Peter Panfil is Vice President Global Power Sales, Emerson Network Power. With more than 30 years of experience in embedded controls and power, he leads global market and product development for Emerson’s Liebert AC Power business.
Emerson’s Liebert AC Power
There are many options to consider in the area of data center power system design, and every choice has an impact on data center efficiency and availability. The data center is directly dependent on the critical power system, and a poorly designed system can result in unplanned downtime, excessive energy consumption and constrained growth.
When making choices, consider the UPS system configuration, UPS module design and efficiency options, and the design of the power distribution system.
Increase Utilization Rate to Improve Efficiency
Most businesses need to consider having some level of redundancy in their UPS system to mitigate the cost of downtime, eliminate single points of failure and provide for concurrent maintenance.
A concern often raised in discussions about redundancy is utilization rate. A 2N UPS system that has the highest availability unfortunately offers the lowest utilization. Each bus of a 2N system can only be loaded to 50 percent so that one bus can provide full load in the event the other bus is not available. Many business critical data centers use 40 percent as the peak loading factor on each bus in this configuration to allow for variations in IT power draw and provide a cushion for immediate expansion capability. Customers have expressed concern that they don’t trust all UPS suppliers to be able to support 100 percent load.
Find a UPS supplier you can trust whose UPS can provide full load across the range of high and low line conditions, temperature to 40C, blocked filter, fan failure and altitude. Potential cost savings to move utilization to 45 percent: $2k/yr
Don’t Gamble on Availability – Fault Isolation Matters
Transformers play a critical role in the power system by providing circuit isolation, localized neutral and grounding points for fault current return paths, and voltage transformation.
Removing the transformers can result in a smaller, lighter footprint that is well suited for installation in the row of racks. Removing the transformers also exposes the UPS system to faults that could reduce the availability or push the critical load over onto utility power more often.
One very common fault that has this effect is a DC ground fault. Shorting the positive or negative battery terminal to ground in a transformer based system results in an alarm, but the UPS continues to provide protected power. Shorting the positive or negative battery terminal to ground in a transformer-less architecture at best results in a transfer to bypass and the load exposed to unprotected power and at worst, drops the critical load.
One transformer-less UPS manufacturer even filmed the performance of their transformer-less UPS on a battery ground fault. The UPS output waveform went through severe gyrations, the UPS groaned, cables shook and the UPS transferred to bypass. That manufacturer touted this as robust performance.
Do you consider transferring to bypass during one of the most common UPS system faults robust? Don’t bet your career on it. Potential Cost Savings of increased availability: $505k per occurrence
Modern Transformer-Based Topologies + Advanced Energy Optimization = State of the Art Technology
There is the misperception that transformer-based UPS systems are “old technology”. This myth is spread for the most part by UPS manufacturers who only offer transformer-less UPS. Modern transformer-based UPS systems deploy the latest DSP-based controls and energy optimization features to offer the best availability for business-critical applications, and at efficiencies that meet or exceed transformer-less offerings.
One such energy optimization mode is Intelligent EcoMode, which provides the majority of the critical bus power through the continuous duty bypass. This technology keeps the inverter active and always ready to assume the load in the event of an outage — a dramatic improvement over energy optimization modes that do not keep the inverter active. These UPS systems that do not deploy the latest active inverter Intelligent Eco-Mode often have a notch in the output waveform going in and out of Eco-Mode. They have to perform an interrupted transfer to turn off the bypass before turning on the inverter. Notch in the output? Interrupted transfer? Gulp! Increased cost savings using Intelligent Eco-Mode: $20,350/yr.
Weigh Safety Risks and Hidden Costs of Alternative Distribution Voltages
480V 3-wire distribution is the norm in enterprise data centers. There has been a lot of discussion about going 400/230V 4-wire direct from the UPS to the server. While this configuration looks good on paper it has some significant limitations. Fault current can be much higher in these direct-to-the-server configurations. This poses an equipment and personnel risk. This configuration also strands capacity in the gear, requires higher ampacity buses and can increase wiring costs. Before going to this extreme consult with your data center trusted adviser to understand the costs and risks associated with this architecture. Potential Cost Savings using higher distribution voltages: $3,500/yr
Do Your Research
Due diligence on the latest UPS technology and efficiency optimization modes will help you choose improved critical power systems with the highest availability and new levels of utilization and efficiency.
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