Use of aluminum power conductors in industrial wiring 1

[pgbengr]

Please help me with comparative advantages and dis- adavantages in using aluminum conductors in industrial power wiring and also transformer winding.
My understanding is aluminum has more resistance and there will be lot more load losses and also we need to use larger size conductor to carry the same current as copper conductor.

I appreciate some references. Are ther any safety issues?

Thanks.
PGBENGR

 

[stephenw22]

Aluminum is cheaper and a lot lighter in weight than copper.

Since the bus bars or terminals you connect to will be copper, you need to make sure to use the right antioxidant grease when making the connection.

It used to be that aluminum cables couldn't handle repeated bending, but I've been told that new alloy formulations allow for flexibility almost as good as copper.

All of the MV and HV overhead wires around here have been aluminum for a long time, and they typically work very well, with few problems. The biggest problem I've seen is that cable splices can overheat and blow apart when the antioxidant grease dries up over time. Periodic thermal inspections of terminations and splices will alert you to any problems like that.

 

[dpc]

Aluminum wiring will be less expensive, lighter and easier to install. It requires larger cross-section to handle the same amperage and thus larger conduits and raceways. The two big problems occur at each end - terminations. Due to some major fires blamed on aluminum wiring in commercial and residential use, aluminum has a really bad reputation in the US for power wiring.

Aluminum exhibits a property known as "cold flow" where the aluminum will tend to flow out of a compression termination, causing a loose connection that can overheat. New installation techniques and termination devices have basically solved this problem, but it still takes a trained, competent electrician to terminate properly. Copper is much more forgiving.

Aluminum windings in transformers is a little different. The main issue is efficiency. However, a failed aluminum winding tends to produce more core damage inside a transformer than a copper winding, so if for big and/or critical transformers, I would always specify copper.

Just my $0.02. As a consultant, I specify copper for all industrial and commercial work and sleep better at night - unless the client insists on aluminum.

(For electric utilities, 95% of underground 15 kV cable is aluminum - it's more cost effective and they have miles and miles of it, so it makes sense for them.)

 

[Scramode]

Just check with local law some counties do not allow aluminun on the load side of metering
Scramode

 

[WoodrowJWeen]

As I understand it, the problem with aluminum cable terminations is that the mechanical type copper lug expands at a different rate than the aluminum wire allowing "cold flow" or "creep". I always specify copper wire on my projects but will allow aluminum in the larger sizes as a cost saving measure only if the wires are terminated with a compression lug or adapter. I have been wondering lately if there is still a danger of cold flow if aluminum wire were terminated in aluminum lugs on aluminum buses? Any comments?

 

[waross]

The main issues with alluminum are related to terminations. Due to the "cold flow" properties alluminum does not handle heat cycling well.
Solid aluminum conductors, (#12 AWG, the most common residential size, when used) are much more likely to break if nicked when the insulation is removed than copper conductors.
aluminum oxide has a high resistance. If the conductor is not properly cleaned the contact area will be reduced leading to a Hot joint, heat cycling, cold flow and failure.
If moisture enters a connection it can lead to corrosion, high resistance joints and failure.
When copper conductors outdoors are connected to aluminum conductors the copper must be located below the aluminum conductor. Rain water on copper will form copper salts that will corrode aluminum.
If the copper is below the aluminum the corrosion is almost eliminated.
Aluminum terminations require more care, skill and training than copper terminations. Aluminum may be used safely and is used by utilities.
Clean the surfaces well.
Use proper anti-oxidizing grease (immediately after cleaning).
Use generaous contact areas to reduce the magnitude of heat cycling and avoid cold flow.
Avoid connections to dissimilar metal in areas prone to moisture.
A lot of us still prefer copper.
respectfully

 

[pgbengr]

Thanks for the valuable input on this topic. Do you have any reference or white paper published on life cycle cost analysis done on copper v/s aluminum winding transformers and distribution feeder conductors?

PGBENGR.
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[ozmosis]

The German Copper Institute do have a vested interest but their websites include some interesting data:

http://www.kupfer-institut.de/lifecycle/

(hold your mouse over the tab marked Life Cycle and information links drop down)
or the Copper Development Association:

http://www.cda.org.uk/frontend/pubs.htm

 

[tommom]

http://www.copper.org/

Try this.

 

[lz5pl]

It was mentioned here several times antioxidant grease for termination to copper terminals. We use bi-metalic inserts between Al and Cu part - if this technique is not used in the US?

------------------------
It may be like this in theory and practice, but in real life it is completely different.
The favourite sentence of my army sergeant

 

[waross]

The most common equivilant of bi-metal inserts in North America may be the spacers in Cu/Al rated split bolt connectors. These are not bi-metal but are compatible with both copper and aluminum. The spacers may be discarded when joining copper to copper but must be used to joint copper to aluminum.
respectfully

 

[GrayTran]

Due to the extremely high cost of copper these days, some cable manufacturers are again promoting larger gauge aluminum cables/conductors.

Aluminum is prone to oxidation especially where it terminates. This can quickly lead to hot spots that excerbate the problem.

Special grit grease can be applied to the termination pots but there is still a requirement for occasional inspection and correction of termination points. Therefore the initial lower cost of installation is offset somewhat by ongoing maintenance.

If the aluminum conductor termination is badly damaged it has to be shortened so additional slack is necessary to allow for this possible situation.

Finally there is potential galvanic corrosion issues related to termination with dissimilar metals as there is typically a point along the conductor route where aluminum ends and the copper begins e.g., motors etc.

Many residential and commercial installation only use alumunium conducter as a main feed.

The best solution to control the cost of copper is to keep the heavier conductor runs as short as possible, i.e., keep the largest loads closest to the power source.

 

[HCBFlash]

I was once told by a utility company lineman/wireman, they they liked AL better than CU for underground cables, precisely due to it's weaknesses; a nicked or damaged cable would fail quickly and unmistakably, making the fault easier to locate.