I do not share that level of praise, as this video has false factual claims, and acts hyper repeating terms in sometimes useful but other times wrong or misleading forms. It's hard to explain in lecture format. It's also a chicken and egg set of issues, where one needs math good engineering students already have (through integral calc of trig), but also the ability to relate theory and practice in ways that are interactive, and visualize electrons and components, in ways standard framing of voltage or current misrepresent a bit relative to quantum physics where some very bright engineer run YT channels have engaged each other over errors or ways to improve the way common systems are presented or described. By then anyone in the game knows how chemists and physicists define positive or negative charges with opposite conventions, and has moved on to joking about which is which. We can't presume most electricians or users here get that. Failure to mention conductor heating as a primary reason VA need to be distinguished from W is a major weakness of this video. We're also in an era where things are more complicated to depict in theory vs practice than a few decades ago, as a HE washing machine may have a variable speed drive 3/4 HP motor, and not a 2-3 speed split phase or shaded pole motor of 1/3 or 1/2 HP as years ago, while switching power supplies or PWM LED dimmers don't follow the historic rules around which IEEE C2 or public utility law and rate based regulations evolved. That tasks engineers and educators with figuring out how to present such topics in useful but also accurate ways, and pretty much everyone with understanding archaic and modern systems that are ever increasingly complicated to get right, if that means factually truthful and not overly complex for users to grasp.
I don't know who your EE profs were, but this wasn't really a good explanation. As usual with him, he's a bit loose with conflating electrical terms that have very specific physical meanings. Also as usual, way too much content/talking for a relatively small amount of information conveyed. It's pretty clear that RUclipsrs do this to inflate their content in terms of total time. They shouldn't. And, there are even mistakes that he corrected with post-processing overlays. Why? Just go back and reshoot the clip the right way. I don't know why it's become socially acceptable on social media for people presenting as teachers to really just be having stream-of-consciousness conversations with themselves about topics. Review your own content. If there's wrong or superfluous information, edit it out. Then post it. Don't share wrong or misleading stuff and then sit back and be happy for the additional engagement of people correcting you in the comments.
Hi German here. We have a funny analogy for this to explain to trainees: KVA as apparent power is like a nicly poored glas of bear 🍺 the hole including the foam is the apparent power, the foam is the reactive (wattless) power and the nice yellow liquid is the active power 🥴 cheers
You explain kva like a hair stylist would explain it to a cook! You have such a confidence! So many mistakes! For example you said transformer induces current! No ! it does not! Transformer induces voltage and current is a function of the load. The first half is completely nonsense and little truth in the second half
My favorite analogy for reactive power and power factor is pushing a kid on a swing. If you give the kid a push at just the right time, it's easy to get the swing to go up high. But if you give a push at the wrong time, it's wayyy harder or impossible to keep things swinging. In the case of motors, you're essentially trying to slow down the motor with the load you have on it. So instead of the AC current "pushes" from the power company being perfectly in sync with it's movements, the load causes the motor to fight against that perfect timing. As a result, the power company is effectively pushing the kid at slightly the wrong time, resulting in wasted power that could have been useful if you had better timing. That's the big reason there's a market for fancy motor controllers and power factor correction devices. You can actually fix the imperfect timing if you're smart about it, resulting in better efficiency. You do it intuitively in the swing example by watching and feeling, in electrical engineering we use carefully tuned inductors/capacitors and computer equipment to do the same thing.
And I guess that is why you have big capacitors on those big air-con units, to tune the reactive load from pure inductance to capacitive/inductance balance.. Right ?
@daveleger2002 Power factor is definitely a part of it, after all a stalled motor is just a dead short... Tons of power consumed for nothing useful out till it gets going. But the capacitors are mostly there to keep your breakers tripping and wiring lighting on fire... The capacitor stores energy that's used for the initial push that's needed to get it moving. Typically when people talk about power factor it's a longer term, steady state description. Temporary fluctuations are usually a different concern.
Building on that: A mug of beer costs the same regardless of how much foam is in it. The mug equals the wire and breakers that you have to pay and size for. kW is the amount of actual power you are getting out of the motor. EG: kW = How much beer you get to drink.
@deang5622 Isn’t that what I said? That is what I meant to say at least. P = power output on the device = V * I * cos phi = measured in W (Also real used power = P * ŋ) S = Power measured as the load the device has on the grid = V * I = V / cos phi = measured in VA Edit: meant P / cos phi
Thanks for making this video. This is exactly what has been on my mind for the past few weeks as I was designing an off grid solar system for my farm house. And yes, it was the P=VI formula that kept tripping me! 😄
One thing, though, is that all of these items that you’re listing off like light ballast and most electronic equipment have built-in power factor correction if they are manufactured with any quality. The big item that you have to worry about is motor loads. But in most factories that have a lot of motor loads they also install automatic power correction, for those in order to bring the PF back up.
Thank you for this breakdown. I do a review model for public charging sites where I do assess the power available at the transformer level. For simplicity, I've always referred to the transformer power as "kW," though the the transformer rating is in kVA. What I am looking for in this is the total throughput or power available for the site, so kVA is the more accurate metric. The other factor I am checking for is a discrepancy between the power supply and the rated output power of the chargers themselves. Most often, the transformer is rated for more power (kVA) than the total kW rated output power of the chargers themselves, though some providers (Tesla in particular) can have rated output power at their chargers that is more than double the rated power of the transformer. Basically, checking the transformer enables me to know whether EV drivers will be seeing full, rated power when charging if the site is full or mostly full.
This was the first of your videos that went over my head, but that's definitely not on you. This was a great explanation. It gave me enough concepts that when I hear it five more times in different ways, it'll finally click. You got the concepts into me, though! And I appreciate that.
This is a good video. The power triangle is the most important thing to understand. Watts Real P is the X axis. VAR reactive is the Y and VA is vector sum (hypotenuse). When you're using real and imaginary numbers you can evaluate the rectangular sum or polar vector quantity in your head. With alternating current capacitors and inductors are reactive components and they store and release energy at different times. In perfect systems the real is the only part actually using real power, but you still need to account for the reactive components. It's why power factor correction is important because the power company still has to supply and transport the power in VA regardless of what is consumed and even if the load give it "back" every half cycle.
This was really good... And a real topic that clears the concepts that often caused me confusion within my own studies. It was fun, objective and to the point! Thanks
Thanks! I’ve noticed this on transformers and wondered this myself, especially when reviewing electronics and accessories. My practical tests have come up .9 number, and I’ve always thought it was an exaggeration factor for speccing.
I'm a retired electrician and I find you extremely refreshing, it's really nice to get a well thought out refreshing course I will recommend you to young electricians keep it up . Good job
Excellent class! Taking it a step further.... An explanation of how most of the reactive load in the real world, is due to inductive reactance and how capacitors are used to offset this load with capacitive reactance so that KVA comes much closer to equaling KW decreasing a lot of the wasted reactive energy, would be awesome to follow up with. You covered this subject very practically and better than many of my instructors in both technical school and college.
I’ve been in the game for 49 years. All those years operating and maintaining generators, power plants, transformers, and associated equipment. I taught for a few years as well. This is the best, most succinct, and accurate explanation I’ve heard. Thank you
I've been trying to understand kW vs kVA for about the same amount of time. The explanation in this video didn't help that much. I've learned more from reading these comments.
Yeah, this had me completely confused. I got it now. Very good explanation and completely necessary to understand this. Thanks. Much better than having to answer "well, it's umm, hmm. I don't know"
I really liked the video. The point was understood and the understanding was clear. I get the theory or concept. I believe he did a great job. Expressing a theory is about getting it across to the people you present it to in an understandable way. And this is a good example of that.
So basically, VA mechanically would be gravitational potential field (g⋅h, in J/kg) and mass flow rate (dm/dt, in kg/s) - as seen in a hydroelectric dam - representing the available potential energy transfer capacity, while W (watts) would be the actual mechanical power output, i.e. the portion of that potential energy converted into useful work, factoring in system efficiency (nu) (e.g. turbine losses, friction), expressed as: Preal = nu⋅g ⋅h⋅dm/dt Where: VA is analogous to the total potential power available (like water falling from a height). W is the real power delivered (like the actual electricity generated by the turbine).
