This when was the dominant variety of UPS and is restricted to round the a hundred and fifty kVA array. These units are still mostly used in a few industrial settings (oil and gas, petrochemical, chemical, utility, and weighty marketplace markets) due to the strong mother nature with the UPS. https://taifudo-bodyguard82603.blogzet.com/uninterruptible-power-supply-for-pc-fundamentals-explained-48574283