×
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

Yzn earthing transformers

Yzn earthing transformers

Yzn earthing transformers

(OP)
Hi

In IEC 60076-8 it is stated that YNd and Yzn earthing transformers has the same functionality. I understand the broken delta solution (YNd), but I am struggling with understanding the Yzn solution.

For instance, if you have a 11 kV delta connected system and introduce a 11/0.69 kV Yzn earthing transformer to restrict the earth fault current to 20 A on the 11 kV system, how to you size the resistor connected to the zigzag neutral?

Thanks for Your help

RE: Yzn earthing transformers

In IEC 60076-8 ch. 4.7. it is stated:
"The Z-connected transformer is referred to as an earthing transformer or neutral coupler; see section 6 of IEC 60289."
Since IEC 60289 is withdrawn I think IEC 60076-6 it is instead. See:
http://webstore.iec.ch/preview/info_iec60076-6%7Be...
IEC 60076-6 Power transformers – Part 6: Reactors
ch.8 Current-limiting reactors and neutral-earthing reactors
The zig-zag transformer [ or Neutral Grounding Resistors ] manufacturer could instruct you how to calculate the resistance. For instance:
www.postglover.com
www.eskom.co.za/tenderbulletin/File_Show.asp?ID=11...
and other.

RE: Yzn earthing transformers

I haven't read 60076-8, but for what it is worth a YNd is generally considered equivalent to a Zigzag grounding transformer, not a Yzn transformer. In particular the Y primary is not necessary. A typical Zigzag grounding transformer has no secondary - it simply has a zigzag wound primary that creates a neutral point. The resistor sizing is easy in that case - it should be sized as if it was connected to the primary system's neutral point.

RE: Yzn earthing transformers

A) The relevant standards for Earthing Transformers(Americans call it Grounding Transformer) are as below:
1) IEC 60076-6 :ed1.0 2007 Power Transformers Part 6 Reactors -Section 10 covers Earthing Transformers (Neutral Couplers) Earlier Standard was IEC 289 ed2.0-1968, 1988
2) ANSI/IEEE Std 32-1972( Reaffirmed 1990) Requirements, Terminology and Test procedure for Neutral Grounding Devices
3) Indian Standard IS 5553 (Part 6) -1990 Reactors -Part 6 Earthing Transformers (Based on IEC 289-1988) Earlier Standard IS 3151-1965,1982

B) As per 60076-8, YNd and ZN has same functionality ie provide an earthing neutral to an otherwise ungrounded system. ZN has only one auto connection. With YNd, you can use d for connecting a resistor either internal or external to delta. With ZN advantage is less copper used in windings and the resistor is connected to the neutral of Z winding.Earthing transformers are some times provided with a star secondary to load auxiliaries (ZNyn).60076-6 section 10 covers both Ynd and ZN connections.

YNzn,YNynd(ie delta stabilising connection) and Dyn has same functionality ie distribution transformers feeding four wire distribution system. Advantage of YNzn over YNynd is less copper compared to a star/star connection with stabilising delta winding.Some parts of the world Ynzn is still used for sub-transmission step down.(125 MVA 220/34.5kV YNzn11 in Mumbai)

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