Transmission System Operations

The objective of this course is to examine the function of protection schemes from the point of view of the transmission system operator. Details of the major types of protection relays are discussed with the emphasis on function rather than mechanical construction.

After completion of this course and associated workbook, the participant should be able to understand the following concepts and apply them in day-to-day working activities.

• Causes of electrical faults
• Fault characteristics; changing parameters
• Common types of 3-phase fault
• Effect of impedance on magnitude of fault current, i.e. generator impedance, transformer impedance, line impedance, and fault impedance
• Unbalanced phase conditions due to fault
• Elements of the protection scheme
• Protection relay input and output signal
• Circuit breaker tripping circuit
• CTs and VTs (PTs)
• The need for back up protection
• Protection zones
• Power system grounding
• Protection relay sensitivity, selectivity, and operating speed
• Reporting and analysis of protection relay operations
• The principals of differential protection, instantaneous overcurrent, inverse time overcurrent, directional overcurrent, distance relays (impedance relays), mho relays, pilot protection
• Application of protection schemes to generators, transformers, feeders, transmission lines, and bus bars