DC vs AC voltage drop

[steve66]

Dropping power factor but keeping same watts will result in higher VA which means higher current if volts is same.

Adding power factor correction to a motor circuit near the motor would mean you still have approximately same watts consumed by the motor, but the corrected PF reduces VA on the branch circuit/feeder, which will reduce voltage drop on those conductors.

I still think VD is going to be based more on VA and a lower power factor will mean more VA are present.

Same amps, different power factor, means different voltage drop.

 

[GoldDigger]

Same amps, different power factor, means different voltage drop.

It certainly means a different vector voltage across the wire impedance, but you have to be careful of where you are specifying the current and the voltage drop to get an accurate and useful description.
The magnitude of the voltage across a segment of wire cannot vary when only the phase angle of the current through that same wire changes.

 

[fmtjfw]

:lol::lol: That's so true its scary. Tree trimming is so bad in some pocos. In fact they were a big contributor to the August 14 black out in North America years back.

Excellent explantion:thumbsup: Doesn't frequency also play a role since lightly loaded generator speed up heavy loaded units slow down?

HVDC can actually work around loss of synchronism like this.

First Energy of Ohio was the culprit on the Aug 14 blackout. When they later bought Alleghany Energy's MPCO and PotEd in WV, the PUC here came down on them like a ton of bricks in reference to tree trimming.
Later they cut back on meter reading and did a bad job of estimating bills. MPCO was allowed to read every 60 days, First Energy's MPCO is required to read every 30.

As you can see I'm not a big fan of FE.

Yes you have the frequency changes, but if the recloser is fast enough, it's the phase angle, mostly.

I used to live near the southern terminus of a HYDRO-QUEBEC 750KV DC line that converted it to 300+KV 3-phase.

 

[steve66]

It certainly means a different vector voltage across the wire impedance, but you have to be careful of where you are specifying the current and the voltage drop to get an accurate and useful description.
The magnitude of the voltage across a segment of wire cannot vary when only the phase angle of the current through that same wire changes.

But the voltage that makes it to the load does change. In power engineering, that's usually what we are most concerned with. We want to know if the load has enough voltage to work, and not overheat.

assume we have a 120V source, and 115 volts makes it to the load. now, if the power factor of the load changes, and current and applied voltage stay the same, and we now get 110 volts at the load, I think most people would agree the voltage drop has changed. even if the magnitude of the voltage across the wire is the same.

 

[GoldDigger]

But the voltage that makes it to the load does change. In power engineering, that's usually what we are most concerned with. We want to know if the load has enough voltage to work, and not overheat.

assume we have a 120V source, and 115 volts makes it to the load. now, if the power factor of the load changes, and current and applied voltage stay the same, and we now get 110 volts at the load, I think most people would agree the voltage drop has changed. even if the magnitude of the voltage across the wire is the same.

Which is why, when discussing voltage drop it is essential to make it clear whether you are talking about the drop across the circuit element that is causing the drop or the difference in magnitude of the voltage at the load.
VD calculators, even ones that take inductance and skin effect into consideration, are generally using the former calculation.
Maybe a different term, such as delta V for the latter would help keep the discussion clear?

 

[mbrooke]

First Energy of Ohio was the culprit on the Aug 14 blackout. When they later bought Alleghany Energy's MPCO and PotEd in WV, the PUC here came down on them like a ton of bricks in reference to tree trimming.
Later they cut back on meter reading and did a bad job of estimating bills. MPCO was allowed to read every 60 days, First Energy's MPCO is required to read every 30.

As you can see I'm not a big fan of FE.

Yes you have the frequency changes, but if the recloser is fast enough, it's the phase angle, mostly.

I used to live near the southern terminus of a HYDRO-QUEBEC 750KV DC line that converted it to 300+KV 3-phase.

Why the conversion?

Out of curiosity what is the biggest factor in causing phase angle to change in such a case?

 

[Barbqranch]

Another problem with long distance transmission of HVAC is that 770 miles is approximately 1/4 wavelength at 60 hz. I suspect you don't want to make a huge 60 hz antenna. I don't really know enough about the topic to elaborate, but perhaps someone else can comment.

 

[GoldDigger]

Another problem with long distance transmission of HVAC is that 770 miles is approximately 1/4 wavelength at 60 hz. I suspect you don't want to make a huge 60 hz antenna. I don't really know enough about the topic to elaborate, but perhaps someone else can comment.

The antenna part is not likely to be a problem, especially since the transmission line will consist of a balanced set of wires whose currents will cancel and those wires are very close compared to the wavelength at 60Hz.

A somewhat more interesting concern is that if you treat the transmission path as a constant impedance transmission line, then the 1/4 wavelength segment becomes an impedance transformer:
A short at one end will look like an open circuit at the other end because of standing wave effects.
And an open circuit at the far end will look like a short at the source end. Not very comfortable.

PS: Just had a flash of what a VSWR meter for an HV transmission line might look like.