A TECHNICAL PAPER ON

POWER QUALITY

Authorised BySANTOSH BHARADWAJ REDDYEmail: help@matlabcodes.comEngineeringpapers.blogspot.com

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CONTENTS

INTRODUCTION

COMMON POWER PROBLEMS

WHAT ARE HARMONICS

FACTORS EFFECTING POWER QUALITY

POWER CONDITIONING

ABOUT UPS

ABOUT SURGE PROTECTOR

ABOUT CAPACITOR

ABOUT LIGHTENING ARRESTOR

ABOUT ELECTRONIC FILTER

CONDITIONING OF HARMONIC MITIGATION

CONCLUSION

POWER QUALITY

ABSTRACT

The electrical power in a D C Circuit the power is given by the product of applied voltage

and the electric current in watts.

P = VI

Power = Voltage x Current

Watts=Volts x amperes.

Our paper firstly gives introduction of electrical powerand later deals with the common

power problems that leads to poor qualitative power.Later it describes what harmonics

mean which play key role in quality of power.And next to it ,it gives factors effecting

power quality.conditioning of power i.e, method for improving power quality are

described.In part of it ,it gives note on ups,surge protector,capacitor,lightening arrestor

and electronic filters that have key role in providing high qualitative power to the

electrical system. More over we have to control harmonics.So methods of harmonic

mitigation are also described.Some pictures that gives information about distribution of

power and pictures of ups,surge protector,capacitor,lightening arrestor,low pass and high

pass filters are shown.how perfect and safe electrical power system is also given.We

come across methods like phase staggering,use of active filters for removing harmonics.It

also introduce some words like sag,dip,swell that have their own importance in causing

poor qualitative power.

INTRODUCTION

A perfect power supply would be one that is always available, always within voltage and

frequency tolerances, and has a pure, noise-free sinusoidal wave shape. In the real world,

unfortunately, there are five principal deviations from this perfection that affect power

quality: harmonic distortion; blackouts; under or over voltage; dips (sags) and surges; and

transients.

COMMON POWER PROBLEMS

There are various common power problems.

1. Power failure — Total loss of utility power: Causes electrical equipment to

stop working.

2. Voltage sag — Transient under-voltage: Causes flickering of lights.

3. Voltage spike — Transient over-voltage i.e. spike or peak: Causes wear or

acute damage to electronic equipment.

4. Under-voltage (brownout) — Low line voltage for an extended period of

time: Causes overheating in motors.

5. Over-voltage — Increased voltage for an extended period of time: Causes

light bulbs to fail.

6. Line noise — Distortions superimposed on the power waveform: Causes

electro magnetic interference.

7. Frequency variation — Deviation from the nominal frequency (50 or

60 Hz): Causes motors to increase or decrease speed and line-driven clocks and

timing devices to gain or lose time.

8. Switching transient — Instantaneous under voltage (notch) in the range of

nanoseconds: May cause erratic behavior in some equipment, memory loss, data

error, data loss and component stress.

9. Harmonic distortion — Multiples of power frequency superimposed on the

power waveform: Causes excess heating in wiring and fuses.

WHAT ARE HARMONICS?

Harmonics are currents, usually in multiples of the supply fundamental frequency,

produced by ‘non-linear’ loads such as the AC to DC power conversion circuits.These

power conversion circuits draw only short pulses of current from the supply network and

combine with the source impedance resulting in distortion of the supply voltage.

A view of distribution of electric power.

Electrical power is distributed via cables and electricity pylons like these in

Brisbane, Australia.

FACTORS EFFECTING POWER QUALITY

Power quality is a term used to describe electric power that motivates an electrical load

and the load's ability to function properly with that electric power. Without the proper

power, an electrical device (or load) may malfunction, fail prematurely or not operate at

all. There are many ways in which electric power can be of poor quality and many more

causes of such poor quality power.

No real life power feed will ever meet this ideal. It can deviate from it in the

following ways (among others):

1. Variations in the peak or RMS voltage are both important to different types of

equipment.

2. When the RMS voltage exceeds the nominal voltage by 10 to 80% for 0.5

cycle to 1 minute, the event is called a "swell".

3. A "dip “or a "sag" is the opposite situation: the RMS volage is below the

nominal voltage by 10 to 90% for 0.5 cycle to 1 minute.

4. Random or repetitive variations in the RMS voltage between 90 and 110% of

nominal can produce a phenomina known as "flicker" in lighting equipment.

Flicker is the impression of unsteadiness of visual sensation induced by a light

stimulus on the human eye.

