In-rush "rattle" on elevator in office building

[e57]

Hi all, new to your forums here. I'm an Electrician, not an Engineer, but have a possible engineering question.

I'm dealing with a customer (on a second opinion basis) that has a rather extreme "Rattle" of the conductors in an elevator feed. I noticed it when working on a TI in the building on the second floor! The elevator feed in the basement will rattle like a short on start-up, (really loud) to the point that it can be heard through-out the building. When I first heard it I went all over the building trying to locate it. Its a sound that says "trouble" when heard by an Electrician. After finding out that it was the elevator, I notified the Owner who says they have had nothing but trouble from this elevator. Replacing starters, occasionaly trips contactor, etc. And it turns out the Elevator Rep. and Electrician who installed the feed have been in several arguements about why this is happening. Elevator Rep suggested that the feed was not properly "tri-plexed" (Twisted on install) Ah... good point, but no-one does it, especially in runs this long. (140' through several turns) Then suggested that one could "Dampen" the noise by "Opening the conduit at the couplings, and fill it with expanding foam" This of course sent the Electrician into a rage. (Sent me into fits of laughter)

The Electrician who installed the feed, (250MCM) megged it out OK, and suggested that the 6 pole motor is mis-wired. Which I believe could be an issue, as it does have slightly differend amperage values pole to pole, but is wired OK.

I feel the differing pole to pole values may be due to damage to the motor, via Voltage Drop at Locked Rotor. However the LRA is slightly higher than Manufactures data, but not significant. Its a 200VAC 45HP 3phase 6 pole on a 208VAC system. VD on start-up is at 182. (which I see as borderline exessive, but possibly bad for extended life of the motor, which smells like its on its whay out) In rush amperage is hard to capture without proper PQM equipment, but varies from 650-700A, operating amperage levels out at 185A, 175A, 187A.

So now there are several suggestions for eleiminating this situation.

#1 Replacing feed with "Tri-plexed 4/0 feeder" Smaller than whats there... Or installing step up tranformer at begining, and step down at end of feed. (Via Elevator Rep)

#2 Replace 250MCM feed with 350MCM (Via Electrician who oringinally installed the feeder)

Then theres my opinion... Power Quality Monitoring before anything to get a clearer picture, and possibly replace motor with simular torque and speed but lower LRA via a 208/230 motor, but may take some shopping around to find a match.

So what do you guys think?

 

[jraef]

If the motor is truly rated (on the nameplate) for 200V operation, you are probably OK. The rattle is most likely caused by inrush current creating strong magnetic fields around the conductors that oppose one another, forcing the conductors apart inside the conduit. The forces at full speed are likely not strong enough to notice, but if you are starting across-the-line, 650 - 700A will definitely do it.

"Triplexing" or twisting the conductors would have only worked for a while. It is a trick used by some electricians to avoid call backs until any project hold-backs are paid. The forces would have eventually separated the conductors enough to make them rattle anyway.

The solution is to try to reduce those forces as much as possible by reducing the starting current. Several manufacturers now offer solid state soft starters specifically for the elevator industry. Siemens is one, Allen Bradley was going to do it, but I don't know if they did. Google "elevator soft start". You can't necessarilly use any soft starter because elevators have some specific testing and labeling requirements, and although they are not difficult to get, many manufacturers' product liability insurance prevents them from knowingly marketing to industries involved in people moving.

Your FLA numbers look a bit high for 45HP at 200V, in fact they even look high for a 50HP. What does your nameplate say?

"Venditori de oleum-vipera non vigere excordis populi"

 

[sreid]

Conduit rattles that screams trouble.

Replacing motor starters.

Contactor sometimes trips.

Motor smells like its "On its way out."

180 A per phase running.

This sounds like an overloaded motor to me. Could there be mechanical binding in the elevator mechanicals?

 

[BJC]

Where's the motor? Is this a traction elevator or a hydraulic?
The feed should be tri-plexed -I can't imagine why it wasn't. The voltage drop is to great. Do the lights dim when it starts? How "stiff" is the main switchboard?
How long is the run? How much of it is vertical? Did the installing electrican install supports?

 

[mpparent]

What's the voltage at the motor?

Mike

 

[e57]

OK my bad..... I took the motor info from what I was told! I went down there myself to get the motor plate info for manufacturer data comparision, and its a 75HP, I orininaly had data from a different motor that someone handed me! ("Should be about the same right?" - NO! Especially at wrong HP!) Couldn't get the spec on-line, but have a call out to Baldor, just to check as now it seems motor may be well within spec at 75HP.

