Total Harmonic Distortion

arunsinha

Member

A

Join Date

Feb 2009

Location

Murrieta CA

Posts

20

• May 25, 2012

• #1

If I have a PLC and am getting inputs for 3 phase power of Voltage, Current, True Power, and Apparent Power...can I program using logic to calculate THD? I've looked up the formulas for THD for voltage and current, but don't know how I'd come up with the harmonics values...

 

Andy6

Member

A

Join Date

Apr 2011

Location

In the garage.

Posts

140

• May 25, 2012

• #2

Don't think so.
You need to measure each harmonic voltage, not line voltage, current, apparent or real power. You need a scope to measure the frequencies and thier values.

 

arunsinha

Member

OP

A

Join Date

Feb 2009

Location

Murrieta CA

Posts

20

• May 25, 2012

• #3

Thank You Andy.

 

Saffa

Member

S

Join Date

Feb 2012

Location

Bay of Plenty

Posts

1,468

• May 25, 2012

• #4

You can purchase power analysers that will provide THD. They're pretty pricy though, and if you've got existing instruments then i'm guessing you're not in a position to purchase new gear? If I had an application like this i'd probably look at using one of these via MODBUS - http://www.carrel-electrade.co.nz/multifunction.htm

 

arunsinha

Member

OP

A

Join Date

Feb 2009

Location

Murrieta CA

Posts

20

• May 25, 2012

• #5

Saffa,

Yep. I worked at Schneider Electric for many years and we had the PowerLogic. I've got a Satec on my desk right now. This client already has an Opto 22 PAC near the motors (there are actually motors) and wanted to try and do it with the controller and I/O modules. Thanks.