What produces Second Harmonic Current?
What produces Second Harmonic Current?
(OP)
Does anyone know what could produce 120 hz current on two legs of a 3 phase system? (120 hz is being produced on a and b phase, not c) We know that it's not a drive misfiring and we know it isn't a transformer saturating. Any input would be so much appreciated!!
Thanks, Ashley
Thanks, Ashley






RE: What produces Second Harmonic Current?
RE: What produces Second Harmonic Current?
Mark
RE: What produces Second Harmonic Current?
Mark1080- I am not sure what you mean by measurement artifact. This was measured over a two day period; and I am beginning to question whether or not a recent client lighting retrofit with high efficiency ballast might be the source; whereas they do have some drives, these are not energized during the predominant period of measurement; but when AC Drive is online and working, approximately 15 minutes out of two days profile, it provided slightly higher 2nd order current as well. I scoped the drives, there is no problem with pulse firing sequences; as that was the first place I looked given historically having seen 2nd order current produced by a misfiring SCR on a six pulse drive. But that is not the case here. Thank you for your reply!
Thanks guys, any thoughts will help! - Ashley
RE: What produces Second Harmonic Current?
RE: What produces Second Harmonic Current?
RE: What produces Second Harmonic Current?
RE: What produces Second Harmonic Current?
RE: What produces Second Harmonic Current?
RE: What produces Second Harmonic Current?
I have also had "nervous" armature current controllers that locks to mains frequency. That also produces even harmonics.
Use a current clamp plus scope and inspect outgoing current in every cable. Then, if you find bad waveshapes, follow that cable and see what is connected to it. You could also use a current clamp with individual harmonics display like a C&A F607.
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: What produces Second Harmonic Current?
These are 277 volt lights; and apparently the client’s electrical installer only used two phases of the system when powering them; no engineering support was used for project install and design. In this case, it might have been for the best; as had all three phases had lighting evenly distributed across them, we might still be wondering as to what the source of this unusual negative sequence component could be. Now that the ballasts have been identified, and approximately 6 amps of 2nd harmonic current are recorded in the system, what would your comments be in next step? Client is soon to add approximately 16 motors and AC Drives to the system; and I am concerned that the negative sequence current poses counterclockwise torque and heating in motor shafts. Would this concern warrant another lighting change out in your opinion? At what levels of 2nd order / negative sequence current would one feel action was needed to protect 480V motor loads in parallel to system lighting circuits?
Thanks,
Ashley
RE: What produces Second Harmonic Current?
The primary issue with other loads is harmonic voltage, not current. Any loads connected in parallel with this lighting will see the system voltages caused by the harmonic currents and the source impedance at the harmonic frequency. If a filter (low impedance path for these currents) is installed, the motors won't see harmonic voltages and will be OK. If there is no low impedance path, then all loads will see the resulting voltages and will be a part of the harmonic current return path. This is the situation you want to prevent.
RE: What produces Second Harmonic Current?
RE: What produces Second Harmonic Current?
RE: What produces Second Harmonic Current?
RE: What produces Second Harmonic Current?
RE: What produces Second Harmonic Current?
Bill
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"Why not the best?"
Jimmy Carter
RE: What produces Second Harmonic Current?