Transformer?

[Brian]

I wonder if it's there to spread uneven loads on the output side nicely, and equally, across the three incoming phases.

 

I'd say that if it's wired correctly, and as you already have it, then it's worth getting an electrician in to check it over. HOWEVER, to be successful at giving you a clean sound supply ALL the sound kit will need to be wired properly.

[richardash1981]

I wonder if it's there to spread uneven loads on the output side nicely, and equally, across the three incoming phases.

It won't ...

 

As others have said, this is a Delta (3-wire) Wye (4-wire) transformer - this is what the last line of the plate means "Kytk. Dyn11". It is the Vector Group of the transformer. Vendor's website seems to be here, but little information on it.

 

The fact that the input and output neutrals are connected to each other doesn't mean it doesn't do something useful, provided that the neutral itself is firmly earthed, either in your premises or close by. It will still ensure:

1. That you don't draw supply neutral current - you will draw unequal phase currents, but no neutral current. As others have said, important if your supply neutral is weak-to-non-existent, and some are. This is both 50Hz neutral current (which sums to zero in a balanced load), and harmonic neutral current, where every 3rd ('triplen') harmonic adds even if the loads are balanced! Non-linear loads (like anything with a rectifier, so most sound kit) generate triplen harmonics, which can overload the neutral conductor if it isn't designed for the job.

2. The phase-to-neutral voltages on the output (which is probably what your equipment runs from) are independent of the phase-to-neutral on the input side (they depend on the phase-to-phase input). This will improve voltage regulation if the incoming delta supply moves relative to it's neutral conductor. This works despite the neutral conductors being joined together, because the transformer outputs a (floating) set of stable voltages, which are then referenced to the incoming neutral. This doesn't stop them being stable though.

 

There are a few reasons why the incoming supply may swing around relative to the local neutral point, whilst the phase-to-phase voltages are stable:

1. Local neutral may have a high resistance (small cable) back to the substation.

2. There may be a lot of neutral current flowing caused by other unbalanced loads - like for instance your lighting installation in some dimming states!

3. The supply may actually be a 400V delta supply, with no real neutral (although you would have trouble running lightning from such a supply). This might have a weak neutral at the substation end, or none at all if the LV network is Peterson Coil earthed (which is certainly possible in Estonia).

 

Because of these, you probably can't just take it out of the system without upsetting matters. You will probably recreate whatever problem caused it to be put in - these things aren't cheap, so someone probably got bitten before it showed up! It is either allowing you to run equipment which would otherwise overload your supply (and eventually black the building out) or keeping your mains voltages sane when the incoming supply is not.

It's obviously a generous size (did someone want a 10kW PA system?), but the standing losses won't be as high as you think they are, because (as others have said), there will be a very low power factor. If you are Billed for reactive power, then you will still pay for this (but at a lower rate), and if you aren't then keep quiet! If the reactive power bills are high, then consider a capacitor set (on the input side!) to improve overall power factor (with the side benefit that they also filter out harmonics, which improves your power quality).