Wonderful! In fact you've explained it better than our prof. I recommend this video to anyone who would wish to know the differences between kW and kVA
A little correction. Not KW and KWA, but kW and kWA. In SI Units "k" - stands for kilo prefix. "K" - stands for Kelvin (temperature). It's ease to remember, usually an uppercase unit is that named after a person. Like Watt and Ampere in this case.
I’m still not so sure I understand the difference, I mean I don’t think I could explain it, but I am closer. Thank you for taking the time to explain this subject! Cheers!
A little more explanation of the power triangle would have been better but pretty good other than that. For those with no understanding of reactive power and the work it does there is the beer example. Head on a beer isn't beer and you can't drink it but a beer without head is useless.
It’s a good video but I encourage you not to use the words “storage or “capacity” when describing the KVA side. It’s not accurate and only confuses. “Storage” means energy with no flow- no current which is measured in KWH (rating of a battery). KVA is the measurement of supply side power before it is converted to useful work. Using “capacity” and “storage “ is a slippery slope.
this is close but it's not entirely right. reactive power can come from both the source and/or the load side and this distinction is actually really important when your designing electrical systems. inductors and capacitors store energy in the forms of elecric and magnetic fields which is what we refer to as "reactive power". but unlike real power, the energy isn't consumed right away. it just moves back and forth in the system until it finds a path to dissipate.
Jeff and Peter. I appreciate both your inputs. Because I'm wanting to be an electrician. In the future but currently don't earn enough at work to go to college. So I'm going to RUclips and just trying to educate myself by watching videos read until I can finally go into college. At least I'll have a starting point.
When working with a pure DC circuit KVA and KW are the same. On an AC circuit, capacitance, inductance, etc. manifest themselves leading to impedance which causes the need to supply more power than the load requires, as the consumed power becomes load required power plus the power lost due to the impedance.
Not exactly that. Let's take a diesel generator capable of 100kVA, if the load consumes 50kW of active power, the diesel engine just have to produce 50kW on its shaft, regardless of the power factor. If power factor is 1, 50kW = 50kVA. But if power factor is 0.7, 50kW = 71.4kVA. But active power is still 50kW, so the thing that changes here is the current that increases, that means more losses in the cables and generator.
A load with a power factor lower than 1.0 will have a phase difference between voltage and current which means that when the maximum current is flowing thru the device the voltage isn't at its maximum so the real power is lower. Simply put, You could look at it as if the device drawing power tries to draw the maximum power when the source (generator or grid) cannot deliver it. Look at it as if the device fails to draw the maximum current when the voltage is at its maximum. It either draws current too early (capacitive load) or too late (inductive load). Think of it as poor timing - the load is trying to do work when the available push from the source isn’t optimal.
Having just been through the process of buying an electric car, I think it would be better to rate batteries in Joules or kJ rather than kWh. I have an electrical engineering degree so it doesn’t bother me, but it seems to be meaningless to many people. Manufacturers are marketing based on range, but this is subjective- is it assuming a jockey driving the car downhill with a tail wind the whole way?
Thank you again. At 57 I feel like I'm in school watching your videos. They are knowledgeable and entertaining. I'm one who may have to watch a couple times as I'm not as sharp as in my youth . Keep up the great work of sharing knowledge you definitely know how to SPARK an interest lol. Thanks
Hi, a mechanical engineer here. I had lessons on electricity during the first year of my study, some 45 years ago. Have forgotten most of that. Thank you for the clear explanation. Make antoher video on reactive power to explain in full.
Thank you. Great video. I wish I knew what screen you are using to draw on. That is an awesome screen. I'm a civil engineer and I relate KVA as potential energy and KW as kinetic energy. When it comes to moving water, we use the energy equation with the supply side on the left of the equation and the right side being the results, such as water velocity, water pressure, + LOSSES, just like the equation you showed. I loved that you explained this concept in several ways. Good job.
Nice to see someone try to tackle this concept. I'd like to add a few ideas, that may provide further insight & accuracy. The actual power that gets utilized is for the alternating current that is "aligned" or "in-the-same-phase" as the alternating voltage. If/when you have perfect alignment, power factor is 1. If you are out-of-alignment, PF < 1, you're not able to extract the maximum power from the given voltage and current, but you don't actually waste all of which could have been available. The bulk of the remaining potential energy gets reflected in a lower load on the generation plant, but also causes various undesirable effects as I pasted from chatgpt below. Hence, the power company incentivizes customers to match the impedence of the load to the impedance of the source (power generating system, or power-plant + distribution), in order to get the PF closest to 1, to reduce losses - this is good economics, as the cost of customer-induced inefficiencies can and should be passed onto customer (and vice-versa). And since there is a limit on how much current any particular line can carry, matching impedances also allow them to deliver more power on the same size lines, precluding the need to add more/new power lines. .. below is information from chatgpt (chatgpt said it was ok for me to repost it) regarding other losses that can occur . 1. Reflection Losses When impedance mismatch occurs, a portion of the electrical energy is reflected back towards the source instead of being delivered to the load. This phenomenon is particularly significant in high-frequency systems, such as radio frequency (RF) transmission lines, where standing waves can develop. 2. Reactive Power Circulation Impedance mismatch often results in a phase difference between voltage and current, leading to the presence of reactive power (measured in VARs). Reactive power does not perform useful work but still flows through the circuit, increasing the total apparent power (measured in VA) and causing additional energy losses due to resistive heating in conductors and components. 3. Voltage Regulation Issues Impedance mismatch can cause voltage drops along the transmission line, resulting in poor voltage regulation at the load. This can lead to inefficient operation or malfunction of connected devices, further compounding energy losses. 4. Harmonic Generation Non-ideal load impedance can cause nonlinearities, leading to harmonic distortion. These harmonics contribute to additional losses in the form of eddy currents and hysteresis losses in transformers, motors, and other magnetic devices. 5. Increased Heating of Components The circulating reactive power and reflected waves can cause overheating in components such as transformers, inductors, and capacitors. This reduces their efficiency and may lead to premature aging or failure. 6. Reduced Power Transfer Efficiency Maximum power transfer occurs only when the load impedance matches the source impedance (for purely resistive systems). An impedance mismatch reduces the power transfer efficiency, meaning less usable power is delivered to the load.
Thanks - a useful clarification. Also interesting to see an example where ChatGPT pretty much gets things right! You didn't need it, though: your summary was more useful!
Amazing explanation. I'm Subscribing to your channel and would happily suggest it to my colleagues and friends. I wish there was a similar channel for Mechanical Engineers.
Excellent presentation! I see you got some borderline hate in some comments. But the best thing about this video is... it gets you to think about why... and answers it. Well done. I've never had anybody explain it this well!
Small comment on 3:00 - if you do the dimensional analysis, where V = Joule/Coulomb, and A = Coulomb/second, then the product V*A = (Joule/Coulomb)*(Coulomb/second) = Joule/second, which is equivalent to a Watt. Empirically, they are exactly the same.
They are both "power". Power is watts. But the values, in watts, can be vastly different between the two. And the direction of travel is also different (opposite). Which is why a distinction is made. Power is actually flowing in both directions at the same time.
@junkerzn7312it’s more correct to say that power is not watts but “energy per unit time”. Watts, Volt-amps reactive, and Volts-amps all have units of “joules/second” and is “energy (transferred) per unit time”. It’s just that saying watts, volt-amps reactive, and volt-amps allows you to talk about real, reactive, and complex power respectively.
Nonsense. In terms of dimensional analysis W=VA=VAR (or kW=kVA=kVAR). The difference comes from a convention that W is used to measure consumption, and VA to measure the production. On general grounds, due to inductors and capacitors, you need to produce more power at the AC source, than that you really consume and the excess power is lost. The convention is to measure the produced power in VA and the consumed in W, to distinguish them with each other.
Another difference to point out about impedance for capacitors and inductors is their formulas. Inductive and capacitive reactance include frequency, which in a DC supply doesn't exist.
