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As part of its Distribution Network Augmentation Program, Tata Power Delhi Distribution, a joint venture of Tata Power and the Government of Delhi, commissioned Indias first 33/11 kV grid substation with dry type power transformers at Model Town, New Delhi in Sept 2013.

The grid substation, developed on the green grid design model, is equipped with dry type power transformers of 20 MVA, manufactured by QRE is used for the first time in India.

The grid is also safe for congested areas like Model Town. It is an unmanned grid and will be remote-operated from TPDDLs state-of-the-art Supervisory Controlled and Data Acquisition Center.

The Transformers are also equipped with Dry Type latest state of art most modern vacuum based motorized On Load tap changers ( OLTC ) to maintain constant voltage levels to the consumers.

These OLTC are also totally maintenance free.

QRE manufactured, Supplied and commissioned

First largest Dry type Power Transformers in INDIA.

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QRE-GREEnEsol PowER TRansfoRmER Co. PvT. lTd.

Some Comparison of Dry Type Transformers and Oil Filled

Transformers

Dry Type transformers use air as the cooling medium. Oil Type transformers are considered a potential fire and safety hazard. Oil Type transformers require maintenance and reliable fire safety extinguishers

Dry Type Transformers can be located closer to the load unlike oil transformers which require special location and civil construction for safety reasons. Locating the transformers near the loads may lead to savings in cable costs and reduced electrical losses.

Oil Type transformers may require periodic sampling of the oil and more exhaustive maintenance procedures.

However, though dry type transformers are advantageous, they are limited by size and voltage rating. Higher MVA ratings and voltage ratings may require the use of oil Transformers alone.

For outdoor applications, oil filled transformers are cheaper than dry types.

The advantages and disadvantages of dry-type transformers versus liquid-filled units depend upon the application. Dry-type transformers can usually be located closer to the load, resulting in cost savings because of shorter cable runs and lower electrical losses.

A liquid-filled transformer, on the other hand, may require

special construction features for the room in which it will be placed because of fire safety considerations. This may dictate a location some distance from the load.

In addition, periodic testing must be conducted on the fluid to determine its dielectric strength, water content, dissolved gases, and other parameters.

In some applications, there is no option to the use of liquid-filled transformers; dry-types are limited in size and voltage handling capability. Liquid-filled types are available in almost limitless kVA and voltage ratings.

Also, if requirements calls for a transformer to be located outdoors, it may be less expensive to purchase a liquid filled unit. With oil as the liquid, the cost would be lower than for a dry-type of equivalent rating; with low-firepoint fluids, the cost would probably be comparable to a dry-type.

For liquid-filled transformers, the main cooling/insulating mediums used today are mineral oil, high-molecular-weight hydrocarbon, and silicone fluid. If a leak occurs in the transformer tank, fire safety becomes an important issue.

Because of hazards associated with tank rupture and the possible ignition of the dielectric, a thorough analysis covering fire safety and the possible effects on the environment should be carried out well in advance of device installation. These considerations can have an effect on installation costs, long-term operating expenses, and maintenance procedures.

QRE-Greenesol Power Transformer Co. Pvt. Ltd.No. 11/23, "SURYADEV", 20th Main Road, 1-R Block, Rajajinagar, West of Chord Road, Bangalore-560 010, India.

Web: www.qgp.in. Email: enquiry@qgp.in

BRIEF COMPARISON TABLE OF OIL FILLED Vs CAST RESIN TRANSFORMER

Sl.No.

Oil Type Transformer Cast Resin Dry Type Transformer

1 Hygroscopic Non Hygroscopic : Complete Embedding of Winding in Resin prevents penetration of moisture into winding and breakdown by ionization. No further Drying is required prior to commissioning.

2 Inflammable Non Inflammable : Insulation system used makes Cast Resin Transformers self-extin-guishing, which eliminates the need of costly fire extinguishing systems.

3 Low Short Circuit Strength High Short Circuit Strength : Cast Resin Windings have highest possible strength levels for generated electrodynamic short circuit forces.

4 Low Impulse Strength High Impulse Strength : Resin after casting act as interturn & inter winding insulation to enhance the impulse strength of transformer.

5 High Losses Low Losses : In view of lower copper losses the transformer is more efficient when work-ing at optimum & higher loading conditions, thus making the transformer more cost effective over a period of time.

6 Low Life Cycle High Life Cycle : Owing to negligible ageing of insulation the life of these transformers is considered to be higher as compared to 20/25 Years of oil filled transformers

7 High Maintenance Low Maintenance : Except occassional dust cleaning no maintenance is required

8 High Cost Installation Low Cost Installation : Possibility of installing these transformers closer to load centers reduces cost of LT Cabling & soak pits.

9 large Space Space Saving : The size of these transformers is less compared to oil filled transformers

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