Relay Work Group (RWG)
2018 Misoperations Report Highlights
May
155 North 400 West | Suite 200 | Salt Lake City, Utah 84103
www.wecc.org
Introduction
Background
The NERC 2019 State of the Reliability Report (SOR) published the annual misoperation rates for each
region to evaluate the performance of protection systems. The misoperation rate is the ratio of
protection system misoperations to total protection system operations. NERC’s Event Analysis Process
has identified that protection system misoperations significantly increase the severity of events. Even
though misoperations in the Western Interconnection are below the NERC overall average,
misoperations are still a major area of concern because many reported misoperations involve human
factors that can be corrected. That is why WECC worked with entities in the Western Interconnection to
develop reduction strategies for protection system misoperations. Strategy components are referenced
and linked throughout the document.
Figure 1:Five-year protection system misoperation rate by region, Q4 2013 through Q3 2018
7.96%
10.19%
7.58%
13.29%
7.78%
7.02%
5.69%
8.56%
0%
2%
4%
6%
8%
10%
12%
14%
FRCC MRO NPCC RF SERC Texas RE WECC
NERC
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Purpose
The Relay Work Group (RWG) performs a quarterly review of the misoperations that are reported
through the NERC Misoperation Information Data Analysis System (MIDAS) tool for the Western
Interconnection. Part of this review includes performing a detailed analysis, which is used to—
• Provide trend analysis of protection system misoperation data and possible root cause
identification
• Form conclusions and recommendations from the analysis to reduce the likelihood of future
misoperations
• Develop guidance and best practices for industry through technical documents and webinars
pertaining to protection system misoperation trends, conclusions, and recommendations
• Along with the WECC’s Event Analysis Team, publish results to WECC’s Event and
Performance Analysis Subcommittee (EPAS) and WECC members
The RWG’s focus is on misoperations by cause to potentially identify ways to reduce future
occurrences resulting from similar causes. Each of the eight categories of misoperation causes was
analyzed in an individual and a group setting.
The impact of a misoperation on the BES was not considered in this analysis. The impact of a
misoperation on the BES is captured through the ERO Event Analysis Process if the misoperation is
involved in a reportable event.
Data
Misoperation data from January 1 through December 31, 2018, was used for a one-year analysis. Data
from January 1, 2016, to December 31, 2018, was used for trending.
• The data was obtained by WECC from the NERC 1600 reporting template with defined
categories and causes.
• WECC entities reported 267 misoperations during 2018.
• The 2018 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 2018 misoperation data was reviewed quarterly by the RWG. During this review, the RWG
identifies submissions that need clarification or include errors. WECC staff works with the
entities to address these issues and resubmit these records to MIDAS.
2018 Misoperation Analysis
This section presents an analysis of the 2018 data with comparisons to the 2016 through 2018 data sets
for trending analysis. The sub-group analysis, conclusions, and recommendations for misoperations by
the eight causes follow.
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Misoperation by Cause Category
A high-level summary of misoperations can be created from those attributed to human error or to a
protection system component.
1. 47% of all misoperations can be attributed to these cause categories that involve human error:
• Incorrect settings/logic/design errors
• As-left personnel error
2. 35% of all misoperations can be attributed to these protection system component type cause
categories:
• AC system
• Communication failures
• DC system
• Relay failures/malfunctions *“Unknown/unexplainable category” and “Other/Explainable” categories not included in this breakdown
The reduction strategies have identified specific factors that lead to misoperations caused by human
error. These include human performance during commissioning, and the relay setting validation
process in place within companies.
From this general breakdown, the RWG investigated the distribution of misoperations by cause as
shown in Figure 2. “Incorrect setting/logic/design errors” was the largest cause, constituting 36% of all
misoperations, followed by the “Relay failures/malfunctions” representing 17%. Thus, more than half
of all misoperations fall into these two causes.
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Figure 2: Misoperation by cause 2018 data
The bar chart of Figure 3 shows the trending of misoperations by cause from 2016 through 2018. From
the trend, the top two causes for misoperations within the Western Interconnection are “Incorrect
setting/logic/design errors” and “Relay failures/malfunctions.” Averaging “As-left personnel error”
over the three-year period becomes the third-most-frequent cause. Two of the three most common
causes involve human error. The leading causes for human error may be attributed to experience and
less-than-adequate processes. This coincides directly with the “knowledge transfer” aspect of the
reduction strategies. Many entities lack an intentional way of retaining and transferring knowledge
within their departments. Using templates, developing proven processes, implementing a mentor
program, and keeping a current succession plan are a few ways entities can transfer knowledge within
their protection departments.