5. Abrupt, very brief increases in voltage, called "spikes", "impulses", or

"surges", generally caused by large inductive loads being turned off, or more

severely by lightning.

6. "Undervoltage" occurs when the nominal voltage drops below 90% for more

than 1 minute. The term "brownout" is an apt description for voltage drops

somewhere between full power (bright lights) and a blackout (no power - no

light). It comes from the noticeable to significant dimming of regular

incandescent lights, during system faults or overloading etc., when insufficient

power is available to achieve full brightness in (usually) domestic lighting..

7. "Overvoltage" occurs when the nominal voltage rises above 110% for more

than 1 minute.

8. Variations in the frequency

9. Variations in the wave shape - usually described as harmonics

10. Nonzero low-frequency impedance (when a load draws more power, the

voltage drops)

11. Nonzero high-frequency impedance (when a load demands a large amount of

current, then stops demanding it suddenly, there will be a dip or spike in the

voltage due to the inductances in the power supply line)

POWER CONDITIONING

• Power conditioning refers to conditioning the power to improve its quality.

An uninterruptible power supply can be used to switch off of mains power if there

is a transient (temporary) condition on the line. However, cheaper UPS units

create poor-quality power themselves, akin to imposing a higher-frequency and

lower-amplitude sawtooth wave atop the sine wave.

A surge protector or simple capacitor can protect against most overvoltage

conditions, while a lightning arrestor protects against severe spikes.

Electronic filters can remove harmonics.

Solutions to power quality problems include using larger neutral conductors to handle

harmonic loads, better grounding systems to dissipate transients and lightning.

ABOUT UPS

An Uninterruptible Power Supply (UPS), also known as an Uninterruptible Power

Source, Uninterruptible Power System, Continuous Power Supply (CPS) or a battery

backup is a device which maintains a continuous supply of electric power to connected

equipment by supplying power from a separate source when utility power is not

available. There are two distinct types of UPS: off-line and line-interactive (also called

on-line).

An off-line UPS remains idle until a power failure occurs, and then switches from utility

power to its own power source, almost instantaneously. An on-line UPS continuously

powers the protected load from its reserves (usually lead-acid batteries or stored kinetic

energy), while simultaneously replenishing the reserves from the AC power.

The on-line type of UPS, in addition to providing protection against complete failure of

the utility supply, provides protection against all common power problems, and for this

reason it is also known as a power conditioner and a line conditioner.

A small free standing ups

ABOUT SURGE PROTECTOR

A surge protector is an appliance designed to protect electrical devices from voltage

spikes. A surge protector attempts to regulate the voltage supplied to an electric

device by either blocking or by shorting to ground voltages above a safe threshold.

A view of surge protector

ABOUT CAPACITOR

A capacitor is an electrical/electronic device that can store energy in the electric field

between a pair of conductors (called "plates").

Various types of capacitors. From left: multilayer ceramic, ceramic disc, multilayer

polyester film, tubular ceramic, polystyrene, metallized polyester film, aluminium

electrolytic.

ABOUT LIGHTENING ARRESTOR

Lightning arresters, also called surge protectors, are devices that are connected between

each electrical conductor in a power and communications systems and the Earth.

These provide a short circuit to the ground that is interrupted by a non-conductor,

over which lightning jumps. Its purpose is to limit the rise in voltage when a

communications or power line is struck by lightning.

"Lightning-Protector"

An early type of dissipater-arrester, which the patent states to prevent and safely

dissipate lightning strikes

ABOUT ELECTRONIC FILTER

Electronic filters are electronic circuits which perform signal processing functions,

specifically intended to remove unwanted signal components and/or enhance wanted

ones. Electronic filters can be:

• passive or active

• analog or digital

• discrete-time (sampled) or continuous-time

• linear or non-linear

• infinite impulse response (IIR type) or finite impulse response (FIR type)

T filter

Pi filter

A view of passive filters

CONDITIONS OF HARMONIC MITIGATION

Phase Staggering

1. Phase staggering is simply the phase shifting of individual loads such that the

harmonics produced by one or more loads cancels the harmonics produced by

others.

2. For phase staggering to be successful at least two balanced loads of similar ratings

are required.

Active Filters

AIM (active injection mode) Filter

1. AIM filters are the most technically advanced and effective solution in reducing

the total harmonic current distortion to below 5%.

CONCLUSION

The perfect power system will provide a significantly more robust system that can

respond to weather ,aging and other threats,ensuring power during

emergencies.Inaddition the perfect power system will automate high voltage switching

throughout the electrical system.,eliminating equipment damage resulting from human

error.