what happens to a transformer when it is first connected to a power line
Electricity transformers
past Chris Woodford. Terminal updated: August 23, 2021.
The mighty power lines that criss-cross our countryside or wiggle unseen below city streets bear electricity at enormously high voltages from power plants to our homes. It's not unusual for a ability line to be rated at 300,000 to 750,000 volts—and some lines operate at even higher voltages. [1] But the appliances in our homes utilize voltages thousands of times smaller—typically just 110 to 250 volts. If you tried to power a toaster or a Tv set set from an electricity pylon, it would instantly explode! (Don't even recall about trying, because the electricity in overhead lines will almost certainly kill you.) So in that location has to exist some way of reducing the high voltage electricity from power plants to the lower voltage electricity used by factories, offices, and homes. The piece of equipment that does this, humming with electromagnetic free energy equally it goes, is called a transformer. Let'southward take a closer await at how it works!
Photo: Smash from the past: A strangely shaped transformer at the Chickamauga Dam near Chattanooga, Tenn. Photographed in 1942 past Alfred T. Palmer, Role of War Administration, courtesy of The states Library of Congress.
Contents
- Why practice we use high voltages?
- How does a transformer work?
- Step-down transformers
- Step-up transformers
- Transformers in your dwelling
- Transformers in exercise
- What are solid-state transformers?
- Find out more
Why do we use loftier voltages?
Your first question is probably this: if our homes and offices are using photocopiers, computers, washing machines, and electric shavers rated at 110–250 volts, why don't power stations simply transmit electricity at that voltage? Why do they use such loftier voltages? To explain that, we demand to know a little well-nigh how electricity travels.
As electricity flows down a metal wire, the electrons that carry its energy jiggle through the metal construction, bashing and crashing about and generally wasting energy similar unruly schoolchildren running down a corridor. That's why wires go hot when electricity flows through them (something that'southward very useful in electrical toasters and other appliances that employ heating elements). It turns out that the higher the voltage electricity you use, and the lower the current, the less energy is wasted in this way. So the electricity that comes from power plants is sent down the wires at extremely loftier voltages to save free energy.
Photograph: Coming down: This onetime substation (pace-downwardly electricity transformer) supplies power in the pocket-size English village where I alive. It's near 1.5m (5ft) high and its task is to convert several chiliad volts of incoming electricity to the hundreds of volts we use in our homes.
But there's another reason too. Industrial plants take huge manufacturing plant machines that are much bigger and more energy-hungry than annihilation you take at home. The energy an appliance uses is straight related (proportional) to the voltage it uses. So, instead of running on 110–250 volts, power-hungry machines might use x,000–30,000 volts. Smaller factories and machine shops may need supplies of 400 volts or so. In other words, different electricity users demand unlike voltages. It makes sense to ship high-voltage electricity from the power station and then transform it to lower voltages when it reaches its various destinations. (Fifty-fifty so, centralized power stations are still very inefficient. Nearly 2 thirds of the energy that arrives at a ability plant, in the form of raw fuel, is wasted in the plant itself and on the journeying to your home.)
Photograph: Making big electricity transformers at a Westinghouse factory during World War II. Photograph by Alfred T. Palmer, Role of War Assistants, courtesy of US Library of Congress.
How does a transformer work?
