POWER BATTERIES (Trf. Div.)(Est. since 1975)

(Mnfg. Of Dist. & Power Transformers upto 10 MVA 33 Kv class) Works : D-2/156-157 Sanwer Road, Industrial Area Indore (M.P.) 452013

Correspondance Address - 296, Tilak Nagar, INDORE (M.P.) 452 001

Managing director: Mr. Amit Dhakad

INTRODUCTIONPOWER BATTERIES (Trf. Div.): Power Batteries (Trf. Div.) is a SSI Unit situated at Indore, the industrial capital of Madhya Pradesh. It is a partnership firm managed by technically and commercially qualified persons of the family with a growth history from 1975. The firm was earlier engaged in manufacturing of automobile batteries and distribution transformers and expanded their horizons to manufacturing of power transformers upto 10 MVA since 1994. The firm is having covered area of 33856 sq. ft. with lifting capacity of 20 tons in 7000 sq. ft. and all required testing facility for routine test of transformers.

HISTORYThe unit was established in 1975 in industrial area with limited infrastructure and space with manufacturing of batteries and supplied the same as OEM to Asiatics, Power Plant Sales & Service, Bombay Plants Pvt. Ltd., Municipal Corporation, PWD and later on the firm was awarded the ancillary status to supply batteries to M.P. State Road Transport. The batteries were tested at CIRT, Pune and awarded A grade. Later on, we were also registered with MPLUN and MPEB for supply of batteries.

In 1979, the firm diversified into manufacturing of distribution transformers and supplied the same to MPEB, RSEB, PSEB and MSEB. Since 1990, we expanded our range by manufacturing power transformers upto 10 MVA, 33 KV class. Our entire range starting from 25 KVA to 5 MVA is successfully type tested and approved by CPRI, Bhopal and/or ERDA, Baroda. Recently we have accorder 3 star label by BEE for our transformers.

PLANT & MACHINERY : Our all the firms are well equipped with necessary plant and machinery along with testing equipments to manufacture and test transformers upto 10 MVA.

We are having in house facility for the following process : y y y y y y CRGO / Lamination cutting Fabrication of tank DPC/TPC covering of wire / strip HV & LV winding Oil filteration and HV testing Full routine testing of transformers.

MANPOWER: We have technical and commercial trained staff wherein most of the staff members are working with us since inception of the unit. We have individual supervisor for all departments looking after the quality of workmanship and manufacturing process.

MATERIAL: We, being one of the oldest unit of Madhya Pradesh are having reasonable understanding with our suppliers associated with us for past many years for supply of necessary raw material. We are having individual stores for each firm to maintain the inventories in systematic fashion.

MACHINE SHOP: We are also having in-house maintenance / machine workshop to handle any kind of breakdown apart from assisting in machining work. The workshop is well equipped with machines like drill, grinder, surface grinder, capston lathe, power sheer, circle cutting, hydraulic bending and other machines which makes our day to day working trouble free and efficient.

We, being one of the oldest firm of central India in manufacturing of transformers can deliver you quality oriented services at mutually agreed terms and conditions on winwin principle as we have all desired facilities and manpower available with us to cater to any kind of requirement.

Some important Indian standards related to transformer are as follows:

Specification for power transformer. Specification for outdoor 3 phase distribution transformer upto and including 100 KVA, 11 KV.

IS2026 (part I to IV) IS 1180 (part I & II)

Specification for dry type transformer.

IS 11171

Specification for control transformer for Switchgear and control gaer for voltages Not exceeding 1000 V A.C. Specification for current transformer. Specification for voltage transformer. Classifications of insulating materials For electric machinery and apparatus In relation to their thermal stability In service. Degree of protection provided by enclosures For low voltage switchgear and control Gear. Specification for new insulating oil.

IS 12021

IS 2705 (part I & II) IS 3156 (part I to IV) IS 1271

IS 2147

IS 335

In-house testing: All industry make transformer are used to carry out the minimum required tests on the transformer(as per the Indian standard) as follows: y y y y y y y Insulating resistance test. Winding resistance test. No load loss test. Load loss test. High voltage test. Oil BDV test. Temperature rise test by impedance loding.

