00crashtest on 2023-10-30 13:04 UTC-7
According to the BSI World Electricity Supplies via Cummins Generator Technologies AGN 203 ISSUE B/1/5, you are right that 105/210 V is used in the 60 Hz region of Japan. However, that source suggests you are wrong that it is
the standard, because 100/200 V is also used in the same region. This means that 105/210 V is only
one (added now: of) the standards used in West Japan. On the other hand, East Japan uses only 100/200 V 50 Hz for single-phase services. I found the source below by using the key phrase
Japan three phase voltage in a search engine.
On that same document, ISSUE B/4/5 also says that both three phase line voltages and single-phase line voltages [in Japan nationwide] must be within 10% of their respective nominal values. Since 115 V is 15% above 100 V, it exceeds the 10% upper tolerance allowed for 100V, which means that 200Y/115.47 V is definitely not used anywhere in Japan for installations compliant to the current codes. Perhaps it may still be in use from legacy installations, but I could not find anything about it, even when using the key phrases of
200Y/115 volts Japan,
"200Y/115" volts Japan,
200/115 volts Japan,
"200/115 volts" Japan,
200Y/115.47 volts Japan,
"200Y/115.47" volts Japan,
200/115.47 volts Japan, and
"200/115.47" volts Japan. On that same page, the only examples of code-compliant new distribution-to-service transformer installations using a wye secondary provide 187.06Y/108, 190.53Y/110, and 190Y/109.70 volts respectively.
However, given that commercial and industrial properties that use three phase power do so because they require a lot of power (and consequently current), it would be incredibly stupid to lower the three-phase line voltage (and consequently increasing the current) when their purpose of using three phase is to be able to overall reduce conductor size (and consequently saving material and associated costs) and reduce line losses from I^2*R heating. So, the only way to be able to supply measured 200 V three phase, while also not exceeding the upper respective tolerance levels for 200 V split phase and 100 V single phase, from a single bank of transformers would be to use a high-leg delta or a corner-grounded delta with an ungrounded centre tap. However, I have never heard of the latter, so Japan probably uses only high-leg delta. Either the less efficient open delta or the recommended more efficient closed delta would suffice because both provide the same set of voltages. So, for three phase services, East Japan almost certainly uses only 100/200 V 50 Hz delta, while West Japan uses both 100/200 V 60 Hz delta and 105/210 V 60 Hz delta depending on the site.
