The situation with the two setups for harmonic measurement was solved, and
the problem was quite simple ...
The resistance of the cables used with the watt meter was 0.25 ohms .
Enough to reduce the harmonics sufficiently.
Not using the appropriate cables was a basic mistake... but I am happy to
have learned another detail that makes difference in an EMC test.
Thanks for all that replied my mail.
Günter J. Maass
Researcher - Power Electronics Development
EMBRACO S.A.
"Robert Macy"
<[email protected]> To:
<[email protected]>, <[email protected]>
Sent by: cc:
owner-emc-pstc@majordo Subject: Re: Harmonics
measurement instrumentation
mo.ieee.org
22/01/02 18:06
Please respond to
"Robert Macy"
Hmmm...measured with a current meter, then measured with a wattmeter and
got
different answers....Harmonics out of phase? contain no power?
- Robert -
Robert A. Macy, PE [email protected]
408 286 3985 fx 408 297 9121
AJM International Electronics Consultants
619 North First St, San Jose, CA 95112
-----Original Message-----
From: [email protected] <[email protected]>
To: [email protected] <[email protected]>
List-Post: [email protected]
Date: Tuesday, January 22, 2002 11:56 AM
Subject: Harmonics measurement instrumentation
List
I would like your precious opinion about a situation regarding harmonic
current measurement (61000-3-2).
First case:
Using a sinusoidal AC power source, with a controlled output voltage
(almost perfect sine, voltage THD lower than the needed, even with load), I
measured the current harmonics using the internal instrument of the power
source.
The 13th and 15th harmonics were right above the limits (Class A limits).
Second case:
I add a digital wattimeter to measure the harmonics.
The harmonic content became 30% lower than the first case (good enough to
pass). And I got this results with the two instruments (the one inside the
power source, and the wattimeter).
My first thought was the increased impedance due to the wattimeter (Zm).
But I got 50mV of drop voltage in this instrument (peak voltage), that is
lower than the specified in 61000-3-2, Annex B (0,15Vpeak maximum).
And the impedance of its current shunt is only 0,008 ohms (data from its
manual).
This put my first guess down ! Theoretically, the wattimeter couldn't
attenuate so much the harmonics !
Any idea of what could be happening ?
Thank you again.
Günter J. Maass
Researcher - Power Electronics Development
EMBRACO S.A.
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