Voltage Sag

Voltage Sag

 What is V

 What is V

oltage Sag ?

oltage Sag ?



 _{Sag ( dip ) is the reduction in rms voltage orSag ( dip ) is the reduction in rms voltage or}

current at the power frequency with a magnitude current at the power frequency with a magnitude between 0.1 to 0.9 pu within the time duration of between 0.1 to 0.9 pu within the time duration of 0.5 seconds  1 minute.

0.5 seconds  1 minute.



 _{Sources Sources ! ! "a"ault ult ( ( short short circuit circuit system) system) StartingStarting}

large loads ( electric motors # arc furnaces # etc ) large loads ( electric motors # arc furnaces # etc )

 Voltage sag Sources



_{Short $ircuit on lines %ower transmission}

or distribution systems



_{Starting of large motor}

Short circuit sources

 &ightning stro'e

 ver voltage (lightning surge  switching surge) will caused electrical strees on isolator that

e*ceed of brea'down voltage strength and lead to isolator brea'down

  +egradation of insulation (present of pollutants materials# corrosion# moisture # aging factors# etc.) resulting in decreased brea'down voltage strength of insulator

 _{,echanical factor (short circuit between two}

conductors through contacts a foreign ob-ect such as an animal  bird or equipment )

Direct lightning strikes on transmission line will cause the voltage wave form of the voltage transient impulses with

steep front time and will propagate towards the substation. /nsulator through which these waves will

e*perience a high electric field stress

Lightning

Strike

ne of the main problems that have been found is the effect produced by pollution in the insulators of electric lines. his

pollution is one of the main causes of flashover in the insulators and

finally will cause short circuit

he present of pollutant in line transmission insulator

The eect of short circuit

1. t the point of fault

 +estructive arcing insulators and conductors  "ire

2 /n a circuit faulted

 3lectrodynamic force can result in deformation of the busbar and cable disconnection

4 igh temperatures can cause damage to the insulator 6 /n another circuit close with a circuit of interrupted

 Sag voltage

 malfunction control and monitoring circuit

 System instability or loss of synchroni7ation on synchronous machine

Starting large motor

 Starting of

induction motors can draw a current of 8 s  d 10 times the full load current # it is because at the time of starting of induction motors require a certain amount of energy to produce a magnetic field in overcoming the moment of inertia

Starting of induction motor (for

example)

 Arc Furnace

Arc furnace is operated in a way to connect an electric short circuit at a stack of metal resulting in arcing to the temperature exceeded 10 thousand der. used to melt the metal pile

Fault on power transmission & distribution sstems

:0; faulted on overhead lines  Stri'e lightning

 "lashover (insulation failure)  $ontact with the birds

Short circuit

Short circuit cause current flow in line became very high

because only limited by impedance line only.

For example ! voltage sag calculaton

oltage Sag deeper when short circuit fault location point is

The tpe of short circuit

 _{Symmetric short circuit !}

 ( 4 phase shor circuitt)

  _{<nsymmetric short circuit}

 %hase to earth short circuit  %hase to phase short circuit

 Ad"ustable Speed #rive

oltage sag will cause dc lin' circuit of S+s e*perience trip

%rogammable ogic $ontroller

(%$)

For example : The efect o voltage sag

"ault at point "4 will generate 0; voltage sag at load 4# 86; at load 2 and 9=; at load 1.

"ault at point "1 will generate voltage sag 0; at load 1 and 50; for all loads

#uration of voltage sag



+uration of voltage sag depends on the

time required by the protection equipment

to detect and isolate fault# generally a few

hundred miliseconds

The Solution of voltage sag



_{$ustomer side}



>y manufacturer of electrical equipments

_{>y utility}

Solution b consumers

$onsumers add aditional equipment such

as power conditioneer on critical loads

Tpes of %ower $onditioneer

Tpes of %ower $onditioneer



 _{"erroresonance ransformers ($s)"erroresonance ransformers ($s)}



 _{<%S (<ninterruptible %ower Supply)<%S (<ninterruptible %ower Supply)}



 _{+ip %roof /nverter (+%/)+ip %roof /nverter (+%/)}



 _{oltage +ip $ompensator (+$)oltage +ip $ompensator (+$)}



 _{Superconducting ,agnetic 3nergy Storage +eviceSuperconducting ,agnetic 3nergy Storage +evice}

(S,3S) (S,3S)



Ferroresonance

Ferroresonance

Transformer

Transformer





_

_{rransformer}

_{ansformer "erroresonance also}

_{"erroresonance also referred}

_referred

to as $onstant oltage ransformers

to as $onstant oltage ransformers

($s) can overcome the problem of

($s) can overcome the problem of

voltage dips. he transformer has a ratio

voltage dips. he transformer has a ratio

of 1! 1 the coil be e*cited high on

of 1! 1 the coil be e*cited high on

saturation curve so that it gives a constant

saturation curve so that it gives a constant

output power and the input voltage

output power and the input voltage

changes is not affected

Ferroresonace

Ferroresonace

Transformers

haracteristic load of !"s againts Sag

!oltage

'ninterupptible %ower Suppl

('%S)

 _{3lectrical energy stored in the battery via charger rectifier.}

+$ %ower from battery is converted to $ power through an inverter to be connected to the load

