×
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

VT, PT load.
4

VT, PT load.

VT, PT load.

(OP)
Dear All.
In lot of applications provided retrofit of protection and metering eq.
load consumption of newer numerical eq is very low, but VT/PT will same with 200-400VA burden.
According to few standards: load consumption on the VT must be 25-100%, if no, errors of amplitude and angle will increase.
What is your practic in this case, did we have add additional rezistors:
in case of revenue meters?
in case of protection?
Thanks in advance.
Slava
 

RE: VT, PT load.

I agree with you. Many utilities standardise the VT parameters throught the system.
This is not a problem with protection relays which concern with the fault situations where the actual voltage could be much lower.
When it comes to revenue meters, the meters tend to record more energy flow (than actual) when the VT is less loaded. This is due to the fact that in order to compensate the regulation partly and keep the errors within limits, the VT secondary windings are provided a few extra turns.
 

RE: VT, PT load.

Slavag-

In the IEC world (and some others) the VT accuracy is rated from 25%-100% rated burden.

In the IEEE/CSA world, the VT accuracy rating is rated from 0 to full burden rating. Judging by the fact you listed 200VA and 400VA burdens, it seems you may be in IEEE world.



 

RE: VT, PT load.

VT accuracy is usually not critical for protection applications. As scottf suggesting, in IEEE world we don't worry about minimum VT load. Meter accuracy is only required to be 2%.  

Alan
----
"It's always fun to do the impossible." - Walt Disney

RE: VT, PT load.

alehman-

I believe the 2% figure you speak of for metering is total system error (I also believe it's a lot tighter than that in many places).

Normal VT metering accuracy class in IEEE/CSA is 0.3. Same for CTs.

A VT rated with a 0.3 class will meet a 0.3 accuracy from 0-full burden.

RE: VT, PT load.

Yes, whole system. Sorry for the lack of clarity.

Alan
----
"It's always fun to do the impossible." - Walt Disney

RE: VT, PT load.

(OP)
Thank you for your inputs.
Scottf, it's GOST word smile.
Best Regards.
Slava

RE: VT, PT load.

GOST = Russia, correct?
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: VT, PT load.

(OP)
Yes, Scotty, you are correct.

GO-gov or country
ST-standard ( same word in Russian).

Best Regards.
Slava

RE: VT, PT load.

Hi Slava,

Agree with Rahgun. I live in Europe and in my country, VTs which are meant for revenue purposes must be loaded at least above 25%.  For protection purposes, it doesn't matter AFAIK

Regards
 

RE: VT, PT load.

(OP)
Thanks Yuma.
In parallel, I check this point with few companies.

Recommended pay attention also on the VTs for the protection like to 21, distance protection, not only metering and  revenue meter.

Best Regards.
Slava

RE: VT, PT load.

Slava-

I question the advise to load VTs to 25% of burden for protection applications.

As an example, for a VT with a metering rating of Cl. 0.5-30VA, the error when loaded at 2VA is going to be approx. 1% if indeed the VT is designed to only meet accuracy class from 25%-100% rated burden. In actuality, most of the VTs for Europe are designed to meet class from 0-full burden.

 

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