04 - transformer sizing

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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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


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



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



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 )%



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



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)



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



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



Transformer MVA Sizing Page

Update automatically

when you press these

buttons

Transformer Rating Page

Transformer Rating Page


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Automatic System Parameter

Update


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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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MVAR Delivery Curve


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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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04 - transformer sizing

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