H.T. & L.T. Motors :
Fundamentals of induction motor; slip-torque
characteristics, motor-generator brake; Equivalent circuit; transient model; v/f control;
Synchronous motor : torque-angle characteristics, Summary of protections for cage &
wound rotor induction motor and synchronous motor.
Protection of H.T. Motors :
Protection of cage motors; different abnormal
operating conditions; commonly used comprehensive motor protection relays; major
protection elements; thermal over load; over current vs overload; critical review of motor
and relay thermal characteristics; major short comings.
Locked rotor; speed switch requirement; negative sequence; unbalance vs
negative sequence; short-circuit ground fault (zero sequence); stabilizing resistor
calculations; use of residual connected CT and CBCT; other protective functions; start
protection; differential protection; under voltage protection; under current protection;
detailed calculations for motor protection settings; Setting calculation for Motor
Protection Relay: special protection requirement for wound motor; rotor unbalance;
additional protection for synchronous motor; loss of field.
Protection of L.T. Motors :
Causes for LT Motor damage, Bimetal overload relay,
HRC fuses, Comprehensive or compact, cost effective Motor Protection relay for contactor
controlled motor, Co-ordination between fuse and relay, Application of thermistors.
