ELECTRICAL SYSTEM DBR

1.0 INTRODUCTION:

Project ROP (Revamping of Power Reactor Fuel Reprocessing (PREFRE) plant) at Tarapur is a radio chemical facility with a reprocessing capacity of 100 Te of spent fuel, which is aimed to facilitate life extension and the capacity augmentation of the existing PREFRE plant at Tarapur. Power Reactor Fuel Reprocessing (PREFRE) plant was designed, built and commissioned in 1974, to re-process the spent fuels from CIRUS, RAPS, NAPS and MAPS reactors. As the existing PREFRE plant is nearly three decades old, its process systems and the auxiliary support systems like effluent handling in tanks, the piping network, waste storage etc. are proposed to be up-graded through the ROP Project. Also as some new atomic power stations have been recently commissioned at Kakrapara, Kaiga and Kota, capacity augmentation of PREFRE is planned through the ROP project within the PREFRE complex.

Owing to the nature of processes employed, which involve handling of highly radioactive process solutions, efficient performance of the Electrical Power system is critical to plant safety. Availability of a reliable and adequate Mains power supply is very critical for safe operation of the plant. Similarly the emergency power supply systems need a high degree of reliability for plant safety and environment protection.

2.0 SCOPE OF THE DESIGN BASIS REPORT

This Design Basis Report covers mainly design criteria, system description, salient features of

components electrical system of ROP sub-station, criteria for selection of safety and non-safety

related electrical equipments, postulated initiating events and their consequences on safety related

systems to meet their intended functions. Separate DBR has been prepared for ROP facility.

3.0 DESIGN OBJECTIVES

3.1 Class-IV Mains Power Supply System (33 KV)

33KV `Mains’ HT power system shall be designed to provide 33 KV mains power to ROP, PREFRE and proposed UNCF.

3.2 Class-IV Mains Power Supply System (415 V)

415V `Mains’ LT power system shall be designed to meet the needs of class-IV power supply of projects ROP, AWTF and SFSF.

3.3 Class-III power for ROP, AWTF & SFSF

The system design shall ensure availability of class-III power supplies for ROP, AWTF and SFSF projects.

3.4 Class-II Power Supply System (230 V)

The system shall be designed to meet the needs of 230V, class-II power supplies (UPS) for C&I loads of ROP project.

3.5 Class-I DC Power Supply System (110 V)

The system shall be designed to meet the needs of 110V, DC class-I power supplies for switchgear controls and exit lights of ROP project.

3.6 To ensure safety of plant and the O&M personnel

System design shall ensure the safety of plant equipment and that of operating/ maintenance personnel during normal as well as emergency conditions like power outages, flooding and outbreak of fire.

3.7 To provide adequate illumination levels

The design shall ensure adequate illumination levels in the plant areas for ease of operation and maintenance.

3.8 To ensure Continuous availability of Power

Electrical design facilitates periodic in-service inspections and preventive maintenance for ensuring availability of power to the important plant systems.

3.9 To reduce man-rem expenditures.

The design shall facilitate remote maintenance for the electrical equipments planned to be installed in the radioactive areas, so as to reduce man-rem expenditures.

3.10 To enhance system safety

Enhancement of system safety by using requisite quality materials/ equipments.

3.11 Provisions for Future Expansions

The system design shall have provisions for expansion and up gradations in future.

4.0 DESIGN CRITERIA

The ROP electrical system shall be designed to meet the following criteria :-

4.1 Load requirements: HV systems

4.1.1 The entire 33KV ‘Mains’ HT power system shall be designed for catering to a total power requirement of about 15 MVA at a fault level of 1500 MVA to feed and provide electrical power to PREFRE, ROP and proposed UNCF substations for normal Operation and Maintenance of these plants. The 33 kV Mains incomers shall be capable of meeting this power requirement independently.

4.2 Load requirements: LV systems

4.2.1 The 415 Volt electrical system consisting of Class IV power supply system, Class III power supply system, Class II power supply system and Class I power supply system shall be capable of meeting the class-IV power requirement of about 2455 kVA, class-III power requirement of about 850 kVA, class-II power requirement of about 41 kVA and class-I power requirement of about 25 kW or 350 A for half an hour.

4.3 References/ Guidelines

The compliance of following codes shall be ensured :

-Indian Electricity Rules

-NEC-85

-AERB Codes (SGD-11) & guides

-Latest applicable IS & IEEE standards.

