International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 10 Issue: 05 | May 2023
p-ISSN: 2395-0072
www.irjet.net
Design and Analysis of Induction Motor thermal Model for Numerical Protection Mrs. Rajitha T.B1, Mrs. Srilakshmi.I2 1HoD, Electrical Engg. Dept.,BVIT, Kharghar, Navi Mumbai, Maharashtra 2Lecturer, Electrical Engg. Dept., BVIT, Kharghar.
---------------------------------------------------------------------***--------------------------------------------------------------------The rate of increase of the temperature is given by the Abstract - As it employs high speed DSP algorithms in equation expressing the thermal equilibrium condition as,
microprocessor based relays, present day numerical technology is able to perform much more protection functions in a more reliable and effective manner as compared to its earlier counterparts. The paper discusses one such advancement that became possible in the field of motor protection. IEEE Standard C37.96-2000, Guide for AC Motor Protection [11], recommends the use of overcurrent relays for overload and locked rotor protection. But the simple dynamics of an over current relay cannot provide adequate thermal protection for a motor. In the paper the author derives, the thermal model from the thermal limit curves of the motor, which can be used in the relay algorithm to calculate the temperature rise on real time. The relay can be programmed to initiate a trip command, when the heating reaches the threshold. Correlation between the temperature and current has been established, for a 280KW, 6600V motor.
Power Supplied – losses = …….(2) Cs – Specific heat of the winding m – Mass of the winding Power supplied =
………………..(3)
Losses =
………………… (4)
And,
Key Words: Numerical Protection, Thremal model,
where R is the thermal resistance in °C/Watt. Now the equation no.2may be rewritten as,
Thermal limit curves, adiabatic process, locked rotor.
1.INTRODUCTION The simple dynamics of an over current relay cannot provide adequate thermal protection for a motor. The thermal limit curves are the characteristics of thermal models that enable microprocessor relays to continuously calculate and monitor motor temperature in real time. Employing thermal limit curves of thermal protection instead of over current relays is one way of optimizing motor protection, because of the varying thermal effects during starting and running of an induction motor.
……………………….(5) (Or)
It can be arranged and written for current as:
II.THERMAL MODEL FUNDAMENTALS
……………….(7)
The first order thermal model of an induction motor derived considering motor as a heated homogeneous body following non-adiabatic principle of thermal dynamics is given below. Let the winding temperature rise, θ above the ambient be written as,
The mass m multiplied by the specific heat Cs is known as C, the thermal capacity of the system with units of joules/°C. It represents the amount of energy in joules required to raise the system temperature by one degree centigrade. The product of the thermal resistance R and the thermal capacitance C has units of seconds and represents the thermal time constant.
……………. (1) where , θ is defined as the winding temperature rise
τ = R.m.Cs = R.C…………….. (8)
θW above ambient temperature θA.
© 2023, IRJET
|
Impact Factor value: 8.226
|
ISO 9001:2008 Certified Journal
|
Page 1280