Exactly. The "reactive" power comes about when the current flow and the voltage in an AC circuit are out of phase. Both travel in sine waves, but inductors and capacitors cause a phase shift between them. With DC power, there are no sine waves to get out of phase.
@frankely6378I went to Navy Avionics School in 1972. We had a saying for everything. For voltage and current we had ELI and ICE. ELI is voltage leads current in an inductive circuit . ICE is current leads voltage in a capacitive circuit. The sayings we learned for transistor configuration and resistor color codes would be banned here.
@ntal5859A DC motor is always switching poles so the current and voltage will have some ripple. The faster the motor runs the less visible this is on an oscilloscope.
@Chris_at_Home Right. I knew one causes lead and the other lag, but school was a long time ago, and I was trained as a mechanical engineer. We got just enough of an intro to power systems to keep us from melting the wires. But I also know that if you under or over excite a synchronous motor, it will act like an inductor or capacitor. It wasn't uncommon for a factory to have a couple of over excited synchronous motors sitting in the corner doing nothing but fixing the power factor from all of the induction motors in the plant. These "rotary capacitors" could save the company a bunch of money on their electric bills.
At the generaton source kw=kva. At the load, if inductive, it usually is not the same. The difference is calculated from the voltage and current angles due to being out of sync (current lagging) as power factor. Most utilities bill on kwh and not kva, so power factor penalties may be applied to recover the cost of "lost energy" through kva/kw differences. To find total kw, divide measured kw by power factor as a decimal number. Transformers and generators must be sized to deliver this kw without being overloaded. The 2 options for adequate power are to increase capacity or improve power factor through the proper application of capacitors in kvars to offset the kvar's (kva reactive) to the load. This will save on supply as well as line loss/voltage drop. Dc circuits do not have power factor or kva issues.
Yeah - the kw is not equal to kva at the generator unless it is unity power factor. Generally, it is taken that the kw (true power) is controlled by the generators governor that controls torque, and kVAr (reactive power) is controlled using the AVR that controls rotor field excitation.
Also AC has a frequency component which is never talked about. If you raise the frequency like they do on airlines, and if you place a resonant device on that line, you can draw a lot more current than what you calculate by pure resistance. If you look at Ohms law, the calculation for Watts is V*I or Voltage times Amperage, however look carefully, the formula, its for DC circuits, or for AC with a pure resistive load.
@rty1955 that is because voltage is not constant for AC. The formula is still correct for any specific point in time, however for each cycle the voltage will be in 0 then +V then 0 then -V Hence while it's impractical for a human to do these calculations on the fly, it's very easy for an oscilloscope and why they are an essential piece of equipment for anyone working with AC circuits. To put it another way, if the formula, ie Ohm's law, didn't apply to AC then an oscilloscope would be effectively useless as the only thing they measure is voltage - all the other "smarts" and useful information they are capable of presenting hinge on said formulas being true
@deang5622 why would a generator have a power factor at all? It neither requires power for a workload nor consumes power, so how exactly are you going to calculate working power from apparent power? The only thing silly here is the amount of ppl who have no idea what they are even saying.... who are arguing with other ppl who also have no idea what they are saying 😂 If you don't know what a "flyback diode" is you almost certainly don't know what power factor is. Reciting wikipedia is not knowledge, it's performance art.
Excellent explanation with good examples. I’m an Aero-Mechanical Engineer with 45 years experience and I’ve always had problems with kW vs. kVA. When questions arose, I had to consult with one of my Electrical Engineer colleagues to get through the issue. No one explained it as clearly as you thought. Thanks!
So it seems to be that they are the same except a bunch of electrical engineers decided to use KVA in some circumstances just as a convention, for poorly defined reasons.
@normandiebryant6989 No, the difference is explained in the video. If non-ohmic resistance, such as capacitances and inductances, is present in the circuit, phase shifts occur between current and voltage due to these capacitances and inductances. This is referred to as reactance and apparent impedance. To express the total power provided, the unit [kVA or VA] is used. If there is only ohmic resistance and no phase shift, then the power supplied is equal to the power consumed, and the unit is [kW or W]. The power factor in this case is 1.0, meaning there is no phase shift. He explains nothing else in the video.
excellent refresher for me and awesome examples and scenarios as you well know understanding something thoroughly is being to explain the subject in layman's terms and theory both two thumbs thank you!
Thank you for explaining it to people who already know the basics! Even when a video is titled "Why KW and KVA are not the same" they'll spend hours explaining basics that anyone searching for this video already knows. You explained it better than my engineering professors did!
You should take this lesson a step further and do power factor correction in the field. And calc the total kVa required for the capacitors and then how much the power factor penalty is costing vs installing the capacitors to fix the low factor %.
The power factor more or less MUST be corrected at some point prior to getting all the way back to the generator. Generators can typically operate with a lagging power factor of 0.8 to 1.0. Any lower and you risk overheating and a trip-off.... i.e. the whole grid would go down at that point.
Well... for a battery charger there actually is almost no difference because there is no reactive energy sloshing about... battery chargers will have near unity power factor and the batteries are exactly unity because they are DC. But, as we all know, certain types of equipment require labeling in kVA by code anyway. Reactive power is basically reflected power. Reflected power can only occur in AC systems (or ripple in DC systems, but ripple is usually... not always, discounted). Because it is reflected power, it travels through the cabling and generating/inverter equipment twice rather than once... which means that the internal resistance of said cables and equipment dissipate more energy than the actual watts delivered to the equipment that is doing useful work. Reactive power is NOT doing useful work, but it has to be dealt with. And how it is dealt with depends on the type of equipment. * An inverter will see reactive power as ripple on the DC side and can actually recover a good chunk of that energy and reinject it into the inverter. However, the reactive energy still generally has to flow through the inverter's components in the reverse direction before being recovered. Hence some heat, hence the inverter must be rated in kVA because that is what is actually limiting its function, not watts delivered and not even watts received from the DC side of the inverter (from the battery). * A generator will usually see reactive power as additional mechanical load... and basically it must dissipate it as heat. It has to work against the mechanical load to overcome it == heat. Which is why generators have to disconnect from the grid if the power factor goes too far out of spec... if they didn't they would melt or explode or otherwise let the magic smoke out. * Cables see reactive power (reflected energy) as going through the cable in the opposite direction.... which still has resistance and still dissipates some energy. So if something is sending 1000W through a cable and 200W is reflected back by XYZ appliance, the cable actually has 1200W worth of power flowing through it (not quite, but that's a good rule of thumb). Thus breakers are protecting against kVA rather than watts delivered. * You can also "recover" reactive power (not convert it to heat) with the appropriate LC "power factor correction device". Which is the ideal solution, but relatively difficult to do because the power factor is changing all the time and the reactive power is still dissipating heat through components prior to getting to the recovery device. Batteries are loads during charging... they are absolutely consuming the energy. They're just storing it rather than converting it to heat. The reason why a battery is rated in kW is because it is a DC component. You can't actually get any significant reactive power from charging or discharging a battery... reactive power is a function of AC, not DC (sans DC ripple which is a whole different conversation). -Matt
@adon8672 Quite a few inverters are mislabeled, yes. They are all limited by kVA in reality, though, DC side ratings can be in watts. AC output ratings are basically kVA but are often labeled as watts. It isn't just marketing material... spec sheets often get it wrong too. The Europeans are sticklers for using the proper terminology so something like an SMA inverter or a Victron inverter is actually labeled and marketed in kVA terms. But a lot of Chinese-made products still get the terminology confused and that flows through to many products. It's a real mess, actually. One could get technical and talk about where the reactive power recovery occurs in an inverter, but in almost all cases the recovery occurs on the DC side, after the reflected power has gone through the AC circuitry in reverse, so the inverter is still limited by kVA and not by watts even if a good chunk of the reflected power is recovered and reinjected.
If I was building a battery charger and keeping the circuitry simple, you could feed it a pure sine wave AC input, but its current draw would only be in brief pulses when the sine wave is near peak and there’s forward current flow through the rectifiers. The transformer probably (?) needs to be rated to handle the full current of those pulses (in KVA), at least to avoid voltage drop, but the actual energy transfer over time will be less (in KW).
