×
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

Line impedance calculations

Line impedance calculations

Line impedance calculations

(OP)
I was wondering if anyone can give me a formula or somewhere I can find it to get positive and zero sequence line impedances and angles for a transmission line.  Thanks

RE: Line impedance calculations

For what application, you are looking for this calculation, normally you can get this thing from the manufaturer and the angle you are talking about is the angle between the Sending end and receiving end voltage. if this is what you are looking for, you have to calculated it using basic modelling technique , if it is a short, medium or long transmission line.
cheers !

RE: Line impedance calculations

(OP)
The situation is that I am replacing existing KD-10 relays with SEL-311A relays and the customer has no line data.  Getting the reach off of these relays is not really an issue, but according to the KD-10 manual the reach setting (if desired) can be affected by the impedance angle.  I have nothing from the original setting of this relay.

RE: Line impedance calculations

The only way to get the information you are looking for is to know the conductor type (and quantity) and line geometry.

RE: Line impedance calculations

Probably if you provide basic information there will better responses. For instance:

1- Is the transmission line underground or overhead?

2- What is the phase conductor size and physical configuration?

3- Any shield wire(s) and size.

4- Any information on soil resistivity?


RE: Line impedance calculations

(OP)
1- overhead

2- 795 mcm ACSR and vertical configuration with all 3 phases on one side of a pole. It is a 46 kV circuit with a second circuit on the other side of the pole.

3-  static line on top of pole

4-  no info on soil resistivity

RE: Line impedance calculations

Unfortunately, it doesn't sound like you have any software to model this with.  We use 795 ACSR commonly for our subtransmission.

You will have to dig into either a power engineering handbook, or a wire company's electrical data (such as southwire) to get the positive, and zero sequence for a given length (usually per thousand feet).  Find out how many feet of line you have and you should be able to calculate it out.  

For your phase distance elements you can find the angle by converting from rectangular to polar form after you have the total line impedance.  For your ground elements, the same applies, but I believe the 311A also uses a Ko factor which you will need to find the calculation for.

RE: Line impedance calculations

There are formulas for calculating positive and zero sequence impedances, however if you don't know the values (positive sequence impedance is provided by the manufacturer and does not change zero sequence depends on soil quality, season etc), the best thing to do is to carry out a Line Parameter Testing. To do that, you need to de-energise the line and carry out injections to the next substation. If there is another line on the same tower, you will need the zero sequence mutual impedance between the two lines as well, because in case of one line out of service and earthed at both ends, your zero sequece impedance can change considerably.
If injection is not possible find what type of conductors are used and refer to manufacturer information. For overhead lines the angle is around 75 Deg. If you can not find any information on conductors, use 0.4 ohm/km as a safe approximation.

RE: Line impedance calculations

Equations for calculating line impedance (with angles) and typical values for transmission lines can be found in the Westinghouse T&D Reference Book.

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