Electro Industries/GaugeTech Nexus 1250, Руководство по установке и эксплуатации

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Electro Industries/GaugeTech
Doc #: E107-7-06-121
1-1
Single Phase
2 Wires
Chapter 1 Chapter 1
Basic Tutorial on AC Power Measurement Basic Tutorial on AC Power Measurement
1.1: Single Phase Power Systems 1.1: Single Phase Power Systems
The economics of electric power distribution networking dictate several configurations of AC power
transmission. The number of phases and voltage levels characterize these configurations.
A single phase system is the basic, two-wire system used in low-power distribution applications, such as
residential communities and offices. The voltage is typically 120VAC. For higher power requirements,
such as small commercial facilities, the typical power configuration is two lines of 120VAC opposite in
phase. This system produces 120 volts from line-to-neutral for lighting and small appliance use. The
line-to-line voltage is 240V AC, used for higher loads such as water heaters, electric dryers, ranges and
machinery.
n
Power (W) in a single phase system is:
E = potential, I = current, and cos = phase difference between the potential and the current.
n Power (W) in a 120/240VAC system is:
Phase differential between the potential and the current results from a non-resistive load, either
reactive or capacitive.
n n Reactive power (VAR) is the additional power consumed that does not produce any work but must
be delivered to the load:
This is a measure of the inefficiency of the electrical system.
n n
Apparent power (VA) is the total power delivered to the load, and the vector sum of real power and
reactive power.
Single Phase
3 Wires
Neutral
Line
Line 1
Neutral
Line 2
Figure 1.1: Single Phase Power Systems
È
I E W cos
× × =
) cos ( ) cos (
2 2 1 1
Θ × × + Θ × × =
Line Line Line Line
I E I E W
Θ × × =
sin I E VAR
Courtesy of NationalSwitchgear.com