Technology

ASTA Technology is all about supremacy in reliability and economics.

In the recent past, world has witnessed unprecedented innovation and efficiency enhancement of Transformers without compromising its reliability. Continual improvement of ASTA CTCs – the life line of Power transformers – has enormously contributed to this success.

ASTA offers of Quality winding solutions for large power transformers – whether GSUs or Inter-Tie transformers. It is the constant dialogue between ASTA technical team and transformer designers that has made it possible to bring out the most valuable changes in the winding design – where reliability and economic aspects have been emphasized as foremost factors.

The designing of power transformer requires knowledge in various complex technology fields, such as – Magnetic field, stray flux, eddy currents, loss generation, temp rise, hot spot, internal & external cooling and oil flow, hydraulics, mechanical design, short circuit, noise, seismic requirements, transport, electric network, impulse tests, voltage transients, resonance, dielectric design, electric field, electric withstand for AC and impulse etc. The technology of winding material, therefore, demands knowledge of finer points of these fields.

Challenges  offered by LV winding of GSUs – like, high current, high magnetic stray field- especially high radial component at the winding ends, radial compressive forces during short circuit, risk of bulking etc – have been comprehensively met by ASTA by providing solutions like Giant CTCs –which help to improve the space factor. Using it with Netting tape (ASTA patent) instead of paper insulation, not only even further increases the space factor (up to 30%), it also improves the thermal performance (decrease in temp gradient by over 50%).

To make the winding short circuit-proof, epoxy bonding has been used for CTCs. In order to withstand the compressive radial forces without bulking, a minimum stiffness of conductor – which is dependent on the property of the material and section modulus of the conductor-  is necessary. CTCs without bonding naturally have a low section modulus – not sufficient enough to make the winding of a large GSU transformer short circuit-proof.

Similarly, in HV windings of GSU transformers, epoxy bonding is only possible if the insulation of the single conductor is enamel coated instead of paper wrapped. The additional advantages include – better space factor, more economic design, increased competitiveness, a more compact winding with higher resistance against short circuit forces and also a better performance with respect to load noise generation. It also eliminates the risk of corrosive sulphur effects due to the direct contact of oil with bare copper surface- further ASTA R & D projects pending.

ASTA Low-Chip technology ensures freedom from problems of standard full-epoxy applications. During polymerization, epoxy from fully covered strips flows down especially towards free space between corner radii. This results in non-soluble gas inclusions getting trapped in such areas causing partial discharge at high electrical stresses.

ASTA Low-Chip technology offers enormous advantages such as : partial discharge-free HV windings as per IEC standard, no tilting during pressing process, suitable for inter-leaved disc coil HV winding having high series capacitance, compact winding (increase of winding factor up to 7%), high short circuit force stability, high efficiency of transformer, saving on winding supports, optimal cooling, improved throughput, cost saving potential up to 5-10%.

If we look at the Inter-tie transformer/Auto transformer, its tertiary windings, though have low voltage, low rating – often suffer from short circuit problems. On the other hand, the LV-HV windings have high stray flux – generating eddy losses and hot-spot problems. Also have high voltage – resulting in dielectric problems especially for impulse testing. It is difficult to make them short-circuit-proof, especially the inner common winding which is prone to buckling failures. Depending on type of regulation and consequently on its position, the TAP winding may cause severe short circuit and impulse testing problems. ASTA offers confident solutions to transformer designers to tame down all such issues.

For different and sometimes contrary requirements regarding the proper winding design in large
Power transformers, ASTA offers solutions which allow to design reliable and yet competitive transformers. In evaluation of a consequent application of ASTA’s fleet of conductor materials, studies have demonstrated that based on the total cost of a transformer savings of about 3% to 5% are achieved.

On top of these savings, with ASTA inside – what is granted for the life of the transformer are –Highest Quality and Long-term reliability !