@kc9scott Basically the only correct way to make a battery charger at decent power levels is with a regulator that incorporates a power factor correction circuit. If you just try to rectify the AC and throw it into a switching regulator without a power factor correction circuit, it won’t pass code. Power factor correction in switching regulators is very easy to do these days. Basically instead of rectifying the AC into a buffer capacitor, the rectified AC goes into a switching circuit which pulls current from every part of the rectified AC waveform and pushes that into a buffer capacitor via (usually) a small transformer + diode + capacitor combo. You wind up with a power factor greater than 0.95 by doing that. -Matt
kW means that amount of power is being delivered one-way. It's staying in the load. With kVA, some of that power is coming back out. It's a mite simpler viewed in energy terms. kW indicates energy is being delivered irrevocably; kVA allows that some of that energy is gonna come back out toward the source, analogous to the energy stored in a spring.
You're right: the power factor can be written as cos phi Phi being the phase shift between the voltage and the current. The difference between being a power supply and a power load is 180° in phi...
As a mechanical engineer, I was exposed to this in the circuits course that I had to take, and understood it fairly well. But my memory of it drifted over the years. I was kind of lost in your explanation until you talked about the vector sum of resistive and reactive loads, then it became more clear.
So, the title and some statements here are actually totally wrong. kW and kVA are truly identical, always. This is even demonstrated in the video with power factor. Power factor would not be a unit-less ratio if they were not identical. As they are identical, the units in the numerator and denominator cancel. The issue as explained is different than what is stated in the title and repeatedly in the video. What happens many times is that we have the same units for different things and we want to distinguish between them for clarity. We see this with torque and energy. Both can be measured in N•m. But this gets really confusing, because commonly you'll be dealing with energy and torque at the same time. So we prefer to use J (1 J = 1 N•m) for energy, while we leave torque with N•m. So the real issue is that consumption and supply aren't the same thing, but they have the same units, and we want to distinguish between them more easily so we write them with different-appearing units that aren't actually different. It's a pure labeling thing for clarity. But, truly, kW and kVA are identical, always. Thinking otherwise is confusing a convenient choice labeling with what the units actually are.
No. EE here. The flow of energy depends upon whether the load is mostly inductive as for motors or heater coils, or mostly a capacitive load such as maybe a DC power supply that often uses many capacitors as a filter, for example. The typical local power company would like the power factor to be as close to unity, or one, as possible.
@Bridgeman416 It doesn't matter if it's EE or not. How do the units cancel in the numerator and denominator for power factor? Because even in EE they're identical. The issue is that the things they're used for are not the same and we would rather differentiate more clearly, just like with energy v. torque. So we make them look different despite them being identical. 1 kW =1000 kg•m^2/s^3. 1 kVA = 1000 kg•m^2/s^3. Labeling them as kW or kVA is nothing but a matter of convenience, as kg•m^2/s^3 is a mouthful. But if you think that makes them different, then you are confounding convenient labeling with the actual units.
One is 100% useful or usable power, (kW) the other is not. kVA includes power factor which has the current either in front of the AC voltage as it rises from zero (leading) or behind the voltage (lagging). It used to be described as ‘wattless current’ and is essentially wasted power. So the power factor tells what is actually usable (true) power in kW, rather than what is actually needed to power the entire load (resistance+ inductance + capacitance) or the apparent power. Only in a purely resistive circuit can kW be equal to kVA and kVA only exists in an AC circuit as it is to do with the alternating voltage as it rises and falls 50 or 60 times a second.
Thank you Sir! The best explanation I have ever heard. I remember seeing a gauge in the B747-200 Flight Engineers Panel showing KVARS. I guess this was KVA.
Excellent highly educative video i have seen in you tube.Many many heartfelt thanks to the author for the effort being taken in educating on KW AND KVA. BEING AN ENGINEERING PERSON MY PROFESSOR DID NOT BRIEF TO THIS EXTENT
Long-time electrician here ... very lively video, and very well explained ... of course these concepts are always difficult to explain and understand ... but excellent effort here ... thank you. 🙏 🤙☺️🇺🇸
Folks, he's explaining this better than my EE profs did (which I instantly forgot as soon as the exams were over). This is great stuff.
Who cares ?
@tucoremirezfulmost people watching this vdo except you.
I do not share that level of praise, as this video has false factual claims, and acts hyper repeating terms in sometimes useful but other times wrong or misleading forms.
It's hard to explain in lecture format. It's also a chicken and egg set of issues, where one needs math good engineering students already have (through integral calc of trig), but also the ability to relate theory and practice in ways that are interactive, and visualize electrons and components, in ways standard framing of voltage or current misrepresent a bit relative to quantum physics where some very bright engineer run YT channels have engaged each other over errors or ways to improve the way common systems are presented or described.
By then anyone in the game knows how chemists and physicists define positive or negative charges with opposite conventions, and has moved on to joking about which is which. We can't presume most electricians or users here get that.
Failure to mention conductor heating as a primary reason VA need to be distinguished from W is a major weakness of this video.
We're also in an era where things are more complicated to depict in theory vs practice than a few decades ago, as a HE washing machine may have a variable speed drive 3/4 HP motor, and not a 2-3 speed split phase or shaded pole motor of 1/3 or 1/2 HP as years ago, while switching power supplies or PWM LED dimmers don't follow the historic rules around which IEEE C2 or public utility law and rate based regulations evolved.
That tasks engineers and educators with figuring out how to present such topics in useful but also accurate ways, and pretty much everyone with understanding archaic and modern systems that are ever increasingly complicated to get right, if that means factually truthful and not overly complex for users to grasp.
@tucoremirezful Those that seek knowledge...
I don't know who your EE profs were, but this wasn't really a good explanation. As usual with him, he's a bit loose with conflating electrical terms that have very specific physical meanings. Also as usual, way too much content/talking for a relatively small amount of information conveyed. It's pretty clear that RUclipsrs do this to inflate their content in terms of total time. They shouldn't.
And, there are even mistakes that he corrected with post-processing overlays. Why? Just go back and reshoot the clip the right way. I don't know why it's become socially acceptable on social media for people presenting as teachers to really just be having stream-of-consciousness conversations with themselves about topics. Review your own content. If there's wrong or superfluous information, edit it out. Then post it. Don't share wrong or misleading stuff and then sit back and be happy for the additional engagement of people correcting you in the comments.
Hi German here. We have a funny analogy for this to explain to trainees: KVA as apparent power is like a nicly poored glas of bear 🍺 the hole including the foam is the apparent power, the foam is the reactive (wattless) power and the nice yellow liquid is the active power 🥴 cheers
That is the same analogy that was used to introduce the concept to us in the electricity subject.
Best Case - Kölsch without foam, worst case - incorrectly poured Hefeweizen
I'll drink to that! 🍻 cheers
You explain kva like a hair stylist would explain it to a cook! You have such a confidence! So many mistakes! For example you said transformer induces current! No ! it does not! Transformer induces voltage and current is a function of the load. The first half is completely nonsense and little truth in the second half
Now I'm thirsty
My favorite analogy for reactive power and power factor is pushing a kid on a swing. If you give the kid a push at just the right time, it's easy to get the swing to go up high. But if you give a push at the wrong time, it's wayyy harder or impossible to keep things swinging.
In the case of motors, you're essentially trying to slow down the motor with the load you have on it. So instead of the AC current "pushes" from the power company being perfectly in sync with it's movements, the load causes the motor to fight against that perfect timing. As a result, the power company is effectively pushing the kid at slightly the wrong time, resulting in wasted power that could have been useful if you had better timing.
That's the big reason there's a market for fancy motor controllers and power factor correction devices. You can actually fix the imperfect timing if you're smart about it, resulting in better efficiency. You do it intuitively in the swing example by watching and feeling, in electrical engineering we use carefully tuned inductors/capacitors and computer equipment to do the same thing.
