NATIONAL TRANSMISSION & DESPATCH COMPANY (NTDC) LIMITED PAKISTAN High Voltage Voltage AND SHORT CIRCUIT LAB RA!AT
I"te#"$hi% Re%o#t
S'itte B*+ Muhammad Mohsin
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Co"te"t$ Abstract:...........................................................................................................................................2 1.0 Introduction:..............................................................................................................................3 1.1.1 Type Test:............................................................................................................................3 1.1.2 Routine Test:.......................................................................................................................3 1.1.3 Special Test:........................................................................................................................3 1.2 Generator:..................................................................................................................................3 2.0 Observations:.............................................................................................................................5 2.1 Tests:......................................................................................................................................5 2.1.1 i!!erentiation on t"e #asis o! Test Type:............................................... ........................5 2.1.2 i!!erentiation on t"e #asis o! Section Type:.................................................................5 2.2 S"ort $ircuit Test:......................................................................................................................% 2.2.1 S"ort $ircuit Testin& 'acilities:..............................................................................................( 2.3 Trans!or)er Turn Ratio Test:................................................................ .................................. ...( 2.* Resistance:.................................................................................................................................+ 2.5 ,o -oad -osses:................................................................................ ..................................... 10 2.One /inute oer 'reuency it"stand Test:........................................................................11 2.% Induce Over 4olta&e Test:........................................................................................................12 2.( li&"tnin& i)pulse Test:.............................................................................................................13 3.0 $onclusion:..............................................................................................................................1* *.0 Re!erences:..............................................................................................................................15
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A'$t#a,t+ In High Voltage And Short Circuit Lab Rawat, diferent types o test are perormed to chec! the de"ices by applying diferent #eld conditions$ Ater the tests, it is chec!ed that either the de"ice has withstood the test or not$ In short Circuit test all the routine test%&ransormer &urn Ratio, 'inding Resistance, (o Load Losses etc) are to be perormed beore and ater the short circuit test$ *eore short Circuit Routine test con#rms that either transormer is #t or short circuit test or not and Ater short circuit Routine test con#rms that either the de"ice has withstood short circuit or not$
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-./ I"t#o,tio"+ High Voltage and short circuit lab is used to test the diferent de"ices by applying ma+imum se"ere condition on the de"ice$ I de"ice withstand with the condition then test is said to be passed otherwise test is said to be ailed$ Ma+imum se"ere conditions are those conditions that can actually be happened with de"ice in the #eld$ &here are two sections in the High Voltage and Short Circuit labs$ $ High -ower .$ High Voltage /or con#rming the speci#cations and perormances o a distribution transormer it has to go through numbers o testing procedures$ &here are three types o test which are done in HV 0 SC Labs$ $ &ype &est .$ Routine &est 1$ Special &est -.-.- T*%e Te$t+
