Protective Relay Subcommittee Misoperations … Protective...Protective Relay Subcommittee Misoperations Whitepaper ... Considerations provided for phase and ground instantaneous overcurrent,

Protective Relay SubcommitteeMidwest Reliability Organization

Protective Relay SubcommitteeMisoperations Whitepaper

Summary Overview

Mark Gutzmann, Xcel EnergyMRO Reliability ConferenceMay 25th, 2016

MRO Protective Relay Subcommittee

- Background -

In 2015, NERC announced that the industry should work towards a goal of reducing misoperations by 25%.

In 2015, 34 events of 50 transmission system disturbances (Event Analysis) had associated Misoperations *

97% of the 34 events experienced Misoperations that increased the severity *

The “relay ground function” accounted for 11 Misoperations in 2014 and 6 Misoperations for qualified events in 2015 *

To assist in this effort, the MRO PRS embarked on a project to identify causes of, and opportunities to reduce, misoperations that occur within MRO.

* NERC 2016 State of Reliability Report – May, 2016

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Regional Entity Initiatives

FRCC – peer reviews of Misoperation analysis/corrective actions; condition and risk assessments to coordinate protection outages

NPCC – peer reviews of Misoperation analysis/corrective actions; reviews microprocessor-based Misoperations for shared knowledge

RFC – training to member entities on protection topics

SERC – developed best practices document; developed metric to measure risk based on cause, category, voltage, Misoperation rate and CAP response time

SPP – whitepaper on communication and setting/logic/design Misoperations within SPP

TRE/ERCOT – 40% of setting/logic/design Misoperations due to ground overcurrent settings, developed whitepaper on ground faults and ground protection schemes

WECC – Operational Practices Survey added protection topics to establish member practices



- Background -



- Background -

The PRS whitepaper identifies specific protection schemes that have a disproportionate share of misoperations within MRO for events from 2010 through 2014

The whitepaper proposes approaches that will effectively help to reduce their occurrence

In this initial whitepaper, completed in April 2016, four schemes are discussed

Second whitepaper will be prepared over the winter of 2016/2017 to address several other schemes and provide effective mitigation approaches for these additional schemes.

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Scheme 1: Overcurrent Setting Errors

Overcurrent protection has been in use since the power system began▪ Simple, easy and fast! ▪ Performance affected by system contingencies, growth (or reduction) and directionality▪ Require ‘coordination’ timing with adjacent elements to ensure proper operating order

Accounted for 68 Misoperations for the time period▪ Ground (residual or neutral) instantaneous overcurrent element highest contributor in this

category

Possible Mitigations▪ Considerations provided for phase and ground instantaneous overcurrent, as well as inverse

time ground overcurrent elements▪ Assure setting loadability for phase elements and adequate margins for growth and

contingencies▪ Ensure study of mutual coupling (NERC Lessons Learned) for ground overcurrent elements▪ Specific use on transmission transformers▪ Ensure adequate margins for CT, modeling and relay measurement error

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Overcurrent Misoperation Type/Scheme

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Table 2 Overcurrent Type/Scheme Application Count: Percent:

Ground IOC Issue 21 36% Ground TOC Issue 15 25% Echo Key Issue 9 16% DCB Blocking Scheme/Issue 5 9% Phase OC Issue 5 9% Directional Issue 3 5%

Totals 58 100.0%


Scheme 2: Overcurrent Protection in Pilot Schemes

Overcurrent elements used for fault detection in pilot schemes

Sensitivity required to ensure protection for high resistivity faults

Price of this sensitivity is security during communication failures

Possible Mitigations▪ Remote/local coordination of fault detecting elements▪ Use of ground distance elements vs. ground overcurrent, where available and

practical▪ Close attention to polarization methods

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Scheme 3: Directional Comparison Blocking (DCB)

One of the earliest pilot protection systems

Powerline Carrier (PLC) based communication

Communication failure tends to cause overtripping (Misoperations)

Historically used sensitive ground overcurrent elements for fault detection

Possible Mitigations▪ Remote/local coordination of fault detecting elements▪ Use of ground distance elements vs. ground overcurrent, where available and practical▪ Close attention to polarization methods▪ Utilize matched devices on each protected end▪ Ensure testing practices employ internal as-well-as external faults▪ PLC communication design, settings and channel monitoring

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Scheme 4: Direct Transfer Trip (DTT)

Use for breaker failure, transformer, shunt reactor and limited number of piloted systems

80% of Misoperations due to transient or noise induced operations (31 total DTT Misoperations)

Majority of Misoperations on Powerline Carrier systems

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Possible Mitigations▪ Validation timer settings▪ Review channel design considerations▪ Redundancy (voting) schemes ($$)▪ Noise mitigating scheme improvements (channel bandwidth and skewed hybrids)▪ Numerous industry references for PLC consideration▪ Install fiber! ($$$$)

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Summary and Conclusions

PRS White Paper completed in April, 2016

Targets MRO specific concerns based upon past performance▪ Phase and ground overcurrent elements▪ Overcurrent elements in piloted systems▪ Directional Comparison Blocking (DCB) systems▪ Direct Transfer Trip (DTT) systems

Follow-up paper with potential topics in Q1, 2017▪ Breaker failure▪ Loss of potential▪ Line differential/phase comparison▪ Current only systems (bus, line and transformer differential)

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Protective Relay Subcommittee of the MRO

Protective Relay Subcommittee Misoperations … Protective...Protective Relay Subcommittee Misoperations Whitepaper ... Considerations provided for phase and ground instantaneous overcurrent,

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