And I guess that is why you have big capacitors on those big air-con units, to tune the reactive load from pure inductance to capacitive/inductance balance.. Right ?
@daveleger2002 Power factor is definitely a part of it, after all a stalled motor is just a dead short... Tons of power consumed for nothing useful out till it gets going. But the capacitors are mostly there to keep your breakers tripping and wiring lighting on fire... The capacitor stores energy that's used for the initial push that's needed to get it moving.
Typically when people talk about power factor it's a longer term, steady state description. Temporary fluctuations are usually a different concern.
I like the mug of beer, with the beer and the foamy head expressed in real beer and apparent beer.
Good analogy! 👍
I like that analogy 👍🏻, it perfectly visualises the phase (angle) difference between the V and A
A pretty good discussion of a very difficult topic. I have not seen better. Your practical applications help to clarify.
My favorit analogy: KW = beer (actual power) KVA = beer + foam (apparent power)
Perfect...and refreshing. I may steal that one next time someone asks 😀
The problem with this analogy is that the foam appears on the top of the beer and not in the beer.
I would say KW = utilized power, and KVA = total power taken from the grid.
Building on that: A mug of beer costs the same regardless of how much foam is in it. The mug equals the wire and breakers that you have to pay and size for. kW is the amount of actual power you are getting out of the motor. EG: kW = How much beer you get to drink.
@deang5622 Isn’t that what I said? That is what I meant to say at least.
P = power output on the device = V * I * cos phi = measured in W
(Also real used power = P * ŋ)
S = Power measured as the load the device has on the grid = V * I = V / cos phi = measured in VA
Edit: meant P / cos phi
Thank you for the refresher, still find it's interesting looking back from 50 years of electronic service engineering and electrical work.
Best explanation I’ve heard on this subject. Many thanks!
Thanks for making this video. This is exactly what has been on my mind for the past few weeks as I was designing an off grid solar system for my farm house. And yes, it was the P=VI formula that kept tripping me! 😄
One thing, though, is that all of these items that you’re listing off like light ballast and most electronic equipment have built-in power factor correction if they are manufactured with any quality. The big item that you have to worry about is motor loads. But in most factories that have a lot of motor loads they also install automatic power correction, for those in order to bring the PF back up.
Thanks for another great vid. You break topics down really well. Clear and understandable
This video was really helpful. It has clarified some confusion I was struggling with for years. I really appreciate
Thank you for this breakdown. I do a review model for public charging sites where I do assess the power available at the transformer level. For simplicity, I've always referred to the transformer power as "kW," though the the transformer rating is in kVA. What I am looking for in this is the total throughput or power available for the site, so kVA is the more accurate metric.
The other factor I am checking for is a discrepancy between the power supply and the rated output power of the chargers themselves. Most often, the transformer is rated for more power (kVA) than the total kW rated output power of the chargers themselves, though some providers (Tesla in particular) can have rated output power at their chargers that is more than double the rated power of the transformer.
Basically, checking the transformer enables me to know whether EV drivers will be seeing full, rated power when charging if the site is full or mostly full.
This was the first of your videos that went over my head, but that's definitely not on you. This was a great explanation. It gave me enough concepts that when I hear it five more times in different ways, it'll finally click.
You got the concepts into me, though! And I appreciate that.
This is a good video. The power triangle is the most important thing to understand. Watts Real P is the X axis. VAR reactive is the Y and VA is vector sum (hypotenuse). When you're using real and imaginary numbers you can evaluate the rectangular sum or polar vector quantity in your head. With alternating current capacitors and inductors are reactive components and they store and release energy at different times. In perfect systems the real is the only part actually using real power, but you still need to account for the reactive components. It's why power factor correction is important because the power company still has to supply and transport the power in VA regardless of what is consumed and even if the load give it "back" every half cycle.
This was really good... And a real topic that clears the concepts that often caused me confusion within my own studies. It was fun, objective and to the point! Thanks
Thanks! I’ve noticed this on transformers and wondered this myself, especially when reviewing electronics and accessories. My practical tests have come up .9 number, and I’ve always thought it was an exaggeration factor for speccing.
You rock! This is the best explanation I've ever heard. Really well done!
I'm a retired electrician and I find you extremely refreshing, it's really nice to get a well thought out refreshing course I will recommend you to young electricians keep it up . Good job
Thanks. A nice refresher. In air-conditioning I dealt with this alot.
Excellent class! Taking it a step further.... An explanation of how most of the reactive load in the real world, is due to inductive reactance and how capacitors are used to offset this load with capacitive reactance so that KVA comes much closer to equaling KW decreasing a lot of the wasted reactive energy, would be awesome to follow up with. You covered this subject very practically and better than many of my instructors in both technical school and college.
This is the first time ever I understood the difference between kva and kw. You are a great teacher.
I’ve been in the game for 49 years. All those years operating and maintaining generators, power plants, transformers, and associated equipment. I taught for a few years as well. This is the best, most succinct, and accurate explanation I’ve heard. Thank you
I've been trying to understand kW vs kVA for about the same amount of time. The explanation in this video didn't help that much. I've learned more from reading these comments.
@kimstockdale632😂 some people read better than they hear, it's a great video and fantastic comments. 🎉
Your way of explanation is fantastic.Thanks for your time ❤
Yeah, this had me completely confused. I got it now. Very good explanation and completely necessary to understand this.
Thanks. Much better than having to answer "well, it's umm, hmm. I don't know"
I really liked the video. The point was understood and the understanding was clear. I get the theory or concept. I believe he did a great job.
Expressing a theory is about getting it across to the people you present it to in an understandable way. And this is a good example of that.
Clear as mud. Just like the magician who says watch carefully. Shows you the cards, then bam, he pulls the card out of your ear.
I haven't studied this in over 30 years. Nice refresher
Thank you, i was wondering why some solar inverters are rated in KW and some in KVA.
Now that was excellent! I will watch the whole thing again. Thanks a lot.
I generally look at this from a kinetic (W) vs potential (VA) energy viewpoint, but I like this overview that better covers the arguement.
Ah this remark helped a lot. Makes sense, for potential impedance doesnt matter, but of course for the actual it does!
So basically, VA mechanically would be gravitational potential field (g⋅h, in J/kg) and mass flow rate (dm/dt, in kg/s) - as seen in a hydroelectric dam - representing the available potential energy transfer capacity, while W (watts) would be the actual mechanical power output, i.e. the portion of that potential energy converted into useful work, factoring in system efficiency (nu) (e.g. turbine losses, friction), expressed as:
Preal = nu⋅g ⋅h⋅dm/dt
Where:
VA is analogous to the total potential power available (like water falling from a height).
W is the real power delivered (like the actual electricity generated by the turbine).
This is the way I look at this too. It doesn’t seem to me that they both have the same units as stated in one of the comments above.
your explanation for power factor is amazing. I finally understand it... the power used by the machine to do/doing/that does the actual work :)
A watt is 1 joule per 1 second. A volt-amp is coulmbs per second scaled by volts. Volts are joules per coulomb, so the couldmbs cancel out.
Wow! I learned this stuff back in the early 80's in Navy electronics school. Great explanation! Thanks for the refresher!
Thank you. It's a revision study for me. And I like the way you explained it.
Great video, I am a electrician for over 40 years. This was very clear and easy to understand. Thank you.
A very useful simplification and exactly what I needed, thanks.
Your explanations of electrical concepts are the best I've seen on RUclips. Thanks!
Thank you for the great, very well explained videos! It's easier to understand electricity watching your videos
It would be helpful to talk about how the waveform gets distorted with reactive power and how that relates to the entire concept.
Yes it needs more power factor discussion 🐱
Wonderful! In fact you've explained it better than our prof. I recommend this video to anyone who would wish to know the differences between kW and kVA
I have been an electrician my whole life and this is the best explanation I have ever heard of KVA/KW! tThanks for an understandable explanation.
You mean PF = KW/KVA
I also think this is a brilliant way of explaining it.
Excellent video. We tend to forget the important theory taught by our professors in school. Indeed this is a great refresher and explanaiton
A little correction. Not KW and KWA, but kW and kWA.
