and design errors were further investigated, as shown in Figure 20, it shows two significant causes of Misoperations are due to incorrect ground overcurrent settings and mis-coordinated transfer trip scheme settings. In 2019, the number of Misoperations in which the cause remained undetermined went to zero. A continued improvement of identification is a positive sign. Potential contributing factors include a higher installed percentage of microprocessor relays, in which event record data is easily available and supports Misoperations analysis.
Figure 20: 2019 Misoperations by Root Cause
Figure 21 shows that the trend “Unnecessary trip—during fault” continues to lead the Misoperations category with the three-year average making up two-thirds of all Misoperations. This indicates that most protection schemes lean toward dependability over security, but they remove more facilities than
88 12 0 0 84 16 0 0 82 18 0 0 77 23 0 0 0 10 20 30 40 50 60 70 80 90 100
Setting Errors Logic/Design Errors Unknown Misclassified 2016 2017 2018 2019 21% 11% 10% 1% 57%
Ground Overcurrent Ground Distance Transfer Trip Min Trip Set Below Load Other Total Misoperations
2016—128 2017—128 2018—95 2019—103
Figure 21: Misoperations by Category for Incorrect Setting/Logic/Design Errors, 2016–2019 Trending
Incorrect Setting/Logic/Design Errors Misoperation Conclusions and Recommendations:
Entities should:
• Perform peer review including verifying that the fault system model is correct, the coordination study is complete, the contingencies within the study are correct, proper setting values of the elements applied, and the elements for the application are enabled;
• Develop standards/guides for fault studies and a process for reviewing new and existing settings to ensure changes to the system do not result in Misoperations. The new standard PRC-027 will address the periodic review of Protection Systems;
• Establish a training program for protection schemes and applications; and
• Develop an applications-based testing method and apply as a quality assurance measure to new and modified relay applications.
Additionally, entities should review the IEEE Power System Relaying Subcommittee report to provide additional technical guidance for quality control of protective relay settings; “Processes, Issues, Trends and Quality Control of Relay Settings” (Working Group C3 of Power System Relaying Committee of IEEE Power Engineering Society, March 2007).
Communication Failure Cause Analysis
There were 26 Misoperations attributed to Communication Failure during 2019 within the cause category grouping.
Figure 22 shows the Communication Failure cause category grouping can be subdivided into eight
4 3 63 30 2 1 65 33 3 3 72 22 2 0 64 34 0 10 20 30 40 50 60 70 80 Failure to trip—during
default Slow trip—during default Unnecessary trip—during fault Unnecessary trip—other than fault 2016 2017 2018 2019 Total Misoperations
2016—128 2017—128 2018—95 2019—103
Figure 22: 2019 Communication-related Protection Misoperations by Sub-cause
Figure 23 shows the trends in the communication-related cause category within WECC from 2016 through 2019. The various cause categories for which events actually occurred were spread among multiple causes with no apparent trend.
However, for 2019, there was a noticeable increase in the Channel Noise and Communications Settings categories. For the previous three years, this had not been an issue. On review, there were several entities reporting Misoperations caused by channel signals. Entities’ Corrective Action Plans were the replacement of existing hardware with new technology and digital systems. Many of the existing systems were past their stated life cycles.
Figure 23: Communication-related Protection Misoperations, 2016–2019 Trending
4 10 7 1 3 1 Channel Failure Channel Noise Comm Settings Microwave Eqpt Power Line Carrier Other 5 2 3 0 0 8 0 2 0 4 2 2 0 1 2 1 3 2 1 10 0 2 0 0 4 10 7 0 1 3 0 1 0 2 4 6 8 10 12 ne l F ai lu re ha nne l N oi se om m Se tti ng s Ba d W ires cr ow av e E qp t Po w er L in e C ar ri er W ro ng C ard / Fi rm w are Othe r 2016 2017 2018 2019
Communication Failure Misoperation Conclusions and Recommendations:
Communication Failure Misoperations have been few over the period covered by the RWG yearly analysis, a trend that continued in 2019. No recommendations are made at this time.
In the future, Communication Misoperation causes may increase as entities move to new technology and packet-based communication systems for use in Protection Systems. Migration to new technology, in particular packet-based, has not widely occurred. The impact of implementation of new
communication system technology on Misoperations is not well understood. It may be that current installations are not causing Misoperations, or that there is not enough detail in the Misoperation submission data fields to show the type of technology used. When employing new technology, thorough testing and verification should be performed to assure Protection System reliability. Relay Failures/Malfunctions Cause Analysis
There were 23 Misoperations attributed to “Relay failures/malfunctions” within this cause category in 2019. The data was divided by relay technology as shown in Figure 24. The microprocessor relay technology Misoperations in 2019 (17) were roughly double the 2018 (8) Misoperations, while the number of electromechanical and solid-state relay failures were down substantially (total 6 versus 23). The 2019 failures were down to half or less than the number of Misoperations in 2017 and earlier. For the 2019 “Relay failures/malfunction” data supplied, the sub-cause column in the reporting
template showed 12 instances as either blank or unknown. Often the description gave enough detail to identify the problem. In 10 cases there was not enough detail in the description to identify what failed in the relay, or the entity did not know, but their planned corrective action was to replace the relay.
Figure 24: 2019 Misoperations for Relay Failures/Malfunctions by Relay Type
3
3
17
Relay failures were analyzed as a function of the technology versus the Misoperation category in Figure 25. Most relay failures caused an “Unnecessary trip—other than fault,” indicating these failures are prone to cause a trip without a fault present.
Figure 25: 2019 Relay Failures/Malfunctions Misoperations by Relay Type
Trending in Figure 26 shows the relationship between overall failures by relay technology for 2016 - 2019. WECC has consistently experienced more failures of microprocessor relays than the other technologies. One possible reason for this might be due to aging of the first and second generations of microprocessor relays. The fractions of equipment protected by each technology is unknown, so a meaningful comparison is not really possible. There does seem to be a downward trend in failures of electromechanical and solid state relays.
Figure 26: Misoperations by Relay Type, 2016–2019 Trending
0 0 3 0 2 1 1 3 13 0 5 10 15
Failure to trip Unnecessary trip—during fault Unnecessary trip—other than fault
Electomechanical Solid State Microprocessor
21 8 21 9 5 32 11 12 8 3 3 17 0 5 10 15 20 25 30 35
Electromechanical Solid State Microprocessor 2016 2017 2018 2019
The trends in Figure 27 show relay failures that caused an “Unnecessary trip—other than fault” still lead the categories of failures by a substantial margin, though there has been a definite downward trend since 2016. “Unnecessary trip—during fault” has also shown a downward trend, though not as consistently as ” Unnecessary trip—other than fault.” Failures to trip and slow trips stayed at low levels (typically zero to two events each year).
Figure 27: Misoperations by Category for Relay Failures/Malfunctions, 2016–2019 Trending
Relay Failures/Malfunctions Cause Category Conclusions and Recommendations:
Determining the actual causes of Misoperations is critical to identifying root causes, which then determine the proper corrective action to apply, either to the individual failing Protection System or across all similar installations in the entity’s systems. Many entities either replaced the relay as the planned corrective action, with no further investigation, or are working with the manufacturer to understand the cause. As root causes are found, the fixes should be applied on similar Protection Systems throughout the entity’s system.
As-left/Personnel Error Cause Analysis
There were 14 reported “As-left/Personnel Error” Misoperations for 2019, which was down 50% from the previous year. From Figure 28, all “As-left/Personnel Error” Misoperations fell into the
“Unnecessary trip—during fault” category. The unnecessary trips affect the reliability of the system as more elements are removed from service for the same event.
