Advanced Metering –4 Quad, TLC, PT/CT Correction€¦ · Advanced Metering ‐–4 Quad, TLC,...
Transcript of Advanced Metering –4 Quad, TLC, PT/CT Correction€¦ · Advanced Metering ‐–4 Quad, TLC,...
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EXCHANGING EXPERTISE SINCE 1893
NWEMS
Advanced Metering ‐ – 4 Quad, TLC, PT/CT Correction
August 2017| Track D | Matt Anthony, Schneider Electric
EXCHANGING EXPERTISE SINCE 1893
» 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
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Agenda
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» 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)
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Quadrants
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» 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
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Terms of Accuracy Performance
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» 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
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Terms of Accuracy
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» 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
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Current TransformersANSI CT Accuracy Class
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» 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
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Voltage TransformersANSI VT Accuracy Class
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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.
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EXCHANGING EXPERTISE SINCE 1893
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.
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VT Transformer Correction Factor
EXCHANGING EXPERTISE SINCE 1893
» 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
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CT/PT Correction
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CT/PT Correction
Ratio correction factor
Phase angle in minutes
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» 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”
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CT/PT Correction
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Correcting for CT/PT in Meter
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» 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
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Transformer Loss Compensation
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» 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...
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Transformer Loss Compensation
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» 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
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Transformer Loss Compensation
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» We need to calculate the transformer var losses
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Transformer Loss Compensation
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» 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
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System Loss Compensation
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» 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
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System Loss Compensation
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» 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
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System Loss Compensation
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» 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
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Watt Loss Constantson
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» Total load watt losses
– TLW = FLW + LLW + CLW
» Total load var losses
– TLV = FLV + LLV + CLV
» Let's summarize our calculations so far...
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Total System Losses
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Var Loss Constants
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» 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
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SLC Calculations for Delta Load
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Calculating SLC via Spreadsheet
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Some Use Cases
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Any questions before concluding?
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Thank you