How Do You Calculate the Temperature Rise of a Bimetallic Strip in an MCB?

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SUMMARY

The calculation of temperature rise in a bimetallic strip used in Miniature Circuit Breakers (MCBs) involves the formula MC(dT) = I²Rt, where I represents the current, R is the resistance, and t is time. However, this formula is limited as it does not account for heat loss to the environment and assumes constant resistivity. To achieve accurate results, it is essential to incorporate a convective heat transfer term, utilizing an estimated heat transfer coefficient. This adjustment allows for a more realistic assessment of temperature changes under operational conditions.

PREREQUISITES
  • Understanding of bimetallic strip properties and applications in MCBs
  • Knowledge of electrical resistance and heat generation principles
  • Familiarity with thermal dynamics, specifically convective heat transfer
  • Ability to perform calculations involving resistivity and temperature changes
NEXT STEPS
  • Research methods for calculating convective heat transfer coefficients
  • Learn about the thermal properties of materials used in bimetallic strips
  • Explore advanced heat transfer analysis techniques for electrical components
  • Investigate the impact of varying resistivity on temperature calculations
USEFUL FOR

Electrical engineers, circuit designers, and technicians working with MCBs and thermal management in electrical systems.

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I am studying the bimetallic strip used in MCB.
I am trying to theoretically calculate the temperature rise of the strip when 1.13In (safe value of current for which the MCB shouldnot trip) is passed through the bimetallic strip. I am having the dimensions, resistivity, modulus of elasticity, flexivity, density of the strip.

I even have the practical values with me for ever few secons of current passed.
I tried to use the relation MC(dT)=I^2Rt
that is all the heat generated is used in the temperature rise.
But practically other things need to be considered like heat loss with environment, also the above formula holds good for only few seconds and here the resistivity I have taken constant will also vary.
Please help me out with a relevant solution.
 
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To correct the equation being used, one would need to include a convective heat transfer term, using an estimated heat transfer coefficient to the surroundings.
 

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