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Alia Zulkifli

on 17 September 2015

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Induction motor:
-Single phase
~Commonly used for smaller load
-Three phase
~Used commonly in industrial drive
~Rugged and economical

Three phase induction motor:
-Consists of stator and rotor (no electrical connection)
-Both stator and rotor made up of highly magnetize core
-Providing low eddy current and hysteresis losses

Three-phase induction motor is widely used in industrial fields.
Important for it to be protected.
To design a protection system against certain cases.
Case of faults:
-If one of the power supply is absent (single phasing) and
-If temperature is suddenly increases
Thus, the protection system will detect and cut the connection to the load.

To understand the working principle of induction motor.
To recognize type of faults that might be encounter by the motor.
To identify the factors and effects of single phasing and overheating.
To find the effective way to protect the motor.

Single phasing
-3 phase power supply is important for the motor to work properly.
-Motor still can operate if 1 phase is missing
~Missing of any phase in power supply
~Feeder/step down transformer fuse blow
~Protection device open in one phase of motor
~Motor heat up
~The remaining phase current increases

~Motor overloading
~Distortion in supply voltage
~Impaired cooling capability
~Unbalanced supply voltage
~Degradation of stator insulation
~Deformation of rotor conductors
~Electrical fire
~Reduce in motor’s life span

This type of motor encounter some problems during production and operation process.
Type of failure:
-Mechanical (i.e. over mechanical load, mechanical stress)
-Electrical (i.e. phasing faults, over and under voltage, voltage unbalance)
-Environmental (i.e. radiation, conduction, surrounding heat)

The total amounts of three transformer step-down with the capacity of 230V/12V are connected in star connection at the primary coil.
The AC output from the transformer will be convert to the DC using the rectifier.

The output of 12V then will be supplied to the voltage regulator.
For single phasing protection:
-The direct current output (12V) will then be supply to three inverting input of the LM339.
-Three non-inverting inputs, the voltage output from the voltage regulator (5V)

For over temperature protection:
-The remaining available inverting input will be supplied with 5V received form the voltage regulator
-The remaining non-inverting input are connected with a series of thermistor over the 5V supply.

The op-amp will act as the comparator
Potential dividers are connected to the inverting and non-inverting input to give some voltage at terminal.
Supply voltage (12V) given to +V terminal
-V terminal is connected to the ground
Non-inverting > inverting = logic high
Non-inverting < inverting = logic low

Those four relay are normally close (NC) contacts which is arranged in series.
If one of the comparator gives an output high, the respective relay will be open
If all four relay is closed, the current will flows to the load

There are many way of protection system that can be use such as:
-Zigbee Protocol
-Programmable Logic Controller (PLC)
-Particle Swarm Optimization
But in this case, the comparator op-amp will be used to detect the faults

No power is supplied to the circuit
Circuit not complete as no current flows
No current flow to the load.

Switch1 is open as a condition of single phasing
Comparator compares the input and detect the absence of power supply 1
Results in high logic output
No current flows to the load

All switch is closed and voltage is supplied to the circuit
Comparator compares the voltage input and results in low logic output
The current flows to the load side.

Switch 2 is open
Red LED near the comparator output is light up to indicate the faults happened at power supply 2
No current flows through the load side

Switch 3 is open as if the single phasing happened there.
Comparator detect the changes of the input
Sends low logic output
Trip the respective relay
No current flows

Circuit improvisation
-The transformer is replaced by the DC power supply
-The DC motor is replace since the lamp not represented the combination of inductance and resistance as a motor
-The 3 CO relay is removed since the DC does not need the 3 phase supply to it

Normal operation
-12V power supply is connected to the circuit
-If no faults is detected, the motor will start to run
-The red LED near the DC motor will light up to shows the current flows.

During fault condition
-When one of the power is turn off, the comparator will detect the faults, or
-When the thermistor detect the changes in temperature, signal the comparator to produce output low
-Motor will stop running

Early development of the circuit
-3 step-down transformer and 3 CO relay is used
-3 lamp in delta connection is used
-These component is removed due to certain problem

There are several suggestion:
-By providing the monitoring system
-Different type of sensors to detect more faults
- On-line protection
The objective of this project is completed
The protection system circuit has been design and can be used to demo the protection system
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