As available real estate continues to diminish, and become more expensive, data center developers are embracing the reality that if you can’t build out, you must build up. Typically, building up is more expensive especially if you stay within the constraints of low voltage power distribution systems (480 Volts, typical). In an effort to help contain those costs, consideration should be made for shifting to a medium voltage power distribution system (i.e., 5kV to 69 kV, typical) solution that brings lower cost of implementation and maintenance, along with a more reliable and stable power source with less carbon emissions. That said, medium voltage power distribution in a multi-story data center is a complex undertaking which requires careful planning and attention to detail to ensure that power is delivered reliably and safely to the equipment. The following are some considerations when exploring this solution.
Medium voltage (MV) refers to the voltage range from 4,160 Volts (5 kV class) up to and including 69 kV.
Scenario Parameters:
· 2 or more story building
· 13,200 Volt (15 kV class) medium voltage power distribution
· Centralized electrical distribution system, with dual ended, main-tie-tie-main substations located on the floor adjacent to the data centers
Getting from 13,200 Volts to 480
MV power distribution in multi-story data centers use electrical switchgear and transformers to step down the incoming medium voltage power from the utility grid, and on-site power generation, to the appropriate voltage level (typically 480 Volts) required for the equipment. This involves the use of MV switchgear, distribution equipment and substations with step down transformers to distribute utility power, and on-site power generation in the event of a commercial power failure. At the utility, distribution automatically transfers between the services, and in the event of a total commercial power failure, transfers to on-site standby generators.
Substations should be placed close to the end user’s load to reduce installation and copper costs. The distribution costs are lower for large amounts of electrical power at higher voltages because a single 4” conduit can distribute up to 4,000 kW of electrical power at 13,200 Volts, whereas at 480 Volts, this will require up to 12x4” conduits (or busway) requiring significantly more copper, heat and complications.
Substations are positioned in a main-tie-tie-main arrangement with each side of the substation in physically separated rooms. Separate MV circuits are provided for each side of the substation as well as an independent MV generator supply and a primary cross tie between the substations.
These are just some of the design considerations that are important for a successful MV conversion.
Design it Safe
With the efficiencies and cost savings gained from using MV distribution systems, consideration must also be made for safety. Medium voltage power can be extremely dangerous, and it is important to take appropriate safety measures to protect people and equipment. The electrical system must be properly designed and installed to minimize the risk of electrical faults, which can be a significant safety hazard in a multi-story data center environment that utilizes medium voltage distribution. The safest way is to provide an electrical distribution system that allows for shutdown of each path of the electrical equipment to perform maintenance and operation of de-energized equipment (a concurrently maintainable system). In case of a power outage or failure, this may involve the use of backup generators and Uninterruptible Power Supply (UPS) systems to ensure that critical equipment remains powered and operational.
Additional safety precautions may involve using advanced monitoring and control systems to detect and isolate faults before they can cause damage or pose a risk to personnel. This can also include the use remote operators, such as a Human Machine Interface (HMI) located out of the arc flash zone to operate the distribution equipment, as well as remote operating equipment to safely rack-in and rack-out the breakers from safe distances. Additionally, the design should include the installation of safety features like automatic shutoffs in the event of an electrical fault.
Go With the Pros
Using experienced engineers who are well versed in medium voltage power distribution systems, and all of the unique characteristics and considerations for multi-story data centers, can be the key to realizing a beneficial shift to this solution. A solution that will provide construction cost savings while reducing maintenance requirements for long-term operations.
