Testing, Maintenace and Protection of Transformer.pptx

All About Transformer

1. TESTING, MAINTENANCE & PROTECTION OF TRANSFORMERS Engr. Shirajul Islam BSc.(EEE), MSc. (ETE, CUET) [email protected] 01845324741

2. WH A T IS A TRANS F ORMER? TRANSFORMER IS A S T A TIC DEVICE W H ICH TR A N S FO RM S A. C . ELECT R ICAL P O WER F R OM ONE V O L T A GE T O AN O THER V O L T A GE KEEPIN G THE FRE Q UE N C Y S AM E BY ELECTROMAGNETIC INDUCTION.

3. TYPES OF TRANSFORMER BY APPLICATION 1. DISTRI B U T ION T RANS F ORM E R 2.P O WER T RA N S F O RM E R 3. CUR R E NT T RANS F ORM E R 4. P O T E N T IAL T RANS F ORM E R 5. FURN A C E T RANS F ORM E R 6. B O O ST E R T RANS F ORM E R 7. R E CT IFIER T RANS F ORM E R 8. LO C OM O T IVE T RANS F ORM E R 9. MINING T RANS F ORM E R 1 .PHAS E SHIF T IN G T RANS F ORM E R 11 . WEL D ING T RA N S F O RM E R 1 2.HIGH V O L T A GE T E STIN G /S C T E STING T R F . 1 3 .G R OU N DING T RANS F ORM E RS 1 4 .CO N V E R T E R T RANS F ORM E R

4. DISTRIBUTION TRANSFORMER TRANSF O RME R WHICH IS USED FOR THE PUR P O SE OF DI S TRIBUTI O N OF P O WER. 1 1 KV / 4 3 3V is t he sta n dard v ol t a g e r a tin g . S T AN D AR D K V A r a tin g s a r e 25,63,100,160,200,250,315,400,500,630,75 , 100 , 1250,1500,2000,2500 KVA. IS-2026 is the NATIONAL I S STANDARD.

5. MAIN FEATURES OUTDOOR, O IL COO L E D , 3 PH A SE, 5 0HZ PRIMA R Y IS DE L TA C ONN E CT E D AN D SECON D A R Y IS S T A R C ONN E CT E D . N A TURA L Y COOLE D (ONAN TYPE). AMONG S T AL L THE TYPES OF TRANSF O RMER S THIS IS THE M O S T RE Q UIRED AN D MO S T USED TYPE.

6. PARTS OF TRANSFORMER MAIN T ANK RADIATORS CONSERVATOR EX P L O S ION VENT L I F TI N G L UGS AI R RE L EASE P L UG OIL L EVEL I N D I C A T OR T A P CHAN G ER WHEELS HV/ L V BUSHI N G S F I L TER V A L VES OIL F I LL I N G P L UG DR A IN P L UG CA B L E B O X

7. TESTING OF TRANSFORMER T E STING IS C A RR I E D O UT A S P E R I S -2026. R OU T INE , T Y PE T E STS & S P E CIA L T E STS R OU T INE T E STS ( T O B E CARRI E D OUT ON E A C H J OB ) 1. Me a surement of w inding r esista n ce 2. Me a surement of i ns u l a tion r esista n ce 3.Seperate source voltage withstand test (High Voltage tests on HV & LV) 4.Induced Over voltage Withstand test (DVDF test) 5. Me a surement of v olt a g e rat i o 6. Me a surement of N O L O A D LOSS & c u r r en t . 7. Me a surement of L O A D LOSS & IMPED E NC E .(EFFICIE N C Y & R E GUL A T ION) 8. V ec t or G r o u p V e r ifi c a tion 9. O i l B DV tes t. 10 . T ests on O L TC (if Atta c hed)

8. TYPE TESTS THESE TESTS AR E CA R RIE D O UT ON L Y ON ONE TRANSF O RME R OF THE L O T . Al l r o u tine t ests Additionally following tests are included in type tests L i gh t ening Im p ulse t est. T emper a t u r e r ise t est

9. SPECIAL TESTS Ad d ition a l Im p ulse test Sh o r t c i r c u it test Measurement of zero Phase sequence Impedance test. Me a su r eme n t of a c o u stic n o ise l e v el. Measurement of harmonics of the no load current. Ma g ne t ic bal a nc e tes t .