Class of insulation: We are using excellent insulating materials like NOMEX, GLASS, FILM etc which are strong enough and better in dielectric strength, as a result we can increase the maximum allowable temperature resulting the overload strength is strong specially in case of DRY transformer. We are maintaining the maximum temperature rise limited to the previous class of insulation, such as if we claim class of insulation H , temperature rise will be limited to class of F (usually we consider ambient temperature as 45 deg. C. if not specified by the client.) As per IS and other international standard Tempt. Class max. total tempt. Of insulation

y y y y y y

A E B F H C

105* C 120* C 130* C 155* C 180* C 180* C above

Transformer Basics: Transformers plays a crucial role in the power distribution network and any failure creates disruption of power supply to consumers and the extent of effect depends upon the rating of transformers. For this a well balanced design meeting the GTP and capable to withstand all special tests / type tests / Acceptance tests is essential in first stage. In second stage the quality of materials used play a greater role in deciding the life of transformer. Well-established systems should exist to ensue that right quality of material is released for manufacturing. Further, duringmanufac-turing, the following practices are recommended in every stage to ensure that the quality is build and transformers give a satisfactory life.

CORE ASSEMBLY: y y y y y Prime quality /grade core need to be used. Burr free core slits are available for further processing. Core assembly should be neatly done Assembly should ensure perfect magnetic circuit Ensure smooth surfaces of core assembly on all the sides. This can be achieved by maintaining perfect slit widths as per the design.

CORE CLAMPS /CHANNELS Avoid sharp corners / edges and ensure that the welds are uniform

WINDINGS Ensure defect free enamelled or paper covered conductors from suppliers. (Check that the conductor sizes are meeting the design data and the tolerance limits provided in ISS. y Good quality of insulation (edge strip, runners, press board, Kraft/ ED paper) be used as per design details. y y y Windings are to be made tight maintaining the designed overall dimensions. All leads are to be well insulated at the bendings. Pressing & bonding is recommended for rectangular coils to maintain phase to phase clearances. y In power transformers coil compression process be adopted for eliminating slackness in winding. y In case of multiple strips for IV coil and if the strips are placed one above the other, the transposition is must.

CORE COIL ASSEMBLY Check that the coils & core assembly dimensions are well within design dimensions. Ensure that coils are not too tight during assembly.Maintain the phase to phase clearances are as per the design / voltage class.Check that the insulations provided are as per the drawing for maintaining phase to hhase and phase to earth clearances.Complete the yoke assembly so that the magnetic circuit is perfectly closed.Tighten the core coil assembly for providing the mechanical strength and eliminating the slackness.

DRYING PROCESS * Core coil assemblies are dried in heating / vacuum oven to eliminate moisture. Heating cycle is to be run to ensure that temperature attained by active part is between 80UC to 100IJC.and water collection level comes down to less than 50 ml for at least two consecutive hours.( in case of vacuum drying oven)

TANK FABRICATION Inside positive tolerances are to be maintained for ensuring required phase to earth clearances. Ensure that sharp corners and unnecessary of projections inside the tank are avoided. Qualified welders to be used in tank fabrication and all welds are to be made uniform. y Before tanking operation., the core coil assembly has to be tightened for eliminating the slackness resulted during the heating cycles. y CCA to be well placed and secured in the tank for ensuring the earth clearances based on design / voltage class. y Transformer oil filling to be done under vacuum level less than 5 tar, if possible.

y

As transformer oil plays critical role in the life of transformer, it is to be ensured the oil characteristics meets IS-335 standard and oil filling is done at 60 Deg.C with a minimum oil BDV of 60kV

y

All the gaskets used to be placed in position & tightened for eliminating the leaks at gasket portions.

y

Transformer filled with oil is to be pressure tested at 0.35 kg / Cm as per IS-1180 for ensuring that there are no leaks.

y y

The quality of all accessories should be uniform. In case of conservator mounted transformer, air is to be released from the bushing pockets before testing.

TESTS y A transformer can be stated healthy, if it passes all routine/ acceptance tests as per IS 2026. y However impulse and short circuit test on a sample transformer may be carried out in any of the independent lab like CPRI, IREDA & NTH etc., y The above measures in different stages will ensure service free transformers except for preventive checks as per the standard procedures.

