Previous in Forum: RJ9/4P4C to Mini Jack   Next in Forum: what will happen if I use 50hz motor in place of 60hz motor?
Close

Comments Format:






Change Mode
Close

Subscribe to Discussion:

CR4 allows you to "subscribe" to a discussion
so that you can be notified of new comments to
the discussion via email.

Close

Rating Vote:







Add Vote
6 comments
Rate Comments: Nested
mahmoud
Participant

Join Date: Jan 2008
Posts: 3

Percentage Ompedance

01/16/2008 8:09 AM

a transformer of capacity 40 MVA , transformer ratio (127 KV/11 KV) and the name plate percentage impedance 14.5% , now the transformer will operate at 71.5 KV at primary side instead of rated value (127KV). so, what will be the new percentage impedance?
Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.
Stinky Pete
Power-User

Join Date: Jul 2007
Location: The cigarette-stained drunkard living in the cardboard box outside Marks & Sparks delivery entrance, Eastgate Shopping Centre, Basildon.
Posts: 487
#1

Re: Percentage Ompedance

01/16/2008 8:48 AM

You could ask the person who is designing it to operate at the reduced voltage <sneeze>.

__________________
 Essex jobs for Essex yobs! <Burp>.
Register to Reply
Anonymous Poster
#2

Re: Percentage Ompedance

01/16/2008 10:42 AM

Hello,

The rated percentage impedance will not change, since there is no physical change in the windings. But, the Transformer capacity will be limited to 22.518 MVA at 71.5 KV (if the primary winding is delta connected).
Register to Reply
ramvinod
Guru

Join Date: Jun 2007
Location: chennai,India
Posts: 592
Good Answers: 19
#3

Re: Percentage Ompedance

01/16/2008 11:13 PM

The impedance of the transformer will not vary,once it is manufactured.This is a physical property.Therefore, Percentage impedence will not vary.

__________________
 Ramesh,Freelance Electrical/automation Consultant
Register to Reply
Anonymous Poster
#4

Re: Percentage Ompedance

01/17/2008 12:15 AM

Hi,

The actual impedance (in ohms) of the transformer will not change. However, the percentage impedance (in % or pu) should be modified according to the new operating voltage.

Znew% = Zold%*(127/71.5)^2

Regards,
Register to Reply
MUKULMAHANT
Guru
Engineering Fields - Systems Engineering - New Member Hobbies - Model Rocketry - New Member

Join Date: Dec 2006
Location: Long.92E,Lat.26N
Posts: 1336
Good Answers: 14
#5
In reply to #4

Re: Percentage Ompedance

01/18/2008 9:25 AM

This is the real picture of PER-UNIT impedance which is not something you measure with a multimeter .
Register to Reply
Anonymous Poster
#6
In reply to #5

Re: Percentage Ompedance

01/18/2008 12:56 PM

The leakage impedance (%) is calculated from the short circuit test and transformer manufacturing rated voltage. Due to voltage rating change, the modified per unit (or %) impedance should be used in system analysis (for example in symmetrical short circuit calculation or load flow analysis).
Register to Reply
Register to Reply
Have a Different Question?
6 comments
Copy to Clipboard

Users who posted comments:

Anonymous Poster (3); MUKULMAHANT (1); ramvinod (1); Stinky Pete (1)

Previous in Forum: RJ9/4P4C to Mini Jack   Next in Forum: what will happen if I use 50hz motor in place of 60hz motor?

Advertisement

Got Something to Say?
Ask a Question
Start a Discussion

Search this Forum
Electrical Engineering:
Go

CR4 Sections
Aerospace
BioMech & BioMed
Chemical & Material Science
Civil Engineering
Communications & Electronics
Education and Engineering Careers
Electrical Engineering
General Discussion
Instrumentation
Manufacturing
Mechanical Engineering
New Technologies & Research
Software & Programming
Sustainable Engineering
Transportation

Site Directories
Forum Directory
Blog Directory
User Group Directory
RSS Feeds

CR4 Rules of Conduct
CR4 FAQ
Site Glossary

Who's Online (62 right now)
Show Members
Advertisement