This document discusses transformer sizing methods in ETAP software based on industry standards. It describes how ETAP considers factors like cooling type, altitude, temperature, load variation, and impedance requirements to calculate the required transformer MVA size. The sizing results section shows the required size along with the next standard larger and smaller sizes. The ratings are automatically updated when clicking buttons in the transformer rating page. The document also covers unit transformer sizing in ETAP to optimize tap settings considering voltage variation and auxiliary loads.

1. © 1996-2010 ETAP/Operation Technology, Inc. – ETAP Workshop Notes
Transformer MVA Sizing

2. Slide 2© 1996-2010 ETAP/Operation Technology, Inc. – ETAP Workshop Notes
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

3. Slide 3© 1996-2010 ETAP/Operation Technology, Inc. – ETAP Workshop Notes
MVA Sizing Page
Transformer
MVA Loading
Correction
Factors & Load
Variation
Sizing Results
Section
•Larger
•Required
•Smaller
•Impedance
Short-Circuit
Impedance
limits
Consider
Growth Factor
for Max. MVA

4. Slide 4© 1996-2010 ETAP/Operation Technology, Inc. – ETAP Workshop Notes
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

5. Slide 5© 1996-2010 ETAP/Operation Technology, Inc. – ETAP Workshop Notes
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

6. Slide 6© 1996-2010 ETAP/Operation Technology, Inc. – ETAP Workshop Notes
Load Variation
• Growth Factor
– Allowance for future load growth
• Load Factor
– The ratio of the average load to the peak load
over a designated period of time
– Load Factor = 100 x ( kWi x Ti ) / ( kWp x Tt )%
– Load Factor = 100 x E / ( kWi x Tt )%

7. Slide 7© 1996-2010 ETAP/Operation Technology, Inc. – ETAP Workshop Notes
Where:
I = interval of time when the load is non-zero
kWi = load at interval i
Ti = number of hours of interval i
kWp = 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 the
interval

8. Slide 8© 1996-2010 ETAP/Operation Technology, Inc. – ETAP Workshop Notes
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)

9. Slide 9© 1996-2010 ETAP/Operation Technology, Inc. – ETAP Workshop Notes
Connected or Operating Load
• Connected Load
– Determine the radial load connected to the transformer
secondary
– Can include spare loads for conservative results
• Operating Load
– PowerStation’s 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

10. Slide 10© 1996-2010 ETAP/Operation Technology, Inc. – ETAP Workshop Notes
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 Rating
page of the transformer

11. Slide 11© 1996-2010 ETAP/Operation Technology, Inc. – ETAP Workshop Notes
Update automatically
when you press these
buttons
Transformer Rating Page
Transformer Rating Page
Transformer MVA Sizing Page

12. © 1996-2010 ETAP/Operation Technology, Inc. – ETAP Workshop Notes
Unit Transformer Sizing
Presented by Farrokh Shokooh

13. Slide 13© 1996-2010 ETAP/Operation Technology, Inc. – ETAP Workshop Notes
Unit Transformer Sizing
• Based on IEEE C5F-116 Standard
• Optimize unit transformer turn ratio
• Consider system voltage variation
• Consider generation station auxiliary load
• Automatically detect generator, cable
impedance and bus nominal kV
• Generator reactive vs. capacitive plots
• Optimization reports

14. Slide 14© 1996-2010 ETAP/Operation Technology, Inc. – ETAP Workshop Notes
Transformer Tap Optimization
Page
Primary / Secondary
Cable Impedance
Optimization
Results Section
Transformer
Impedance
Section System kV
Information
Generator
Information
Auxiliary Load
Information

15. Slide 15© 1996-2010 ETAP/Operation Technology, Inc. – ETAP Workshop Notes
Automatic System Parameter
Update

16. Slide 16© 1996-2010 ETAP/Operation Technology, Inc. – ETAP Workshop Notes
Primary Fixed Tap Editor
• Use 0.1% Tap Step to obtain best
Optimization results
• Set the maximum/minimum fixed tap range

17. Slide 17© 1996-2010 ETAP/Operation Technology, Inc. – ETAP Workshop Notes
MVAR Delivery Curve

18. Slide 18© 1996-2010 ETAP/Operation Technology, Inc. – ETAP Workshop Notes
Unit Transformer Tap
Optimization Reports
• Input Data
• Optimal Tap Position
• Transformer Power Input and output at
different system voltage levels (system
voltage variation)
• Generator Power Output at different system
voltage levels
• Generator and System voltage at different
system voltage levels

19. Slide 19© 1996-2010 ETAP/Operation Technology, Inc. – ETAP Workshop Notes