What is Uninterruptible power supply?
Uninterruptible Power Supply (UPS) or commonly called as UPS system or Uninterrupted Power Supply is a very critical component of power distribution system of data center. UPS system is a device which supply pure, safe and continuous power supply to your critical IT load of Server room. Basic question arises that why UPS is so important for Datacenter?. Answer is very simple. Power delivered from your utility grid is not steady and pure power always. May times it is with transient power fluctuations like Sag, Swell/Surge/Spike or even power outage. These fluctuations can damage IT equipment in Data center. Even if you have Generators to provided backup power, but still you have to face problems from transient power fluctuations. These fluctuations are beyond our controls a which can generated due to various reasons in utility grid. Hence we need to have device to protect IT equipment in Datacenter from these problems. UPS is solution for these all problems. With help of storage batteries, UPS system not only provide backup power but also it provides clean & safe power to your IT equipment.
UPS power backup can be designed for required backup time depending on criticality of data center services, frequency of power failure and availability plus capacity of other backup devices like Generator. UPS System are mainly of three types namely off line, line interactive and On line UPS based on how and when inverter gets on. Data center and Industrial Uninterruptible Power Supply are on line type only.
UPS Design Configurations for Data center.
Maximum availability of power is always desired by computer Data centers operation. To achieve highest uptime of power, we need ensure highest uptime of UPS System which can be achieve removing single point of failures and by building more redundancy. Hence multiple UPS connected in different configuration to achieve highest reliability and availability of power from it. There are basic three configurations namely Standalone (N), Hot standby and Parallel Redundant (N+1). It is desirable from UPS configuration that it should ensure highest availability of power, should allow to carry out concurrent maintenance of it's any components without transferring to utility power and minimize or remove single point of failure. lets discuss these UPS design configuration in details.
Standalone UPS Configuration
As name suggesting, single Uninterruptible Power Supply serving to 100% load of Data center. It is most common configuration used which has low cost and availability of power. In event of Fault in UPS system or absence of input power, UPS will transfer to battery mode. When battery backup completely drains, UPS will transfer in static bypass model and hence exposing to unsafe utility or generator power. This configuration consist of multiple points of failures. During regular maintenance of UPS or Batteries, datacenter needs shutdown for minimum 2 to 4 hour. Hence this is most undesirable configuration for critical datacenter. If Data center load is say 'X' Kva, then even if single unit of X' Kva capacity or two units of say 'X/2' capacity connected in parallel is standalone configuration.
Hotstandby UPS Configuration
This configuration of consists of two UPSs, Primary or Master UPS and Secondary or Slave or Standby UPS. Master UPS feeding to load, while input connected to utility/Generator Power through ATS. Static bypass of Mater UPS connected to Output of Slave UPS which also taking input from utility/Generator power through ATS. On event of fault in UPS or input failure, Master UPS will feed load from its battery. Once battery of Master UPS drains, It transferred to it's static bypass and hence supply power to load from battery of slave UPS. Advantage of this configuration is that it provide UPS fault tolerance, UPSs of different make or model can be use & cost is low. Major disadvantage is that, it's reliability is fully depend on reliability of static bypass of Master UPS & capacity of slave UPS to take sudden step load from Master UPS.
Parallel Redundant UPS Configuration
This configuration ensures highest availability of power for data center and minimize points of failures. In this configuration minimum two or more UPS of same capacity, make & models are connected in parallel mode. This means if two UPSs connected in parallel mode then both communicated to each other with help of Parallel kit installed in both UPS and connected by Data Cable. Input for both UPS is from same source while output connected to common parallel bus. During Normal condition or on input failure, each UPS shares 50% load. In event of fault in any one of UPS system other UPS take 100% load to ensure high availability of power. Also power capacity can be easily increase by connecting additional UPS unit in parallel. Major disadvantage is that all UPS need to be of ame make, model and capacity.
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