CCG Facilities Integration, A Morrison Hershfield Company

Innovating Mission Critical Systems

Research & Whitepapers

Direct Current Isolated‐Parallel UPS Systems


Authored by
Michael J. Mosman, PE
Vice President and Chief Technical Officer

e Isolated‐Parallel (“Iso‐Parallel” or “IP”) configuration for rotary diesel UPS systems debuted in 2006. The first installations were in wholesale data centers where several customers shared a common facility. Operators of these facilities face the problem of “stranded capacity.” The power demands of one customer might grow beyond the capacity of their allotted UPS while another customer used only a portion of their UPS, and there was no way to let the overloaded customer share the extra capacity of the lightly loaded customer without each being exposed to the faults or maintenance activities of the other.

Iso‐Parallel (IP) systems solved this problem. By connecting individual UPS systems to a common bus through fault isolating inductive reactors (“chokes”), power was allowed to flow from a lightly loaded system to an over‐demanding customer. The chokes presented little impedance to normal data center power flow, but exhibited high impedance to low power factor fault current flow. All UPS systems end up with identical power output regardless of individual customer demands, because all customer differences are leveled through the Iso‐Parallel Bus, and a fault on one system is isolated from all other systems by the natural action of the chokes.

To read the full whitepaper, please click Direct Current Isolated‐Parallel UPS Systems.pdf to download.