First off, welcome aboard!
Let's see what we can do to answer these questions.
*** DISCLAIMER ***
First, if you open the the ground that goes to the Xo lug on the secondary side of a Delta-Wye transformer are some of the 120V devices at risk of receiving 208V?
Please Do Not Perform Any Alterations To Any Power Systems' Grounding Means As Described Below!!! The Examples Are Explanitory Only!!! Hazardous Conditions Apply Here!!!*** DISCLAIMER ***
If you are merely lifting the Grounding Electrode Conductor, but leaving everything else connected as "Normal", the system will continue to function normally.
The system is now an Ungrounded 3Ø 4 Wire Wye - only in the consept that there is no connection between the Power System (Secondary side of the Transformer) and the Earth.
It (the Secondary side) is still Bonded to the Metallic Enclosures - which will result in a short circuit condition between any given Line and the Bonded Metallic Equipment (Line-Ground Fault).
Along with this, the Voltage between L-G / L-N ("N" = Common Neutral) will remain "Somewhat Normal" - at least the L-N Voltage will be relatively stable
If the Common Neutral Conductors are detached at the "X0" Terminal, then things change a bit. The Loads are now in a Series connection scheme.
The L-N Loads (devices) will not see a full Voltage of 208, but will see a Voltage according to their individual Impedance.
The Loads with the higher Impedance will have a higher Voltage impressed across them, and the lower Impedance will have lower Voltages impressed acros them.
If the Loads' Impedances are equal, the Voltage Drop across each one will be equal - so they both will have 104 Volts impressed across them.
Refer to the following thread for additional information: Losing Neutral
Second, when the voltage to a motor increases does the current increase or decrease and if the voltage decreases does the opposite happen?
It depends on the type of Motor, the type of Load, and to what degree of increase / decrease is affecting things.
The effects are very different across these parameters - some Motors lose speed and do less work, others lose smoke and flames, but not much speed, still others will try to work harder but not succeed, and some will adjust Current Levels to keep the input KVA figure steady - but will only do so for a limited percentage of "offset" before things turn ugly!
This is the type of question which requires a specific Motor and output Load target type to be known, before an accurate answer may be given.
Edited to fix UBB linking syntax screw-up event
[This message has been edited by Scott35 (edited 12-01-2004).]