TRANSFORMER

Transformer:

A transformer is an electrical (static) device which transfers power from one circuit to other circuit magnetically at a constant frequency. In fact transformer works for AC power. The two circuits namely primary and secondary (LV- low voltage & HV- high voltage) are electrically isolated but coupled magnetically. The power levels of LV side and HV side are same and maintain a constant frequency however the voltage and current parameters varies based on the turns ratio. Turns ratio (K) is the ratio of Secondary turns to primary turns. Transformer is generally rated in KVA.

If one side of the transformer circuit has less turns compared to other side it is treated as LV side (as voltage directly depends on the no. of turns of a coil) and HV side is the one which has more no. of turns. On LV side the transformer operates on low voltages, high currents and on HV side its opposite.

Transformer structure

Transformers in Solar PV applications:

Particularly for solar PV power plant applications transformers are generally used to step up the voltages to higher values (Several KV’s).  In detail, Transformer’s input is connected to the inverter output and its output is connected to the utility grid. It functionality includes stepping up the voltage levels of the generated power from the PV panels , equaling it to the grid voltage levels so as to have safe on grid operation.

On other side it also provides galvanic isolation between DC input and AC output side (Grid) & filters the harmonic content from the inverter output.

The High voltages in transmission and primary distribution sides leads to low power losses, so generally engineers prefer transformers for having high voltages to cut down losses.

Transformers in PV application are generally categorized as:

1. Distribution transformers

          2. Power transformers 

Distribution Transformer:  Pole, pad mounted are two types of distribution transformers. Pad mounted distribution transformers are common type of transformer used in solar array fields, while pole types are frequently used in conventional distribution systems. Typical power rating varies between 50KVA -2500KVA. In general, primary sides are connected to the inverters (string type) output (typically 230V, 440V AC), Outputs of distribution transformers (33KV maximum, however some vendors offer higher voltages on request)are connected to substation lines or power transformers in the case of large solar PV plants.

Distribution transformer

Power transformers: Power transformers are step-up transformers; these will step-up the voltages to very high levels (66KV, 132KV, 220KV, 400KV) and transmit the power. Higher voltages are preferred to reduce the losses. Typical power rating is 200MVA & above. For large PV power plants power transformers are used to synch with the grid to allow the transfer of generated power to the utility grid.

Power transformer

Solar PV plant incombination with Distribution and Power transformer

Again, two types of distributed transformers based on the coolant used Dry and Liquid type. Liquid type (windings are of oil immersed - NONA (Natural Oil Natural Air)) because it dissipates heat quickly, also it is smaller in size (doesn’t require thick insulation, core material) and comparatively has lower cost.

For typical indoor installations Dry type (transformer windings are encased with Epoxy resin) transformers are used, however these are fire proof and non- explosive. These are not design flexible and are of particular ratings & complex manufacturing process makes it more costly.

Single Line diagram of solar PV plant: The pointer indicates the use of transformer in PV power Plant.

Important parameters of transformers: 

Voltage, basic impulse level, winding connections, impedance, efficiency, winding material, temperature rise, cooling, insulation class, seismic resistance, altitude derating.

Voltage: It is important to mention the voltage rating (ranges b/w 300 – 700AC), as inverter output determines the low voltage (LV) level of the distribution transformer. The output voltage of the distribution transformer will determines the voltage level of power transformer.

Winding connections: It is important to mention the winding connection type for the design of protection scheme, the most common 3-phase distribution configuration for transformers in solar applications is the delta-to-wye configuration, with the wye grounded or ungrounded. This configuration allows for an independently derived neutral on the wye-connected secondary winding, which not only is essential for safety purposes but can also provide multiple voltages at the inverter pad without requiring additional transformers. The delta-connected primary winding provides a reliable configuration for the utility, because it allows harmonic currents to circulate within the transformer. This prevents harmonics from flowing into the electrical distribution system.

Substation transformers usually use the grounded wye–to–grounded wye configuration. However, substation transformers are multi winding transformers that also have a tertiary delta winding. This delta winding prevents harmonics from circulating in the electrical transmission system and stabilizes the neutral point when loads become unbalanced.

