- BETTER EFFICIENT TRANSFORMERS
Low loss Transformers are called `better efficient transformers.' Operating losses are less causing less heat generation and effecting longer life. One of the prime components of losses is the no-load loss which can be drastically reduced by better design and using superior grades of electrical steels. It can be further reduced in case conventional electrical steel is replaced by Amorphous metal.
By using improved grades of CRGO laminations, the no load loss can be reduced to 32 per cent than that specified by REC upto and including 100 KVA transformers. Numerically, the no-load loss specified by REC for 25 KVA transformers as 100 watts may be brought down to 68 watts with the use of superior grades of CRGO lamination. Similarly for other ratings like 63 KVA and 100 KVA transformers, the no-load loss may be reduced to 123 watts and 176 watts from REC specified values of 180 watts and 260 watts respectively.
Further, there is a huge scope of reducing the load losses to a much lower value to make the transformers more energy efficient. Maintaining the maximum efficiency to occur at 38 per cent loading, as recommended by REC, the load losses may further be reduced to 466 watts, 844 watts and 1192 watts as against 685 watts, 1235 watts and 1760 watts specified earlier by REC for 25 KVA, 63 KVA and 100 KVA transformers respectively.
The numerical computations of other higher rated transformers could not be made as both REC and ISS are silent on the specific requirements of losses in their standards. These have been left to the choice of the individual buyer to specify their need to restrict the total losses in the Tender specification.
On the whole, the manufacturers have the ability and resources to offer a better cost effective, low loss, energy efficient transformers having conventional stack core construction, which have a definite scope of reducing the total losses to 32 per cent.
We should not forget to mention here the excellent low no-load loss property of Amorphous metal transformers. There has been constant search for transformer core, materials, which may have the least loss. Iron-Boron-Silicon amorphous alloy has evolved, as the low loss material for distribution transformers. Molten metal when cooled to solid state at a very high-speed rate, retain a random atomic structure which is not crystalline. This metal is called amorphous. This resembles with glass and also referred as `glass metal'. Need to achieve the required cooling rate restrict the thickness of the metal to 0.025 mm i.e. almost 1/10'h of the thickness of conventional CRGO steel.
Due to small thickness and low saturation factor, larger core and consequently larger coils and tank size are required as compared to CRGO core transformers. The problem of small thickness has been overcome to some extent with the development of amorphous metal strips. This is achieved by compacting number of thin ribbons. This strip is commonly known as `POWER CORE' and upto a thickness of 0.25 mm having been developed.
Amorphous strips are four times harder than CRGO steel. Hardness along with reduced thickness make slitting and shearing difficult. The brittleness property of amorphous metal has also make it un-friendly to the transformer manufacturers. Due to these and other limitations, the amorphous core technology has been limited at present to very few customers in India and abroad. Amorphous metal core has some merits. The non-crystalline structure and random arrangement of atoms give low field magnetization and high electrical resistively. Due to low field magnetization, hysteresis loss is low and due to low electrical resistively eddy current is suppressed. As such core losses of amorphous metal alloys are reduced to by 42 per cent and magnetizing current by 53 per cent.
The most attractive characteristic of amorphous alloy is obviously its extremely low core loss and low magnetizing current. Except these two properties, practically all other properties o£ amorphous alloy are inferior to those of CRGO steel, which offer a challenge to the engineers to overcome them so that the low no-load property is exploited in the most cost effective way.
The amorphous metal saturates almost at 1.55 tesla whereas CRGO steel saturates at almost 2.03 tesla. Thus amorphous metal core-transformer results in increase of core size, conductor, tank and insulating oil. Overall cost of amorphous core transformer is approximate 20 to 30 per cent costlier than conventional core transformers.
Looking to such limitations, it is advisable that the buyers should not get mixed up the issues of CRGO steel transformers with amorphous metal transformers. They should be deltwith separately. A separate tender may be invited for amorphous metal transformers if the buyer so desires to purchase such transformers on academic point of view. It is further stressed that the SEBs may go in for buying a limited quantity of amorphous metal transformers for monitoring their performances in the present days distribution network as well as make themselves friendly in maintenance and repair of such transformers.
