Harmonic question

[tw/nci]

We recently attatched an analyzer to a dc power supply that supplys a PLC, the PLC controls conveyers in a power plant. We suspected that the power supply was dropping out. My question is in analyzing that data we had high harmonic levels in the 44th to 50th order, what would cause high harmonics in this area. Thanks in advance for your help

 

[StephenSDH]

Were you testing the incoming AC power to the DC power supply? Where you testing for Voltage Harmonics or Current Harmonics? What was the magnitude of the harmonics? You will always find harmonics, but generally the magnitudes are so small it doesn't mean anything.

 

[whalesurvivor]

harmonics

harmonics

Good question, I'll be interested to learn from others on your unique situation.

From what little i know, some data centers will oversize their neutral leg to help mitigate harmonics related to the high inductive load.

 

[mivey]

High harmonics in currents may not mean anything if there is very little current draw. Instead of just dividing the currents by the the fundamental to get a percentage (THD), divide it by the rated fundamental or historic peak fundamental to get the Total Demand Distortion (TDD).

You can take the THD percentage from the meter and multiply it by the percent of rated (or peak) current flow.

 

[jim dungar]

From what little i know, some data centers will oversize their neutral leg to help mitigate harmonics related to the high inductive load.

Over sized neutrals simply cope (live with) the harmonics, they do absolutely nothing to mitigate them or their effects.

 

[Besoeker]

We recently attatched an analyzer to a dc power supply that supplys a PLC, the PLC controls conveyers in a power plant. We suspected that the power supply was dropping out. My question is in analyzing that data we had high harmonic levels in the 44th to 50th order, what would cause high harmonics in this area.

Possibly the switching frequency if it is a switch-mode PSU.