Dear Mr. Emadshaaban1987 (Electrical)(OP)
Can you take a picture of the name-plate? The connection ( for different voltage output) may be shown on the name-plate.
Che Kuan Yau (Singapore)

Dear Che
This is the name plat

• https://files.engineering.com/getfile.aspx?folder=0f5faec4-62b2-4d37-b524-c

That’s a single phase 120/240V generator.

" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

D ear Mr.Emadshaaban1987 (Electrical)(OP)4 Jun 22 17:26
"...A very old 37.5kva GM generator with Markon alternator. #1. It gives 3ph 220 volt with manual voltage regulator (external auto transform)....#2. I would like to convert the system to be 3ph 400v but the connection .... This is the name plat..".
#1. The name plate shows it is a Single-phase 120/240V alternator. I don't understand how can " it gives 3ph 220V with manual voltage regulator ....." .
#2. If you are having 3ph 220V but wish to be 3ph 400V, a simple way is to add a 3ph 220/400V step up transformer. Connect the 220V to the 220V input terminal. You get 400V on the output.
FYI: Usually we use step down transformer. This is the same transformer where the 220V is connected on the 220V terminal. You will get 400V on the 400V terminal. That is to say, any transformer can be a step up or a step down transformer.
Che Kuan Yau (Singapore)

If it's a 12 lead generator it can be wired as single phase or 3 phase, high voltage or low voltage configurations. If it's a 12 lead generator it should be able to provide 400V if wires in a high configuration.

Hi Emadshaaban1987,

As the other colleagues say, it is a Single-Phase generator. See attached file. These alternators won´t work with three-phase loads.

Best Regards

Petronila

• https://files.engineering.com/getfile.aspx?folder=3a41acbd-5fe7-4dd4-85a8-3

Nice info, petronila.

Muthu
www.edison.co.in

The reconnection strap area looks awfully three-phase-ish to me. It is hard to see from either of these photos. But in the reconnection area photo, the upper six terminals appear to be connected as a wye point, with three large neutrals leaving the box. The lower six appear to be the 3 active phases. So I would guess the nameplate had it connected as single phase originally, and somebody already reconnected it once, for 127/220Y from the appearances.