A Connection Symbol - 3-phase, open-delta, grounded at the common point.
This file was derived from:
 IEEE 315-1975 (1993) 1.9.5.svg
IEEE 315 Transmission Path Symbols (75).svg
(in English) (1993)  315-1975 - IEEE Standard American National Standard Canadian Standard Graphic Symbols for Electrical and Electronics Diagrams (Including Reference Designation Letters), IEEE, p. 15  DOI:  10.1109/IEEESTD.1993.93397. ISBN:  0738109479.
Michel Bakni