Some transormer tests are carried out or con#rming the basic design e+pectation o that transormer$ &hese tests are done mainly in a prototype unit not in all manuactured units in a lot$ &ype test o transormer con#rms main and basic design criteria o a production lot$
-.-.0 Roti"e Te$t + Routine tests o transormer is mainly or con#rming operational perormance o indi"idual unit in a production lot$ Routine tests are carried out on e"ery unit manuactured$ -.-.1 S%e,ial Te$t+ Special tests o transormer is done as per customer re2uirement to obtain inormation useul to the user during operation or maintenance o the transormer$ -.0 2e"e#ato#+ Short Circuit 3enerator in High "oltage and short Circuit Lab Can produce ma+imum "oltages o 45V%4666V)$ &his means that *
ma+imum capability o -roducing "oltages o generator is 4666V$7ther Characteristics o the generator are as ollows$ $ Speed o 3enerator is 866 rpm%Radian -er Minute)$ .$ /re2uency o the 3enerator is 86H9$ 1$ 3enerator has &hree -hases and /our -oles$ :$ Ma+imum Current is 146;A$ 8$ /ield Current is ;.:A$ 4$ <+citing Voltages o 3enerator is 866V$ *eore the generator there is a induction motor which is used to run generator$ Initially, generator is run on almost rpm o . or =6 to .6 minutes$ &he initially low rpm is used to maintain the temperature o oil$
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0./ O'$e#3atio"$+ 0.- Te$t$+ &here are diferent tests which are done in HV 0 SC Labs$ &hese tests can be diferentiated on the basis o &est type and Section &ype$ 0.-.- Di4e#e"tiatio" o" the Ba$i$ o5 Te$t T*%e+ &here are three diferent types o tests$ Roti"e Te$t$+ $ &&R &est%&ransormer &urn Ratio &est) .$ Short Circuit &est 1$ Resisti"e LV and HV :$ 'inding Resistance%-rimary and Secondary) 8$ (o Load Losses%Iron Losses) 4$ Load Losses%Copper Losses) >$ -ower /re2uency &est ;$ Induce 7"er Voltage &est T*%e Te$t+ $ &emperature Rise &est .$ ?i@
&&R %&ransormer &urn Ratio) &est Short Circuit &est$ Load Losses &est (o Load Losses &est
8$ 'inding Resistance &est%-rimary And Secoandary)
High Voltage+ $ Lightning Impulse Voltage 'ithstand &est .$ -ower /re2uency Voltage 'ithstand &est 1$ Induce 7"er Voltage 'ithstand &est :$ -artial ?ischarge &est 8$ Radio Inuence Voltage 4$ Humidity &est >$ Salt /og &est
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0.0 Sho#t Ci#,it Te$t+ Sometimes in the #eld due to some e+ternal distortion all the phases are short circuited$ So either it will withstand that short circuit or some time or notB In HV 0 SC lab, this type o shot circuit #eld is made to test the de"ice by applying short circuit test$ *eore short circuit test some routine tests are to be done to chec! either transormer is #t or the short circuit test or not$ /irst o all &emperature o the transormer is measured$ &hen, &ransormer turn ratio is chec!ed and then winding resistance and (o Load Losses are measured$ Ater the routine tests short circuit test is to be done$ Short Circuit test is also use to #nd load losses which are also called copper losses$ /or short circuit test, we need to eed the transormer with rated current to either H& side o the transormer or to the L& side o the transormer by !eeping the other side short circuited$ As it is easy to attain rated current or HV side because current on HV side is less than the Current on LV side$ So, in short circuit test we will gi"e Rated Current to the HV side o the &ransormer$ &otal = shots o short circuit are ta!en$
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the HV side$ Ater reaching at rated current o HV side, all three instruments reading %Voltmeter, Recorded$ &he ammeter reading gi"es the primary e2ui"alent o ull load current$ As the "oltage applied or ull load current in short circuit test on transormer is 2uite small compared to the rated primary "oltage o the transormer, the core losses in transormer can be ta!en as negligible here$
0.0.- Sho#t Ci#,it Te$ti"g 7a,ilitie$+ S"ort $ircuit Generator :
4!", 86H9, 1 -hases, : -oles, 866rpm *ac!up Circuit *rea!er 1-hases, Indoor &ype, 4!V, 86H9 Ma!ing Switch 1DSingle -ole, Indoor &ype, Air *last &ype, 45V, 15A Current Limiting Reactor 45V, 86H9 EF6$6, 6$6., 6$6:, 6$6;, 6$4, 6$1., 6$4:, $.;, .$84, 8$. ?isconnecting Switch Manual 7peration with Au+iliary Switches Short Circuit &ransormer Single -hase, 7utdoor &ype, 86 MVA *asis Low Voltage High Current &ransormer I -hase, Indoor &ype, 4!"G.86VD. Main Capacitor *an! Ma+imum ?c Voltages :;65V at .$8micro /arad ma+ capacitance :6micro /arad at .65V$ Air Core Reactor /or Adusting Amplitude and re2uency o inection Current rom Main Capacitor *an!
