Starting Motor causing brown out (shipboard wiring)

[AdelaCruzJr]

We have a 3-phase, 240 VAC switchboard that supplying power throughout the boat. Every time a motor (15 hp and above such as air compressor) is started, we noticed a significant drop of our voltage, from 240VAC to 200VAC, on our switchboard meter, and then the voltage will creep back up to nominal voltage when the motor starting sequence is over. This voltage drop also causes the lights throughout the boat to dim. These lights are hooked up to our step-down transformer. Sometimes this significant voltage drop causes other running equipment to trip. Any suggestions or idea why is this happening? One thing I noticed is that this boat is hooked up to the pier that has over 1000 feet or more of shore tie cable. Any input is appreciated.

 

[jumper]

I am approving this post on the assumption the OP is electricaly related in his military profession.

 

[ptonsparky]

You are suffering from VD, a rather bad case of it. The cable length, pier transformer size, and possibly connections are combining to cause you grief.

please note my location and take it into consideration.

 

[kwired]

Another currently active thread with a very similar situation - even includes on ship air compressor of 15hp, must be a common problem on these vessels?

http://forums.mikeholt.com/showthread.php?t=171400

 

[petersonra]

it does seem like a VD problem. I doubt there is a really good answer to this problem while the boat is on shore power.

 

[Tony S]

I wish people would refer to volt drop rather than VD. But that would seem to be the problem in this case.

The 1000Ft of shore hook up cable is obviously undersized. It may be rated for the current but at that length ? ? ? ?

It would help to know both the cable size and nominal loading

 

[ptonsparky]

I wish people would refer to volt drop rather than VD. But that would seem to be the problem in this case.

The 1000Ft of shore hook up cable is obviously undersized. It may be rated for the current but at that length ? ? ? ?

It would help to know both the cable size and nominal loading

Similar to getting a BS degree at college.

 

[Tony S]

Some I know that have an engineering BSc, BS merchant would be a better term.

 

[templdl]

Ko

Ko

I wish people would refer to volt drop rather than VD. But that would seem to be the problem in this case.

The 1000Ft of shore hook up cable is obviously undersized. It may be rated for the current but at that length ? ? ? ?

It would help to know both the cable size and nominal loading

If you can't resolve the voltage drop with a change in the feeder you may wasn't to consider a soft start which ramps the voltage/ current when staring the motor which should help alleviate the voltage drop issue.

 

[Tony S]

If you can't resolve the voltage drop with a change in the feeder you may wasn't to consider a soft start which ramps the voltage/ current when staring the motor which should help alleviate the voltage drop issue.

I was using a ship to shore link it would be a bit longer than 1000Ft. I’m on the other side of the Atlantic. I'd be lucky to get a 60W lamp to work.

A soft start may help the OP but from reading his post there’s more than one motor involved. The cable size needs proper evaluation with a view to uprating.

 

[Tony S]

Using the analogy of a 60W lamp. The volt drop the OP is experiencing reduces the lamp to 42W with significant drop in light output.

Its 03:00 here, I’m not looking for the calculation now but the drop in luminance from 60 to 42W isn’t linear but exponential. It’s a wonder they can see at all.


Some input from the OP would help, he's lurking about ;-)

 

[templdl]

I was using a ship to shore link it would be a bit longer than 1000Ft. I’m on the other side of the Atlantic. I'd be lucky to get a 60W lamp to work.

A soft start may help the OP but from reading his post there’s more than one motor involved. The cable size needs proper evaluation with a view to uprating.

It is not all that unusual that with a lack of specific knowledge with regard to the installation there will be plenty more of speculation. It appears as though the law of physics will not change, trying to make a silk purse out of a sows ear. Yes, I agree that the only option is to reevaluate the size of the cable. Also, using a step up/ step down transformer combination may be more cost effective rather than replacing 1000' of cable.
But'again'
Aat this point may it be that we are shooting at shadows?

 

[Tony S]

I did consider the two transformer option and then thought of weight. But if the land based transformer is fitted with wheels it has got to be better than dragging a 1000Ft of far heavier gauge cable about.

Unless the OP comes back with some facts and figures we’re just talking amongst ourselves so I’m out of this discussion.

 

[templdl]

I did consider the two transformer option and then thought of weight. But if the land based transformer is fitted with wheels it has got to be better than dragging a 1000Ft of far heavier gauge cable about.

Unless the OP comes back with some facts and figures we’re just talking amongst ourselves so I’m out of this discussion.

Good call. I'm not into spinning my wheels either. I'm gone.