The ubiquitous transformer is the perhaps the most indispensable component in the power T&D segment. In this exclusive interaction, we have Praveen Gargava, Additional Chief Engineer, Madhya Pradesh Power Transmission Company Ltd, sharing keen insights on the role of transformers in the field of power transmission. A veteran with over 35 years of experience in EHV substations having published several research papers, Gargava also discusses the importance transformers in the context of Madhya Pradesh – a state that is witnessing high growth in power demand, especially from the agriculture sector. An interview by Venugopal Pillai.
Please discuss the criticality of transformers for a state power transmission utility like MPPTCL.
Transformers are the most important, costliest and critical equipment of transmission system. The system may have ample generation but power evacuation and transmission is not possible without transformers. A transformer is a vital link in any transmission system.
Although transformers are designed to have a useful life of 25-30 years, some do fail prematurely. Transformer outage is a huge financial loss; it severely affects reliability of supply. The procurement and replacement of a failed transformer takes considerable time and energy. Further, repairing of a transformer at the works takes additionally long time, as it involves dismantling and transportation of the transformers to works.
Thus, procurement of healthy transformer is a prime and the most important requirement. If we have procured a wet and unhealthy transformer, it cannot be dried or easily repaired at site. Moisture is the biggest enemy of transformer. Therefore, pre-dispatch inspection and stage inspections are very important in which core building, winding preparation and VPD (vapor phase drying) are thoroughly checked. These inspections should be carried out by experienced and knowledgeable engineers.
What is the current population of transformers of MPPTCL and what is the aggregate transformation capacity (in MVA)?
The MPPTCL system has three voltage levels – 400kV, 220kV and 132kV. The 132/33kV transformers are fed into the discom network. Currently, MPPTCL’s network has over 1,000 transformers with aggregate transformation capacity of 78,328 MVA.
We are expecting around 6 per cent growth in demand per year, and have been successfully meeting the same. Maximum growth has been observed on the 132kV side due to high demand from the irrigation sector. As you are aware, Madhya Pradesh is a pioneer in the irrigation sector. Over the past 15 years or so, the state’s irrigated area has increased from 8 lakh ha to 45 lakh ha.
Since the last few years, farmers in MP are in fact growing three crops instead of two. This has been possible because of increased power availability and new irrigation schemes. Thus transformer capacities are being utilized in a better way in the rural sector. In the agricultural season of 2022-23, MPPTCL could successfully meet electricity demand of 17,170 mw.
What is the average transformer failure rate in MPPTCL’s transformers? What steps are being taken by MPPTCL to bring down the failure rate?
Though the average failure rate of transformers in MPPTCL’s transmission system is low — less than 1 per cent — it is a cause for concern as failure of even a single transformer can affect supply or reliability of a big area. MPPTCL is making efforts in all directions to bring down failure rates. We are ensuring to procure completely healthy and dry transformers. We are ensuring five-stage inspection — right from tank manufacturing to final inspection. Our specifications are stringent. We are getting five years guarantee on almost all equipment.
Please discuss the preventive maintenance techniques adopted by MPPTCL, including remote monitoring.
In service, full attention is paid on conditioning monitoring and preventive maintenance of transformers as per guidelines of CEA. Field engineers are using modern sophisticated testing kits to measure Tan delta of transformer & bushings, winding resistance, SFRA, etc. Regular dissolve gas analysis (DGA) and oil parameters testing is being carried out to assess health of transformers.
What is typically the most common cause of transformer failure, and how is MPPTCL tackling the situation?
The major cause of failure and fire in big transformers is bushing failure. MPPTCL is now procuring RIP (resin impregnated paper) bushings for all 400kV and 220kV class transformer. MPPTCL is also replacing old transformer which have served more than 25-30 years of service and whose testing parameters are deteriorating. In last 5-6 years alone, we have replaced close to 100 old transformers.
MPPTCL has relatively high failure rate in the 132kV system. One of the major causes of failure is increased numbers of through fault in our 132kV system. Fault MVA of system has become high. Each 33kV feeder fault is fed by high current. The fault current creates high electromotive force inside transformer.
This frequent mechanical force/stress disturbs the alignment of winding. Thus, mechanical damage is converted into an electrical internal fault. If 33kV lines fault, which is being maintained by discoms, is controlled or reduced, the failure rate of transformers will automatically reduce.
It has been experienced that sometimes internal faults of transformer do not involve winding, rather they are to do with OLTC, bushings, or bushing leads. Such faults can be attended at site, provided the location of fault is detected and access to location is possible. If transformer faults are repaired at site, it saves a lot of time, energy and cost.
Our transformer procurement orders specifically mention space for free movement in transformer tank for inspection. Companies are asked to provide details of passage and free space provided inside the main tank should be indicated in concerned drawing, so as to allow free movement of at-least two persons for inspection of active parts etc.