0.1 T#a"$5o#e# T#" Ratio Te$t+ &ransormer &urn ratio test is perormed to chec! the "oltage ratio o primary to secondary windings$ In High Voltage And Short Circuit Lab, &ransormer &urn Ratio is measured by using Multi@ Amp &ransormer 7hmmeter$ &he perormance o a transormer +
largely depends upon perection o speci#c turns or "oltage ratio o transormer$ So transormer ratio test is an essential type test o transormer$ &he "oltage should be applied only in the high "oltage winding in order to a"oid unsae "oltage$ /ollowing is the procedure to perorm the test and measure the &ransormer turn Ratio by Voltage Ratio &esting$ $ /irst, the tap changer o transormer is !ept in the lowest position and LV terminals are !ept open .$ &hen apply 1 phase :8 V supply on HV terminals$ Measure the "oltages applied on each phase %-hase to phase) on HV and induced "oltages at LV terminals simultaneously$ 1$ Ater measuring the "oltages at HV and LV terminals, the tap changer o transormer should be raised by one position and repeat test$ :$ Repeat the same or each o the tap position separately$
/ollowing is the procedure to perorm the test and measure the &ransormer turn Ratio by &urn Ratio &esting $ &ransormer ratio test can be done by &ransormer &urns Ratio Meter %Multi Amp &ransormer 7hmmeter)$ It has in built power supply, with the "oltages commonly used being "ery low, such as ;, 6 V and 86 H9$ .$ &he HV and LV windings o one phase o a transormer %i$e$ R@ 0 r@n) are connected to the instrument$ 1$ Values are recorded at each tap in case o tapped windings and then compared to calculated ratio at the same tap$ &ransormer turn ratio is calculated by the ollowing ormula TTR=
AB an
&he allowable tolerance in the "alue is J@6$8K$
0.8 Re$i$ta",e+ 'inding resistance measurements in transormers are undamental importance or the ollowing purposes $ Calculations o the I.R component o conductor losses$
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.$ Calculation o winding temperature at the end o a temperature test cycle$ 1$ As a base or assessing possible damage in the #eld$ &ransormers are subect to "ibration$ -roblems or aults occur due to poor design, assembly, handing, poor en"ironments, o"erloading or poor maintenance$ Measuring the resistance o the windings assures that the connections are correct and the resistance measurements indicate that there are no se"ere mismatches or opens$ Many transormers ha"e taps built into them$ &hese taps allow ratio to be increased or decreased by ractions o a percent$ Any o the ratio changes in"ol"e a mechanical mo"ement o a contact rom one position to another$ &hese tap changes will also be chec!ed during a winding resistance test$ &he resistance o the transormer is measured to chec! the ?C resistance o the windings o the transormer$ &he ?C "oltage gi"en or this purpose ha"ing such magnitude that should not afect the inter turn insulation o the windings$ &he resistance is measured rom both H& side o the transormer and also rom the L& side o the transormer$ In HV and SC Lab, the output "alues o resistance is then con"erted into .6C ater the "alues ta!en at ambient temperature in order to compare these "alues with -ost Short Circuit resistance "alues$ *eore measurement the transormer should be !ept in 7// condition without e+citation at least or 1 to : hours$ ?uring this time the winding temperature will become e2ual to its oil temperature$ Measurement is done with ?C$ &o minimi9e obser"ation errors, polarity o the core magneti9ation shall be !ept constant during all resistance readings$ Voltmeter leads shall be independent o the current leads to protect it rom high "oltages which may occur during switching on and of the current circuit$ &he readings shall be ta!en ater the current and "oltage ha"e reached steady state "alues$ In some cases this may ta!e se"eral minutes depending upon the winding impedance$ &he test current shall not e+ceed 8K o the rated current o the winding$ Large "alues may cause inaccuracy by heating the winding and thereby changing its resistance$ 11
0.9 No Loa Lo$$e$+ &hese are also called iron losses or core losses$ &he test method which is used to calculate these losses is called open circuit test$ And to calculate these losses we need to apply rated "oltage either to H&%666) side or L&%:8) side$ AS it is easy to attain :8 "olts instead o 66 "olts so we will apply rated "oltage to L& side o the transormer$ Core is made up o NColled Rollen 3rain 7riented Silicon SteelO sheet material$ &hese are #+ed losses irrespecti"e o load$ Iron losses is urther classi#ed into losses$ )HysteresisLosses &o reduce this losses ,silicon steel is used$ .)
