Hot Armature Resistance

  

• Let us consider that the initial temperature or room temperature says 20 degree centigrade and final temperature of armature be 60 degree centigrade.

As

    R2 = R1 ( 1 + αt₀ )

    R₂₀ = R₀ ( 1 + 20α₀  )

    R₆₅ = R₀ ( 1 + 65α₀  )

    Where α₀ = 1 / 234.5 ohm / ohm / ⁰C

Therefore

    R₆₅ /  R₂₀ =  [ R₀ ( 1 + 65α₀  ) ]  / [ R₀ ( 1 + 20α₀  ) ]

    R₆₅ /  R₂₀ =  [ 234.5 + 65 / 234.5 + 20 ]

    R₆₅ = 1.17 R₂₀

•  If initial armature resistance at 20 degree centigrade was 1 ohm , it will become 1.17 ohm at 60 degree centigrade. 
• It is called as hot armature resistance

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