The waveform of the zero line at the input end of the three-phase uncontrolled rectifier to the negative pole of the output voltage

easthewj

The waveform of the zero line at the input end of the three-phase uncontrolled rectifier to the negative pole of the output voltage [Copy link]

 

Please tell me why the waveform of the zero line at the input end of the three-phase uncontrolled rectifier to the negative pole of the output voltage looks like this

呜呼哀哉

Why is your picture a frame?

maychang

"Why is the waveform of the neutral line at the input end of the three-phase uncontrolled rectifier to the negative pole of the output voltage like this?"

The picture is down, I can't see it.

soso

Please find this icon in the edit box and upload the picture again.

easthewj

Thank you for your enthusiastic response. The pictures have been uploaded as attachments.

maychang

easthewj posted on 2021-4-25 14:47 Thank you for your enthusiastic responses. The pictures have been uploaded as attachments

This waveform does not fit this circuit.

In the simulated three-phase power supply, the neutral line may be grounded by default. The OP connected the neutral line to channel A, so the display of channel A naturally became a flat line. Channel B is connected to the positive end of the rectifier output, which is a three-phase half-wave rectifier waveform.

maychang

easthewj posted on 2021-4-25 14:47 Thank you for your enthusiastic responses. The pictures have been uploaded as attachments

This is a simulation. If the actual three-phase power supply is connected in this way, it is equal to D2D4D6 connected at both ends of the three-phase winding, and I am afraid that the protection will trip.

easthewj

The moderator may have made a mistake!

maychang

easthewj posted on 2021-4-25 14:47 Thank you for your enthusiastic responses. The pictures have been uploaded as attachments

Under normal working conditions, the positive end of the three-phase rectifier output is positive to the neutral line of the three-phase power supply (if the three-phase AC phase voltage is 220V, then the positive end of the capacitor input filter is 310V to the neutral line), and the negative end of the output is negative to the neutral line.

maychang

easthewj posted on 2021-4-25 14:47 Thank you for your enthusiastic responses. The pictures have been uploaded as attachments

If you want to see the waveform of the three-phase rectifier output, you should connect the oscilloscope ground wire to the three-phase neutral wire, and connect the two channels to the positive and negative ends of the rectifier output respectively. The waveform of the rectifier output positive end to the negative end is the algebraic sum of the two channel waveforms.

When the output is no-loaded, the ripple of the rectifier output is very small and may not be readable (both the positive and negative ends are a flat line).

easthewj

maychang published on 2021-4-25 16:12 Under normal working conditions, the positive end of the three-phase rectifier output is positive to the neutral line of the three-phase power supply (if the three-phase AC phase voltage is 220V, then the capacitor input filter positive end...

Moderator, please explain in detail, I don’t quite understand this sentence!

maychang

easthewj posted on 2021-4-25 15:24 The moderator may have made a mistake!

You can try changing the simulated rectifier circuit to this.

Oscilloscope channel B can be connected twice to the positive end (node 4) and negative end (node 0) of the rectifier output to see the waveform.

maychang

easthewj posted on 2021-4-26 09:23 Moderator, please explain in detail, I don’t quite understand this sentence!

"Please explain in detail, I don't quite understand this sentence!"

Wait a minute. Let me draw a few pictures.

easthewj

maychang posted on 2021-4-26 12:18 You can change the simulated rectifier circuit to this and try it. Oscilloscope channel B can be divided into two parts, connected to the positive end (node 4) and negative end (node...

The simulated waveform looks like this, but I don’t quite understand why it is like this!

maychang

easthewj posted on 2021-4-26 14:12 The simulated waveform looks like this, but I don’t quite understand why it is like this!

The 14th floor picture is not exactly the same as the 12th floor picture.

The "cold end" of channel A of the oscilloscope on the 14th floor (that is, the external shielding layer of the oscilloscope probe) is connected to the negative end of the rectifier output, while this end on the 12th floor is grounded.

The "cold end" of channel B of the oscilloscope on the 14th floor is connected to the neutral line of the three-phase power supply, while this end on the 12th floor is also grounded.

In an actual oscilloscope, the "cold ends" of the two channels are connected together and connected to the oscilloscope housing.

easthewj

maychang posted on 2021-4-26 14:42 The 14th floor picture is not exactly the same as the 12th floor picture. The "cold end" of the oscilloscope A channel on the 14th floor (that is, the external shielding layer of the oscilloscope probe) is connected to...

Does this problem not exist when using a high voltage isolation probe?