×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

thrid harmonics vs transformer grounding

thrid harmonics vs transformer grounding

thrid harmonics vs transformer grounding

(OP)

We are in the process of selecting a grounding criteria for a Dy1 power transformer. We have two alternatives:

1. Use a low resistance grounding of neutral point of secondary. (1500 A)
2. Use a high resistance grounding of neutral point of secondary. (1500 A). (300 or 400 A)

My question is regarding the third harmonics in the system and secondary.

According to my theory if you use a direct neutral grounding (no resistance) you allow third harmonic currents to flow through the neutral and the lines in the secondary, and probably dont have third harmonic voltages distortions. On the other hand if i dont earth the neutral (floating neutral) you dont allow third harmonic currents but have big distortion on the voltages on the secondary.

How the resistance grounding affect this theory?
Whats better? have third harmonic voltages or third harmonic currents?

Thanks and regards.


 

RE: thrid harmonics vs transformer grounding

cmelguet ,
what kind of load at low voltage, MVA and kVs of transnformer?

RE: thrid harmonics vs transformer grounding

Quote:

According to my theory if you use a direct neutral grounding (no resistance) you allow third harmonic currents to flow through the neutral and the lines in the secondary, and probably dont have third harmonic voltages distortions. On the other hand if i dont earth the neutral (floating neutral) you dont allow third harmonic currents but have big distortion on the voltages on the secondary.
fwiw, your conclusion is very logical to me, assuming the secondary supplies three-phase balanced but non-sinusoidal loads like 3-phase diode/scr bridge.

=====================================
(2B)+(2B)'  ?

RE: thrid harmonics vs transformer grounding

Third harmonic component of current will only flow if your load has star point connected to ground and if you have as electricpete said 3-phase diode/scr bridge third harmonic component of current will not flow no mather if star point of transformer is connected or not connected to ground.

 

Milovan Milosevic

RE: thrid harmonics vs transformer grounding

(OP)
Thanks electricpete and milovan. I have some comments on this.

1. Assume a 50 MVA transformer 23 kv / 4.16 kv.

2. the load are MV motors, VFD, other transformers, etc.

3. I though transfomers itself introduce a third harmonic component due to magnetizing current. In delta transformers the third harmonic  is kept in the delta of the primary. On the secondary side, if i dont allow the third harmonic to flow in the system you will get voltage distortion, is this not correct?. How the groundging (hight or low resistance) affect the third harmonic currents and voltages?

Thanks again.
 

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources