Uninterruptible power supply (UPS) is one of the most important component of efficient data center. UPS acts as barrier to protect your important IT equipment installed in server room from power impurities. Prime jobs of UPS is to supply power and offer power backup to load whenever required without interrupting loads. Power we get from grid consists of lots of impurities like sag, swell, harmonics, over voltages, spike etc. IT servers are very sensitive towards these impurities. If IT load directly subject to this raw power then there will be high chances of failure of server and in some cases it can burn also due to high voltages. UPS in data center removes all these impurities and delivers pure power to your servers. Second and most important job of UPS is of power backup. UPS connected to battery bank which store power during normal operation. But when there is power supply fails from grid, then a online UPS supply power to load from batteries without any interruption. Transfer of power source to grid to batteries takes place without any delay. Even if there is generator with auto start facility, it will take few minutes to start and during this delay UPS takes care of your IT load.
Components of Uninterruptible Power Supply (UPS).
For Server room and datacenters only online configuration of UPS is recommended. A online UPS system consists of rectifier, inverter, battery bank, static bypass and manual bypass. Function of these parts are as below:
- Rectifier : Rectifier receives AC power from input source and converts it to DC power to give input to inverter and to charge battery bank.
- Battery Bank: Main function of battery bank is to store power during normal condition and discharge whenever required. With online UPS generally sealed maintenance free lead acid batteries or Nickel Cadmium batteries are used.
- Static Bypass: It also called as automatic bypass. If there is fault in UPS then input power source transfers to static bypass without any break.
- Manual Bypass: It is also called as maintenance bypass. It is use when user like to repair or do maintenance of UPS.
- Inverter : Job of inverter to convert DC power received from rectifier or batteries to AC. It works on Pulse width modulation (PWM) method to deliver required voltage and frequency at output of UPS.
How Data center UPS works?
To understand working of UPS, we need to consider following its following three working modes.
- Normal Mode of operation: In this mode UPS receiving power from mains which has voltage and frequency within input window for which UPS is designed for. During normal mode of operation rectifier converts AC power to DC and supply to inverter and batteries for charging. Inverter will deliver output by converting DC power to AC with help of PWM method.
- Battery Mode of operation: UPS will transfer on batteries if there is input power failure or input power voltage is out of input window or input frequency is out of input window or both voltage and frequency out of input window or there is fault on rectifier side. In such condition inverter start drawing power from batteries without any delay and deliver power to load. When battery get drained then UPS will transfer on static bypass.
- Bypass mode: Unit will transfer on static bypass if there is fault in UPS or power supply failure from grid and battery got drained. In such situation UPS will supply power through bypass as long as voltage and frequency in set limit.
Configuration of Server room UPS.
To achieve high power availability, UPS can be connected in different configuration. Even if datacenter is powered by single UPS even though your server room equipment expose to interruption if there fault occurs in that single UPS. Hence there is facility to connect unit in parallel redundant configuration. In this configuration two or up to eight units can be connecting in parallel, sharing equal load hence creating redundancy. We will discuss data center UPS parallel redundant configuration in detail in coming articles.
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