7.3.2  SWITCHGEARS (GENERAL FEATURES)

(a)  33 kV

The 33 kV switchgear panel comprise of:

i) 2 Nos. of 33 kV, 1250 A/1500 MVA vacuum incoming circuit breakers.

ii)  1 No. of 33 kV, 1250 A/1500 MVA bus section vacuum circuit breakers

iii)    8 Nos. of 33 kV, 1250 A/1500 MVA outgoing vacuum circuit breakers.

The switchgears shall feed all ROP and PREFRE transformers and shall also extend main power supply to proposed UNCF project at 33 kV level through 2 nos. under ground cables. The switchgears shall be  of draw out type and are dust and vermin proof with IP-52 enclosure. Access to circuit breakers' operating mechanism shall be through compartment doors provided with hinges and key-type locks. Instruments and relays are mounted on hinged type panels. Different components shall be housed in different compartments to enhance their accessibility for maintenance.

Various metering devices shall be provided for monitoring the performance of the 33 kV switchgear. Technical particulars of 33 KV indoor VCB switchgear are listed in Table V.

Numerical Protective devices (relays) shall also be installed on the switchgear for protection against various fault conditions.

SALIENT FEATURES OF NUMERICAL RELAYS

 -Multiprocessor architecture with parallel processing offers high speed of fault detection at 

  competitive price.

  -Decentralized modular approach with a separate processor for each task admits of ease of 

   modification or addition.

  -Since relay settings are software governed, modifications can be made over a large dynamic

   range without any physical modification.

 - Reliability and security are greatly enhanced.

 -Algorithm dependent performance of relay is predictable to a high degree of accuracy.

 -User friendly yet highly capable.

 - Increased Communication ability.

(b) 415 VOLTS

415 V class-IV switchgear panel in sub-station shall comprise of  :

i) 2 Nos. of 415 V, 4000 A/46 MVA incoming air circuit breakers.

ii) 1 No. of 415 V, 4000 A/46 MVA bus section air circuit breaker

iii) 36 Nos. of outgoing feeders comprising of 415 V ACBs and MCCBs.

iv) 2 Nos.of 2000 A tie-line air circuit breakers for PREFRE switchgears.

v) 2 Nos.1000 A air circuit breakers for SFSF switchgears.

vi) 2 Nos. 630A MCCBs for AWTF.

7.3.3   BUS DUCT (GENERAL FEATURES)

2 Nos. of 415 V, 4000 Amps, 46 MVA, 3 Phase,TPN compact bus duct shall be laid between medium voltage switchgears and 33 /0.433 KV transformers.

Busduct system shall be low impedance, sandwich epoxy resin insulated type construction of approved manufacturer, current ratings as detailed on the drawings/schedules and complying to degree of protection IP54. The duct is so fabricated that it shall be in a position to withstand, without damage, pressures (internal/ external) resulting from maximum fault condition. The busduct shall have heat and fire resistant surface that would prevent corrosion. A readily accessible ground strip shall run along the entire length of the duct.  The ground conductor running along the bus duct shall be of copper of minimum size 50x6 mm² . The ground bus (50x6 sq.mm copper strip) shall be provided with clamp type terminals at the end for connection with earth mat system. The busduct supports shall withstand thermal and mechanical stresses.

The Busbar shall be designed and manufactured to comply with BS EN 60439-1&-2  (IEC 439) and IS-8623 (1&2). This should be suitable for up to 1100 volt, 3 phase, 4 wire, 50Hz system, and capable of withstanding prospective fault level currents of 65kA rms.

The bus duct insulation shall be epoxy / mica-polyster insulated class F type of 1000V grade, coated concentrically over the entire length of the conductor. The insulation shall be non-toxic, chemically inert, stable material and also fire-retardant. The insulator shall posses sufficient mechanical strength to withstand the forces due to momentary short circuit and mechanical shocks generated by 65 kA short circuit current.

The bus duct enclosure shall be 1.6 mm thick CRCA sheet housing with epoxy powder coating. The epoxy paint thickness over the enclosure shall be minimum 50 micron. The enclosure should provide excellent rigidity and mechanical strength. The degree of protection shall be IP-54. The bus-duct system should carry rated current up to an ambient temperature of 40°C. Maximum temperature rise admissible shall be limited to the insulation class-B when loaded with continuous rated current.

Class-IV non-safety related systems of ROP are listed in the following table:

Group-A Non Safety Related Systems	Group-B Non Safety Related Systems
CLASS-IV NPCC PANEL MCC –1 (V1 + V2 SUPPLY FAN)	MCC –2 (V1 + V2 SUPPLY FAN)
MCC (PCW–RUNNING)	MCC (PCW –STANDBY)
MCC (FHA - NORMAL )
MCC  (A/G + MUA-2 )
MCC (MUA-3 + DM WATER AREA )
MCC (A/G + HUT BASIN)
MCC  (MUA – 1)
MCC (NO2 GAS AREA)
MCC (TSA-1) MCC (TSA-3) MCC (TSA-2) MCC (DECONTAMINATION ROOM ) MCC (AHU -RECONVERSION LAB))
MCC (FORMALDEHYDE AREA ) BOILER & COMPRESSOR MCC CHILLER MCC HIGH BLOCK –MLDB-N & 6 Nos. LIGHT. POWER DBs 3 NOS. LIGHTING PDBs 1 No. AIR HANDLING UNIT POWER- DISTRIBUTION BOARD

7.3.4  OPERATING PHILOSOPHY OF CLASS-IV POWER SYSTEM

7.3.4.1 In case of loss of power supply on one bus-section of NPCC (Normal Power Control Centre), power supply to the other bus-section shall be restored by closing the bus-coupler breaker of NPCC automatically/ manually.  