In SI Units "k" - stands for kilo prefix. "K" - stands for Kelvin (temperature).
It's ease to remember, usually an uppercase unit is that named after a person. Like Watt and Ampere in this case.
Correction to correction. Its actually kW and kVA.
@exponentmantissa5598 Yes, of course
@RustedCroaker You can edit your post (click on the three dots to the right).
@zevfarkas5120 LOL I know
@RustedCroaker So, why not do it? (Of course, this whole chain of comments will then be left dangling...)
I’m still not so sure I understand the difference, I mean I don’t think I could explain it, but I am closer. Thank you for taking the time to explain this subject! Cheers!
A little more explanation of the power triangle would have been better but pretty good other than that.
For those with no understanding of reactive power and the work it does there is the beer example. Head on a beer isn't beer and you can't drink it but a beer without head is useless.
Incredibly explained! Thaonk you for this, for teaching us so well!
It’s a good video but I encourage you not to use the words “storage or “capacity” when describing the KVA side. It’s not accurate and only confuses. “Storage” means energy with no flow- no current which is measured in KWH (rating of a battery). KVA is the measurement of supply side power before it is converted to useful work. Using “capacity” and “storage “ is a slippery slope.
this is close but it's not entirely right. reactive power can come from both the source and/or the load side and this distinction is actually really important when your designing electrical systems. inductors and capacitors store energy in the forms of elecric and magnetic fields which is what we refer to as "reactive power". but unlike real power, the energy isn't consumed right away. it just moves back and forth in the system until it finds a path to dissipate.
Jeff and Peter. I appreciate both your inputs. Because I'm wanting to be an electrician. In the future but currently don't earn enough at work to go to college. So I'm going to RUclips and just trying to educate myself by watching videos read until I can finally go into college. At least I'll have a starting point.
@KnightHunter9989 no problem! good luck with your studies!
@PeterMikeSolomon Thank you.
@KnightHunter9989where in the world are you? Many electrical jobs hire and train from scratch. Might be a way to go?
This is the very best explanation of this stuff. Thank you very much (from Germany) for this video 🙂
When working with a pure DC circuit KVA and KW are the same.
On an AC circuit, capacitance, inductance, etc. manifest themselves leading to impedance which causes the need to supply more power than the load requires, as the consumed power becomes load required power plus the power lost due to the impedance.
Not exactly that. Let's take a diesel generator capable of 100kVA, if the load consumes 50kW of active power, the diesel engine just have to produce 50kW on its shaft, regardless of the power factor.
If power factor is 1, 50kW = 50kVA. But if power factor is 0.7, 50kW = 71.4kVA. But active power is still 50kW, so the thing that changes here is the current that increases, that means more losses in the cables and generator.
A load with a power factor lower than 1.0 will have a phase difference between voltage and current which means that when the maximum current is flowing thru the device the voltage isn't at its maximum so the real power is lower.
Simply put, You could look at it as if the device drawing power tries to draw the maximum power when the source (generator or grid) cannot deliver it. Look at it as if the device fails to draw the maximum current when the voltage is at its maximum. It either draws current too early (capacitive load) or too late (inductive load). Think of it as poor timing - the load is trying to do work when the available push from the source isn’t optimal.
May I correct you:
You have to write kVA and not KVA
You have to write kW and not KW
as stated in the International System (SI) of Units.
Many thanks
And Joules uses capital J
Having just been through the process of buying an electric car, I think it would be better to rate batteries in Joules or kJ rather than kWh. I have an electrical engineering degree so it doesn’t bother me, but it seems to be meaningless to many people.
Manufacturers are marketing based on range, but this is subjective- is it assuming a jockey driving the car downhill with a tail wind the whole way?
Excellent job explaining an in depth concept!
Thank you again. At 57 I feel like I'm in school watching your videos. They are knowledgeable and entertaining. I'm one who may have to watch a couple times as I'm not as sharp as in my youth . Keep up the great work of sharing knowledge you definitely know how to SPARK an interest lol. Thanks
You’re never too old to learn something new.
Hi, a mechanical engineer here. I had lessons on electricity during the first year of my study, some 45 years ago. Have forgotten most of that. Thank you for the clear explanation. Make antoher video on reactive power to explain in full.
I learned more in this 10min video, then I did in one day of college class.
@Gaspar314 Agreed. As a home owner, you're forced to learn how things work, if you want to save money fixing things.
Thank you. Great video. I wish I knew what screen you are using to draw on. That is an awesome screen. I'm a civil engineer and I relate KVA as potential energy and KW as kinetic energy. When it comes to moving water, we use the energy equation with the supply side on the left of the equation and the right side being the results, such as water velocity, water pressure, + LOSSES, just like the equation you showed. I loved that you explained this concept in several ways. Good job.
Nice to see someone try to tackle this concept. I'd like to add a few ideas, that may provide further insight & accuracy. The actual power that gets utilized is for the alternating current that is "aligned" or "in-the-same-phase" as the alternating voltage. If/when you have perfect alignment, power factor is 1. If you are out-of-alignment, PF < 1, you're not able to extract the maximum power from the given voltage and current, but you don't actually waste all of which could have been available. The bulk of the remaining potential energy gets reflected in a lower load on the generation plant, but also causes various undesirable effects as I pasted from chatgpt below. Hence, the power company incentivizes customers to match the impedence of the load to the impedance of the source (power generating system, or power-plant + distribution), in order to get the PF closest to 1, to reduce losses - this is good economics, as the cost of customer-induced inefficiencies can and should be passed onto customer (and vice-versa). And since there is a limit on how much current any particular line can carry, matching impedances also allow them to deliver more power on the same size lines, precluding the need to add more/new power lines.
.. below is information from chatgpt (chatgpt said it was ok for me to repost it) regarding other losses that can occur .
1. Reflection Losses
When impedance mismatch occurs, a portion of the electrical energy is reflected back towards the source instead of being delivered to the load. This phenomenon is particularly significant in high-frequency systems, such as radio frequency (RF) transmission lines, where standing waves can develop.
2. Reactive Power Circulation
Impedance mismatch often results in a phase difference between voltage and current, leading to the presence of reactive power (measured in VARs). Reactive power does not perform useful work but still flows through the circuit, increasing the total apparent power (measured in VA) and causing additional energy losses due to resistive heating in conductors and components.
3. Voltage Regulation Issues
Impedance mismatch can cause voltage drops along the transmission line, resulting in poor voltage regulation at the load. This can lead to inefficient operation or malfunction of connected devices, further compounding energy losses.
4. Harmonic Generation
Non-ideal load impedance can cause nonlinearities, leading to harmonic distortion. These harmonics contribute to additional losses in the form of eddy currents and hysteresis losses in transformers, motors, and other magnetic devices.
5. Increased Heating of Components
The circulating reactive power and reflected waves can cause overheating in components such as transformers, inductors, and capacitors. This reduces their efficiency and may lead to premature aging or failure.
6. Reduced Power Transfer Efficiency
Maximum power transfer occurs only when the load impedance matches the source impedance (for purely resistive systems). An impedance mismatch reduces the power transfer efficiency, meaning less usable power is delivered to the load.
Thanks - a useful clarification. Also interesting to see an example where ChatGPT pretty much gets things right! You didn't need it, though: your summary was more useful!
good, but i dont know why the consumption system measured in kw rather in kva?
Amazing explanation. I'm Subscribing to your channel and would happily suggest it to my colleagues and friends.
I wish there was a similar channel for Mechanical Engineers.
Excellent presentation!
I see you got some borderline hate in some comments.
But the best thing about this video is... it gets you to think about why... and answers it.
Well done. I've never had anybody explain it this well!
So pointing out where his simplification goes wrong is hate...? 🙄
He doesn't even care about (or know) the difference between K (Kelvin) and k (kilo).
Just an excellent explanation. Thank you for sharing your knowledge.!!!!!!
Small comment on 3:00 - if you do the dimensional analysis, where V = Joule/Coulomb, and A = Coulomb/second, then the product V*A = (Joule/Coulomb)*(Coulomb/second) = Joule/second, which is equivalent to a Watt. Empirically, they are exactly the same.