OPEN CIRCUIT TEST

CIRCUIT DIAGRAM

The secondary of the transformer is left open-circuited. A wattmeter is connected to the primary. An ammeter is connected in series with the primary winding. A voltmeter is optional since the applied voltage is same as the voltmeter reading. Rated voltage is applied at primary. If the applied voltage is normal voltage then normal flux will be set up. As the Iron loss is a function of applied voltage, normal iron loss will occur. Hence the iron loss is maximum at rated voltage. This maximum iron loss is measured using the wattmeter. Since the impedance of the series winding of the transformer is very small compared to that of the excitation branch, all of the input voltage is dropped across the excitation branch. Thus the wattmeter measures only the iron loss. Since the secondary of the transformer is open, the primary draws only no load current. This no load current is negligible. As the copper losses depend on current they can be neglected. Current, voltage and power are measured at the primary winding to ascertain the admittance and power factor angle. Another method of determining the series impedance of a real transformer is the short circuit test.

SHORT CIRCUIT TEST The purpose of short circuit test is to determine the series branch parameters of the equivalent circuit. as the name suggests, in this test primary applied voltage, the current and power input are measured keeping the secondary terminals short circuited. Let these values be Vsc, Isc and Wsc respectively. The supply voltage required to circulate rated current through thetransformer is usually very small and is of the order of a few percent of the nominal voltage. The excitation current which is only 1% or less even at rated voltage becomes negligibly small during this test and hence is neglected. The shunt branch is thus assumed to be absent. Wsc is the sum of the copper losses in primary and secondary put together. The reactive powerconsumed is that absorbed by the leakage reactance of the two windings

CIRCUIT DIAGRAM

CAUSES OF FAILURE OF DISTRIBUTION TRANSFORMERSThe followings are some of the causes of failure of transformers in service, being attributed to the users. Probable remedial measures have been highlighted to reduce the rate of failure, which are assuming alarming in the present days distribution network across the country. Prolonged overloadingSingle-phase loading Un-balance loading Faulty termination Power theft & hooking Wrong earth connection Prolonged short circuit Less or no maintenance Operation of tap-switch on load Poor quality of L.T cable '

1. IMPROPER INSTLLATION It has been discussed, in brief, each of the above causes to surface out the reasons of failures as well as few remedial measures to curb such unhealthy, pre-matured failure of transformers in service. 2. PROLONGED OVERLOADING Distribution Transformers are generally not recommended for continuous overloading. l however overloading for a short duration cannot be avoided. It is one of the prime responsibilities of the utilities to keep a check on the loading of a transformer and should record the loading Patton on a history card. In case of overloading the additional loss generates more heat, which effects the burning of winding insulation, causing ultimate failure of the transformer.. In most cases, it has been observed that the Line Operators use higher rating of re-wirable fuses to avoid frequent breakdown of supply caused by overloading necessitating replacement of fuses. Proper sizes of fuse elements on both H.T and L.T side will definitely reduce the probability of failure of transformer due to overloading. Measurement of load current with a Tong Tester at frequent intervals, especially during peak loading hours, will give a fair idea about the load demand of the locality. In case the overloading is more than 20% during peak hours and if it persists for days together, it is recommended to replace the existing transformer with a bigger rating, or else a second unit may run in parallel. Furthermore, the Line Operators should have some elementary knowledge of rating-wise correct size of fuse elements. The utilities should make their own standard of rating wise fuse elements and should communicate the same to the Line Operators for use in the field. Moreover utilities must ensure the availability of such proper size of fuse elements at the appropriate time. It has been seen in many occasions that the Operators use two of thin fuse wires instead of one correct fuse element, because of non-availability. This procedure is wrong and must be discouraged.

3.SINGLE PHASE LOADING A distribution transformer should ideally be loaded uniformly on all the three phases. But there are few occasions, especially running irrigation pumps in the state of Punjab, where a 3-phase heavy-duty pump is made to run by initial mechanical priming with a single phase supply form a 3-phase transformer. As a result the load on one phase goes drastically high causing operational problems thereby leading to failure of transformers. Such like abuses of transformers for no fault of the manufacturers should be stopped. It is recommended to educate the ultimate users the effect of such single phase loading on the performance of transformer. It has been seen that in most cases, the agricultural customers using power, are the cause of single phase loading on a 3-phase transformer.. It would be advisable to encourage such customers to own their transformers including the overall maintenance responsibility as has been introduced by PS.E.B recently. Only then, the failure due to single-phase loading will considerably be reduced, except for those when the system runs on single-phase inadvertently without the knowledge of the users.