7.3.4.2 In case of failure of incomer breaker of an MCC or the cable incomer of MCC or upstream breaker of corresponding NPCC, standby motor shall be started from the corresponding group of MCC.

7.3.4.3 In case of failure of any motor-starter or the outgoing feeder of an MCC, standby motor shall be started from the corresponding group of MCC.

7.4 CLASS -III POWER SUPPLY SYSTEM

7.4.1   415 V SWITCHGEARS

  

415 V class-III switchgear panel in sub-station shall comprise of  :

i)  2 Nos. of 415 V, 2500 A/46 MVA incoming air circuit breakers.

ii) 2 Nos. of 415V, 1600 A/46MVA incoming air circuit breakers.

iii)2 Nos. of 415V, 2500 A/46 MVA bus section air circuit breakers

iv)2 Nos. of 415 V, 1000 A/46 MVA spare air circuit breakers.

v) 28 Nos. of outgoing feeders comprising of ACBs and MCCBs.

vi) 2 Nos 630A  MCCBs for SFSF.

vii)2 Nos. 630A MCCBs for AWTF.

Technical specification of PCC (NPCC and EPCC) panels is enclosed vide Table-VIII.

7.4.2  DIESEL GENERATORS

Two numbers of diesel generator sets of capacity 1010kVA each conforming to ISO 3046 shall be installed in sub-station for providing 415V, 50Hz grounded AC power supply to the plant's safety related loads during normal power failure/ outage conditions.  The DG sets shall have the capability to start from cold condition, reach synchronous speed and be ready to take the load, without undue stress, in about 10 seconds from the initiation of start impulse.  The generators shall

be capable of accepting their maximum rated load in single or multi steps.  When the machine is running in no-load condition at the rated voltage and speed, the transient voltage drop at its terminals on starting the exhaust fan motor drawing a huge starting current at 0.3 power

factor shall not exceed 10% of the rated voltage. When the machine is running at 80% load at 0.8 power factor at the rated voltage and speed, the corresponding voltage drop on starting the same motor shall not exceed 15%.  The response of the regulator and excitation system shall be  such

that following a step  application or rejection of rated load at rated power factor and subsequent to the drop or alternator rise of sub-transient voltage, the generator will recover its set voltage within 0.5 second.  The alternator shall be capable of taking momentary overload.  Rating of the two DG sets shall be so chosen that the entire emergency load of the plant can be continuously fed even if one of the sets fails.

The control panel design shall include microprocessor based fast and reliable control system.  The DG sets shall be provided with an independent cooling tower.  Each DG set shall also be provided with an independent day tank of 2500 ltr. capacity for storing the fuel. On consideration of fire safety, these tanks shall be  located outside of the room in which the DG sets are installed. In

addition to the local storage of fuel, supply of fuel for 7-day continuous operation of one DG set, from the bulk storage facility shall also be made available.

In the event of normal power failure, the DG set will start automatically.  The entire essential base loads like plant lighting, health & safety instruments, plant communication equipments etc., shall be fed within 30 seconds.  The design envisages manual connection of bulk loads like exhaust and off-gas fans one by one in a pre-set sequence to protect the generator from the effects of surge currents arising immediately after connecting a bulk load.

Technical specification of DG set is enclosed vide Table-IX.

The Safety related power supply system is categorized into two groups, Group-A and Group-B. Power Supply System belonging to Group A Safety Related System and Group B Safety Related System are identified in the following table:

Group-A Safety Related Systems	Group-B Safety Related Systems
CLASS-III EPCC PANEL (GROUP-A) MCC –1 (E2 FAN)	CLASS-III EPCC PANEL (GROUP-B) MCC –2 (E2 FAN)
MCC –1 (OFF GAS FAN)	MCC –2 (OFF GAS FAN)
MCC-E (FHA) MCC  (E- COMPRESSOR)
HIGH BLOCK-MLDB-E & 6 NOs. LIGHTING PDBs
UPS SET – 1	UPS SET – 2
UPS DB- 1	UPS DB – 2
DC SWITCHBOARD-1 1 No. LIGHTING PDB	DC SWITCHBOARD-2

7.4.3 OPERATING PHILOSOPHY OF CLASS-III POWER SYSTEM

7.4.3.1 In case of loss of power supply on one bus-section of EPCC (Emergency Power Control Centre), power supply to the affected bus-section shall be restored by starting the DG set of that section automatically/ manually.

7.4.3.2 In case of failure of incomer breaker of an MCC or the cable incomer of MCC or upstream breaker of corresponding EPCC, standby motor shall be started from the corresponding group of MCC.

7.4.3.3 In case of failure of any motor-starter or the outgoing feeder of an MCC, standby motor shall be started from the corresponding group of MCC.