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Posted By: e57 Triplexed feeders (re-post) - 04/02/05 01:54 AM
Had this in the less frequented therory area, figured it might get more attention here.

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I am about to have to re-install a feeder (By someone else) for an elevator with a haunting rattle. In-rush current rattles the conduit so badly the it can be heard all over the building. (Not that I think this will help much) It has been suggested that Triplexed conductors (Twisted) would help reduce this noise.
Although I am unsure of to what degree it would help, I was trying to explain the benifits of it to our PM today. I was wondering if anyone could confirm anything that should be should be listed, ammended or removed from this list.

Reduction of Eddy Currents (Minor)
Reduction of parrelel coupling through induction
Conductors "pull together" in in-rush situation as opposed to "rattle" (Mocking sine wave)

I learned about triplexing conductors some time ago, and can not find any good referances about it anywhere.

Thanks in advance, Mark
Posted By: SteveFehr Re: Triplexed feeders (re-post) - 04/02/05 04:23 AM
Data lines do this all the time; if it works to reduce EMI, I'd think it would do just as well to reduce inductive rattle.

In theory, if the 3 phases are drawing identical current, the magnetic fields *should* cancel completely once twisted.

[This message has been edited by SteveFehr (edited 04-01-2005).]
Posted By: Dave55 Re: Triplexed feeders (re-post) - 04/02/05 04:54 AM
I have absolutely no experience in this, Mark, but do you think over-sizing the feeders would help?

Dave
Posted By: SteveFehr Re: Triplexed feeders (re-post) - 04/02/05 08:35 PM
If magnetic induction from the amount of current is causing the rattle, larger conductors might stiffen it, might even slow the accelleration (f=ma) enough to reduce the rattle but the magnetic field would remain unchanged. So it would probably still rattle pretty badly.

I wonder if filling the conduit with expanding foam or epoxy might eliminate the rattle...

[This message has been edited by SteveFehr (edited 04-02-2005).]
Posted By: Dnkldorf Re: Triplexed feeders (re-post) - 04/02/05 09:59 PM
If it is inrush causing this, I assume you measured it, why not a soft start controller?

How big of motor we talking here?

Dnk...
Posted By: Trumpy Re: Triplexed feeders (re-post) - 04/02/05 11:56 PM
Steve,
Quote
I wonder if filling the conduit with expanding foam or epoxy might eliminate the rattle...
Wouldn't that cause a heat dissipation problem?.
Posted By: SteveFehr Re: Triplexed feeders (re-post) - 04/03/05 04:01 AM
Yes, it would, you'd be seriously de-rated. But since the in-rush is short term only, it may be OK.
Posted By: e57 Re: Triplexed feeders (re-post) - 04/03/05 04:52 AM
I had more of this info posted in another thread, of which I can't find any longer. And this one too. https://www.electrical-contractor.net/ubb/Forum1/HTML/005673.html

Anyway:

Its a 75HP motor. 1300+ LRA on a soft start pulling 650A+ Its a BEAST! http://www.markhellerelectric.com/motordata.htm

Soft Start is a Thyssen Dover Krupp 787AC-14
Of which I can find little information on. But simular to this one: http://www.elevatordrives.com/resources/hpv100_techmanual_tm5590.pdf

Feed is about 175' as the crow flies, but I got down there to map out a path and turns out to be 230+' of 250MCM. And has some exessive voltage drop, down from 208 to 180V at start.


Anyway, this thing has been battled out a few different ways. Elevator guy says its the feed, the electrician who installed the feed says its the elevator. And owner of it is confused and going for what makes sense to him.

Elevator guy suggested the foam filled conduit idea, the same as SteveFehr. But since this feeder heats up in frequent use, and it being a bad idea anyway, I laughed hyserically when I heard it. I should then derate the run for fill at 100%? He also suggested the triplexing idea...

Then theres me: I don't think Upping the size of the conductors to 350MCM is going to do anything except a slightly lower pitched rattle. 350 and triplexed I think will help. But the high in-rush will still be there. Many other people have had various thoughts on it, and range from locked up hydro pump, pump valves opening or closing during improperly timed during in-rush below speed, reversed windings, bad starter, voltage drop, triplexing, etc. no one whats to stick a 43B with 1000A, or 3000A CT's on the main to learn any more about the problem for a few hundred bucks, but would rather spend a few thousand on changing out the wire. And our PM bit on this agaist my judgement on staying away from it. She's pricing it for a regular 350 run in exiting conduit (Probhably too low as usual), and they'll bite. So guess who gets to pull it, me and my crew.