4. UNBALANCE LOADING If Delta/Star connected transformer with earthed neutral system, it is recommended that all the three-phases are uniformly be loaded. This is infact very difficult to achieve with the distribution network available in the suburban and metro cities. However an unbalance loading upto 10% may not be that serious to create an operational problem for a delta/star connected transformer. For a 3-phase balance load, the potential on L.V neutral is zero. In case of unbalance loading, a voltage is generated on the neutral and will remain floated between neutral and earth. Since the neutral is solidly earthed through external link, a circulating current will flow through the loop of delta winding. This additional circulating current will superimpose on the main branch current of the delta winding and will cause additional heat, which may lead to the failure of the winding insulation.

It is recommended to keep a check of load current including the current flowing through the neutral at frequent intervals and should be recorded in the history card. As long as the neutral current is within 10% of the load current, the matter may be ignored. In case the neutral current exceeds 10% limit, the remedial measure should be taken to bring down the neutral current within acceptable limit.

5. FAULTY TERMINATIONS In many occasions we have the experience to witness heavy electric sparks coming out from the bushing termination joints, especially on L.V connections. In most of the cases, these sparks are because of loose terminations during the course of installation or else have been loosen due to bad service conditions. Once spark occurs at the cable termination, it causes melting of the busing sealing gaskets, effecting oil leakage from the bushing top, resulting failure of transformer in due course of time because of low oil level The incoming and outgoing termination should be done through proper connectors. ISS and REC have recommended such details with drawings of lugs and connectors. Users must ensure that the cable connections have been done with proper lugs and connectors. Direct Connection of cable/conductor to the bushing terminal stud, should be avoided. During termination, we should not forget the effect of bi- metallic action. If aluminium cable or conductors are to be connected with brass/copper terminal or vise-versa, a proper bi-metal should remain in between. Otherwise due to bi-metallic action, a milli-volt will generate causing a localized current and may deteriorate the current carrying thread.

6. POWER THEFT AND HOOKING OF MAINS We have the.experience to witness the stealing of power by hooking the system. This has been a regular phenomenon in the unauthorized colonies to use electricity without paying the cost of it. Power utilities do not pay much attention to such occurrences. But ultimately the transformer manufacturers are paying the dividend. Since such hooking make the transformers to run in overload/unbalance load and may cause failure in due course of time. This is one of the major causes of failure of distribution trans-formers for which the manu-facturers are

blamed all the time. This is a serious national problem and the power utilities must think upon stopping such power theft by hooking Lot has been written and debated in various forum at national level. Almost all utilities are taking number of measures to curb the menace of theft but the results do not appear to be upto the mark. However we suggest that firstly, meters are required at every substation to find out how much pilferage is actually taking place and what amount is really lost due to technical problems related to transmission. Quite a few SEBs claim that they are in a process of installing tamper proof electronic meters. These meters record the time at which theft has been committed and how much has been stolen. But it needs huge invest-ment. And there are other ways of checking power theft. A significant part of the revenues loss on account of theft is due to inadequate billing. This can certainly be rectified by minimum investment. All that needed is more will and sincerity on the part of power engineers. Regular energy audit and surprise raids can mitigate the evil to some degree. The best way to con:abat theft is to privatize power distribution. Take the case of Mumbai/Calcutta where there are private distribution agencies have been doing business since long. The losses on account of T & D and pilferage together are only 10 to 12% less than half of national average. Similarly in the case of Noida Power Company limited, a subsidiary of Calcutta Electric Supply, who undertake distribution of power in Greater Noida where the total losses including the theft is less than 5%. These are very old private utilities. Recent privatization of SEBs/utilities in Delhi & Orissa etc. which come have come up for the last 3 to 4 years have not indicated promising results. Unless open access is introduced the monopolistic attitude of DISCOMS cannot be changed.