10. ROUTINE TESTS 1 . Meas u r ement of w i n d ing r esistan c e This test measu r es the r esistan c e of the HV & L V w i n d in g . The values of resistance should be balance for all three phases and sho u l d m a t c h the de sig n ed v al u e s . Equipme n t used : D i g ital r esistan c e mete r .

11. ROUTINE TESTS 2 . Meas u r ement of insul a tion r esistan c e Measures the insulation resistance of HV & LV windings with respect to earth (body) and between LV & HV winding. IN S UL A T I ON TES T ER OR M EG G ER IS USE D . Rec o mmen d ed V al u es a re 2 M o hms f o r H V & 500 M o hms for L V .

12. ROUTINE TESTS 3.Seperate source voltage withstand test (High Voltage tests on HV & L V ) - T h is test c he c ks the in s ul a tion p r o p e r ty bet w een P r ima r y to earth, Secondary to earth and between Primary & Secondary. HV high voltage test : LV winding connected together and earthed. HV windi ng con nected tog e ther an d g i v en 28 K V ( for 11KV trans fo r mer ) for 1 min u t e . LV high Voltage test : HV winding connected together and earthed. LV winding connected together and given 3 KV for 1 minute. Eq u ip m ent u s ed : High V oltage test e r ( 100 K V & 3KV )

13. ROUTINE TESTS 4.I n du c ed O v er v oltage W ithstand test ( D V D F test ) - This test c he c ks the inter tu r n insul a tion. For a 11KV/433V transformer,866 Volts are applied at the 433V winding with the help of a Generator for 1 minute.This induces 22KV on 11KV side.The frequency of the 866V supp l y is als o inc r eased to 10 H Z . Equipm e nt used : M O T OR GE N ER A T OR SET

14. ROUTINE TESTS 5.M e asu r e m ent of v oltage r a tio This test measures the voltage ratio as per the customer’s requirement. V1/V2 = N1/N2 The v oltage r a tio i s e qual to the tu r ns r a tio i n a transformer. Using this principle, the turns ratio is measured with the help of a turns ratio meter. If it is correct , then the voltage ratio is assumed to be correct. Equipm e nt used : T u r ns R a tiom e ter

15. ROUTINE TESTS 6.M e asu r e m ent of N O L O A D LOSS & c u r r ent. The iron losses and no load current are measured in this test.The 433V winding is charged at 433V supply & the 11KV w i nding is lef t open .The p o w er c onsu m ed b y the transformer at no load is the no load loss in the transformer. Effect of actual frequency must be taken into account. Equipment used :Wattmeters or power analyser.

16. ROUTINE TESTS 7 . Meas u r ement of L O A D L O S S & I M P E DE N CE.(EF F ICI E NCY & REGU L A TI O N) This test measures the power consumed by the transformer when the 433V winding is short circuited and The rated current is passed through the 11KV winding. Equipme n t used : W a t t mete r s or p o w er a na l yse r .

17. ROUTINE TESTS 8 . V ec t or G r o u p V e r ific a tion test This test verifies the Dyn-11 vector group of a distribution transformer. Equipme n t used : v ol t mete r .

18. ROUTINE TESTS Oil B D V TES T . Oil breakdown voltage is checked as per IS-335. 1 m m L X 70 m m B X 8 m m Ht. gl a ss p o t. 5 0ml Oil samp l e . S p he r ical ele c t r o d es with gap of 2.5 mm Rec o mmen d ed v al u e : 6 KV Equi p me n t used : O I L B D V TEST SE T .

19. TYPE TESTS LIG H TENING IMP U LSE TEST Al l the diel e ct r ic t e sts c he c k the insu l a tion l e v el of t he jo b . Im pul s e gener a tor is u s ed to p r o d uce the sp ecified v oltage im p ul s e w a v e of 1 . 2/ 5 mic r o secon d s w a v e One impulse of a reduced voltage between 50 to 75% of the full test voltage and subsequent three impulses at full voltage. For a three phase transformer, impulse is carried out on all three p h ase s in succes si o n . The voltage is applied on each of the line terminal in succession, k eepi n g the other te r mi n al s ea r thed. The current and voltage wave shapes are recorded on the o s cill o sc o pe an d a ny di s to r tion in th e w a v e sh ap e is the c r ite r ia for failure.

