05-04-2010, 08:01 PM
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AUTOMATION IN POWER FACTOR IMPROVEMENT USING PROGRAMMABLE INTERFACE CONTROLLER
INTRODUCING THE TOPIC
Definition of power factor.
Definition of power factor correction.
Leading and lagging power factors.
Importance of power factor to be unity.
OBJECTIVES OF THIS PROJECT
To counteract the undesirable effects of electric loads that create a power factor that is less than one.
To improve the stability and efficiency of transmission network.
Monitoring the power factor changes using PIC and LCD in real time basis.
AVERAGE AND INSTANTANEOUS POWER
Average power.
Instantaneous power.
Difference between average power and instantaneous power.
TYPES OF POWER FACTOR CONTROLLER
Passive PFC.
Active PFC.
Synchronous PFC.
CAPACITIVE POWER FACTOR CORRECTION
Resistive and inductive components of current.
Types of capacitive power factor correction
Bulk, static, inverter and solid state soft starter.
DESCRIPTION OF COMPLETE SYSTEM
DETAILED DESCRIPTION OF CIRCUIT COMPONENTS
Voltage and current step down arrangement
To step down voltage and current using CT and PT
To isolate control circuit from high voltage and current in the circuit.
Analog to digital converter
Converts the load voltage and current waveforms from sine to square.
Zero crossing detector is used to detect whether power factor is lagging
or leading.
PIC MICROCONTROLLER
It is the heart or core of the entire operation.
High operating speed , good interrupt capability.
A single 5V source is required for programming.
Low power consumption.
Capacitor banks are switched according to the output of PIC.
SWITCHING UNIT AND CAPACITOR BANKS
Switching unit consists of relays and contactors.
PIC switches on/off the relays according to the power factor.
Contactors at KEL have rating of 440V, 32A and 440V, 63A.
Capacitor banks are connected in parallel.
At KEL 4 capacitor banks are used, 25KVAR,10KVAR,20KVAR,20KVAR.
LIQUID CRYSTAL DISPLAY AND DC POWER SUPPLY
Dot matrix liquid crystal display HD44780U is used.
Can display up to one 8- character line.
Requires a low power supply.
PIC microcontroller and OPAMP IC requires a 5V DC supply.
Relays require a 12V DC supply.
CURRENT AND VOLTAGE WAVEFORMS
CIRCUIT DIAGRAM
DEMERITS OF CAPACITOR PF CORRECTION
Capacitor selection must be based on magnetizing current of motor.
Over correction can cause equipment failure.
Harmonics on the supply can cause over current in the capacitors.
It can be reduced by using harmonic filters.
Detuning reactors in series with capacitors can also reduce harmonics.
APPLICATIONS OF PFC
Used in electrical industry for power factor correction of linear loads.
Also used in power factor correction of nonlinear loads in power supplies.
Also helps in reducing supply harmonics.
CONCLUSION
A PIC microcontroller based power factor controller is capable of adding capacitor banks across the load
automatically when the power factor is lagging and is capable of removing capacitor banks from load when there
is leading power factor. This work also facilitates to monitor the power factor changes on LCD in real time
basis This is suitable for applications where manual switching of capacitors is to be replaced by automatic
switching.
