Darect on line statar
Overload relays may be solid-state devices with adjustable trip setting also called as the electronic relay or by interacting with related temperature sensors called as a thermal relay or if only operates for excess current flow then called as a magnetic relay.
For most motors, the maximum rating of the overload protection device is 125% of the full load ampere rating. The DOL starter connects the 3-phase main with the motor.
Direct online starter (DOL) connects 3-phase motors directly across 3-phase supply, and the beauty of this type of starter is in spite of motor connected straight, it doesn’t cause any harm to the motor.
The acceleration torque is the torque developed by the motor minus the load torque, and will change as the motor accelerates due to the motor speed torque curve and the load speed torque curve.
The start time is dependent on the acceleration torque and the load inertia.
When motor draws excessive current to meet the load requirement and If load requirement goes beyond the rated limit, termed as Overload.
Overload protection is a type of security when motor draws over current or excessive current and causes overheating of the equipment. So overload relays are employed to limit the amount of current drawn.