a. DINF (making current magnetic release)
This consists of a laminated magnetic circuit. This is placed under the lower current terminal pole. This is provided for all the three poles. It has a core that rotates in the air gap. It is held by spring. During protection the magnetic forces developed overcome the spring tension and the core is attracted. The mechanical force developed is used to trip the breaker. This protection acts during the closing of breaker if any fault exists. The current is set to 5 times the rated current.
b. DIRS (short time magnetic release)
The construction is same as DINF, but it has a mechanical timer, which can be set accordingly. This protection acts when any fault comes during breaker in service. The current rating is set to 3 to 8 times the rated current.
*c. DIT – (thermal over load protection)**
This consists of a three bimetallic strip, which gets heated up when over loaded and trips the breaker by a lever. It is placed in front of the breaker. Setting range is 60% to 100%.
