WorldWide Drilling Resource

73 WorldWide Drilling Resource ® DECEMBER 2013 DC Backup Power (UPS) that isn’t Monstrous in Size and Cost Part 2 by CJ Kirst Project Management Professional Conley Equipment Company Let’s review a few points from last month’s article. Uninterruptible power supply (UPS) systems are typically thought of as hav- ing short run times, long enough to cover the gap between utility AC power going out and the generator kicking in. How- ever, due to site locations, the UPS option can be overlooked as a longer run time option due to the concern for footprint requirements and cost. Large-scale power distribution centers (PDCs) include UPS technology. They are commonly designed with large battery banks, chargers, invert- ers, and switches, and are located within mobile PDC buildings or roll-off skids next to wellheads. The mechanics and parts are similar to the UPS box you may have under your desk, but on a much larger scale, both in cost and footprint. How- ever, there is a large amount of equipment that can be backed up for long UPS run times (24/28 hrs) without large expense and floor space. Now let’s look at some examples and budgets. Take for instance a 500 watt (=5 amps @ 120VAC) equipment load that needs to have a UPS backup of 48 hours. This can be achieved in a 2-foot by 2-foot foot- print and not higher than 72-84 inches tall. The battery backup is generated from four shelves of 12-volt (100-170 amp-hour) batteries. The batteries are kept on float charge in standby until they are required in a backup situation. The float charge comes from the primaryAC power source and is fed into a rectifier which charges the batteries as well as converts the AC current to DC. The charger/rectifier con- troller monitors and controls many things; charging demands, alarm notifications for high and low voltages either coming in from the primary AC power or the bat- tery voltages, battery capacities, temper- atures, etc. This controller is also designed to provide remote monitoring. If the pri- mary power has experienced an outage, the batteries are automatically called in to take over the demand the load is requir- ing by sending the DC power from the batteries to the inverter where this current is converted back to AC (in this case 120VAC nominal) and delivered to the load (equipment) without any gap between the power outage and the backup UPS. Overall, the costs can be kept near $10,000 for the entire system. As site de- mands are unique, this configuration can be designed for various specifications such as 208/240VAC “in” with 120VAC “out”, 120VAC “in” and 24VDC “out” to the load (equipment needing power), etc. The chassis for the batteries, rectifier/controller, inverter, and grounding are contained in a 23-inch wide relay rack secured at the top and bottomand designed for seismic zones. The next time you are tasked with backup power demands, consider UPS/ DC. There are many system integration companies that can provide a turnkey fully enclosed solution. CJ admin@ worldwidedrillingresource.com