I have a couple of questions about an existing system that I have encountered:
System consists of qty (3) 480VAC, 1125 KVA, continuous rated generators. Each generator feeds a piece of paralleling switchgear at the 480VAC level, which then feeds individual 480V:12.47kV wye-wye step-up transformers. This then feeds the common power distribution network at the 12.47kV level. Note: There is no common bus at the 480V level; the common point is at the 12.47kV level. Voltage is then dropped to 480V at various points in the facility using 12.47kV:480V wye-wye transformers.
My questions center around the grounding of this system and more specifically at the generators. The case of the generator is grounded (via a 4/0 wire) to a common ground ring. The neutral (100%) of the generator is brought to the neutral bus bar of the paralleling switchgear. The neutral bus bar of the paralleling switchgear is grounded (via a 4/0 wire) to the common ground ring through a current transformer (ground fault monitoring). The neutral was not brought out to the wye-wye step-up transformer. The star points on the wye-wye step-up transformers are grounded (via a 4/0 wire) to the common ground ring.
1) Should the neutral have been brought out to the star point of the wye-wye transformer – i.e. directly connected?
2) Is the only reason that this system works, due to the indirect connection between the paralleling switchgear neutral bus bar and the star point on the wye-wye transformer via the common ground ring? I am thinking that the zero-source current needs a path back to its source.
3) If the paralleling switchgear neutral bus bar and star point on the wye-wye transformer were not tied together via the common ground ring, would the entire power distribution system be ungrounded? I am thinking that the zero-source current would only have the earth to travel through (once it got back to the step-up transformers) to get back to the star point on the generator.
4) Is it ok to have both the direct connection between the generator and the wye-wye transformer via the neutral and the indirect connection via the ground ring? Or does this cause any issues?
At the end of the day, we are adding additional generator capacity to this system. I would like to ensure that it is done correctly and not necessarily match the existing setup.
Thanks in advance.
System consists of qty (3) 480VAC, 1125 KVA, continuous rated generators. Each generator feeds a piece of paralleling switchgear at the 480VAC level, which then feeds individual 480V:12.47kV wye-wye step-up transformers. This then feeds the common power distribution network at the 12.47kV level. Note: There is no common bus at the 480V level; the common point is at the 12.47kV level. Voltage is then dropped to 480V at various points in the facility using 12.47kV:480V wye-wye transformers.
My questions center around the grounding of this system and more specifically at the generators. The case of the generator is grounded (via a 4/0 wire) to a common ground ring. The neutral (100%) of the generator is brought to the neutral bus bar of the paralleling switchgear. The neutral bus bar of the paralleling switchgear is grounded (via a 4/0 wire) to the common ground ring through a current transformer (ground fault monitoring). The neutral was not brought out to the wye-wye step-up transformer. The star points on the wye-wye step-up transformers are grounded (via a 4/0 wire) to the common ground ring.
1) Should the neutral have been brought out to the star point of the wye-wye transformer – i.e. directly connected?
2) Is the only reason that this system works, due to the indirect connection between the paralleling switchgear neutral bus bar and the star point on the wye-wye transformer via the common ground ring? I am thinking that the zero-source current needs a path back to its source.
3) If the paralleling switchgear neutral bus bar and star point on the wye-wye transformer were not tied together via the common ground ring, would the entire power distribution system be ungrounded? I am thinking that the zero-source current would only have the earth to travel through (once it got back to the step-up transformers) to get back to the star point on the generator.
4) Is it ok to have both the direct connection between the generator and the wye-wye transformer via the neutral and the indirect connection via the ground ring? Or does this cause any issues?
At the end of the day, we are adding additional generator capacity to this system. I would like to ensure that it is done correctly and not necessarily match the existing setup.
Thanks in advance.