&he HV side o the transormer is !ept open$ (ow with the help o "ariac, applied "oltage gets slowly increased until the "oltmeter gi"es reading e2ual to the rated "oltage o the LV side$ Ater reaching at rated LV side "oltage, all three instruments reading %Voltmeter, Ammeter and 'attmeter readings) are recorded$
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0.:O"e Mi"te Po6e# 7#e;e",* !ith$ta" Te$t+
0.< I",e O3e# Voltage Te$t+
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&he test is basically used to chec! inter turn insulation o the windings$ 'e need to apply double the "oltage and double the re2uency to LV side by !eeping HV side open Circuited$ Here at HV0SC Lab, there is phase generator with .66 H9 re2uency$ &est "oltage applied to LV side can be calculated as ollows$ Voltage F :8G √ 3 F.:6D. F:;6V (ow :;6 test "oltage will be applied by !eeping re2uency : times o the rated re2uency as shown in #gure i$e 86H9D: F .66H9$ &he time re2uired or this test is calculated by using ollowing ormula$ Rated Frequency∗120 T = Test Frequency
sec
i$e or 66H9 the time re2uired will be 46 sec or minute and i$e or .66H9 the time will be 16 sec 6r 6$8min$
0.= light"i"g i%l$e Te$t+ Lighting is a common phenomenon in transmission lines because o their tall height$ &his lightning stro!e on the line conductor causes impulse "oltage$ &he terminal e2uipment o transmission line such as power transormer then e+periences this lightning impulse "oltages$ Again during all !ind o online switching operation in the system, there will be switching impulses occur in the networ!$ &he magnitude o the switching impulses may be about 1$8 times the system "oltage$ Insulation is one o the most important constituents o a transormer$ Any wea!ness in the insulation may cause ailure o transormer$ &o ensure the efecti"eness o the insulation system o a transormer, it must con#rms the dielectric test$ *ut the power re2uency withstand test alone can not be ade2uate to 1*
demonstrate the dielectric strength o a transormer$ &hat is why impulse test o transormer perormed on it$ *oth lightning impulse test and switching impulse test are included in this category o testing$ Light"i"g I%l$e+ &he lightning impulse is a pure natural phenomenon$ So it is "ery diQcult to predict the actual wa"e shape o an lightning disturbance$ /rom the data compiled about natural lightning, it may be concluded that the system disturbance due to natural lightning stro!e, can be represented by three basic wa"e shapes$ ) /ull wa"e .) Chopped wa"e and 1) /ront o wa"e Although the actual lightning impulse disturbance may not ha"e e+actly these three shapes but by de#ning these wa"es one can establish a minimum impulse dielectric strength o a transormer$ I lighting disturbance tra"els some distance along the transmission line beore it reaches the transormer, its wa"e shape may approach to ull wa"e$ I during tra"eling, i ash@o"er occurs at any insulator o the transmission line, ater the pea! o the wa"e has been reached, the wa"e may become in orm o chopped wa"e$ I the lightning stro!e directly hits the transormer terminals, the impulse "oltage rises rapidly until it is relie"ed by a ash o"er$ At the instant o ash @ o"er the "oltage suddenly collapses and may orm the ront o wa"e shape$ &he efect o these wa"e orms on the transormer insulation may be diferent rom each other$ 'e are not going here in detail discussion o what type o impulse "oltage wa"e orms causes what type o ailure in transormer$ *ut whate"er may be the shape o lightning disturbance "oltage wa"e, all o them can cause insulation ailure in transormer$ So lighting impulse test o transormer is one o the most important type test o transormer$&his test is applied or $. micro sec ront time with 16K tolerance and 86 micro second retail time with .6K tolerance$ S6it,hi"g I%l$e+
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&hrough studies and obser"ations re"eal that the switching o"er "oltage or switching impulse may ha"e ront time o se"eral hundred microseconds and this "oltage may be periodically damped out$ &he I
1./ Co",l$io"+ In High Voltage And Short Circuit Lab Rawat, diferent types o test are perormed to chec! the de"ices by applying diferent #eld conditions$ Ater the tests, it is chec!ed that either the de"ice has withstood the test or not$ In short Circuit test all the routine test%&ransormer &urn Ratio, 'inding Resistance, (o Load Losses etc) are to be perormed beore and ater the short circuit test$ *eore short Circuit Routine test con#rms that either transormer is #t or short circuit test or not and Ater short circuit Routine test con#rms that either the de"ice has withstood short circuit or not$
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8./ Re5e#e",e$+ "ttp:.electrical*u.co)trans!or)er6indin&6resistance6)easure)ent !INDIN2 RESISTANCE TEST SET MODEL !RT>-// Ma"al
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