Uninterruptible Power Supplies (UPS) is designed to provide power protection in case of a power failure or disruption. However, specific applications are sensitive to downtime and require redundancy provided by the UPS as well as their related components. This article will discuss the basic UPS configuration options that offer the highest level of protection.
UPS design configurations
The following UPS design configurations are designed to offer higher levels of redundancy.
- Isolated redundant
- Distributed redundant
- Capacity or N design
- Parallel redundant
- System plus system
Even though N configuration is the most common type of Uninterruptible Power Supply, it does not have the capacity to cater to large data centers or organizations that cannot afford to have downtimes. For such enterprises, it is advisable to either opt for distributed redundant or system plus system. Let us now discuss each in detail.
Distributed redundant designs were crafted to provide complete redundancy at a reasonable cost as compared to buying several Uninterruptible Power Supply units.
The design utilizes up to three or more UPS modules with autonomous input and output feeders. The output buses use multiple PDUs to connect to the downstream critical load. In some cases, it also uses static transfer switches (STS).
An STS has two inputs and an output. It receives power from two different UPSs and feeds the load with conditioned power from one of them. In case of the failure experienced by primary UPS, the STS transfers the load to secondary UPS within 4-8 milliseconds. As such, it keeps the system running by providing power protection at all times.
While there are multiple options for configuring a distributed redundant design, they should allow for continuous maintenance and reduce single failure points. Configurations may also get complex, so it is necessary to ensure that the systems are loaded uniformly.
System Plus System
The system plus system model is a reliable design in the industry that is developed to avoid a situation where the load never runs on raw utility power. It goes by many other names such as multiple parallel bus, and double-ended or isolated parallel.
Similar to the distributed redundant model, several options exist for configuration with varying degrees of complexity regarding system plus system model. The fundamental idea is that each electrical equipment piece can fail or be turned off without the need for any critical load to be transferred to utility power.
This requires bypass circuits that make it possible to shut down sections of the system and bypass it to an alternate source of power. This helps in maintaining Uninterruptible Power Supply to all loads at all times. Simply put, the design offers two power paths to all critical loads and absolute redundancy from the entrance of the service, all the way to critical loads.
Needless to say, the system plus system design is the most expensive design due to a higher number of redundant components and its relative energy inefficiency. However, its cost is pretty reasonable as per the loads it protects. Indeed, many organizations across the world protect their critical loads with the help of this system.