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Thanks again guys! I will keep you updated. Meanwhile, I'll go over and review my engineering books to refresh myself about all those phase sequence components. Good luck to you on your work and have a nice day!

jraef and albursara, Thanks for sharing your thoughts. You're right about the soft starters as a now more viable option for starting the motor. By the way, York (one of our chiller brands) implements current imbalance protection on their more expensive units (meaning with factory installed...

Hi fellows, Just some follow-up developments on my monitoring of the chiller compressor motors. I thought also that perhaps the startup current were too high and caused voltage sags making the imbalance current worse. But this isn't exactly the case. 1. Both motors are connected to the same...

Hello mc5w, thanks for the info. I'll keep those in mind should I come up with similar problems. best regards!

hello rraghunath, thanks for your post. I talked to the chiller operators and they do not approve of this experiment. No matter. I have already started monitoring the site and as of this writing, the initial data I got showed current unbalance of 7% with utility voltage unbalance of about 0.6%...

Hello Marke, Thanks for the post. Your suggestions make sense. My only problem now is how to convince the chiller operator. They can easily desensitize the current imbalance relay by increasing its tolerance or increasing the trip time delay. My previous monitoring of this motor showed that at...

thanks jraef. that made me think. I already suggested to the chiller service people to either increase the trip delay or increase the imbalance threshold to 25% (instead of 15% provided that none of the phase currents exceed the full load current.) It is also my belief that current imbalance is...

thanks mc5w! Just a follow up question: could a three-phase contactor (3 poles) be used for single-phase application, given that the single-phase load does not exceed the current carrying capacity of the contactor? I ask because one of the arguments proposed by the chiller technicians is that...

Hi guys, My questions are: How do I know if the contactors used in the motor starter is properly matched to the load? Could an under-rated contactor aggravate the situation of voltage imbalance at the contactor terminals thereby causing yet higher current imbalance to the motor? Let me...

Hi Fellows, Thanks very much for letting me pick your brains. I am now better informed to support my recommendation to the customer. I believe the prudent suggestion would be to have them replace the contactors (next time it failed) with one of higher rating. This is justified owing to the...

So sorry about that invalid link above. Please try this other link again: http://rapidshare.de/files/1344746/contractorProblem.zip.html This is a free web hosting site so you might have to wait 30 seconds before the file is available for download. It contains images of the failed contactor and...

Hi Guys, Thanks for all the information. The more I read about them the clearer the picture gets. Here's what I gathered so far: 1. The rectifier-inverter is IGBT (not SCR as I mentioned before) 2. Contactor rating at AC-3: 500V, 30kW 3. Motor rating (elevator hoist motor itself) loadside of...

Hi Jraef, skogsgurra, I am looking now at the diagram of the elevator controller. Its a vvvf system (I believe that would be variable voltage variable frequency.) I see that the contactor is located as mentioned before. I cannot post the diagram but here's as much as I can describe from line...

jaeref, thanks for the very quick reply. it's all useful! I played with the numbers and tried to see what Amps I would get for a 610V line and 32kW (32kVA assumed) load: the figures came from the "AC-3". The initial figures and the AC codes reveal some clues already. I will return to site...

I was called to try and figure out why a contactor in an elevator panel keeps burning out. This was the second time it happened. Although I suspect the contactor was under-rated I want to make sure. I got this on the partially burned nameplate of the sprecher+schuh brand contactor: AC-1... AC-3...