220-110 Step Down Transformer (Korea)

[2manynotez]

Forgive me first off as I am not an electrician. I have a question regarding a step down transformer and I figured there has to be a ton of experts on this forum that can answer it in their sleep. I live in Seoul and work for the USACE here in Korea.

Korea's residential power in older apartments, like mine, is 220v. Two hot legs, no neutral, no ground. (grounding is another issue for a later time)

I have a 5000w Step Down transformer with tap changer (2 down, 2 up). Without power connected, my ohm meter reads a completely open connection (no connection) between the 220 legs or the 110 legs to the Transformer Case.

When powered on, I get ~88 volts to the case from one 110 leg, and ~35 volts to the case from the other 110 leg. (This is the reading for both front outlets and the backside hard wire 110 terminals)

My question: is this normal, and why? The case is NOT grounded and is sitting on a vinyl floor.

The same exact readings happen with a 2000w Step Down transformer I have. I have used this transformer with no problem, except for no ground for surge protection, for 3 years like this and just today happened to bring out the Fluke.

I would really appreciate an experts opinion on this. I hope I have given you enough details to picture my conditions.

I have added photos of the front and back of the transformer. Note: even though you see a 3 prong outlet on the front, the ground on the two outlets are tied together inside and nothing else. They are just there to accept a 3 prong plug without adapter.

Thanks in advance for any help.

 

[Dennis Alwon]

I am allowing this thread but please no how to fix it.

 

[gar]

120211-0901 EST

My guess is capacitive coupling and the use of a moderately high input impedance meter. A Simpson 260 on the 250 V range and 5000 ohms per volt is an impedance of 1.25 megohms. Put a 25 to 100 W incandescent bulb across the metering points and the voltage will probably drop to near zero.

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[Joethemechanic]

I'm with Gar on this one. The fluke is a very sensitive meter.

A couple of questions out of curiosity though.

Why are there 4 binding posts on the back? Are two of them 220V and two of them 110V?

Also is there any information on this unit in English? Manufacturer? Model # ?

 

[ActionDave]

Sounds to me like there is no connection between the secondary of the transformer to the case, or since nothing is equipment grounded voltage readings to the case can be anything.

 

[2manynotez]

I'm with Gar on this one. The fluke is a very sensitive meter.

A couple of questions out of curiosity though.

Why are there 4 binding posts on the back? Are two of them 220V and two of them 110V?

Also is there any information on this unit in English? Manufacturer? Model # ?

First, thank you everyone for your input! And taking the time to consider my questions.

Yes Joe, Two are 220v In, and two are 110v out.

As far as data in English, only the front panel that says: 220V, 110V, 60Hz, 45.5 A - Everything else is in Korean.

 

[cadpoint]

Your service only reflects what available and including what's being transposed in a transformer, there is no power conversion.

Without power connected, my ohm meter reads a completely open connection (no connection) between the 220 legs or the 110 legs to the Transformer Case.

As it should read.

One doesn't want to have a connection between legs. Your reading the potential differnce of power if hot, nothing if one is reading the difference of the circuits not on.

I'll give Fluke the credit that their meter can read what it usually looks for or suppose to read about or per the model.

 

[cadpoint]

Your service only reflects what available and including what's being transposed in a transformer, there is no power conversion.

I want to correct myself and state of course one is makeing a power conversion, it's the fact that the set-up you
have is not what your expecting! IE your only converting and reading existing service that your not use too!

 

[hurk27]

Welcome to the forum.

Being that you stated you are not an electrician please refrain from asking any "how to questions" that would involve you doing the work as it is against the forum rules for us to help you to preform work outside of your given scope of being an engineer, knowledge type questions are fine and can help many of us learn new things but we must refrain to helping those who are not qualified to preform such work to protect the forum and we appreciate your understanding in this.

With that said to understand the voltage you are reading you must understand the capacitive and inductive coupling effect of having energized conductors in close proximity of un connected metal parts or other conductors, placing two conductors close to each other one with voltage on it, and one without any type of connection to anything can cause a capacitive coupling that will show a voltage on a meter with very high input impedance, this is an effect that can confuse many into thinking that they must have a connection when there is none, and can confuse the right course of action in troubleshooting a circuit, it is also why we ground or bond these metal parts to prevent this voltage, but for the most part to use a loaded meter (with a resistance load) when doing measurements will give you the true voltage, this is what Gar was speaking of in post 2 here in the states we tend to call these voltages ghost voltages as they have very low current available and almost any loading will drop them to zero volts.

 

[2manynotez]

Welcome to the forum.

Being that you stated you are not an electrician please refrain from asking any "how to questions" that would involve you doing the work as it is against the forum rules for us to help you to preform work outside of your given scope of being an engineer, knowledge type questions are fine and can help many of us learn new things but we must refrain to helping those who are not qualified to preform such work to protect the forum and we appreciate your understanding in this.

Again, I thank everyone for their input and help. I have spent the last 42 years designing, building, and training people how to build high voltage transmission lines, distribution systems and power generation facilities around the world - but anything past the meter base or with wire sizes smaller than 4/0, and well, I get brain cramps... so I usually leave that to the electricians.

In my line of work, no work is ever done without visable grounds in place so I just get goosey without a ground around, even at low voltages. Your responses here have made me feel more comfortable - which was my goal.

Again, THANK YOU ALL