NATIONAL ALUMINIUM COMPANY LIMITED - Rites

Following power utilization standard voltage levels shall be adopted for various systems:
1. Station supply
3. Power supply to PLC extension 240 V, 1 phase, 2 wire, 50 Hz, A.C. (from UPS)
4. DC control supply
220 V, 2 wire, unearthed
5. Plant illumination
6.
7.
Welding socket / power 415 V, 3 phase, 50 Hz, A.C. outlets
receptacles
240 V, 1 phase, 2 wire, 50 Hz, A.C. outlets
Special socket outlets for 24 V, 1 phase, 2 wire, 50 Hz, A.C. through suitable
portable lamps
transformers
8. Sockets for electrical tools, etc 240 V, 1 phase, 2 wire, 50 Hz, with one point earthed
9 Emergency illumination 220 V DC
d) Permissible variations
The system / unit / plant / equipment shall be designed suitably for following variation in
voltage and frequency;
Permissible variation with rated performance and control
effectiveness maintained
Permissible variation for control and regulation equipment with
rated performance and control quality maintained
Permissible voltage dip at HT switchgear bus during starting of
motor
- 15 % -
Permissible voltage dip at MCC bus during starting of LT motors - 15 % -
e) Symmetrical short circuit ratings
The short circuit ratings of all the equipment like MCCs, motors, PDBs / LDBs, cables, power
socket & lighting cabinets, etc shall be selected keeping in view the fault level capacities of the
Purchaser’s electrical equipment.
The three phase symmetrical short circuit rating at 33 kV level shall be 25 25kA. The three phase
symmetrical short circuit rating at 415 V level shall be 50kA.
The rated short circuit withstand duration for 33 KV shall be 3 sec, whereas for 415 V system,
it shall be 1.0 sec.
f) Criteria for selection of voltage levels ffor
drive motors
Technical Specification:Sec-6, Electrical
33 kV, 3 phase, 3 wire, unearthed system
415 V, 3 phase, 4 wire, solidly earthed
240 V, 1 phase, 2 wire, 50 Hz, A.C.
Voltage Frequency
+/-10% 10% +/-5%
+/- 10 % +/-5%
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