Contactor selection criteria for reactor startor induction motor

[jimmy2times]

I would like some assistance with selection of appropriate contactors (start and run) for a 440V, 83kW, 60Hz induction motor.

Unfortunately the details of the reactor are unavailable so not sure what the starting current would be limit to. The existing contactor details also unavailable other than old school arc chute type contactors.

I was looking to replace both (start and run) with modern day sealed contactors.

Would I be safe in selecting both contactors for the DOL duty, i.e. would the START contactor have sufficient short time withstand capability

 

[Skogsgurra]

Yes, I would say so.

The reactor reduces current - but makes starting time longer. So the instantaneous heat is less (current squared) but the heating time is longer. I think that those two effects compensate each other rather nicely. Not perfectly, but well enough that you shouldn't have a problem.

If this is critical equipment, it could be worth while recording the starting currents using a current clamp and an oscilloscope/recorder.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[ScottyUK]

Why do you want to change them?

Block contactors have the advantage of being smaller and cheaper than the old fashioned bar & shaft type. The old style hold most of the other advantages - reliability, overload capability, ability to operate with severe breaking conditions, maintainability. If you have space, bar & shaft types are still available from ABB, Siemens, possibly Telemecanique (certainly used to make them), Hubbell, and others.

 

[jimmy2times]

The existing are installed in the worse excuse for a switchboard that ive come across. Directly above (80mm) them is a circuit breaker for a different circuit. The operators report that significant arcing is witnessed out of top of contactor arc chutes during starting of motor. I dont know if that is normal as ive never used these type of contactors before, i.e. Is there a specific clearance that must be observed?

Anyway this has lead to heat damage on cable and terminal of one phase of the circuit breaker above.

Ive requested that they check the timer sequence of start and run contactor change over in case issues there or if there is issues in the changeover of contacts.

The whole switchboard/MCC has been condemned for various reasons, obsolescence, safety, suspected high compartment air temperatures (in ship), cable degradation. The plan is to replace next year with a simple feeder section and then take the motor controlgear out and place in local starters next to plant. Then derate switchgear if there is a local high temp issue, (currently investigating this thermography, thermal stickers etc).

In interim period they have to keep the existing ticking over.

Pending above i was considering other options until i get to see for myself when ship next in port.

 

[waross]

The arcing may be a timing issue. Possibly a bad operating sequence. Reactor start is generally closed transition. I would not expect arcing on starting unless there is an open transition from the reactor contactor to the run contactor. Arcs are generally observed when the contactor opens under load. The de-ion plates may need cleaning.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

All contactors arc. The issue is likely just that on those old bar and shaft contactors, you can SEE the arc!

But from a safety standpoint if they want to be able to upgrade the equipment and separate the circuits (so that they don't have to open the doors and WITNESS the arcs), then it might be a good idea to replace those contactors.

So yes, you can definitely use DOL rated contactors to build a Reduce Voltage Primary Reactor starter. The reactors will typically have two taps, one at 50% voltage, the other at 65%. At the 65% voltage tap, the starting current is reduced to 42% of normal (.65²). Yes, it can take longer to start, but that consideration should be built-in to a standard contactor design. The total amount of energy it takes to start a motor from a dead stop to full speed is a fixed amount and can be represented as a curve between axises of power and time. All you do with Reduced Voltage starting is to change the shape of the curve, not the area of the curve. The Run contactor carries all of the motor current once it is started so it must be DOL rated. Although the Start contactor can be technically applied at 50% of the motor FLA, most people do not do that, it's common practice to use identical contactors. At 83kW, the difference in cost between the contactors would make it pointless anyway in my opinion.

"Will work for (the memory of) salami"

 

[waross]

I know that all contactors arc. The point is, they arc much more when the circuit is opened than when the circuit is closed. The di-ion plates in the arc chutes cool the arc. If they become dirty, the cooling effect is less and the arcs may extend further out of the chutes.
The starting contactor in a reactor starter should be bridged by the run contactor and should not open under load, hence there should be no arcing when starting.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

Bill,
My apologies, I failed to notice that he said "when starting" with regard to arcing. You are right.

jimmy2times,
"Ive requested that they check the timer sequence of start and run contactor change over in case issues there or if there is issues in the changeover of contacts."
There should be no "changeover" on a Reactor Starter; the Start contactor pulls in and power goes through the reactor, then the Run contactor just closes around it, shorting out the reactor. The Start contactor usually stays closed and they both open together on Stop. There should be no arcing during the start sequence. Either that, or you don't have a Reactor starter, you have an old style Open transition Autotransformer Starter, meaning it is NOT a "Korndorfer" Autotransformer starter. If there are three contactors, it is a Korndorfer Autotransformer starter. If there are only two contactors, then it could be a Reactor or Open Transition Autotransformer starter.

The inductor devices will look very similar, but there are subtle differences. If it has just 3 tabs on each winding, and your contactor leads are connected to two sets only, it's a Reactor.

If it has multiple taps and shorting links on one end of the windings, it's an Autotransformer and that explains the arcing.

You might want to consider getting rid of that altogether, it is very bad for not only the motor, but the entire power supply of your ship!

"Will work for (the memory of) salami"

 

[jimmy2times]

Yes it is reactor start not an AT starter. I probably added confusion by using the phrase changeover.

The circuit is arranged so START contactor and REACTOR are in parallel with the RUN contactor. The control circuit should close the RUN after set time delay. Then the START contactor should drop out. Hence why I used the phrase changeover.

I just heard from operators and contactor arcing does only occur at the "changeover".

 

[waross]

If it's arcing during the changeover, the reactor contactor is probably opening too soon. It may have been changed by someone familiar with auto-transformer starters and not familiar with reactor starters. If the start contactor is opening during starting, then as jraef says, it is not good for the motor, or the ship's supply system. When the run contactor closes after an open transition, it may produce transient currents that have the potential to damage the motor, including broken shafts.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Marke]

Sounds like an open transition, open the start contactor before close run which is really bad for the contactors and the motor as well as the driven load.

By all means, replace the contactors and as Gunnar and Jeff have advised,use DOL rated contactors, but check the control wiring and ensure that if the start cntactor is opened, it only opens after the run contactor is closed. There should be zero arcing at changeover!!

Best regards,'
Mark.

Mark Empson
Advanced Motor Control Ltd