Transformers can seem complicated, but in reality are really very simple machines. Salespeople, and marketing teams capitalize on uniformed buyers to upsell unnecessary and expensive features and accessories. Here are 4 fake facts that will have you paying more for your transformers than you need to.
Fake Fact #1: Natural ester fluid (AKA, FR3) gives your transformer magical powers
Neither claims are backed by research, or are even logical. Even the environmental effects are over-blown. According to the EPA (as of January 2020), the exact same clean-up procedures are required for an FR3 spill as for mineral oil. While it may be bio-degradable, it won’t cost you less on the clean up!
There are actually a couple of drawbacks to the fluid.
Drawback #1) High viscosity - it’s thick
Because of this, transformer manufacturers have to wind the coils with wider duct work. Duct work are the spaces between the windings where the cooling fluid circulates. This isn’t really an issue, as long as the fluid stays warm. Mineral oil is thinner, and therefore a more efficient coolant.
Drawback #2) It absorbs moisture faster than mineral oil
Any ingress of moisture into the transformer tank will immediately be wicked up by the FR3, sometimes causing oil and electrical tests to come back bad. There normally should never be any moisture in a transformer, but it may be introduced if the unit is opened during a repair or inspection, and FR3 will make sure it gets sucked right into the unit.
It's not a bad fluid, but it's not all it's cracked up to be either. Sorry guys. FR3 is not the fountain of youth. And with a price tag of $10-$15/gallon compared to around $5/gallon for mineral oil, you might want to skip the FR3.
Fake Fact #2: Copper windings are better than aluminum windings
Both copper and aluminum have been used as electrical conductors since the invention of transformers. During WW2, electrical manufacturers increased the use of aluminum as their conductor due to copper shortages, and it stuck. Aluminum is cost effective, and performs similarly to copper as transformer winding material.
Efficiency ratings are now governed by the US Department Of Energy. So unless you’re specifying a particular efficiency rating, or have specific loss requirements. An aluminum wound transformer from any manufacturer will be the exact same efficiency as its copper wound counter part.
Transformers are built to IEEE standards which dictate certain running temperatures for transformers (65C for example), regardless of winding conductor. Again, copper and aluminum are built to the same standards.
The biggest contributor to longevity in transformers, besides being free of manufacturing defects, is the integrity of the insulation paper, not the conductor material. The misconception that copper windings last longer than aluminum windings may have come from the observation that aluminum oxidizes in open air faster than copper does. However transformer windings are always immersed in cooling fluid (if liquid filled) or encased in resin (if dry-type) and are not exposed to open air, so they never oxidize.
In summary, aluminum wound transformers are as efficient, and reliable as their copper wound counterparts. Save 20-30% on your transformer, and stick with the industry standard aluminum windings!
Fake Fact #3: Step up transformers are different than step down transformers
Transformers run on AC (alternating current) electricity. In the US, the current changes direction (alternates) at a frequency 60 times per second. So which direction is the electricity flowing through the transformer? Both directions. The transformer doesn’t care if it’s stepping up, or stepping down. There is technically no such thing as a "step up transformer", or a "step down transformer". They are the exact same machine.
The machine becomes a “step down transformer” when the load is on the low voltage side, and the power source is on the high voltage side, and inversely it becomes a “step up transformer” when the load is on the high voltage side, and the power sources is on the low voltage side.
There are (2) design features that are more common in step up applications than step down applications. These two things might indicate the transformer was designed for step up operation.
It might be a step up transformer if...
1) The low voltage is delta connected, and the high voltage is wye connected
Primary voltages tend to be delta connected, and secondary voltages tend to be wye connected.
2) The adjustment taps are on the low voltage side (small 600V class transformers)
This only applies to small 600v transformers! Medium voltage transformers (2400v and above) keep the taps on the high voltage side regardless if they’re for step-up or step-down operation.
Some manufacturers (Maddox included) stamp “Suitable for step-up operation” on the nameplate. But this is just to put uninformed users at ease.
There’s no difference between a step up transformer, and a step down transformer. You might pay a little more for a step up transformer, but that's only because of supply and demand. It has nothing to do with the way the transformer is actually built.
Fake Fact #4: You need to change your oil every once in a while
This is the most shameful upsell by service companies out there.
The oil in your transformer does NOT break down over time like the oil in your car engine. Transformers have no moving parts, so the only thing that causes oil to breakdown in a transformer is internal electrical issues. If you’re needing to change or filter the oil in your transformer, something is wrong, and your transformer may need to be repaired! Don’t mask the issue by blindly replacing or filtering the transformer. That just erases the evidence of a potentially fatal issue.
Before paying for "premium" transformer features, be sure to do a basic cost-benefit analysis. Be weary of transformer axioms like "copper is better" or "FR3 makes it last longer". The price premium often carries little to no performance increase.