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Critical Power Group - Design, Installation and Support of Mission Critical Power Systems (UPS, TVSS, PDU and more). Virginia VA, Maryland MD, Washington DC
Issue 26: Will a Transformerless UPS Work for Your Data Center? May 2013

IGBTs and the Transformerless UPS

In the past, virtually all UPSs were designed with transformers. But then things changed with the Insulated-Gate Bipolar Transistor (IGBT) which is the core technology of the transformerless UPS. This got rid of bulky transformers and large iron-core output filters.

Mid-1990s is when transformerless designs started appearing in smaller UPSes. By the eyar 2000, this was the mainstream design. The newer systems use IGBT for more efficient AC to DC input conversions. This granted the DC bus and the inverter the ability to hold the output voltage steady over a broader range of input voltage and frequency variations without using the batteries.

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Transformerless vs. Transformer-Based: What's More Effective?

Transformers reducing energy efficiency is one argument that is in favour of the transformerless system. Older transformers lost 2-3%, however since the introduction of the TP-1 rated transformer, this has improved to 1.5-2%.

It would seem efficiency is still second to reliability and availability. Sometimes it comes down to personal preference. The choice is often made by the specifying engineer or who makes the final decision on the purchase. Then there is the factor of manufacturer loyalty.

This leaves us with the million dollar question: Are there any solid differences or benefits between the two designs?

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The Rise of the Transformerless UPS

These two different types of systems are significantly different in size, weight and cost.

Without a transformer, the size of the UPS has changed significantly which meant the UPS could fit within the limited spaces of small data centers. Also, a large drop in price for the UPS allowed for it to fit in to many budgets for various modular redundant designs. The reliability and availability issue can now be overcome.

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The Advantages of a Transformer-Based System

Let's not count transformer-based UPSs out. Whether the transformer is contained in the UPS or located along the stream form the UPS, transformers are inherently part of many power systems.

They have greater tolerance to phase imbalance from single phase loads (in which these imbalances overload the UPS) than their transformerless counterparts. Not only that, but transformers can limit the instantaneous over-current from a circuit fault. They also help mitigate harmonics caused by a less-than-perfect sine wave from the inverter output and also by the non-linear loads cause by the IT equipment's switching power supply. An input transformer will help to limit the energy intensity of some spikes and surges to the UPS.

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The Market Will Decide

In the end, customer demand will guide which direction vendors will move. As long as there is demand for transformer-based UPSs, manufacturers will continue building them.. Eventually transformerless UPSs will will have established a record of reliability and when that time comes, the market will decide which type of UPS will be the favoured choice. They will continue to grow their market unless a rash of failures shows up in the transformerless UPSs.

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Download for More Information

To read the complete article, download the Will a Transformerless UPS Work for Your Data Center document, which this letter is about, from the Critical Power Group website.

Critical Power Group is the leading provider of Uninterruptible Power Supplies.

For complete information about Uninterruptible Power Supplies and how they can benefit you, visit our Uninterruptible Power Supplies page on our website or call CPG for cut sheets, consultation and design ideas now at 703.443.1717.

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In This Issue

- IGBTs and the Transformerless UPS
- Transformerless vs. Transformer-Based: What's More Effective?
- The Rise of the Transformerless UPS
- The Advantages of a Transformer-Based System
- The Market Will Decide
- Download for More Information

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