Now on a different note: I have some interesting expeirances with large motor starting.
While in the military, we had RO machines with 100HP pumps, which ran rather well on a 60KW gen set, but start-up would rock the gen set pretty harshly. Most of the time we would paralell up 2 60's for start, and use 1 to run. The cable we used for it was 250/4. (FYI most cables are twisted/triplexed.) Which would kind of jolt a bit at start, noticable. We ran out of that once, and used 4/0-4, and it would flex like a snake very noticably for the first few seconds of start-up, kinda wriggle a bit slowly. Ran out of both on occassion, and used THW individual conductors, no conduit as it was a temp feild operation in Somalia, the conductors jumped all over the place. So I figure triplex will help, to what degree, I don't know. As this elevator feeder rattle is like nothing I have ever heard. Imagine a 20A on 12's short circuit in 1/2", 1000%.
Posted By: shortcircuit Re: Triplexed feeders (re-post) - 04/03/05 12:26 PM
e57...according to table 430.250 (2005NEC) a 75HP motor at 208volts has a full load current value of 211amps. So, 211amps x 125%=264 amps for the minumum ampacity of conductors for the feeder to this motor.Table 310.16 places a maximum allowable ampacity of 250mcm at 255amps from the 75 degree column.

So, the original feeder used is undersized according to my math. Figure in the distance of the feeder, the temperature of the area the feeder passes through, and the inrush amperage of a motor that size @ 208 volts and I'm suprised that those feeder conductors don't jump right out of the conduit with the magnetic field induced upon start up.

Now I don't have any experience installation such as this, but a motor this size at that voltage seems a poor design to begin with?

I agree with you that a triplex wire installation will reduce the amount of wire slap the feeder is producing because of the tight wrap of the conductors. But the heat dissipation that you would have with a single condutor installation would be better. Also the 350mcm replacement feeder should help, 500mcm would be better.

1) What size conduit is installed?
2) What is the temp. in the area of the equipment and couduit run?
3) If it was even allowed, how would you fill a 230ft run of conduit with foam [Linked Image]


shortcircuit
Posted By: SteveFehr Re: Triplexed feeders (re-post) - 04/03/05 03:12 PM
The derating tables are not so much for insulative effect, as for heating of adjacent wires- if a particular wire is bounded on all sides radiating heat at 60C, then it's going to get hot, just from residual heat from its neighbors even if it has no current. This is not the case in foam fill; you won't have to derate 100%. You'd have to find the thermal conductivity of the foam and calculate your own derating table. Or, rather, let your PE run the numbers and stamp it [Linked Image]

With what you're dealing with, it might just end up to be cheaper that way.

[This message has been edited by SteveFehr (edited 04-03-2005).]
Posted By: Dnkldorf Re: Triplexed feeders (re-post) - 04/03/05 03:18 PM
Just another thought, and don't know if it would work:

Could you install a transformer on both sides of the feeders and reduce the voltage drop and current flowing through the feeders from the disconnect to the softstarter?

208X480 and then 480X208 on the other side?
Posted By: e57 Re: Triplexed feeders (re-post) - 04/03/05 06:56 PM
The 2 1/2" conduit runs through conditioned office spaces. And back to backing two tranformers was a thought, but no place to put them on either side.

Shortcircuit - The wire size is just under as the motor is 206 FLA, but I totally agree, a big mess up was done on planning the design for that voltage, distance, wire size. And I too am weary of 350, being too low as well. Although the use is intermitant, it is frequent, so LRA constitutes 50% of actual run time. I had given some thought to buss duct for major portions of it, but a little cost prohibitive. More than to replace with larger conduit to accomodate 500MCM w/ ground.

Now Steve, I know of no UL listed product for that purpose. We are also talking about a huge amount of cubic inches of conduit.
Posted By: Scott35 Re: Triplexed feeders (re-post) - 04/03/05 10:20 PM
Quote

Had this in the less frequented therory area, figured it might get more attention here.

Sad news for me to read, but unfortunately it is very true - the Theory area is the least active / posted to.
Hopefully your question(s) will be answered in this area.

