Ac power measurement, Single phase system, Chapter 1 ac power measurement – GE EPM 5200 User Manual
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CHAPTER 1: AC POWER MEASUREMENT
GE Multilin EPM 5000 series Advanced Power Meters
1
CHAPTER 1
AC POWER MEASUREMENT
The economics of electric power distribution networking dictate several configurations of AC power
transmission. The number of phases and voltage levels characterize these configurations.
1.1: Single Phase System
A single phase system is a basic two-wire system used in low power distribution applications, such as
residential communities or offices. Typically, the voltage is 120V AC. For higher power requirements,
such as small commercial facilities, the typical power configuration is two lines of 120V AC opposite in
phase (see Figure 1.1 B, below).
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.
Line
Neutral
Line 2
Line 1
Neutral
A)
Single Phase
2 Wires
B)
Single Phase
3 Wires
Figure 1.1: Single Phase System: (A) Two-Wire, (B) Three-Wire
The power (W) in a single phase system is:
Θ
cos
•
I
•
E
=
W
E = potential, I = current, and cos
Θ = phase difference between the potential and the current.
Power in a 120/240V AC system is:
)
cos
•
I
•
(E
+
)
cos
•
I
•
(E
=
W
2
Line
2
Line
1
Line
1
Line
Θ
Θ
Phase differential between the potential and the current results from a non-resistive load, either reactive
or capacitive.
Reactive power (VAR): The additional power consumed that does not produce any work but must be
delivered to the load:
Θ
⋅
⋅
in
s
I
E
=
VAR
. This is a measure of the inefficiency of the electrical system.
Apparent power (VA): The total power delivered to the load, and the vector sum of real power and
reactive power.
Power Factor (PF): The ratio between real power and apparent power:
PF =
W
VA
W
W
VAR
2
2
=
+