Isolation Transformer Source, Make, Model?

[botanybay]

Originally Posted by OldMan

Charles needs to update their line of isolation transformers, AFAIK, they still use "E" class cores vs toroid. Toroid is more efficient and less weight.

I agree, however, I have been told that specific requirement (full current carrying shield) is not possible on a torroidal transformer. I tried to have one custom wound that way.

The CE boat spec does not require anything like that and as my boat is a European build I work to ensure everything I change continues to meet the European standards.

I only know of the Charles transformers which met that particular requirement which makes the requirement a bit of an 'odd duck' in my thought.

The torroidal transformers are much lighter, much smaller, less noisy, and are much safer than not having one at all. At $700 for 32A@120 v it is better value in my opinion than the galvanic isolators with their required test circuits.

[GrowleyMonster]

Originally Posted by OldMan

Charles needs to update their line of isolation transformers, AFAIK, they still use "E" class cores vs toroid. Toroid is more efficient and less weight.

Agreed. But nobody else seems to be making acceptable toroid iso transformers, either.

[OldMan]

Originally Posted by botanybay

I agree, however, I have been told that specific requirement (full current carrying shield) is not possible on a torroidal transformer. I tried to have one custom wound that way.

The CE boat spec does not require anything like that and as my boat is a European build I work to ensure everything I change continues to meet the European standards.

I only know of the Charles transformers which met that particular requirement which makes the requirement a bit of an 'odd duck' in my thought.

The torroidal transformers are much lighter, much smaller, less noisy, and are much safer than not having one at all. At $700 for 32A@120 v it is better value in my opinion than the galvanic isolators with their required test circuits.

Originally Posted by GrowleyMonster

Agreed. But nobody else seems to be making acceptable toroid iso transformers, either.

Victrons are toroids.

[smac999]

Originally Posted by OldMan

Victrons are toroids.

I think they are CE certificated for Europe but not UL certified for north america?

[botanybay]

Originally Posted by OldMan

Victrons are toroids.

Exactly. They don't have a 'full current carrying shield'.

Then again the Europeans have been using ELCIs at least since 1990 when my boat was built. With an ELCI on the input any leakage would trip.

[Cadence]

Originally Posted by smac999

I think they are CE certificated for Europe but not UL certified for north america?

Sorry! I can't help myself, UL is a joke. If it doesn't do on fire in the first 5 min. it gets a sticker.

[OldMan]

Originally Posted by botanybay

Exactly. They don't have a 'full current carrying shield'.

Then again the Europeans have been using ELCIs at least since 1990 when my boat was built. With an ELCI on the input any leakage would trip.

Can you provide a reference for this?


I'm struggling to understand what you mean? The shield or the wire connecting to it?

[foggysail]

Originally Posted by CharlieJ

Xfmrs with primary and secondary windings are required to have an electrostatic shield between the windings that is connected to the safety ground on the shore side. Switch mode xfmrs do not have windings so they are exempted from this requirement.

A transformer with no windings? Could you explain.

[foggysail]

Originally Posted by botanybay

The torroidal transformers are much lighter, much smaller, less noisy, and are much safer than not having one at all. At $700 for 32A@120 v it is better value in my opinion than the galvanic isolators with their required test circuits.

I don't know where you got the idea that a toroidal transformers are smaller, lighter, less noisy and safer. Nonsense! I have been away from circuit design now for too many years to start quoting design equations.

And yes a toroidal can be shielded and toriods are a bitch to wind. The noise you referred to in a laminated construction is lessened by impregnating the cores in a plastic like materials including tar. The purpose of a shield is to prevent capacitive coupling between the windings. In doing so it can also provide some protection between a primary and secondary short. But this is for sure, if there is even one shorted turn in a transformer of any construction type, the transformer has failed and most likely will cause overcurrents that result in other protective circuits ....fuses/circuit breakers to open.

[wsmurdoch]

Originally Posted by botanybay

I agree, however, I have been told that specific requirement (full current carrying shield) is not possible on a torroidal transformer. I tried to have one custom wound that way.

Toroidal transformers are available with a safety shield between the primary and secondary windings.

http://www.noratel.com/fileadmin/con...en/General.pdf
See the text at the bottom right of page 1 and the sketch at the top right of page 2.

The ABYC says...

11.9.1. If used, an isolation transformer shall be of the encapsulated type and shall meet the requirements of UL 1561, Dry Type General Purpose and Power Transformers and the following additional requirements: (See E-11.7.2.2, DIAGRAM 6, DIAGRAM 7, DIAGRAM 8, DIAGRAM 9, DIAGRAM 10, and DIAGRAM 11.)

11.9.1.1. A metallic shield shall be located between the primary and secondary winding and be electrically insulated from all other portions of the transformer. It shall be designed to withstand, without breakdown, a high potential test of 4000 volts AC, 60 Hz, for one minute, applied between the shield and all other components such as windings, core, and outside enclosure.