Per the loud and noisy bouncing Conductors at Locked Rotor, I have only a suggestion - which may or maynot be effective:

Noise Is Enhanced By External Issues - Locate And Nullify The Culprite

In the past, found a few noisy feeders where the noise was greatly Amplified from several ambient / external conditions - each scenario adding to each other:

<OL TYPE=A>

[*] Conduits loose in strapping means (not completely fastened),


[*] Loose Fittings - Setscrews not tight, or Compression "Nuts" loose,


[*] Conduits not completely set into Couplings - with the securing methods loose (as listed above),


[*] Excessive spacing between strapping means - like 15 feet or more between straps, where there should have been straps at 10 foot intervals,


[*] Loose Conduits + examples above, run on light gauge steel studs - with the framing being very loose fitting, or with loosly attached materials inside wall cavities,


[*] Same types of walls with abilities to create "Standing Waves", and/or resonate easilly from the vibrations of the feeders,


[*] Loose Flex against easilly resonated walls,


[*] Loose Flex against T-Bar Ceiling grids and supports for long distances.
</OL>

Found these scenarios from either an excessive starting surge (LRA), or fault condition.
Securing Conduits on one, along with applying some "External Damping Techniques", greatly reduced the noise of Locked Rotor situation - but did not eliminate it 100%

Wish I had conclusive examples and advise, but your condition may be like the ones covered above... who knows!

Scott35
Posted By: e57 Re: Triplexed feeders (re-post) - 04/04/05 01:01 AM
Hey Scott, I did not mean to bag on the Therory area... Lots of nice things happen down there at the bottom of the page. [Linked Image]

Anyway, this is all exposed in open cieling office space, and seeing that the sound can be heard 2 floors above, I doubt closing it would help. It's fairly well supported, and I hit most of the fittings with an impact wrench already.
Posted By: shortcircuit Re: Triplexed feeders (re-post) - 04/04/05 01:46 AM
e57...although a most difficult installation, has MC cable been considered as a replacement for the conduit?

shortcircuit
Posted By: e57 Re: Triplexed feeders (re-post) - 04/04/05 07:36 AM
shortcircuit
THAT is a darn good idea!

Not sure if I can use it, but a darn good idea. You'd have to strap it down almost the whole length, as it will move on start-up.... Hmmmm...
Posted By: earlydean Re: Triplexed feeders (re-post) - 04/04/05 01:04 PM
I'm confused. What would force the MC cable to move upon start-up? The forces would try to push the conductors apart, not whip the cable about.
Posted By: shortcircuit Re: Triplexed feeders (re-post) - 04/06/05 12:46 AM
e57...you will let us know what you will do to fix the rattle and hum of that pesky feeder to that mamouth electron devouring elevator motor,won't you?

shortcircuit
Posted By: e57 Re: Triplexed feeders (re-post) - 04/06/05 01:14 AM
I was due to replace it with 350mcm (Not my choice...) in the existing conduit, but all hell broke loose when I told them I had to shut down the house side of the main, that contains 2 other elevators, 4 house lighting, and some massive air handlers on the roof. Other-wise, I'd have to get inside the 1600A busses to pull it in. That and one tenant will have to vacate for 2 days during the pull. (1 day out, the next in. If it comes out at all!) So right now its on hold.


But I am there tomorrow to trouble shoot poss harmonic +/or neutral problem in one of the tenant areas that I didn't do...... Go figure! So might get some PQM then.... Apparently the lower floor has turned into a discotech. Lights and computers flickering on occasion. Maybe this service call will lead me into the main. I'm dying to open it up.

Maybe I'll take the camera, I have some pipe work you guys and gals might find interesting.
Posted By: DougW Re: Triplexed feeders (re-post) - 04/06/05 04:16 AM
Hey e57...

you been letting Randy (lostAZhell) sub for you or something?

This sounds like the type of deals he usually gets! [Linked Image]

[This message has been edited by DougW (edited 04-06-2005).]
Posted By: e57 Re: Triplexed feeders (re-post) - 04/07/05 02:13 AM
Nah, Randy's jobs are safe from me. Most of my Service work days are done, all I get are wanantees, and occasionally, like this "pick-up" work from buildings that I do TI's in. This is actually one I would like to "put-down".

I went there today, and they had lights going on and off at wierd time, and flashing. (No power went off, like they had described.) So I'm taking a look.... Asking what happened. "So they flashed, and then they went off, then you turned them back on, and they went out again? This started on Monday? Every 2 hours huh?" I went and looked at the timer panels, and it seems they all Y2K'ed it on Sunday night. Erased all of the programming, and the time changed to, I assume some wierd hour, as when I got there it was 87:39! Yep, thats eighty-seven-thiry-nine! All of the off sweeps were gone and relays set to default factory programming. So anyway, I did alot of programming, but no trouble-shooting. I still have other pick-up work and things added to my TI's, so I will be back....

While ther I got some pic's of some of my conduit work, that some of you gent's might like to see.
http://www.markhellerelectric.com/bar/bar.htm
Posted By: mxslick Re: Triplexed feeders (re-post) - 04/07/05 06:49 AM
e57:

You sir, are an artise and craftsman of the highest calibre!! That is without a doubt the finest examples of conduit work I've ever seen!!

Bravo!!!

Tony
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