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BEPC13 (Electrical) (OP)
12 Mar 04 14:02
Does anyone know what the differences are? I am buying about 20k feet of 5kV power cable and found that the 2 main choices are EPR insulation with a PVC jacket or XLPE insulation with a PVC jacket. What are the tradeoffs of the two?

On a side note should I get shielded cable for this voltage class? I have heard it is difficult to get completely unshielded cable anymore. What is everyone's thoughts?

Thanks for the help.
Helpful Member!  dpc (Electrical)
12 Mar 04 14:50
You'll get a lot of varied responses on this question.  Here's my take:

EPR insulation has shown, over the years, a higher resistance to "treeing" of the insulation in the presence of moisture.  For industrial projects, at least in the US, EPR is used almost exclusively.  While Tree-retardant XLPE has definitely improved, most specifying engineers do not regard it as ultimately as reliable as XLPE.  EPR is also regarded as somewhat easier to install.  

XLPE has two main advantages - lower cost and lower dielectric losses.  The dielectric losses of medium-voltage solid-dielectric cable are quite small in the overall scheme of things, but there is no doubt that XLPE losses are significantly lower than EPR.  This (and the low cost) is why utilities still favor XLPE for long runs of URD cable.  

For more info on relative pros and cons - just talk with your local Okonite and Southwire reps.  They will be able to talk for hours on the subject.

As for shielding - I'd go shielded if I had 20,000 ft.  
Helpful Member!  jghrist (Electrical)
12 Mar 04 17:07
My 2ยข worth:

EPR is more tree resistant than plain old XLPE but Tree Retardent TR-XLPE is just as good as EPR from that standpoint.  EPR does tree contrary to some sources; you can't see the trees as easily as in XLPE.

EPR is more flexible and from that standpoint is easier to install, particularly for large sizes.

It can be difficult to strip the semicon from EPR without damaging the insulation.  

EPR is not a standard compound like XLPE.  There are differences among manufacturers.  Make sure that you use a reliable manufacturer.

EPR has higher dielectric losses, but at 5 kV this would be negligible.

I would use shielded cable at 5 kV.
cuky2000 (Electrical)
12 Mar 04 21:17
The selection of EPR solid dielectric cable for MV application up to 15 kV had been traditionally more popular than the XLP insulation. However, recent study shows slightly advantage of XLPE cable over EPR in term of failure and losses performances.
alehman (Electrical)
12 Mar 04 21:54
Try doing a search in this forum for EPR or XLP.
ScottyUK (Electrical)
13 Mar 04 3:20
It's interesting that EPR is dominant in the US. Pretty much the opposite is true in the UK, for new install at least.

What's the minimum cable-pulling temperature for EPR? We don't pull XPLE below about 4DegC officially, although we occasionally take the chance on a smaller cable for a breakdown repair. I'm guessing that EPR has a much lower minimum pulling temperature: given that the northern US is pretty cold for several months, could this be another reason?



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jbartos (Electrical)
13 Mar 04 7:00
gordonl (Electrical)
15 Mar 04 13:31
We use Install XLPE down to -40C, but this is a special order -20C is standard in Canada.  EPR is also not popular here.

Along with all the other comments so far, with which I agree, I would add that when it comes to flame tests EPR beats XLPE, for medium volatge applications and up.  From my experience you can't get an unarmoured XLPE MV cable with a "Tray Cable" rating.  So for applications in tray where "TC" is required unarmoured EPR is likely cheaper than armoured XLPE.
alehman (Electrical)
16 Mar 04 0:53
As previously mentioned EPR is far more common in the US than XLPE for <35kV. The industrial/commercial market is almost exclusively EPR. Many utilities use EPR as well. There is some interest in TR-XLPE but I think the fear factor is still high with anything called XLPE.

IEEE 525 recommends a minimum pulling temperature of -40C for EPR and XLPE.
jbartos (Electrical)
16 Mar 04 8:39
Comment: EPR tends to be preferred where applications might include elevated temperatures, e.g. ~100degC +
XLPE or TRXLPE tends to be preferred where applications might include low temperatures. This is in an agreement with other postings in this thread.
brupp (Electrical)
16 Mar 04 10:19
A lot of great responses here.  The original question didn't specify utilization voltage or application (underground, cable tray, conduit) which would be strong determining factors.  

Tree resistance has been discussed, which would suggest EPR for underground or wet applications.

Temperature has been discussed.  My experience is that EPR is significantly more flexible, although your choice of PVC as a jacket material means that you will have a stiff cable anyway.  