BIL (Basic impulse level): In terms of product safety BIL is very important as it determines the withstand capacity of the winding insulation inside the transformer. Normally the transformer is subjected to impulse voltage levels which are very high than the rated voltages (max./operating) to make sure will defend themselves in case of any faults or malfunction.

Impedance: It is the opposition to the AC power, characterized by Z (can be reactive, resistive). Normally it is rated as %Z, it is used to determine the voltage drop and at no load it can be taken the voltage drop of the transformer.

Transformers under 50KVA have impedances of less than 2%, for 75KVA – 2500KVA transformers; the standard nominal impedance value is 5.75%. The IEEE standard allows a tolerance of +/- 7.5% for two winding transformers and 10% in multi winding transformers.

Efficiency: Transformer efficiency is defined as the ratio of output power to the input power, it depends on the capacity of the transformer. According to NEMA (National Electrical Manufacturers Association) for 75KVA – 1000 KVA transformer the range of efficiencies would be normally 98% - 99%. The loss of power is due to the internal losses of the transformer.

Winding material: Manufacturers offer transformers with copper or aluminum windings. Copper offers better electrical conductivity by volume than aluminum but aluminum offers better electrical conductivity by mass. Copper made transformers are more likely compact and are more costly.

Temperature rise: During the operation of transformer the losses inside will result in heat which inturn results in temperature rise, this effect reduces the performance of the machine. Technically it is defined as the average temperature rise of the windings compare to the ambient temperature is about 40 deg Celsius when the machine is at its nominal rating.

For liquid filled transformers are 55 – 65 deg Celsius, dry types are about 115 – 150 deg Celsius. If a technician installs a liquid-filled transformer with a temperature rise of 65°C in a 40°C environment and loads it at its nameplate rating, the average temperature of its windings should not exceed 105°C.

Transformers used at PV projects experience more thermal cycling than a typical utility distribution transformer. A solar project transformer starts cold in the morning and reaches its peak temperature midday during peak ambient and peak energy periods. Then it cools back down and starts the cycle over again. Special consideration needs to be given when selecting a solar project transformer to ensure that the cooling system can handle the temperature swings. An O&M team is also important to carefully monitor and reset the pressure system in some geographic locations.

Insulation class: A transformer’s insulation class correlates to its temperature-rise value. Manufacturers provide electrical isolation in the transformer with enamel-coated wires and insulating material between the winding layers, and they vary materials and different thickness to achieve different insulation-class ratings. After they have insulated the transformer winding, they impregnate the coils with varnish to minimize the possibility of moisture intrusion, increase mechanical strength and improve heat transfer, and they then mount the transformer winding in a protective enclosure.

Cooling: Dry-type transformers are self-cooled and rely on passive methods conduction, convection and radiation to transfer heat from the transformer to the environment. Liquid-type transformers are more common in solar applications.

Transformers steel enclosures filled with a nonconductive dielectric fluid, which insulates the internal components and helps keep them cool, protect liquid-type transformers. The heat that the windings generate transfers to the dielectric fluid, which circulates via natural convection. The heat then dissipates into the environment via the transformer’s oil cooler, which is an external heat exchanger or radiator. This is a rather elegant and energy-efficient cooling method.

As shown in following, the industry classifies liquid-filled transformer cooling according to internal cooling medium, internal cooling mechanism, external cooling medium and external circulation method.

For example, pad-mounted distribution transformers have a cooling classification of ONAN: O indicates that the cooling medium in contact with the windings is an oil with a flash point of 300°C or less; the first N indicates that the oil circulates via natural convection; A indicates that the external cooling medium is air; the second N indicates that the air circulates via natural convection.

