T.F Testing&Protection
Transcript of T.F Testing&Protection
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INTRODUCTION
A Transformer is electro static device used for transferring power from one circuit to another without change in frequency.
Working principle of a transformer:-It works on the principle of mutual induction
EMF equation of transformer:-
,
RMS value of emf induced intransformer is ,
E=4.44fNB mA
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(b) copper losses:-y C opp er loss (I2R plus str a y loss) is measured b y the
sho rt- circuit test .Maximum eff icien c y of tr ans former occu rs when
Iron loss=C opp er loss
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TRANS F OR ME R F AI L UR E S
F ailures due to faults arising in the transformer called internalfailures.
F ailures due to faults occurring on any part of the system beyondthe transformer called external failures.
I nternal F ailures:-The causes for internal failureof transformer are due to
1. Earth faults2.Phase to phase faults
3 . Interterm faults4. Core faults5 . Tank faults
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winding in sulat ion fa ilure:-y Ins ula ti on is recognize d as one of the most impo rt ant
constr ucti onal elements of a tr ans former. Its ch ief function is to con f ine the current to use ful pa ths, preventin g its flowint o ha rmful cha nne ls.
y The mo st diff icult tr ans former win din g fault for which topro vide prote cti on is the fault tha t initi all y inv ol ves on l y one turn . Initi all y, the ins ula ti on breakdow n leads tointern al arcin g, which res ults int o a low cu rrent, high
imp edance fault .
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Ex ter n al Fa ilures:-y 1. O ver loady 2. O ver v oltage
i) Trans ient Surge VoltageTransient o ver v oltage arise f rom s witch in g and
lightnin g dist urbances and are liable to cau se inter-t urn faults .
ii) Power Frequency over VoltagePower f req uen c y o ver v oltage causes bo th an in crease
in stress on the ins ula ti on and a p ropo rti onate in crease in the workin g flux.
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TRANS FORM ER TESTSy W ind ing res istance testy Load testy
Open c ircu it testy Short c ircu it testy Polar ity test
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W inding res ista n ce test:-y This is nothin g bu t the resist ance measurement of the win din gs b y appl ying a small d.c v oltage to the win din g andmeasurin g the current through the same.
Load test:-y L oad Test helps to deter m ine the total loss tha t takes place,
when the tr ans former is loaded.
L oad test is used ma in l y ,
1.to deter mine the rate d load of the mach ine and the te mp erature rise 2. to deter m ine the v oltage regulati on and eff icien c y of the tr ans former.
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O pen circuit test:-By conducting this test we can find out the core losses.
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Sh ort c ircu it test :-
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B y conduc tin g this test we can f in d ou t the copp er losses .
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P olar ity test:-y
This is nee ded for identi f ying the prima ry and secondary pha sor pola rities . It is a mu st for pol y pha se conne cti ons .Both a.c. a nd d.c m et hod s can be used for dete ctin g the pola rities of the in duced emf s.
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TRANS FORM E R P ROTEC TI ON
G as Operated (Buccholz ) R elay:-y The re la y serves as ma in prote ction for any min or or
majo r faults t ha t ma y deve lop insi de a tr ans former.y Such faul ts alwa ys result in gener ation of gases, which
causes t he operation of mercury s witches givin g signal
for aud ible alarm o r isolates t he tr ans former f rom the
net work.
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D iffere n t ial P rotect ion :-y The diff erenti al re la y is one t ha t operates when t he vector
diff eren ce of t wo or mo re si m ilar e lectri cal quantitiesexceed a p re- deter mine d v alue.
y Diff erenti al re la y of ty pe DTH 31/32 is emplo yed fortr ans former prote ction .
y Nomen clatureD- Diff erenti al (op eratin g quantity )T Transist or (mo vement )H Harmoni c R estr aint (appl ication )DTH 31 F or t wo win din g power tr ans former.DTH 32 For t hree win din g power tr ans former.
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Over C urre n t a nd Eart h FaultP rotect ion :-
y Dire ctional inverse ti me o ver current and eart h faul t re la ys of ty pe C DD is emplo yed for tr ans former prote cti on against o ver currents .
Nomen clatureC C urrent operate d (op eratin g Qua ntity )D Induc ti on T y pe (Mo vement )
D Dire ctional (Appl ication )y Dire ctional re la ys are a v ailable in sin gle pole versi on on l y .
These pro vide backup fo r the ma in prote cti on of IC Ts.
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Restr icte d Eart h Fault P rotect ion :-y A simple o ver current and eart h faul t syste m will not
give good p rote ction co ver for a st ar- conne cte d
prima ry win din g, parti cula rl y if the ne utr al is eart hedthrough impen den ce.y The restri cte d eart h faul t prote ction schema tic shown
in f igure imp ro ves the degree of prote ction very much.
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Conclusion:-
From this project, it is clear t ha t t he powertr ans former is one of the very i mpo rt ant lin ks in a powertr ans missi on and d istri bu ti on syste m.
A tr ans former fault will cause a large interr up tion inpower s uppl ies and the impac t is mo re seri ous than atr ans missi on line ou tage and also cau ses damag e to powersyste m st ab ility .
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Thank youThank you
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