The Locked Rotor Torque or Starting Torque is the torque the electrical motor develop when its starts at rest or zero speed. The magnitude of the Locked rotor current is determined by motor horsepower and design characteristics. Normally it will be 6 to 7 times of the Motor full Load current.
LOCKED ROTOR CURRENT OF A MOTOR
Normally Motor Name plate contains KVA code or Design Letter.
We can calculate the Locked Rotor Current Using the following Formula
Single Phase = (577 x HP x KVA/HP)/V
Three Phase= (1000 x HP x KVA/HP)/V
Find KVA/HP using the Following chart
Example:
Motor Name plate indicates phase 3,300 HP,4160 Volts,KVA Code G
LRC will be
(577 X 300 X 5.60)/4160 to (577 X 300 X 6.29)/4160
=232.02 to 261.73 Amps