This paper presents a Microcontroller based three phase induction motor protection relay. The scheme employs the Hall effect current transducers for sensing motor line currents, and an ‘Auto ranging ’ feature, in order to acquire motor line currents accurately from no load to blocked rotor current. The flexibility of ‘Operator selectable thermal current versus time (I-T) curves feature’ is incorporated in the relay software, in which using the operator fed cold curve points and the thermal time constant of the motor, the corresponding I-T cold and hot curves can be fitted by the relay Software. The relay performance, with the selected I-T curves has been studied in the laboratory by testing on a three phase, 5 h.p. induction motor and it has been observed that the relay to follow the selected I-T characteristics. © 1998 Taylor & Francis.

Vittal, K.P.Fakruddin, D.B.Raghavendra Rao, I.Parthasarathy, K.2026-02-05MicrocontrElectric Machines and Power Systems, 1998, 26, 1, pp. 13-260731356Xhttps://doi.org/10.1080/07313569808955804https://idr.nitk.ac.in/handle/123456789/280421998This paper presents a Microcontroller based three phase induction motor protection relay. The scheme employs the Hall effect current transducers for sensing motor line currents, and an ‘Auto ranging ’ feature, in order to acquire motor line currents accurately from no load to blocked rotor current. The flexibility of ‘Operator selectable thermal current versus time (I-T) curves feature’ is incorporated in the relay software, in which using the operator fed cold curve points and the thermal time constant of the motor, the corresponding I-T cold and hot curves can be fitted by the relay Software. The relay performance, with the selected I-T curves has been studied in the laboratory by testing on a three phase, 5 h.p. induction motor and it has been observed that the relay to follow the selected I-T characteristics. © 1998 Taylor & Francis.