The other components of losses are the load loss. Load loss can be reduced by using thicker conductors. With use of superior grades of electrical steels and thicker conductors for the windings, the losses of transformers may be brought down to minimum. But it increases the initial cost of the transformers and thus become uneconomical during Tender evaluation. This is understood by everybody in the industries, especially a section of the manufacturers who have been shouting all these days in various seminars and in other common platforms.
As have been suggested by the many authors, ITMA also have the same opinion that to accommodate low loss transformers the tenders may be evaluated on `Total owning cost' (TOC) basis. It would have been the right choice which buyers need to look into. We fully agree to the proposal of evaluating a Tender on the basis of `TOC' with some modifications on the indices of `TOC' formula. It may be proposed to give a thought to the average life of distribution transformers in our unplanned distribution system, which is hardly at best 5 to 6 years. Poor workmanship, bad materials, overloads, short-circuit, single phasing, un¬balance load and over and above, power theft etc. are some of the reasons which do not allow distribution transformers stay for a longer period. We propose to calculate the indices of `TOC' formula on the basis of an average life of 10 years, instead of taking 15 years, which is a too long period for distribution transformers. However power transformers may be evaluated on the basis of 15 years average life on the present technology may become obsolete by then.
Banning import of spurious, defective and used electrical steel is again a critical issue which is discussed these days in every seminar. Authors from the manufacturers and power utilities have stressed the need to ban the import of such defective electrical steel, which will not only make everybody to play in a bigger field, but also increase the life expectancy of transformers in service. Probably there must be some constraints for the Govt. to ban the import of such material which we may not be aware. .
We have a unique proposal which can counter the use of such defective materials in the manufacturing of transformers. Let ITMA make a panel constituted by the eminent engineers from its association who should be given charge of carrying out third party inspection on behalf of buyers with a minimum service charge. Manufacturers who are still indulging in these spurious materials may also be included in the panel. With such a combination, the things will be exposed even in the 1st inspection as nothing can be hidden out from the inspection team. It will then be a responsibility of the manufacturers themselves to discourage others from using such bad materials. The modalities may further be discussed when the proposal sounds good and acceptable to the buyers.
- REDUCTION OF LINE LOSSES
Various modalities have been discussed in the Seminar, of which the high voltage Distribution System (HVHS) may be the ideal sfep to reduce line losses. It helps to reduce the length of L.T lines and makes the power available at site close to the users. Reduction of L.T lines effect in reduction of line losses considerably. The high voltage power distribution system also reduces the probability of power theft by hooking HVDS suggests an increase' in installation of small capacity single-phase transformers in the network which again save considerable energy.
The theft of electrical energy has been made a cognizable offence under Indian Electricity Acts, 2003. However the implementation leaves much to be desired. Most of the energy theft are through connivance of lower employee level. In case the situation is to be improved, it would be necessary to plug all loop holes and ensure that the energy theft is substantially reduced (if not eliminated). In some states the enforcement drive has shown encouraging results. However a great effort in implementation is necessary. Inadequate billing may be another aspect which create a huge gap between power generation and economic realization. This aspect remained untouched in the seminar as author had failed to discuss this issue. Inadequate billing and realization is a hot subject and require further discussion in the open forums.
The sharply increasing costs of electrical energy are forcing electrical supply authorities to recognize the critical importance of the cost of electrical losses. Electrical utilities are increasingly required to operate their networks more efficiently and to reduce the total real running costs of the equipments. Transformers (after transmission lines) are the largest loss making components in the electrical networks. There are about 25,26,239 nos. transformers with a total installed capacity of 75,92,39 MW (as on 31.3.2004) in the power system networks. It is estimated that about 35 billion Kwh of energy is lost due to high loss transformers every year. The total losses due to transformers in the electrical network in India exceeds 6 per cent of the total electricity generated which is equivalent to about 8 to 10 per cent of the total loss from the system.
The enormous stock of transformers is often overlooked as a source of cost saving. In fact, avoidable losses from the distribution transformers currently in service would mean release of about 650 mw of generating capacity, which could instead be used to serve customer loads.