Hydralic elevator, pump in basement
98% of run is horizontal 140'250MCM (marginal IMO for this in-rush) well supported
From a 2000A main (Rock solid)
Most lighting is Flour' but did notice "slight" dimming on the job site lighting
Voltage is 208 Drops 13% (182V) on in-rush
Now let me say this "Rattle" is un-godly! Frighteningly loud!

As for the Tri-plexing, I'll tell you why it is almost always never done. It can not be done in field for a run this size or length, and even with special order factory Tri-plexed run is impossible to install through other than straight conduit. Sweep 90 maybe (1 or 2 tops), but definatley no LB's or cans.

Anyway, it looks like its time for a new feed, I'm thinking busswork....

 

[BJC]

e57
Now go check out the rest of what you were "told".
What kind of starter is on the elevator? If it's not a reduced voltage of some kind, it should have been. It sounds like some kind of soft start that's not working (it's running on by-pass).
Sounds like a cheap spec built office building. There good for engineering because we get to go in and fix them up after the builder puts in the cheapest crap they can get away with.
As for tri-plexed cables, I can show you miles of it. It's done in lots of places ( industrial, power, petrochem and office and commercial other than cheap spec built stuff). Call you cable supplier and tell them you want it triplexed. If your buing cable from Home Depot it's hard to get.
Most cabe ( wire ) won't comply with minimum bending radius requirements if it's installed in "normal" sized conduit. Normal being what chapter 9 of the NEC says. Wire that will fit in a 2" GRS conduit won't work thought a lot of 2" LBs, LRs, LLs Etc. Sometimes you gotta plan your pulls- remember the 6 Ps of good construction.

 

[e57]

Starter is "Soft start".... The fifth starter of its type in the last 18 months.

Let think before throwing insulting language around, like... "Home creapo"

The Engineer who spec'ed the build, did not spec tri-plexed, therefore not installed. But yeah, I too have seen lots of it, and if it is not spec'ed, no one in thier right mind will install it. (high mat. cost / availablity lead and install time trying to keep it straight) Due to the fact this is a 200 year old converted warehouse building one of the big S's is invloved. "Structure" So no real straight path is available from point to point. Talk of core saws make people wince from thoughts of liablity.

Anyway... Tri-plexed or not, its the worst rattle I have ever heard. And, heres some data on the motor, seems to be operating at "near" rated values.

Nameplate Data General Characteristics at 200 V, 60 Hz:

Rated Output (HP) 75
Full Load Torque 223 LB-FT
Volts 200
Start Configuration DOL
Full Load Amps 206
Break Down Torque 639 LB-FT
R.P.M. 1770
Pull-Up Torque 360 LB-FT
Hz 60 Phase 3
Locked-rotor Torque 414 LB-FT
NEMA Design Code B KVA Code G
Starting Current 1360 Amps
Service Factor 1
No-load Current 71.4 Amps
NEMA Nom. Eff. 94.1 P.F. 86 Line-line Res.
@ 25°C. 0.14 Ohms
Rating - Duty 55C AMB-S4-50% Temp. Rise
@ Rated Load 46°C
S.F. Amps Temp. Rise
@ S.F. Load


Load Characteristics at 200 Volts, 60 Hz
% of Rated Load 25 50 75 100 125 150 S.F.
Power Factor 49 72 81 84 87 88
Efficiency 91.1 93.9 94.3 94.1 93.6 92.8
Speed 1794 1787 1780 1772 1765 1755
Line Amperes 91 121 159 206 247 296

 

[BJC]

Change out the cable, can't hurt. It's only money. I would do a hand over hand on the whole system first, look for loose joints and loose hangers.
Who made the soft start? IF you have had 5 in 18 months there is something wrong. They should last for years.
If you can borrow something to record the waveform it may tell you something.
Does the hydraulic system have an accumulator and is functional ( is the valve open and a gas blanket on top of it)?
If the motor is pushing the elevator to hard it going to be pulling high starting currents to long.
I am not just throwing around insults. I worked and engineered a fair amount of these. In the last 20 years I have seen more and more crap go into buildings. It use to be people built there own buidling, how it speculators who plan on keeping them a couple of years at best. An engineer can go through the "canned" CSI specs click all the right boxes and still come up with a POS job. Who gets to fix them?

