drbond24
Senior Member
- Location
- Barboursville, West Virginia
This is a waveform capture from out main switchgear that I took last year. Can anyone tell me what would cause the dimples on the peaks?
waveform question
- Thread starter drbond24
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This is a waveform capture from out main switchgear that I took last year. Can anyone tell me what would cause the dimples on the peaks?
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
What the others have said, non-linear loads.
In particular, rectifier input loads have a diode followed by a capacitor. The load will only draw current when the supplied AC voltage is greater than the DC voltage in the capacitor. So instead of having a nice sinusoidal current flow, you have spikes of current which only flow right at the supply voltage peaks.
So you have this sudden surge of current flowing only at the AC peaks...this current flow causes a voltage drop on the impedance of the supply, distorting the supply voltage. Thus the dips in the supply peaks.
The above ignores a bunch of stuff, such as the impedance and inductance between the measurement point and the loads, and is just a handwaving description.
-Jon
In particular, rectifier input loads have a diode followed by a capacitor. The load will only draw current when the supplied AC voltage is greater than the DC voltage in the capacitor. So instead of having a nice sinusoidal current flow, you have spikes of current which only flow right at the supply voltage peaks.
So you have this sudden surge of current flowing only at the AC peaks...this current flow causes a voltage drop on the impedance of the supply, distorting the supply voltage. Thus the dips in the supply peaks.
The above ignores a bunch of stuff, such as the impedance and inductance between the measurement point and the loads, and is just a handwaving description.
-Jon
brian john
Senior Member
- Location
- Kilmarnock, Va
- Occupation
- Retired after 52 years in the trade.
Like this???????
Now thats some serious distortion, black voltage, red current
Now thats some serious distortion, black voltage, red current
76nemo
Senior Member
- Location
- Ogdensburg, NY
Wow, nice and clean! What is that from Brian?
brian john
Senior Member
- Location
- Kilmarnock, Va
- Occupation
- Retired after 52 years in the trade.
Generator feeding a VFD
76nemo
Senior Member
- Location
- Ogdensburg, NY
drbond24 said:
This is a waveform capture from out main switchgear that I took last year. Can anyone tell me what would cause the dimples on the peaks?
Hey, you can't do that on live loads:grin: Unprotected line to switchgear? Life in prison! Castration!
:roll: :grin:
:grin:
drbond24
Senior Member
- Location
- Barboursville, West Virginia
Thanks for the information gentlemen.
Oh ok. Next time I go download a waveform I'll put on a spacesuit before I plug into the port on the outside of the dead front switchgear. :grin: Wouldn't want OSHA to catch me being a nerd within 3 feet of the switchgear without proper PPE. :grin:
76nemo said:Hey, you can't do that on live loads:grin: Unprotected line to switchgear? Life in prison! Castration!
:roll: :grin:
Oh ok. Next time I go download a waveform I'll put on a spacesuit before I plug into the port on the outside of the dead front switchgear. :grin: Wouldn't want OSHA to catch me being a nerd within 3 feet of the switchgear without proper PPE. :grin:
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