10%
11%
7%
1%
36%
10%
17%
9%
2018 Misoperation By Cause
AC System As-left personnel error
Communication failure DC System
Incorrect setting/logic/design errors Other/Explainable
Relay failures/malfunctions Unknown/unexplainable
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Figure 3: Misoperation by cause 2016 to 2018 trending
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. This will
also help entities prepare for the implementation of PRC-027-1 on April 1, 2021, which will require
entities to develop a process for new and revised protection system settings and review implemented
settings within a certain time or based on fault current levels.
Misoperation by Category
“Unnecessary Trips” dominate the number of misoperations when compared to “Failure to Trip” or
“Slow Trip.” The number reflects both widespread redundancy in design and the design of failsafe
measures in protection systems to assure faults are quickly removed from the system, biasing on the
side of dependability. The pie chart in Figure 4 below shows the distribution of misoperations reported
by category. The “Incorrect setting/logic/design errors” have a large impact on the “Unnecessary Trips
during fault” category.
1324 23
7
128
19
543325 25 17 10
128
19
43
1727 2919
3
95
26
45
23
020406080
100120140
Misoperation By Cause Category
2016 2017 2018
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Figure 4: Misoperation by category 2018 data
The bar chart of Figure 5 shows the comparison of the misoperation by category for the period 2016
through 2018.
Figure 5: Misoperation by category 2016 to 2018 trending
Misoperation Category Conclusions and Recommendations:
“Unnecessary Trip during fault” misoperations reduce the reliability of the BES due to unexpected loss
of multiple BES facilities. The “Incorrect setting/logic/design errors” category dominates the
unnecessary trips. Reducing “Incorrect setting/logic/design errors” will improve reliability of the BES
by decreasing the number of events involving the loss of multiple Facilities.
4% 2%
51%
43%
2018 Misoperation By Category
Failure to Trip SlowTrip
Unnecessary Trip other than fault Unnecessary Trip during fault
156
141 139
9 4
131140
11 5
137
114
0
20
40
60
80
100
120
140
160
Failure to Trip Slow Trip Unnecessary Trip other
than fault
Unnecesasry Trip during
fault
Misoperation By Category
2016 2017 2018
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Misoperation by Voltage Class
There are no observable trends based on misoperations by voltage class from 2016 through 2018 except
for a slight, unexplainable downward trend of misoperations on systems greater than 400 kV.
Voltage Class Misoperation Conclusions and Recommendations:
WECC, under the new NERC 1600 reporting template, receives the number of operations to
misoperations per voltage class to provide an indicator of reliability.
An indicator of reliability is attained by knowing the number of Elements in each voltage class, taken
from the transmission availability data system (TADS). The number of misoperations per number of
Elements provides a better trend of what is happening within each voltage class, shown in Table 1
below.
Table 1: 2018 WECC TADS Elements
Voltage Class AC Circuit Converter DC Circuit Transformer Misoperation
Ratio %
0-99 kV 170 0 0 42 5.66
100-199 kV 2552 0 0 151 4.62
200-299 kV 1523 4 3 518 4.76
300-399 kV 166 2 0 146
400-599 kV 278 0 5 214 2.86
The lower misoperations ratio for the >400 kV voltage class could be due to entities having more
experienced engineers create the settings, and a more rigorous setting validation process (such as RTDS
testing) performed on this voltage class.
Misoperation by Relay Technology
Relay technology refers to one of three broad types of relays—electromechanical, representing the
earliest generation of relay technology using basic electrical circuits in conjunction with moving parts;
solid-state, representing a second generation of relay technology using transistorized components; and
microprocessor, representing the third and latest generation of relay technology using integrated
circuit components. The pie chart of Figure 6 shows the distribution of misoperations as reported by
relay technology. As you can see, 75% of misoperations involved microprocessor technology, far out-
pacing the other two types of relay technology.
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Figure 6: Misoperation by relay technology 2018 data
A further analysis of misoperations by relay technology showed the two major causes are “Incorrect
settings/logic/design errors” and “Relay failures/malfunctions.” The inventory of relays by technology
is not known, so it is hard to come to a certain conclusion about these misoperation rates. What is
known is entities are continuing to replace electromechanical and solid-state relays with
microprocessor relays.
