Electrical distribution design is based on three basic parameters – current, short-circuit current, and voltage. The, cost of the equipment, the size of conductors, and the type of equipment are all influenced by these three parameters.
Enhancement of electrical distribution means designing an electrical architecture that uses the most productive equipment at the right place. For a cost effective solution, it is recommended to use the standard equipment with basic performance levels that prevents you from using expensive products suitable for certain niche applications and end up churning out lower production volumes.
Medium Voltage Distribution Optimization for Large Data Centers
When it comes to design optimization, it should ideally start with the medium voltage portion (MV) which is one of the most variable parts of the large data center design. For this purpose, it is important to consider two factors:
- Connection to utility medium voltage distribution
- Medium/large sites directly connected at the grid level: The voltage and short-circuit currents are determined by the distribution grid. Usually, the utility company has already executed a design with low-level currents in order to make their own equipment cost efficient.
- Large and extra sites connected via large power transformer to HV transmission: You can choose medium voltage levels and short circuit impedance in this case. Doing so will allow you to avoid exceeding 2500A for primary electrical distribution. Additionally, it is also possible to tweak the transformer short-circuit impedance which is usually around 11% for 20 to 40 MVA range transformers. It can also be easily designed to up to 17% without adding an extra cost and subsequent power losses.
- Configuration of Backup Set Generator
- Decentralized generators: These are usually positioned at the low voltage level. In that case, the MV distribution is not crucial for site availability. If a site is connected to high voltage transmission grid, then it is advisable to maintain the same MV voltage level as the local electrical distribution grid. Additionally, the short-circuit current should be kept under 20kA and the switchgear at <630A. Doing so will help you use a simple switchgear.
- Centralized MV backup generator power plant: In case of centralized MV generator, the MV distribution will become crucial for the site availability. More often than not, it means there will be complex control and protection mechanisms that would require sophisticated functionalities that are not available with basic switchgear variants. Therefore, the optimized short-circuit current rating will be higher than <25kA to also keep the cable size in check. The crucial thing when using generators is to ensure that the gensets are running parallelly and to check the short-circuit peak current. In most cases, these are the major concerns for generator application.
LV Distribution Design for Large Data Center Applications
For designing the low voltage distribution portion, the MV/LV transformer short-circuit impedance and its power rating will be the determining aspects to ensure that you get the required performance level.
Using large transformers will allow you to limit the use of LV power trains and also reduce the cost of MV electrical distribution. However, you will also be required to use ACBs, also known as double-pole circuit breakers, and double busbars in the main LV switchboard. But it is important to note that this design can drive up the cost in the IT room distribution due to high short-circuit current in the LV IT distribution.
To size a breaker appropriately, you will be required to calculate the potential short-circuit below the MCB and use the selectivity enhanced by tables, given by circuit breaker manufacturers. Each design requirement and design needs must be adapted to the unique needs of a facility. Therefore, you must use the services of a reputed professional to provide suitable solutions. It ensures both quality and safety!