Rectifier configuration Harmonics
Rectifier configuration Harmonics
(OP)
This appliction is two 110 KW, 480 volt three phase rectifiers feeding an electrolysis system.
One rectifier consists of an iso transformer with a double star output with a diode in each output. (6 diodes)
It has a delta primary winding but with back to back SCRs in each line (full wave bridge type)
The second one has identical secondary design but with a primary wye and the same SCR configuration on the primary.
The rectifiers will operate mostly at full load.
If there were NO SCR's the units can be operated togehter and the harmonic spectrum would act as a 12 pulse.
If the rectifiers are being operated at a light load, then I would expect that since the input is a bridge SCR type the combination would behave as a 6 pulse?
If both are operted at full load and the SCR's fully turned on, then I would expect the combination to have a harmonic line spectrum somehwere between a 6 and a 12 pulse? Or maybe more like a 12 pulse?
Any comments?
thank JIM
One rectifier consists of an iso transformer with a double star output with a diode in each output. (6 diodes)
It has a delta primary winding but with back to back SCRs in each line (full wave bridge type)
The second one has identical secondary design but with a primary wye and the same SCR configuration on the primary.
The rectifiers will operate mostly at full load.
If there were NO SCR's the units can be operated togehter and the harmonic spectrum would act as a 12 pulse.
If the rectifiers are being operated at a light load, then I would expect that since the input is a bridge SCR type the combination would behave as a 6 pulse?
If both are operted at full load and the SCR's fully turned on, then I would expect the combination to have a harmonic line spectrum somehwere between a 6 and a 12 pulse? Or maybe more like a 12 pulse?
Any comments?
thank JIM






RE: Rectifier configuration Harmonics
RE: Rectifier configuration Harmonics
The SCR controllers will produce more harmonics as they are phased back or as the voltage is lowered. They will act somewhat like 6-pulse rectifiers when doing this but have no effect when full-on.
RE: Rectifier configuration Harmonics
On the last sentence do you mean that "this but have no effect when full-on." when full on and with one tranformer high side wye and the other delta the combination will then act as a 12 pulse?
Thanks JIM
RE: Rectifier configuration Harmonics
"The SCR controllers will produce more harmonics as they are phased back or as the voltage is lowered. They will act somewhat like 6-pulse rectifiers when doing this but have no effect when full-on."
Do you mean that when full on the two rectifiers (one with primary delta and one with primary wye) toghether will produce a harmonic line spectrum similar to a 12 pulse?
Thank you
JIM
RE: Rectifier configuration Harmonics
I do not see how you get a 30 degree shift from T1 to T2. Can someone explain, it looks to me like a 90 degree shift
RE: Rectifier configuration Harmonics
I might have misread the question. You have 2 transformers.
#1 - Y primary, 2 x Y secondary
#2 - Delta primary, 2 x Y secondary
correct?
Each transformer is powering it's own rectifier with 6 diodes in the rectifier, correct? If so, this is a 6-pulse design.
The primary winding changes from Y to delta between the 2 rectifiers to give the equivalent of a 12-pulse design on the power system as long as both rectifiers are operating at the same current.
The SCR controller will produce harmonics similar to a 6-pulse rectifier as it is phased back. Since it is driving a 6-pulse rectifier there's likely no big difference phasing back or not.
RE: Rectifier configuration Harmonics
Copying excerpts from your note and my answers in CAPS:
"Does the negative connection go back to the Y points of the transformer?" YES SCHEMATIC IS HARD TO READ BUT LOOKS LIKE DC OUTPUT IS FROM DIODES CONNECTION TO THE NEUTRAL
"I might have misread the question. You have 2 transformers.
#1 - Y primary, 2 x Y secondary
#2 - Delta primary, 2 x Y secondary
correct?" YES
"Each transformer is powering it's own rectifier with 6 diodes in the rectifier, correct? If so, this is a 6-pulse design." YES AND YES AGREE
"The primary winding changes from Y to delta between the 2 rectifiers to give the equivalent of a 12-pulse design on the power system as long as both rectifiers are operating at the same current." AND IF THEY ARE OPERATING WITH THE PRIMARY SCR ABOUT FULLY ON BUT AS THEY ARE PHASED BACK (LOWERING OUTPUT) SINCE THERE ARE SCR ON THE PRIMARY, THE COMBINATION OF THE TWO ACT MORE LIKE A 6 PULSE COLLECTIVELY I BELIEVE ?
MOREOVER, AT ABOUT AT AROUND 3/4 LOAD ON BOTH, THE COMBINATION WILL BE PRODUCING A HARMONIC SPECTRUM BETWEEN THE 12 PULSE AND 6 PULSE.?
IF THERE WERE NO SCR ON PRIMARY AND ONLY DIODES ON SECONDARY THEN COMBINATION OF THE TWO WOULD ALWAYS BE AS A 12 PULSE BUT IT WILL BE FULLY ON ANYWAY. I THINK WE AGREE.
"The SCR controller will produce harmonics similar to a 6-pulse rectifier as it is phased back." AGREE
"Since it is driving a 6-pulse rectifier there's likely no big difference phasing back or not." NOT SURE I UNDERSTAND THIS SENTENCE?
THANK YOU SO MUCH FOR YOUR HELPFUL COMMENTS. MUCH APPRECIATED
JIM
RE: Rectifier configuration Harmonics
RE: Rectifier configuration Harmonics
And thanks to this forum, for this valuable service.
JIM
RE: Rectifier configuration Harmonics
Are you sure your are buying your equipment from manufacturer experienced in that field ?