Misoperation by Relay Technology Conclusions and Recommendations:
Most microprocessor relays have a published life cycle much less than what has been found with the
electromechanical relays. Entities will need to follow industry-specific microprocessor failures and
address the aging installed base of relays with a replacement strategy.
Sub-Group Analysis and Observations for Misoperations by Cause
AC and DC Systems Cause Analysis
There were 29 misoperations attributed to AC systems and DC systems for 2018. For analysis purposes,
the misoperations due to AC and DC systems were combined into one cause.
13%
75%
4%
7%
2018 Misoperation by Relay Technology
Electromechanical Microprocessor Solid State Other
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Figure 7: AC and DC systems misoperation totals 2016-2018
Based on descriptions of events reported by entities and their corrective action plans, the RWG
separated AC and DC systems into various triggers. Referring to Figure 8, the largest sources of
misoperations in 2018 were equipment failures at 38%, followed by wiring problems/damage at 34%. In
2017, wiring problems/damage was the leading cause at 47%. The reason for the increase in
misoperations associated with wiring problems/damage from 2017 to 2018 is not known.
17
3029
0
5
10
15
20
25
30
35
2016 2017 2018
AC and DC—Total Misoperations by Year
# of Misops
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Figure 8: AC and DC systems misoperation triggers 2018 data
In 2018, two-thirds of the AC and DC systems misoperation category are triggers that result in an
“Unnecessary Trip other than fault,” with similar numbers over the past three years. The data indicates
that failures in the AC and DC protection system components typically lead to elements unnecessarily
being removed from service.
AC and DC System Misoperation Subcategory Conclusions and Recommendations:
The increase in the number of misoperations attributed to this cause from 2016 correlates with a
decrease in the number reported to the “Unknown/unexplainable” category over this same time. It
appears the review process RWG performs is ensuring the correct cause is being reported.
The RWG maintains that routine maintenance and inspection of wiring and equipment may find most
of the problems before a misoperation. The RWG continues to recommend regular maintenance
practices extend beyond visual inspection. For example, inclusion of fuse replacement, wire checking,
or additional asset/component replacement.
38%
34%
14%
7%
7%
2018 - AC & DC System Misoperation Triggers
Equipment Failure
Wiring problem/damage
CT Saturation
PT Transient Response
DC Noise
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Incorrect Setting/Logic/Design Errors Cause Analysis
In 2018, there were 95 misoperations attributed to “Incorrect setting/logic/design errors,” making it the
largest of all cause categories. This is consistent with previous years. Although still the largest cause
category, the total number of misoperations for this cause is lower in 2018 than the previous two years.
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 in to thoroughly reviewing reported misoperations, engaging
member utilities on potential areas of improvement, and developing strategies for improvement.
Microprocessor relay technology was involved in 94% of all 2018 misoperations caused by “Incorrect
setting/logic/design errors.” The large percentage of misoperations suggests that, while providing
enhanced system reliability and event analysis, the complexity of these devices may also be a
contributor to misoperations. However, without knowledge of the total populations of the relay
technologies, this cannot be confirmed.
The “Incorrect setting/logic/design errors” cause can be subdivided into Setting, Logic, and Design
errors. In 2018, Setting errors make up 82% of the misoperations, while Logic and Design errors
account for 18%. This balance is consistent with 2017.This high number of Setting errors, in conjunction
with statistics on relay type, may be indicative of the complexity of microprocessor relays and their
applications.
When the Setting and Design errors were further investigated, as shown in Figure 9, they showed that
two significant causes of misoperations are due to incorrect ground overcurrent settings and
miscoordinated transfer trip scheme settings. This data has only been tracked since 2016, but all years
show similar results. Furthermore, in 2018, the number of “Incorrect setting/logic/design”
misoperations for which the cause remained Undetermined dropped to only 1%. This improvement is a
positive sign. Potential contributing factors include a higher installed percentage of microprocessor
relays which create event record data and support misoperations analysis.
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Figure 9: 2018 misoperations by Incorrect setting/logic/design errors subdivided into root cause
Misoperation Incorrect Setting/Logic/Design Errors Cause Category Conclusions and
Recommendations:
Entities should:
• Perform peer review consisting of verifying 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/guidelines pertaining to fault studies and a process for review of 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.
• Develop a method for applications-based testing and apply it as a quality assurance measure to
new and modified relay applications.
• Review the IEEE Power System Relaying Subcommittee report, “Processes, Issues, Trends and
Quality Control of Relay Settings,” (Working Group C3 of Power System Relaying Committee
25%
4%
9%
1%
61%
2018 Settings/Design Breakdown
Ground Overcurrent
Ground Distance
Transfer Trip
Undetermined
Other
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of IEEE Power Engineering Society, March 2007) to provide more technical guidance for quality
control of protective relay settings.
Communication Failure Cause Analysis
There were 18 misoperations attributed to Communication Failure during 2018.
The Communication Failure cause code grouping can be subdivided into broad areas. In 2018,
misoperations were reported in five subcategories. Ten of 18 events involved “Unnecessary Trip other
than fault.”
Figure 10: 2018 Communication related protection misoperations by sub-cause
Figure 10 illustrates the reported misoperations in communication-related cause codes within WECC
from 2016 through 2018. The various cause codes assigned to reported system events represented
multiple causes and showed a noticeable increase in the Bad Wires category for 2018. For the previous
four years, this had not been an issue. On review, there were several entities reporting misoperations
caused by bad pilot/copper wires on Hybrid Circuit Breaker (HCB) differential schemes. In addition,
the Bad Wires misoperation count was skewed due to multiple misoperations on the same circuit. For
example, there may have been three misoperations on the same circuit caused by coax cable failure.
The reporting of multiple misoperations on the same circuit is a reasonable explanation for the uptick
in the Bad Wires category.
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Figure 11: Communication related misoperations
Misoperation Communication Failure Conclusions and Recommendations:
The number of Communication Failure misoperations within WECC has been small throughout the
2016–2018 timeframe. The category represented 20 of 301 misoperations (6.6%) in 2016 and 18 of 268
misoperations (6.7%) in 2018.
In the future, Communication failures may increase as entities are moving to new technologies and
packet-based communication systems for use in protection systems. Migration to new technology,
specifically packet-based communication, has not widely occurred yet. The impact of implementing
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 identify 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 37 misoperations attributed to “Relay failures/malfunctions” in 2018. The data was divided
by relay technology as shown in Figure 12. The failure rates for electromechanical and solid-state
technologies remained consistent from previous years, but failures of microprocessor relays were down
about 30%.
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The failures were analyzed versus the misoperation category. Most relay failures caused an
“Unnecessary Trip other than fault.” The data indicated that failures are prone to cause a trip. Figure 12
shows misoperations by relay failures for each category of relay technology.
Figure 12: Misoperation by Relay failures/malfunctions for 2018 subdivided by relay technology
Microprocessor relays consistently experience more failures than the other technologies. Inventories of
each technology are not known individually, so a meaningful comparison is not readily available. One
possible explanation may be due to aging of the first and second generations of microprocessor relays.
Failures in electromechanical and solid-state relays do appear to be trending downward.
Relay Failures/Malfunctions Cause Category Conclusions and Recommendations:
A thorough investigation of the misoperation is important to understand the root cause and determine
proper corrective actions to mitigate similar issues throughout the entity’s protection systems. Many
failed relays are simply replaced as a corrective action with no further investigation. While this may
resolve the issue on that failed unit, it does not provide details on the reason of the failure. Many
entities will work with the manufacturer to understand the cause of failure. As the root cause is found,
the fix can be applied throughout the entity’s fleet.
As-left/Personnel Error Cause Analysis
The three-year average from 2016–2018 moves the “As-left/Personnel Error” to the third-highest cause
for misoperations within WECC. There were 26 reported “As-left/Personnel Error” events for 2018,
with 12 of these misoperations resulting in an “Unnecessary Trip other than fault” event. Four “As-
left/Personnel Error” misoperations led to “Failure to Trip” events. Failure to Trip is considered a high-
impact event to the reliability of the system, as the fault remains on the system longer and will require
additional elements to be removed from service.
From the review of the event description and the corrective action plan, the “As-left/Personnel Error”
was divided into three major contributors: wiring errors, testing errors, and switching errors. The data
suggests that wiring and testing errors led to the most misoperations in 2018.
Misoperation As-Left/Personnel Errors cause category conclusions and
recommendations
Due to the relatively small number of events in this category, few recommendations are proposed. The
largest groups of events were due to wiring and testing errors. These two types of errors can be
Relay Technology Electromechanical Solid State Microprocessor
# of Failures in 2018 10 5 23
Relay Failures by Technology in 2018
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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 fully functionally tested 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 persons performing
the work to ensure all wiring and switches are left in a desired state.
Unknown/Unexplained Cause Analysis
In 2018 there were 23 events reported with the “Unknown/unexplainable” cause category.
Unknown/unexplained 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.
