Transformer primary voltage range ?

[panthripu]

Hello
I am trying to understand the range of variation in the primary side voltage of a step up transformer. For instance , a step down transformer with 33kV as primary voltage nominal voltage . What range of voltage (+/-) variation is acceptable in terms of % ? Ignoring the effect of variation on seconday voltage on load side , what are the factor which limits this range? Is there any standard which says that the voltage should not vary within (x%) on Primary side( HV side in our case)?

 

[templdl]

Hello
I am trying to understand the range of variation in the primary side voltage of a step up transformer. For instance , a step down transformer with 33kV as primary voltage nominal voltage . What range of voltage (+/-) variation is acceptable in terms of % ? Ignoring the effect of variation on seconday voltage on load side , what are the factor which limits this range? Is there any standard which says that the voltage should not vary within (x%) on Primary side( HV side in our case)?

Since your inquiry is very vague you haven't stated the reason as to why this information is important to know as It almost seems as if it is a theoretical we question almost a test question.
You see since a transformers secondary voltage is a given ration of the primary Yt he secondary if the primary voltage varies the secondary voltage will vary in a proportion of the primary. Please understand that a trsnsformer does no regular voltage.
To compensate for a given primary voltage primary +-(2) 2-1/2% full capacity above normal taps and -(2) or (4) 2-1/2% full capacity below normal taps are provide. On very large utility transformer automatic tap strangers sometimes are provided to change the taps as may be required.

 

[Smart $]

ANSI C84.1

 

[Ingenieur]

As others have said ANSI and IEEE have standards
google transformer nameplates, you'lll get an idea

I usually see
2 taps at +2.5% each (total 5%) from rated
2 taps at -2.5% each (total -5%)

some times +3 and -1 at 2.5% per tap

here's a pic from a recent substation I certified

 

[electrofelon]

As others have said ANSI and IEEE have standards
google transformer nameplates, you'lll get an idea

I usually see
2 taps at +2.5% each (total 5%) from rated
2 taps at -2.5% each (total -5%)

some times +3 and -1 at 2.5% per tap

here's a pic from a recent substation I certified

Can you comment on the secondary voltage?

 

[Ingenieur]

Can you comment on the secondary voltage?

those taps give the rated sec v at the indicated tapped primary
in my pic
sec is 13.09 kv

so if prim is 70.725 and you select position/tap 2 sec will be rated 13.09

you can also adjust sec with the taps
say prim is rated 69 kv but you want 12.47 out instead of rated 13.09
Or 5% lower
if you select tap 1 output will be

13090/72450 x 69000 = 12467

 

[electrofelon]

those taps give the rated sec v at the indicated tapped primary
in my pic
sec is 13.09 kv

so if prim is 70.725 and you select position/tap 2 sec will be rated 13.09

you can also adjust sec with the taps
say prim is rated 69 kv but you want 12.47 out instead of rated 13.09
Or 5% lower
if you select tap 1 output will be

13090/72450 x 69000 = 12467

Sorry, what I meant was why is the secondary tantalizingly close to 13.2/7.62? Why the odd voltage? Is that common?

 

[Ingenieur]

Sorry, what I meant was why is the secondary tantalizingly close to 13.2/7.62? Why the odd voltage? Is that common?

5% over 12470 (1.05 x 12470 ~ 13090)
most equipment is rated to operate continuously at 1.05 PU of the design (in this case 12470)
pretty common

 

[Smart $]

5% over 12470 (1.05 x 12470 ~ 13090)
most equipment is rated to operate continuously at 1.05 PU of the design (in this case 12470)
pretty common

A prime example of using equipment made outside and not specifically for use in the U.S. Under U.S. standards (NEMA, ANSI) the rating on the nameplate is "supposed to be" the nominal voltage (12,470).

 

[Ingenieur]

A prime example of using equipment made outside and not specifically for use in the U.S. Under U.S. standards (NEMA, ANSI) the rating on the nameplate is "supposed to be" the nominal voltage (12,470).

never seen them rated at nominal 12470 (or 12460)
even ones made by sunbelt or ABB in the US

that transformer although mfgd in MX is built to ANSI/IEEE as noted by the BIL ratings
and owned by an American company for sale specifically in the US

 

[electrofelon]

never seen them rated at nominal 12470 (or 12460)
even ones made by sunbelt or ABB in the US

that transformer although mfgd in MX is built to ANSI/IEEE as noted by the BIL ratings
and owned by an American company for sale specifically in the US

Are you talking mv to mv? I don't see many of those but every mv to lv one I have seen had the standard nominal voltage on it.

 

[Ingenieur]

Are you talking mv to mv? I don't see many of those but every mv to lv one I have seen had the standard nominal voltage on it.

69kv or 115kv to mv class (12470 or 7200 usually)

the lv 995, 480 are always rated the std nominal

most I see are for mining duty where V drop is a concern: the cable run may be 2-4 miles, so they are rated to operate at +5%

I get all the certs and test docs on them: all ANSI/IEEE standard
trying to dig up a few

 

[Smart $]

never seen them rated at nominal 12470 (or 12460)
even ones made by sunbelt or ABB in the US

that transformer although mfgd in MX is built to ANSI/IEEE as noted by the BIL ratings
and owned by an American company for sale specifically in the US

The only part of your post that I can agree to is the manufacturer is a subsidiary of a U.S. company.

As to the rest, there must be some really small fine print between the lines of text on that nameplate. :lol:

 

[Ingenieur]

The only part of your post that I can agree to is the manufacturer is a subsidiary of a U.S. company.

As to the rest, there must be some really small fine print between the lines of text on that nameplate. :lol:

I get all the certs and test docs
ANSI/IEEE standard
:lol:

 

[Ingenieur]

good reference on transformers http://new.abb.com/docs/librariesprovider27/default-document-library/abb_transfo_handbk.pdf?sfvrsn=2
a lot of info on standards
ABB uses IEC, not IEEE, although there is overlap and they detail it
all standards in this class are voluntary unless contractually specified

good basic info on faults and symmetrical components

another one from a US source
great reference
http://www.ssdservice.pl/~ssdservic...r_transformers_principles_and_application.pdf

 

[panthripu]

voltage variation

voltage variation

Great explainations.......
So if i take 5% variation , it means with nominal voltage of 33kV on primary side , if somehow the voltage increases to 34.65kV , there should not be an issue as long as the transformer is with in rated MVA or little overloaded(as designed by manufacturer).