Introduction

Mirzapur Electrical Industries Limited made its small beginning for the manufacture of Electrical Transformers in the year 1966 and today it is poised for a phenomenal growth into Power Transformers up to 50 MVA/132 KV. Company has many strides in the manufacture and supply of over 40,000 transformers of various capacities and voltages to almost all the Electricity Boards, Industrial customers and other Power Utilities in India. The Company enjoys an excellent image as a reliable Transformer Manufacturing Unit in the Country.

Range of Manufacture

Power and Distribution Transformers from 25 KVA to 10,000 KVA and Voltage Class of 3.3, 6.6, 11, 22 and 33 KV on HV with OFF LOAD/ON LOAD tap changer as per customers requirement.

Sealed, Completely Self Protected and Dry Type Transformers up to 1000 KVA Rating.

Booster and Furnace Transformer as per Customers requirement and specifications up to 10 MVA, 33 KV Class.

Power Transformers up to 50 MVA, 132 KV Class.

Standard And Specifications

The transformers are suitably designed for continuous operation for Indian Weather conditions as per IS : 2026, IS: 1180, IEC : 76, BS: 171, ANSI etc. Transformers up to 10 MVA, 3 KV Class are produced conforming to specific requirements of customers and requirement of the relevant standards. Design And Quality Control : AGRO SONS Transformers are adequately designed and manufactured for Lighting, Power Transmission and also Electric Furnace loads, meeting the most stringent Loading Conditions. Transformers up to 10 MVA, 33 KV Class have been developed by our own well qualified and experienced Engineers. Raw materials are accepted after proper inspection by our Quality Control Department.

Core

Generally all Cores are built from Non-aging high quality Cold Rolled Grain Oriented Silicon Steel Laminations of M4 Grade. Superior material viz. Grades M2H, M3H, MOH are also employed where required. Cores are stepped type and duly clamped by Core frames which are duly finished and painted with hot oil and acid resistant paint.

Tap Changer

The High Voltage Windings are provided with tappings to compensate for any incoming supply voltage variations. The Tap Change is done either by an off-circuit Switch or by an On-Load Tap changer. Off Circuit Tap Changer is made of insulating material and is designed to withstand the Test and Loading Conditions without any danger of Local Heating, arcing or flash over. ON LOAD TAP CHANGER of 9 Position (Linear) in steps of 2.5% and 17 Position (non-liners) in steps of 1.25% can also be provided if specially required.

Windings and Stabilising of Coils

Windings up to 300 KVA, 1 KV are made of paper insulated aluminium Conductors. Paper insulated Copper Conductors are used in Windings for larger ratings. The basic material viz. Aluminium or Copper is of a high conductivity and electrolytic grade.

Different types of Windings are in use :

Spiral or Helical, Crose - over and Continuous disc. The actual type if normally decided by the Transformer rating and the voltage Class. Typical Windings are shown below : The most important stage hereafter, is to balance the LV and the HV Coils electrically (also know as Sizing or Stabilising). This is done by clamping the Coils and air-drying the same in a hot-air, drying oven, primarily to drive out the moisture in the insulation and allowing the Coils to clamp down as they shrink. Proper balancing reduces the possibility of the windings failing under Short Circuit force. the sized coils are then taken up for assembly on the Core.

Coil Assembly, Connection And Final Drying

After assembling of the predried Coils on the Core, preliminary ratio test is done to ensure correct Voltage ratios at different taps. The tapings, brought out from the HV Windings are connected to an Off-Circuit Switch or to the terminal board of an On-Load Tap Changer. Similarly the line leads of HV and LV Windings are brought out for terminating at the Outdoor/Cable Box Bushings. The Core-Coil Assembly, duly connected, is pretanked in its Tank to ensure adequate clearances to earth. The assembly is then taken-up for Final Drying.

Final Drying

Units up to 33 KV Class are dried in a Hot-air, Drying Chamber up to a temperature not exceeding 105 Deg. C and for a duration dependent on the rating and Voltage Class. The dried-out assembly is finally clamped to the pre-established dimensions and tanked in its tank. All Bushings are connected to the Winding terminations, and the Core-Coil assembly is securely located in the tank. Processed oil is then filled and all accessories fitted before the Unit is taken for the final Works Test.

