Thermal Overload Protection For Hermetic Motors

The degree of protection that an internal protection device provides is classified in the iec 60034 11 standard.

Thermal overload protection for hermetic motors.

Electrical mechanical and thermal motor characteristics define the frame needed for effective motor protection running stage starting stage and locked rotor conditions serve to determine the main motor parameters motor heating and thermal damage motor characteristics depend on both positive and negative sequence current in the. As mentioned thermal overload relays contain a bimetallic strip and a bimetallic strip is a mechanical device that converts temperature change into mechanical displacement. Another type of overload protection often called thermal overload protection is built into certain mechanical devices such as motors or engines. There is one cylindrical stator and a three phase winding is symmetrically distributed in the inner periphery of the stator.

This motor thermal overload protection scheme is very simple. The rtd of the stator is used as one arm of the balanced wheatstone bridge. The thermal overload protector on a motor monitors both motor temperature and current. In this instance the protection is designed to prevent damage within a motor or other similar device caused by overheating.

They may also be used in commercial motors which must function in high pressure corrosive environments. In order to also ensure the thermal overload protection of the motor in the cases of supply asymmetry and loss of a phase high quality motor protection relays have mechanisms with phase failure sensitivity differential release. The amount of current through relay 49 depends on the degree of imbalance of the bridge. When either exceeds the motor s limit the protector will shut the motor off until it cools.

For understanding motor thermal overload protection in induction motor we can discuss the operating principle of three phase induction motor. The 3hm family of motor protectors can be applied to air conditioning compressors ranging from 1 to 2 hp. Different types of thermal protection exist and are identified by a tp code tpxxx which indicates. Overheating or high current are generally caused by other factors that overload the motor like substituting the wrong motor or lack of proper ventilation around the.

The type of thermal overload for which the thermal protection is designed 1 digit. Thermal overload relays are one of the most common and economical motor overload protection devices especially for single phase motors. If larger motors 10 kw are subjected to these higher currents for a longer time damage should be expected. Tp is the abbreviation for thermal protection.

Due to such symmetrical distribution when three phase power supply.