Reactive Power Computation

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MEASUREMENT OF SINGLE PHASE

REACTIVE POWER

Internal guide:

Mr. D.B.KRISHNAMURTHY

By

K.Shivaraj

M.Sai Teja

Y.Saidulu


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Aim of the project

The project aims at calculating single phase reactive power

consumed by domestic loads (Low Tension Consumers)

This is done through EMBEDDED SYSTEM employed

Although todays electronic digital signal processing (DSP)

enables reactive energy measurements to be closer to the

theoretical value, there is no consensus in the field of energymetering on the methods of measurement


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Introduction

The amount and complexity of household electrical equipment has

increased tremendously over the last few years

Electronic ballast lighting, computer monitors and air conditioners

are welcome additions to our homes but come with additional

burdens

With the application of non-linear loads to power lines the active

energy no longer represents the total energy delivered. As a response

to improve billing, the measurement of reactive energy is gaining

interest.

Italys leading energy distributor has decided to install more than 20

million household energy meters with active and reactive power

measurement


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Reactive Power AC systems consume both active power and reactive power,

measured in VAR

(REACTIVE POWER) = (APPARENT POWER) * SIN() = V I SIN()

Reactive power is a BYPRODUCT of AC systems

The portion of power flow that is temporarily stored in the form of

magnetic or electric fields, due to inductive and capacitive network

elements, and then returned to source, is known as reactive power


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Why Do We Need Reactive Power

Reactive power (vars) is required to deliver active power

(watts) through transmission lines.

Motor loads and other loads require reactive power to convert the

flow of electrons into useful work.

When there is not enough reactive power, the voltage sags down

and it is not possible to push the power demanded by loads through

the lines.

Increasing reactive power production will sometimes alleviate

transmission constraints and allow cheaper real power to be

delivered into a load pocket.


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Reactive Power and Power Factor

Reactive power is present when the voltage and current are not in

phase One waveform leads the other

Phase angle not equal to 0

Power factor less than unity

Measured in volt-ampere reactive (VAR)

Produced when the current waveform leads voltage waveform

(Leading power factor)

Vice versa, consumed when the current waveform lags voltage

(Lagging power factor)


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Elements Producing Or Absorbing

Reactive Power

Loads :

-Dueto composite characteristics, load bus absorbs

reactive power

Underground Cables :

-Generate reactive power due to their loading less than

natural loading


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Overhead Lines :

-Depending on the load current, either absorb orsupply reactive power

Synchronous Generators:

-Can absorb or generate reactive power depending onexcitation

Compensating Devices :

- Installed in power system to either supply orabsorb reactive power


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Embedded Systems

Embedded System is a combination of hardware and software usedto achieve a single specific task by making use of a microcontroller

Embedded systems are computer systems that monitor, respond to,

or control an external environment.

Environment connected to systems through sensors, actuators and

other I/O interfaces.

Embedded system must meet timing & other constraints imposed on

it by environment.


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Block Diagram


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Major Building Blocks

Microcontroller

Regulated Power Supply

Crystal Oscillator

LED indicators

Potential transformer

Current transformer

Zero crossing detector

Relay unit

LCD (Liquid Crystal

Display)


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Microcontroller

Microcontrollers are specialpurpose computers.

The Microcontroller includes a CPU,

RAM,ROM,I/O ports, Timers etc.., like a standard

computer, but on a single silicon chip.

Microcontroller based systems are designed to

perform a specified task.

The Microcontroller used in the project is PIC

Microcontroller developed by Microchip

Incorporation


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PIC 16F877A


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Specifications

Pic16f877 is a 40 pin microcontroller. It has 5 ports port A, port B,

port C, port D, port E. All the pins of the ports are for interfacing

input output devices.

Consists of 5 Ports for interfacing input output devices

SPECIFICATION INFO

RAM 368 BYTES

EEPROM 256 BYTES

FREQUENCY 20 MHZ

FLASH MEMORY 8 K

I/O PORTS A B C D E


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Crystal oscillator

An oscillator is an electronic circuit that produces

a repetitive electronic signal.

The maximum operating frequency of PIC

Microcontrollers is 20 MHz.

Crystal oscillator is used in the project because ofthe fact that crystal is more stable to temperature

than other types of oscillators.


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Regulated Power Supply

PIC Microcontrollers requires a 5V DC for its operation.

The aim of this block is to convert battery voltage to 5V DC.

The process of conversion is shown below:


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Bridge Full Wave Rectifier

The circuit has four diodes connected to form a bridge

Converts an ac voltage to dc voltage using both half cycles of the

input ac voltage
http://www.google.com/url?sa=i&rct=j&q=full+bridge+rectifier&source=images&cd=&cad=rja&docid=avWwr0ZvYV38aM&tbnid=QW_6YhTBg5MtXM:&ved=0CAUQjRw&url=http://www.amazon.com/BRIDGE-RECTIFIER-SINGLE-PHASE-PACKAGE/dp/B008UTVHGO&ei=3nFYUam1IojZrQftvoHoDA&bvm=bv.44442042,d.bmk&psig=AFQjCNHn4Qsv3x8ikxKbiH5tToicuPHYVw&ust=1364837162499671


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Transformer

Most power supplies use a step-down transformer to reduce the

dangerously high mains voltage (230V in UK) to a safer lowvoltage.

