I've seen many diagrams of three phase power systems where the phasors were given with RMS values.When you express an AC quantity as a Phasor e.g. 150∠0°, the 150 is understood to be the amplitude of a sinewave, the frequency is not specified and the initial phase is 0°. The diagram is in a fuzzy font and I can't see where Ix comes from but the source is 39 times that, whatever it is,
There is nothing wrong with doing it that way of course, but if you've never seen it done it probably looks and feels a bit disconcerting. I've never done it that way because I was not specifically required or taught to do it that way. As always your mileage might differ.I've seen many diagrams of three phase power systems where the phasors were given with RMS values.
In general, you don't know for sure unless there is some note or indication that lets you infer it or back it out. The best bet, if you can't find something in the context of the problem, is to pick one and make a very clear note what assumption you are making and work the problem under that assumption. You could also then include the answer under any other reasonable assumptions or give an explanation of how to find them from the answer using your assumption. In this case it will be a simple matter to just include a second set of answers based on the first set.
I have to admit that my knowledge of polyphase systems is anecdotal at best.I think it pertains to poly phase systems which are given in terms of RMS values.
The way the phasor concept is described though starts with A*cos(wt+ph) and there 'A' is always peak. That could be because peak is natural while RMS is derived.
It's natural to introduce phasors using the amplitude of the signal because in all three of the common approaches taken you are mapping the time domain functions to the phasors as directly as possible. But the mapping is scalable and when dealing with power systems it just makes the most sense, for most things, to work with RMS values.I think it pertains to poly phase systems which are given in terms of RMS values.
The way the phasor concept is described though starts with A*cos(wt+ph) and there 'A' is always peak. That could be because peak is natural while RMS is derived.
It's natural to introduce phasors using the amplitude of the signal because in all three of the common approaches taken you are mapping the time domain functions to the phasors as directly as possible. But the mapping is scalable and when dealing with power systems it just makes the most sense, for most things, to work with RMS values.
Yes it is more or less tradition, so it is like comparing theory vs practice again.Wikipedia's take: https://en.wikipedia.org/wiki/Amplitude
Under the heading "Root mean square amplituce" is found: "For alternating current electric power, the universal practice is to specify RMS values of a sinusoidal waveform.", and even when the waveform isn't perfectly sinusoidal (which it usually isn't these days) RMS does what is wanted.
Well i think it is more about tradition then any real requirement, except it does make things simpler to work in RMS values when dealing with power systems of any kind.I have to admit that my knowledge of polyphase systems is anecdotal at best.
You have to experience something before it has a chance to become a tradition. Sorry about the hole in my experience you could drive a truck through.Well i think it is more about tradition then any real requirement, except it does make things simpler to work in RMS values when dealing with power systems of any kind.
Well i would bet you are familiar with your own power line specifications. Probably either 120vac, 230vac, or less common 100vac. There are actually DC power systems out there in the US also but very uncommon although there had been somewhat recent talk about going to all DC for everywhere as amazing and antihetical to what most of us believe about power transmission. It has to do with reducing losses due to the skin effect and probably proximity effect in light of the more recent low loss switching converters power components.You have to experience something before it has a chance to become a tradition. Sorry about the hole in my experience you could drive a truck through.
I am familiar with the mains power and I've (successfully) built power supplies, I've just never used phasors in conjunction with designing a power supply. I certainly understand Pk-Pk, Amplitude, and RMS in great graphic detail. Never having worked with polayphase systems was what I was referring to.Well i would bet you are familiar with your own power line specifications. Probably either 120vac, 230vac, or less common 100vac. There are actually DC power systems out there in the US also but very uncommon although there had been somewhat recent talk about going to all DC for everywhere as amazing and antihetical to what most of us believe about power transmission. It has to do with reducing losses due to the skin effect and probably proximity effect in light of the more recent low loss switching converters power components.
What would be cool though is if the power company actually installed separate lines to homes in the US that carried 5vdc power so everyone could charge their phones right from the power line with no converter
Oh i see, thanks for the clarification. I worked with industrial power in the past so i was used to seeing something like 3 phase 240vac (rms), 208vac (rms), etc. line to neutral. But even at home the line is almost always referred to as "120vac" and taken to be RMS. Many appliances quote that in the specs or right on the back panel but they dont usually state "RMS" with it, although i guess some could.I am familiar with the mains power and I've (successfully) built power supplies, I've just never used phasors in conjunction with designing a power supply. I certainly understand Pk-Pk, Amplitude, and RMS in great graphic detail. Never having worked with polyphase systems was what I was referring to.