Growing improvements in the power sector have given way to the emergence of new transformer technologies. These new-generation transformers have improved core materials, better safety levels (such as fire resistance), space optimisation, lower costs, reduced failure rates, and increased asset life. In addition, they are equipped with features such as lower noise levels, environment-friendly technology, and adaptability with the smart grid.
Power Line presents a round-up of key advanced transformer technologies…
Smart transformers are an integral component of digital substations. Smart transformers can independently regulate voltage while allowing remote operation by maintaining contact with the smart grid. They use applied semiconductor technology for changing the voltage ratio, and can attain high power density. They also operate at a high frequency, thus reducing both cost and size, making them economical. Additionally, smart transformers minimise energy consumption and greenhouse gas emissions. They can provide stable, optimal power supply and protect electrical equipment from power fluctuations, thereby elongating equipment life.
A phase-shifting transformer (PST) is generally used to control active power flow on three-phase electric transmission networks. Its working principle depends on a phase-shifted voltage source injection into the line by a series-connected transformer fed by a shunt transformer. A major advantage of PSTs is that they empower the grid operator to regulate unexpected loop flows, thus enabling more efficient use of the system. India’s first indigenous PST was commissioned by Bharat Heavy Electricals Limited in December 2014 at the Kothagudem Thermal Power Station Stage VI in Telangana.
HVDC convertor transformers
High voltage direct current (HVDC) transmission is an economical process for the transmission of bulk power over long distances. Since all generating plants produce alternating current (AC), HVDC convertor transformers are required to convert it to direct current (DC). These transformers also convert the DC back to AC for power consumption. They have AC windings connected to the AC system and valve windings connected to converters, which are further connected in a series circuit to build up the necessary level of DC voltage. The advantage of these transformers is high electricity transmission coupled with lower transmission losses.
Energy efficient transformers
Energy efficient transformers (EETs) can be used by power utilities to improve the efficiency of the transmission and distribution (T&D) system and subsequently decrease T&D losses. These transformers are specially engineered to have a high performing design. They use low resistance copper wires and suffer minimal heat losses, besides requiring less coolant and having an increased running time. EETs can reduce losses up to 60 per cent.
Conventional transformers use mineral oils as the insulating fluid. In ester-filled transformers, natural esters are used for liquid insulation of the transformer.
These transformers have the significant advantage of being fire resistant, as natural esters have about twice the fire point of mineral oil at 360 ºC, as well as a flashpoint of 320 ºC. In case of leakage, ester-filled transformers fare better than their conventional counterparts because natural esters are biodegradable, and thus risks of soil contamination are minimised.
Dry-type transformers are an emerging technology wherein the windings with the core are kept within an air-filled, pressurised, sealed tank. They are motionless, solid-state devices without any moving or rotating parts. They do not need to be kept in fire-resistant vaults and do not emit toxic gasses. The two types of dry-type transformers are cast resin transformers and vacuum pressure impersonated transformers. They can reduce the risks of fire hazards and are thus ideal for areas such as residential buildings, offices, schools, hospitals and metro stations. The Kochi metro station has deployed dry-type transformers.
A mobile transformer is a portable device used in mobile substations. It finds deployment in emergency situations where an interim grid connection or temporary power supply is needed, such as during load peaks, replacement of existing substations, or malfunction. It is a trailer-mounted, self-contained system in a ready-to-connect form, with a short installation and commissioning time.
Several transformer technologies are available and emerging that offer cost efficiencies and are environmentally friendly. T&D utilities need to judiciously select the optimal transformer technology based on their requirements and after a thorough cost-benefit analysis.