3 phase generator question

inetdog

Re: 3 phase generator question

BB. wrote: »

I was unclear to me that the Transfer Switch could "switch" the Neutral's separately (usually all three "contacts" switch together)--So I don't expect any "fancy programming" issues.

For both 120/240 split phase (US) and 330Y/230 (three phase wye in much of the rest of the world) it is important to switch the neutral carefully if you are going to switch it at all.

Lifting the neutral while two or more of the phase conductors are still connected can cause up to twice the normal voltage to appear across single phase loads. For that reason a transfer switch which is "safe" for single phase loads will first interrupt the phase conductors on one input, then transfer the neutral to the other input, and only then connect the phase conductors from the second input. They may also have interlocks to prevent out of sequence transfers from happening even in the event of a malfunction.

lazza

Re: 3 phase generator question

Thanks for the replies

In response to Bill. I'm pretty sure Spain has TT type Neutral grounding. That is to say that the neutral is bonded to earth at the transformer station which is a mile down the road. You then have a separate PE cable in your house which is connected to a ground-rod (the voltage difference between the PE in my house today and the transformer ground-bonded Neutral is 6Vac). All RCD devices specifiy L and N separately and these days all breakers are bipolar, so there's no mistaking L for N (although in old systems they are single pole).

I wouldnt say the house requires a floating or grounded neutral (the installation is completely off-grid), I think they wouldnt care and the system would work the same. However, for safety reasons I prefer grounded neutrals as the RCDs are designed to work thus, and if the metal body of the kettle gets somehow connected to the L wire.. the RCD will trip in the case of a grounded N, but wont if N is floating. So I prefer the early warning system.

But what I really want to avoid is a switching system: When the generator is on, its floating; when the inverter is powering its N-grounded. A mess for any diagnostics.

I'm still not convinced with what they told me at Victron, because I'm pretty sure that the PE-N connected within the inverter is at the OUTPUT and not at the input. I have a friend with the same 5kVA inverter and generator backup. The only way I can clear this up is to go to his farm and do some Ground to Neutral voltage testing!

BB.

Re: 3 phase generator question

According to the Victron appendix, the AC input (Generator/utility) provides the Neutral to earth bonding.

In AC Inverter mode, the inverter provides the Neutral to PE grounding (assuming the PE Terminal is Earth Grounded at the home).

The transfer switch does the work.

-Bill