Electrical Drives and Control Heating and Cooling Curves Relation Ship Between Temperature Rise and Time: Heating time constant Cooling time constant MUTHAYAMMAL ENGINEERING COLLEGE

1. Presented by
Dr. R. RAJA, M.E., Ph.D.,
Associate Professor, Department of EEE,
Muthayammal Engineering College, (Autonomous)
Namakkal (Dt), Rasipuram – 637408
MUTHAYAMMAL ENGINEERING COLLEGE
(An Autonomous Institution)
(Approved by AICTE, New Delhi, Accredited by NAAC, NBA & Affiliated to Anna University),
Rasipuram - 637 408, Namakkal Dist., Tamil Nadu, India.
Electrical Drives and Control
Heating and Cooling Curves

2. Heating and Cooling Curves
 A machine can be considered as a homogeneous body developing heat
internally at uniform rate and dissipating heat proportionately to its temperature
rise,
Relation Ship Between Temperature Rise and Time:
8/20/2021 2

3.  Assume that a machine attains a temperature rise after the lapse of time t
seconds.
 In an element of time “dt” a small temperature rise “d” takes place.
Then,
Heat developed = p.dt
Heat developed = Gh.dq
Heat dissipated = Sql. dt
Therefore, total heat developed=heat stored + heat dissipated
8/20/2021 3
Contd..

4. 8/20/2021 4
Contd..

5. 8/20/2021 5
Contd..

6. Heating time constant:
 Heating time constant is defined as the time taken by the machine to attain
0.623 of its final steady temperature rise.
8/20/2021 6
Contd..

7. 8/20/2021 7
Contd..

8. 8/20/2021 8
Cooling time constant
Contd..

9. Thank You
8/20/2021 9