Substation transformers of 10 MVA and larger typically have multiple capacity ratings, such as 12/16/20 MVA, which correspond to different cooling classes, such as ONAN/ONAF/OFAF. In this example, the lowest rating, 12 MVA, represents the self-cooled transformer capacity and has the ONAN cooling class rating. The next one, 16 MVA, is the capacity of the transformer when it uses fans to force air through the oil cooler radiators; this rating has the ONAF cooling class rating. The highest rating, 20 MVA, is the capacity of the transformer with both internal coolant circulating pumps and external fans, and it has the OFAF cooling class rating. Each cooling level typically adds approximately 25% more capacity.

Dielectric fluids can be either mineral oil or less-flammable vegetable-based oils, such as Envirotemp FR3 and BIOTEMP. Transformer products designed for solar applications often use the latter because they are derived from a renewable resource and are biodegradable.

Seismic resistance:  According to the International Building Code contain specific seismic resistance requirements for transformers at certain places. Installations at health care facilities, emergency response locations (such as fire and police stations) and critical government facilities frequently must have seismic certification.

Altitude de-ratings: Because the air is less dense at higher altitudes, the effectiveness of the cooling system and the dielectric strength of the transformer decrease at higher elevations. Therefore, you must either de-rate transformers installed above 3,300 feet or specifically design them for the location. The product safety standard that applies to liquid-filled distribution and substation transformers requires that you de-rate transformer capacity by 0.3% for every 330 feet increase in elevation above 3,300 feet.

Technical parameters of aTransformer:

Transformer configuration: Type of winding connection of the transformer.

Rated power (KVA) : The maximum power the transformer can withstand. It differs for different types of transformers.

Primary voltage (KV): The LV winding of the transformer which is based on the inverter output. It depends on the transformer rating.

Efficiency: It is defined as the ratio of output power to input power of the transformer.

BIL(basic impulse level): It is the maximum withstanding capacity of the insulation winding during the faults/abnormal conditions.

SIL(switching impulse level): It is the maximum withstanding capacity of the insulation winding during the switching operations.

Rated frequency: The maximum deviations with respect to the desired frequency, this should not be high for a good machine.

Type of coolant: The coolant used to dissipate the heat produced inside the machine, the cost does depend on the type of insulation used. Dry type transformer is more costly compared to liquid type. Ex. ONAN, epoxy – resin (dry type).

Tapping (%): Various ranges of voltages can be obtained within a single transformer avoids multi transformer operation if required.

Secondary voltage (KV): Rated output voltage of the transformer. It depends on the capacity transformer.

Temperature rise: This discloses the rate of heat rise inside the machine. It shows significant effect on the efficiency of the transformer.

Liquid Insulation temperature: It is the maximum withstand temperature of liquid (coolant) used inside the transformer.

Impedance (%Z): Percentage impedance data is used to find the voltage drop, voltage regulation.

Load losses @ 75^oC (W): The transformer losses (power) during the loaded condition & at 75⁰C.

No load losses @ 75^oC (W): The power losses of the transformer during no load & at 75⁰C.

Winding materials: The materials used for the transformer winding (LV,HV) usually Aluminium or copper.

Total weight: The total packed weight of the complete transformer.

Datasheet of transformer:

The following datasheet gives the information about a transformer specifically on the different parameters which are mostly discussed above.

Follow the link (open in the new tab):

http://www.coronabd.com/download/ABB%20Oil%20Distribution%20Transformer%20Catalogue.pdf

Pricing of Transformer:

The cost of transformer mainly depends on the active materials used i.e., copper/steel (for making core, windings), no load losses (efficiency) & the type of insulation used (liquid/dry).

Generally the active material costs 50% of the total cost of the transformer. However, the different vendors have different price lists. But the below information will give us a rough idea about the price.

Eg: A 100KVA typical distribution transformer is around 3000 euros, 400KVA is around 7000 euros and 1000KVA is around 12000 euros.

Manufacturers:

The following are the well known Transformer manufacturers across India.

