Station Transformer Sizing Report for Arar

TCE CONSULTING ENGINEERS LIMITED

30421007-3CL-00006-P0A

33/4.16kV STATION TRANSFORMER

SIZING REPORT

SHEET OF i

P0A29-07-2004

DG SR

REV NO . DATE PREPARED BY CHECKED BY CLEARED BY APPROVED BY

FILENAME : Station Transformer sizing report for Arar.doc

i

TCE FORM 032 R1

SAUDI ELECTRICITY COMPANYEASTERN OPERATING AREA

Dammam, Saudi Arabia

GENERATION EXPANSION OF ARAR POWER PLANT(CONTRACT NO :30421007/00)

DESIGN BASISFOR

33/4.16kV STATION TRANSFORMER SIZING

DOCUMENT NO. : 30421007-3CL-00006-P0A

JULY 2004

ENGINEERING CONSULTANTTCE CONSULTING ENGINEERS LIMITED

73/1, ST. MARKS ROADBANGALORE 560 001

INDIA

CONTRACTOR:AL-TOUKHI COMPANY FOR INDUSTRY & TRADING

P.O. BOX 497, RIYADH 11411, KINGDOM OF SAUDI ARABIATEL. 00966-1-4633660 : FAX. 009661-4631150

TCE CONSULTING ENGINEERS LIMITED CONTENTS

30421007-3CL-00006-P0A

33/4.16kV STATION TRANSFORMER

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CONTENTS

CLAUSE No. DESCRIPTION PAGE No.

1.0 INTRODUCTION 1

2.0 OBJECT 2

3.0 REFERENCES 3

4.0 ASSUMPTIONS / CONSIDERATIONS 4

5.0 SIZING CALCULATION 5

6.0 CONCLUSIONS 7

TCE CONSULTING ENGINEERS LIMITED WRITEUP

30421007-3CL-00006-P0A 33/4.16kV STATION TRANSFORMER

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1.0 INTRODUCTION:

1.1 Al-Toukhi company for Industry & Trading has been awarded turnkeycontract for Open Cycle Gas Turbine based CPS expansion project atArar of Saudi Electric Company-Eastern Operation Area (SEC-EOA),Saudi Arabia.

1.2 The project consists of design, engineering, procurement, installation,testing and commissioning of two (2) Nos. 60.16MW @ 50?C, PG7121(EA) model Gas Turbine Generator unit of GE make along withassociated Generator Transformer and other balance of plant electro-mechanical equipment.



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2.0 OBJECT:

2.1 The object of this report is to determine the following :

2.1.1 The rating of Station Transformers, T401 & T402 required to feedthe GT Starting Motors & Station Auxiliary loads and to providebackup power supply to Unit Auxiliary Switchgears for proposedGas Turbine Unit#7 and Unit#8 to be installed at Arar CentralPower Station, Saudi Arabia.



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3.0 REFERENCES:

3.1 Document No 30421007-3CL-0003-POA- Station & Unit AuxiliaryTransformer sizing report.

3.2 Key One Line Diagram: Drawing No.30421007-E3-00001-P0A.



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4.0 ASSUMPTIONS/CONSIDERATIONS:

The following assumptions are made for purpose of StationTransformer sizing calculations.

4.1 A power factor of 0.85 and an efficiency of 0.95 has beenconsidered for GT starting motor.

4.2 As per SEC-EOAs clarification vide A40 of clarification set No 04dated 10th Dec 2003, starting of only one GTG starting motor hasbeen considered at a time.

4.3 An overall margin of minimum 10% is considered on StationAuxiliary loads at 480V Station Switchgear over and above the baseload kVA rating. This is to take into account variations in theestimates during detailed engineering and for future addition ofloads.

4.4 The final rating of the transformer will not be less than the ratingindicated in the Technical proposal.

4.5 For Station Transformer sizing, the following conditions areconsidered.

4.5.1 Under normal conditions, each Station Transformer will feed thestation loads connected to its bus section with the bus coupler inopen condition.

4.5.2 During failure of one ST, the other ST will feed the entire 4.16kVSwitchgear loads. Under this condition, outage of two UATs andstarting of one 4.16kV Starting motor is considered, such that theST will be feeding the starting motor, entire station loads and twoUnit auxiliary Switchgear loads.



