transformer sizing

ETAP 5.0Transformer MVA Sizing

Copyright 2003 Operation Technology, Inc.

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 transformerCopyright 2003 Operation Technology, Inc. Workshop Notes: Transformer Sizing Slide 2

MVA Sizing PageTransformer MVA Loading Short-Circuit Impedance limits

Correction Factors & Load Variation

Sizing Results Section Larger Required Smaller Impedance

Consider Growth Factor for Max. MVA

Copyright 2003 Operation Technology, Inc. Workshop Notes: Transformer Sizing

Slide 3

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


Slide 4

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

800 meter

900 meter

1000 meter

1100 meter

1200 meter


Slide 5

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 )%


Slide 6

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


Slide 7

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)


Slide 8

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 systemsCopyright 2003 Operation Technology, Inc. Workshop Notes: Transformer Sizing Slide 9

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 transformerCopyright 2003 Operation Technology, Inc. Workshop Notes: Transformer Sizing Slide 10

Transformer MVA Sizing Page Update automatically when you press these buttons

Transformer Rating Page

Transformer Rating PageCopyright 2003 Operation Technology, Inc. Workshop Notes: Transformer Sizing Slide 11

ETAP 5.0Unit Transformer Sizing

Presented by Farrokh ShokoohCopyright 2003 Operation Technology, Inc.

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 reportsCopyright 2003 Operation Technology, Inc. Workshop Notes: Transformer Sizing Slide 13

Transformer Tap Optimization PageTransformer Impedance Section Primary / Secondary Cable Impedance Generator Information System kV Information

Auxiliary Load Information Optimization Results Section


Slide 14

Automatic System Parameter Update


Slide 15

Primary Fixed Tap Editor Use 0.1% Tap Step to obtain best Optimization results Set the maximum/minimum fixed tap range


Slide 16

MVAR Delivery Curve


Slide 17

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 levelsCopyright 2003 Operation Technology, Inc. Workshop Notes: Transformer Sizing Slide 18


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transformer sizing

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