Schneider Electric 4000

Chapter 4—Metering Capabilities 63230-300-212

Power Analysis Values April 2001

The circuitmonitor provides a number of power analysis values thatcan be

usedto detect power quality problems, diagnosewir ingproblems, and more.

Tab l e 4–5 on page 68 summarizes the power analysis values.

•THD.Total Harmonic Distortion (THD) is a quick measure of the total

distortionpresent in a waveformand is the ratio of harmonic content to the

fundamental.It provides a general indication of the “quality”ofa

waveform.THD is calculated for both voltage and current. The circuit

monitor uses thefollowing equation to calculate THD where H is the

harmonic distortion:

•thd. An alternate method for calculatingTotal Harmonic Distortion, used

widelyin Europe. It considers the total harmonic currentand the total rms

content ratherthan fundamental content in the calculation. The circuit

monitor calculatesthd for both voltage and current. The circuit monitor

uses the followingequation to calculate thd where H is the harmonic

distortion:

•TDD. TotalDemand Distortion (TDD) is used toevaluate the harmonic

voltagesand currents between an end user and a power source. The

harmonic valuesare based on a point of common coupling (PCC), which

is a common point thateach user receives power from the power source.

Thefollowing equation is used to calculateTDD where Ihis the magnitude

of individualharmonic components, h is the harmonic order,and ILis the

maximum demandload current in register 3233:

•K-factor.K-factor is a simple numerical rating usedto specify

transformersfor nonlinear loads. The rating describes a transformer’s

ability to servenonlinear loads without exceeding rated temperaturer ise

limits.The higher the K-factor rating, the better the transformer’sability to

handle the harmonics.The circuit monitor uses the following equation to

calculateK-factor where Ihis harmonic current and h is the harmonic

order:

x100%

THD =

Total rms

x100%

thd =

K = h )

SUM I2

rms

SUM