SIZING REPORT FOR NEUTRAL GROUNDING RESISTOR OF 33/4.16kV STATION TRANSFORMER
SHEET i OF i
SAUDI ELECTRICITY COMPANY EASTERN OPERATING AREA Dammam, Saudi Arabia GENERATION EXPANSION OF ARAR POWER PLANT (CONTRACT NO :30421007/00)
DESIGN BASIS FOR NEUTRAL GROUNDING RESISTOR OF 33/4.16kV STATION TRANSFORMER DOCUMENT NO. : 30421007-3CL-00007-P0A
JULY 2004
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 ARABIA TEL. 00966-1-4633660 : FAX. 00966–1-4631150
SIZING REPORT FOR NEUTRAL GROUNDING RESISTOR OF 33/4.16kV STATION TRANSFORMER
WRITEUP SHEET 1 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 Arar 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 with associated Generator Transformer and other balance of plant electromechanical equipment.
SIZING REPORT FOR NEUTRAL GROUNDING RESISTOR OF 33/4.16kV STATION TRANSFORMER
SHEET 4 OF 4
SIZING CALCULATION : Neutral Grounding Resistor Sizing for Station Transformer
4.1
Neutral Grounding Resistor of 33/4.16kV Station Transformer shall be sized to limit the earth fault current to 400A for 1 minute as indicated in SEC-EOA’s drawing No.KT-808215 Rev A attached with Specification PTS-1022.
4.2
The Resistance value of the Resistor is calculated as per the following equation: Resistance ( R ) in ohms =
EL 3
x I
where E L = Line to Line voltage in volts
=
4.16kV
I = 400A for 1 minute as per Cl.No.5.6.1 above. Resistance ( R ) in ohms
= 4.16 x 1000/ 1.732 x 400 = 6 ohms
4.3
Hence, 6 Ohms, Neutral grounding resistor rated to carry 400A for one minute has been selected.
5.0
CONCLUSION:
5.1
The final selected ratings of NGR for Station transformer is tabulated below Sl.No.
Parameter
Unit
NGR
1
Resistance
ohms
6
2
Current Rating
A
400 for 60 seconds
Reference As per Cl No.4.3 above As per Cl No.4.3 above
