Design Basis for NGR Sizing for Existing IBT-30.05.2005- Raf

TCE CONSULTING ENGINEERS LIMITED SIZING REPORT FOR NEUTRAL GROUNDING RESISTOR OF 33/13.8 kV EXISTING INTER BUS TRANSFORMER T01 & T02

30421008-3CL-00029-

SHEET OF i i OF 4

SAUDI ELECTRICITY COMPANY EASTERN OPERATING AREA Dammam, Saudi Arabia GENERATION EXPANSION OF RAFHA POWER PLANT (CONTRACT NO: 30421008/00) DESIGN BASIS FOR NEUTRAL GROUNDING RESISTOR OF 33/13.8 kV EXISTING INTER BUS TRANSFORMERS T01, T02 DOCUMENT NO. : 30421008-3CL-00029-P0A MAY’ 2005

ENGINEERING CONSULTANT TCE CONSULTING ENGINEERS LIMITED 73/1, ST. MARK’S ROAD BANGALORE 560 001 INDIA

CONTRACTOR: AL-TOUKHI COMPANY FOR INDUSTRY & TRADING P.O. BOX 497, RIYADH 11411, KINGDOM OF SAUDI ARABIA TEL. 00966-1-4633660 : FAX. 00966–1-4631150

P0A 30-05-2005

MP

SR

REV NO . DATE

PREPARED BY

CHECKED BY

FILENAME : 278084648.doc

CLEARED BY

APPROVED BY TCE FORM 032 R1

TCE CONSULTING ENGINEERS LIMITED

30421008-3CL-00029-

SIZING REPORT FOR NEUTRAL GROUNDING RESISTOR OF 33/13.8 kV EXISTING INTER BUS TRANSFORMER T01 & T02

CONTENTS SHEET OF i i OF 4

CONTENTS

CLAUSE No.

DESCRIPTION

PAGE No.

1.0

INTRODUCTION

1

2.0

OBJECT

2

3.0

REFERENCES

3

4.0

SIZING CALCULATION

4

5.0

CONCLUSIONS

5

ISSUE P0A FILE NAME: F120R1

FORM NO. 120 R1

TCE CONSULTING ENGINEERS LIMITED 30421008-3CL-00029-

SIZING REPORT FOR NEUTRAL GROUNDING RESISTOR OF 33/13.8 kV EXISTING INTER BUS TRANSFORMER T01 & T02

WRITEUP SHEET: 1 OF 5 OF 4

1.0

INTRODUCTION:

1.1

Al-Toukhi company for Industry & Trading has been awarded turnkey contract for Open Cycle Gas Turbine based CPS expansion project at Rafha 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. 29.92MW @ 50 Deg C, Gas Turbine Generator unit of GE make along with associated Generator Transformer and other balance of plant electro-mechanical equipment.

ISSUE P0A FILE NAME: F120R1

FORM NO. 120 R1

TCE CONSULTING ENGINEERS LIMITED 30421008-3CL-00029-

SIZING REPORT FOR NEUTRAL GROUNDING RESISTOR OF 33/13.8 kV EXISTING INTER BUS TRANSFORMER T01 & T02

WRITEUP SHEET: 2 OF 5 OF 4

2.0

OBJECT:

2.1

The object of this report is to determine the following :

2.1.1

The rating of Neutral grounding Resistor and Disconnector Switch (Isolator) for the Existing 33/13.8 kV Inter Bus Transformers T01 & T02.

ISSUE P0A FILE NAME: F120R1

FORM NO. 120 R1

TCE CONSULTING ENGINEERS LIMITED 30421008-3CL-00029-

SIZING REPORT FOR NEUTRAL GROUNDING RESISTOR OF 33/13.8 kV EXISTING INTER BUS TRANSFORMER T01 & T02

WRITEUP SHEET: 3 OF 5 OF 4

3.0

REFERENCES:

3.1

Key One Line Diagram: Drawing No.KA-667082, Rev-P0E.

3.2

Electrical System Study Report-Doc No: 30421008-3CL-00013-P0B

3.3

APPENDIX-A –Attached.

ISSUE P0A FILE NAME: F120R1

FORM NO. 120 R1

TCE CONSULTING ENGINEERS LIMITED 30421008-3CL-00029-

SIZING REPORT FOR NEUTRAL GROUNDING RESISTOR OF 33/13.8 kV EXISTING INTER BUS TRANSFORMER T01 & T02

WRITEUP SHEET: 4 OF 5 OF 4

4.0

SIZING CALCULATION :

4.1

Neutral Grounding Resistor Sizing for Existing Inter Bus Transformers:

4.1.1

Neutral Grounding Resistor of 33/13.8kV Existing Inter Bus Transformers T01 & T02 shall be sized to limit the earth fault current to 16A and the time duration shall be selected 10 seconds in line with the existing 13.8kV generator neutral grounding resistor which are pertaining to HT Room substations. (Refer to APPENDIXA attached)

4.1.2

The Resistance value of the Resistor is calculated as per the following equation: Resistance ( R ) in ohms =

EL ------------------3 x I

Where EL = Line to Line voltage in volts

=

13.8kV

I = 16A for 10 seconds as per Cl.No.4.1.1 above. Resistance (R) in ohms

= 13.8 x 1000/ 1.732 x 16 = 497.97ohms

4.1.3

Hence, 497.97 Ohms, Neutral grounding resistor rated to carry 16A for 10 seconds has been selected.

4.2 Disconnector Switch (Isolator) 4.2.1

Disconnector Switch(Isolator) shall be selected to carry the earth fault current of 16A.

4.2.2 The selected value would be multiplied by 120% to provide a safety design margin. Hence, the rating wouldl be 16A x 1.2 = 19.2A. 4.2.3 The final rating of disconnector switch would be selected as 32A.

ISSUE P0A FILE NAME: F120R1

FORM NO. 120 R1

TCE CONSULTING ENGINEERS LIMITED 30421008-3CL-00029-

WRITEUP

SIZING REPORT FOR NEUTRAL GROUNDING RESISTOR OF 33/13.8 kV EXISTING INTER BUS TRANSFORMER T01 & T02

SHEET: 5 OF 5 OF 4

5 CONCLUSION: 5.1 The final selected ratings of NGR for The Existing Inter Bus transformer T01 & T02 is tabulated below: Sl.No.

Parameter

Unit

NGR

1

Resistance

ohms

498

2.

Current Rating

A

16 for 10 seconds

3.

Voltage Rating

V

13800

Reference As per Cl No.4.1.3 above As per Cl No.4.1.3 above

5.2 The final selected ratings of Disconnector switch (Isolator) for the Inter Bus transformer T01 & T02 is tabulated below Unit

ISOLATOR

Reference

Current Rating

A

32

As per Cl No.4.2.3 above

2.

Voltage Rating

V

13800

3.

Motor/Manually operated

Motor Operated

4.

Indoor/Outdoor

Outdoor

Sl.No.

Parameter

1.

ISSUE P0A FILE NAME: F120R1

FORM NO. 120 R1