2 1 12 35 3 2 9 32 2 0 13 23 1 0 5 17 0 5 10 15 20 25 30 35 40
Failure to trip Slow trip Unnecessary trip—
during fault Unnecessary trip—other than fault 2016 2017 2018 2019
Figure 28: 2019 As-left/Personnel Error Misoperations
There were three causes identified for the Personnel Error Misoperations in 2019: wiring errors, testing errors, and switching errors with a fairly even distribution for each of these causes. The trending in Figure 29 shows the data is fairly consistent from year to year with no appreciable changes for the category of “Unnecessary trip—during fault.” For the category of “Unnecessary trip—other than fault” and “Failure to trip” there was a significant decrease for 2019. The decrease may be tied to reduced replacement of relays systems or new facilities, causing the decrease in wiring and testing errors for this category.
Figure 29: As-Left/Personnel Errors, 2016–2019 Trending
77% 23%
Unnecessary trip—during fault Unnecessary trip—other than fault
3 0 4 0 0 0 0 0 8 6 12 10 12 8 10 3 0 2 4 6 8 10 12 14 2016 2017 2018 2019
Failure to trip Slow trip
As-Left/Personnel Errors cause category conclusions and recommendations
Due to the relatively small number of events in this area, there are no drastic changes recommended. The largest groups of events were due to wiring errors and testing errors. These two types of errors can be reduced through commissioning and maintenance processes. Some of the best practices in the industry to avoid “As-left/Personnel Error” are as follows:
• To avoid leaving incorrect settings on a relay, the technicians performing the work should compare the “As-Left” settings on the relay to the desired settings given by the setting engineer. • To avoid wiring errors, the relay scheme should be tested fully to make sure all inputs and
outputs are functioning as desired with the proper response.
• To avoid leaving wiring open, loose, or missing, which can lead to a failure to trip or false trip, each company should develop and implement a process to be used by the people performing the work to ensure all wiring and switches are left in the correct state.
Unknown/Unexplainable Cause Analysis
In 2019 there were 30 events reported with the “Unknown/unexplainable” cause category. “Unknown/unexplainable” is used when no clear cause can be determined. After extensive investigation, the submitting entity may select this cause when no other option is suitable or the
operation is still under investigation. If reporting under this cause because the investigation is ongoing, the category should be updated at the conclusion of the investigation.
In 2019, “Unknown/unexplainable” Misoperations represented 12.3% (30/244) of all reported
Misoperations. In comparison, the 2016, 2017 and 2018 data represented 11% (33/301), 6% (17/284) and 8.6% (23/267) respectively of all reported Misoperations.
When the reason for a Misoperation is unknown, corrective actions cannot be taken to prevent another Misoperation from occurring at that terminal, nor can knowledge be gained that would allow the prevention of a similar Misoperation from occurring at another terminal. Therefore, it is desirable to reduce the number of Misoperations that cannot be explained and are categorized as
“Unknown/unexplainable”.
Figure 30 shows the total number of Misoperations reported as “Unknown/unexplainable” for each year from 2016 through 2019. A trend line is provided to demonstrate Misoperations reported as “Unknown/Unexplainable” are overall trending flat.
Figure 30: Percentage of Misoperations for Unknown/Unexplainable, 2016–2019 Trending
Misoperations reported as “Unknown/unexplainable” were further categorized by relay type and Misoperation category for this report.
In 2019, the percentage of “Unknown/unexplainable” Misoperations associated with each of the relay types continued toward a higher percentage of microprocessor technology, Figure 31. The higher percentage could suggest the larger installed fleet of microprocessor relays naturally result in a higher percentage of overall Misoperations or as entities upgrade/replace older technologies, microprocessor relays may be sensitive to issues older relays weren’t. The RWG will continue to monitor the
percentage for future years.