Customer's Inspection And Dispatch

If required, transformers are arranged for final test and visual inspection and for any other testes agreed upon in the Contract. After Customers' inspection, the Unit is painted, all accessories separately packed and 100% inspected before the packing cases are closed. This ensures complete supply of all accessories at site.

The main accessories are briefly described below :

Tank And Accessories

The Transformer Tank is fabricated from low carbon steel of SAIL or TISCO make. Thickness of plates are chosen to withstand specified pressure test (or Vacuum Test, in the case of Voltages above 33 KV). In addition, the Tank plates are adequately stiffened by use of Standard Rolled Sections of folded Sections. The under base is designed for uni/bi-directional rollers. Welding of the Tank, Stiffeners, Under base, Conservator etc. is done by experienced welders. Empty tanks are tested with Oil/Air for any leakages. After the Tank passes the leak test, it is dressed and cleaned for a first coat of Red-Oxide primer on the outside, and hot-oil and acid resistant paint on the inside. Two additional coats of enamel Grey are given on the outside. Epoxy painting is also done for polluted atmospheric condition. The Conservator is of Sufficient Volume to take care of expansion of oil in Tank. It is fitted with Standard fittings, viz. oil level gauge, oil filling and oil drain plug/valve etc. The Conservator is connected to the main Tank with provision to fit a Buchholz relay and shut off valve, if required.

Special Fittings
01. Oil temperature Indicator with Rigid stem or Capillary Tubing with max. Reading Pointer, Alarm and Trip contacts and   Resetting Device if required.

02. Double Float Buchholz Relay with Alarm and Trip contacts.

03. Magnetic Oil level gauge with low oil level alarm.

04. Winding Temperature indicator with Alarm and Trip contacts.

05. Radiator shut off valves.

06. Bi-directional rollers with plain/Flanged Rollers.

07. Sampling device attached to the filter valves.

08. Netural Current transformer.

09. Disconnecting chambers between the tank and the cable Box/bus duct on HV/LV side as required.

10. Marshalling Box with control terminals wired up to the Box and from the accessories.

11. On load Tap Changer and remote control panel with/without automatic voltage regulating relay.

Transformer Oil

Transformers are filled with filtered oil as per IS:335/1983. This insulating oil is of low viscosity and is duly refined by Oil purifiers. Instructions for regular maintenance of this oil are given in our Maintenance Manual.  

Bushings 

Bushings up to 36 KV for outdoor service are made of Brown glazed Porcelains as per IS:3347, IS : 2099 and IS : 8603. Bushings for compound filled cable boxes are as per IS : 9147. Leak proof Oil Seal or Gasket is provided between insulator and the Tank. For HV and LV Bushings, stems of Copper/Brass are used depending on the current rating. Terminal connectors and single gap fixed type Arcing Horns are provided as per customers requirements.

Paint

The inside of the tank is painted with hot oil and acid resistant anticorrosive Paint, Two coats of special Red oxide Zinc Chromate Primer are given on the outside of the tank. Two coats of synthetic enamel finish Paint, colour D.A. Grey as per shade no. 632of IS:5 are given prior to dispatch. 
TESTS : Each transformer is routine tested at our Works prior to dispatch.

Tests Conducted Are

01. Induced over potential withstand Test.
02. High Voltage withstand Test.
03. No Load Current and No Load Loss Test.
04. Impedance, Voltage and Load Loss Test.
05. Turn Ratio test.
06. Insulator strength measurement.
07. Measurement of Resistance.
08. Dielectric strength of oil.
09. Pressure and Vacuum Test for leakage detection.
10. Measurement of Zero sequence impedance.
11. Temperature Rise Test.
We also conduct Type Test such as Impulse and Dynamic Short Circuit Tests as per IS : 2026 in reputed Laboratories viz. C.P.R.I. Bangalore and Bhopal. More than 500 Nos. Transformers of ratings from 25 KVA to 1000 KVA have undergone Impulse/Short Circuit Tests successfully.

Technical Staff

AGRO SONS Transformers are designed and manufactured under the supervision of well qualified and experienced Engineers. We are fully equipped to manufacture power Transformers up to 10 MVA, 33 KV Class and our Factory for 132 Units is under construction. We have a team of experienced staff and workmen and assure our Customers of prompt after sales service, in addition to erection and commissioning.