1. CORE BUILDING
2. COIL WINDING
3. ASSEMBLY
4. DRYING AND TANKING
5. TESTING AND INSPECTION
6. FINISHING AND DISPATCH

1. CORE BUILDING

The received material is stacked after passing quality inspection. The Core clamps are assured to suit the dimensions specified in the design. The Core laminations are then stacked one over the above as per the design specification. The core is due clamped by core clamps and tightened by core bolts. The tightened assembly is then positioned vertically.

The test: The preliminary core loss test will be conducted before passing to the assembly stage.

2. COIL WINDING

The received raw materials is checked for dimensions and insulation thickness at random as per the quality plan and measured values are recorded in the goods inspection note. Generally the winding is made of either copper or aluminium.Care will be taken to ensure that the H.V and L.V windings are manufactured as per the design. As soon as the coil is removed, the dimensions are checked and stored in a separate area.

3. ASSEMBLY

The built core is first kept erect and the three limbs are tightened with webbing tapes.The LV coils are placed over the limbs of the core, above which the cylindrical HV coils are placed with proper insulation.The insulation materials like pre-compressed press boards and kraft paper are used. It is ensured that all the electrical clearances are maintained as per the design. The HV and LV connections are made and the tap changer is fixed in proper position and the complete active part is placed in the oven for drying.

The test: The turns ratio test will be conducted before passing to the drying stage.

4. DRYING AND TANKING:

First the insulation resistance is checked and the active part assembly is kept in drying oven. The temperature is maintained at around 100deg C for the required number of hours. The insulation resistance is then measured at frequent intervals and when the required levels are achieved, the core coil assembly is taken out of the oven, tightened and then tanked. The tank is then filled with filtered hot oil. It is ensured that all the electrical clearances are maintained as per the design.

5. TESTING & INSPECTION:

The following routine tests will be conducted in-house in relevance with IS-2026 / IEC-60076 .

• Measurement of insulation resistance
• Measurement of voltage ratio and vector relationship.
• Measurement of winding resistance.
• Measurement of impedance voltage and load loss.
• Measurement of no-load loss and no-load current.
• Dielectric tests:
• Separate source withstand test.
• Induced over voltage test.

The following type tests / special tests will be conducted at reputed testing institutes like CPRI, ERDA and ANNAUNIVERSITY as per the customer’s requirement.

• Temperature Rise test.
• Lightning impulse test.
• Dynamic ability to withstand Short circuit.
• Noise Level test.
• Harmonic Analysis test.

6. FINISHING & DISPATCH:

All the standard and optional fittings, accessories are fitted before dispatch.