SUB-STATION SPECIFICATION
1 Switching Surge and Power Frequency Over Voltages: The 400 kV system switching surge
over voltage and power frequency over voltage shall be limited to 2.5 p. u. and 1.5 p. u. respectively. The
initial value of temporary over voltages could be 2.0 p. u. for 1-2 cycles.
2 Overall Fault Clearance Time: Overall fault clearing time may be designed preferably less than
100 m sec. for 400 kV, 120 m sec. for 220 kV and 160 m sec. for 132 kV levels under comparable
conditions.
3 Duty Cycle of Circuit Breakers: The duty cycle of CBs installed in 420 / 245 / 145 kV System of
the Concessionaire shall be “O-0.3 sec-CO-3 min-CO”. The Surge Arrester shall be suitable for such
circuit breaker duties in the system.
4 Degree of Protection: The degree of protection for enclosures of the Control Cabinets, Junction
boxes and Marshalling Boxes, panels etc. shall as under:
i) Installed Outdoor: IP- 55
ii) Installed Indoor in air conditioned area: IP-31
iii) Installed in covered area: IP-52
iv) Installed Indoor in non air conditioned area where possibility of entry of water is limited: IP-41.
v) For LT Switchgear (AC & DC distribution Boards) : IP-52
5 General Electrical Clearances: Inter equipment arrangement and distances – bay length, bay
width etc. shall be maintained in accordance with the reviewed design of Single Line Diagram (SLD) and
General Electrical Lay-Out (GELO) of the substation.
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