Transformer oil. Insulating oil. Whatever you call it, this high temperature, high resistance oil is used in many of the things which keep our modern world afloat. Knowing is half the battle, of course, so let’s dive in and talk about what this oil does and how it’s made and graded.
Knowledge is power, and transformer oil is necessary for power. That alone should keep you posted.
What is transformer oil used for?
Apart from the obvious use, which is within oil-filled transformers, transformer oil finds a wide variety of applications in the world of high-voltage electricity.
In addition to its namesake, it’s also used in high-voltage switches, some capacitors, and circuit breakers. The essential qualities of these oils, namely that they’re able to handle both extreme temperatures and remain non-conductive, makes them well-suited for any application which requires high-voltage.
The general idea is that transformer oil can be used to prevent some of the problems which come with any situation that has a lot of electricity. These include basic insulation, the prevention of arcing shocks, and to prevent corona discharge.
What are transformer oils made of?
Transformer oils have undergone a couple of changes since being introduced.
The original transformer oils were comprised of polychlorinated biphenyls, or PCBs. While these chemicals had the desired profile for insulation and heat resistance there quickly proved to be a major problem.
Not only are PCBs toxic, they’re also bioaccumulative. They build up in the body over time, which means that a person can be slowly poisoned by being around them for an extended period of time. The body simply doesn’t eliminate PCBs at any reasonable rate.
Modern transformer oil, on the other hand, is comprised of a special variety of mineral oil. Specifically, the designation for the oil used in transformers is ASTM D3487. The oil must meet those standards, at the very least, in order to qualify as transformer oil.
The hidden dangers of the past
There is an unfortunate side effect to having used PCBs in the past for transformer oil. Namely, the modern mineral oil formulation is completely miscible with the old PCBs. In older equipment this means that the oil is often contaminated with the toxic compound.
It’s a fairly common occurrence. Fortunately, modern methods have begun to sort things out. There are a variety of scrubbers and other filtration methods which have been developed over the last few decades which are designed to remove PCBs entirely.
That’s an important difference, especially in areas where PCB contaminated oils are heavily regulated. In California, for instance, anything above 5 ppm of PCB molecules classifies the oil as hazardous waste.
There are continuing efforts in many countries to both reclaim the oil and to get rid of any equipment which is contaminated. The continuing efforts are ongoing at this time, since the usage of PCB compounds was so prevalent in the past.
Testing of transformer oil
Transformer oils are a safety precaution, and they need to be tested regularly. Like any other oil, insulating oil will eventually become contaminated and have it’s properties altered.
Oils are a complex liquid, not comprised of a single molecule but instead of many different compounds. This leads to a relatively unstable fluid as the chemical reactions which occur within heated or electrified oil are quite complex.
The guidelines for the testing vary a bit, but in general the oil should be inspected on-site twice a year, a sample should be sent away for dissolved gas analysis once a year, and Furan testing every two years once the transformer has been in operation for a minimum of half a decade.
These required tests aren’t just red-tape, either. Insulating oil is used to prevent arcing and other dangers which naturally begin to occur once you get into high-voltage applications.
They’re also used to cool these electrical components, so the oil needs to retain both of it’s primary applications: high resistance and the ability to withstand high temperatures.
Provided that it retains these qualities, all is well.
While transformer oil is minimally reactive, it will still degrade over time. Most of the problems which occur will come from water seeping into the system and particulate matter getting lodged. There’s also the issue of oxidation from coming in contact with other materials contained within the transformer.
Sludge formation is a serious problem. The precipitate can get on the transformer’s components and reduce the amount of heat dispersed in the oil over time.
Oxidation is the main enemy of most oils. When they react with oxygen they form acids which alter the chemical, mechanical, and electrical properties of the oil. It causes both sludge formation and the overall decomposition of the oil.
Damaged oil can function for quite a while, but it becomes less and less feasible to purify it on-site as time goes on. The owner of the equipment is also looking at damage to their machinery, or in more extreme cases, complete failure. It’s not just mandatory to check the oil regularly, it’s also a sound business decision.
But what can be done about the limited, albeit long, shelf life of transformer oils?
Regeneration of transformer oil
When transformer oil has reached the end of its lifespan, the owner of the equipment will have a few choices to face. The first thing done in most cases, however, is testing for PCBs.
If they fall under a maximum threshold level(in most cases 2ppm) the oil can often be regenerated onsite. However, if the oil is over the threshold but still under a certain level(generally 50ppm) it can be sent off site to a recycling facility.
Fortunately, nearly complete regeneration of transformer oil is possible with modern techniques. Through the use of something like DST they can be returned to their original state.
With some forethought, business owners can reduce their expenses by making sure they have everything in place before their oil begins to decay. It’s not so tall of an order, and in the end it’s often a much more environmentally friendly solution.’
Demand for transformer oil is currently climbing quickly. While the demand in the Western world might be relatively static, developing countries like China and India are increasing the size of their respective power grids which means a higher demand for the oil.
Like all petroleum products, there’s only a limited amount of oil to go around. Regeneration isn’t just economically smart, it’s also environmentally sound. Replacing insulating oil is certainly feasible, and in the case of especially contaminated oils it may even be desirable, but the truth is that the more of it that remains in circulation the better.
Put simply: if it can be recycled, it probably should be.
An overlooked part of the modern world
Without transformer oils, every power substation on the planet would be a potential death trap for anyone who entered. They’re absolutely essential to the infrastructure for anywhere that plans on having electricity.
While they can seem a bit complicated, insulating oils are actually much more simple to understand than many of the other varieties of lubricant on the market. Provided it can pass the specifications laid out it’s usable.
While it is concerning that there seems to have been a false start with PCBs, modern efforts to handle contaminated equipment and regenerate old oils while removing the impurities seem to be increasing all the time. The market for transformer oils certainly isn’t going out of style anytime soon, as increasing power needs also require that the oil be supplied.
The good news is that nearly all of this oil can be regenerated with minimal loss. The modern world continues to surprise, and it’s looking like transformer oil will be folded into the future circular economy of oil rather than being discarded.
And that’s a good thing for everyone.