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CHAPTER 1: AC POWER MEASUREMENT THREE-PHASE SYSTEM
EPM 5300 SERIES ADVANCED POWER METERS – INSTRUCTION MANUAL 1–3
1.2 Three-Phase System
A three-phase system delivers higher levels of power for industrial and commercial
applications; the three phases correspond to three potential lines. A 120° phase shift exists
between the three potential lines.
A typical configuration has either a Delta connection or a Wye connection (see Figure 1.3,
below).
In a three-phase system, the voltage levels between the phases and the neutral are
uniform and defined by:
FIGURE 1–3: Three-Phase System: (1) Delta, (2) Wye
Voltages between the phases vary depending on loading factors and the quality of
distribution transformers. The three-phase system is distributed in different voltage levels:
208V AC, 480V AC, 2400V AC, 4160V AC, 6900V AC, 13800V AC, and so on.
Power measurement in a poly phase system is governed by Blondel's Theorem. Blondel’s
Theorem states that in a power distribution network which has N conductors, the number
of measurement elements required to determine power is N-1. A typical configuration of
poly phase system has either a Delta connection or a Wye connection (see Figure 1.4,
below).
3
E
3
E
3
E
EEE
acbcab
cnbnan
=====
B
A
C
N
A
B
C
1) Delta
2) Wye