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Hendrix Essentials

Where is the cable and hardware manufactured?

Cable is manufactured in Milford NH. Spacers and Insulators are manufactured in Amherst NH. Ductile iron and galvanized brackets are outsourced to others under our name, design and control.

Are you working with anyone in Florida?

Our Florida representative is Electric Sales Associates www.electricsalesinc.com.  We currently have applications in multiple utilities across Florida.

Product

What is a Tree Wire?

The use of “Spacer Cable” (3 heavily covered conductors supported by a messenger and separated and hung by spacers) versus “Tree Wire” (the same heavily covered conductors strung in an open wire configuration on cross-arms with polyethylene insulators) is mostly a difference in configuration. 

Spacer cable has the benefits of being an extremely low profile (about a foot side to side), protects the phase conductors with an overhead messenger (keeps the trees/branches from electrically contacting the conductors, thereby providing mechanical and electrical protection), has improved engineering benefits (lower impedance, 25% improved voltage profile, better voltage regulation, higher power factor, lower losses, etc.), is more suited to multiple circuits, has a better ability to maximize Right-of-Way (ROW) utilization, and has a higher reliability than tree wire, among the primary differences. 

Another difference is that Tree Wire usually utilizes ACSR or AAAC since it must support its own weight. Spacer Cable, on the other hand, normally utilizes AAC, since phase conductor tensile strength is not required (all the strength is in the messenger), it has better ampacity, is lighter, and can be compacted (smaller diameter, uses less polyethylene, and has a lower physical profile for wind and ice loading, not to mention pole loading and guying).

The photos below illustrate Tree Wire (left) and Spacer Cable (right).

Are Aerial Cable variation available in a wire?

PLS-CADD wire files have been developed for most conductor and messenger combinations and are available upon request for customers working with us. Contact your Hendrix Regional Sales Manager or authorized Hendrix representative, available at www.Hendrix-wc.com – Aerial Cable Section.

Does the low density conductor cover have water tree retardant like XLPE UG primary cable?

No. The reason is that there is no concern for electrical treeing in aerial covered conductor applications. In UG cable, there is a grounded neutral outside the insulation, so that 100% of the voltage is impressed across that very thin insulation wall. Any moisture available from the stranded conductor is influenced by the extremely high electric field to migrate from the conductor to the neutral. This is electrical treeing, and it can degrade the insulation integrity severely. In aerial covered conductor applications, there is no concentric neutral, there is no severe electric field intensity or voltage drop across the insulation wall, and as such no mechanism for electrical treeing to take place.

A client has requested the use of a tree-wire cable in a spacer cable system with a messenger, presumably to allow for flexibility with future modifications. Can you comment on this application?

Spacer Cable can be modified in the future just as simply as a bare wire system can be modified in the future.  “Tree wire,” indicates a type of construction different from spacer and typically using standard cross arm construction with covered reinforced conductors.

The hardware are different then OH conductor. Do you have range of hardware needs to be used for termination, tap off, dead end etc?

Hardware used for Spacer Cable is minimal. Tangent, Angle and Dead end Brackets, angle clamps (same as for bare wire), insulator pins, and covered grips are available from Hendrix. The hardware used for transitions, such as at riser poles, or transitions to bare wire, are not different.

When it comes to terminations, taps, and dead ends, there are a few differences between spacer cable and bare wire that are worth mentioning.
Terminations – Spacer cable is terminated in a coated performed grip, whereas bare wire normally uses a full tension deadened shoe, regardless of technology (automatic, bolted, shoot on, etc., etc.) Hendrix supplies the full range of coated preformed dead end grips required.

Taps – Spacer Cable, since there exists a covering, requires that the covering be stripped before a connection is made. Any standard connector can be used. At that point, there are two options for taps. The tap can be covered (insulation and BIL fully restored), or left bare (which is necessary in the case of a connector with a stirrup). In the latter case, two precautions are necessary. The first is that a 4’ section of Line Duc be installed on top of the messenger and secured in place with a tie. The second is that a surge arrester be used on the tap. When a 3 phase tap is made, the taps also need to be staggered 24” longitudinally, so that they are not all lined up in a row.


Can you discuss the safety considerations of this cable for things such as accidental contact by cranes, etc.

