This when was the dominant style of UPS and is also restricted to across the 150 kVA vary. These units remain mainly used in some industrial configurations (oil and fuel, petrochemical, chemical, utility, and significant industry markets) a result of the sturdy nature on the UPS. Case in point #7 https://mapengineoptimize71470.total-blog.com/uninterruptible-power-supply-system-an-overview-59053338