To Study and Improve the Contact Pressure of MCCB Contact System by Analysing the Spring Performance Used in MCCB

Abstract

MCCB's are widely used as protection device in industries. The main purpose of MCCB is to make, carry or break the current under normal as well as under abnormal conditions such as short circuit and Overload. During the working condition of MCCB, the contact system is closed and current flows through current carrying path which consists moving and fixed contact. Contact system includes driveshaft, contact spring, upper contact, and spring cap and contact buttons. As the current flows there is a temperature rise of the contact system and that rise in temperature gives rise to CREEP phenomenon which affects the functioning of contact system. After a period of time there is decrease in the load and free length of the contact spring which directly affects the contact pressure between the moving and fixed contact of MCCB contact system. Decrease in spring length and load is also termed as spring SET. Due to this Low contact pressure is created which makes poor contact between the contact buttons thus increase the milli-volt drop of this joint. High milli-volt drop joint always increases the temperature generation rate which affects the performance of the MCCB and also electrical life of the MCCB. The present work emphasis on the improvement of the contact system by studying existing contact system on practical basis to know the scope of improvement and limitation. Based on the outcomes, new design, improvements is proposed and prototyping is tested to calibrate the contact pressure of the breaker. Creo software is used for 3D modelling of the proposed designs. Oven is used to conduct practical test. Prototypes of the proposed design is validated by practical test on 630A Frame MCCB. On successful completion of design validation, proposed design has been implemented to improve the contact pressure of the MCCB.