Virtual Power Laboratory-D.E.I.

To study protection of Induction Motor using numerical relay.

1. Three phase Induction Motor Rating:
   3-phase, 50 Hz, 415V, 5kVA, 1500 rpm
2. Current Transformer
3. Numerical Relay L&T 300 MPR

Induction Motor Protection
The three phase induction motors are very reliable and robust, modern designs operate much closer to the limits of thermal margins and to give adequate protection, sophisticated protective relays are required. In addition, increased industrial use of power electronics leads to incorporate different harmonics in the system, which adversely affect the induction motor performance and cause considerable rotor heating.
The numerical relay (L&T MPR 300) has been designed to protect the motor against five major problems which are Thermal overload, Single phasing, Earth fault, locked rotor and under current.
It is a low cost solution, offering five major protections for motors widely used in fans, pumps, crushers, mills, compressors, belt conveyors, centrifuges, mixers, ventilators, escalators, motorized valves etc. Major advantage is that it provides E/F co-ordination in contactor-started motors, thus offering greater security, operator safety and economy. The relay is microcontroller based, highly user friendly and compact with inbuilt CTs. The relay can also be used for protection of larger motors by using external CTs. medium voltage and high voltage sub-stations.
MPR 300 has very few controls/ settings on the front panel. There are two potentiometers - one for setting the motor rated current and the other for setting the Earth fault pick up level. A DIP switch is provided for selection of thermal overload trip class and enable / disable of Locked Rotor protection and under current protection. There are six LEDs for indication of different 5-faults and one for reset. A numerical relay is a solid state relay also called static relay. It contains electronic circuitry which may include transistors, ICs, diode and other electronic components. There is a comparator circuit in it, which comparing 2 or more voltages or currents gives output applied to either a slave relay or a thyristor circuit.
The slave relay is an electromagnetic, semi static relay which closes its contacts .The numerical relay as low burden on CT, PT, fast operation, absence of mechanical inertia and contact trouble,long life and less maintenance. So, they are superior to electromagnetic relay, but they are costly and required more maintenance.

1. Switch ON CB for input supply
2. Press the start button.
3. Observe the induction motor is running in normal mode
4. Create single phasing fault by pressing button F1.
5. The relay tripped the motor and LED indicator glows for single phasing fault.
6. Reset the relay by pressing reset button.
7. Again start the motor and repeat the process for other faults.