NATIONAL ALUMINIUM COMPANY LIMITED - Rites

Capacity
Nominal voltage (kV) 33
Max system voltage (kV) 35
Power frequency withstand voltage (kV) 75
System earthing
No. of phases
Frequency
Impulse test withstand voltage (kV) 170
Short time current rating (for all current 25 kA for 3 sec
carrying parts)
Fault level (3 phase symmetrical) 25kA
Type of Cooling
Connection HV winding DELTA
Connection LV winding STAR
Connection Symbol
HT/LT transformers shall be of the latest design, oil immersed type as per IS : 1886 and testing
as per IS 2026 part I. . All dry type air natural transformers shall be suitable for indoor use line
up with power control centre as unit type.
Bidder shall ensure that manufacturer shall have his own in in-house house core cutting facilities on
CNC machines.
Special care shall be taken ken to make enclosed equipment proof against entry of rats, lizards and
other creeping reptiles which may create electrical short short- circuits inside live equipment. The
design of each transformer shall be such that the risk of accidental short short-circuits due to
reptiles or vermin shall be obviated.
The transformer shall be of cast resin type. The tap changing arrangement shall be of
removable link type.
Each transformer shall be suitable for operation at full rated power on all tappings without
exceeding the temperature rise of 800C over the ambient of 50
shall be F.
o Each transformer shall be suitable for operation at full rated power on all tappings without
C. Minimum class of Insulation
The transformers shall be designed to be capable of withstanding, without injury, the thermal
and mechanical effects of short short-circuits between phases or between n phase and earth at the
terminals of any winding with full voltage applied across the other winding. All transformers
shall be capable of withstanding specified through fault current for minimum of 2 seconds as
per IS: 2026 (Part-1).
The transformers shall all be designed to suppress harmonic currents, especially the third and
fifth, so as to eliminate distortion in the wave form and consequent additional insulation
Technical Specification:Sec-6, Electrical
Low resistance earthed
3
50 Hz
ONAN
Dyn 11
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