They are both "power". Power is watts. But the values, in watts, can be vastly different between the two. And the direction of travel is also different (opposite). Which is why a distinction is made. Power is actually flowing in both directions at the same time.
@junkerzn7312it’s more correct to say that power is not watts but “energy per unit time”. Watts, Volt-amps reactive, and Volts-amps all have units of “joules/second” and is “energy (transferred) per unit time”. It’s just that saying watts, volt-amps reactive, and volt-amps allows you to talk about real, reactive, and complex power respectively.
Nonsense. In terms of dimensional analysis W=VA=VAR (or kW=kVA=kVAR). The difference comes from a convention that W is used to measure consumption, and VA to measure the production. On general grounds, due to inductors and capacitors, you need to produce more power at the AC source, than that you really consume and the excess power is lost. The convention is to measure the produced power in VA and the consumed in W, to distinguish them with each other.
@ΖαχαρίαςΦθενάκης
I think it's not so easy.
See: 1kW+1kW=2kW but 1kVA+1kVA≠2kVA
How do you explain the difference when you declare all as the same?
@maxmustermann9587Oh yes. It is so easy. Who says that 1+1 not equal 2? These are units. They don't have to do with the physics behind the AC.
This was such a great explanation. Thank you
Another difference to point out about impedance for capacitors and inductors is their formulas. Inductive and capacitive reactance include frequency, which in a DC supply doesn't exist.
Exactly. The "reactive" power comes about when the current flow and the voltage in an AC circuit are out of phase. Both travel in sine waves, but inductors and capacitors cause a phase shift between them. With DC power, there are no sine waves to get out of phase.
Are but you forget all inductors still have a very small DC resistance... A tiny loss .
@frankely6378I went to Navy Avionics School in 1972. We had a saying for everything. For voltage and current we had ELI and ICE. ELI is voltage leads current in an inductive circuit . ICE is current leads voltage in a capacitive circuit. The sayings we learned for transistor configuration and resistor color codes would be banned here.
@ntal5859A DC motor is always switching poles so the current and voltage will have some ripple. The faster the motor runs the less visible this is on an oscilloscope.
@Chris_at_Home Right. I knew one causes lead and the other lag, but school was a long time ago, and I was trained as a mechanical engineer. We got just enough of an intro to power systems to keep us from melting the wires. But I also know that if you under or over excite a synchronous motor, it will act like an inductor or capacitor. It wasn't uncommon for a factory to have a couple of over excited synchronous motors sitting in the corner doing nothing but fixing the power factor from all of the induction motors in the plant. These "rotary capacitors" could save the company a bunch of money on their electric bills.
another good one on explaining how it all comes together.
At the generaton source kw=kva. At the load, if inductive, it usually is not the same. The difference is calculated from the voltage and current angles due to being out of sync (current lagging) as power factor. Most utilities bill on kwh and not kva, so power factor penalties may be applied to recover the cost of "lost energy" through kva/kw differences. To find total kw, divide measured kw by power factor as a decimal number. Transformers and generators must be sized to deliver this kw without being overloaded. The 2 options for adequate power are to increase capacity or improve power factor through the proper application of capacitors in kvars to offset the kvar's (kva reactive) to the load. This will save on supply as well as line loss/voltage drop. Dc circuits do not have power factor or kva issues.
Yeah - the kw is not equal to kva at the generator unless it is unity power factor.
Generally, it is taken that the kw (true power) is controlled by the generators governor that controls torque, and kVAr (reactive power) is controlled using the AVR that controls rotor field excitation.
Also AC has a frequency component which is never talked about. If you raise the frequency like they do on airlines, and if you place a resonant device on that line, you can draw a lot more current than what you calculate by pure resistance.
If you look at Ohms law, the calculation for Watts is V*I or Voltage times Amperage, however look carefully, the formula, its for DC circuits, or for AC with a pure resistive load.
@rty1955 that is because voltage is not constant for AC.
The formula is still correct for any specific point in time, however for each cycle the voltage will be in 0 then +V then 0 then -V
Hence while it's impractical for a human to do these calculations on the fly, it's very easy for an oscilloscope and why they are an essential piece of equipment for anyone working with AC circuits.
To put it another way, if the formula, ie Ohm's law, didn't apply to AC then an oscilloscope would be effectively useless as the only thing they measure is voltage - all the other "smarts" and useful information they are capable of presenting hinge on said formulas being true
No it doesn’t, power is generated including the reactive component!
@deang5622 why would a generator have a power factor at all?
It neither requires power for a workload nor consumes power, so how exactly are you going to calculate working power from apparent power?
The only thing silly here is the amount of ppl who have no idea what they are even saying.... who are arguing with other ppl who also have no idea what they are saying 😂
If you don't know what a "flyback diode" is you almost certainly don't know what power factor is.
Reciting wikipedia is not knowledge, it's performance art.
I work in the renewable energy industry and forwarded this to my colleagues. Great explanation in a reasonable time.
Good explanation. It would even be better if you write k in small caps. The SI units are kW and kVA.
The SI units are W and VA. The k is lowercase because it’s a prefix to the unit.
Very well explained, I fully understood that. Subbed!
Excellent explanation with good examples. I’m an Aero-Mechanical Engineer with 45 years experience and I’ve always had problems with kW vs. kVA. When questions arose, I had to consult with one of my Electrical Engineer colleagues to get through the issue. No one explained it as clearly as you thought. Thanks!
So it seems to be that they are the same except a bunch of electrical engineers decided to use KVA in some circumstances just as a convention, for poorly defined reasons.
@normandiebryant6989 No, the difference is explained in the video. If non-ohmic resistance, such as capacitances and inductances, is present in the circuit, phase shifts occur between current and voltage due to these capacitances and inductances. This is referred to as reactance and apparent impedance. To express the total power provided, the unit [kVA or VA] is used. If there is only ohmic resistance and no phase shift, then the power supplied is equal to the power consumed, and the unit is [kW or W]. The power factor in this case is 1.0, meaning there is no phase shift. He explains nothing else in the video.
excellent refresher for me and awesome examples and scenarios as you well know understanding something thoroughly is being to explain the subject in layman's terms and theory both two thumbs thank you!
I have studied four years Electrical engineering in Univercity and I did not undrestand this. Thank you . I realy do
This video is a good example of apparent knowledge passing for real knowledge.
Thank you for explaining it to people who already know the basics! Even when a video is titled "Why KW and KVA are not the same" they'll spend hours explaining basics that anyone searching for this video already knows. You explained it better than my engineering professors did!
What the heck is a Kelvin-Watt?
Yeah, it's k-kilo, K-Kelvin
The k is in lower case, the w and k are just differently sized fonts.
@willdukes1768😂
I have always wondered the difference. Great explanation Thankyou!!
You should take this lesson a step further and do power factor correction in the field. And calc the total kVa required for the capacitors and then how much the power factor penalty is costing vs installing the capacitors to fix the low factor %.
The power factor more or less MUST be corrected at some point prior to getting all the way back to the generator. Generators can typically operate with a lagging power factor of 0.8 to 1.0. Any lower and you risk overheating and a trip-off.... i.e. the whole grid would go down at that point.
Perfect explanation for electricians and students alike 👌
Well... for a battery charger there actually is almost no difference because there is no reactive energy sloshing about... battery chargers will have near unity power factor and the batteries are exactly unity because they are DC. But, as we all know, certain types of equipment require labeling in kVA by code anyway.
Reactive power is basically reflected power. Reflected power can only occur in AC systems (or ripple in DC systems, but ripple is usually... not always, discounted). Because it is reflected power, it travels through the cabling and generating/inverter equipment twice rather than once... which means that the internal resistance of said cables and equipment dissipate more energy than the actual watts delivered to the equipment that is doing useful work.
Reactive power is NOT doing useful work, but it has to be dealt with. And how it is dealt with depends on the type of equipment.
