Re: 3-phase Y neutral
Rattus, I worked in an old oil refinery (circa 1918) that used an ungrounded system so I have seen ungrounded 3 phase Wye transformers, however they were not 120/208, but 2300/4160. But an ungrounded neutral on such a system would function correctly. The rub is when there is a ground fault, there is nothing to trip the circuit unless you install a ground fault sensing device (see note below) and a trip relay into the service equipment to provide protection. And any arcing fault to ground not large enough to cause and alarm will send huge voltage spikes everywhere on the system wreak havoc on the insulation of all wires and motor windings causing that equipment to fail prematurely.
The engineering logic around such a system design is that with the proper alarm and ground fault protection one phase of the circuit could become grounded and the circuit would still supply power to the load. When an alarm condition exists the fault could be located, the branch circuit containing the fault is then isolated and repairs can be made. All this and there was no suprise trip of the circuit that would shut down critical equipment and could cause an explosion or the release of liquids and vapors that would be harmful to the environment.
Modern engineeing practices have all but abandoned those configurations, favoring instead a grounded system. And to place the necessary emergency relief and containment in the process equipment to prevent releases or explosions that might be created under a fault trip condition.
But just like nob and tube wiring and open buss motor control centers these older systems do work and are still found in use today. I just wouldn't recommend one for a modern design.
Imagine making a hot tap to a 2300V open overhead buss in order to install a new pump motor or transformer circuit, quite a hazardous task and not one to be done with out taking the proper safety precautions.
Our modern engineeing and safe work practices are a good thing.
Note: One type of ground fault sensing device
is a transformer with a grounded open delta secondary. No current will flow in the secondary until the ground circuit is complete, and the magnitude current will be limited to the resistance of the fault connection. Although there will always be a small amount of current (micro amps in most cases) always present in the secondary, as the insulation of wires and windings begin to loose their dielectric strength the current will rise proportionatley.
On a 2300V system a fault current of more thatn one amp is cause for alarm and most relays will trip at less than 6 amps. (14KW is not a toaster I'd want to see cooking)
Using a special clamp on ammeter with a hoop large enoug to open over the conduit the faulted circuit can be located. The ground current will only show on the conduit containing wires feeding the fault.