Technical Corrigendum 2  
Design, engineering, manufacturing of 140MVA Generator Transformer for NTPC Kawas  
Sl  
Tech specifications  
Bidders Query  
NTPC Comments  
No.  
1
Clause 1.0, S.No 10.0 Please furnish the technical details of oil tanker  
A: Requirement of 6  
KL oil tanker.  
Technical Details :- TROLLEY MOUNTED TRANSFORMER  
OIL STORAGE TANK OF 6 KL CAPACITY.  
Capacity of Tank: 6 KL  
Medium of storage: Transformer oil IES: 296 class  
Material Specification work: IS 2062 for shell Dished  
Ends. Man Hole, Frame work. IS 1239 for Nozzles &  
Piping  
Thickness of Plate: IS 2825 for Both shell & Dished Ends.  
Shell thickness will be 8mm & dished end thickness will  
be 10 mm.  
Finish for Tank Inside & outside: Two Coats of PU Primer  
Two Coats of PU Paint, after cleaning and sand blasting.  
Colour shade: Outside yellow shade, tank inside white  
thickness 60-70 microns. Trailer 2 coats of primer & 2  
coats of PU paint Black Thickness 60-70 microns.  
Trailer: with pneumatic Tyres – 04 nos., Mechanical  
parking brakes with Turn Table arrangement & 4 No’s  
each screw Jacks.  
Oil level indicator: duly fitted on the tank  
Sampling Valve: 15 NB with Dummy plate  
Drain Valve: 15 NB with Dummy plate  
Inlet Valve: 40 NB with Dummy plate  
Outlet Valve: 40 NB with Dummy plate  
Ladder for inside & outside shall be provided  
Silica gel Breather: to be provided  
Tool kit: to be provided  
Inspection Cover: Hinged type at one end  
Inscription on Tank: 6 KL Transformer oil storage tank  
NTPC, KGPP  
In let & out let valves: Diagonal to each other. Ball Valve  
with SS ball & Teflon sheet.  
Over flow pipe: to be provided  
Lifting Hooks: Two lifting hooks on top (one on each  
end) shall be supplied for lifting facility.  
Pressure Test (tank Details): Tank should with stand an  
air / Nitrogen pressure at least 20 PSI for 4 hours.  
Top inspection cover shall be fitted with rubber ring  
gaskets.  
2
Technical parameters  
Clause No.3.1 (p) (VI)  
Minimum creepage distance for HV bushing and  
HV neutral bushing were mentioned as 39 mm/kV.  
Creepage distance of HV and HV neutral bushing is  
agreed upon as 31mm/KV and creepage distance of LV  
Please note that normally as per NTPC standard, 31 bushing is agreed upon 25mm/KV.  
mm/kV creepage distance for bushing are specified.  
As per IS 2099 Cl. 7. I (d), even for very heavily  
polluted atmosphere, the creepage distances  
mentioned as 3 Imm/kV only. So we will provide  
HV & HV neutral bushings with 3 1 mm/kV  
creepage distance.  
Please note that, creepage distances are  
depending on pollution levels. Since the LV  
termination is inside an air filled isolated phase  
bus duct, which is similar to an air filled cable  
box , there is no significance of maintaining  
pollution level/creepage distance.  
As per tender specification, for 24 kV ( LV) bushing,  
the creepage distance mentioned is 58.33 mm/kV.  
Ref to CBIP publication No.317, section A, general,  
Cl.No. 12.15, creepage distance mentioned for 24  
kV bushing is 384 mm only. So we will provide 24  
kV bushing with a creepage distance of 25 mm/kV  
which is more than enough from the values  
mentioned in the CBIP standard. So please accept  
this comment. (Relevant pages of CBIP & IS are  
attached for reference).  
3
Cl 4.4.3 windings  
We will provide winding conductors of electrolyte  
grade copper with CLASS A insulation instead of  
the specified thermally upgraded paper covering  
insulation. Please note that as per IEC 60076-5,  
table 3, for oil immersed transformers, insulation  
class specified is CLASS A . (Relevant page of IEC  
attached for reference.) . Winding conductors with  
CLASS A insulation is used by us even for 400 kV  
transformers already supplied to NTPC. Thermally  
upgraded papers will be provided for all places,  
where the chances of temperature rise is high, as per  
TELK standards and calculation. So kindly accept  
this comment.  
Winding conductor insulation should be as per tender  
specification only. ( i.e., “specified thermally upgraded  
paper covering” only )  
4
Clause 4.5.1 (ac.) &  
ad) — Fittings:-  
Online DGA analyser and online moisture removal  
system is not mentioned in Bill of Quantities. If  
required please furnish the technical specification for  
Online moisture removal system.  
Online moisture removal system is required along with  
the transformer. Technical specifications of online  
moisture removal system are as under:-  
(
The system shall be fitted in an enclosure. Oil Moisture  
measurement probe shall be provided with “Online  
Moisture Removal System”. Alarm / status information  
shall be appropriately wired up to the Common M. box.  
5
6
Annexure IV: Technical  
For LV side bus duct termination, we will provide Flexible connectors along with required fasteners are to  
specification of isolated suitable bushings and bus duct flange. Our scope of be supplied by the vendor only. Required drawings of  
phase bus duct  
existing connectors shall be provided by NTPC during  
detailed engineering.  
supply include up to bus duct flange only. Isolated  
phase Bus duct, Accessories , Flexible connectors etc  
are not included in our scope of supply.  
Indicative list of sub  
vendor for raw  
material and bought  
out items, Sl.No : 15  
Please include subject vendor (specific make) in the  
approved venders list for Bushing CT.  
Bidder shall be providing bushing CT as per approved  
vendor list, which will be decided after award of  
contract to the successful Bidder. ( Given in the tech  
specs is the indicative list of sub vendor for raw material  
&
bought out items )  
(Bushing CT):