Mr. Veerabrahmam from PRDC has spoken about the transformers failures and few of the case studies. Few failures and reasons for failures are also discussed.

1. TRANSFORMER FAILURES AND
CASE STUDIES
By
Veerabrahmam Bathini
Power Research & Development Consultants Pvt. Ltd.,
#5, 11th Cross, 2nd Stage, West of Chord Road,
Bangalore – 560086, Karnataka, India

2. OUTLINE
• Classification of Transformer Failures
• Major Failures in Transformers
• Design Aspects of Transformers
• Protection of Transformers against Problems
• Case Studies
• Conclusions

3. Classification of Transformer Failures
1. Failure Attributed by Users
 Prolonged over loading
 Single phase loading
 Un-balanced loading
 Faulty terminations
 Power theft by hooking
 Faulty earth connection to tank body as well as LV terminal
 Failures due to external short-circuit
 Less maintenance
 Improper installation

4. Classification of Transformer Failures
2. Failure Causes at Manufacturer’s end
 Faulty design
 Poor quality of material
 Bad workmanship
 Improper transportation
 Sharp edges of conductor
 Incomplete drying
 Bad insulation covering on conductor
 Improper joints or connection

5. Fig. 1. Winding Insulating Process
Fig. 2. Improper Joint

6. Classification of Transformer Failures
3. Failure During Working Condition
 Deterioration of oil
 Faults in magnetic circuit
 Inadequate pre shrinkage of the winding
 Inter turn faults
 System Transients and Overvoltages,

7. Fig. 3. Failure due to Moisture
content in Oil
Fig. 4. Internal Faults

8. Fig. 5. Core Insulation Failure Fig. 6. Failure due to Paper Block
Shrinkage

9. Transients in Power Systems
10-4
10-3
10-2
10-1
100
101
102
103
104
105
106
Frequency f in Hz
FrequencyRange2FrequencyRange1
Very Fast Transients, SF6 Transients
Fast Transients, Lightning
Slow Front Transients, Switching
Temporary Overvoltages, ferroresonance
Steady State Overvoltages
Subsynchronous resonance
Transient Stability: Machine–rotor
Dynamics
Interarea Oscillations
Mid term & long term Stability:
Automatic Generation Control
ElectromagneticPhenomenaElectromechanicalPhenomena

10. Classification of Overvoltages
• Steady state
• Temporary
• Slow front
• Fast front
• Very fast front

11. Major Failures in Power Transformers
• Winding Failure
• Bushing Flashover
• Tap Changer Failure
• Core Failure
• Tank Failures
• Protection System Failure
• Cooling System Failure

12. Design Aspects of Power Transformers
• Accurate electromagnetic field calculations
—Minimization eddy and stray losses
—High rate of loss capitalization
• Withstanding against system Overvoltages
—Reliable high voltage insulation design
• Stray loss evaluation and Control
• Short Circuit Stresses and Strength
—Analysis of Dynamic Behavior
• Elimination of hotspots in
—Core , Winding and structural parts
• Robust Structural Design
—Seismic withstand, transport induced stresses
• Design of Cooling Systems
• Lower Noise Levels

13. Protection of Transformers against
problems
• Overfluxing Conditions
• Part winding resonance
• System generated Overvoltages
(FFO,VFTO, SFO)
• Ferroresonance
• Power System harmonics
• Geomagnetic Disturbances
• Static electrification phenomenon

14. Case Studies
• Bushing Failure due to combustible gases formation in Oil

15. Case Studies
• Transformer failure due to Part winding resonance

16. Case Studies
• Transformer Insulation Failure Wind Energy Applications

17. Conclusions
• Proper Design
• Proper Workmanship
• Proper Maintenance
• Properly rated Surge Protective Devices
• Protective Relays

18. Discussions?