Any Transformer Experts here?

[Mark Cunningham]

Hi,

I am working up a project that uses a larger transformer of a specific model wired a specific way.

I think I have it worked out but I'd like to double check my theory before I purchase and let the "magic blue smoke" out of my system.

Any experts want to take a stab at it?

Thanks for your time.

[Rob Beckers]

Hi Mark,

I'm not a transformer specialist per-se, just a general purpose electrical engineer that believes to have a decent understanding of those beasts. I'd be happy to take a stab at it. Warranty is worth what you paid for the advice... :notrust:

-RoB-

[Mark Cunningham]

Thanks Rob.

I appreciate it. This is a technical post. Hope it does not spook you. I will issue the standard disclaimer. I alone am responsible for the consequences of my actions.

I am in the Philippines. We are given 2 wire 220vac. We are not given ground or neutral lines.

I have been working on a way to match RP -> US electrical systems that is cost effective, long lived, and easy to put into place.

After conversations with an individual that specializes in remote places, I may have found a workable solution.

I think I can do this with a Hammond Power Systems Titan Q007YEKF (http://www.ideadigitalcontent.com/files/11516/BR_sTitan-Cu.pdf) Single phase Isolation Transformer.

I've attached the wiring diagram.

I'd like to tie input 220vac to a transformer primary. On the secondary pull 110vac and create a neutral/gnd that is relative to that secondary 110vac.

The transformer has 4 inputs labeled "H-1 -> H-4".

For my application, connect H-1 and H-2 to input AC. H-1 to one line, H-2 to the other.

This transformer has 4 outputs. "X-1 -> X-4".

On the secondary, connect X-2 and X-3 together and tie those two lugs to a physical ground rod driven in the earth.

This will give me "Leg 1" 110vac measured between X-1 and X-2/X-3(gnd)

AND

"Leg 2" 110vac measured between X-4 and X-2/X-3(gnd).

This is identical to U.S. style three wire 220vac. 2 separate 110AC feeds that are 180 degrees out of phase with each other and a neutral line that is bonded to ground. The transformer physically isolates from the grid.

I run an off-grid Outback system. My inverter is a VFX-3648. It has an optional input for 120vac input. Grid-tie or Gen-set.

If this works I'd like to pull one of my "new" 110vac circuits into the AC input on my inverter. That would give me extra charging amperage for bank maintenance, and options during the dark monsoon season.

Thanks for looking at this.

[Rob Beckers]

Hi Mark,

Nothing complicated about this one. It's exactly as you say (connections as you describe). I've used transformers like this one lots of times. Test it with a fuse or breaker in the lines feeding H1 and H2, and measure the output Voltages between X2-X3 and X1 and X4, to make sure they are indeed 120V. If that checks out work on that ground for X2-X3 and a more permanent hookup.

For transformers, don't exceed 80% of rated output power, at least not for continuous duty. They get hot as hell if you do. The wiring sheet you attached doesn't show the power rating, for transformers it's normally "VA" (for Volt-Ampere), basically the same as Watt for what you're doing with it.

Best of luck!

-RoB-

[Mark Cunningham]

don't exceed 80% of rated output power

Thank you Rob.

Its comforting to know that my dusty, rusty theory hat still fits.

That particular xformer is a 7.5kva model. My nominal load is 15 amps @ 120vac.

Which, if my math is correct, is double the nominal capacity I need. For nice cool operation and long life.

Wanna take a stab at part two of that design? Surge protection.

[Rob Beckers]

At 7.5 kVA the secondary windings are good for about 31 Amp peak. So 15A should work fine.

Regarding surge protection, I've written something about that before: https://www.solacity.com/lightning-protection/

Not sure how helpful that would be, it's geared towards wind turbines.

-RoB-

[Mark Cunningham]

https://www.solacity.com/lightning-protection/

Thank you. I'll definitely look at that in the morning.

If I pull the grid into my inverter through a transformer, then I am susceptible to the "line nastiness" that is so prevalent here.

So I am trying to over-design a bit.

Rayvoss Model: 120-2S-M3-3-06-A-H, Type 2 - Surge Protective Device (SPD). (http://www.raycap.com/wp-content/uploads/2014/08/Rayvoss-Strikesorb-Installation-Guidelines-G09-00-047-Final-web.pdf)

One device for each transformer output line. For a total of 3 devices, X-1, X-4, and Gnd/neutral.

The Rayvoss device connects inline on the line in question meaning that the feed from X-1 goes into the appropriate input lug on the Rayvoss and the "protected" output comes out on the Rayvoss output lug. This output goes to feed the electrical loads.

The Rayvoss device has a separate ground line that needs to be connected for a path to send whatever surge hits to the earth.

Tell me what you think. How can this be improved?

[Rob Beckers]

From the description these are pretty good devices Mark!
Looks like they are MOV based, which means they have a hard cut-off Voltage and react very quickly.

Because MOVs generally fail in short-circuit, you should have a double-breaker (in both phases of the split-phase, or on the primary of the transformer) upstream of them.

Wiring has some effect on how well this works in curbing surges; you may want to have a look at the "single point ground" part of my surge protection story. Other than that, very nice device! What do they sell for?

-RoB-

[Mark Cunningham]

What do they sell for?

On Ebay you can find them in the range of $35. But I am leery of "used" surge suppressors. New they are about $100 each.

Thank you for the gnd heads up. I will read that. Give me a bit to absorb it.

I planned to have an input breaker/maintenance cut off on the input to the transformer.

I don't plan on having the transformer in circuit full time. Just periodically for bank maintenance and support during the dark monsoons.

I sent an email to Brian to see if he was interested in the reading material. If memory serves he has a smaller NiFe set. In addition to my NiCd bank I have a 1000ah Changhong NiFe bank.


You might drop a bug in his ear in the case that his spam filters caught my message.

Thanks again for the link.

[Mark Cunningham]

"single point ground"

Good stuff.

Part of it I already knew. Part was news to me.

My current grounding system is the "islands" style. They are all tied together by fat runs and multiple rods.

My rods are probably too close together. They are spaced one rod length apart. My rod connections are not cad-welded. I did not have the equipment. They are torch welded.

I did incorporate my well casing, (it is stainless), and I tied into the rebar in my septic system, (a trick I learned from an island I worked on).

So I do have significant energy sinks in my grounding system. That being said, following your docs, I can improve it. For not much extra coin.

Thank you.

[Rob Beckers]

The article describes how the industry does it, where (mostly) cost is less of an issue and the tools are available. Of course, all we can do is make the best of it with the means available.

Sounds like you already went well beyond what most off-grids do in terms of surge/lightning mitigation!

You can send Brian a Private Message. The GPT notifications should get through his spam filter.

-RoB-