PROTECTION AND SWITCHGEAR
To introduce the students to the various abnormal operating conditions in power system and
describe the apparatus and system protection schemes. Also to describe the phenomena of current interruption to study the various switchgears.
i. To discuss the causes of abnormal operating conditions (faults, lightning and switching surges) of the apparatus and system.
ii. To understand the characteristics and functions of relays and protection schemes.
iii. To understand the problems associated with circuit interruption by a circuit breaker.
UNIT I INTRODUCTION 9
Importance of protective schemes for electrical apparatus and power system. Qualitative review of faults and fault currents - relay terminology – definitions - and essential qualities of protection. Protection against over voltages due to lightning and switching - arcing grounds - Peterson Coil - ground wires - surge absorber and diverters
Power System earthing – neutral Earthing - basic ideas of insulation coordination.
UNIT II OPERATING PRINCIPLES AND RELAY CHARACTERISTICS 9
Electromagnetic relays – over current, directional and non-directional, distance, negative sequence, differential and under frequency relays – Introduction to static relays.
UNIT III APPARATUS PROTECTION 9
Main considerations in apparatus protection - transformer, generator and motor protection -
protection of bus bars. Transmission line protection - zones of protection. CTs and PTs and their applications in protection schemes.
UNIT IV THEORY OF CIRCUIT INTERRUPTION 9
Physics of arc phenomena and arc interruption. DC and AC circuit breaking - restriking voltage and recovery voltage - rate of rise of recovery voltage - resistance switching - current chopping - interruption of capacitive current.
UNIT V CIRCUIT BREAKERS 9
Types of circuit breakers – air blast, air break, oil, SF6 and vacuum circuit breakers – comparative merits of different circuit breakers – testing of circuit breakers.