Distribution Transformers - Energy Efficiency & Reliability

Transcription

1 Distribution Transformers - Energy Efficiency & Reliability

2 India Transformers Market Third world s largest transformer market ( ) Distribution 80,000 MVA Power 178,000 MVA Compounded production growth rate - 10% ( ) Distribution transformer installed stocks growth rate 6.4% ( ) Exceeding 5 million distribution transformers, 400 million kva s powering India Total distribution transformer assets valuation > INR 50,000 Crores 2 Distribution Transformers Energy Efficiency & Reliability

3 Reliability A concern Distribution Transformer failure rate ~ 13% (Ranging from 0.8% to 22%) Urban - 0.8% to 4% Rural 6% to 22% Approx. 70% repaired, balance replaced Approx. additional cost to distribution sector - INR 5,000 Crores Repair - INR 3,000 Crores Replacement INR 2,000 Crores Approx. additional burden to consumer 6.5 Paisa per unit!! 3 Distribution Transformers Energy Efficiency & Reliability

4 Material Usage & Industry More than 400 manufacturers, 75% Small & medium enterprises Utility market share > 94% Unhealthy competition Material quality Seconds & scrap CRGO Recycled insulating oil Compliance Major issue 4

5 Government Regulation & Standards Government of India Copper Control Order Distribution transformer up to 200 kva Aluminum wound Copper Control Order withdrew Urban utilities & industries Copper wound distribution transformers Mandatory Energy Performance Standards Rural utility Copper winding share 57% (up to 300 kva) and 100% for higher rating Urban utility & industry copper winding share 100% 5

6 Why High Failure Rate? Management Maintenance? Lowest first price purchases Man Poor Design, Workmanship Machine SME mfgs, process control? High Failure Rate 6 Monitoring? Measurement Substandard material, Al winding Material Frequent switching, Cold pickups Method

7 HT Aluminum Coil Most Vulnerable HT Coil damaged towards inner side HT Coil damaged from inner side moved to outer side HT Coil damaged towards center HT Coil damaged maximum from inner side 7 HT Coil damaged maximum from inner side HT Coli deformed and damaged from inner side

8 HT Coil Failures HT coil deformed badly from inner side HT coil damaged heavily from inner side HT coil damaged maximum on inner side HT coil damaged on top and maximum from inner side 8 HT coil deformed badly and punctured at middle of the coil width HT coil damaged badly from inner side

9 Why HT Coil? Three types of stresses Thermal Stress Electrical Stress & Partial Discharges Mechanical Stress Smaller cross-section area Important mechanical properties always ignored by electrical designer & manufacturing process designer Metal fatigue Stress & stain Elasticity of metal Elastic limit Metal Creep Endurance limit 9

10 Failure Mechanism Due to Creep in HT Winding Conductors Radial spacers arrangement in transformer HT windings Progressive creep strain reducing specified clearance in adjacent windings between radial spacers 10

11 Creep Test HT Winding Conductor Test Set-up 11

12 Creep Curves of Aluminum HT Winding Conductors 12

13 Creep Curves Copper HT Winding Conductors 13

14 Creep Test HT Winding Copper Vs Aluminium Temperature ( C) Stress (MPa) Time (hours) elapsed to start tertiary creep stage EC grade Electrolytic Aluminum Copper wire wire Not observed till 3000 hours Not observed till 3000 hours Time (hours) elapsed to fracture of the wire EC grade Electrolytic Aluminum Copper wire wire Not 3070 observed till 3000 hours Not 1180 observed till 3000 hours

15 Steady State Creep Rate Temperature ( C) Stress (MPa) Steady state creep rate (per hour) EC grade Aluminum wire Electrolytic Copper wire x x x x x x x x

16 Failure Mechanism Due to Fatigue in HT Winding Conductors Radial spacers arrangement in transformer HT windings Cyclic loading in the innermost loose HV winding conductor 16

17 Fatigue Test HT Winding Conductor Test Set-up Maximum Stress Minimum Stress 17

18 Fatigue Test Copper Vs Aluminium Conductor Aluminium Copper 18

19 Conclusion Creep and fatigue in HT winding conductors greatly affect the performance of the transformers. The steady state creep rates higher for Aluminium conductors than Copper conductors The fatigue and creep in HT winding conductors affect the performance of the Aluminum wound transformers more than Copper wound transformers. The fatigue life of HT winding conductor corresponding to particular stress have been related with the failure tendency of the distribution transformers. 19

20 Conclusion The life of the Copper wound distribution transformers is found more than Aluminum wound distribution transformers fracture indicating the significant elongation prior to fracture. The fatigue curves & creep curves of conductors must be included at the design & production process for producing reliable distribution transformers of improved life. The fatigue curves help in selecting suitable diameter of HT winding conductors Copper is the best choice of conductor for HT winding 20

21 Thank you 21