7. WRONG EARTH CONNECTION The earthing of IV neutral will prevent the presence of any voltage above the normal appearing in the IV circuit and therefore the possible danger to human life will be reduced to minimum. Secondly, the earthing to the neutral point eliminate the possibility of an arcing fault to earth and therefore of fire risk, while it also ensures the rapid disconnection of faulty apparatus from the system without undue delay.

Due to discharge from high voltage the tank may be charged to an abnormal floating potential causing danger to life. In both the occasions provision of solid earth is extremely essential. As per Indian Electricity Rule the tank body is to be earthed of two diagonally opposite points. The purpose is to ensure that in case one of the earth points fails to act, the other will serve the purpose. The earthing should be done with G.I strips having a minimum cross section of 25 x 3mm. Moreover painted surface in and around the earth bolts should be cleaned to ensure proper earthing. It is advisable to check the earthing at regular interval.

8. PROLONGED SHORT-CIRCUIT In case of an external short-circuit on IV side, a fault current approximately 20 to 25 times the rated current will flow through the windings. The windings are designed to take such fault current for 2 to 3 seconds. If the fault persists more than 2 seconds, we are not sure about the fate of the transformer. The transformer is bound to fail on such occasions of prolonged shortcircuit beyond permissible limit. Necessary protections such as O.C.B on HV side, A.C.B o IV side, fuses etc., are recommended. In case of small transformers, H.R.C fuses of appropriate size should be provided. But under no circumstance, ordinary thick wires are not to be used.

9. LESS OR NO MAINTENANCE A well maintained transformer always enjoys a longer life. Transformer is capital-intensive equipment and must be, provided regular maintenance. However the frequency of the maintenance mostly depends on the type of installation, its KVA rating, connected load and place of installation. Users should prepare their own maintenance schedule along with their periodicities.

10. OPERATION OF TAP-SWITCH ON LOAD Approx. 2 to 3% of failures of transformers are caused due to failure of tap-switch for its poor quality. In few occasions the failure occur due to faulty operation of tap-switch on load by the

in-experienced operator. In case of low oil below tap switch, it may also cause voltage failure. If the selection of tap position with respect to the input voltage does not properly match, the transformer may fail due to over excitation. Manufacturers should own the responsibility of failure of tap-switch for its bad quality and should look into for further improvement in their future supply. Failure due to faulty operation and low oil level should owned by the utilities. In case it is necessary to operate the off-circuit tap -switch during service, the transformer should be disconnected from the incoming supply source before operation. Further, the operating handle should be moved from position 1 to 5 (or more) and back before putting the switch to the dsired tap position. This will eliminate the alignment problem in the male-female contacts of the tap-switch and also clean the metal surfaces for better contact. The utilities are very much aware of the fact that they seldom make use of such tap-switch for voltage adjustment during service, especially for medium sized distribution transformers upto 630 KVA and below. It is therefore a matter for the users to re-think on the requirement of tap-switch for their future tenders. It will not only eliminate the cause of failure of transformer due to tapswitch, but also the overall cost of the transformer will be reduced by 3 to 4%. Customers like BEST, Bombay has stopped using tap-switch upto 990 KVA transformer, UHBVNL (formally known as HSEB) have already withdrawn the requirement of tap-switch for their 200 KVA transformers. RSEB don't use tap-switch upto 250 KVA ratings, UPPCL has withdrawn tap-switch upto 160 KVA transformers. Other SI?B's may also look to this proposal for eliminating tapswitch upto atleast 630 KVA transformers. Even if the utilities want to incorporate tapings on HV side to regulate secondary voltage, it is recommended to use link-Board (instead of rotary switch) as has been made mandatory by Calcutta Electric Supply (CESC) for last few decades. It is a glass- fiberboard having a minimum thickness of 10 mm, fitted above the yoke with the help of four studs. Taping of each phase are terminated on the board and two of the tapings of each phase are shorted with an external link. Studies on use of rotary tap-switch vis-a-vis their failure revealed that although the switches are the easiest means of changing tap at site, their operation are seldom used. On the contrary,

loose contact due to sludge deposition on the contacts are very common which involve not only regular maintenance at site, but at times lead to failure of transformer. Tap link board instead of tap changer switch was introduced by CESC in 70's to avoid failure of tap changer switch due to inconvenience, involved during tap changing operation. With the introduction of tap link board, the failure rate of the transformers due to tapswitch at CESC has gone down to less than 0.2% as against 3% on National average.

