• Electrical India
  • Jan 5, 2017

Strengthening Power Distribution Systems

If we look at the huge costs of maintenance, repairs & replacements for oil type transformers spent every year, then the differential cost between oil type and dry type transformers should not be a too big amount, if it helps reduce transformer failures…

- Aviral Gautama, Sailesh Purohit


 Electricity is one of the vital infrastructures for economic development of the country. With government of India taking necessary steps to improve ease of doing business, the prospects of return of glorious days of high and sustainable growth of the country doesn’t seem to be a distant dream. Infrastructure developments have already been planned in various sectors of economy viz. railways, highways, smart cities, renewable energy, electricity etc. However, a lot of this success would depend on reliability of our power distribution system. Power generation has kept pace with the growing needs of the economy by meeting the objectives of 12th Five-year plan, however transmission and distribution systems need to be strengthened further to enable sufficient evacuation of power from generating stations.

  It is high time that the utilities should look into the other new options of technologies that are more sophisticated & advanced to keep pace with the growing needs of the country. Electricity would be one of the key deciding factors, if India could accelerate at the pace of growth that the world is expecting from it in the next decade & become an economic power of the world. We understand that many of the progressive and forward looking utilities are already on the lookout for new technological solutions – that can make them more efficient and improve their services – and in turn contributing towards progress of the country.

Figure 1: Failure Analysis of Distribution Transformers (Based on the survey of Utilities in India)…

Issues in the distribution systems

  Power distribution system in India is plagued with problems of high failures in distribution transformers. There are more than 60 utilities in the country, considering failures in all the utilities, the amount of financial loss to the country is humongous. There are approximately 4.5 million distribution transformers installed in the country, out of which the average failure of the country is about 9.2%, while in some states it is as high as 25-30%. This is huge when compared with failure rates in developed world of less than 1%. As per the industry estimate, the failure in DTs puts total financial burden of close to 200 Cr. on the utilities per year towards replacements & repairs of transformers.

  The cash strapped utilities have to allocate almost 15-20% of their annual budgets towards repairs and replacements costs in their systems. This is huge when we know that they are already in huge debts and such finances are not easy for them. These huge costs of failures also make introduction of new and innovative technologies difficult to make inroads in their systems. Government of India has already initiated steps to reduce debt burden of utilities (with UDAY scheme), which will also help them improve their operational performance by upgrading technologies in their distribution systems.

Key reasons for failures in Distribution Transformers (DTs)

  As per our survey of more than 20 utilities in the country, the key reasons identified for high failures in distribution transformers are as given below –

1. Prolonged overloading
2. Oil pilferage or leakage
3. Non-topping up of oil
4. Single phasing
5. Improper size of fuses
6. No lightning arresters installed/faulty
7. Faulty earthing
8. Tree cutting
9. Improper sag in lines and miscellaneous maintenance reasons

  Our analysis of all the reasons of failures in distribution transformers indicates that 60% of all failures are due to oil or related to insulation. If we could address these causes for failures in distribution transformers, the total failure rate in distribution systems would come down drastically.

  We have a case study conducted by an International Firm, Cedar Consulting, which has analyzed costs for repairs of transformers due to various causes. This study from the US is used here as a reference to highlight that the insulation failure leads to highest failures in transformers and has biggest cost impact.

  The Indian Utilities can conduct a similar study for their systems. We expect that the study would reveal a grim scenario in India as the transformer failures in India are much higher than US.

  The life of a distribution transformer is expected to be at least 25 years (as per CEA guidelines), however the utilities repair their transformers at least 2-3 times within this period. In most of the cases, distribution transformers don’t even complete their expected life of 25 years in operation, and are discarded once cost of repairs become too high (generally >40% of new transformer’s cost). Hence, an alternate technological solution needs to be looked into to solve the issue of high transformer failures with the utilities as the financial loss is exorbitant.

Figure 2: Transformer Insurance Loss Analysis for different types of failures…

Assessing technological solutions in transformers

  There are various solutions in the market, let’s analyze all available solutions to come out with the best solutions:

1. Conventional Oil filled Transformers

  The oil filled transformers have proved their performance over several decades, however there are limitations in this technology that can’t be addressed by changing designs or just changing protection systems. The issues are related to oil which will still remain. Refer Table 1.

2. Nomex Engineered Dry Type Transformers

  We had conducted a survey with more than 20 utilities across the country to understand the main concerns in their distribution systems. The surveys revealed that the biggest concerns of utilities are reducing failures, improving reliability and mitigating risks of fire in the oil type distribution transformers. We conducted failure analysis of oil type distribution transformers (as per Fig. 1) to understand the main causes of the high failures of transformers.

