Auto Transformer Starting System for Induction Motor

Has it worked fine for a while and just began nuisance tripping, or is this a new installation and this is happening from the outset?

If this is old and was worked nag fine before, has anything changed? Even if you think it shouldn't have made a difference, report back on ANY change, mechanical, electrical, timer changes, wet conductors, anything.

If this is new, what type of autotransformer starter configuration is it? Open transition or Closed transition (Korndorfer method)?

This is old one, after dry dock it is not working, before dry dock it was working. During dry dock nothing done on this thruster. We decoupled motor from thruster, but same breaker tripping.

Is the amp draw within spec? Have you checked the battery voltage before and during operation? (I think there is a 10% drop max limit)....Did you try cleaning the brush contact surfaces?

http://www.boatered.com/forum/topic.asp?TOPIC_ID=138016

How do you use a autotransformer on a DC system?

https://www.deepdyve.com/lp/institute-of-electrical-and-electronics-engineers/multiport-dc-dc-autotransformer-for-interconnecting-multiple-high-lrMoJgYlld

The first thing you're going to check is to see if the breaker is functioning properly....that means you need to check the amp draw to see if the breaker is weak or it's operating properly...Since there is no information on this, either this guy has no idea what he's doing, or he's just screwing with us....We have no idea what the size of this thruster is, so I'm not sure he even knows what an autotransformer is....

Clearly I don't know what he has, maybe you could explain it to me......please go into as much detail as possible....

Thrusters are auxiliary propellers in the bow and stern of large seagoing vessels that are intended to provide axial thrust, i.e. at right angles to the keel, used to assist in making tighter turns and in docking. Small boats will often use PMDC motors, but on big vessels that have on-board AC power generation systems, they will use large induction motors for these, anywhere from 150-1000HP depending on the size of the vessel, because of the lack of needed maintenance on commutators and brushes.

Because these motors can be very large, it's commonplace for them to use reduced voltage starting because the power generation is limited. Modern systems now use VFDs or at least soft starters, but older vessels used RVAT starters.

From the OP (et seq.), all should know that this is an AC induction motor with an autotransformer starter. There is still an unsettled question of whether the starter is open-transition versus closed.

Many AT starters have 50/65/80% taps for selecting the reduced voltage. The choice of these taps, plus the choice of a time-delay setting, can minimize the "bump" current that occurs at switchover between reduced/full voltage.

If it was working fine and suddenly started tripping though, it's not in the settings of the starter. it has to be in the windings or conductors somewhere.

If you decoupled the motor from the thruster, then it can't be load related. You likely have a short circuit somewhere, I would start by looking at insulation of conductors, transformer and motor windings.

Does the breaker trip immediately on starting or does the motor attempt to start?

Is the starter an open transition or a closed transition (Korndorfer) autotransformer?

Their connection is like the above diagram; I have no idea about open transition and closed transition.

Open and closed transition most likely have to do with switch positions on your diagram as related to a start on the motor.

The far right switch should be closed during initial phase of start, whilst the same switch should open once start-up is complete. Note that left pair of switches/contactors is are ganged and thus are designed to be in closed position during start and in run.

Is there a trip signal controlled trip coil in the breaker? Perhaps a faulty trip signal circuit is the problem?

yes, main breaker trippin with I sd (short circuit)

Auto transformer starter will have contactor and timer to apply less voltage across motor initially then full voltage after motor picks up speed .

Please find out when the breaker trips, is it during initially or during change over from less voltage to full voltage.

If it trips during transition , check timing

The breaker will trip if full voltage applied at the wrong moment.

How about a unidentified foreign object [UFO] jamming the thing to which the motor is connected:

• A shredded rowing boat?
• An old, smelly, double bed mattress?
• A dead body?
• etc

I agree, maybe someone dropped a screwdriver or a bit, or a screw during dry dock.

I say it is on the dry dock crew. Go back in, and have it fixed, with a fine on the collected monies from the overhaul.

Was it inspected and found free to turn before it was placed back underwater?

Look for a lockout tag, somebody may have left a safety ground at the motor terminals. Then check the motor to see if it turns freely, if not uncouple it again and see if the thruster prop shaft turns freely. If all the mechanical checks are good then have a machinist check the bearings and realign the coupling.

When the cause has been discovered and corrected, please do let the forum know what it was.

the problem not solved yet, we are waiting vessel.

The forum waits with baited breath.

Ewwww. Fish bait - baited breath. That squid was past its expiration date....

Oh please, not squid breath, or shrimp breath! Too early in the morning for that here!

While we await the outcome, the "baited breath" and rotten squid comments reminded me of a related story. I once installed a 300HP soft starter for a refrigeration compressor on a fishing boat in Seattle and while on a white fish run in Alaska, the soft starter tripped on Short Circuit. The technician on the boat, a last minute replacement for the guy I had trained, had no clue how to troubleshoot it. I tried in vain to walk him through it on the radio, to no avail, he was thick headed and angry about the soft starter tripping. I made that comment about "waiting with baited breath" for them to get back so I could take a look at it, but as it turned out it wasn't funny. When they arrived, the entire 12 ton hold of fish had rotted. They took it out of the hold and dumped it at the garbage transfer station near downtown Seattle, it stunk up the entire City for a week, lingering long after they removed the actual fish. The City fined the vessel owners $100,000 for the mess.

I had to go onto the vessel and even after cleaning, it made me toss my cookies. Turned out there was nothing wrong with the soft starter, the compressor had seized and the soft starter was doing its job of protecting the motor as they continuously attempted to re-start it into a locked rotor. They had a backup compressor on board but only the one starter, yet because the guy assumed it was a problem with the soft starter, he didn't bother switching it over to the backup compressor.

Yes, you would think that someone desperate to save the haul of fish would have tried everything available to him.