shore power for ships

[drtymex]

Well my situation here is that we have a ship for years dock using shore power with a 3 phase 480 volt nominal.

But recently,we've had a problem where the voltage goes up to 492 volts on at least two of the legs (sorry about the description,they just called me about it at home)only when the ship is using shore power.The last time this happened it burned out a couple motors and blew a few lamps.
Could it be back feeding from the ship?
Any comments,references and opinions of course would be appreciated!!

 

[brian john]

Re: shore power for ships

1. Check the voltage with the power to the ship off,
2. Possible primary tap changers stuck, bit unusal two would stick but possible.

 

[iwire]

Re: shore power for ships

492 volts on a 480 system is nothing to worry about, this is only about 2.5% over voltage.

The POCOs many times allow + or - 5% of the service voltage.

Here is a reference from a POCO web site.

The American National Standard ANSI C84.1(1) establishes nominal voltage ratings and tolerances for 60-hertz (alternating current, AC) electric power systems above 100 volts and through 230, 000 volts. Voltage operating ranges are recommended for two voltage categories: 1) the service voltage, typically the point of connection between utility and customer; and 2) the utilization voltage, typically the termination point to equipment. The utilization voltage range takes into account a voltage drop within the end user?s distribution circuits. ANSI C84.1 expects equipment to operate at service voltages between 95% to 105% with a utilization voltage range of 87% to 106% (120V to 600V) Refer to ANSI C84.1 for additional operating voltage ranges).

I do not know why you blew out motors I suspect there is more going on than just the 2.5% over voltage.

[ November 22, 2003, 01:00 PM: Message edited by: iwire ]

 

[charlie b]

Re: shore power for ships

During my nine years of naval service, I was responsible for the electrical distribution systems, including the shore power connections, on three ships. I believe that all US Navy ships have an ?ungrounded delta? configuration. But what varies from ship-to-ship is the type of connection to the shore power facility, and the ability (or lack thereof) to operate in parallel with the shore power (i.e., during the transfer from ships power to shore power, or the transfer back to ships power). A thousand questions come to my mind, so I don?t know how to begin to help. I would start by reiterating that 492 volts would not cause a 480 volt motor to burn out. You would need to start your investigations, and come back with more specific information, before I could offer any advice.

 

[dkerwin]

Re: shore power for ships

Good point made by charlie - if the system is ungrounded, and if 2 legs are experiencing voltage rises, then you may be looking at a developing ground (still at high impedance) on the 3rd leg.

Does the system (shore or shipboard) have ground detectors? If they are of the old 3-light type, a 'developing' ground may not be evident.

Ditto - tell us more about the system!