NOTE: Breakdown is considered to have occurred when the current which flows as a result of the application of the test voltage rapidly increases in an uncontrolled manner.

11.9.1.2. A separate insulated wire lead or terminal identified as the shield connection is to be solidly connected only to the shield, and brought out for external connection and shall be equal to or greater than the aggregate circular mil area of the largest transformer phase conductor(s).

11.9.1.3. The shield and its connection are to be of sufficient ampacity to provide a sustained fault current path for either the primary or secondary windings to ensure operation of the main shore power disconnect circuit breaker when subjected to a fault current level in accordance with TABLE V - B .

11.9.1.4. The transformer shall be tested and labeled by an independent laboratory to establish compliance with the requirements of E-11.9.1

11.9.1.5. The transformer case is to be metallic with a grounding terminal provided.

[foggysail]

Originally Posted by GrowleyMonster

Couple more questions for The Experts

So, If I connect the primaries of two 120v transformers in series to a 240V shore power source, and connect the two secondaries in parallel for 120V, assuming Marine UL certification of the transformers, would this be ABYC compliant? Maybe with a breaker to select between Series and Parallel connection of the primaries?

NO, NO! Theoretically it would work, practically is another matter. The problem is with the secondaries, if there is the slightest voltage difference seen on the two windings, it will react the same way as shorted turn and cause a current loop in the secondaries. It will result in a higher primary current...........could even be enormous. This will cause internal heat build up in both transformers that ultimately will result in a failure.

[OldMan]

Originally Posted by wsmurdoch

Toroidal transformers are available with a safety shield between the primary and secondary windings.

http://www.noratel.com/fileadmin/con...en/General.pdf
See the text at the bottom right of page 1 and the sketch at the top right of page 2.

The ABYC says...

11.9.1. If used, an isolation transformer shall be of the encapsulated type and shall meet the requirements of UL 1561, Dry Type General Purpose and Power Transformers and the following additional requirements: (See E-11.7.2.2, DIAGRAM 6, DIAGRAM 7, DIAGRAM 8, DIAGRAM 9, DIAGRAM 10, and DIAGRAM 11.)

11.9.1.1. A metallic shield shall be located between the primary and secondary winding and be electrically insulated from all other portions of the transformer. It shall be designed to withstand, without breakdown, a high potential test of 4000 volts AC, 60 Hz, for one minute, applied between the shield and all other components such as windings, core, and outside enclosure.

NOTE: Breakdown is considered to have occurred when the current which flows as a result of the application of the test voltage rapidly increases in an uncontrolled manner.

11.9.1.2. A separate insulated wire lead or terminal identified as the shield connection is to be solidly connected only to the shield, and brought out for external connection and shall be equal to or greater than the aggregate circular mil area of the largest transformer phase conductor(s).

11.9.1.3. The shield and its connection are to be of sufficient ampacity to provide a sustained fault current path for either the primary or secondary windings to ensure operation of the main shore power disconnect circuit breaker when subjected to a fault current level in accordance with TABLE V - B .

11.9.1.4. The transformer shall be tested and labeled by an independent laboratory to establish compliance with the requirements of E-11.9.1

11.9.1.5. The transformer case is to be metallic with a grounding terminal provided.

IMO, The wire size portion of 11.9.1.2 is ludicrous as long as 11.9.1.3 is met (for primary). It's unclear how a fault between the secondary windings and screen could ever cause the main shore power disconnect circuit breaker to open.

[foggysail]

During all my circuit design engineering years, a shield was never intended to assume a safety protection role. Its function was to minimize the capacitance between the windings. Some transformers even had double shielding with one over the primary and one over the secondary. And along comes ABYC. Sure, anything can happen in real life. I am looking to gather some moon dust

[Cadence]

Originally Posted by OldMan

IMO, The wire size portion of 11.9.1.2 is ludicrous as long as 11.9.1.3 is met (for primary). It's unclear how a fault between the secondary windings and screen could ever cause the main shore power disconnect circuit breaker to open.

Internet searches are great aren't they!

[foggysail]

Secondary to shield shorts----OK, the shields are normally bonded to ground. If a short should occur between a shield and a secondary in essence there is a short between somewhere in the secondary winding and ground.

There are two scenarios here. First it is highly unlikely that a properly constructed transformer will have such a condition. For discussion, assume this happened. If that short included more than a single turn.....the transformer's primary will look into a short circuit EVEN IF ONLY ONE TURN IS SHORTED and that would be the result of a bridge between two turns.

Next... assume the shield only affects a bridge between the shield and a single secondary turn. If that secondary is referenced to ground someplace in the circuit, you then have a shorted secondary that will cause unpleasant things to happen depending on the normal impedance/resistance to the secondary and ground.