Thermal Memory is associated with Circuit Breaker tripping on Overload condition. Overload trip devices have inverse characteristics. ACB/MCCB/MCB/MPCB are used as protection switchgear for Cable and Load.
Thermal Memory Feature of a breaker helps it to remember previous fault till the conductor cools and comes to Ambient temperature, if in case this breaker is closed before this time duration it will enable breaker to trip faster than the previous fault.
When Circuit Breaker trips on overload, as per standard Electrical Operating Process, Operator must rectify the fault which caused this trip, post that Operator can again close the Circuit Breaker. Due to any reason Operator fails to do so, Operator may close the Circuit Breaker on fault and this second fault may badly damage the Cables and Load. To avoid this, the Circuit Breaker should trip in less time compared to first trip which can reduce the risk.
To facilitate this, Bimetals have the natural characteristics, for example, 250A Circuit Breaker equipped with Bimetal Thermal release, if that feeder trips on overload, Bimetal in the Circuit Breaker would have taken 10 Seconds to bend by 5mm after this trip this Bimetal would again take 25 seconds to return to original place. Now, if due to any reason operator closes Circuit Breaker before this 20 seconds, Circuit Breaker will take lesser time to trip. This phenomenon increases operator and Asset safety.
Thermal Memory cam be achieved either my Bimetal Strip in trip units Or by following the same algorithm in Microprocessor Based trip units.