11. POOR QUALITY OF L.T CABLE In multiple occasions, it has been seen that the transformers fail due to poor quality as well as under-rated PVC IV cables as the PVC insulation melts or get charred due to heat, causing dead short-circuit in the transformer. Poor quality of PVC cable sometimes affects the insulation resistance of the IV circuit also. Users should make a note of it while selecting the size of cable. Effect of bi-metallic action may also be looked into while connecting aluminium cable with brass copper terminals or vise-versa. Cable supports and clips should be provided in such a way that the cable should not create unnecessary load on the bushing terminals. It has been seen in few occasions that the L.V cables are hanging against the terminal bushings without any support, pulling the terminal down due to its own weight and affecting leakage of oil from the sealing gaskets of the bushings. Such octurrences are very common in most of the Metros and Suburban cities (except Mumbai and Calcutta). In case of transformer with L.T cable box, much care should be taken while selecting L.T cables. It is safe to use the 31/2-core cable. If single core cables are used, the gland plate should preferably be of non-magnetic material (either brass or aluminium) for transformers ranging from 500 kVA and above. Otherwise it will create unnecessary induction heating due to magnetic flux linking around the entry of the cable in the box. M.S gland plate cut and further welded with non-magnetic material may also serve the purpose.

12. IMPROPER INSTALLATION In case of pole-mounted transformer with exposed outdoor bushings, adequate earth clearances are to be maintained. Breather, arcing horns etc. should be placed to their

respective locations. Generally the breather is sent separately in sealed condition. The adhesive tape being provided to seal the air passage at the bottom plug of the breather is removed before putting the breather in position. The oil tray inside the breather container should be filled with oil before energizing the transformer. The colour of silicagel should be checked (which is essentially to remain blue)

In case there is a growing tree near the bushings, necessary precaution should be taken to ensure that in near future it should not come in the vicinity of the bushings. Since the bushings used in distribution transformers are of oil communicating type, the trapped air inside the bushings should be released before energizing. The trapped air inside the tank cover or in the radiator (for bigger transformer) should also be released through the air-release plug provided for this purpose. Oil level of the transformer upto the normal marking should be ensured only after the air-release operation is done. In case a transformer is installed after a long storage (generally beyond one year), the dielectric value of oil may be checked in conformity with IS-1866. Explosion vent diaphram should be checked for its soundness. All the above including the pre-energizing insulation resistances should be recorded in the HISTORY CARD. If rollers are provided for pole-mounted transformer, the same should be removed before installing the transformer on the H-Pole or should be locked in their position after installation. If possible, after installation the leveling of the transformer may be checked with the help of a spirit level.

13. CONCLUSION With the increase in the market competition, it has been observed that the safety margins of the distribution transforms have been brought down to bare minimum, just sufficient to satisfy standard specification and ideal loading conditions. As a result users have been put to constrain of running the plant within the specified capacity throughout the year. It is difficult for an urban electric supply to maintain such an ideal network condition throughout the year due to unpredictable load growth-during festive seasion or outage of an adjacent source in the thickly

populated area. In such a situation, two options are open to the utilities. Either under utilization of the transformer would result into uneconomical network Or introduce safety margins within the specification.

Considering the economical factor it is suggested to review the specification, which may include the following: y Reduce permissible oil and winding temperature rise from 50/55 (as specified in IS2026) to 30/45 to take care of poor ventilation in some locations and to permit marginal overloading. y Stipulation on the grade and type of core material and the maximum flux density in view of the switching surge due to load shedding and to permit a certain degree of over fluxing. However further studies are necessary on the effect of over fluxing and the possibility of specifying the maximum level is to be explored. y Restriction on the number of HV coil sections per phase and limitation on the winding current density to enhance the cooling and reduction of winding gradient and hot spot temperature etc. are to be judiciously implemented. y It has been observed that despite specifying flux and current densities, the loss figure of the transformers vary widely. Since it is difficult to check the current and flux densities of finished trans-formers, specifying loss figures including minimum weight of core and winding material (Aluminium or Copper) instead of densities may be considered for implementation in the specification. y Temperature rise test may be carried out by feeding total loss corrected to 100C.