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5.0 SIZING CALCULATION :

5.1 Calculation of load during starting of one 4.16kV GT Starting motorwith 100% base load on 4.16kV Switchgear:

5.1.1 Maximum Load to be fedfrom one StationTransformer during startingof one GT Starting motorwith 100% base load on4.16kV Switchgear

= Starting kVA of GT Startingmotor + Base load in kVA on4.16kV Switchgear

5.1.2 Maximum Base load on 4.16kV switchgear = 1765kVA

(Refer to Page 2 of 2, Annexure-II of Doc.No.30421007-3CL-00003-P0A: Station and Unit Auxiliary transformers sizing report )

Considering 10 % margin, Base load = 1765 x 1.1 = 1941.5 kVA

5.1.3 The input kVA of Starting motor is calculated considering efficiency& power factor.

Starting motor rating = 663 kW at a Power factor of 0.85 and anefficiency of 0.95

(As per preliminary load list. This rating would be confirmed withSub Vendor)

Starting Motor kVA = 663 / 0.85x0.95

= 821 kVA

As per Cl.No.6.10.05.B.3, Page 214 of 336 of PTS-1022, the lockedrotor currents at rated voltage shall not exceed 550% of the full loadcurrent. (the actual starting current of GT motor would be verifiedwith Sub vendor)

Hence, kVA of the motor during starting = 5.5 x full load kVA

= 5.5 x 821

= 4515.5 kVA



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5.1.4 Hence, maximum Load tobe fed from one StationTransformer during startingof one GT Starting motorwith 100% base load on4.16kV Switchgear

= Starting kVA of GT Startingmotor + Base load in kVA on4.16kV Switchgear

= 1941.5 + 4515.5

= 6457 kVA

5.2 Calculation of load during running of one 4.16kV GT Starting motor

with 100% base load on 4.16kV Switchgear:

5.2.1 Maximum Load to be fedfrom one StationTransformer during runningof one GT Starting motorwith 100% base load on4.16kV Switchgear

= Running kVA of GT Startingmotor + Base load in kVA on4.16kV Switchgear

5.2.2 Maximum Base load on 4.16kV switchgear = 1765kVA

(Refer to Page 2 of 2, Annexure-II of Doc.No.30421007-3CL-00003-P0A: Station and Unit Auxiliary transformers sizing report )

Considering 10 % margin, Base load = 1765 x 1.1 = 1941.5 kVA

5.2.3 Running load required for Starting Motor = 663 / 0.85x0.95

= 821 kVA

5.2.4 Hence, maximum Load tobe fed from one StationTransformer during runningof one GT Starting motorwith 100% base load on4.16kV Switchgear

= Running load in kVA of GTStarting motor + Base load inkVA on 4.16kV Switchgear

= 1941.5 + 821

= 2762.5 kVA



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5.3 The minimum kVA rating of Station Transformer shall be such that:

i) it shall be able to deliver the running load requiredcontinuously.

ii) For the starting period of one GT Starting motor, the StationTransformer shall be able to meet the load kVA requirementwithout exceeding the permissible temperature rises.

iii) during starting of GT Starting motor, Voltage dip shall belimited to 12.5% as per clause 4.03 of PTS-1022 Page No.90 of 336.

5.4 As per Cl.No.5.2.4 above, the minimum Station Transformer ratingshall be 2763kVA to meet the full load requirements. However, asper clause 3.03.2 of PTS-1022, Page No. 37 of 336, 7500kVAtransformer is the minimum rating required.

Hence, kVA rating of Station Transformer selected = 7500kVA.

5.5 As can be seen, 7500kVA rated transformer is meeting therequirements of Cl.No.5.3 (i) & (ii) above. Also, voltage dip duringmotor starting is observed to be 6% as per System studiesconducted which is well within the limit of the allowable 12.5%.

6.0 CONCLUSION:

6.1 The final selected ratings for Station Transformers are tabulatedbelow :

Sl.No. Parameter Unit ST Reference

1 Rating kVA 7500 As per Cl No.5.0above

2 Voltage ratio (Noload) kV 33/4.16As per Cl No.3.03.2

of PTS-1022

3 %Impedance % 8 As per Cl No.3.03.2of PTS-1022

4 Vector Group - Dyn1 As per Cl No.3.03.2of PTS-1022

5 Cooling Type - ONAN As per Cl No.3.03.2of PTS-1022

6 Indoor / Outdoor - Outdoor As per Cl No.3.03.2of PTS-1022



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Sl.No. Parameter Unit ST Reference

7 Dry type /Oil filledtype

- Oil Filled As per Cl No.3.03.2of PTS-1022

8 Tap changer -

Off circuittap

Changer+/- 5%

As per Cl No.3.03.2of PTS-1022

Where, ST : - Station Transformer

Documents

Station Transformer Sizing Report for Arar