ABSTRACT Thermal overload relays are economic electromechanical protection devices which offers reliable protection for electric motors in the event of overload or phase failure. Presently there are two types of overload relays which depend on the temperature characteristics of metals to provide protection by tripping the circuit. These relays lack accuracy as they do not activate the trip circuit at any exact specified temperature. In this paper we introduce a new form of thermal over-load relay actuated by ferrofluid. The ferrofluid has a very accurate transition temperature known as curie temperature. It acts as a ferromagnetic material below the curie temperature and loses the property of ferromagnetism above this temperature. By using this property of the fluid we propose an alternative method for more accurate op-eration under overload condition. This relay finds application in the protection system of electrical machines. Thus, in this paper we present a novel and simple technique for protection against thermal overloading using ferrofluid.
Cite this paper
B. Rajagopalan, M. Hayagrivan and M. Praveenkumar, "Ferrofluid Actuated Thermal Overload Relay," Smart Grid and Renewable Energy, Vol. 3 No. 1, 2012, pp. 62-66. doi: 10.4236/sgre.2012.31009.
 “Motor Thermal Protection,” Danaher Motion, Document Number: A-RT-000-18 Rev 3.
 T. A. Franklin, “Ferrofluid Flow Phenomena,” Massachusetts Institute of Technology, Cambridge, 2003.
 C. Scherer and A. M. F. Neto, “Ferrofluids: Properties and Applications,” Brazillian Journal of Physics, Vol. 35, No. 3, 2005. doi:10.1590/S0103-97332005000400018
 S. L. Herman, “Electrical Motor Control,” 9th Edition, Cengage Learning, Delmar, 2007.
 C. Bussmann, “Selecting Protective Devices Handbook,” Motor Circuit Branch Circuit Protection, 2005, p. 132.
 Desensitizing Electric Motor Controls, Pacific Gas and Electric Company, August 2004.
 “Transformer Protection—The Importance of Effective Transformer and Control Transformer Protection,” Littlefuse POWR-GARD? Products, Littelfuse, 2010.