Advanced Metering –4 Quad, TLC, PT/CT Correction€¦ · Advanced Metering ‐–4 Quad, TLC, PT/CT Correction ... Current Transformers ANSI CT Accuracy Class. ... Correcting for

8/3/2017

1

EXCHANGING EXPERTISE SINCE 1893

NWEMS

Advanced Metering ‐ – 4 Quad, TLC, PT/CT Correction

August 2017| Track D | Matt Anthony, Schneider Electric


» Four‐quadrant metering

– Why do it?

» CT/PT correction

– Why do it?

– Reading an instrument transformer test card

– Entering into meter software

» System Loss/Transformer Loss Compensation

– What is it and why is it done?

– Using a spreadsheet to calculate coefficients

2

Agenda

8/3/2017

2


» This diagram shows the concept of quadrants for noting W, VAR, and VA

» There is a correlation to the meter's vector diagram

Relation to power factor:

– Q1=Lag (+W, +VAR)

– Q2=Lead (‐W, +VAR)

– Q3=Lag (‐W, ‐VAR)

– Q4=Lead (+W, ‐VAR)

3

Quadrants


» Ratio Correction Factor

– Ratio of true ratio to the marked ratio

• Burden (secondary load) will affect the true ratio

• In the case of a CT, the primary current magnitude will affect the true ratio (i.e. 10% or 100% current)

» Phase Angle of an Instrument Tran

– The phase angle is the difference in minutes between the primary voltage or current and the secondary voltage and current

4

Terms of Accuracy Performance

8/3/2017

3


» Phase Angle (continued)

– Phase angle is important because in order to calculate Watts, the angle is needed as shown in the equation below:

– W + E x I x Cos(e), where e is the phase angle

» Transformer Correction Factor (TCF)

– Correction for overall error due to both ratio and phase angle error

5

Terms of Accuracy


» Current Transformer Parallelograms

– The results of the test must be within the outer parallelogram for the transformer to meet the 0.3 accuracy class at 10% of rated current

– The results of the test must be within the inner parallelogram for the transformer to meet the 0.3 accuracy class at 100% of rated current

6

Current TransformersANSI CT Accuracy Class

8/3/2017

4


» Voltage Transformer Parallelogram

– 0.3 Accuracy class shown

– The results of a transformer test must be within the parallelogram for the transformer to meet the 0.3 accuracy class

7

Voltage TransformersANSI VT Accuracy Class

EXCHANGING EXPERTISE SINCE 1893 8

CT Transformer Correction Factor

For example, the overall correction will never exceed .3% at 100% rated current for a transformer in the 0.3 accuracy class. If the ratio correction factor is 1.003 the maximum allowable phase angle is +15.6 minutes. The transformer correction factor is:

The corresponding ratio correction factor and phase angle for any point inside the 0.3 class parallelogram for 100% rated current will always give a transformer correction factor between .997 and 1.003.

8/3/2017

5


For example, the overall correction will never exceed .3% for a transformer in the 0.3 accuracy class. If the ratio correction factor is 1.003 the maximum allowable phase angle is – 15.6 minutes. The transformer correction factor is:

The corresponding ratio correction factor and phase angle for any point inside the 0.3 class parallelogram will always give a transformer correction factor between .997 and 1.003.

9

VT Transformer Correction Factor


» Correct for instrument transformer inaccuracies

» Corrections are typically applied to all values in the meter

» Values to enter in the meter software come from the instrument transformer test card

» Improves system accuracy

10

CT/PT Correction

8/3/2017

6


CT/PT Correction

Ratio correction factor

Phase angle in minutes


» What if the original test card is not available?

– Shop Test

• Knopp KC1500, for example

– Comparator will give phase angle and ratio correction valuesbelow:

– Field Test

• Test CTs in‐service to get the necessary data

– Be aware of the loading on the CTs

– May not be enough current to put CT in “sweet spot”

12

CT/PT Correction

8/3/2017

7


Correcting for CT/PT in Meter


» Transformer loss compensation (TLC) is used when the billing point is on the high voltage side of a transformer and the metering point is on the low voltage side

» Through calculations in the meter, it is possible to account for the iron (core) loss and copper (load) loss associated with the transformation

14

Transformer Loss Compensation

8/3/2017

8


» Can be used in combination with instrument transformer correction to maximize system accuracy

» It may be possible to show compensated and uncompensated values on the meter's display

» The information for calculating TLC is generally collected from the power transformer's nameplate

» Let's look at an example...

15



» In order to calculate the TLC coefficients, we need to find out some information about the transformer

» Typically located in the transformer test report or on the nameplate

16


8/3/2017

9


» We need to calculate the transformer var losses

17



» System loss compensation (SLC) takes into account the load losses associated with a metering system

» May be composed of things like

» Transmission lines

» Substation conductors

» Each component can be characterized in terms of watt and varlosses and use to calculate the total load loss

18

System Loss Compensation

8/3/2017

10


» One component of SLC is transmission line losses

» Let's consider an example

– Transmission line is 36 miles long and has a negligablecapacitive effect. At 60Hz and 50oC it has 0.306Ω resistance and 0.451Ωreactance per mile per line

19



» In the substation, there are losses associated with the conductors between the secondary of the power transformer and the metering point

» Example

– Total length = 156 ft

– Conductor resistance = 0.005Ω/1000 ft

– Conductor reactance = 0.09Ω/1000 ft

20


8/3/2017

11


» Current transformer ratio, CTR = 500:5 = 100:1

» Voltage transformer ratio, VTR = 7200:120 = 60:1

» Meter voltage rating, Vm

– Assume 120V

» Inom, meter test amps

– TA = 5A

21

Watt Loss Constantson


» Total load watt losses

– TLW = FLW + LLW + CLW

» Total load var losses

– TLV = FLV + LLV + CLV

» Let's summarize our calculations so far...

22

Total System Losses

8/3/2017

12


Var Loss Constants


» When calculating the percentage loss constants for a delta load, the VT ratio and metered voltage is different from our previous example of wye load

24

SLC Calculations for Delta Load

8/3/2017

13


Calculating SLC via Spreadsheet


Some Use Cases

8/3/2017

14


Any questions before concluding?

27

Thank you

Advanced Metering –4 Quad, TLC, PT/CT Correction€¦ · Advanced Metering ‐–4 Quad, TLC, PT/CT Correction ... Current Transformers ANSI CT Accuracy Class. ... Correcting for

Documents