Name of the company		Address
ABB India		NA
Transformers and Rectifiers india ltd.		Survey No. 427 P/3-4, & 431 P/1-2, Sarkhej-Bavla Highway, Moraiya, Sanand, Ahmedabad–382213, Gujarat, INDIA.Phone No. +91 2717 661661 Email ID: marketing@transformerindia.com, purchase@transformerindia.com
Alstom T&D India		A-18, First Floor, Okhla Industrial Area, Phase – II, New Delhi – 110 020,Contact Number - 011- 41610660.
Siemens India		130, Pandurang Budhkar Marg, Worli, Mumbai, Maharashtra 400018 Phone - 022 2498 7000
Kirloskar Electric Company Limited
Gujarat Transformers Pvt. Ltd		JD Nagar, Maneja, Vadodara, Gujarat 390013 Phone - 0265 264 2422
Uttam Bharat		B-189/A , Road No.9 (F), VKI Area, Jaipur - 302013 Rajasthan India
Urja Techniques (India) Pvt. Ltd		B-17 Shriram Industrial Estate, G.d. Ambekar Road, Wadala.
Kotsons Pvt. Ltd		C-21, U.P.S.I.D.C., Site-C, Sikandra, Agra, Uttar Pradesh 282007 Phone:0562 264 1422
Danish Private Limited		F-679, Sitapura Industrial Area, Jaipur- 302022. INDIA
Century transformers pvt. Ltd.		Century Transformers Pvt. Ltd, 5, Jatia Road, Bally, Howrah – 711201, India,Mobile : 09830258414, +91 9903256404 E-Mail: swarup_t@yahoo.co.in, info@centurytransformer.com
Technical associates ltd.		Technical Associates Ltd., 8th km., Faizabad Road, Ismailganj, Lucknow, U.P. – 226016. Phone No. +91(522) 4053600 E-mail: contact@techasso.com
LE transformers india ltd.		LE TRANSFORMERS INDIA LTD, Old No. 2, New No.10,Bagavathi Amman Street , Lakshmi Amman Nagar, Erukkancherry. Chennai – 600118. Tamilnadu, India Phone : +91-44-25595271, Fax : +91-44-25594271 E-mail: kucheraa@yahoo.com / letindialtd@gmail.com
Vaibhav Group		Vaibhav Group, 1 – Ra- 11 Vigyan Nagar, Kota, Rajasthan. Phone No: +91 744 2427809 E-mail ID: info@vaibhavgroup.com
RUNTHALA INDUSTRIES		A-68, Road No. 1, Vishwakarma Industrial Area, Jaipur-302013 (Raj.) Phone No. +91-141-2330875, +91-141-3130875 Email ID: info@runthalaindustries.com, purchase@runthalaindustries.com
Prima transformers		Mr. Ajit M. Pimple (technical Director), Prima Transformers Pvt. Ltd, Plot No.809/2, Kothari Ind Estate, Kothari Cross Road, Santej, Gujarat, India – 382721. Phone No. +91-2764-286115/02764286645(j), 9825866827 Email ID: info@primatransformer.com
Mahashakti energy limited		MAHASHAKTI ENERGY LIMITED, A-8, New Focal Point, Dabwali Road, Bathinda -151 001, Punjab, India Phone No. +91-164-2280058, 2281778 Email ID: info@mahashaktienergy.com
Vijai Electricals ltd.		Vijai Electricals Ltd, 6-3-648/1&2, Off Raj Bhavan Road, Somajiguda, Hyderabad – 500 082. Andhra Pradesh, INDIA. E-mail ID: websales@vijaielectricals.com
Bharat Bijlee pvt. Ltd.		Corp. office : Electric Mansion 6th Floor Appasaheb Marathe Marg Prabhadevi Mumbai 400 025 T: +91 22 2430 6237 / 6071 Email: bblcorporate@bharatbijlee.com
Synergy transformers		"Diksha Parva" Maheshwar Madhi Main Road, Pipaliya Nagar, Mangrol Road, Keshod. Dist: Junagadh. (Gujarat) INDIA Phone : +91 02871 231791 +91 02871 253077 Web : www.synergytransformers.com