Energized conductors are never “safe.” However, some are safer than others. Contact with an energized bare wire entails the risk of drawing full short circuit current, and this can often result in a fatality. Even trucks and cranes touching a bare wire run the same risk of fatality, fire, or serious injury. Hendrix covered conductor is designed to limit the charging current on the surface of the cable to 1/3 ma (higher for larger conductor sizes or higher kV classes). Current required for fibrillation is in the 7-10 ma range. So available current from a Hendrix covered conductor at 15 kV class is only 3-5% of the fibrillation threshold. This is still not “safe” but neither is it fatal. 
It should be noted that NESC 230D requires that covered conductors need to be treated as bare conductors for all work rules and practices.


What is the purpose of the Alumoweld messenger? Why not just use EHS steel?

Two reasons:
Ampacity – the messenger is also used as a shield wire and either all or part of the neutral system. AW or AWA alumoweld can be designed with a much higher ampacity than what EHS provides.
Corrosion resistance – Spacer cable is often used in seaside and/or industrial sites where corrosion is a concern. Alumoweld has a much higher corrosion resistance than EHS galvanized steel, which has a notoriously low corrosion resistance.


Would Hendrix be suitable for low-voltage dc application (e.g. neutrals of HVDC systems)?

Spacer Cable has not yet been used for HVDC applications although that is something worth discussing further, as industry interest increases in DC.

Any problems/issues with squirrels chewing on the conductor?

In a Spacer Cable configuration, should an animal make oral contact with the energized conductor, the messenger is only inches away. The argument has been made that this 60 Hz “buzz” is the reason we have never heard of nor seen chew marks on the spacer cable configuration. This argument would be absent in a tree wire configuration, where there is no neutral nearby. We have heard rumors of animal chewing on covered conductor, but believe this was on the old thin-walled weatherproof wire from the 60’s and 70’s. We have not heard of chewing incidents on tree wire systems using the Hendrix High Density PE covered conductor. It is important to point out that the old thin-walled weatherproof wire was never a Hendrix product.

What type of insulation is used? XLPE or EPR.

Insulation is a 3-layer system. A Semicon shield is applied over the bare conductor, followed by a High Molecular Weight inner layer, then a High Density Polyethylene outer layer. The total thickness of the 3-layer covering system varies with kV class.

What is largest reel length 795?

Typically 5,000’ on standard reels. However, larger, customized reels are available for specific project lengths. Limiting factors are typically physical size, weight, available lifting and handling equipment on the job site.

Can you make a 90-degree corner with continuous conductor?

Yes. The conductor is turned around two insulators, so it only sees a maximum 45 degree angle. It should be noted that in heavy angles (greater than 60 degrees) the messenger is double dead ended on the pole.

Do you apply the insulation in one continuous process or three separate process?

One continuous process.

Parasite and rodent protection?

In a Spacer Cable configuration, should an animal make oral contact with the energized conductor, the messenger is only inches away. The argument has been made that this 60 Hz “buzz” is the reason we have never heard of nor seen chew marks on the spacer cable configuration. This argument would be absent in a tree wire configuration, where there is no neutral nearby. We have heard rumor of animal chewing on covered conductor, but believe this was on the old thin-walled weatherproof wire from the 60’s and 70’s. We have not heard of chewing incidents on tree wire systems using the Hendrix High Density PE covered conductor.

Since this conductor would appear to be less likely to produce large fault currents even when damaged or down, are you aware if companies that utilize this aerial cable utilize a different method of protection than they do for bare conductor?

In companies we have talked to, we have never heard a change in relay/recloser/breaker/sectionalizer settings for use of spacer cable compared with their bare wire protection scheme settings.

Can ACS be used on a delta primary system? Does the messenger need to be grounded?

ACS can be and is used on systems configured in delta. The messenger would be recommended to be grounded in the event it was intended to be used as a lightning shield.

Can the messenger wire be supplied with fiber optic cable for SCADA system?

Yes.

Would you please repeat, in a spacer cable system, how the messenger acts like a neutral?

The messenger can be used as a neutral. In express lines (no taps or transformers), the messenger is used as the only neutral. On lines where there is a transformer on many of the poles, it is common to also run a system neutral below the spacer cable line. The neutral is bonded to the messenger.

