dave*99
Well-known member
I studied this in college. Both in the classroom and the pub.
Reactive Power
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LopezBart
Well-known member
"Double your voltage, double your flux, double E, double E, double E *****" is what the EEs said when I was in college.
And everyone studied beer - the undergrads, the graduate students and the (younger) professors.
And everyone studied beer - the undergrads, the graduate students and the (younger) professors.
tool_scrounge
Well-known member
That is a great example that most folks can relate too!
pancho400cid
Well-known member
I "get it", but I don't agree with it.
Reactive current isn't wasted..... the physics don't work without it. It's the current that goes into making the electric fields in capacitors, and the magnetizing current for electric motors and other inductive loads.
You wouldn't want to live in a Watts-only world.
...
Reactive current isn't wasted..... the physics don't work without it. It's the current that goes into making the electric fields in capacitors, and the magnetizing current for electric motors and other inductive loads.
You wouldn't want to live in a Watts-only world.
...
LopezBart
Well-known member
It is in terms of buying wire.... reactive current is real in terms of the resistive losses it creates... which is why the power company wants power factor correction if your loads are too skewed.
pancho400cid
Well-known member
I hear ya... I just don't agree with the term "wasted" . What the KVARS are doing is just as necessary and useful as what the Watts are doing. The magnetic fields of a transformer are just as necessary as the turning shaft of the motor it's powering.
You can do on-site power-factor correction and get by with smaller transmission lines to the site.... but you can't eliminate the reactive current. It's gotta come from somewhere. Fortunately, as you said, in a lot of cases, a few tens of thousands worth of power-factor correction capacitors, etc. can sometimes eliminate the need for much more expensive transmission cables and generating capacity.
...
You can do on-site power-factor correction and get by with smaller transmission lines to the site.... but you can't eliminate the reactive current. It's gotta come from somewhere. Fortunately, as you said, in a lot of cases, a few tens of thousands worth of power-factor correction capacitors, etc. can sometimes eliminate the need for much more expensive transmission cables and generating capacity.
...
ArcReactorKC
Well-known member
I have spent hours attempting to educate data center stationary engineers on what Var really is and why they need to care. They always bring up the beer mug analogy but then can't extrapolate that to their gear and systems.
exranger06
Well-known member
I agree that reactive power serves a purpose, and we do need it, but IMO, that just makes the beer analogy even more accurate. Obviously you wouldn't want a beer that's mostly foam, but you DO want at least a little foam on top (though I guess it depends on personal preference). The foam helps bring out the flavor and aroma of beer, and reduces the carbonation, which makes you less bloated. So:
No foam, all liquid beer : no reactive power, all real power = bad
Lots of foam, little liquid beer : lots of reactive power, little real power = bad
A little foam, mostly liquid beer : a little reactive power, mostly real power = good.
mark-NJ
Well-known member
The beer & foam example is how we explain it to the mechanical engineers I work with. The rest of us use trigonometry...
(Not trying to be a [email protected]'m dead serious)
(Not trying to be a [email protected]'m dead serious)
LopezBart
Well-known member
As an ME I always thought of this as the phase angle between the voltage and current, but perhaps some are happier with the beer analogy....
theoldwizard1
Well-known member
Engineers use "i". Mathematicians use "j".
Or is it the other way around?
Or is it the other way around?
LopezBart
Well-known member
Engineers generally use "i" for current; j for complex numbers. Math folks use i for complex numbers.
mark-NJ
Well-known member
...and "E" for voltage. (All the young guys at work insist on "V")
Debcrow
Well-known member
The mug is used to transmit the beer from the tap to you, the consumer.
Plugging your lips on the edge and tilting, it is distributed to your system for its intended use.
After consumption, you are pretty much going to track a sine wave as you walk.
electricity, Elementary Watt's On.
I know, we need a 'groan' icon
Plugging your lips on the edge and tilting, it is distributed to your system for its intended use.
After consumption, you are pretty much going to track a sine wave as you walk.
electricity, Elementary Watt's On.
I know, we need a 'groan' icon
LopezBart
Well-known member
"You know why plugging an extension cord into your neighbor's garage and trying to boil water takes forever?"
"Because a poached Watt never toils."
"Because a poached Watt never toils."
kaffine
Well-known member
When did they change that? I had thought it was a 4 year vs 2 year degree thing but the 4 year guys are now using V.
Jack Ryan
Well-known member
Generally, people think of emf and voltage as the same thing but they are not. Not that it usually matters.
Aside from that, voltage seems easier to say and 'v' is easier to write.
Jack
Aside from that, voltage seems easier to say and 'v' is easier to write.
Jack
mark-NJ
Well-known member
I'll be "Team E" until I die...(but I'm old! )
EDIT: maybe it worth also mentioning: ISO uses U for voltage. Add that to the pile...
)EDIT: maybe it worth also mentioning: ISO uses U for voltage. Add that to the pile...
MBfreak
MEMBER EMERITUS
Being a firm believer in understanding the math and physics in electrical circuits I believe that
being able to calculate a circuit before tearing into it, is the way to go. For DC static circuits quite easy.
For switched DC, some understanding of Lenz law and derivate calcs help a lot.
For power frequency circuits where currents and voltages are reasonable you need a solid understanding of "j" ( math guys use "i")
and symmetrical components.
For obscene voltages and currents ( like 1050 kV AC in China) or 970 kA at 25 kV short circuit currents in a large nuclear power station
you need a bunch of people with varying skills.
However, electrical power circuits are mundane for the math lovers, most everything can be calculated with reasonable skills and accuracy.
This is sharp contrast to calculating air flow around an object at Mach 3.
Ola
being able to calculate a circuit before tearing into it, is the way to go. For DC static circuits quite easy.
For switched DC, some understanding of Lenz law and derivate calcs help a lot.
For power frequency circuits where currents and voltages are reasonable you need a solid understanding of "j" ( math guys use "i")
and symmetrical components.
For obscene voltages and currents ( like 1050 kV AC in China) or 970 kA at 25 kV short circuit currents in a large nuclear power station
you need a bunch of people with varying skills.
However, electrical power circuits are mundane for the math lovers, most everything can be calculated with reasonable skills and accuracy.
This is sharp contrast to calculating air flow around an object at Mach 3.
Ola