Ampacity of Bundled Conductors

[mbrooke]

Grinding through IEEE 738 is a lot of work

It is, something I try to avoid if I can.

I wish Southwire would have used 100*C, as this is what most line hardware is rated for.

I'm interested in your case. How did re-generation lead to no cap banks and no AVR? The voltage shot up over bandwidth for a feeder fault or switching?

But yes, typically voltage drop is what gets you, especially in radical applications.

 

[mivey]

sag causing clearance and phase separation issues and annealing are the main concerns

 

[mbrooke]

sag causing clearance and phase separation issues and annealing are the main concerns

Annealing... a 10% loss of strength is not a concern due to the steel reinforcement? I'm clueless to be honest, I have to much faith in ACSR.

I know of POCOs who run over 100*C.

 

[mivey]

Strength depends on conductor type. Types like ACSR get about 1/2 of their strength from the Al so annealing matters. ACSS depends mostly on the steel so Al strength is not a big factor.

High temps can effect the steel protective coating. If the steel gets damaged it can corrode and cause the Al to turn to powder.

High temps can cause differential elongation outside specs and result in birdcaging or excess compression.

POCOs operating over 100C are either playing the risk game or using higher temp wire.

There are emergency overload ratings for wire but one must consider the limiting assumptions and if they are applicable at the time.

 

[mbrooke]

Strength depends on conductor type. Types like ACSR get about 1/2 of their strength from the Al so annealing matters. ACSS depends mostly on the steel so Al strength is not a big factor.

High temps can effect the steel protective coating. If the steel gets damaged it can corrode and cause the Al to turn to powder.

High temps can cause differential elongation outside specs and result in birdcaging or excess compression.

POCOs operating over 100C are either playing the risk game or using higher temp wire.

There are emergency overload ratings for wire but one must consider the limiting assumptions and if they are applicable at the time.

I'm getting load flows and even official documents going over 100*C for peak load no elements out steady state at 2ft s+w. I can't figure it out.

Here is an excerpt from PJM's rating doc insinuating operation over 100*C as one example:

https://imgur.com/OzlZglh

 

[GoldDigger]

That would make sense.

So in essence aluminum and copper from sag, but steal in terms of ferromagnetic properties changing with temp?

Ferromagnetic properties would only apply to an iron core inductor, not an isolated wire. Any change in the magnetic properties of a circuit consisting of Cu or AL would be from the combination of change in length and change in diameter of the wire. Both small.

 

[mbrooke]

Ferromagnetic properties would only apply to an iron core inductor, not an isolated wire. Any change in the magnetic properties of a circuit consisting of Cu or AL would be from the combination of change in length and change in diameter of the wire. Both small.

Makes sense. But this would not hold alone for iron, nickel and cobalt, correct?

 

[paulengr]

It is, something I try to avoid if I can.

I wish Southwire would have used 100*C, as this is what most line hardware is rated for.

I'm interested in your case. How did re-generation lead to no cap banks and no AVR? The voltage shot up over bandwidth for a feeder fault or switching?

But yes, typically voltage drop is what gets you, especially in radical applications.

Special case. The load in this case is a 10-15 MVA excavator. They have synchronous condensers (aka synchronous motors) in a Ward Leonard loop drive system. Old tech. Anyways so they pull about 10-12 MW for about 10 seconds then 30-40 seconds later they source 2-4 MW (braking/regeneration) with the synchronous motor (resonance is about 2 Hz) doing its best to attempt to maintain a slight leading power factor (.85 leading) to offset other inductive loads on the system during normal operation. Voltage usually varies +15/-20% at the one big load with a 50-60 second cycle. In other words every dig cycle. Now try that with 3 or 4 of them. During some dig cycles (moving dirt from a new cut to the bottom of the pit) you can actually see potential energy harvesting...net power production rather than use over time.

AVRs and cap banks at best would just have to run static settings but even if you tried to compensate for loaded conditions then you’d also have the regenerative scenario (overvoltage) to deal with, which is not a normal situation, I considered DSTATCOMs which would be fast enough and easily stabilize things but the prices were insane. In the end we got a new machine with VFDs sized to run leading or at least 1,0 power factor and essentially the active front ends acted like the synchronous motors minus the resonance and tended to stabilize the line. If you must know this was the largest load in Duke East (Progress Energy). 90 MW load. Not sure after the merger if this is still true.

Mining is fun. It’s like a miniaturized power system with big network issues.

 

[mbrooke]

Whoa. Sounds like fun. Any details on the drive system? Never heard of it, but then again I know nothing about mining.

 

[GoldDigger]

Makes sense. But this would not hold alone for iron, nickel and cobalt, correct?

That might influence skin effect in those types of wire, but for lower frequencies the fact that the flux generated by the current does not really link the wire as if it were the core of a wound inductor.