Chapter 9—Power quality

PowerLogic™ PM5100 series user guide

 

 

THD and thd calculations

The meter supports two methods of calculating total harmonic distortion: THD and thd.

THD is a quick measure of the total distortion present in a waveform and is the ratio of harmonic content to the fundamental. The meter uses the following equation to calculate THD:

HC

THD = -------- × 100

H1

Where H1 is equal to the fundamental harmonic.

thd is an alternate method for calculating total harmonic distortion. It uses the RMS value for the total harmonic content rather than the fundamental content. The meter uses the following equation to calculate thd:

thd =

HC

× 100

(H1)2 + (HC)2

TDD calculation

TDD (total demand distortion) evaluates the harmonic currents between an end user and a power source. The harmonic values are based on a point of common coupling (PCC), which is a common point where each user receives power from the power source. The meter uses the following equation to calculate TDD:

TDD = ( (HCIA)2 + (HCIB)2 + (HCIC)2 ) ⁄ (ILoad) × 100

Where ILoad is equal to the maximum demand load on the power system.

Displaying harmonics data

The meter displays the numeric magnitude and angle of the fundamental (first) harmonic.

Viewing harmonics using the front panel

You can view harmonics data using the front panel.

1.

Navigate to Harm. The Harmonics % screen displays, with the following menu

 

options:

 

 

 

Harmonics % display screens

 

 

 

 

 

 

 

 

IEEE mode

IEC mode

Description

 

 

 

 

 

 

 

V L-L

U

Line-to-line voltage harmonics data

 

 

 

 

 

 

 

V L-N

V

Line-to-neutral voltage harmonics data

 

 

 

 

 

 

 

Amps

I

Current harmonics data

 

 

 

 

 

 

 

TDD

TDD

Total demand distortion

 

 

 

 

 

2.

Press the voltage or current harmonics you want to view. The fundamental (1st)

 

harmonic’s numeric magnitudes and angles for all phases are displayed.

3.

Press 3-11or 7-15to view the graphs for the 3rd to 11th or 7th to 15th harmonics,

 

respectively. For example, to display the 7th to 15th harmonics screen, press 7-15.

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Schneider Electric PM5100 Displaying harmonics data, Viewing harmonics using the front panel, THD and thd calculations