GIVEN DATA FOR GENERATOR TRANSFORMER SIZING ..................................... 2
6.0
CALCULATION FOR GENERATOR TRANSFORMER SIZING ................................ 2
7.0
DECISION OF GENERATOR TRANSFORMER SIZING ............................................. 3
ATTACHMENT#1 HEAT BALANCE DIAGRAM PRELIMINARY ATTACHMENT#2 TRANSFORM SIZING CALCULATION ATTACHMENT#3 LOADING GUIDE FOR OIL IMMERSED POWER TRANSFORMER
ATTACHMENTS: 1. Attachment#1 is the basis for maximum output however this is still a preliminary document. This value can only be considered once the diagrams have been approved.
MD10E505060001_GEN. TR Size_RA
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MONG DUONG POWER STATION PH.1 Calculation for Generator Transformer Sizing
1.0
Rev. A
PURPOSE This calculation is prepared to determine and verify the capacity of generator transformer (525kV/21kV) for Mong Duong Thermal Power Plant Phase 1 Project in Vietnam .
2.0
CODE & STANDARD IEC 60076: Power Transformers
3.0
SITE CONDITIONS The site climatic conditions and the site design conditions are as follows :
c) Ambient design temperature
℃ : 39.5 ℃ : 39.5 ℃
d) Humidity range
: 1892%
a) Absolute minimum air temperature
: 0.2
b) Absolute maximum air temperature
4.0
CALCULATION CRITERIA To calculate transformers sizing, the following points are considered. a) The load for the Unit Auxiliary Transformer will not be considered. b) The capacity of generator transformer will be capable for the operating power factor range of 0.85 lagging to 0.9 leading at the generator terminals. c) The maximum generator output based on the maximum turbine output(VWO condition) is considered as follows ; 
Output : 552.955 MW (Refer to Attachment #1) Voltage : 21 kV 5% , 50 Hz Current : 15,202.3 Amperes Power Factor : 0.85 Lagging
±
d) Generator transformer voltage ratings are as follows ;  High voltage : 525.0 kV WYE with grounded neutral  Low voltage : 21.0 kV DELTA e) Generator transformer will be operated at its ODAF rating under most condition. MD10E505060001_GEN. TR Size_RA
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MONG DUONG POWER STATION PH.1 Calculation for Generator Transformer Sizing
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Rev. A
GIVEN DATA FOR GENERATOR TRANSFORMER SIZING a) The generator will be operated with max. continuous rating 650.535 MVA (552.955 MW at power factor 0.85 lagging). Operating Condition
Description
(Case : VWO)
Ambient Air Temperature
34.5 °C
Cooling Water Temperature
30.5 °C
Relative Humidity
85.0 %
Power Factor
0.85 lagging
Power at the Generator Terminal
552.955 MW
Remark
Refer to Heat Balance Diagrams (Attachment #1)
b) The generator will be operated in any of the following power factor ranges ;  Case I  Case II  Case III
6.0
: : :
0.90 P.F Leading 1.0 P.F 0.85 P.F Lagging
CALCULATION FOR GENERATOR TRANSFORMER SIZING The generator output based on the maximum turbine output(VWO condition) is calculated as follows ; 
Power factor 0.90 Leading : MVA = 552.955 / 0.9 = 614.394 MVA at 39. 5°C amb. temp.

Power factor 1.0 : MVA = 552.955 / 1.0 = 552.955 MVA at 39. 5°C amb. temp.

Power factor 0.85 Lagging : MVA = 552.955 / 0.85 = 650.535 MVA at 39. 5°C amb. temp.
The capacity of generator transformer will be sized to cover the generator output at the power factor ranges of 0.85 lagging to 0.9 leading as calculated above and therefore, generator transformer capacity at 39. 5°C amb. temp should be : 620.538 MVA or above @ 0.90P.F. Leading 558.485 MVA or above @ 1.0P.F. 657.041 MVA or above @ 0.85P.F. Lagging
MD10E505060001_GEN. TR Size_RA
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MONG DUONG POWER STATION PH.1 Calculation for Generator Transformer Sizing
Rev. A
The rated capacity of transformer has been selected as 660MVA(based on ODAF) at the ambient temperature 39.5°C, which has the output capabilities by ambient temperature as listed below. Also, this capacity will satisfy to have minimum 1% margine for generator output for all ambient temperature condition as shown in Attachment #2.
Ambient Temperature
0.2°C
34.5°C
39.5°C
Transformer Capacity [MVA]
842.1
682.8
660
* Note) The transformer capacity is calculated as per the loading factor at the different ambient temperatures. (Refer to the attachment #3, IEC 60354 Loading Guide for Oilimmersed Power Transformers, 3.3 Normal continuous Loading – Table 6. Acceptable load factor for continuous duty K24 at different ambient temperatures (ON, OF and OD cooling)).
7.0
DECISION OF GENERATOR TRANSFORMER SIZING Because the capacity of transformer means a value of input power to transformer, the capacity of generator transformer should be equal or larger than the output of generator.
Based on the calculation results given above, the capacity of the generator transformer is selected as below;
660MVA(220MVA x 3), ODAF, 525/21 kV
Z=14.5% @660MVA
On load HV tap changer ±17 x 1.3% taps
MD10E505060001_GEN. TR Size_RA
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MONG DUONG POWER STATION PH.1 Calculation for Generator Transformer Sizing
Rev. A
Attachment #1 Heat Balance Diagram preliminary
MD10E505060001_GEN. TR Size_RA
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MONG DUONG POWER STATION PH.1 Calculation for Generator Transformer Sizing
Rev. A
Attachment #2 Transformer Sizing Calculation
MD10E505060001_GEN. TR Size_RA
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GENERATOR TRANSFORMER SIZING CALCULATION 1. GENERATOR RATING BASED ON 34.5Deg.C GEN MVA PF 650.5353 0.85 552.9550 1 614.3944 0.9
2.TRANSFORMER IMPEDANCE DATA BASED ON 39.5Deg.C %z 14.50% X/R RATIO TOLERANCE 7.5% MARGIN 101%
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