Flame retardance was briefly mentioned.  One cannot say that one material is always more flame retardant than any other, but EPR tends to be more flame retardant in general.  That's because the standard way to make cable insulation more flame retardant is to dope it up with halogens (mainly chlorine and bromine).  They add to the insulating properties of EPR but subtract from the insulating properties of XLPE.  As a result, it's easy to make EPR flame retardant and harder to add flame retardance to XLPE.  At 5kV and standard insulation thicknesses, though, XLPE can be made reasonably flame retardant.

For cable tray applications and others, XLPE and XLPO are making headway as low-smoke, low halogen insulating and jacketing compounds.  Those same halogens that make EPR flame retardant are lethal during a fire.  Once again, your choice of PVC as a jacket material suggests that you aren't concerned about low-smoke.

My impression is that the XLPE compounds are VERY similar between manufacturers but there is very little similarity between EPR compounds between manufacturers.  They all have their proprietary recipes for EPR.  That is why it is very important to use a reputable manufacturer.

The comment above about difficulty stripping EPR insulation is something to consider but the problem has been overcome by the really good manufacturers.

If your utilization voltage is 2.4 kV you might consider unshielded cable.  Otherwise don't even think about it.  The only manufacturer that I'm aware of who would try to sell you an unshielded cable for >2.4kV is Kerite.  Let's just say their opinion differs from the mainstream in that regard.
GOTWW (Industrial)
16 Mar 04 11:17
We have had massive MV XLPE cable failures in a intermitantly waterlogged duct system. They lasted 10-12 years. Big investment gone south. The money people were screaming that we could have continued to clean pole insulators for less!
This time I specify EPR, the salesman say they should be good for 30-40 years, longer than most people will ever remember.
jbartos (Electrical)
16 Mar 04 13:30
Comment: Some EPR Cable manufacturers, e.g. Okonite, can evidence better test results for EPR cables than other manufacturers for XLPE cables.
busbar (Electrical)
16 Mar 04 22:30

A major institutional operation in an ANSI region has some peculiar text in their CSI Division-16 boilerplate.   
    High voltage cable (4160 volt and 12000 volt systems) shall be 5KV and 15KV, EPR type, with 133% insulation and shall be warranted for 40 years.
From a procurement/construction-contract standpoint, is this specification enforceable?  Is such a terse mandate administratively feasible?  
  
advidana (Electrical)
17 Mar 04 2:11
I have install epr cable in the early sixties that is still operating. But the xlpe cable I have installed has failed after 10 to 15 years. my installations are for services and facilites, short run under 10,000 ft . All my installations are done in good weather with temperatures at 40 to 100 degree f and located under local frost levels. The phyical looks of all these cable, when we are able to pull them out looks like the cable have the mumps, from the treeing.

utilites usually have crews train to deal with cable failures on a day to day basis. but if you are doing work for a plant, you do not that type of trained people available and must contract them out . Which takes a lot of  time and lost production. So usually epa is used for plants. But for the power co. the xlpe is the way to go.
BEPC13 (Electrical) (OP)
17 Mar 04 15:06
Thanks everyone for your help. I should have said this earlier but the sytem voltage is 4160V with a restively grounded Y transformer feeding it. I have decided on a 5kv/8kv EPR with CPE jacket cable. This gives me more insulation than needed in the event of an overvoltage due to a ground fault and also gives me some marging so failures won't be as likely. I decided on the EPR because some of this cable will be running through duct bank that is usually underwater. I also decided on shielded cable. The large footage mentioned in my first post is not one run. It will be many runs to all the medium voltage loads throughout our plant in a cold climate. Again thanks for all the great replys I will definately be visiting this forum again.
busbar (Electrical)
17 Mar 04 18:24

Not to oversimplify circumstances, but it may be worth mentioning that there are often inherent differences in operational philosophies of industrial (and institutional) compared to utility electrical-distribution systems.  Utilities tend buy and stock larger quantites of very standardized materials and plan on in-house fast-turnaround replacement as needed.  

Industrials tend to be geared to specify the original system (and initial capital outlay) using more conservative components and methods, with expectations of fewer repairs by more specialized firms over the life of a facility.  
  
alehman (Electrical)
17 Mar 04 21:43
busbar - Kerite has no time limit on their warranty for manufacturing defects on their EPR cable.
jbartos (Electrical)
17 Mar 04 22:19
Suggestion: Tree Retardant Cross-Linked Polyethylene (TRXLPE) cable is somewhat better than regular XLPE cable. Visit
http://www.generalcable.com/North_America/NA_Assets/ProductBrochures/EmpowrLinkSS.pdf
for TRXLPE cable .24 reported failures per 100 miles.

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