 

[e57]

If I change out the cable it is definately money IN pocket, not out.... Which is why I am reluctant to do so, if it is not the cable. I have been trying to get the owners to do some PQM for this, and have passed on to our company owner not to bid to replace otherwise. (I would hate to go do another feed, and then find out there is a bad motor, or the starter is a harmonic generator.) Unfortunately there are too many opinions, and no real solid answers yet. What I want is a real picture of what is happening, and think PQM is the next step. The owners of the building are good family people, and thought they were getting the best when this elevator was installed. So far they have gotten the shaft, so to speak, and a headache for an elevator.

 

[mc5w]

You definitely DO NOT want 2 transformers back to back. A typical dry transformer has a 5.4% impedance times 2 equals 10.8% at full load. You would be better off putting in a second conduit in parallel with same size conductors. One problem is keeping the wire length the same as you go around bends. Also, if not all of the wire strands are not conducting because someone was too lazy to use silicon carbide paper, elbow grease, then electrical grease as recommended by the Consumer Product Safety Commission, you will only have 1/2 the wire strands conducting. Thanks to catalytic converters copper wire fails just as fast as aluminum. See my website

http://home

dot earthlink dot net/~mc5w for more details on how to make a real electrical connection.

Your voltage drop on starting is excessive. Your rattling could also be due to the conduction angle of a soft starter particularly if the hydraulic valve cuts in too soon.

I have found that it actually PAYS to use oversize conduit, particularly if I cannot hook up a wire pulling winch or forklift truck. 2.5 inch schedule 80 conduit for three 4/0 conductors is a heck of a lot easier to pull than 1.5 inch conduit. In chapter 9 of National Electrical Code there is fine print note #2 about jamming in bends with the minimu size conduit. If you look in manufacturer's data for LBs and so forth there is a maximum wire size based on wire bending space. A 1.5 inch LB is NOT listed for 4/0 wire because of the wire bending space issue.

If your motor is smelling you probably need to upgrade to a larger motor. I encountered an alledgedly 3 HP pump that needed a 5 HP motor to turn it. Somebody thought they could drop a decimal point. See "pump runout" and "motor runout" in this forum for more details.

 

[N1755L]

I'm not an engineer either, but for those of you who are, doesn't it sound here like the normal operating load is too close to the full load current of this motor? What is the normal acceptable or "code book" percentage supposed to be? I would have thought that a motor should be loaded at no more than 25-50% of it's full load rating for normal operation?

Perhaps you should rule out the possiblility of overload, why this motor is working so hard? Is the motor too small for this hydraulic pump?

If the motor is strong enough for the hydraulic pump, then again, why is it working so hard? You would then have to look at the hydraulic system or, as sreid suggests, is the elevator not moving properly within the shaft?

In any case, if you did need to put in a larger motor which didn't have as large a starting current-surge, considering how much rattle you're getting, sounds like you still would have some rattle and would further need to do something about the feed, so sounds like perhaps more than one repair type.

Seems to me this motor is under too much load, no matter... something wrong this way, unless I'm mistaken about the load being too great for normal operation of this elevator. Someone will correct me if I am.

 

[jraef]

e57,
I still think the rattle is from high starting current, I have witness this many times and would also describe it as horrendous and scary.

Now as to why you are getting high currents even with a soft starter, I think, as others have mentioned, that you need to look at several possibilities.

1)"Starter is "Soft start".... The fifth starter of its type in the last 18 months." BIG RED FLAG HERE! Average life of a soft starter should be 25 years! Several possibilities here. It may not be hooked up incorrectly (i.e. "inside delta" when it was not designed for it, or straight delta when it was designed for inside). It may be getting wet and misfiring, placing a high DC component on the output. that happens a lot if the elevator shaft is vented to outside air and it is cold outside, because the starter heats up with use, then cools off and condensation forms on the PC boards. It does not need to be really cold, the dew point is only 40 deg. F It may have a welded bypass contactor as BJC mentioned earlier. It may just be incorretly set up and starting with too much current. Post some info on it if you have it.

2) There is a hydraulic problem. If the recirc system is stuck or pulsating somehow, you could be getting the motor attempting to start into a closed valve, which in a PD pump is a locked rotor. Soft start or not, at some point you will get big current surges and/or pulsations. You mentioned replacing several things but not the hydraulics. Repeated locked rotor starts would eventually damage any soft starter.

"Venditori de oleum-vipera non vigere excordis populi"

 

[MikeHalloran]

I know nothing about elevators, and a little about hydraulics.

It sounds like this motor is starting against a full hydraulic load, which seems like an odd idea to me. I'd expect to see some kind of hydraulic unloader circuit that allows the motor to get up to speed before it has to come up with any serious torque.

The other thing that Hiking got me thinking about is, is this elevator designed to have a counterbalance? Is it installed?



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA