Chapter 2. APC hardware and software background 3
Chapter 2. APC hardware and software background
In the following chapters, we describe some UPS units that are important for
cluster solutions. All described UPS units are by American Power Conversion
(APC). You can also get the Smart UPS units as an IBM option.
For a correct sizing of the UPS capacity you need some background information
on power.
They are different power types in alternate current (AC):
• Real power
• Blind or reactive power
• Apparent power
Real power is the actual power dissipated by the load and is calculated as
follows:
Where:
P Real power
U RMS voltage
I RMS current
ϕ Phase angle (phi) between the current and voltage
However, with a purely resistive load, there is no phase shift between current and
voltage, hence cos(
ϕ)=1.
Blind power, or reactive power, is the power that swings between generator and
load without any work in the load.
Blind power comes into coexistence if there is a phase shift between current and
voltage.
Apparent power is the quadratic sum of real and blind power:
PUI ϕcos⋅⋅=
PUI⋅=
QUI ϕ
sin⋅⋅=
S
2
P
2
Q
2
+=
SP
2
Q+
2
=
Comments to this Manuals