* An inverter will see reactive power as ripple on the DC side and can actually recover a good chunk of that energy and reinject it into the inverter. However, the reactive energy still generally has to flow through the inverter's components in the reverse direction before being recovered. Hence some heat, hence the inverter must be rated in kVA because that is what is actually limiting its function, not watts delivered and not even watts received from the DC side of the inverter (from the battery).
* A generator will usually see reactive power as additional mechanical load... and basically it must dissipate it as heat. It has to work against the mechanical load to overcome it == heat. Which is why generators have to disconnect from the grid if the power factor goes too far out of spec... if they didn't they would melt or explode or otherwise let the magic smoke out.
* Cables see reactive power (reflected energy) as going through the cable in the opposite direction.... which still has resistance and still dissipates some energy. So if something is sending 1000W through a cable and 200W is reflected back by XYZ appliance, the cable actually has 1200W worth of power flowing through it (not quite, but that's a good rule of thumb). Thus breakers are protecting against kVA rather than watts delivered.
* You can also "recover" reactive power (not convert it to heat) with the appropriate LC "power factor correction device". Which is the ideal solution, but relatively difficult to do because the power factor is changing all the time and the reactive power is still dissipating heat through components prior to getting to the recovery device.
Batteries are loads during charging... they are absolutely consuming the energy. They're just storing it rather than converting it to heat. The reason why a battery is rated in kW is because it is a DC component. You can't actually get any significant reactive power from charging or discharging a battery... reactive power is a function of AC, not DC (sans DC ripple which is a whole different conversation).
-Matt
Thanks for the thorough breakdown. I noticed most inverters, unlike AC generators, are rated in KW, and not Kva. Why is that?
@adon8672 Quite a few inverters are mislabeled, yes. They are all limited by kVA in reality, though, DC side ratings can be in watts. AC output ratings are basically kVA but are often labeled as watts. It isn't just marketing material... spec sheets often get it wrong too.
The Europeans are sticklers for using the proper terminology so something like an SMA inverter or a Victron inverter is actually labeled and marketed in kVA terms. But a lot of Chinese-made products still get the terminology confused and that flows through to many products. It's a real mess, actually.
One could get technical and talk about where the reactive power recovery occurs in an inverter, but in almost all cases the recovery occurs on the DC side, after the reflected power has gone through the AC circuitry in reverse, so the inverter is still limited by kVA and not by watts even if a good chunk of the reflected power is recovered and reinjected.
If I was building a battery charger and keeping the circuitry simple, you could feed it a pure sine wave AC input, but its current draw would only be in brief pulses when the sine wave is near peak and there’s forward current flow through the rectifiers. The transformer probably (?) needs to be rated to handle the full current of those pulses (in KVA), at least to avoid voltage drop, but the actual energy transfer over time will be less (in KW).
@kc9scott Basically the only correct way to make a battery charger at decent power levels is with a regulator that incorporates a power factor correction circuit. If you just try to rectify the AC and throw it into a switching regulator without a power factor correction circuit, it won’t pass code.
Power factor correction in switching regulators is very easy to do these days. Basically instead of rectifying the AC into a buffer capacitor, the rectified AC goes into a switching circuit which pulls current from every part of the rectified AC waveform and pushes that into a buffer capacitor via (usually) a small transformer + diode + capacitor combo.
You wind up with a power factor greater than 0.95 by doing that.
-Matt
Spot on from a geezer. Took this in 2nd year physics in the 60's.
Beautiful easy explanation straight to the point ❤
kW means that amount of power is being delivered one-way. It's staying in the load. With kVA, some of that power is coming back out. It's a mite simpler viewed in energy terms. kW indicates energy is being delivered irrevocably; kVA allows that some of that energy is gonna come back out toward the source, analogous to the energy stored in a spring.
You're right: the power factor can be written as cos phi
Phi being the phase shift between the voltage and the current.
The difference between being a power supply and a power load is 180° in phi...
Also congratulation for being the only person here who can write the units with correct capitalisation.
As a mechanical engineer, I was exposed to this in the circuits course that I had to take, and understood it fairly well. But my memory of it drifted over the years. I was kind of lost in your explanation until you talked about the vector sum of resistive and reactive loads, then it became more clear.
So, the title and some statements here are actually totally wrong. kW and kVA are truly identical, always. This is even demonstrated in the video with power factor. Power factor would not be a unit-less ratio if they were not identical. As they are identical, the units in the numerator and denominator cancel. The issue as explained is different than what is stated in the title and repeatedly in the video. What happens many times is that we have the same units for different things and we want to distinguish between them for clarity. We see this with torque and energy. Both can be measured in N•m. But this gets really confusing, because commonly you'll be dealing with energy and torque at the same time. So we prefer to use J (1 J = 1 N•m) for energy, while we leave torque with N•m. So the real issue is that consumption and supply aren't the same thing, but they have the same units, and we want to distinguish between them more easily so we write them with different-appearing units that aren't actually different. It's a pure labeling thing for clarity. But, truly, kW and kVA are identical, always. Thinking otherwise is confusing a convenient choice labeling with what the units actually are.
No. EE here. The flow of energy depends upon whether the load is mostly inductive as for motors or heater coils, or mostly a capacitive load such as maybe a DC power supply that often uses many capacitors as a filter, for example. The typical local power company would like the power factor to be as close to unity, or one, as possible.
Indeed. Why muddy the clarity of kVA with capacity (AH)? Ugh.
@Bridgeman416 It doesn't matter if it's EE or not. How do the units cancel in the numerator and denominator for power factor? Because even in EE they're identical. The issue is that the things they're used for are not the same and we would rather differentiate more clearly, just like with energy v. torque. So we make them look different despite them being identical. 1 kW =1000 kg•m^2/s^3. 1 kVA = 1000 kg•m^2/s^3. Labeling them as kW or kVA is nothing but a matter of convenience, as kg•m^2/s^3 is a mouthful. But if you think that makes them different, then you are confounding convenient labeling with the actual units.
It's just power expressed two different ways.
One is 100% useful or usable power, (kW) the other is not. kVA includes power factor which has the current either in front of the AC voltage as it rises from zero (leading) or behind the voltage (lagging). It used to be described as ‘wattless current’ and is essentially wasted power. So the power factor tells what is actually usable (true) power in kW, rather than what is actually needed to power the entire load (resistance+ inductance + capacitance) or the apparent power.
Only in a purely resistive circuit can kW be equal to kVA and kVA only exists in an AC circuit as it is to do with the alternating voltage as it rises and falls 50 or 60 times a second.
Brilliant bro... Super informative. Thank you.
Wow. You are magical at this. You are speaking at the perfect level for me. I'm grateful. Thank you!
Thank you for this concise and CORRECT(!) information.
I greatly appreciate your channel. Thanks for all you teach me.
Excellent video. So clear explanation by the gentleman
I love this breakdown. Keep up the good work!!
Thank you Sir! The best explanation I have ever heard. I remember seeing a gauge in the B747-200 Flight Engineers Panel showing KVARS. I guess this was KVA.
This is a beautiful explanation of the difference between kVA and kW. My mind got super clear after watching this video..❤❤❤❤❤ this electrical guy.
Thank you, very well described and now fully understood.
Excellent highly educative video i have seen in you tube.Many many heartfelt thanks to the author for the effort being taken in educating on KW AND KVA.
BEING AN ENGINEERING PERSON MY PROFESSOR DID NOT BRIEF TO THIS EXTENT
Excellent video and excellent explanation thank you very much
Excellent explanation! Thanks for the video.
You explain it in a very basic language so that any person can understand it instantly...... amazing way of explaining....thank you
hehe, this is like... Deja Vu... for today. Literally, had the same essential conversation.
Thank you for the video!
Brother, I really enjoy your videos and it's a plus that you have a translation. Gracias
very good video, learnt something wonderful again
Long-time electrician here ... very lively video, and very well explained ... of course these concepts are always difficult to explain and understand ... but excellent effort here ... thank you. 🙏 🤙☺️🇺🇸
Thank a lot of explanations.... More people's now understand about electric fundamental❤❤❤
Great explanation of a tough subject.
Very clear. It was a bit surprising to me until now.