MAHENDRA TRANSFORMERS (P) LIMITED		Add : F – 10, South Side of G.T. Road Industrial Area Near N.H. 24, Ghaziabad – 201009 (UP), INDIA Phone : 0120 –4561635, 2840474, 2840781 Mobile : +91-9818140474, +91-9818450084 Fax : 0120 – 4561635 Email : mahendratransformers@gmail.com & ag.mktg@hotmail.com URL : www.mahendratransformers.com
Kappa electricals pvt. Ltd.		KAPPA CONSOLIDATED PVT. LTD., SOUTHERN ELECTRIKS 19, MOUNT ROAD, SAIDAPET, Chennai, TN, 600 015, Phone : +91 - 44 - 22454709, 22454516, Fax : +91 - 44 - 22351662, 22451693
Marson's Electricals		Artoni, Mathura Road Agra, DH, 282 007 Phone : +(91)-(562)-2642327 Fax : +(91)-(562)-2641435
Muskan power infra structure ltd.		Muskaan Power Infrastructure Ltd Sua Road, Industrial Area - C Dhandari Kalan Ludhiana, PN, 141014 Phone : +91-161-2510641/2510642 Mobile : +91-9417033948 Fax : +91-161-2510645
P.M. electronics ltd.		B-10 & 11, Surajpur Site C, Surajpur Noida, UP, 201306 Phone : +91-120-2560890 Fax : +91-120-2560891
Prismatic india		Prismatic India Prismatic Engineering Pvt Ltd.Plot No 308,Link Road Jigani Industrial Area Bangalore, KK, 560105 Phone : +91-80-27826274 Fax : +91-80-27826278
Raksan transformers pvt ltd.		Raksan Transformers Private Ltd - Mohali, Punjab. Plot No.1413 HSIDC Industrial Estate-rai Sonepat, HY, Phone : +91-130-6535990 Fax : +91-130-2366991
Tesla transformers		30 "B", Industrial Area, Govindpura Bhopal, MP, 462023 Phone : +91 - 755 - 2586778 Fax : +91 - 755 - 2581865
Reacon power equipments pvt. Ltd.		Recons Power Equipments Pvt. Ltd Plot No. 38 Sector – 25 Faridabad, HY, 121004 Phone : +91-129-4062114/4062115 Mobile : +91-9871921777 Fax : +91-129-4151323
Roland electronics and devices		152C, Sarat Ghosh Garden Road Kolkata, WB, 700031 Phone : +91-33-4155525 Fax : +91-33-4158723
Standard transformers pvt. Ltd.		Standard Transformers Pvt. Ltd. P.B.No.8, Plot No-95 GIDC Industrial Estate Canacona South Goa, GO, 403702
T.S. international		Level 6, Chennai Citi Centre. 10/11 Dr.Radhakrishnan Salai Chennai , TN, 600004
Transformers and electricals kerala ltd.		Angamally South Ernakulam District Cochin, KL, 683573 Phone : +91- 484 -2452251 Fax : +91-484 -2452363, 2452873
UP transformers india pvt. Ltd.		UP Transformers (India) Pvt. Limited UPSIDC Industrial Area, Site – 2, Plot No. B1 - B2 Amawa Road Raebareli, UP, 229316 Phone : +91-535-2217110 Mobile : +91- 9415335102
Mahindra electrical works		Plot No. A-433, Road No. 28 Wagle Industrial Estate, Thane , MH, 400604 Phone : 91-22-2582 3743/2580 1110 Fax : 91-22-2582 2461
EMCO		1st Floor,Piramal Tower, Peninsula Corporate Park, G. K. Kadam Marg, Lower Parel, Mumbai - 400 013 Email: emco.corporate@emco.co.in
Sukam power systems. Ltd.		SU-KAM POWER SYSTEMS LTD. Corporate Office Plot No. 54, Udyog Vihar, Phase VI, Sector-37, Gurgaon - 122001, Haryana, India

* Note: The above information may subject to vary without any notice and we will be not responsible for such happenings.

Here, the information source manufacturers list is companiesinindia.net and indiacatalog.com