The distribution region has a large number of distribution transformers of various powers. Any failure of these distribution transformers can cause great inconvenience to the consumers and give financial losses to the utilities, so it is crucial to avoid the transformer failure. Distribution transformers manufacturers India effectively works to overcome this issue.
Reasons for Distribution transformer’s failure and poor performance:
- Poor performance of transformer can be due to low oil level
- It can be due to draining of oil due to leakage
- The failure can be due to improper earthing of the transformer
- The failure of the transformer can be because of the frequent faults on LT (Low Tension) lines due to loose spans and leading to short circuits.
- It can be due to Mechanical failure of winding
- It can be because of improper tree clearance of LT lines
- It can be due to a defect in the breather and consequent ingress of moisture
- It can be due to the low electric strength of oil/winding insulation
- Corrosion may be there in the core laminations.
These reasons may cause poor performance and lead to transformer failure.
The other reasons can be due to improper protection due to:
- Using defective or overrated fuses
- Consistent overloading
- Not providing LAs (Lightning Arrestors)
There can also be manufacturing defects such as
- Improper or Inadequate design structure of the transformer
- Poor quality of material like a binding, tank, and other parts of the transformer
- While assembling transformers, there can be manufacturing defects done by Workman and due to imperfect short circuit withstand capacity.
All reasons for transformer failure are classified as under
- Aging/duration
- Producing defects
- Inadequate/Poor design
- Improper Workmanship
- End turn Insulation and proper sleeving
Under these factors, we can classify the transformer failure reasons.
Let’s see all these factors in detail:
- Ageing/duration
The expected life span of the distribution transformers above 100 kVA capacity is about 35 years, and up to 100 kVA capacity is about 25 years.
Experience of Distribution transformers manufacturers India shows most transformers that the failures begin to occur even before 20 years of its life.
But later, many manufacturers have adopted the cost-benefit approach in the design of transformers, just about managing to satisfy the requirements of IS specification. So, the result is that they compromise on both quality and reliability requirements of IS specification.
While the Distribution transformers Manufacturers India meet the requisite standards during the testing period before and immediately after installation, they fail to do so after a few years of operation due to aging. So that’s the reason why transformers are unable to serve the whole life period, and even if they are in service, they are likely to fail before the expected life period due to the lower reliability.
Many distribution transformers fail after a few years of service and have to be repaired twice or thrice during their lifetime. Earlier, Distribution Transformer Manufacturers India incorporated many more safety factors in design.
- Producing defects
Now let us discuss the producing defects. In the past, distribution transformers worked for more than 60 years, which is double the life expectancy. Still, many distribution transformers fail after a few years of service and have to be repaired twice or thrice during their lifetime.
- Inadequate/Poor design:
Transformer tank size, Percentage impedance (mechanical strength of coil), improper use of aluminum wires, Improper use of interlayer papers used for the insulation purpose, use of inferior quality materials.
The trend of the transformer design is towards luring the production cost per unit and even if it is at the expense of the quality. Moreover, the tender appraisal confines the initial cost with no consideration for the maintenance of the transformer up to the end of its reasonable life period. Consequently, the safety factor is affected at the worst. The cost of repairs during the fair life period plus the initial cost is called the estimated cost of the transformer.
Percentage impedance relies on the following aspects.
The wire size used in High Voltage coils
A reasonable size of coil results in lower size gauge wire, but this decreases the mechanical capacity of coils. As an outcome, the coils may not overcome higher current densities during the short circuit conditions.
The radial distance between High Voltage and Low Voltage coils, Axial assistant, Improving the radial distance between High Voltage and Low Voltage coils increases the percentage impedance. Better mechanical strength of the coil to combat higher short circuit stresses developed during short circuit conditions. The short circuit stresses are equal to the square of the short circuit current.
If the impedance increases from 4.5% to 5%-5.5%, the short circuit stresses developed in the transformer decrease considerably.
Other reasons for transformer failure under inadequate/poor design
Improper use of aluminum wires Directs to High Voltage coil failure.
The use of aluminum conductors approved for windings up to 200 kVA transformers.
- Improper Workmanship
Improper alignment of HV winding, Improper clamping at the management, improper connections, inadequate tightening of the core.
Improper use of interlayer papers:
- End turn insulation and proper sleeving
Avoided by using folding papers and reinforcing the end turn insulation with proper sleeving.
Uniform separation of the High Voltage coil and the inner coil, using spacers, helps avoid pressing of end turns and any further shrinkage during service. We use appropriate spacers while the coil is placed in the transformer so that oil can pass through the coil.
Conclusion
Thus, there can be numerous reasons that can lead to failure in the distribution transformer. To avoid these failures, you need to maintain them regularly.