In 2018, “Unknown/unexplainable” misoperations represented 8.6% of all reported misoperations. In
comparison, the 2016 and 2017 data represented 11% and 6% 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.”
The bar graph of Figure 13 shows the total number of misoperations reported as
“Unknown/unexplainable” for each year 2016 thru 2018. A trend line is provided to demonstrate
misoperations reported as “Unknown/Unexplainable” are overall trending downward.
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Figure 13: Percentage of misoperations for cause Unknown/unexplainable—Trending 2016-2017
Of note is that many of the unknown causes have a corrective action plan to test the system, monitor or
work with the manufacturer. This category is often used when entities perform their quarterly
reporting while still attempting to find the root cause. The RWG has observed some misoperations with
an unknown cause have a corrective action plan and known cause in MIDAS. As an
“Unknown/unexplainable” is resolved and a cause is determined, the entity should resubmit with the
correct cause category to avoid skewing the numbers.
Misoperation Unknown/Unexplainable cause code Conclusions and
Recommendations:
The number of misoperations reported as “Unknown/unexplainable” cause has increased slightly from
2017 but is still well below what has been reported in previous years. Some entities have found success
by strategically placing Digital Fault Recorder (DFR) on sections of their systems where there are more
electromechanical relays, or have a history of unknown caused operations. These DFRs can provide
helpful information about the event that electromechanical relays do not.
Conclusions
The trending of 2016 through 2018 indicates the total number of misoperations has remained constant
from year to year. Misoperations due to “Incorrect setting/logic/design errors” is the leading cause. The
majority of misoperations due to setting errors are preventable. Best practices and techniques used to
prevent the application of incorrect settings for new protection systems include peer reviews, increased
training, more extensive fault studies, and standard templates for setting standard schemes using
complex relays. In addition, processes should be created for installed fleet to include periodic review of
0
5
10
15
20
25
30
35
2016 2017 2018
Misoperation Unkown/Unexplainable Cause
RWG 2018 Misoperations Report Highlights
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existing settings and when there is a change in system topography. PRC-027 may affect the number of
misoperations in the future as it becomes enforceable.
In 2018, WECC saw the “Unknown/unexplainable” cause reduce from initial collection of data.
Previous years the number of reported misoperations in “Unknown/unexplainable” were either
categorized incorrectly or never updated when the investigation was concluded by an entity. The
change to the data can be attributed to the review of the submitted quarterly reports by the RWG.
The NERC 1600 reporting template added sub-cause categories in 2018 to the “Incorrect
setting/logic/design errors” and “Relay failures/malfunctions.” Although the sub-cause entry is not
required, entities who choose to use it will help to give better detail of the cause leading to root cause.
The NERC MIDAS Work Group Data Reporting Instruction being drafted in 2019 will improve the
quality of data reporting by providing better documentation and examples. The RWG found 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 review of quarterly misoperation by the RWG is beneficial and should continue.
2. “Unnecessary Trip during fault” reduces the reliability of the BES due to unnecessary loss of
multiple BES facilities. WECC entities should target “Incorrect setting/logic/design errors”
which contribute to “Unnecessary Trip during fault” to reduce multi-facility loss for a fault or
perform periodic review of settings.
3. A second indicator of reliability is attained using the number of misoperations ratio per number
of Elements in a voltage class. Trending is required to verify improvement to the reliability of
the BES within the Western Interconnect.
4. The RWG should use the same voltage class ranges entities report operations to NERC MIDAS
for analysis.
5. Entities should:
a. Perform peer review—consisting of verifying 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.
b. Develop standards/guides pertaining to fault studies and a process for review of 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.
c. Establish a training program for protection schemes and applications.
d. Develop an applications-based testing methodology and apply as a quality assurance
measure to new and modified relay applications.
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6. The RWG maintains that routine maintenance and inspection of wiring and equipment may
find most of the problems before a misoperation. The RWG continues to recommend regular
maintenance practice extend beyond visual inspection, for example, inclusion of fuse
replacement, wire checking, or additional asset/component replacement.
7. The actual cause of a “Relay failure/malfunction” is important in understanding a root cause to
determine the proper corrective action to apply either to the protection system or across all
similar installations. Many entities either replaced the relay or are working with the
manufacturer to understand the cause. As the root cause is found, the fix should be applied
throughout the entity’s fleet.
8. Best practices in the industry to avoid “As-left/personnel error” are as follows:
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 persons
performing the work to ensure all wiring and switches are left in a desired state.