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
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.
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.
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.
Alan
----
"It's always fun to do the impossible." - Walt Disney
RE: VT, PT load.
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.
Alan
----
"It's always fun to do the impossible." - Walt Disney
RE: VT, PT load.
Scottf, it's GOST word
Best Regards.
Slava
RE: VT, PT load.
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If we learn from our mistakes I'm getting a great education!
RE: VT, PT load.
GO-gov or country
ST-standard ( same word in Russian).
Best Regards.
Slava
RE: VT, PT load.
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.
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.
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.