Hello Samhitha,
Great questions. Rick has given a good overview of what kinds of over current protection and voltage stabilizer circuits are available, and what they do.
To expand on some of the questions you’re asking, I think it would be good for you to expand your background on how voltage and current are related. You mentioned that your teacher said some questions were “out of your scope” - let’s work on making your scope bigger! Bear with me if this is post is a bit long, and feel free to reply with more questions.
Before I get to answering your questions, let’s go over some basics. Voltage and current are two important concepts to understand whenever there is a discussion about using electricity to transfer energy.
Voltage means the amount of energy pushing the “stuff” flowing in a circuit. The “stuff” that carries energy in an electronic circuit is called charge, and these charges can be electrons (in the case of a copper wire), ions (in the case of electricity traveling in a solution like salty water), etc. The unit for voltage is the volt, which is one joule per coulomb - so, energy per unit charge.
Current means the rate of “stuff” flowing in the circuit. The unit for current is the ampere, which is one coulomb per second - so, charge per unit time.
The purpose of many of the electronic devices we encounter every day is to deliver power (which means to transfer energy over time). The air conditioner you are mentioning is one such device. The way that electronics power our appliances is by pushing energy via charges - the more energy per charge (voltage), and the more charges per second (current), the more power. The equation relating all this stuff together is:
(energy per second) = (energy per charge) * (charges per second)
or,
Power = Voltage * Current
One last thing before I get to your questions - there are a couple different ways of getting electrical power from a power source to an electrical device that consumes power. Two types of power sources you may have heard of are: Direct Current (DC) and Alternating Current (AC).
DC means that the voltage of the power source is a constant value. This is the kind of power you get when you use a battery, or when you plug into the USB port of a computer to get power.
AC means that the voltage of the power source is constantly fluctuating from positive to negative (negative voltage simply means that the voltage “push” on your electrical charges switches direction). This is the kind of power you get when you plug something into a standard wall outlet, and in the USA, the frequency with which the voltage switches back and forth is 60 times per second. The RMS* voltage we get in the USA is about 120 volts for small appliances, and 240 volts for bigger things like dryers and electric stoves.
*Quick aside: You might be thinking that, if the voltage keeps switching back and forth sixty times per second, isn’t the average voltage 0 volts? How can it be 120 volts? If so, that is a good thought. RMS means “root-means-squared”, and is a way of taking the average *magnitude* of something, even if it has an average value of zero. For example - say that I push on a rock for 1 second with 1 pound of force - then I switch to pulling on the rock for 1 second, again with one pound of force. The average force I put on the rock over those two seconds is zero. However, I was using my muscles the whole time, and it isn’t really fair to say that I was doing nothing for those two seconds! If I take the average *magnitude* of my force on the rock (ignoring push/pull and only taking the amount), I would get 1 pound of force for the entire two seconds. That’s what RMS is, and that’s why we use it to measure the magnitude of AC voltage.
The air conditioner unit (which ironically is also abbreviated as AC - please don’t get this AC confused with the electronics “AC” I was just talking about, and that I’m about to use later in this sentence!
) is plugged into AC power. It is designed to work with a consistent AC voltage level - if the RMS voltage is higher than expected, it might burn out, and if the RMS voltage is lower than expected, it might fail to work at maximum effectiveness, or, depending on the design, burn out. So, it is important that it get a stable RMS voltage from the outlet it is plugged into. That’s the purpose of the voltage stabilizer that you noticed.
Now, to your questions!
1. We aren’t trying to stabilize current flow, so much as voltage. Remember the distinction - if I crank the air conditioner up to full blast, we want its voltage to be stable! So, we want it to consume more current (because we need to consume more power, and power is voltage times current).
However, I think what you are trying to ask here is: Where does the remaining energy go, if we are stabilizing above-expected voltage by lowering voltage? And, where do we get the extra energy to stabilize below-expected voltage by raising voltage? The answer to the first part is: it either gets dissipated as heat (and thus wasted, at least from an electrical point of view), or it gets stored electrically for later use. The answer to the second part is: we either need to take more energy out from the wall to do this, or we need to use some stored energy.
2. I think the question you are trying to ask here is: “Why are there fluctuations in voltage?” After all, it is a voltage stabilizer that you were looking at. The answer to this is that we don’t live in a perfect world, and the power sources we have in our electronic circuits (like the AC circuit connected to the wall) can’t always respond perfectly to large surges in energy demand. For example, have you ever noticed that often the lights in your room might dim if you turn on the vacuum cleaner or hair dryer? The reason is that the voltage in your home’s AC circuit has dipped because of the momentary demand from your high-power appliance, which caused your lights connected to the same circuit to dim. Similarly, your home’s AC power could get a spike in voltage if a load on the circuit changes quickly. Simple devices like light bulbs can deal with these fluctuations without much difficulty, but some devices, especially things with motors or compressors (like an air conditioner) can get damaged if they don’t receive the voltage that they are designed for.
3. Depending on the design of the voltage stabilizer, yes! There are three so-called “passive” circuit elements that you may have heard of: the resistor, the capacitor, and the inductor. (It’s actually a bit more complicated than that, but let’s focus on the basics.) The resistor dissipates energy - when current flows through it, there is a drop in voltage, and the resulting loss in energy is removed as heat (or heat and light, in the case of an incandescent light bulb, which is just a glorified resistor). The capacitor and the inductor both can temporarily remove energy from a circuit, store it, and then spit it out later. A circuit designed with these kind of elements (called “reactive” elements, in contrast to the dissipative resistor) can remove energy from a circuit and then use that energy at a later time. It is feasible that the voltage stabilizer that you saw utilizes a circuit containing these elements (sometimes called a “tank circuit”) in order to store energy from voltage spikes and use that energy later on to maintain the proper voltage during voltage dips.
Feel free to reply with more specific questions, or if you’d like more details on a specific circuit. Rick’s post above is a great starting point for a summary of the different solutions for voltage stabilization.
There are also a number of great resources online for a more general background on electronics - the Wikipedia pages on Voltage, Current, and Alternating Current would be good places to start.
