Isolating Transformer Alternative

The signal is AC power, not a control signal(discrete). And our company only deals with LV products, but my question really is more general than relates to the particular application I mentioned earlier.

I appreciated your participation in this thread.

Good answer, but I'll add one note. The isolation transformer is 1:1 primary to secondary winding ratio, and its sizing is determined by the power it needs to deliver, not by the voltage. It needs to be large enough to deliver the required power without saturating. The fact that it's spec'd as 220 in / 220 out is irrelevant per se -- except that the insulation on the windings must be adequate for 220. That doesn't affect the size of the core to any extent.

The alternative that ignator describes -- AC to DC to HF AC and back -- actually can be used to deliver isolated power in a smaller and lighter package. There are situations it may be justified, but it won't be on the basis of cost.

Thank you, this pretty much answers it.

Since this is a laboratory there can be many different reasons for the use of a specific isolation transformer that will not be obvious to many. During testing an instrument and/or device under test (DUT) may be pulsed or sustained at a voltage different than ground potential. Ground loops can make reading tiny signals impractical if not impossible. Having a power feed path with a core at or near saturation can reduce non-linear switching noises from the grid to enter sensitive circuits. Isolating power can be a safer usage for electrocution can only happen with two errant circuit paths.

This is not an exhaustive list of reasons an isolation transformer may be used. Without knowing why a transformer was inserted in the power feed, an alternative cannot be offered. Very often in a legacy design, an isolation transformer may have been needed at one time but with optical and wireless coupling capabilities of sensors and the real possibility of a test no longer being performed the need can be no longer present for an isolation transformer.

There have been many reasons to isolate and not to isolate.

Current North American codes would require the grounding of the secondary of your transformer - unless it is a special application, then Ground Fault Indication/Protection would be required.

You did not state 1 or 3 phase, KW / Kvar, or the reason it needed to be isolated.

With legacy 3 phase to DC power conversion equipment isolation transformers were sometimes used to provide the necessary impedance for the converters. Three phase reactors can often be used just as effectively.

More description and application details would be welcome.

Be very careful when using an isolated supply to power more than one class 1 device as the isolated supply will not detect a first fault to frame, and any subsequent fault to frame via the other active conductor, and a person coming between the two could prove fatal.

Ground fault indication can be built in to the secondary side of the supply, and is recommended.

Also this can be used to trip the supply either on the secondary or primary depending on requirements of the distribution system

For what's is the purpose you want to use isolation Trafo? If it is to limit fault, you can use Short ckt current protector.

Isolation is at Life-saving level for men and equipment.

Its power-rating depends on the load put on this transformer.

Input voltage may vary from 240V but output must be 240V as it is specified for the equipment put on its load.

NB: The voltage indicated generally means the normal supply voltage of the country / area and not a tight binding as you will notice in different countries on 110 V(normal) quite a variety is:

110, 115, ..

and for 220V (Normal) 220, 230, 240.

In star that is 3+N for output of 2 phases 380, 400, ...

So look for the the tolerance for input and output voltage requirement and you will be relaxed.

Have a good day.