Figure 31: 2019 Misoperations for Unknown/Unexplainable by Relay Type
33 17 23 30 0 5 10 15 20 25 30 35 2016 2017 2018 2019 47% 37% 3% 13%
The majority of Misoperations reported as “Unknown/unexplainable” fell within the “Unnecessary trip—other than fault” category in Figure 32. An “Unnecessary trip—other than fault” can be more difficult to diagnose. The difficulty is under conditions of no fault, other monitoring equipment such as digital fault recorders or other relay events are not triggered and are not available to assist in the analysis.
Figure 32: 2019 Unknown/Unexplainable Misoperations
Of note is many of the unknown causes have a corrective action plan to test the system, monitor, work with the manufacturer, or replace with microprocessor relays. The analysis in progress shows the entity attempting to find the root cause. Reporting to the NERC 1600 has improved as an entity now updates the progress state of an investigation and what investigation actions are being taken to determine the Misoperation.
As an “Unknown/unexplainable” instance is resolved and a cause is determined, the entity should resubmit updating the correct cause category of the Misoperation.
Misoperation Unknown/Unexplainable cause category Conclusions and Recommendations:
The number of Misoperations reported as “Unknown/Unexplainable” has increased slightly from 2018 and the trend is relatively flat.
Conclusions
The trending of 2016 through 2019 indicates the total number of Misoperations has had a downward trend 301/284/267/244 over the past four years. “Incorrect setting/logic/design errors” is still the leading cause of Misoperations within WECC. The majority of Misoperations due to setting errors are
3%
23%
73%
Failure to trip Unnecessary trip—during fault Unnecessary trip—other than fault
templates for setting standard schemes using complex relays. Processes also should be created for installed fleet to include review of existing settings, periodically and when there is a change in system topography. PRC-027 has those requirements and it may affect the number of Misoperations in the future.
In 2019, WECC saw the “Unknown/Unexplainable” become the second-most-common cause of Misoperations. This appears to have happened because of a sharp drop in the number of “Relay failure/malfunction“ Misoperations.
The NERC 1600 reporting template added sub-cause categories in 2018 to the “Incorrect
setting/logic/design errors” and “Relay failures/malfunctions” at the request of NPCC and SERC. Although the sub-cause entry is not required, entities who use these will help to better determine a root cause.
The NERC MIDAS Work Group Data Reporting Instructions drafted in 2019 and updated in 2020 will improve the quality of Misoperation reporting by providing examples to the entities’ main compliance contacts and the engineering staff performing the analysis. The RWG found that event descriptions continue to improve but are still lacking in establishing the root cause. A root cause is necessary to determine the proper corrective action to apply either to the Protection System, entity processes, or across all similar installations in the entity’s system.
Recommendations
1. A quarterly review of Misoperations by the RWG is beneficial and should continue.
2. The RWG maintains that routine maintenance and inspection of wiring and equipment may show many of the problems associated with the AC or DC cause before a Misoperation. The RWG continues to recommend that regular maintenance practice extend beyond visual inspection.
3. Entities should—
a. Perform peer review including verifying that the fault system model is correct, the coordination study is complete, the contingencies within the study are correct, proper setting values of the elements are applied, and the elements for the application are enabled. b. Develop standards/guides for fault studies and a process for reviewing new and existing
settings to ensure changes to the system do not cause Misoperations. The new standard PRC-027 will address the periodic review of Protection Systems.
c. Establish a training program for protection schemes and applications.
d. Develop an applications-based testing method and apply as a quality assurance measure to new and modified relay applications.
5. Some of the best practices in the industry to avoid “As-left/Personnel Error” are—
a. To avoid leaving incorrect settings on a relay, the technicians performing the work should compare the “As-Left” settings on the relay to the desired settings given by the setting engineer.
b. To avoid wiring errors, the relay scheme should be fully functionally tested to make sure all inputs and outputs are functioning as desired with the proper response.
c. To avoid leaving wiring open, loose, or missing, which can lead to a failure to trip or false trip, each company should develop and implement a process to be used by the people performing the work to ensure all wiring and switches are left in the correct state.
