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Old 06-06-2012, 02:39   #1
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Isolation Transformer Problem

Hello all. I have a US boat that I moved to Sweden. Prior to move I had a Charles islolation transformer installed to allow 240V European input and 115V output. When I plugged into the shore power the shore breaker tripped. After talking to Charles Marine they suggested the inrush current was tripping the breaker. That makes sense so I purchased a Mastervolt softstart and installed it between the shore power and the transformer. Unfortunately the breaker still tripped when I turned it on. I have attached my crude diagram of the installation (although I can't see the attachment this is my first post so maybe is shows up when I submit this). The soft start is Mastervolt 13kw. Specs 230V, 2.5 to 13KW. The documentation with the unit is terrible. The Charles Marine transformer is a 93-IXFRM-3/8I-A. It is 3.8kva and can accept 240V or 120V input/output. Does anybody have any suggestions on what is wrong here. Both units are new and I think the wiring is per instructions. Ideas are appreciated. Thanks, Don
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File Type: pdf Transformer wiring diagram.PDF (115.2 KB, 113 views)
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Old 06-06-2012, 04:00   #2
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Re: Isolation transformer problem

Greetings and welcome aboard the CF, Don.

I'd ring out the transformer, looking for a short circuit.
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Old 06-06-2012, 06:18   #3
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Re: Isolation transformer problem

Do you have the load on the boat turned off when engaging the shore power breaker?

Looking at the Mastervolt unit, it has a 25 ohm resistor that limits the surge to ~9a until the relay latches up. Hopefully the relay takes more than one cycle to connect (20ms) so the transformer has time to power up.

It would be interesting to defeat the relay in the Mastervolt, with no load on the secondary, see if the breaker tripped with the resistor in the circuit for a longer time. It could be a bad breaker.

Or as Gord said, the transformer could have a leak.
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Old 06-06-2012, 08:42   #4
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Re: Isolation transformer problem

Don,
Hopefully by now you have isolated the problem and are on the way a fix. If not so:

My first guess on the problem would be the cord or adapter between the shore receptacle (240V/16A) and the receptacle on your boat (120V/30A). This is not a standard cable so you either made it up yourself or had someone make it for you. Have you checked it for a short. Does the shore breaker trip with that cord disconnected from the boat? I think most shore breakers in Europe are GFCI types and will trip if there is any current in the green wire.

Did you use the transformer in the US before departing for Europe? if it worked with 120VAC input and120VAC output then the windings should be OK. I assume the jumpers on the secondary side of the transformer (X terminals) isolate half the secondary windings when you are stepping the voltage down. In that case when you are not changing the primary and secondary voltages (as in the US) the full windings on both sides of the transformer would be in use.

Double check your primary, secondary and jumper wire connections to the transformer to make sure they are tight and secure. Double check everything you have already checked.

Good luck,

John
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Old 06-06-2012, 09:02   #5
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Re: Isolation transformer problem

Thanks for the replies. DotDun. The secondary load is off when I test the unit. I have not tried bypassing the relay just to see what happens, the resistor says 25ohm, 25W. I am afraid it might destroy the resistor if I do this?

jstevens, I made up the adaptor by taking a US 30A to 15A adaptor pigtail and replacing the 3 prong household plug with a European 3 prong marine plug. I will try plugging in the cord with the adaptor disconnected from the boat, I didn't try that. I haven not made many tests since I put the softstart in the system as I was at the end of a long day, but before installing the softstart I removed the adapter pigtail and ran wires direct from the European cord to the transformer. It tripped. The transformer was installed in the boat after I left for Europe and the boat was shipped later. It has only ever been wired for the 240 to 115 application so I doubt if the shop tested it. I will check all the wires again as you say. Also I will check that the resistor is in fact 25 ohms. I am not 100% sure that I have managed to keep the hot wire colors all matched up. The Europe plug has Brown wire (matched to black), a Blue wire (matched to white) and a green/yellow ground wire (matched to green). It is possible the brown and blue could be crossed from the Europe plug to the Adapter, but I undertand the Europe 240V wiring has no neutral but two hot wires and with the isolation transformer this should not matter which wire connects where ( ie line and neutral can be either of the two). Even so I think I have matched the colors correctly. Final note, again before installing the softstart I disconnected the output wiring from the secondary to remove any chance that the boat wiring could be causing the trip. It still tripped.

I will be back at the boat on the weekend so any further tips are appreciated. I will be double checking everything and following up on your suggestions. Thanks Don
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Old 06-06-2012, 09:48   #6
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Re: Isolation transformer problem

You are tripping the dock GFI. Leave the transformer disconnected, and measure the resistance between the green wire on the input side and the load or neutral wire on the input. Also the load or neutral on the input to the load or neutral on the output. If anything is less than 25,000 ohms, you have a bad transformer. If the resistance is more than 50,000 ohms and the dock still trips, it is probably an unbalanced inrush current and you may have to disconnect the green wire.
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Old 06-06-2012, 10:14   #7
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Re: Isolation transformer problem

Thanks Don. I will check these resistance measurements, I see what you are getting at. Not sure what you mean by unbalanced inrush current and disconnecting the green wire. You mean disconnect the ground wire input to the transformer?
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Old 06-06-2012, 11:24   #8
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Re: Isolation transformer problem

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Originally Posted by donpjr View Post
Thanks for the replies. DotDun. The secondary load is off when I test the unit. I have not tried bypassing the relay just to see what happens, the resistor says 25ohm, 25W. I am afraid it might destroy the resistor if I do this?
Good point. I would *expect* the transformer to draw less than 25W with no load, but Charles does not publish that data so it is a possibility. The resistor can take the 2kw surge for a few milliseconds before the relay engages but probably not for a much longer time.

