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Question for Power EE's

J

jmcoreymv

Diamond Member
In the real world, what kind of loads would be purely resistive? What kind of loads would be capacitive? Would inductive loads be like heavy machinery?
 
None... none... and huh? In the real world, It's very hard to find pure anything. But then again, I'm a circuits EE. Maybe Power EEs will have a different opinion.
 
Well I dont mean pure. But, what types of things would have an overall capacitive loading effect or almost purely resistive effect, etc?
 
i'm no power ee but i'm pretty sure heating elements are virtually purely resistive and motors are heavily inductive
 
Originally posted by: jmcoreymv
What about capacitive loads? I heard they are rare but what are they....
Click to expand...

cant think of any heavily capacitive loads... maybe extremely long power lines?
 
Originally posted by: jmcoreymv
Well I dont mean pure. But, what types of things would have an overall capacitive loading effect or almost purely resistive effect, etc?
Click to expand...

Oh.. ok. So you're looking for real-life non-circuit examples? I guess umm... the heating coil of an electric stove would be an example of a mostly resistive load. Cap cap cap.. umm... gimme a sec.. i want to say battery but I think there's a better one.
 
Originally posted by: jmcoreymv
In the real world, what kind of loads would be purely resistive? What kind of loads would be capacitive? Would inductive loads be like heavy machinery?
Click to expand...


An example of purely resistive would be heaters or heating rods in an industrial oven. (Capacitance and inductance so low that it has no effect of the impedance of the system)

An example of a capacitive load would be a DC power supply (obiously, it uses large caps to smooth as well as maintain DC power). A battery would also have a larger capacitance than either inductance or resistance. If a battery had a high resistance, it would deplete very quickly...not to mention get very hot (as it does when you short it out..but that's because of high current! )

Inductive would include AC motors in many types of machinery.

All of these items have a component of everything...but for all practical purposes, several components are essentially zero for calculations.

There may be corrections to my above information....it's so easy to forget some of this stuff! 😉


 
Originally posted by: jmcoreymv
Originally posted by: dighn
Originally posted by: jmcoreymv
What about capacitive loads? I heard they are rare but what are they....
Click to expand...

cant think of any heavily capacitive loads... maybe extremely long power lines?
Click to expand...

I thought power lines had inductive effects?
Click to expand...

yeah... but not if they very close, but then those are usually very short... so disregard that part
 
Originally posted by: jmcoreymv
Originally posted by: dighn
Originally posted by: jmcoreymv
What about capacitive loads? I heard they are rare but what are they....
Click to expand...

cant think of any heavily capacitive loads... maybe extremely long power lines?
Click to expand...

I thought power lines had inductive effects?
Click to expand...

They have all 3. The reason that voltage is transformmed up is to lower the current on the lines. Lower current = lower power (Power = I^2 * R). So if you cut the current in half, you cut the power loss in the lines by 75%. Hence, power is jacked up to very high voltages (7,500, 25,000, 50,000 volts or higher) and sent along the lines at a very low current (low losses). Then it is transformmed back to a lower voltage/higher current for public use. Like I said above, most items have all 3 components, just a very low amount of certain components.


PS - I'm not a power engineer...but an Controls/Automation Engineer. I work with 600volts down using up to 200 amp circuits for those voltages. 🙂
 
Fluorescent lighting has a capacitive effect, but it is small compared to inductive loads. That's why banks of capacitors are sometimes introduced into substations for power factor correction.
 
I'd imagine heating elements at dc are the only things that have absolutely no inductive or capacitive effects.
 
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