Measuring the rectifier output voltage

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I my plant we have a rectifier for electrolytic cleaning. 7500A and
30V(Max). We give the reference for current. The problem is when we
measure the current through out PLC analog channel we find it
fluctuating. The current waveform exactly follows the voltage
waveform. The configuration is 2 half wave 3-phase rectifiers working
in paralle through the interphase transformer. Should I add something
to get an steady feedback. I suspect the fluctuation has to do with
the scanning of the AI channel of the PLC. we should send the coltage
as DC without harmonics rather than the way it is now.

 

[legg]

I my plant we have a rectifier for electrolytic cleaning. 7500A and
30V(Max). We give the reference for current. The problem is when we
measure the current through out PLC analog channel we find it
fluctuating. The current waveform exactly follows the voltage
waveform. The configuration is 2 half wave 3-phase rectifiers working
in paralle through the interphase transformer. Should I add something
to get an steady feedback. I suspect the fluctuation has to do with
the scanning of the AI channel of the PLC. we should send the coltage
as DC without harmonics rather than the way it is now.

Filter the measurement or synchronize it to the phase period.

RL

 

[Mark]

I my plant we have a rectifier for electrolytic cleaning. 7500A  and
30V(Max). We give the reference for current. The problem is when we
measure the current through out PLC analog channel we find it
fluctuating. The current waveform exactly follows the voltage
waveform. The configuration is 2 half wave 3-phase rectifiers working
in paralle through the interphase transformer. Should I add something
to get an steady feedback. I suspect the fluctuation has to do with
the scanning of the AI channel of the PLC. we should send the coltage
as DC without harmonics rather than the way it is now.

Does the "rectifier" have any filtering?

If not, what you are seeing is correct.

The current waveform will follow the voltage waveform.

But for your application, it probably doesn't matter, what counts is
the AVERAGE current. So you can read the average current with a meter
or matematically figure the average current value of your waveform.

Mark

 

[Spehro Pefhany]

I my plant we have a rectifier for electrolytic cleaning. 7500A and
30V(Max). We give the reference for current. The problem is when we
measure the current through out PLC analog channel we find it
fluctuating. The current waveform exactly follows the voltage
waveform. The configuration is 2 half wave 3-phase rectifiers working
in paralle through the interphase transformer. Should I add something
to get an steady feedback. I suspect the fluctuation has to do with
the scanning of the AI channel of the PLC. we should send the coltage
as DC without harmonics rather than the way it is now.

What is the output of your current sensor? If it's something like
0-10V you may be able to add a simple low-pass filter to give you
average current, and, if necessary, fiddle the value a bit to get it
to agree with the instrumentation on your baths. If it's a 5A CT you
may have to add signal conditioning ahead of the PLC analog inputs.

Best regards,
Spehro Pefhany