Salient Features

• Uttara Power Ltd. transformers are low loss , Reliable , Moisture Resistant
• Standards                : IEC – 76 , BS – 171 , ANSI C57.12 , VDE 0537.
• Frequency                : 50 Hz , on request 60 Hz.Ratings          : Up to 10 MVA33 KV.
• Tappings                  : ± 2.5 % ; ± 5 % or ± 2×2.5 % ; -7.5 % and others on request.
• Core : Kawasaki / Nippon Steel , JAPAN.
• Insulation : Weidmann , Switzerland.
• Super Enemelled . Copper: BRB / RR / Gazi Wires , Bangladesh.
• Copper Strip : BRB / RR / Gazi Wires , Bangladesh.
• Oil : HYRUX , Malaysia / Savita , India.

Core Building  for

Power and Distribution Transformers Transformer cores are built with CRGD (Cold – Rolled – Grain Oriented) low-loss silicon steel laminations.

Use of HIB Grade and laser scribed laminations for the core significantly reduces no load losses and noise levels as committed. A.

Well core sleeping and cropping offer stress-free laminations without burrs for fully aligned core building.

Specially dimpled sheets provide space between laminations for the most effective cooling. The laminations foremen the magnetic circuit are assembled on a special core building fixture.

These step-lap or mitered joints at the core corners ensure a streamlined magnetic flux path. The core limbs are held with resin-bonded glass bands to eliminate limb boards.

Yokes are clamped by solid mild steel plates with Yoked studs, ensuring high rigidity for withstanding mechanical shocks during transportation and short circuits.

Winding

Electrolytic great copper or super enamel are used to design horizontal requirements. Windings are made on the vertical winding machines with a great core by well-experienced tech – no craftsmen in a clean and safe environment, with positive pressure for superior reliability high-quality per – compressed insulation, per shrunk by a specially designed process, ensure grated pepper enabled.

long service stability. Termally up emergency overloaded beyond nameplate reting, wherever desire.

The winding has axial and radial cooling ducted to ensure effective heat dissipation in the oil and eliminating the hot spots, For high voltage windings, disc coil with excellent mechanical strength are used to take the stresses due to voltage level.

A special interleaved or shielded construction offers the most uniform voltage distribution despise system transients.

Core Coil Assembly

The winding is rigidly supported by a common pressure ring of dignified wood at the top and bottom, for precise alignment.

Oil profiled align rings are placed between HV and LV windings to reduce voltage stress levels. The ends and tapping leads of all windings are connected by special extra flexible, insulated copper cables which are rigidly braised in position. In oil-forced units, oil is circulated inside the windings by specially designed pipes of insulating materials.

High mechanical rigidity is achieved by hydraulic pressing at calcu – lated force and tightening all special crews. The core coil assembly is put into the tank with locating arrangements.

Tap Changer

For any kind of transformer tap changer is made of high-quality homogeneous insulating board or synthetic resin mold is mounted below oil level for changing the connections of tapes in the primary winding.

Tapping is adjusted by off circuit tap changer in the case of a distribution transformer of 11 KV class assembled on the top of the core – coil assembly.

Conservator Tank

The conservator tank is detachable by providing a flange at its point of connection to the tank cover.

The connection to the main tank cover will beat the highest point to prevent the trapping of air in the conservator tank which shall be detachable to facilitate cleaning.

Transformer Tank

It is made with steel sheet and covers are fabricated by welding. Tank is tested under pressure for finding any leakage. Tanks employed for housing the core-coil assembly are mechanically strong. For removing weld splatters, mill scales we have to paint shot and sandblasted the steel parts. Tank finish consists of three coats. One coat of anti-corrosive zinc chromate primer and two coats of weatherproof finish paint. Each coat is applied uniformly and cured at even temperature.

Radiator

Proper making of radiator is very important. Pressed steel radiators are specially made from ” D ” grade CRCA sheets with profile formed and elements are resistance welded with seam/arc welding machine. Each individual element and radiator under assembled conditions is tested with air pressure of approximately 3kg / cm2.

Routine Test

Uttara Power Ltd. Test laboratory is approved by BSTI, Electricity licensing Board of Energy Ministry. All test instruments are kept calibrated. Though all tests and checks are done during the production process and completed transformer.

Following routine tests are conducted:

• Insulation Resistance Test
• Induced over voltage test
• Separate source voltage withstand the test

1. HV High voltage test b. LV Low voltage test

• Turn ration test, polarity, and phase relationship test
• HV and LV resistance test
• No Load current and No-Load Loss measurement test
• Load Losses test at rated current and frequency
• Percentage Impedance
• Core Insulation test
• Insulation oil test
• Function of tap changer test

Type tests (one in each lot):

• Temperature rise test
• Overload test
• Noise level test
• Oil leakage test

Note: Short circuit test and impulse test can be conducted from BUET Dhaka upon negotiation.