Since you've never witnessed the unit operating, there is a possibility the jumpers on either the primary or secondary side are miss-wired on the board, it'd be worth closer examination. If either is connected wrong, you could be shorting out a winding or connecting one half backwards.
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Old 06-06-2012, 11:46   #9
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Re: Isolation transformer problem

Thanks DotDon. I spoke to the tech at Charles Marine and since everything I told him sounded OK, he also suggested a remote possibility of miswiring of the transformer. I will check some resistance measurements on the weekend to see if I can confirm the transformer coils are wired as planned and not shorted and that the labels match the intended purpose of each wire. It is a mystery so far.
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Old 06-06-2012, 11:52   #10
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Re: Isolation transformer problem

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Originally Posted by donpjr View Post
Thanks Don. I will check these resistance measurements, I see what you are getting at. Not sure what you mean by unbalanced inrush current and disconnecting the green wire. You mean disconnect the ground wire input to the transformer?
I had a friend with a transformer on his shore power and it would trip the dock breakers in Italy about 2 out of 3 times it was plugged in--once it didn't trip, all was fine until the next time power was interrupted--then he was out in the middle of the night fiddling with it again. The GFI system trips if the difference between the current in the load and neutral wires exceeds 5 to 20 milliamps, depending on whose breakers. The inrush current when you first energize a transformer may be different enough to trip these breakers. Disconnecting the ground wire when you first plug the transformer in may help, as the green wire is another path for current to go during the startup transient.

BTW, I had a transformer on the same dock and had no problems, but mine was a cheap Singapore transformer and his was an expensive Taunton.
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Old 06-06-2012, 11:53   #11
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Re: Isolation transformer problem

Keep in mind that ( I believe) the European 220 V system is not isolated above ground like the US system. I don’t know anything about your isolation transformer but I ran into a horror story about a European boat connecting to our 220 V system.

I would start at the dock and plug in your adapter then turn on the power if that holds then plug in just the cord not connected to the boat if that holds then go in and disconnect the wires as the transformer and isolate them then plug cord into the boat if that holds your transformer is at fault. Just my two cents, Mike.
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Old 06-06-2012, 11:56   #12
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Re: Isolation transformer problem

double check the transformer normally you have to change the "jumper wire" on the transformer to change the voltage, if this is incorrect the primary current will more than double and trip the breaker, never disconnect the earth wire on a 220/110 ac volt installation
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Old 06-06-2012, 14:36   #13
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Re: Isolation transformer problem

I think it could be something else. The transformer in the duty you are using it, is purely as a transformer, not an isolation transformer. I am not familiar with the actual unit you have. Transformers are ferro-resonant devices. They are thus sensitive to frequency more than voltages etc. The whole flux field has to set up and decay and re setup in the opposite polarity at 50, or 60 Hz. The mass of the iron in the transformer is calculated to oscillate a flux at either but not both of those frequencies.

I have an isolation tx. It is 220/230 volt in and out at 50 Hz. When I plug in the shorepower, very often the breaker shoreside trips. I can work around it by switching the breaker on 2 or 3 times in rapid succession.

When I am in the USA, it ALWAYS trips the c/b shoreside. It was not designed to run at 60hz. It also gets a lot hotter. In the US, I get around the problem by bridging the c/b on shore out for the start only. I attach jumpers in the box, plug in, then take the jumpers out while its hot. Its a PITA when the power goes out and re-establishes, have to do it all over again.

The best advice I got on the ferro resonance problems was from the engineer at March pumps. He really explained the whole flux field thing very well.

Ask your tx provider what freq it was designed for, and if he says 50/60 then he must mean it was calculated for 55 Hz. There is only one harmonic point near there, the next ones are factors of 2 away..

You might be able to help things with a capacitor....one used to run a 2Kw AC motor or a PFC one....
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Old 06-06-2012, 14:55   #14
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Re: Isolation transformer problem

Thanks sy_gilana. The transformer I have is serving as an isolation transformer as it separates the boat from the shorepower. This takes care of any corrosion due to leakage back through the shore power system. The unit itself is rated for 60 or 50 hertz and 120 or 240V. It is designed for exactly what I am using it for which is hooking a US boat to the European shore power. Most of what I have aboard will operate on 50Hz so the frequency for practical use is not critical for me. I don't really understand the comments about the flux etc so can't comment on that. I have read somewhere that whether the inrush current trips the shore breaker or not can be dependent on what part of the cycle the AC power is at when it is switched. Maybe that explains why after a few tries it might work. But I'm a mechanical engineer and this electron stuff is certainly not my speciality. I called the supplier today and reviewed my setup with diagrams and photographs. He says everything is connected exactly right. My next step is an hour with the multimeter to measure every resistance I can think of on the unit.

Delcrest, the jumper wires have been set up for the appropriate voltage. I confirmed this with Charles Marine as well, so I don't think my problem is there. Thanks for the suggestion.

Florida Mike. I agree, this weekend I will be starting at the shore power and working my way towards the transformer testing everything along the way. Europeans will have a horror story if they try to connect a European 240V boat to US 220V, it is completely different wiring. 240V over here is 3 wire with two "hots" and a ground.
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Old 06-06-2012, 15:24   #15
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Re: Isolation transformer problem

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Originally Posted by sy_gilana View Post
..... It was not designed to run at 60hz. It also gets a lot hotter. ....
That's interesting as the higher frequency is easier on the transformer. They stress test a 50/60hz transformer at 50hz.

From our friends at wikipedia.....

Quote:
By operating at higher frequencies, transformers can be physically more compact because a given core is able to transfer more power without reaching saturation and fewer turns are needed to achieve the same impedance.
Transformer - Wikipedia, the free encyclopedia
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