Eaton Power Xpert PXM 4000, Руководство пользователя и инструкция по установке

Страница: 15 / 292

www.eaton.com
IM02601004E
Page 7
1 Introduction
1.5. AC Power Measurement Concepts Used in this Manual
There are three types of power systems we’ll discuss:
• Single-Phase
• Three-Phase
• Poly-Phase
SINGLE-PHASE
Single-Phase power distribution systems are two-wire systems used to supply 120 VAC
(measured from line-to-neutral). Such systems are typically used for lighting, heating, data
equipment, and small appliances. This configuration is usually found in residential and of -
fice environments. For higher loads, such as larger resistance heaters used in water heat -
ers, electric dryers, and the like, three-wire, single-phase systems are used that provide
240 VAC (measured from line-to-line).
Two and Three-Wire Single Phase Wiring
Line Neutral
Line 1 Neutral Line 2
Single-Phase Power Equations
The following equations provide the basis for calculating Power (W), Reactive Power
(VAR) and Apparent Power in single-phase systems. You’ll see these terms used through-
out the manual when discussing AC power measurement.
Power (W) within a two-wire, single-phase system is calculated as:
Where:
V is Potential
I is Current
cos is the phase difference between the Current and the Potential.
Power for a three-wire, single-phase system is calculated as: