Distribution System Training

The objective of this module is to present the fundamental requirements and features of distribution system protection, so as to provide a firm foundation for more detailed study of specific protection schemes and equipment which follows in succeeding modules

On completion of this module and associated workbook, the participant will be able to understand the following concepts and apply them in day-to-day work activities.

• The need for protection equipment on all sectors of the power system
• Definition of a “hazardous” condition
• Equipment overload condition versus “fault condition”
• The requirement to detect, evaluate and clear a fault
• Typical causes of faults; (i.e. equipment failure, physical accidents, natural events (usually weather related))
• Classification of faults
• Consequences of a fault
• Calculation of fault current magnitude
• Calculation of voltage at different locations under fault conditions
• The significance of power source impedance on fault current magnitude and terminal voltage
• The significance of distance to the fault on a radial circuit
• Means of disconnecting the faulty circuit by interrupting high magnitude fault current
• Applications and disadvantages of fuses
• Applications of the circuit breaker-protection relay combination
• Application and limitations of reclosers
• The need for coordination of relay settings to ensure correct tripping sequence when a faulty circuit is cleared
• Protection relay input and output signals
• Characteristics of voltage transformers and current transformers
• Function of the protection relay as a signal processor
• Typical circuit breaker tripping circuit, including relay trip contacts and manual trip contacts
• Relay annunciation
• Basic construction of electromechanical relay
• Basic construction of solid state (static) relays
• Basic construction of digital relays