Send both AC and DC voltages down the cable
Send both AC and DC voltages down the cable
(OP)
I was just told by someone that you can send both AC and DC voltages down the same cable at the same time (to a Wye motor winding). There's a sensor gauge that requires DC voltage and has a lead connected to the Wye neutral. The guy's reasoning is that the motor only sees the AC components, and at the Wye neutral, both AC voltage and current should be zero (this I agree). So at neutral there's only DC components left, which feeds to the sensor gauge.
I honestly had never heard of this before...maybe it's just because I just graduated and dont' have much experience yet. Could someone validate this? Thanks.
I honestly had never heard of this before...maybe it's just because I just graduated and dont' have much experience yet. Could someone validate this? Thanks.






RE: Send both AC and DC voltages down the cable
But industrial systems have both harmonics and transients so you need a hefty filter to make any use of this possibility. Also, you will have to send 1/3rd of the current down each motor wire so you do not DC brake the motor (of course, only if the current is more than a few percent of motor rated current).
Where would you connect the other end?
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Send both AC and DC voltages down the cable
What kind of effects would harmonics & transients do to the system (either motor or sensor gauge)?
It's interesting to know it's possible to have AC in kilo-volts and DC in 120V in the same 3-phase cables.
Thanks.
RE: Send both AC and DC voltages down the cable
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RE: Send both AC and DC voltages down the cable
This technique may not work for motor currents.
respectfully
RE: Send both AC and DC voltages down the cable
Answer:
Sum of harmonics is not always zero (like sum of three-phase fundamental is). For instance, sum of triplenes add.
Transients are seldom cancelling across the phases. They are more often common mode or occuring (starting) at different time, like closing and breaking transients. So, there will be heavy voltage shifts in the wye point when these occur.
Bill, I think the OP was thinking three-phase system.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Send both AC and DC voltages down the cable
120VAC (wall)--->Current Regulator----|
|---Choke--Load
100VDC (DC supply) --->Diode-->Choke--|
I've never dealt with 2 power supplies at once before. So here are my questions:
1. I'm afraid some of the AC coming from the wall to the load will divert to the DC supply equipment and damage it. I don't know if having a choke in the DC line is enough to stop it or do I need that diode?
2. I'd like to regulate the current coming from AC. Any advice on what I can use for current regulation?
Thanks
RE: Send both AC and DC voltages down the cable
RE: Send both AC and DC voltages down the cable
RE: Send both AC and DC voltages down the cable
RE: Send both AC and DC voltages down the cable
I have not addressed code or safety issues - these need to be considered.