Generator Selection

The sole duty of the Data Center Physical Infrastructure is to provide a high business continuity environment for the IT devices hosted there. It provides this duty with high energy consumption. Under normal conditions, the cheapest energy source is the mains electricity to be delivered to the field.

The Data Center is not in a position to handle any failure, maintenance or interruption that may occur in the electrical network. Even an infrastructure at the lowest criticality (Tier) level requires an alternative energy source.

The generator is an important infrastructure system used as an alternative energy source. In cases where the mains energy is cheaper, generators only perform their first work and provide energy in the event of a mains outage. When the mains energy returns, they transfer the critical load to the network and switch to standby after a certain period of time.

The outage during this transition lasts for a time interval between seconds and minutes. Critical loads that are not resistant to even an energy outage during this period can spend this short period uninterruptedly with the use of an Uninterruptible Power Supply (UPS).

There is generally a huge misconception about the importance of the generator in the Data Center Infrastructure. Since generators are referred to as “alternative energy sources”, there is a perception that the main thing is grid energy.

Especially in infrastructures that will have Tier 3 and Tier 4 criticality levels, generators should be selected and configured as the “main source”. Any interruption in the network, including the interruption of this energy line for days or even weeks due to natural or human reasons, should not interrupt the Data Center Physical Infrastructure operation. This is only possible with generators or similar energy sources installed on site and under internal control.

Generators are systems that take up significant space. Due to the provision of high cooling air flow and the removal of fuel exhaust gas, the resulting high noise level and the need for physical security, their placement on site should be done carefully.

There are many elements to consider regarding the application of generators. If these elements are not taken into account, the targeted criticality level cannot be achieved and large investments may be wasted. The main ones are as follows:

Generators are in trouble with capacitive load. Therefore, this situation should be avoided in all kinds of operations. For example, in cases where the reactive power compensation system is used, precautions should be taken against the capacitive behavior of the IT load that will occur in the bypass state in places where the Blade server is used.

The generator gets its energy during its first start-up from the battery array. This system may need to be carefully designed and monitored.
Generators are very sensitive to the sudden inputs and outputs (step loads) of the load they feed and the electrical disturbances (harmonics) they create during normal operation. Poor selection and improper precautions may prevent the generators from starting.
They are used with Automatic Transfer Switch Systems to feed the load alternately with the grid energy. All smart system behaviors such as detection of grid outage, initial start-up of the generator and reaching the load-meeting state, synchronization of more than one generator if used in parallel, and error coordination are possible with well-designed automation.
The generally used nominal powers of generators are defined in the variable load chart based on building or facility loads. Data Center Infrastructure power requirement is not compatible with this type of definition. The selection should be made carefully.