CDCP Data Center Power Infrastructure 2

Question 1

What is the purpose of a static transfer switch (STS) in a data center power system?

Accepted Answer

To automatically transfer an IT load from one power source to another in less than a quarter cycle (4ms or less) without interruption

Answer

To gradually ramp up generator output to prevent voltage surges during startup

Answer

To isolate a faulty UPS module while the system remains on bypass

Answer

To convert single-phase power to three-phase power for high-density rack deployments

Question 2

What is the purpose of an isolation transformer in a data center power distribution system?

Accepted Answer

To electrically isolate equipment from the power distribution system, reduce common-mode noise, and provide a separately derived system for grounding

Answer

To step up utility voltage from 480V to 13.8kV for transmission within a large campus

Answer

To synchronize generator output frequency with the utility feed before transferring load

Answer

To prevent reverse current flow from UPS batteries back into the utility grid

Question 3

What does 'kVA' measure in the context of data center power systems, and how does it differ from kW?

Accepted Answer

kVA (kilovolt-amperes) measures apparent power including reactive components; kW measures real (active) power. The ratio kW/kVA is the power factor.

Answer

kVA measures power consumed by cooling equipment; kW measures power consumed by IT equipment.

Answer

kVA is used for three-phase circuits; kW is used for single-phase circuits.

Answer

kVA includes transmission line losses; kW is the net power delivered to equipment.

Question 4

In a 2N UPS configuration, how is the IT load typically distributed between the two UPS systems during normal operation?

Accepted Answer

Each UPS carries 50% of the total IT load, so each operates at 50% capacity and either can support 100% of the load alone if the other fails

Answer

One UPS carries 100% of the load (primary) while the second is in hot standby (backup) at 0% load

Answer

Each UPS carries its assigned half of the racks; there is no cross-connection between the two systems

Answer

The load is dynamically balanced by a load-sharing controller to equalize battery wear

Question 5

What is the function of a power distribution unit (PDU) in a data center?

Accepted Answer

To receive high-voltage power from UPS or transformers and distribute it to individual racks at the appropriate voltage and with circuit protection

Answer

To convert DC battery power to AC for server use during utility outages

Answer

To monitor server power consumption and report data to DCIM software

Answer

To provide automatic voltage regulation (AVR) for sensitive laboratory equipment

Question 6

What is the typical battery runtime design target for data center UPS systems, and why isn't it designed for longer runtimes?

Accepted Answer

10–15 minutes — long enough for generators to start, transfer to load, and stabilize; longer battery runtimes are expensive, heavy, and unnecessary if generators are on-site

Answer

4 hours — to bridge all maintenance windows during business hours without starting generators

Answer

72 hours — to provide full operation during extended grid outages without generators

Answer

30 seconds — only needed to provide a clean shutdown signal to servers before power loss