How To Achieve Transformer Reliability

Transformer failures can potentially lead to unplanned power outages, in addition to costly and time-consuming repair and replacement. - Dr. Murhari Sopanrao Kele, Chairman-cum-Managing Director, Tripura State Electricity Corporation Ltd

In an interview with Subhajit Roy, TSECL’s Chairman-cum-Managing Director Dr. Murhari Sopanrao Kele explains how to achieve reliability in terms of transformer performance. Dr. Kele has varied and rich experience of over 30 years in power sector across Maharashtra State Electricity Board, Torrent Power Ltd, MSEDCL, Madhya Pradesh Paschim Kshetra Vidyut Vitaran Company Limited, and presently handling TSECL from North Eastern region.

How important is distribution transformer for a distribution company?

Electric power is the basic infrastructure for economic development of any developing country like India. Distribution transformer is soul for any distribution company as it plays very important role of voltage transformation in upward and downward direction level as per requirement of system. Distribution transformers is contributing approximately 20 per cent of total asset value of a distribution company (DISCOM). Fortunately, Tripura State Electricity Corporation Limited (TSECL) is working with generation, transmission and distribution under one umbrella, thus we are dealing with all types of transformers in system. Nowadays, the demand of distribution transformers is increasing due to increase in generation capacity of both conventional and non-renewable sources due to increase in per capita consumption of electricity, new centrally-aided projects like IPDS, DDUGJY, Saubhagya schemes and new avenues like electric vehicle charging stations etc. Replacement of old transformers with energy efficient transformer is one of the key activities which is going on presently.

How much attention one needs to pay to make a transformer reliable?

Transformer failures can potentially lead to unplanned power outages, in addition to costly and time-consuming repair and replacement. Even though every equipment is important in power system, transformer plays very critical role to maintain reliable power supply to consumers. Every consumer knows about transformer, so its common complaint of common consumer about transformer. It is the only part where we need more attention to keep system reliable. Any DISCOM needs proper attention to maintain quality and quantity of transformers. Starting from the design of transformer of transformer, its core, material used for winding, cooling system, energy efficient capability, specifications and standard needs, type tests, protection system, etc. need to be kept in mind while purchasing of transformers by any utility.

Moreover, transformer oil level, neoprene gaskets, transformer conservator tank or transformer body, HT and LT bushings, HT and LT terminals, and silica gel in breather provided to transformers should be proper externally. About earthing issues, neutral and transformer body of the transformer shall be provided with two distinct earth connections to one earth electrode using adequate size earth leads. Regarding protection, use of AB switches for isolation, lightening arresters, proper size of DO fuses from HT side, use of distribution box with MCB will also play important role in betterment of transformers in power distribution utility.

What are the kinds of distribution transformer failures in your area and what are the key reasons?

Failure of distribution transformers is the headache for any utility as it affects reliability of power supply. TSECL is facing very big challenges due to its geographical conditions and natural calamities faced by north east region. In the area of TSECL there are very peculiar problems which include storm or cyclone prone area, heavy lightening strokes, 60 per cent forest area, transportation, manufacturing defect, lack of testing facilities of transformers, lack of maintenance, poor repair of transformer, overloading or unbalance loading, lack of protection, earth fault due to tree branches, oil leakage, theft of oil, less oil, improper connections and other various reasons.

How can these failure issues be addressed and what are the steps being taken by TSECL to resolve these issues?

Generally, every year, from the month of March, our transformer failure starts increasing up to July, it reaches at peak in the month of May and June. We are having DTR failure 12 per cent as compared with national average of 8 per cent. It is subject of worry for us. Condition monitoring, online monitoring, routine diagnostic, scheduled maintenance, and condition-based maintenance (CBM) are some of the most common transformer asset management methods. We are taking proper measures for reduction failures in transformers. We have first sensitised our field engineers for preventive routine maintenance as per schedule, we have discussed with manufacturers and repairers of transformers and taken suggestion from them for improvement. We have arranged workshops and seminars with the help of CBIP, CPRI, Indian Transformers Manufacturers Association of India, Indian Copper Association of India, oil manufactures, etc which have created awareness in our engineers and upgraded their knowledge by giving exposure to them. We have given them task and also wanted to start incentive or award scheme for less failure of transformers. Before monsoon and before Durga Pooja, we are taking care of proper maintenance of system. Proper monitoring and stock position are monitored at higher level.

What are your views on the quality control order? And has it helped distribution transformer companies in improving the benchmark for making their asset quality better?

Standard technical specifications by utilities, energy efficient provisions decided by Bureau of Energy Efficiency, EESL parameters, use of good-quality material, experiments in design of transformers, protection issues, transformers health monitoring system, etc. should be considered by manufacturers. As no load losses of AMDTs are less than CRGO core distribution transformers, these distribution transformers may be preferred in villages where peak load comes for a short period and most of the time distribution transformer remains lightly loaded. Use of newly introduced oil is used in utilities like Tata Power, demonstration of use of copper winding in Indore and other places by ICAI has given better results but cost benefit analysis should be done properly as it will be easy to adopt new technology by public utilities.

Also, to maintain quality there should be three tire system for testing of transformers. First material should be tested by third party agency before assembling, thereafter type test or routine tests should be carried out by inspectors and thirdly, after receipt of transformers at utility’s store minimum 10 per cent sampling checking with well-established laboratory is needed. It will avoid failure of transformers due to manufacturing defect within guarantee period.

When you repair a distribution transformer, do you think active repair can be adapted for legacy transformer?

The lifetime of a transformer highly depends on its insulation condition owing to a higher probability of insulation failure compared with its other components. Moreover, aging of transformer insulation is a function of insulation moisture, oxygen amount, and internal temperature specifically at the hottest spot, which is mainly governed by transformer loading and ambient temperature. The effect of temperature, thermal aging factors, and electrical aging factors on transformer insulation is experimentally analysed.

Any electrical equipment can be failed in system. Transformer is also major component in system which contributes major investment. Approximately more than 20 per cent may be the cost of transformers in system. Every time installation of new transformer in system in place of failure is not possible due to cost constraints. For system strengthening new transformers are added, some transformers capacity is augmented, new infrastructure is created but what we thought about replacement of failed transformers? How many times old, failed transformers can be repaired? These are points of discussion. As per my views after two times of repair, it should not again be repaired as it will contribute to increase in losses and its capacity may be de-rated by repairers.

When I was Director (Technical) in Madhya Pradesh Indore DISCOM, we had implemented a very good best practices maintenance program and due to which DTR failure rate was also reduced from 18.6 per cent to 9.5 per cent within one year. Testing facilities were increased and eight transformers manufacturing agencies were blacklisted for three years for not supplying quality transformers.

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