How is the Fiber Optic cable accommodated in a Hendrix cable circuit?

The fiber can be run as OPMW, that is, inside the messenger. It can also be run as a separate ADSS line, either above, below, or beside the spacer cable line.

Are there any security requirements that have impacted aerial fiber following the Metcalf substation attack a while back?

Substation exits are a common application of spacer cable and interest has increased with the added attention of the Metcalf event and the CIP-014 regulations to mitigate substation damage.  Hendrix, as a leader in reliability solutions, is looking to support this industry effort.

Design/Technical

Do you have PLS CADD libraries for the insulators and conductors?

PLS-CADD wire files have been developed for most conductor and messenger combinations and are available upon request for customers working with us. Contact your Hendrix Regional Sales Manager or authorized Hendrix representative, available at www.Hendrix-wc.com – Aerial Cable Section.

What is the ratio of bending radius to cable diameter?

12 to 1.  This is an ICEA rule and generic across conductor diameters.

What amount of inductive reactance does your system gain per mile?

Since GMD is smaller than that for bare wire systems, mutual inductance is similarly reduced. Total impedance is reduced by 15-20%, with the result that voltage regulation is actually 15-20% better than bare wire systems.

How many fiber strands can be incorporated into the messenger wire?

- We have used numerous OPMW constructions, from 48 fiber (diameters of 0.496" and 0.591"), up 144 fiber count Custom fiber can include a higher number. An increase in the number of fibers results in only a minimal increase in the OPMW diameter. The only limitation would be the maximum diameter OPMW which can be accommodated by the spacer. Since the spacer can accept messenger up to 0.75" in diameter, and OPMWs with 72 fibers are available, even with very high RTS (rated tensile strength), in diameters well below the 0.75” restriction.

How about the separation between cables?

Separation between phase conductors and between the phase conductor and messenger is determined by the size of the spacer used.

Spacer

Phase-Phase (in.)

Phase-Messenger (in.)

RTL-15

8

8.5

RTL-46

11 1/2

11 3/4

RTL-GO95

18

18

RTL-69DM

29 13/16

36 7/16


How do you rate the ampacity of your cable? Open air bare conductor? Insulated in air?

We use standard IEEE formulas for determining the ampacity of the cable. Standard ampacities are given in the table below. Non-standard ampacities (considering special cases of operating temperature or unusually high ambient temperature) are calculated on a case by case basis.

It should be noted that the ampacity of a 15 kV covered cable is similar to the ampacity for a bare wire cable. There are minimal de-ratings at higher kV classes due to the increase in covering thickness. However, and this point is key, the de-rating is minimal, and in no way can be compared to the massive de-rating suffered by UG cables which require much larger conductors than either bare wire or covered conductor.

Question: Does separation between cables, by spacer, meet Canadian standard, CSA, CEC?

As of June 2015, it does not. We are working with the OH lines Committee (CSA 22.3 No. 1-10) for a modification to Clause 5.2.4 “Conductor Classification for Clearances” which we hope will be included in an addendum to CSA 2015, but make no claims to speak for CSA as they are an independent body. It should be noted that spacer cable is currently used and installed in all major Canadian utilities (except Manitoba and Saskatchewan), has been installed across Canada for over 50 years, and can be used with the approval of a P.Eng.

Is treeing the failure mode of the conductor shield?

No. See response on electrical treeing above.

What class of poles should we be using to prevent the collateral damage of heavy trees / tree branches coming down on the ACS?

This is a design decision which must be made considering what type of trees may come down, how this affects the safety factor, etc. Contact your Hendrix Regional Sales Manager or authorized Hendrix representative, available at www.Hendrix-wc.com – Aerial Cable Section.

It should be noted that a properly designed Spacer Cable System taking into account (anticipating in the design stage) collateral damage would behave differently than a bare wire system in a similar heavy tree or tree branch fall impact, and go a long way in improving reliability.

Applications

Can you discuss requirements to re-conductor existing ASC systems? We have a circuit of OLD ACS that is scoped to be replaced. Management wants to go with open wire.

