Power Generation, Transmission, And Distribution; Generation And Transmission - Compaq 226824-001 - ProLiant - ML750 Basics Manual

Figure 2 shows the sine waves for a three-phase transmission. Figure 2 also shows how the three
phases can be delivered using a Wye transformer. At the distribution center the three-phase voltage
is stepped down to the required voltage and delivered to the local customers either as single-phase or
three-phase AC power. The voltage of each phase is represented by a sinusoidal wave that alternates
between positive and negative values at a frequency of 60 cycles per second (cps) or Hz, or at 50
Hz in many European countries.
Figure 2. Properties of three-phase AC power with transformer windings (Wye configurations)
Three-Phase Electrical Current
200/240V
-200/240V
1
Time
NOTE:
A glossary at the end of this paper provides definitions of these and other
electrical terms.

Power generation, transmission, and distribution

Before power can reach a data center or an individual server, it must be generated and transmitted.
The following sections discuss in general how each of those steps occurs. Specifics about electrical
power may vary from one region to another; therefore, the reader will want to consult sources
including the local electric utility for the specifics of each area.

Generation and transmission

Power is generated at different voltages and frequencies throughout the world. Power is normally
generated in the United States at voltage levels from 115kV to 765kV. Generation at voltage levels
from 345kV to 765kV is considered Extra High Voltage (EHV). Voltage levels from 115kV to 230kV
are considered High Voltage (HV). Transmission lines carry generation voltage levels from the
generating station to local substations (systems designed to switch power and change delivery
voltages) located throughout the country. Distribution voltage levels from 2400V to 69kV are
considered Medium Voltage (MV). Pole lines or distribution lines carry distribution voltage levels from
local substations to small industrial and commercial facilities. Utilization voltage levels from
120/240V or 120/208V to 600V are considered Low Voltage (LV).
With any type of public, commercial electric power generation, the voltage variations must be limited
to within plus or minus 5 percent, and frequency variations must be maintained within plus or minus 1
percent. The IT professional should be familiar with the location of the power generation station and
its distance from the data center. When the power plant or generating station is close to the data
center, reliability and dependability are generally excellent. With increased distance between the
generating station and the data center, reliability and dependability might decrease. Many
distribution areas use a grid distribution system, and multiple power plants and substations may be
involved in delivering power to the end user. Publicly regulated grids are managed by cooperative
Transformer Windings
2
Phase 1
Neutral
Phase 2
Phase 3
3