The “Power” of PDUs

By Evan Owen, Global Product Manager, Static Transfer Switches, Power Distribution Units and Magnetics, PDI (Power Distribution Incorporated)


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Figure 1. PDI 50 kVA PDU in Data Center — built in 2002 (Photo credit: Hurricane Electric)

Consider this -- the United States began its power grid construction in the late 1880s and today, it is responsible for delivering electricity to more than 144 million end users throughout the nation. There are seemingly endless points of failure when you consider there are over 450,000 miles of high-voltage transmission lines, distribution systems and power management systems being fed by more than 5,800 major power plants. For so many data center operators it's not a question of will the power fail? It's a question of when will the power fail?

Exacerbating the problem of our aging grid is the integrity of the power systems contained within the data center. Precedent has been set for power failures inside the data center. These failures scale from merely being a nuisance to critical outages that affect global operations. Case-in-point:

  • In July 2013, the headquarters of Shaw Communications, one of Canada's largest telcos, experienced a significant power outage that wreaked havoc on the entire city, affecting everything from hospital surgeries to an IBM Data Center. This power failure was determined to be an explosion of a transformer within the building.
  • In September 2015, the Japanese conglomerate of Fujitsu located in Silicon Valley, experienced a power outage that impacted services including the Fujitsu TPS5 public cloud, the Fujitsu private hosted cloud as well as other services. The cause of this issue was determined to be the power transmission equipment.
  • Most recently, in May 2017, British Airways cancelled more than 400 flights and stranded 75,000 passengers because an engineer had disconnected a power supply at the airlines’ data center located near London's Heathrow Airport. This human error caused a power surge, which according to the Press Association, "Resulted in the total immediate loss of power to the facility, bypassing the backup generators and batteries. It was turned back on in an unplanned and uncontrolled fashion, which created physical damage to the system."

From the aging components of our power grid to human error, there is a constant assault on every data center’s energy flow. The good news is that there are methods to mitigate these risks when upgrading or designing data centers and it takes the form of more innovative and intelligent Power Distribution Units (PDUs).

When power from the grid enters any mission-critical facility, it typically needs some form of voltage transformation. In order to accomplish this transformation there are a number of elements that must be carefully considered such as voltages, current, harmonics and other power factors. The end game is to combine high-efficiency technologies with cost minimizing designs. These considerations will help to increase reliability and uptime as well as protect equipment against low frequency interference.

Facility managers also need to consider various transformers. Low voltage transformers are good for energy efficiency and cost savings, delivered through lower heat generation. It’s important to note that any low voltage transformer should always safely isolate the distribution system from hazards of harmonics and power disturbances and engineered to meet DOE2016 efficiency ratings.

Aside from these considerations, floor mounted PDUs must also be given proper consideration because they provide that all-important lifeline-bridge between a building’s primary power and the various equipment racks within the data center.

Today’s most innovative PDUs are also designed to minimize the floor footprint, allowing for more revenue-generating server racks. The PowerPak2 PDU from PDI is a good example that accommodates up to a 400kVA DOE2016 high efficiency transformer and a cabinet size of only 40” deep by 42” width.

Figure 2. PDI PowerPak2 – PDI PowerPak2 PDU is the market’s smallest power distribution unit, with hundreds of possible distribution configurations, and true front accessibility.

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Figure 2. PDI PowerPak2 – PDI PowerPak2 PDU is the market’s smallest power distribution unit, with hundreds of possible distribution configurations, and true front accessibility.

But the PDU innovations do not stop at smaller footprints. They also include new safety enhancements, such as power compartmentalization to simplify maintenance and increase safety of operators. A higher degree of safety is achieved by isolating the controls and high-voltage compartments within the main cabinet. Compartmentalized components include high-voltage input breakers and panel boards as well as controls and logic printed circuit boards and displays.

When considering innovative PDUs, data center managers should consider these features:

  • Flexibledistribution options for multiple distribution panel board and sub feed options -- in-cabinet and in optional sidecars.
  • Adaptable service entrances with top/bottom entry/exit configurations.
  • Manual dual with keyed interlocks allowing for a “make before break” transition of power.
  • Front access infrared scanning of bolted line and load connections for easy preventative maintenance.
  • Air containment skirts to provide back-pressure for HVAC systems when installed on a raised floor.

No Sweat Heat and Cooling

And it goes without saying that these mission-critical PDUs must go through rigorous stress testing that would make any car manufacturer proud. To ensure a PDU’s operational integrity, the PDU transformer is heat tested to find the steady maximum temperature reached by the windings, when fully loaded at the kVA rating. The steady maximum temperature should be less than the specified temperature, which the insulation can safely withstand.

The PDU enclosure also undergoes convection-cooling testing.  This form of testing is needed because the transformer and electronic components are increasingly designed into smaller and smaller footprints, which makes it more difficult to dissipate the heat.  There is also the trend to run data centers at higher ambient temperatures and must be taken into account when testing the cooling efficiency of the enclosure. Just like any other piece of critical equipment, a PDU’s cooling should be considered early in the design process to help in adequately dealing with heat dissipation.

If cooling is implemented poorly, the power required to cool a data center can match or exceed the power used to run the IT equipment itself. A good resource to check is the ASHRAE TC9.9 thermal guidelines:ASHRAE TC9.9 Data Center Power Equipment Thermal Guidelines and Best Practices.

PDU Management - More Stakeholders/More Visibility

Perhaps, one of the most innovative PDU features is really one of the most vital pieces to running any type of power unit or IT device -- the ability to share data. Intelligent PDUs offer greater insights into the entire power-management chain, providing vital information that can impact the facility’s uptime.

In fact, the value of data is changing and intelligent PDUs are in lockstep with this metamorphosis. These intelligent devices can help optimize the facility by determining:

  • How much total power is being used?
  • Where do I have stranded power?
  • Is it possible to predict power failures?

Imagine the questions that can be easily and accurately answered when a holistic view of the entire power chain is achieved.

In the age of Internet-of-Things, all critical power-chain components can no longer contain silos of information, but must share data among an ever-increasing amount of stakeholders. It is no longer solely the domain of the facility manager to be monitoring the data center’s power performance. Sure, IT personnel have always had an interest within power data in order to perform asset management, but now the CFO is requesting this information as well as the CEO in order to make more informed business decisions. 

Given all the aforementioned PDU value traits to mission-critical facilities, it's evident that these devices were never “dumb,” they were just silent as they harbored information waiting for an organization to give them a voice and unlock their value potential. No longer should there be a black hole in the power chain, nor should the facilities manager walk the floor to manually collect data and enter it into an Excel spreadsheet. PDUs can now share their information with Building Management Systems (BMS) and even Data Center Infrastructure Management (DCIM) platforms in the same manner as “smart” switches and routers have been sharing their data for decades. So, don’t overlook PDUs, they are a vital component of your data center for monitoring, optimizing and reducing operational expenses.


PDI (Power Distribution Incorporated)