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Old 07-01-2011, 08:19   #1
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Isolation Transformer question for you Profi's

Oh no.... not another isolation transfomer question.... Hey this ones different and I need some advice.

I have no isolation transformer and I am just about to fit one.

Currently, I have a device that makes sure the AC is between 190 and 260v, or 80 and 130v depending where I am. It also stops spikes so this is good when starting the AC generator.

In Europe sometimes you get 400v instead of 220v when at a marina as the 220v is tapped off the 3 phase... so any error and you might get 400v down the wires. This blows up all 220v appliances switch on at the time. I have seen this a few times.

I have a 3 way switch to choose between shore power, generator and inverter. Then comes the special voltage and spike control device mentioned above.

This means that the shore power voltage is controlled and also the generator is controlled so all 220v devices are protected against high voltage and spikes.

When I install the isolation transformer then I have 2 possibilities ...
1 - Install it on the shore power line before the selection switch which is the correct place ... however then it is not protected against high voltage from the shore power. Victron says the 220v transformer cannot handle 400v up it without damage, so I would like to do option 2.
2 - Install the Isolation transformer after the voltage protection device....This way the transformer is protected against high voltage to.
However then (depending on the selection switch position) the transformer would receive its input power from either...shore power or the generator or the inverter.

So my question is .... would this matter??

I have thought about it and it seems ok to me....or am I missing the point??

John
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Old 07-01-2011, 08:54   #2
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Quote:
Originally Posted by john Fussell View Post
... I would like to do option 2.
2 - Install the Isolation transformer after the voltage protection device....This way the transformer is protected against high voltage to.
However then (depending on the selection switch position) the transformer would receive its input power from either...shore power or the generator or the inverter.
So my question is .... would this matter??
I have thought about it and it seems ok to me....or am I missing the point??
John
No problems come to mind, except for some minor transformer losses* (particularly when on precious battery→inverter power).

* Transformers have two major components that drive losses: the core and the coils. The typical core is an assembly of laminated steel. Core losses are mostly related to magnetizing or energizing the core. These losses, also known as no-load losses, are present the entire time the transformer is powered on, regardless of whether there’s any load or not.

No-Load Core losses, can be categorized into five components: hysteresis losses in the core laminations, eddy current losses in the core laminations, I2R losses due to no-load current, stray eddy current losses in core clamps, bolts and other core components, and dielectric losses. They are roughly constant from no-load to full-load when feeding linear loads.


The coil losses, commonly referred to as load losses, are associated with feeding power to the connected load. For linear loads, these losses are predominately I2R losses including heat losses and eddy currents in the primary and secondary conductors of the transformer.

Load Losses increase by the square of current (increase with loading) from no-load to full-load, driven by the resistance of the coil.

There are some very rough rules of thumb, such as total losses at 1% to 1.5% of rating, and no-load losses at .25% to .50% of rating, commonly used to size ventilation and cooling systems for transformer rooms. Some manufacturers provide loss data, again intended primarily for determining cooling load, in their catalogs or on their webpages. However, actual losses can vary significantly between manufacturers and transformer types for the same voltage and kVA ratings.


Measurement of transformer loss are usually conducted during open-circuit and short-circuit tests. With the open-circuit test (load = 0) the measured losses are the no-load loss. During the short-circuit test the secondary is shorted and primary voltage adjusted to achieve a full load current flow. Short-circuit tests give the total transformer loss from which the load loss can be calculated by subtracting the no load loss.
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