A transformer is based on a very simple fact about electricity: when a fluctuating electric current flows through a wire, information technology generates a magnetic field (an invisible pattern of magnetism) or "magnetic flux" all effectually information technology. The strength of the magnetism (which has the rather technical proper name of magnetic flux density) is direct related to the size of the electric current. So the bigger the current, the stronger the magnetic field. At present there's another interesting fact about electricity too. When a magnetic field fluctuates effectually a piece of wire, information technology generates an electric current in the wire. Then if we put a second coil of wire next to the first one, and transport a fluctuating electric current into the first coil, nosotros volition create an electric electric current in the 2nd wire. The current in the first coil is usually chosen the main current and the electric current in the second wire is (surprise, surprise) the secondary electric current. What we've done here is laissez passer an electrical current through empty infinite from one coil of wire to another. This is called electromagnetic induction considering the current in the starting time curlicue causes (or "induces") a electric current in the second coil. Nosotros can make electrical energy pass more efficiently from one gyre to the other past wrapping them around a soft iron bar (sometimes chosen a core):
To make a coil of wire, we simply curl the wire round into loops or ("turns" every bit physicists like to phone call them). If the second coil has the aforementioned number of turns as the start coil, the electrical current in the second ringlet will be nearly the same size every bit the one in the kickoff coil. Just (and hither's the clever part) if nosotros take more than or fewer turns in the second coil, we tin make the secondary current and voltage bigger or smaller than the primary current and voltage.
I important matter to note is that this trick works simply if the electric current is fluctuating in some fashion. In other words, you take to utilize a blazon of constantly reversing electricity called alternate electric current (Air conditioning) with a transformer. Transformers practice not work with direct current (DC), where a steady current constantly flows in the same direction.
Step-down transformers
If the first curl has more turns that the second coil, the secondary voltage is smaller than the master voltage:
This is called a step-down transformer. If the second coil has half as many turns as the get-go whorl, the secondary voltage will be half the size of the primary voltage; if the second gyre has one 10th every bit many turns, it has ane tenth the voltage. In general:
Secondary voltage ÷ Chief voltage = Number of turns in secondary ÷ Number of turns in primary
The current is transformed the opposite way—increased in size—in a step-downward transformer:
Secondary electric current ÷ Main current = Number of turns in primary ÷ Number of turns in secondary
So a step-downwardly transformer with 100 coils in the primary and 10 coils in the secondary will reduce the voltage past a factor of 10 but multiply the current by a cistron of 10 at the same time. The power in an electric electric current is equal to the electric current times the voltage (watts = volts ten amps is one way to think this), so yous can run across the power in the secondary coil is theoretically the same as the power in the primary whorl. (In reality, there is some loss of power between the primary and the secondary because some of the "magnetic flux" leaks out of the core, some energy is lost because the core heats up, and then on.)
Step-up transformers
Reversing the situation, we can make a step-up transformer that boosts a depression voltage into a high ane:
This time, we have more turns on the secondary coil than the primary. It's still true that:
Secondary voltage ÷ Primary voltage = Number of turns in secondary ÷ Number of turns in master
and
Secondary electric current ÷ Main current = Number of turns in primary ÷ Number of turns in secondary
In a step-up transformer, nosotros use more turns in the secondary than in the main to get a bigger secondary voltage and a smaller secondary electric current.
Considering both pace-down and step-up transformers, you can see it'southward a general dominion that the coil with the most turns has the highest voltage, while the coil with the fewest turns has the highest current.
Transformers in your home
Photo: Typical home transformers. Anticlockwise from meridian left: A modem transformer, the white transformer in an iPod charger, and a cellphone charger.
As we've already seen, there are lots of huge transformers in towns and cities where the high-voltage electricity from incoming power lines is converted into lower-voltages. Merely there are lots of transformers in your home likewise. Large electric appliances such as washing machines and dishwashers utilise relatively high voltages of 110–240 volts, merely electronic devices such as laptop computers and chargers for MP3 players and mobile cellphones utilise relatively tiny voltages: a laptop needs about 15 volts, an iPod charger needs 12 volts, and a cellphone typically needs less than vi volts when you charge up its battery. So electronic appliances like these have small transformers built into them (often mounted at the end of the power lead) to convert the 110–240 volt domestic supply into a smaller voltage they can use. If you lot've ever wondered why things like cellphones have those big fat chunky ability cords, information technology'southward because they contain transformers!
Photos: An electric toothbrush continuing on its charger. The battery in the brush charges by induction: in that location is no direct electrical contact betwixt the plastic brush and the plastic charger unit in the base. An induction charger is a special kind of transformer split into two pieces, ane in the base and one in the brush. An invisible magnetic field links the 2 parts of the transformer together.
