04 - transformer sizing
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8/13/2019 04 - Transformer Sizing
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ETAPETAP 5.5.00
Copyright 2003 Operation Technology, Inc.
Transformer MVA Sizing
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Copyright 2003 Operation Technology, Inc. Workshop Notes: Transformer Sizing Slide 2
Transformer MVA Sizing
Based on ANSI C57 and IEC 60076 standards
Considers multiple cooling stages and transformer
types (3-phase & 1-phase)
Considers altitude correction factors
Considers temperature correction factors
Load variation
Considers short-circuit impedance requirements
Use connected load or operating load to size the
transformer
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Copyright 2003 Operation Technology, Inc. Workshop Notes: Transformer Sizing Slide 3
MVA Sizing Page
Transformer
MVA Loading
Short-Circuit
ImpedancelimitsCorrection
Factors & Load
Variation
Sizing Results
Section
Larger
Required
Smaller
Impedance
Consider
Growth Factor
for Max. MVA
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4/19Copyright 2003 Operation Technology, Inc. Workshop Notes: Transformer Sizing Slide 4
Temperature Correction
Ambient temperature in degree Celsius
For air cooled transformers use the air
ambient temperature
For water cooled transformers use the water
temperature
Based on C57.92-1981 and IEC 76-2
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5/19Copyright 2003 Operation Technology, Inc. Workshop Notes: Transformer Sizing Slide 5
Altitude Correction
Derate the transformer capacity based on
altitude of the installation
Derating starts above 1000 m or 3300 ft
Based on C57.92-1981 and IEC 76-2
1000
meter
1100
meter
900
meter
800
meter
1200
meter
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6/19Copyright 2003 Operation Technology, Inc. Workshop Notes: Transformer Sizing Slide 6
Load Variation
Growth Factor
Allowance for future load growth
Load Factor
The ratio of the average load to the peak loadover a designated period of time
Load Factor = 100 x ( kWi x Ti ) / ( kWp x Tt )%
Load Factor = 100 x E / ( kWi x Tt )%
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7/19Copyright 2003 Operation Technology, Inc. Workshop Notes: Transformer Sizing Slide 7
Where:
I = interval of time when the load is non-zero
kWi = load at interval i
Ti = number of hours of interval ikWp = peak load
Tt = Ton + Toff
Ton = total hours when the load is on
Toff= total hours when the load is off
E = energy (kWh) consumed by load over theinterval
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8/19Copyright 2003 Operation Technology, Inc. Workshop Notes: Transformer Sizing Slide 8
Short-Circuit Impedance
Size Requirement Use Primary Short-Circuit kA and FLA to
Calculate Impedance Primary 3-Phase FLA = MVA / (kVLL *3)
Primary 1-Phase FLA= MVA / (kVprimary)
Zcalculated =100*(FLAprimary / ISC_primary)
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9/19Copyright 2003 Operation Technology, Inc. Workshop Notes: Transformer Sizing Slide 9
Connected or Operating Load
Connected Load
Determine the radial load connected to the transformer
secondary
Can include spare loads for conservative results
Operating Load PowerStations load flow program determines the power
flow through the transformer
Automatically updated in the transformer required MVA
field (load flow study case info page option)
Can determine loading in radial or looped systems
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10/19Copyright 2003 Operation Technology, Inc. Workshop Notes: Transformer Sizing Slide 10
Sizing Results and
Automatic Updating Sizing results include MVA and % Z for
Required Size (Actual calculated Size)
Next Standard Larger Size
Next Standard Smaller Size
Automatically Update the calculated rated
MVA, Max MVA and % Z into the Ratingpage of the transformer
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11/19Copyright 2003 Operation Technology, Inc. Workshop Notes: Transformer Sizing Slide 11
Transformer MVA Sizing Page
Update automatically
when you press these
buttons
Transformer Rating Page
Transformer Rating Page
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Copyright 2003 Operation Technology, Inc. Workshop Notes: Transformer Sizing Slide 15
Automatic System Parameter
Update
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Copyright 2003 Operation Technology, Inc. Workshop Notes: Transformer Sizing Slide 16
Primary Fixed Tap Editor
Use 0.1% Tap Step to obtain best
Optimization results
Set the maximum/minimum fixed tap range
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Copyright 2003 Operation Technology, Inc. Workshop Notes: Transformer Sizing Slide 17
MVAR Delivery Curve
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Copyright 2003 Operation Technology, Inc. Workshop Notes: Transformer Sizing Slide 18
Unit Transformer Tap
Optimization Reports Input Data
Optimal Tap Position
Transformer Power Input and output at
different system voltage levels (systemvoltage variation)
Generator Power Output at different systemvoltage levels
Generator and System voltage at differentsystem voltage levels
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Copyright 2003 Operation Technology, Inc. Workshop Notes: Transformer Sizing Slide 19
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