To be more specific minimum clearance from outermost winding/connection leads to tank shall not be less than 300 mm on all four sides with suitable platform on bottom of the tank in order to facilitate free movement of persons all around inside the tank.
Using this facility since last few years, MPPTCL adopted practice of internal inspection of transformers before dispatching transformer for repair at the works of manufacturers or deciding to write it off as a failed transformer. Thanks to better internal inspection, MPPTCL could repair several old EHV transformers at site, over the past few years.
It is widely believed that India has the highest failure rate as far as distribution transformers are concerned. Though MPPTCL would normally not deal with distribution transformers, what is your overall view on the subject?
In my view, LT line conditions are very bad particularly in the rural sector. Each fault reduces the life of a transformer. Unbalanced loading, over loading and poor earthing are the main causes of failure. Fault clearing time is also very high. Sometimes faults are cleared from DO (dropout) fuse of HV side. Theft of energy also causes overloading and more fault, which does not become the basis of replacement of transformer due to overload.
Although most discoms are now following BEE guidelines, it is only with respect to efficiency of transformers. Stringent quality check measures are required before dispatch.
Does MPPTCL conduct international competitive bidding for transformers or is it limited to domestic suppliers?
In cases where MPPTCL gets funding from multilateral agencies like ABD, JICA, KfW, etc, for system development and system strengthening, it conducts international competitive bidding for transformers.
However, I would like to add that Indian companies are manufacturing world-class transformers and also catering to the exports market. It is to be noted that Indian companies have indigenously manufactured transformers of 1,200kV rating, which is the highest system voltage in the world.
“MPPTCL tries its best to adhere to “Make in India” policy.”
What is your view on testing facilities available in India, especially with respect to testing of high-voltage transformers?
The situation has greatly improved after commissioning of the testing lab of National High Power Test Laboratory Pvt Ltd (NHPTL) at Bina, Madhya Pradesh. This has reduced our dependence on foreign labs like KEMA, etc. Not only are Indian manufacturers using the facilities of NHPTL, but even foreign companies are availing services here.
It is felt that the current L1-based procurement policies of state utilities result in the induction of substandard equipment. What is your view? How does MPPTCL ensure that only quality transformers are purchased?
Being a state government-owned company, MPPTCL follows standard government procurement policies. When it comes to substandard equipment, one cannot fully blame the L1-based procurement policy though it poses some limitations.
In MPPTCL, tender documents are prepared with strong technical and financial criteria. Our specifications are very stringent. We ensure that only reputed companies supply us equipment, and we are getting five-year guarantee on almost all EHV equipment.
Our vendor policy also restricts new vendor for getting order of complete lot. As far as transformers are concerned, our acceptance tests before dispatch are as per guidelines of CEA; moreover, we have also inducted some special tests.
In the long-term, does MPPTCL have plans of deploying transformers of 765kV rating?
Prima facie, there is no technical hesitation in deploying 765kV transformers. However, being a geographically centrally-located state, Madhya Pradesh has the natural advantage of the Central transmission network of Power Grid Corporation of India Ltd (PGCIL). There is already a big network of around nine 765kV substations of PGCIL in the state.
When it comes to 765kV substations and transformers, they are needed most for evacuation of bulk power. Currently, we do not envisage the need for such transformers but yes, if there any mega power generation project comes up in the state, MPPTCL will definitely consider deployment of 765kV rating transformers.
“We are currently studying the pros and cons of using ester oil in transformers.”
Does MPPTCL have any plans of deploying green transformers? Is there is any official regulation mandating the use of such transformers?
We are currently studying the pros and cons of using ester oil in transformers. Though there is no official Central government directive to this effect, but we are proactively trying to incorporate green transformers wherever possible. Power utilities are still getting used to the culture of green transformers, and there is also lack of clarity on technical issues over the use of synthetic and natural ester oils used in such transformers. The overall experience of power utilities in this field is still limited.
While ordering transformers, we are trying to have, say, one out of ten transformers designed for the use of ester oil. We are also investigating the replacement of mineral oil by ester oil in existing transformers, wherever technically feasible.
It must be understood that transformers, especially high-voltage transformers, need to be specially designed for using them with ester oil. In low-voltage distribution transformers, the use of ester oil is relatively easier, from a technical perspective.
We understand that the current aggregate transformation capacity of MPPTCL is around 78,300 MVA. Where do you see this reaching in the medium term, say 3-5 years?
MPPTCL’s transformation capacity is on a rising trend. Growth in MPPTCL’s transmission system is also being fuelled by new intrastate projects being developed under tariff-based competitive bidding (TBCB) route. The power transmission capacity of the ISTS (interstate transmission system) network is constantly rising due to new projects by PGCIL as well as private developers.
Yes, currently, MPPTCL’s transformation capacity is around 78,328 MVA and this is expected to reach 81,421 MVA by end of FY25 and further to 86,748 by end of FY28.