20. SPECIAL TEST Sho r t c i r c u it w i thstand a b il i ty t est. This tests measures the ability of the transformer to withstand the mechanical and thermal stresses caused by the external short circuit. HV terminals are connected to the supply bus of the testing plant.The LV is short circuited. The testing plant parameters are such adjusted to give the rated short circuit current. Supply is made on and closed after specified duration of short circuit. The record of cu r r ent w a v e f o r m is n o ted. There should not be any mechanical distortion, fire to the transformer during this test. Similarly no wave form distortion.The transformer should also withstand the r ou ti n e tests afte r t he s h o r t c i r c u it test. The reactance of the winding measured before and after the S.C. test should not v a r y b e y o n d the l i mit s st a ted in t he IS 2 2 6.

21. MAINTENANCE OF TRANSFORMER Transformer is the heart of any power system. Hence p r e v en t i v e main t en a nc e is a l w a ys c o st ef f ec t i v e and time saving. Any failure to the transformer can extremely affect the whole functioning of the organization.

22. MAINTENANCE PROCEDURE OIL : Oil level checking. Leakages to be attended. Oil BDV & acidity checking at regular intervals. If acidity is bet w een . 5 t o 1mg K OH, oil sh o uld be k e p t u n d er observation. B D V , C ol o r a nd smell of oil a re indi c a ti v e . DGA T est a n d An a l ysis

23. MAINTENANCE PROCEDURE Sludg e , dust, di r t ,moistu r e can be r e m o v ed b y filtration. Oil when topped up shall be of the same make. It may lea d to sludge fo r m a tion an d acidi c conte nt s . Insulation resistance of the transformer should be c he c k ed on c e in 6 month s . Megger v alue s alon g with oil v alue s indic a te the co n dition o f transf o r m e r . Periodic Dissolved Gas Analysis can be carried out.

24. MAINTENANCE BUSHINGS Bushings should be cleaned and inspected for any cracks. Dust & dirt deposition, Salt or chemical deposition, cement or acid fumes depositions should be carefully noted and rectified.

25. MAINTENANCE Periodic checking of any loose connections of the te r min a tions of HV & L V sid e . Breather examination. Dehydration of Silica gel if necessary. Explosion vent diaphragm examination. Cons e r v a tor to be cleane d f r om inside aft e r e v e r y th r ee years. Regula r inspection of OIL & WINDI N G TEM P ER A TU R E METER r eading s . Cleanliness in the Substation yard with all nets, vines, sh r ubs r em o v ed.

26. PROTECTION OF TRANSFORMERS The best way of protecting a transformer is to have good p r e v en t i v e main t en a nc e s c hed u l e . Oil T emper a t u r e I n dic a t o r s . Win d ing T em p er a t u r e in d ic a t o r s . Bu chholz Rel a y . Ma g ne t ic Oil l e v el Ga u g e . Ex p losi o n V e n t.

27. PROTECTION OF TRANSFORMERS HT fuse & D . O . f u s e . L T circ u it b r ea k e r . HT C i r c u it b r ea k er with O v er load , Ea r th F au l t r el a y tripping. Oil S u rge Rel a y f o r O L T C . P R V for O L T C . HORN GA P S & Ligh t ening A r r est o r . Breather.

28. FAILURES & CAUSES I n su f ficient Oil l e v el. Seep ag e of w a ter in oil. P r olo n ged O v er loadin g . Single Phase loa d in g . Unbalanced loadin g . F ault y T e r min a tion (I m p r op e r s i ze d lug s etc) P o w er Theft. P r olo n ged Sho r t C ircuit. F ault y o per a tion of tap c hanger s w i t c h. La c k of i nstall a tion c he c k s .

29. FAILURES & CAUSES F ault y design P o o r W or k ma n s h ip Imp r op er fo r m a tion of cor e . Im p r o p er cor e b o l t in s ul a tion. Bu r r to the lamin a tion b lades Improper brazing of joints. Bu r r /s h a r p edges to the windi n g con d u cto r . Inc o m p let e d r yin g . Bad ins u l a tion c o v e r in g . Ins u fficient cool i ng ducts in t he windin g .

30. FAILURES & CAUSES Bad Qua l ity of r a w m a te r ial. T ransi t da m a g ed transf o r me r s . After failure , transformer is removed and replaced with new/repaired one without removing the cause of failure whi c h r esul t s in immedi a te o r sho r t time f ailu r e .

31. Thankyou