In this project we use two transformers, one is a step down

transformer which provides power supply to relays &microcontroller and the other is a step up transformer to sense the

load current.
http://www.google.com/url?sa=i&rct=j&q=small+transformers&source=images&cd=&cad=rja&docid=_40AgtKkAREtuM&tbnid=sQpoJjuRmrF5DM:&ved=0CAUQjRw&url=http://www.istpower.com/products-applications/aviation-and-special-small-transformers/&ei=SjJXUdLbNMWJrAf5ooD4Dg&bvm=bv.44442042,d.bmk&psig=AFQjCNHhyV1Mz2EDvBNWx2bFZLN3uWt8xg&ust=1364755376364892


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Potential transformer

We are making use of PT (potential transformer) for capturing the

zero-crossing point of voltage wave form.

PT converts the high voltage AC to a low voltage measurable

quantity.

PT of type step-down transformer.
http://www.google.co.in/url?sa=i&rct=j&q=potential+transformer&source=images&cd=&cad=rja&docid=9J5gY7J-KOYPZM&tbnid=2z_bv6aJgakmoM:&ved=0CAUQjRw&url=http://www.indiamart.com/saraswathyelectricals/electrical-and-electronic-transformers.html&ei=nglXUY2AAYTtrAfV7IHIBA&bvm=bv.44442042,d.bmk&psig=AFQjCNEzbRis2FEpUqp9iNm8XYWPY1IloQ&ust=1364744971888074


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Current transformer

CT are used for current measurements.

We are making use of CT (current transformer) for capturing

the zero-crossing point of current wave form.

CT is of type step-up transformer.
http://www.google.com/url?sa=i&rct=j&q=current+transformer&source=images&cd=&cad=rja&docid=eJxkpyxmiGm5NM&tbnid=_ar4MWT9wgaiYM:&ved=0CAUQjRw&url=http://www.turbosquid.com/3d-models/support-type-current-transformer-3ds/673937&ei=LwpXUe3JDM2Orgf4qYDQDA&bvm=bv.44442042,d.bmk&psig=AFQjCNHkXAPhQaVbWecI4P1CVRJT8RbosQ&ust=1364745061110344


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LED Indicators

LED (Light Emitting Diode) is a

semiconductor light source used as

indicators.

In this project we are using LED indicators

for checking Microcontroller working

status and various status indications.

This usually works on 2 volts, 10 mA.


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Zero crossing detector

Zero crossing detection is the process of finding the variation of

waveform from zero as reference point.

In this project this is used to find out whether both current and

voltage wave forms are leading or lagging or in phase with each

other.


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Voltage Regulator

A voltage regulator is an electrical regulator designed to

automatically maintain a constant voltage level

The output voltage is maintained irrespective of the

fluctuations in the input AC voltage.


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Relay unit

A relay operation depends upon the electromagnetic effects ofcurrent flowing in an energizing winding.

Relay is used for controlling high voltage device using low

voltage signal.

This works on electromagnetic principle.

Relay takes the commands from the (microcontroller) controlunit.

It controls the high voltage electrical devices like Lamp, Fan,

Water pump, Circuit breaker etc.
http://www.google.com/url?sa=i&rct=j&q=electromagnetic+relay&source=images&cd=&cad=rja&docid=NEVoPLve66kNDM&tbnid=ou39iDEGE6F8wM:&ved=0CAUQjRw&url=http://www.finglai.com/product/relay/electromagnetic-relay/LY3J.html&ei=XDVXUeMiic6tB9fcgcgD&bvm=bv.44442042,d.bmk&psig=AFQjCNEh_yReolLqDjvdsPtSTnYWWjpX-g&ust=1364756178263844http://www.google.com/url?sa=i&rct=j&q=electromagnetic+relay&source=images&cd=&cad=rja&docid=NEVoPLve66kNDM&tbnid=ou39iDEGE6F8wM:&ved=0CAUQjRw&url=http://www.finglai.com/product/relay/electromagnetic-relay/LY3J.html&ei=XDVXUeMiic6tB9fcgcgD&bvm=bv.44442042,d.bmk&psig=AFQjCNEh_yReolLqDjvdsPtSTnYWWjpX-g&ust=1364756178263844


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LCD (Liquid Crystal Display)

A liquid crystal display (LCD) is a thin, flat electronic visual

display that uses the light modulating properties of liquid

crystals.

The LCD display used in the project is 16X2.

We use this display to show the SIN()and Current value.


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Choke Coil

An electromagnetic coil (or simply a "coil") formed when a

conductor (usually a solid copper wire) is wound around a core

or form to create an inductor or electromagnet

Used as an inductive load in the project which absorbs reactive

power; which is to be computed
http://upload.wikimedia.org/wikipedia/commons/2/2a/Ressort_de_compression.jpg


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Circuit Diagram


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DESCRIPTION

This circuit consists of DC power supply unit, zero voltage crossing

detectors, Micro-controller, LCD display, Relays and Load circuit

For the calculation of the SIN()by the Micro-controller we need

digitized voltage and current signals

The micro-controller calculates the time difference between the zero

crossing points of current and voltage

Sends information regarding time difference between current and

voltage and SIN()to the LCD display to display them


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Advantages

Advantages of reactive power measurement includes:

Actual total energy delivered to low tension consumers can be

computed

Revenue can be improved (if applied)


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Disadvantages

Initial Investment required is more

Implementation is little bit complex


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Future Scope

Incorporating reactive power measurement in the

energy meter for low tension consumers.


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Conclusion

By adopting the above technology total actual

power delivered to the domestic loads can be

computed and billing can be done accordingly.


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Reactive Power Computation

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