Induction chargers
Many home transformers (like the ones used by iPods and cellphones) are designed to charge up rechargeable batteries. You tin see exactly how they work: electricity flows into the transformer from the electricity outlet on your wall, gets transformed down to a lower voltage, and flows into the battery in your iPod or phone. But what happens with something like an electric toothbrush, which has no power lead? It charges upwards with a slightly different type of transformer, which has one of its coils in the base of the brush and the other in the charger that the brush stands on. You can find out how transformers like this piece of work in our article about induction chargers.
Transformers in practice
If you've got some of these transformer chargers at home (normal ones or induction chargers), you'll have noticed that they get warm after they've been on for a while. Because all transformers produce some waste oestrus, none of them are perfectly efficient: less electrical energy is produced past the secondary gyre than we feed into the principal, and the waste heat accounts for most of the difference. On a small home cellphone charger, the heat loss is adequately minimal (less than that from an old-fashioned, incandescent light seedling) and non unremarkably something to worry almost. But the bigger the transformer, the bigger the current it carries and the more oestrus it produces. For a substation transformer like the one in our photo upwards in a higher place, which is nigh as wide as a small car, the waste heat can be actually significant: it tin damage the transformer'due south insulation, seriously shorten its life, and brand information technology much less reliable (let's not forget that hundreds or even thousands of people can depend on the power from a single transformer, which needs to operate reliably not just from mean solar day to twenty-four hour period, but from year to year). That'south why the likely temperature rise of a transformer during operation is a very of import gene in its design. The typical "load" (how heavily it's used), the seasonal range of outdoor (ambient) temperatures, and fifty-fifty the altitude (which reduces the density of the air and therefore how effectively information technology cools something) all need to be taken into account to figure out how finer an outdoor transformer will operate.
In exercise, most big transformers have congenital-in cooling systems that use air, liquid (oil or water), or both to remove whatever waste heat. Typically, the main part of the transformer (the cadre, and the principal and secondary windings) is immersed in an oil tank with a oestrus exchanger, pump, and cooling fins attached. Hot oil is pumped from the acme of the transformer through the heat exchanger (which cools it down) and back into the bottom, fix to repeat the wheel. Sometimes the oil moves effectually a cooling circuit by convection lonely without the use of a divide pump. Some transformers have electric fans that blow air past the oestrus exchanger'south cooling fins to dissipate oestrus more than effectively.
Artwork: Large transformers have built-in cooling systems. In this case, the transformer cadre and coil (red) sit inside a large oil tank (gray). Hot oil taken from the pinnacle of the tank circulates through one or more heat exchangers, which misemploy the waste heat using cooling fins (light-green), before returning the oil to the aforementioned tank at the bottom. Artwork from US Patent 4,413,674: Transformer Cooling Construction by Randall N. Avery et al, Westinghouse Electric Corp., courtesy of US Patent and Trademark Part.
What are solid-state transformers?
You volition accept gathered from reading what's above that transformers can be very large, very clumsy, and sometimes very inefficient. Since the mid-20th century, all kinds of neat electrical tricks that used to be carried out by large (and sometimes mechanical) components take been done electronically instead, using what'south chosen "solid-state" technology. Then, for example, switching and amplifying relays have been swapped for transistors, while magnetic hard drives have increasingly been replaced by flash memory (in such things as solid-state drives, SSDs, and USB retentiveness sticks).
Over the last few decades, electronic engineers have been working to develop what are called solid-country transformers (SST). These are essentially compact, high-power, high-frequency semiconductor circuits that increase or subtract voltages with better reliability and efficiency than traditional transformers; they're likewise much more controllable, then more responsive to changes in supply and demand. "Smart grids" (future power-transmission systems, fed by intermittent sources of renewable free energy, such as wind turbines and solar farms), are therefore going to exist a major application. Despite huge interest, SST technology remains relatively little used and then far, but information technology's likely to exist the most exciting area of transformer blueprint in the futurity.
