Dynamic Study Modelling

[MohandesDawood]

I'm doing a dynamic study for a utility. I'm facing following obstaches. If you have any idea kindly help me.

(1) If I know the positive sequence impedance of a tranmission lines and transformers, how I can find out and calculate the zero sequence impedance for both: lines and transformers.

(2) For the three-winidning transformer, is the impedance leakages for all: primary to secondary winding (Zps), secondary to tertiary winding (Zst), and primary to tertiary (Zpt) are equal. i.e. Zps=Zst=Zpt????.

(3) For the three-winding transformer,Is the MVA rating for windings are equal .i.e MVAp=MVAs=MVAt???????

 

[RAMConsult]

1.)You can't without knowing the physical arrangement of the transmission line and the design of the transformer. All the data you seek should be readily available from the utility's engineering dept.

2.&3.)Probably not, the impedances and ratings are a function of the transformer's design, check with the manufacturer or the nameplate.

It's not clear what type of dynamic study you are considering- dynamic stability, transient loading, voltage profile, etc.- but actual parameters are required to yield meaningful results. I suggest that you contact a Power Engineer who has performed this type of work in the past.

 

[SMB1]

Zps,Zst,Zpt
Can not be equal.

 

[MohandesDawood]

Thanks,

But I'm away from the utility, and difficult to cantact them.

I'm doing voltage and frequency dynamic study.

Can you guide me who is the expert (eng-tip member) for this study in this website.

 

[nag400]

Dear MohandesDawood,
Plese look for standards from Westinghouse T&D book.(If members can provide link of the above..??)
The book contains the zero sequence impedances to be considered for different voltages of transmission line. We take usually 2.5 times the positive sequence impedance for transmission line .. But this is a thumb rule.. and shall not be treated as guideline.
For transformers.. Generally 85 - 90% of the positive sequence impedance is considered as zero sequence impedance.
Regarding the 3 winding transformer, The three impedances will not be equal. we use the general formulae as follows,
Zp = (Zpt +zps -zst)/2;
Zs = (Zst + Zsp - Zpt)/2;
Zt = (Zts+ Ztp -zps)/2 ;
Note the thumb rule :
If you sum / subract any of the two impedance. it should almost be equal to the third one (based on some typical transformer data on the same base)
MVA rating of the transformer on primary, secondary and teritiary will be different. But if the question is for calculating the impedance you have to really check out the transformer nameplate for the base MVA which is usually the primary MVA.

regards,
-nag400

 

[jbartos]

Suggestion:
I'm doing a dynamic study for a utility. I'm facing following obstaches. If you have any idea kindly help me.
///Follow the mention referece above and similar ones, i.g. Standard Handbook For Electrical Engineers by Fink and Beaty\\(1) If I know the positive sequence impedance of a tranmission lines and transformers, how I can find out and calculate the zero sequence impedance for both: lines and transformers.
///See the cited reference in above posting, Westinghouse Reference Book.\\(2) For the three-winidning transformer, is the impedance leakages for all: primary to secondary winding (Zps), secondary to tertiary winding (Zst), and primary to tertiary (Zpt) are equal. i.e. Zps=Zst=Zpt????.
///Depending on one line diagram, power distribution specifications, load study, system description, etc., the following set may be modified:
Zp = (Zpt +zps -zst)/2; Set Zp=0+j0, pu
Zs = (Zst + Zsp - Zpt)/2; Zs=Zt
Zt = (Zts+ Ztp -zps)/2 ; Zt=Zs
or if you have those impedances available, use those.\\
(3) For the three-winding transformer,Is the MVA rating for windings are equal .i.e MVAp=MVAs=MVAt???????
///Often MAVp=MVAs + MVAt, and MVAs=MVAt
However, follow your specifications or load study results for MVAp, MVAs and MVAt. Set MVAp=MVAs + MVAt\\

 

[jbartos]

Suggestion: Visit

http://www.engr.usask.ca/~tss690/EE342Assn2.pdf

http://edt.uow.edu.au/indulkar/chap06.pdf

etc. for more info