When you see a power substation, probably the last thing you think about is green technology. After all, aren’t all those transformers laced with PCBs and other hazardous chemicals? Well, some of them still are, but there is an increasing trend toward green transformers. These are starting to radically transform the environmental footprint of substations, as well as many other applications where transformers are used.
Transformers operate at high voltages, and therefore the high voltage transformer parts need to be well insulated. The traditional way of doing this is to fill the transformer with a non-conducting oil that prevents electrical arcs from the transformer to the ground, as well as coronal discharges – where the area around the transformer becomes electrically charged and glows blue. The same insulation approach is also used with certain other types of electrical equipment, including some high-voltage capacitors, switches and circuit breakers.
One of the best types of fluid for doing this is a class of compounds known as polychlorinated biphenyls (PCBs) – largely because these fluids are not flammable. However, the problem with PCBs is that they don’t break down when they are released into the environment – instead they build up in plant and animal tissues. Here, they can mimic hormones, causing toxic and mutagenic effects – including cancer and serious deformities. PCBs also release other highly toxic compounds when they are burned – including dioxins.
However, the effects of PCBs only started to be noticed in the early 1970s, and so they were widely used until then. Once the effects were known, PCBs were banned and substitutes started to be used – such as mineral oils. While these weren’t as dangerous as PCBs, they still did have a negative effect on the environment. However, the big problem was that PCBs dissolve in mineral oil – so when the PCBs were replaced, the mineral oil often became contaminated.
Now, mineral oil is starting to be replaced in new green transformers by other more eco-friendly compounds. For example, back in July, Siemens announced that it had produced the first large-scale transformer in the world that uses vegetable oil. All of the oil in the transformer comes from sustainable sources, is biodegradable and is actually less flammable than mineral oil. The vegetable oil also acts as an efficient coolant for the transformer, matching the performance of mineral oil for this purpose. The Siemens transformer is due to be installed at a substation near Karlsruhe, Germany, where it will connect the substation to the grid.
Another technology which is gaining traction is gas-insulated transformers. In these, the mineral oil is replaced with an inert gas – usually sulfur hexafluoride. This has good insulating properties, and also allows the size of the transformer to be reduced. This type of transformer is already in use at a number of power generation plants around the world, particularly in the Far East. However, the technology hasn’t made it into North America until very recently – the Bagnell Dam plant, located in Ameren, Missouri, is the first and only electricity generation plant in North America to deploy these transformers. The last of three gas-insulated units was installed there in September, and the plant expects to phase out its old transformers by 2014.