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Microprocessor-Based Relays: Implementation, Conflicts, and Corrective Actions. Steven V. Deases AEP – Station Engineer. Intro: Discussion Focus. Level: High-Level Topic Discussion Scope: Station Protection Questions: Reserve Questions until the Conclusion

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Microprocessor-Based Relays:Implementation, Conflicts, and Corrective Actions

Steven V. Deases

AEP – Station Engineer

intro discussion focus
Intro: Discussion Focus
  • Level: High-Level Topic Discussion
  • Scope: Station Protection
  • Questions: Reserve Questions until the Conclusion
  • Time Limitation: Approximately 30 minutes total
  • Prospective: AEP’s Experiences
intro discussion focus3
Intro: Discussion Focus
  • Structure:
    • Implementation Strategy
    • Conflicts Encountered
    • Corrective Actions
  • Topics:
    • Engineering Processes
    • SCADA Communications
    • Commissioning Procedures
intro presenter s background
Intro: Presenter’s Background
  • Work Group:
    • AEP Transmission Region Operations – Texas
    • Technical Support Engineering
    • Station Equipment and Protection & Controls
  • Job Functions:
    • Application Engineering & Design Review
    • Technical Aid to Field Personnel
    • Project Coordination & Administrative Support
    • Technical Training of Technicians and Engineers
    • Process Improvement & Quality Control
    • System Performance Analysis & Reporting
microprocessor technology
Microprocessor Technology

Evolution of Protection Devices





microprocessor technology6
Microprocessor Technology
  • Advantages
    • More sensitive and scalable
    • Communication Options
    • Fault Oscillography and SER data
    • Better targeting and annunciation
    • More reliable; failure alarm also included
    • Advanced protection features all in one box
    • Economical both Financially and Physically
  • Disadvantages
    • Shift in Thought: Digital Logic v. Circuitry
    • More Complex Logical Systems
    • Longer Commissioning Procedures
    • Additional Training Requirements
engineering processes
Engineering Processes

Engineering Aspects Affected:

  • Standards
  • Design
  • Documentation
  • Philosophy
engineering processes8
Engineering Processes

Implementation Strategy:

Develop internal Standard Schemes for Protection & Control using Microprocessor-based Relays that would replace existing Electromechanical Relays and phase them out

These replacement schemes would be designed with a “protection zone” scope (Line, Bus, Transformer, etc.)

The developed standards defined details such as:

  • relay brand/model options
  • general protection scheme with generic wiring
  • relay panel plate configurations
  • relay setting templates with predetermined logic
engineering processes9
Engineering Processes


The intent of the documentation was to communicate the standards to the design groups for implementation

Application Guides were written which described

  • What standard schemes were available
  • Where the standard schemes were to be applied
  • What kind of protection was intended
  • The general relay setting philosophy

CAD drawings with multiple layers were also developed to match the standard relay schemes

engineering processes10
Engineering Processes

Conflicts Encountered:

Despite the large effort in strategizing the implementation process, there still were several conflicts encountered:

  • Perpetual evolution of “standards” due to newly gained experiences
  • Design Interpretation of standards resulted in inconsistent implementation
  • Lack of adequate communication and training of standards
engineering processes11
Engineering Processes

Corrective Actions:

To combat these engineering problems, we created and adopted…

  • “Design Module” concept that specifically lays out the entire intended design package of protection for a specific station application
    • E.g. – 25MVA Power Xfmr w/ LV CB (Xfmr and LV Bus protection included)
  • Consistent Relay Setting Calculation Sheets
  • Additional Training of how to use these tools and the philosophy intent
  • Revision control of Standards
scada communications
SCADA Communications

SCADA Communication Components:

  • Relay
  • RTU
  • SCADA Master
scada communications13
SCADA Communications

Implementation Strategy:

  • Send all potentially necessary data points to RTU, then filter which were actually deemed necessary for Dispatchers to be sent to the SCADA Master
  • Let local personnel decide which points the SCADA system are needed, configure the devices themselves, and commission the data path
  • Use existing equipment and communication protocols when able
scada communications14
SCADA Communications

Conflicts Encountered:

  • Inconsistent amounts / types of data being sent to Dispatch
  • Project Slowdown due to communication discussions on every project
  • Little documentation of what was implemented
  • Confusion regarding data identity due to lack of data point naming conventions
  • SCADA Alarm Logging was not chronological
scada communications15
SCADA Communications

Corrective Actions:

  • RTU Point Assignment documentation
  • Communication Configurations for relays & RTUs delivered by engineering
  • Training of advanced commissioning techniques
  • Convert RTUs and Communication Protocol


Hard Wired




SCADA Master






SCADA Master






SCADA Master


Commissioning Aspects:

  • Practices
  • Procedures
  • Troubleshooting

Implementation Strategy:

It was initially assumed that commissioning Microprocessor-based relays was essentially very similar to commissioning Electromechanical relays.

Test each protection element individually while monitoring trip output.

Technician can create his own test plan based on past electromechanical procedures.


Conflicts Encountered:

The “Black Box” phenomena: one device that performs multiple functions with several different outputs (trips, alarms, targets, annunciations, etc.)

Element Testing vs. Functional Testing

Those installing the scheme often asked, “What’s the intent of the design?”

“How should the scheme operate for this scenario?”

The procedure for troubleshooting a mis-operation or failed test is much different than that of an electromechanical relay scheme


Corrective Actions:

  • Commissioning Guides
  • Automated Testing Procedures with Pre-determined Test Plans
  • Design Intent Documents provided with each engineered job
  • Logic Diagrams matching actual programmed internal logic
  • New Training Program at New Training Facility
lessons learned
Lessons Learned
  • Process Improvements
    • Re-engineering the process is sometimes needed
    • Continual auditing of the process
  • Specify Process Feedback Loops
    • Identify Experts for Focus Groups
    • Defined Time Interval for Revisions to take place
  • Quality Control
    • Adding quality analysts to team
    • Strengthening peer-review ideals
  • Workforce Solutions
    • Invest in additional engineers, technicians, and support staff
    • Invest in Training Programs