LV air circuit breaker in motor service

[oldfieldguy]

Here's another problem I'm looking at. We have several 200 HP submersible cryogenic pumps that we feed with 480 v 3-phase from a 1980's vintage GE low voltage switchgear. We are using GE AKR low-voltage circuit breakers with Multilin 239 motor protection relays.

My problem is that these breakers have been being used in motor starter service over the last twenty-odd years. They are beating themselves apart with the starting and stopping which translates to a lot more operations than a circuit breaker would normally see.

A few years ago at an electrical trade show in Houston, I remember seeing a vendor who retro-fitted a circuit breaker frame with a large-size NEMA motor contactor as a solution to this problem.

Two questions: Does anyone know who the vendor is/was? Does anyone have any other solutions to the problem other than rebuilding these poor old breakers or doing a costly upgrade to eliminate the breakers and install a line-up of Size 6 or 7 NEMA contactors?

old field guy

 

[dpc]

How often are the motors cycling? There's nothing inherently wrong with using LVPCBs for motor starting as long as they are not operating 10 times a day.

I used to work for a large consulting firm that did this as a standard practice for any motor over 100 hp. But we were designing large power plants where the motors might have 10-20 starts a year.

It's probably less expensive to rebuild the breakers than to retrofit Size 5 starters.

 

[Laplacian]

We have a lot of GE AKR circuit breakers that have been retrofitted with a vacuum contactor. Westinghouse did the original retrofit in the early to mid 1990's. Cutler Hammer (Eaton) offers a newer kit today. Order of magnitude cost for a unit is $30K USD.

If you are in the US, I can put you in contact with a vendor.

 

[oldfieldguy]

dpc--

They start anywhere form several times a day to a few starts per week. We blow that "10-20 starts a year" out the door.

Yes, I know I can do a lot of rebuilding of existing breakers for the cost of ripping them out and putting in a dozen new NEMA Size 6 or 7's. I'm looking for something that makes sense here.

My problem with rebuilding is that even the "manufacturer" rebuild is of questionable value. Up to this point, we've been pulling breakers out for repair, and the contractor who does the repair basically fixes what is wrong, and maybe, just maybe he sees something that's close to failure, and fixes that, too. Then the breaker goes back into service and stays until another component gives up the ghost.

Repairs are pricey. Rebuild to "like new" is even more so. And due to the frequency of operation, I just don't think that these circuit breakers are the best option for the application, but they're what I have now.

I was intrigued by the starter retrofitted into the breaker frame.

old field guy

 

[Laplacian]

I meant $18K per unit. The $30K was for two units quoted recently.

 

[dpc]

I'm just thinking if the old breakers lasted twenty years, that isn't too bad. I'm not sure the new starters would last any longer, the way things are built these days.

Re-built breakers should be readily available. I wouldn't think this option could be more expensive than new starters, but I'm not burdened by a lot of actual knowledge so it's easy to assume things.

I guess the new vacuum contactors are getting smaller, but I'm surprised that they can fit a Size 6 or 7 starter in the space occupied by a LVPCB - that a new one - I'll have to check into it for future reference.

Good luck.

 

[Laplacian]

They do that and install current limiting fuses to maintain fault current interrupting rating all in the same breaker frame. I don't know if the mech is replaced or not. A local Siemens shop did this for our site starting in the early 90's. ECP Tech Services is on vendor for the Cutler Hammer retrofits.

http://www.ecptech.com/

 

[oldfieldguy]

Laplacian--

Funny you should mention those folks. I worked for them once upon a time. I just talked with them about options.

Me, I'm not a big fan of using these circuit breakers for motor control, but I didn't build the place, so I have to live with it as it is.

On the same subject, I had a client who used a 15 kV PowerVAc breaker to control a 7000 HP motor that was started two or three times a day. Every quarter we'd check the contact wear, and if it approached limits, we'd swap that breaker out with one that served as a transformer feeder that saw one operation every three years. In that service, contact wear wasn't an issue. We did that move twice in the eight years I worked on the gear.

Fortunately, he had a lot of transformer feeder breakers and only a couple of those pumps.

old field guy

 

[jraef]

Why would someone use an ACB as a motor starter on something as small as 200HP? Talk about overkill... But then again if you are going to use a Multilin anyway and you already have an edict to use switchgear style breakers in that size range, I suppose another contactor downstream probably seemed redundant to the original designer.

Siemens makes a small LV vacuum contactor for a 200HP 460V motor that would likely fit into that AKR frame. Look for the 3RT12 series. The max. dimmensions are 210mm (8.27") H x 175mm (6.9") W x 206mm (8.1")deep. Joslyn Clark also makes a compact 480V vacuum contactor that may fit as well, I think it's called the MVC series.

The bigger problem you are going to have with this is that the AKR was providing the short circuit protection, but no contactor is going to have a short circuit fault interrupt rating because they are not considered an interrupting device. They will have a withstand rating, based on an upstream protective device since that is the intended use, but withstand is not the same as interrupting. You will also have to modify the trip system from the breaker to open the contactor now and that will not be a UL listed system no matter who does it so there may be insurance consequences etc.

If I were you I would leave the AKR in place as a breaker only, then put a contactor on the wall downstream and have the Multilin open the contactor on a fault, not the AKR.

 

[swn1]

The older AKR breakers hold up to rebuilds well. There are a lot of them in the junk yards so you'll be able to keep it going for years.

For 480V service there is room for both a vacuum contactor and a set of fuses on the frame, but you have to modify the platform some.

You can have the shop that builds it for you include a latching relay to mimic the close/trip operation if you don't want to modify the control circuits.

You can also build the motor protection relay onto the frame in place of the original trip unit. If you also include a control power transformer it becomes a completely self-contained motor starter on a breaker frame.

One of the saddest things we're seeing is people who have bought vacuum breakers to replace old solenoid-operated air-magnetic breakers as medium voltage motor starters. The contacts may last forever but the stamped sheet metal mechanisms wear out in a couple of years.

 

[dpc]

Jeff,

Use of LVPCB for motor control used be quite common in the days of air break motor contactors. Above NEMA Size 4, contactors were huge, had problems with coil burnout, etc.

It all depends on the number of starts expected. We used them in large power plants for anything over 100 hp. But these motors typically averaged maybe 1 or 2 starts per day (once commissioning was done).