TVSS Delta or Wye.

[pqsl]

Which TVSS is appropriate to use on 600/347V MCC?

Transformer feeding this MCC is has neutral solidly grounded at MCC. Neutral bus is not available to connect TVSS. Ground bus is available to connect TVSS.

1. Delta TVSS is connected to the above MCC. What are the advantages and disadvantages/problems. (Delta TVSS is designed for ungrounded systems).
2. Wye TVSS is connected to above MCC where Neutral and Ground wire are both connected to ground bus. What are the advantages and disadvantages/problems.

Thanks

 

[alehman]

You say the neutral is solidly grounded at the MCC, but it is not available? Why is that? If the MCC is the service point and the system is grounded wye, the neutral and ground are the same.

It is generally best to have surge protection phase-to-phase, phase-to-ground and phase-to-neutral. At the service, neutral and ground are the same, so phase-to-phase and phase-to-ground/neutral would be adequate.

1. This will provide protection for phase-to-phase transients only. Common-mode (phase-to-ground) will not be protected. Many transeints have common-mode components so this is less desirable.

2. Phase-to-ground protection only is better than phase-to-phase only.