Jorge Piñeros, HUB SAM application engineer, from Hitachi ABB Power Grids, explained that special transformers are necessary in the mining activity primarily because they adapt the supply voltage from the network to the input voltage to the rectifiers, isolate the rectifier from the mains supply and limit short-circuit currents, relieve the motor and/or mains supply from common mode voltages, and reduce the effect of radio interference from the rectifier unit.

At Heading to PERUMIN, he explained that within mining production lines it is very common to find variable speed drive systems due to the association of pumps and motors that normally have non-linear loads, where energy conversion processes can occur through VSD (Variable Speed Drive) or VFD (Variable Frequency Drive) devices, depending on the different types of load.

"In the mining segment it is very common to have all these elements with particularities and that affect the transformer and the power grid," he said.

"The main function of VSD devices is to set the speed of the unit to which it is connected (motor or pump), set the torque and to help save energy and improve the efficiency of the system".

This way, he said, in mining, modern rectifier units need special designed transformers , but not normal or standard transformers, since the latter can lead to accelerated deterioration of the transformer insulation system and therefore give rise to a failure or unplanned interruptions in production lines.

"Fortunately, this challenge is supported by the IEC 61378-1 and IEEE C57.18.10 standards, which establish criteria and methodologies for the design and manufacture of industrial transformers, helping to raise the performance, reliability and duration of the system" said the specialist.

He also added that the design stage of the special transformer must consider the increase in dielectric stress, thermal problems (in relation to harmonics), increased mechanical stresses and internal connections for phase shifts and multi-winding designs.

Harmonic currents increase losses

At another point in his presentation, Jorge Piñeros warned that harmonic currents increase additional losses in the windings, connecting bars, core flanges and main tank walls, thus leading to thermal problems such as premature aging of the transformer.

"Let us remember that the increase in temperature damages the insulating function of the transformer and with it the useful life of the equipment. So, as we have more harmonics, there will be more temperature and more losses in the transformer".

In this sense, he recommended a study of the distribution of temperatures along the coil to correctly dimension the cooling system and control the increase in temperature generated by harmonic currents.

Digitization of transformers

Later, Jorge Piñeros highlighted that digitization can also help increase the reliability of special transformers, through the TXpert monitoring platform from Hitachi ABB Power Grids, which works with a"condition"  based model for transformer maintenance and replacement, favoring the mitigation of maintenance costs, reduction of unplanned outages and an increase in the useful life of the equipment.

"The digitization process consists of capturing past and present information from the transformers and this allows the operations team to understand the current condition of the equipment. In addition, it allows connecting to other areas to send relevant information in real time and thus make assertive decisions".