Eaton Power Xpert PXM 4000, User And Installation Manual

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IM02601004E
Page 9
1 Introduction
The following equation defines the voltage levels between the phases:
Three-phase systems are distributed in different voltages, depending on load factors, which typi-
cally are:
• 208 VAC
• 480 VAC
• 2,400 VAC
• 4,160 VAC
• 6,900 VAC
• 13,800 VAC
POLY-PHASE
To measure power in a poly-phase system, one must apply Blondel’s Theorem. This states that in a
system having N conductors, N-1 properly connected meter elements will provide a measurement
of electrical power. Properly connected means that all potential coils must have a common tie to the
conductor to which there is no current coil. Typically, poly-phase systems are configured as either a
Delta or a Wye connection.
UNDERSTANDING POWER CONCEPTS
The following defines power consumption, demand, power factor, waveforms, and harmonics.
Consumption The total electrical energy used over a period of time. This is typically
measured in Wh (or more likely, kWh). It is defined by the following formula,
which utilities use to calculate power consumption within a specified billing
period (T). W in this equation is instantaneous power.
Wh=WXT
Demand The average energy consumed over a specified time period. Utilities deter -
mine exactly what that period of time is, and it’s typically either 15 or 30 min-
utes. This measurement deviates from average consumption, which forces
utilities to provide sufficient generating capacity to satisfy this measurement.
Power Factor A poor power factor, transferred over a distribution network, results in a loss
of energy. Utilities monitor this and penalize customers for poor power factor
in an effort to force them to improve their systems.
Waveforms Ideally, power distribution systems should exhibit sinusoidal waveforms
for both current and voltage. However, real-world applications have power
consuming devices that create distortions. Such distortions are harmonics of
the fundamental frequency. Harmonic distortion is something to avoid as it
poses a safety hazard, reduces the working life of distribution transformers,
and interferes with electronic equipment.
Some of the terms and concepts you’ll encounter in this manual are:
Sinusoidal Waveforms: This is defined by the following equation:
Distorted Waveforms: This is defined by the following: