In a grounded star or grounded wye connection, the neutral point of the bank is solidly grounded (earthed). This means that the neutral need not be insulated to the full system BIL level.
When one of the plates of an isolated capacitor is grounded, does the charge become zero on that plate or just the charge on the outer surface become zero? The charge on that plate becomes the same as the charge on Earth.
Do I need to connect a polarized capacitor to ground?
So for capacitors, if a capacitor is polarized (has a + and - node), then all you need is to make sure that the voltage at the + node is greater than or equal to the voltage at the - node. You do NOT have to connect the - node to ground. YOu still need a decent discharge path on that.
Regarding your original question about capacitors: "Ground" is an arbitrarily selected reference point that means 0V. ANY point in a circuit could be declared as the 0V "ground" point without affecting how it works. In general, absolute voltages never mean anything - all that matters is the voltage DIFFERENCE between the two terminals of a device.
Do absolute voltages really matter if a capacitor is polarized?
In general, absolute voltages never mean anything - all that matters is the voltage DIFFERENCE between the two terminals of a device. So for capacitors, if a capacitor is polarized (has a + and - node), then all you need is to make sure that the voltage at the + node is greater than or equal to the voltage at the - node.
Delta connection of capacitors requires two bushings. Since there is no connection to ground, the capacitor bank cannot be a 'sink' for any ground currents or zero sequence currents. Individual branch of the delta connected capacitor need to be protected against phase-phase short circuit by a current limiting fuse.
When a capacitor is being charged, negative charge is removed from one side of the capacitor and placed onto the other, leaving one side with a negative charge (-q) and the other side with a positive charge (+q). The net charge of the capacitor as a whole remains equal to zero.