 _{/f the supply of electrical energy from the utility is fault#}

n ine '%S sstem

/n both normal condition and when voltage sag occurs# load is supplied

Standb '%S ( ine '%S)

/n normal conditions the load is supplied from a source

directly# when voltage sag occurs # the load will be supplied from the <%S through an automatic switch

brid '%S sstem

$ prevent switching load to the <%S circuit until the voltage sag down to the level where the $ is no longer able to cope

The Application of '%S



<nit control systems



_{$ontrol room  ,onitors}

$omputer networ's

 Application of '%S in power

Substasion

#ip proof inverter (#%*)

<nder normal condition# the rectifier will charge the capacitor and the load is conected directly to the power supply# when sag voltage occurs# the load will be connected to the +%/ for 1 @ 4 seconds in which +%/ will supply a square wave $ voltage.

 Voltage dip compensator

(V#$)

 Voltage dip compensator

connection

Superconduction magnetic

energ storage (S,-S) device

Invete  Voltage egulato  !T" s#it$% &upe$ondu$ting Magneti$ 'C &uppl( )ote$ted load *ine Insulation s#it$%

S,-S



_{Storing electrical energy as well as <%S .}

S,3s are designed in a range of 15 ,A



_{dvantages !}

 he si7e is much smaller than the <%S

 +oesnBt need battery

 less cable connection than the <%S

 igher reability

-lectrical e.uipment

problem



_{$onsumers generally donBt 'now or}

understand the performance characteristic

of electrical equipment bought

The solution b manufacturer

1+ Manufa$tue of ele$ti$al e,uipment must in$lude in detailed

infomation a-out pefoman$e $%aa$teisti$s of t%e e,uipment against voltage sag so t%at uses $an detemine t%e t(pe of e,uipment #%i$% $oesponding to t%e desied

2+ Manufa$tue in ma.ing ne# e,uipment must -e %aving t%e po$edue #it% egad to t%e impotan$e of usa-ilit( e,uipment/ e+g+ a ele$ti$al applian$es t%at ae $iti$al of sag voltage s%ould -e designed so t%at t%e e,uipment is $apa-le of opeate popel( 0given pote$tion if t%ee is a voltage sag/ $onvesel( if t%e e,uipment is not sensitive to t%e e,uipment ma( not -e needed pote$tion against voltage sag

 Advantage for consumer



_{$onsumers 'now  understand}

performance characteristics of electrical

equipment# so can choose the apropriate

equipment

Solution of the utilit side

dvantages



 o prevent damage to the ectrical

equipment



 _{%rovide services that can providing}

satisfaction for users

+isadvantage !

*nsulator problem

 _{he pressure of the electric field (the}

Cor'ing oltage# overvoltage of lightning surge  switching surge)

 _{,echanical stresses (heavy}

conductors# windswept# icesnow)

 _{%ressure environment (rain# damp#}

dust# sand# salt# etc.) give rise to the e*istence of a thin layer of insulator surface pollutants# as result flashover voltage conductor will decline reaches 2025; of the normal voltage

Solution problem of

insulator

 _{/nstallation rrrester (protection against high}

pressure electric field of lightning surge or switching surge)

 _{shielding wire on the phase conductor}

 _{he addition of the number of suspension}

insulator to increase the strength of the dielectric material

 _{/nsulator washing}

 Arrester

rrester serves to cut the lightning impuls voltage. /n normal

conditions# the arrester acts as isulator but in abnormal conditions act as a conductor

The Addition of Arrester

 _{Denerally the arrester is placed on the protected}

equipment such as near a transformer# or placed in one pole is considered frequent lightning

stri'es. his way less effective because of

lightning flashover will cause fashover can result in short circuit

 _{Cith the addition of arrester on line will reduce}

the voltage sag because the waves would be split by lightning arester in line# so as to minimi7e the occurrence of flashover

The addition of arrester on lines power

Titi. &am-aan peti 

 2este 

Ta%anan pentana%an

gelom-ang

peti  gelom-angpeti 

Shield wire on tower o transmission lines

Dround wire transmission line aims to protect from direct lightning stri'es. he ground wire is mounted above the wire transmission line.

 Addition the number of

insulator

*solator washing

 _{/nsulation is an important part of the power}

system. /n coastal regions or areas of desert

places# /nsuations will be contaminated by dust or salt so it can descrease the insulation brea'down streangth#so flashover or brea'down voltage can occur as a result of failure of isolation# therefore insuation needs to be cleaned periodically

$utting of tree

 _{Short circuit # temporary or}

permanent faults is often

caused by trees with branches and twigs that hit the

distribution networ's # to the prevention needs to cut

+epair fault clearing



_{ddition recloser}



,odification feeder design

_{ddition networ' loop}

+ecloser

 _{,ost fault on ransmission}

lines are transient # so that power can be recovered after the multiple periods. ,ost

automatic circuit brea'ers are designed to cover the bac' in 4 or 6 times . hat circuit

brea'er in the distribution system is 'nown as the ?ecloser

 Addition recloser

-efoe adding e$lose 

3use Ci$uit 4ea.e  Main feede  &u-station 5e$lose  added 5edu$ed num-e of momenta(

inteuption