One would look first at condition of messenger. That is, can it be used with the larger conductor being installed? The spacers, insulators, brackets and other accessories would also bear inspection, as they might still be viable for use with the larger conductor. If everything were to be removed, then re-conductor would be a little different than a new installation. An item which would be added to this list is that the pole classes should be verified with the larger conductor.
Spacer to spacer re-conductor is easier than converting back to open wire due to the ability to move the conductor bundle independent of the messenger and attachments, and also due to less space in stringing; even if components have to be changed.

What is the reason for a span over a lake? Standard bare wire construction should not be a problem there...

Hendrix has used Spacer Cable for river and lake crossings in many locations and for many different reasons. Some of them are economics (one pole instead of three for long spans), safety (sailboat masts contacting bare wires), permitting (permission to install one pole vs three), reliability (bare wire conductor clashing problematic on long spans), among others.

Costs

Can you give an estimate per mile for a 3 phase 2/0 AA 15kv line in a spacer cable system?

Messenger, spacers and accessories would be about $4/circuit-foot. Another measure would be total installed costs are about 15% (and up) higher than bare wire equivalent. Total cost would depend on span length, elevation changes, number of angles, NESC loading, poles required, labor, etc. You will be contacted for further clarification.

Could you please say something about the costs as compared to bare conductor installation

Total installed costs for spacer cable at 15 kV can be approximately 15% (or more) higher than equivalent sized bare wire costs. Labor costs will vary per location, since spacer cable is usually used in the more challenging applications (reliability problems, tree issues, ROW issues, multiple circuits, etc.). ACS to bare wire labor costs for the same location would be roughly similar with an experienced crew. Line crews who run ACS regularly install it as fast as or faster than bare wire, because the 3 phase conductors are pulled in at once.

What is the Hendrix experience in terms of approximate cost differences between Aerial system, Overhead line with bare conductor & Underground distribution system at medium voltage levels?

It depends on the comparison being made. Direct buried UG can be 3x to 4x or as expensive as spacer cable. If comparison is to duct/trench or something more extensive, UG can be 10x more costly than spacer cable, or much more than that. If we are talking a river crossing, UG is easily 20-30x or more.

How much was the over-river system again? $1Million?

520m River Crossing – Indiana
• Option 1 – submarine cable – cost $1million
• Option 2 – build around shoreline – cost $800,000
• Option 3 – Spacer cable – cost $250,000

Installation

How can the user prepare an installed cable for a new tap?

Spacer Cable, since there exists a covering, requires that the covering be stripped before a connection is made. Any standard connector can be used. At that point, there are two options for taps. The tap can be covered (insulation and BIL fully restored), or left bare (which is necessary in the case of a connector with a stirrup). In the latter case, two precautions are necessary. The first is that a 4’ section of Line Duc be installed on top of the messenger and secured in place with a tie. The second is that a surge arrester be used on the tap. When a 3 phase tap is made, the taps also need to be staggered 24” longitudinally, so that they are not all line up in a row.

What is your recommended distance between poles for 69 kV distribution to prevent against line failure from fallen branches?

How do you transition from overhead installation to underground shielded cable?

The transition from aerial Spacer Cable to underground shielded cable would be done essentially no differently than the transition would be done with bare wire. The insulation is stripped back and the bare wire is inserted into the termination. The minor differences would be that the messenger above the transition point would be covered with Line Duc.

What about spacers for aerial fiber that runs with the power line poles? Distance separation between power and fiber?

For a 15 kV system, and using table 235-5 of the NESC, the top of communication space begins 44.48” below the elevation of the bottom phase (40” + .4” per kv over 8.7kv). In any case, the same NESC rule would apply to spacer cable as would apply to bare wire. If the company maintaining the power line and the communication line is one in the same, the NESC allows the fiber to be in the same “space” as the power line. In this case it is also possible to put the fiber in the messenger (OPMW).

Does the messenger cable serve as a static wire?

Yes, but it must be grounded a minimum of every 500 ft. to a resistance of 25 ohms or less. In high lightning areas it is recommended to ground at every pole.

How is the cable terminated on dead end poles?

The cable runs through the dead end grip and is simply severed and covered with an end cap at that point. The other detail is that lightning arresters are required as would be at any dead end (bare, covered, or UG).

