liquid cooled starter

[cvirgil]

we received a submittal on a liquid cooled starter for a chiller. Can anyone share thier experiences with these types of starters. I've never used one and am looking for some pros and cons.

 

[jraef]

Very complex, very dangerous. How big is this chiller anyway?

I have some other questions for you though.

Is it really liquid cooled, or is it a liquid resistance starter on a wound rotor slip ring motor?

If not a wound rotor, is it really just a starter or is it a drive, such as an LCI drive (its common to call those "soft starters" in some extreme applications)?

I can't imagine why a starter would need liquid cooling. I have built 1600A soft starters with air cooling, my company has built up to 3000A without needing to go to liquid.

Sometimes on extremely big motors where the power system is weak, they will use drives to get the motor up to speed, such as the LCI drive mentioned above. Then they run at full speed after that just like a soft starter would. If that is the case, liquid cooling may be necessary if the drive is in the circuit all the time, again depending on the size. A better alternative however would be a synchronous transfer to an across-the-line contactor once it is at full speed. Siemens / Robicon does this all the time.



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[cvirgil]

The starter has SCRs which are cooled by pump driven water circulating in a closed loop through the SCR heat sinks and heat exchanger.

It's an 600 ton chiller at 480v.

 

[jraef]

Electrical engineers typically don't know from "tons", but I can assume it is probably a 600HP motor. Liquid cooled is SERIOUS overkill for a solid state starter of that size. Not worth the risk of catastrophy or even the additional complexity IMHO. I'm not a big fan of liquids and fluids in the saame environment. Electrical accidents can do a lot of damage, and if fluids are in the same cabinet, that damage can be seriously componded.

If the starter is being supplied as an integral part of the chiller package, it is probably liquid cooled because the chiller mfgr is trying to squeeze the starter into a really small box that looks good on their chiller, which leaves no room for a bypass contactor. Since they are pumping cold fluid anyway, they just pipe the coolant in through the heat sinks. The design philosophy on this is that if the coolant leaks, it must be shut down anyway since it is common fluid with the chiller system. The downside is that when it happens, you lose everything, not just the starter. I personally wounld't do it, but you may find that if it is integral, you may have no choice with that chiller mfgr.

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[EEJaime]

I think someone needs to get you additional information. A 600 ton chiller is much too small to incorporate something this complex. A standard soft start VFD is all we use on something of this size. The only time I have seen any liquid involved in the start circuit is for massive, 5000+ ton systems where cooling water is circulated through the hollow busbars of a variable frequency drive. It is overkill and overly expensive to try to use anything like that on a common 600 ton chiller. We recently put two Trane CVHF-770, 700 ton chillers at a new central plant for a hospital. These draw just over 500 Amps at full load at 480V/3ph. We used a packaged, unit mounted, VFD to track output with the load and provide a soft start to the systems. Pretty standard stuff, (but do watch the harmonics as they are horrendous from these VFD's). In any case good luck with your project, but I would certainly discuss this with the Mechanical doing the chilled water design to confirm this.

 

[LionelHutz]

I agree with the others, that seems to be overkill and I can't see how it could be cheaper or why someone would even propose it to you. I doupt you'll even save much if any space with that solution compared to a soft-starter with a built-in bypass. A standard soft-starter with a built-in bypass would be your best compromise for small size, low heat production, simplicity and price.