Hello friends, my name is Chinmay Deshpande. In this video lecture we are going to discuss about reactive power control. The sub topic is necessity of reactive power. Now let's have a look for the analogy of reactive power. There are numerous physical analogies for this quantity and one important analogy is reasonably accurate and it is the process of filling the water tower tank with the water and one bucket at a time. Suppose you want to fill a water tower tank with the water and only way that you can do it is nothing but climbing up a ladder carrying the bucket of the water and then dumping the water into the tank. You then have to go back down from the ladder and we have to take more water from the tanker. So let's say this tanker is nothing but a source of the water and here as we have to pour the water with the help of bucket so it will act as a loom. So strictly speaking if you simply go up a ladder without carrying anything and come back down from the ladder without carrying anything you have not done any work in the process. Now remember that the people going up and down the ladders do not absorb or produce energy over a complete cycle and are therefore analogous to the reactive power. Now what is the total work which is to be done? climbing the staircases up with the bucket of water then we have to pour this bucket of the water in the tank and again we have to come down from the stairs so total work done is nothing but climbing the staircase up plus staircase down Now while coming down from this tank towards the source, is there any increase in the level of the water? No, there is no any increase in the level of the water. But still it is required, why it is required? To fill the bucket of the water from the source, that is from a tanker. So, therefore, whatever the direction of flow of the water through the bucket from source to this load, it is nothing but an active power. And on the other hand, coming down from this tank towards the source, it is nothing but what? It is nothing but reactive power. The second analogy that one can take it is nothing but a foam on the beer. It is a fairly good example here because the space in the glass is taken up by the useless foam. If you see this is the thing but the useless foam. It is not of having any use. Leaving less room for the real beer. So therefore if you see here this is nothing but your total is nothing but apparent power which is denoted by a full glass. So, electricity is nothing but what here it is available from the utility. What is the real power? Whatever portion of the beer which is actually drinkable then we can say in case of electricity we can say which is able to do a work. So this will be treated as a real power. And what is the reactive power whatever foam which is there it is basically useless. So therefore electricity which is unable to do the work it is nothing but what it is related to the reactive power. So that's why in this analogy the power factor is then the ratio of wear that is a true power to the entire volume of the mug that is wear plus foam or we can say total apparent. The third analogy we can take is nothing but this is what is your packet of the wafers. Now let's say in the packet of the wafers it will be up to this level only. So actual amount of the wafers that we are going to consume it is nothing but what? It is your real part or in terms of power you can say that it is true power. So what is your some kind of preservatives will be added and some amount of air has to be there within this packet. So this air, it is not used basically, but it is required for packaging purpose. It is required for keeping that wafer at a good quality. So therefore, this air, we are not going to consuming this air, so it will be treated as a reactive power. But we are paying for a total packet. We are not paying for... Only 10 or 15 number of wafers which are present in the leaves or any kind of wafers packet. So therefore we are paying for total power which is nothing but apparent. So let's have a discussion about number of definitions which are given in the literature related to reactive power. Now active power will contribute to the energy consumed or transmitted but reactive power does not contribute to the energy. But why reactive power or VAR is required? It is very important. It is required to maintain the voltage. to deliver the active power that is vast throughout the transmission line. If we don't have enough quantity of reactive power, there will be a problem of a voltage sag, there will be reduction in the amount of the voltage, and it is not possible to push the power which is demanded by the load through the line. Third definition we can say, reactive power is essential to move the active power through the transmission and distribution system towards the consumer. Next is the thing what reactive power is amplitude of the power oscillations with no need transfer of energy and it is caused by energy storage components which are there in electrical engineering. There are only two energy storing energy components that is nothing but capacitor and inductor. This is again a very good definition of reactive power. It is basically described as the quantity of unused power that is developed by a reactive component such as inductor or the capacitor in an AC circuit. I like this definition very much because it is very interesting definition. It is a simple exchange of energy between two dissimilar energy storing forces. Now we have two extreme examples of time relationship between voltage and current which are found in the inductor and capacitor. What is inductor? Inductor is a coil of wire that is used to make the motors and the capacitor is made of parallel conductive plates which are separated by some amount of insulating material. The electrical properties of these two devices are such that if they are both connected to the same AC voltage source, the inductor absorbs the energy during the same half cycle that the capacitor is giving the energy. And similarly the inductor produces the energy during the same half cycle that the capacitor absorbs the energy. So, neither of them, neither inductor nor capacitor will absorb any kind of real power over one concrete cycle. Therefore, when the motor needs or motor requires reactive power, it is not necessary to go all the way back to electrical power generators on the transmission grid to get it. We can simply put a capacitor at the location of the motor and it will provide the VAR which is needed by the motor. So if you see please remember your capacitor C it is nothing but positive VAR which is always provides the reactive power and inductor L is nothing but negative VAR. This is also one kind of definition that's why purposefully I have keep this definition at the end reactive power is useless power now we cannot say directly it is a useless power. Whatever analogy we discussed earlier, if I have a bucket of water, if I want to go towards the tank and if I want to pour it, that is nothing but actual work because the level of the water will increase. But when I come down from that tank towards the source, that is towards the tanker, there will not be any significant increase or change in the water level. That's why one can say that coming down from that tanker towards your or coming down from whatever the storage towards tanker it is of useless no but it is required to take next bucket of them. So in the same way we can say that even though in the literature it is mentioned it is useless power but it is required to maintain the voltage and to deliver the active component of them. Now let's have a discussion about what is the necessity of the reactive power. Now we know that we have a number of equipments which are generally designed to operate at a certain level of the voltage and whatever permissible change within the voltage is plus or minus 5%. Now voltage control in an electrical power system is very important. Why it is important in order to have a proper operation of electrical power equipment. In order to prevent the damages such as overheating of the generators and the motors reduces the transmission losses and to maintain the ability of the system to withstand and prevent the voltage. Now what happens at a low voltage? As our devices our equipments are designed to operate at a certain voltage. So the voltage which is applied to such equipment if it is low then it performs poorly. For example, light bulbs provide less illumination, induction motor can overheat and it can be damaged and some kind of electrical equipment will not operate satisfactorily. Again there is a second thing, if we have a low voltage which is given to the equipment, these are the issues that we discuss here. But if we give a high voltage to the equipment, again it will damage and it will shorten their lifetime. So what we have to comment here whatever devices which are designed for a certain voltage range the voltage should not go too low beyond certain limit it should not go too high beyond certain limit. So in general decreasing reactive power can cause the voltage to fall while increasing in a reactive power can cause voltage to rise. Now reactive power or VAR it is used to maintain the voltage to deliver the active power throughout a transmission line that we already discussed previously in a definition of reactive. Motor nodes and other nodes require reactive power in order to convert the flow of electrons into a useful. So when there is not enough reactive power the problem occur is nothing but a voltage sag that is reduction in the voltage level and it is not possible to push the power which is demanded by the load through the line. A voltage collapse will be occur because of that whenever the system tries to serve much more load than the voltage can support. If the voltage reduction continues it will cause additional elements to treat. which it will lead to a further reduction in the voltage and the loss of the load. That results of these entire progressive and uncontrollable declines in a voltage is that the system is unable to provide the reactive power that can be required by the supply or that can be required by the load. So here when reactive power supply lowers the voltage now we know that as the voltage drops the current must be increased because if I want to maintain let's say power if I take here active power P we know that active power P is VI into cos phi. So I will think about only these two parameters. If I want to keep the power constant lower the voltage what we have to do. current will be increased or what happens with the voltage draw the current must be increased in order to keep your power constant or maintain the power supplied. What happens because of that? causing the system to consume more reactive power and again further it leads to the voltage now we know that losses are denoted by I square R so if the I is increased here then losses I square R will also increase as the losses increase there will be difference in the sending in voltage and receiving in voltage and again it leads to a voltage drop. If the current increases too much, the transmission lines go offline overloading other clients and potentially causing cascading failure. So, that's why if the voltage drop is too low, some generators will disconnect automatically to protect themselves. Voltage fallout occurs when an increase in the load or a waste generation or transmission facilities causes a dropping voltage, which causes a further reduction in the reactive power from the capacitor and the line charging. And still there are further voltage reductions. Thank you for watching this video. In this video we discussed about what is reactive power, what is necessity of reactive power along with some analogies. Thank you.