How long can a span be without requiring a splice?

Theoretically, a span can be as long as required. We have built spans to 2,100 ft. We can manufacture cable for a single reel, depending on size of the reel, to 5,000, 6,000 or more feet. If the question is in regard to how long a pulling section can be, that would depend on how much we can get on a reel, and that would depend on the conductor size and kV class. Consult the factory for a specific application.

How easy is it to add laterals and transformers along a route?

As easy as it is adding laterals and transformers with a bare wire system. The difference here is that the cable needs to be stripped at the connection point. With Spacer Cable taps, since there exists a covering, it requires that the covering be stripped before a connection is made. Any standard connector can be used. At that point, there are two options for taps. The tap can be covered (insulation and BIL fully restored), or left bare (which is necessary in the case of a connector with a stirrup). In the latter case, two precautions are necessary. The first is that a 4’ section of Line Duc be installed on top of the messenger and secured in place with a tie. The second is that a surge arrester be used on the tap. When a 3 phase tap is made, the taps also need to be staggered 24” longitudinally, so that they are not all line up in a row.
In the case of laterals, it is recommended that the connected be fully re-insulated with taping methods. If the lateral is to use a sectionalizing or protection device (i.e., recloser, fuse, switch), then arresters need to be added and Line Duc placed over the top of the messenger.

Maintenance

What does the annual inspection consist of?

The annual inspection would start with a visual inspection. Items, which looked suspicious, would be investigated further. More in depth inspections use a predefined checklist with a lineman walking from pole to pole verifying things with greater degree of scrutiny. Hendrix offers complete packages complete with full inspections and preventative maintenance recommendations.

How long before covered conductors start to be exposed to the elements?

Covered conductor systems need to be designed taking into account the local environmental challenges present, IEC 60815, and selecting components specifically for that location. It should be noted that ACS systems installed in 1951, 1952, and 1953 (the first years of system introduction) are still in operation today. Regarding elements radially penetrating the covering itself, we could add that this is not a concern, unless the covering becomes compromised.

If insulation gets damaged what do you typically recommend: replacing the cable section or repairing the insulation?

It depends on the extent of the damage. If minimal, the covering can be cut down, smoothed out and taped with proper high voltage materials. If extensive, the damaged section may be cut out and a new section spliced in. It should be noted that the covering system consists of three layers. The first layer over the bare wire is a semicon shield, which smoothes out the electric field distribution when the phase conductor is in contact with a grounded or partially grounded object (i.e., a tree branch), and also results in the cable having a higher BIL than would be achieved with a 2-layer covering design. The inside layer is made of a High Molecular Weight Polyethylene, without fillers or additives, which provides a high BIL as well as high 60 Hz Withstand Rating. The outer layer of covering is composed of High Density Polyethylene. Besides having weathering and additive packages which provide the UV inhibition and track resistance, it also has a high Impact Resistance and Abrasion Resistance, making physical damage to the outer covering less of a concern.

What type of testing/frequency do you recommend for the cable?

Minimal would be annual visual inspections. Spacer Cable lines built on inaccessible ROWs should be checked after major storms.

Branches, trees, and downed lines won't fully fault covered wire, so how can you detect if there is a problem if there is no fault? Will fault indicators still work?

If a tree is covering a line, there will not be enough current to operate a relay. Either you will have to rely on a customer calling in, or wait for the next line patrol. Suffice it to say, long-term contact is not desirable from any standpoint and periodic line patrols are recommended.

Will fault indicators still work?

Fault indicators will work in detecting a fault. They will not detect downed trees which are essentially high impedance faults. Select fault indicators which do not have exposed metallic parts or clamps.

Has a study been done on how long before covered conductors start to be exposed to the elements? If yes, please expand.

Yes. There was a study conducted over a one-year period and the results published in an IEEE paper entitled “SPACER CABLE SYSTEMS FOR RURAL ELECTRIC COOPERATIVES” by Carl Landinger and presented in the NRECA Conference in Louisville, KY in 2000. A link to this paper (and two other papers with similar subjects) was sent to the individual who submitted this question. It is similarly available to anyone who contacts us either through your local representative or our company website (www.hendrix-wc.com).