Advanced Metering 4 Quad, TLC, PT/CT Correction

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1 NWEMS Advanced Metering 4 Quad, TLC, PT/CT Correction August 2017 Track D Matt Anthony, Schneider Electric Agenda» 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 1

2 Quadrants» 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 Terms of Accuracy Performance» 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 2

3 Terms of Accuracy» 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 Current Transformers ANSI CT Accuracy Class» 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 3

4 Voltage Transformers ANSI VT Accuracy Class» 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 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 the maximum allowable phase angle is 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

5 VT Transformer Correction Factor For example, the overall correction will never exceed.3% for a transformer in the 0.3 accuracy class. If the ratio correction factor is 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 CT/PT Correction» 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 5

6 CT/PT Correction Ratio correction factor Phase angle in minutes 11 CT/PT Correction» 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 6

7 Correcting for CT/PT in Meter 13 Transformer Loss Compensation» 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 7

8 Transformer Loss Compensation» 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 Transformer Loss Compensation» 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

9 Transformer Loss Compensation» We need to calculate the transformer var losses 17 System Loss Compensation» 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 var losses and use to calculate the total load loss 18 9

10 System Loss Compensation» One component of SLC is transmission line losses» Let's consider an example Transmission line is 36 miles long and has a negligable capacitive effect. At 60Hz and 50oC it has 0.306Ω resistance and 0.451Ω reactance per mile per line 19 System Loss Compensation» 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 10

11 Watt Loss Constantson» Current transformer ratio, CTR = 500:5 = 100:1» Voltage transformer ratio, VTR = 7200:120 = 60:1» Meter voltage rating, V m Assume 120V» I nom, meter test amps TA = 5A 21 Total System Losses» Total load watt losses TLW = FLW + LLW + CLW» Total load var losses TLV = FLV + LLV + CLV» Let's summarize our calculations so far

12 Var Loss Constants 23 SLC Calculations for Delta Load» 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 12

13 Calculating SLC via Spreadsheet 25 Some Use Cases 26 13

14 Thank you Any questions before concluding? 27 14