t.f testing&protection

8/6/2019 T.F Testing&Protection

1/23

1


2/23

2

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


3/23


4/23

(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

4


5/23

5

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


6/23

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 .

6


7/23

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.

7


8/23

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

8


9/23

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.

9


10/23

10

O pen circuit test:-By conducting this test we can find out the core losses.


11/23

Sh ort c ircu it test :-

11

B y conduc tin g this test we can f in d ou t the copp er losses .


12/23

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.

12


13/23

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.

13


14/23

14


15/23

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.

15


16/23

16


17/23

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.

17


18/23

18


19/23

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.

19


20/23

20


21/23

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 .

21


22/23

22

Thank youThank you


23/23

23

t.f testing&protection

Documents