Wye-Delta skelter

[ga1279]

I am not an electrical engineer and I don't play one on TV. I am working on a Trane CVHA-025, with a wye-delta closed transition starter. The motor design is 208 volts, 392 RLA, 3860 LRAD, 1265 LRAY, OLTA is 425. The Allen-Bradley time inverse overload is calibrated to trip at 247amps and to hold 1278 amps for 41 seconds at start up. The overload point of 247 amps is not the question, the high amperage, which is more then the lock rotor wye is what I am concerned about. I know under certain starting conditions it may take a motor a while to come up to speed, but allowing it to draw more then lock rotor for 41 seconds sounds a bit extreme. Also the Cutler- Hammer contacts are cooked, but not just the contact area the copper bridge is discolored from heat as are the copper bases of the 2 mounted contacts. This is on the three major contactors, all contacts.The contactors are rated at 250 amps @ 480 volts (1M and 2M) and 200 amps @480 volts (shorting). The chiller starts okay but the shorting contactor sounds like there is arcing going on as the motor starts and begins to come up to speed (last about 10 seconds) I am thinking the contacts are undersized for the load. The 1M and 2M are Cutler-Hammer C32LN-3, and the shorting is C/H C32KN-3 and both are series A-1. The motor itself checks out okay any of the 6 t-legs to ground show 475 meg ohms to ground and 1 gig ohm between the 3 windings. I believe the chiller came with this equipment from Trane back in 1982 when the chillers were installed.

[Randy S.]

Theoretically the "main" and "delta" contactors each only carry 67% of the rated full load when running.

The "star" and "main" would be the ones taking the most beating on start up.

Is there a big voltage drop at start up?

[Tranetek]

Sound like you are hearing alot of noise from the shorting contactor is that right? If so pull the front off the contactor and see if the ring has come out of the magnetic frame. If it has this causes the magnetic field pulling in the contactor to get screwed up and causes the contactor to make a loud buzzing noise.

[ga1279]

Randys, a minimal voltage drop of 2 volts and the motor doesn't hesitate it does come right up to speed in wye configuration. When I look at the size of the contacts 1M & 2M are 1/2" in diameter and the shorting is about 1/2" square and the amount of current that has to pass thru them and the copper support for the stationary and bridge of the movable 1270 amps seems way too much to pass thru unimpeded. I have another account that has 5, 208 volt Tranes CVHE's and they have contacts as big as your fist. They are 500 Tons each and each contactor has it's own enclosure. They are about the size of a old phone booth. The ironic thing is these machines are very slow starters and the LRA on those machines isn't much greater for a machine 2 and 1/2 times the machines I'm talking about(200) ton CVHA's. Tranetek, all the shorting rings are epoxied to the armatures. Thanks-GEO

[MKnyc]

Those meg readings don't sound so hot to me. When was the last time the bearings been changed?

[Randy S.]

How about the shading coils on the iron core of the contactor?

The copper loop thingy.

[MKnyc]

Definitely agree Randy, dis-colored copper is never good. Always clip back my motor connections. Good pick-up.

[chiller rob]

208 can always be a pain...
especially when your inverted...
i would be looking at a soft starter install if you are thinking about rebuilding any of these contactors...
some care needs to be given on how to wire it into your chiller control...
pay particular attention to your signal resitor circuit...
being around a 208 starter and that kind of current in wye is always interesting...

Stay safe...!

[acjourneyman]

PICTURE?

[ga1279]

To all, Meg readings of 475,000,000-ohms to ground is pretty good as is 1,000,000,000 ohms between the windings (T1-T2,T1-T3 and T2-T3) As I said in my previous thread (part deux) all the shorting rings are tight and have been epoxied to the armature laminations from Cutler-Hammer. The wire termination to the contactors, from the contactors and overloads are not burnt or discolored in any way. The only part that is burnt are the actual contacts themselves. All three of the contacts on all three of the main contactors. The shorting (S), 1M and 2M. This leads me to believe that the contactors are too small for this application. Randy, I can type up a storm but I'm not the computer literate to put a picture here, wish I could. Thanks again-GEO

[Randy S.]

Possibly, it has something to do with the size of the transformer feeding the building.

As others have said, the 208 current draw when starting is tremendous, and it just may be to do with the sizing of the starter contactors.

[drivewizard]

It is probably safe to assume that these are not the original contacts in contactors due to the age of chiller.
Have they been replaced recently, when did this problem begin?
Have you been the only one working on it, doing repairs?
If they are not the original, or OEM replacement contacts they may be some aftermarket knock offs that have slightly different dimensions.
This can cause less than adequate pressure between contact surfaces resulting in arcing.
Someone may have elected to get "cheaper" contacts, or the originals were no longer available.
Be carefull, you could be playing with an Arc Flash incident waiting to happen.

[ga1279]

Randy, that is my thought too! But why is the 2M also burnt ? I think I'm going to try and contact Cutler-Hammer with the part #'s and see what they think. If you look at the large wire size involved compared to how small the contact area is. I would have thought I would get a lot more voltage drop at start-up and a slower acceleration time, but thats not the case at all. The contactors do say they can carry 1400 amps locked rotor, but that's at 480 volts. Anyway I appreciate your advice. Thanks-GEO.