  Based on this understanding, DuPont worked on the technological solutions to address the concerns of the utilities. The Nomex engineered dry type transformer technology was developed by experts from DuPont. Technical experts applied their global knowledge & local understanding to develop this product with built-in features that can address the key issues in power distribution system. We will now see the details of the technology and benefits for power distribution companies.

Figure 3: Technical characteristics of Nomex Insulation…

Nomex engineered Dry Type transformers technology

  The Dry Type Transformers technology that we are discussing here is also called “VPI (stands for Vacuum Pressure Impregnated)” transformer technology. It has lots of advantages for utilities as given below:

1. The transformers can be conveniently loaded beyond rated capacity as they can endure peak loading up to 140% for 3.5hours (120% continuously, 130% up to 8 hours & 140% up to 3.5 hours) without any effect on life of transformer. This is unlike oil transformers where the transformers are under-utilized by cutting off at about 80% rated capacity to provide buffer during peak loading.
2. There is flexibility in designing these transformers as per environmental conditions (Passed Class E2: Frequent condensation, high humidity and heavy pollution) & climatic conditions (Passed Class C2: Operating at ambient temperature of -25 °C) at site of operation.
3. The transformers are virtually maintenance free because there is no oil as such no need for any periodic maintenance.
4. The transformers are easily reparable at site. Although fails less, but in case of any failure, the coil(s) can be conveniently replaced at site. This reduces repair costs and delays when it gets repaired outside.
5. The Nomex engineered dry type transformers ensure fire safety (Passed Class F1: Highest safety against fire hazards) which is required in densely populated locations. As against Oil filled technology which has more than 50% inflammable materials, the dry type transformers have less than 5% total combustible material with respect to the total weight of transformer.
6. The dry type transformers can be installed closer to load which reduces transmission losses and costs of cabling.
7. All materials conform to the standards of UL, IEC, IS Standardsfor Dry Type Transformers.
Nomex has high Limiting Oxygen Index & high Optical Transmission Factor even at temp. up to 250 °C.

Figure 4: LOI and OTP for Nomex. Fire Behaviour test on Nomex engineered dry type transformer…

Economics of the Dry type transformers technology

  The failure of transformers results in two main financial losses to the utility:

1. Repairs and replacement costs of distribution transformers 
2. Loss of business due to supply disruptions

Repairs and replacement costs of distribution transformers

  Every year utilities spend almost 15-20% of their annual budgets on repairs and replacement costs for failed equipment in their system, which is a significant amount.

  The failures do not occur at all locations but generally in certain zones which are identified as high risks. If utilities can identify all locations with high failures, and address the problems with better technological solutions, it would bring down the huge costs of repairs and replacements.

  Some of the possible locations where these trials can be conducted are mentioned below:

a. Remote locations that are difficult for maintenance of oil type transformers
b. Agricultural belts or locations that suffer during seasonal peak loading
c. Crowded areas where there are risks of fire hazards with oil type transformers

  If we look at the huge costs of maintenance, repairs & replacements costs for oil type transformers spent every year, then the differential cost between oil type and dry type transformers should not be a too big amount, if it helps reduce transformer failures.

Loss of business due to supply disruption

  Every failure in transformer results in business loss due to supply disruptions. Supply disruptions also lead to social costs due to public unrests.

  We have another case study by International Firm, Cedar Consulting, on the business loss due to supply interruptions. This study from US, used here as a reference for our understanding, highlights the magnitude of loss to business due to transformer failures.

  With much higher transformer failures in India than US, we expect the financial impact to be more severe in India.

Conclusion

  Though oil type transformers technology is still considered the best technology for most of the applications, we need to appreciate a few limitations in this technology.

  Every need in the market begets new solutions and innovations, which either address the problems or improve upon the performance from existing solutions.

  Nomex engineered dry type transformers technology is developed after understanding the issues faced by the utilities and providing a solution to address them.

  The lifetime cost of Nomex engineered dry type transformer is estimated to be at least 30-35% lower than oil type transformers.

  This is due to lower failures, lesser need for maintenance, reduced repair costs and also capabilitsy to load beyond the rated capacity of transformer.

  We are confident that many utilities would find the solution beneficial in the long run – and their progressive steps would take the country to a next level of growth and development for future.


Aviral Gautama
Key Account Manager
DuPont Protection Solutions
Aviral.Gautama@dupont.com

Sailesh Purohit
Technical Marketing Manager
DuPont Protection Solutions
Sailesh.Purohit@dupont.com

If you want to share thoughts or feedback then please leave a comment below.