Observe out more
On this website
- Electricity
- Electrical motors
- Induction chargers
- Magnetism
- Voltage optimization
On other websites
- The History of the Transformer: A very good timeline from the Edison Tech Center, with some fascinating photos and videos.
Books
For older readers
- Transformers Design and Applications by Robert G. Del Vecchio et al. CRC Press, 2018. A detailed guide to power supply transformers.
- Transformer and Inductor Design Handbook by Colonel William T. McLyman. CRC Printing, 2011. A detailed, applied guide to designing electrical machines using inductance.
- Electrical Transformers and Power Equipment by Anthony J. Pansini. Fairmont Press, 1999. Explains the theory, construction, installation, and maintenance of transformers and the dissimilar types of transformers earlier going on to embrace related ability devices such as excursion breakers, fuses, and protective relays.
- Transformers and Motors past George Patrick Schultz. Newnes, 1997. This book has a much more than "hands-on," practical experience than some of the other books listed here; it's intended more for electricians and people who take to work with transformers than those who want to blueprint them.
More full general books for younger readers
- DK Eyewitness: Electricity by Steve Parker. Dorling Kindersley, 2005. A historic look at electricity and how people have put it to practical use.
- Ability and Energy by Chris Woodford. Facts on File, 2004. One of my own books, this describes how humans have harnessed energy (including electricity) throughout history.
Patents
There are hundreds of patents roofing electricity transformers of dissimilar kinds. Hither are a few particularly interesting (early) ones from the US Patent and Trademark Office database:
- Usa Patent 351,589: Arrangement of electric distribution by Lucien Gaulard and John Gibbs, October 26, 1886. Gaulard and Gibbs outline how transformers tin be used to step upwardly and step downwardly voltages for efficient power distribution—the basis of the modern electricity supply organization throughout the globe.
- US Patent 433,702: Electrical transformer or induction device by Nikola Tesla, August v, 1890. Tesla outlines a stage-shift transformer (i that can produce a phase deviation between the primary and secondary currents).
- United states of america Patent 497,113: Transformer motor by Otto Titus Bláthy, May 9, 1893. A combined transformer and motor produced by one of the inventors of the transformer.
- US Patent 1,422,653: Electrical transformer for regulating or varying the voltage of the current supplied therefrom by Edmund Berry, July 11, 1922. A transformer with a punch that allows you to adjust the output voltage.
News articles
- The Transformers: Superheroes of Electric Inventions by Vaclav Smil. IEEE Spectrum. July 25, 2017. There are billions of transformers on the planet—in your smartphone, your laptop, your toothbrush, and elsewhere; isn't it time we appreciated them a bit more? Includes a potted history.
- Smart Transformers Will Make the Grid Cleaner and More Flexible by Subhashish Bhattacharya, IEEE Spectrum, June 29, 2017. Looking to a time to come powered by solid-state transformers.
- A Drill to Replace Crucial Transformers (Not the Hollywood Kind) past Matthew Fifty. Wald. The New York Times. March 14, 2012. If transformers are an essential role of the ability grid, how can you remove them during maintenance or component failure?
- Next for the Grid: Solid State Transformers by Michael Kanellos, Green Tech Media, March 15, 2011. An overview of how solid-country transformers could revolutonize our power grids.
References
- ↑ Manual voltages vary from country to country according to the distance over which electricity needs to be sent, but typically range from virtually 45,000–750,000 volts (45–750 kV). However, some long-distance lines operate at voltages of over 1 million volts (1,000,000 volts or 1000 kv). See Protection Technologies of Ultra-High-Voltage Air conditioning Transmission Systems by Bin Li et al. Elsevier, 2020, pp.1–5. High-voltage lines are classed every bit 45–300 kV; actress-high voltage range from 300 kV–750 kV; and ultra-high voltages are generally in a higher place 800 kV, co-ordinate to Overhead Power Lines: Planning, Design, Construction by Friedrich Kiessling et al, Springer, 2003/2014, p.6.
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