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Active Contributor

Join Date: Nov 2009
Posts: 11

PT Accuracy Class 3P & 0.2S

10/28/2017 4:02 AM

what will be the error %age if 3P cores of PT will be used in metering circuit ?

we have 2 cores in our GIS . core #1: 15VA, 132kv/110v, 0.2S and core#2: 30VA, 132KV/110V, 3P.

we have one metering cubicle from the electricity board and we have some meters in our CRP. the measuring core of 0.2S needs to be connected exclusively to metering unit of electricity board. so, we dont have any option for connecting the meters in our CRP other than the core of 3P. what will be the error in metering ?

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Guru

Join Date: May 2006
Location: Placerville, CA (38° 45N, 120° 47'W)
Posts: 4541
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#1

Re: PT Accuracy Class 3P & 0.2S

10/29/2017 11:37 AM

Besides the possibly unknown meanings of your acronyms and units, something sounds strange here. Do you really have a Three Phase Power Transformer that converts from 132kV directly to 110V at a power level of only 30VA?

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Power-User

Join Date: Jan 2010
Location: Hyderabad
Posts: 159
Good Answers: 3
#2

Re: PT Accuracy Class 3P & 0.2S

10/30/2017 2:50 AM

IEC defines metering accuracy for a protection CT core. For example, 5P core will have metering accuracy class 1 in load current range. I couldn't find similar notes for protection VTs.

I have been specifying dual accuracy class for VTs like 0.5/3P and vendors do not have a problem supplying the same.

In your case, you may test the protection VT that you may already have at site, for accuracy between 80 & 120% of the rated voltage (and burden between 25 & 100% of rated). Or else, approach the vendor for advice, giving VT name plate details.

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Raghunath
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Active Contributor

Join Date: Sep 2017
Location: Russia, Moscow
Posts: 22
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#3

Re: PT Accuracy Class 3P & 0.2S

10/30/2017 6:57 AM

http://www.rsisolsec.com/en/accuracy-of-current-transformers.html

The coil for relay protect not use for energy accounting.

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Guru
Engineering Fields - Power Engineering - New Member

Join Date: May 2007
Location: NYC metropolitan area.
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#4

Re: PT Accuracy Class 3P & 0.2S

10/30/2017 7:55 PM

You are trying to calculate the difference between the readings obtained from a metering-class PT on the utility side, and an instrumentation-class PT feeding the Customer Revenue Panel. You will need to obtain the calibration curves for both, as well as the burdens of their respective circuits, then calculate how each will react under changing primary voltages/loadings, and compare the results.

The alternative would be to energize the bus with no load, inject varying current steps into the CT secondary circuit, and record the readings on both kW/kWh meters.

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Guru

Join Date: Oct 2009
Posts: 2029
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#5

Re: PT Accuracy Class 3P & 0.2S

11/10/2017 2:14 AM

+/- 3% between 5% and 100% of rated primary voltage and between 25% and 100% of rated burden (at 0.8pf) connected to the secondary.

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