How do transformers increase voltage? Learn how transformers increase voltage in this article on transformer basics electrical engineering.
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A step up transformer works simply by having more turns of wire on the secondary side. This increases the voltage but it decreases the current.
A step down transformer works by having less turns of wire on the secondary side. This reduces the voltage but increases the current.
Now this isn’t a magical device that produces more energy than it receives. For example a step down transformer might receive 240 volts and it outputs 120 volts. We see that the voltage halves but the current doubles. If we multiply the voltage and current we see the same value on each side. This is the volt amp value which is the power or apparent power and that has to remain the same. So if the voltage changes then the current has to change in proportion to maintain the power. So why do transformers use the units of kVA instead of kW?
Well the transformer is just transferring power between the coils so we use the volt amp unit. The kilowatts depend on what you connect to the transformer. The manufacturer doesn’t know what you will connect to the transformer, so they state the total rated apparent power in volt amps. That’s because in AC circuits the load depends on the true power in kilowatts and the power factor which is basically efficiency and this varies depending on the device. Some energy is consumed but it produces no work it is just wasted as heat and we call this reactive power with the units VAr.
Power factor is just the ration of true power and apparent power. If you think of a glass of beer, the liquid beer is the useful part, this is your true power in kilowatts. But there is always some foam which is useless, we don’t want that. This is the reactive power or the volt amp reactive. You pay for the total volume of the glass regardless of how much foam and beer is inside. This is your apparent power in volt amps. Now if you have a good bartender you will get a little foam and lots of beer for your money, but if you have a bad bartender then you’re going to get lots of foam and not so much beer for your money. The transformer manufacturer is basically saying this transformer can handle a glass this big, but its up to you how much beer and foam you put into that. The less foam you try to pass through, the more beer you can get out. So the more efficient the device is that you connect, the more things you can power.
