Induction Motor Protections

8/13/2019 Induction Motor Protections

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Submitted by:


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Project overview

Block diagram

Power supply

Thermistor

Comparator

Relay

Schematic & Working of the project

Advantages Applications

Future scope

Conclusion


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The basic idea for the development of theproject is to provide safety to the Induction

Motor.

If any of the phases, out of the 3 phases is

missing and also if the temperature of themotor during operation exceeds the prescribed

value, the supply to the induction motor is cut

off immediately.

The kit is supplied with a 3phase power i.e.,

the three transformers are connected to the 3

phases supply.


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The 230V AC supply is first stepped down to12V AC using a step down transformer.

This is then converted to DC using bridgerectifier.

The AC ripples is filtered out by using acapacitor and given to the input pin ofvoltage regulator 7805.

At output pin of this regulator we get a

constant 5V DC which is used for MC andother ICs in this project.

A blocking diode is connected to take thepulsating waveform.


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A thermistor is a type of resistor whose

resistance varies significantly (more than in

standard resistors) with temperature.

The word is a portmanteau of thermal and

resistor. Thermistors are widely used as inrush current

limiters, temperature sensors, self-resetting

over current protectors, and self-regulating

heating elements.


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op amps & comparators look very similarBut a comparator gives a logic output

indicating the relative potentials on its

two inputs

An op amp amplifies the differential

voltage between its two inputs and is

designed always to be used in closed-loop

applications


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Potential dividers are connected to the inverting

and non inverting inputs of the op-amp to givesome voltage at these terminals.

Supply voltage is given to +V and V is connected

to ground.

The output of this comparator will be logic high

(i.e., supply voltage) if the non-inverting

terminal input is greater than the inverting

terminal input of the comparator.

If the inverting terminal input is greater than the

non-inverting terminal input then the output of

the comparator will be logic low (i.e., gnd).


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A relay is an electrically operated switch.

Current flowing through the coil of the relay

creates a magnetic field which attracts a

lever and changes the switch contacts. The coil current can be on or off so relays

have two switch positions and have double

throw(changeover) switch contacts as

shown in the diagram.


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Relays allow one circuit to switch a second

circuit which can be completely separate

from the first.

For example a low voltage battery circuit canuse a relay to switch a 230V AC mains circuit.

There is no electrical connection inside the

relay between the two circuits, the link is

magnetic and mechanical. To drive relay through MC ULN2003 relay

driver IC is used


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In normal operations RV1, RV2, RV3 & RV4 are so set

that the output of the comparators is held lowresulting in 4 relays in deactivated condition whilethe 3CO relay is in active operation.

In the event of failure of any phase thecorresponding comparator output goes high thatdrives the relay the contact of which opens todiscontinue the DC supply to the 3CO relay.

The phase motor connected in series with the NOcontacts thus open to stop the motor.

Similarly while the temperature goes high on thebody of the motor the mounted Thermistor resistancefalls to develop logic high for Q4 to operate R4 &disconnect the DC voltage to the 3CO relay.

Thus in the process motor is protected against any

phase failure or high temperature.


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Induction Motor Protections

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