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Impedance grounded corner delta might give the result you saw if you were using a wiggy. I really don't understand all I know about those systems and I never actually saw one.
We do have some corner delta around here tho, usually in something like a lift station where the whole load is 3p L/L, basically just the motor and the controller.

I suspect that would be 400hz, which is very common in aerospace. I believe that it became a standard from about 1940s onwards, because it was the most efficient for weight/iron loss in transformers, long before power conversion electronics became available.
However, I've heard of 400hz gear in military naval roles, where weight presumably isn't an issue. I've wondered why.
The systems I worked with were always 200v 3 phase/115v to ground.

We used a lot of 400 hz in the big iron computer days. They either use big MG sets or the Liebert UPS inverters that produced 400 hz directly.

In the Navy they used 400 hz in servo systems to point guns. That was for the same reason. The magnetic elements could be smaller. You also got better precision.
Since it was available, other folks may have used it but I was in the pointing the gun business. That is all I know about.

On the aircraft carrier, we had 400 Hz systems for airplanes. It was my understanding that the Soviet aircraft used 300 Hz for same reasons. We typically ran the ships service generators at slightly over or under 60 Hz so the fifth harmonic did not overpower the passive SONAR systems listening for 300 Hz.

I was told that the 400Hz was chosen because it wasn't a harmonic of 60Hz AC. The Soviet is probably the same thing but calculated for 50Hz power.