NATIONAL ALUMINIUM COMPANY LIMITED - Rites

Static Transfer Switches
The static transfer switches shall use SCRs and other static devices, for automatic transfer of
load from the Normal source to the Alternate source. The continuous capacity of each static
switch shall be equal to the full load capacity of one inverter. Maximum transfer time including
sensing shall not be more than 1/4 cycle. The transition shall be "make before break" in both
directions. The static switch shall be provided with fuses in both `normal' and `alternat `alternate'
power source. Provision for annunciation of failure of fuse or failure of alternate source shall
be made. The switch shall be provided with surge suppression networks and shall also be rated
to withstand transient voltages upto 150% of rated voltage. Th The e short time rating of the switch
shall be 150% of the rated full load current for two (2) minutes.
Three phase/single phase Transformer and voltage stabilizer
The transformer connection shall preferably be of Le Blanc type with delta connected winding
on the three phase side or of open delta connection type. Other alternatives shall also be
considered, provided the connection has minimum unbalance on the primary side. The
transformer shall be encapsulated in Class B insulation. The transformer shall be adequately
rated for the duty involved. The actual value may be slightly increased to take care of any
losses in the static voltage stabiliser.
The voltage stabiliser shall employ silicon solid state circuitry and shall maintain the specified
output voltage for 0 to 100% load, with maximum input voltage variation as specified specified.
Manual Bypass
Switch The manual bypass switch shall be a four (4) position swit switch. ch. It shall be used to isolate a
static switch from its load and alternate power supply and to take it out of service without
power interruption to the load. It shall be ‘make before break’ type contacts, so that power
supply to the loads is continuous du during ring switch operations. It shall be capable of carrying rated
continuous full load inverter current.
Fault Diagonistic Unit
Unit Fault diagonistic unit shall be provided to supervise UPS operation. Facility to take print
out and recording of important pparameters
arameters shall be provided. All the alarms shall be interfaced
with DDCMIS.
Battery
DC battery shall be VRLA, sealed maintenance free type. Battery capacity should be 500Amp
Hr with float charger of 110 Amps. Float cum boost charger should be 110Amps also. Battery
shall be located in the battery room. Battery shall be suitable to maintain the power supply for
at least 60 minutes (battery back time) in the event of mains failure.
Technical Specification:Sec-6, Electrical
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