Iwire,
It's a Grounded AC System. Advantage is the system has a Grounded Conductor, so Voltage to Ground is stabilized to somewhere around 240 VAC maximum, whereas an Ungrounded version of this same Delta system would have an unstable Voltage to Ground (plus no Grounded Conductor).
This system does not need the Ground Fault Sensing equipment of it's Ungrounded Counterpart.
It is mostly used on 240 VAC systems, whereas the Ungrounded version was commonly used for 440-480 VAC systems.
This system (the grounded Delta) was posted here for discussion, in order to point out it's main characteristics, which differ it from an Ungrounded Delta (or a 4 wire Delta).
Another reason for posting it was to try and cover it's Grounded Conductor.
Using a 4 Delta for example, the Grounded Conductor of that system would be the Center Tapped "Noodle", derived from the Midpoint of the "Lower" coil (between terminals X1 and X2 on the lower part of the Triangle).
That Center Tap works in the same fashion as the Center Tapped Noodle of a 1Ø 3W Secondary - because it is the same thing!
In this scenario, the Center Tap (Noodle) will be at 1/2 Potential of the coil (magnetic flux drives across the entire coil, but drives currents at 1/2 the full coil's potential between the centertap and one end of the coil).
Let me know if you need further information regarding this function.
Along with the center tap's 50% potential, the currents will flow in a "Balanced" fashion across the entire coil's length, and any imbalanced currents will be driven through the center tap, still at 1/2 potential.
On a 4 wire Wye, the Common Grounded Conductor is the point where all three coils are "Bound Together" at the star point. This Circuit Conductor does not act like the Center Tapped "Noodle", since it is more like an extension of each 1Ø 2 Wire coil, so the term Common is the more logical choice here.
This Common point is Grounded, and the Circuit Conductor becomes the Grounded Conductor for a 3Ø 4W Wye system.
BTW: If these systems were not grounded, the Circuit Conductors described above would function just as they would if they were Grounded. The difference being an unstable Voltage to Ground systemwide.
Now that we have briefly covered commonly found Grounded Systems, apply this to the 3Ø 3W Corner Grounded Delta.
In this system, we take one (and only one) Secondary Line output, and drive it to Ground Potential by Physically and intentionally bonding it to a Ground reference (in this case, earth ground is reference). This results in a grounded AC system, such as the ones mentioned previously.
In the example schematics, the Line output which would be identified as ØC becomes the Grounded Conductor. It's still ØC and currents flow just like usuall!
Voltage to ground is stabilized at 240 VAC (ØA and ØB will read 240 VAC to ground, and 240 VAC will be read between any L-L points)
Line C is a Grounded Conductor, so it must be treated as would a typical Grounded Conductor - hence the illustrations depicting the Grounded Conductor's placement and location throughout the complete system.
One scenario that should be pointed out for discussion is how the HID Ballasts are connected in a Multiwire-Like circuit.
Notice the useage of the common Grounded Conductor as to where the screwshells terminate?
Hope this brief text is helpful to everyone.
Scott35
