PROTECTION 101

Casco Systems LLCChris McGonagle

Utility Grid and Components

Utility Grid and Components• Why we do what we do

Substation Protection and Control

• Image Source – Google Maps

Substation Protection and Control

• Substations:• Connect Transmission and Distribution lines to form the

“Grid”

• Transform Voltage for maximum efficiency of power delivery

• Provide locations of equipment for control and monitoring of the grid

Substation Protection and Control

Transmission Lines

Bus

Transformers

Distribution Lines

Breakers

Miscellaneous

Substation Protection and Control

• Intelligent digital relays calculate fault location based on impedance

• Potential Overreach Transfer Trip (POTT) scheme used to increase accuracy

• Line Current Differential provides high speed tripping for faults on the line

• Reclosing allows minimal down time for lines when faults are short-term

Protection examples– Transmission Lines

Substation Protection and Control

Protection examples– Transmission Lines– Potential Overreach Transfer Trip

Substation Protection and Control

Protection examples– Transformers

• Intelligent digital relays dedicated to High voltage and Low voltage protection• These relays are required to work in harmony for all

around protection

• Transformer Differential provides high speed tripping for faults occurring in the windings

Substation Protection and Control

Protection examples– Bus

• Various Bus configurations provide unique requirements to ensure every segment of the system is protected• Single Bus

• Dual Bus

• Ring Bus

• Bus Differential measures and compares current on each of the connections to the bus

Substation Protection and Control

Protection examples– Bus Configurations

Substation Protection and Control

Protection examples– Breaker Failure

• Scheme trips electrically adjacent breakers to interrupt the path from power sources to the fault

• Older methods used electromechanical, manually resettable lockout switch to apply a trip to the electrically adjacent breakers

• Through substation modernization and IEC 61850, messages can be sent electronically through the network to have neighboring relays trip breakers in failure conditions

• For breaker failure on transmission lines, BFTT schemes utilize fiber or other communication methods to send a signal to the remote end of the line to trip the remote breaker to isolate the fault

Substation Protection and Control

Protection examples– Breaker Failure on a Single Bus Scheme

Substation Protection and Control

Protection examples– Breaker Failure on a One-and-a-Half Breaker Scheme

Substation Protection and Control

Protection examples– Substation Controls

• Breaker Bay Control and Protection utilizes a digital relay to provide overcurrent

• The aforementioned relay also asserts “Open” and “Close” commands to the breaker and line / bypass switches that are motor operated

• These commands are sent manually from SCADA networks or the local station HMI

Substation Protection and Control

Recent Projects

• 115kV and 34kV Breaker Replacements

- Line and Breaker Protection Upgrades

- P&C Elementary and Wiring Design

• 115/34kV Substation Protection and Integration Upgrade

• Steam Generation 34kV Intertie & Generator Protection, Integration and Control engineering support

• Hydro Generator Protection & Automation Upgrades

• Coordination, Equipment Rating and Arc Flash Studies

• References• IEEE C37 Series• “Protective Relaying Principles and

Applications” by J.L. Blackburn• Casco Systems Engineering

• Graphics Provided by:• Electrical 4 u – Electrical Bus System And

Electrical Substation Layout• Atlantic City Electric• Casco Systems Engineering

P r o t e c t i o n 1 0 1C a s c o S y s t e m s L L C

C h r i s M c G o n a g l e

Thanks for Listening