The detailed reference list is given in Annexure-1.

4.4 Classification of power supplies

The following power supply systems have been envisaged at ROP substation to meet operational & safety requirements:

4.4.1 Class-IV power supply: Alternating current power supply to meet plant’s O&M loads & the auxiliaries, which can tolerate prolonged interruption without affecting safety of the plant, is classified as Class-IV Power Supply. 415 Volt mains supply has been provided from ROP substation. Two 33KV under ground cable feeders have been brought to the ROP substation from MSEB/NPCIL’s 220 KV switchyard to meet Class-IV power requirement of entire site. 33KV power supply is further stepped down to 415 Volt class IV power in the indoor ROP substation, from where 415 V power is distributed to the ROP, AWTF & SFSF facilities.

4.4.2 Class-III power supply: Alternating current power supply to safety related systems, that can tolerate short interruptions (up to 2 minutes) is classified as Class-III power supply. Under normal conditions, this power supply is derived from Class-IV and in case of loss of Class-IV power supply, standby DG sets are automatically started and connected to the Class-III switchgear systems through AMF logic to meet emergency power requirements of the plant. The diesel generators and the Class-III switchgear systems are provided in the indoor ROP substation, from where 415 V CLASS III power is distributed to the ROP, AWTF & SFSF facilities.

4.4.3 Class-II power supply: Critical control systems viz. Public Address System, criticality monitors, control instruments etc. powered through UPS shall be available continuously. UPS for class II power supply system are provided at the ROP high block building.

4.4.4 Class-I power supply: Direct current power supply to loads which require direct current power is called Class-I power supply. Normally direct current power is derived through an AC to DC rectifier connected to Class-III power supply. Battery back up is provided so that direct current power supply continues to be available even when Class-III power or rectifier fails. Class-I power supply shall be provided in the ROP sub-station.

The break-up of individual maximum demand of above mentioned power supply systems of ROP project is as under:

HIGH BLOCK BUILDING

Class-IV Class-III Class-II Class-I

1000 KVA 495KVA 40KVA 10 KW

LOW BLOCK BUILDING

Class-IV Class-III Class-II Class-I

40 KVA 5 KVA 1 KVA (16 KW) 1 KW

SERVICE BUILDINGS

Class-IV Class-III Class-II Class-I

600 KVA 100KVA - 1 KW

The load list of class-IV, class-III, class-II and class-I power systems of ROP project are given in Table-II, Table-III,

Table-IV and Table-V respectively.

4.5 Functional requirements

4.5.1 The design shall ensure quality power for the electrical drives and devices through two independent mains power

supply and by using safe, reliable, energy efficient and easy to maintain type system components and the associated

distribution network.

4.5.2 The permissible steady state voltage and frequency limits (in terms of maximum, minimum & percentage) for

continuous operation of equipments connected to various voltage levels are indicated below:

System Voltage	Permissible values			System Frequency	Permissible values
System Voltage	Maximum	Minimum	Range in %	System Frequency	Maximum	Minimum	Range in %
Class IV & class III
415 V(AC)	439.9 V	390.1 V	± 6 %	50Hz	51.5Hz	48.5Hz	± 3%
230V AC	243.8 V	216.2 V	± 6 %	50Hz	51.5Hz	48.5Hz	± 3%
Class II
230V AC	235.75V	224.25V	± 2.5%	50Hz	50.5 Hz	49.5 Hz	± 1%
Class I
110V DC	112.75 V	97.25 V	± 2.5%

4.5.3 The permissible transient state voltage and frequency limits ( in terms of maximum,

minimum & percentage) for continuous operation of equipments connected to various voltage levels

are indicated below:

System Voltage	Expected Transient Voltage Variation			Expected Transient Frequency Variation
System Voltage	Magnitude	Percentage	Recovery Time	Magnitude	Percentage	Recovery Time
Class-IV	556 V	+34%	50 msec.	54.25Hz	+8.5%	15 sec. To
415 V AC	290.5 V	-30%	200 ms.			52.5 Hz

Class-III	556.1 V	+34%	50 msec.	54.25Hz	+8.5%	15 sec. to
415 V AC	498 V	+20%	2.4 sec	52.5Hz	+5%	52.5 Hz
	332 V	-20%	2.4 sec.	47.5Hz	-5%	2.4 sec.

Class–II	253 V	+10%	50 msec.	51Hz	+2%	----
230 V AC	207 V	-10%	50 msec.	49Hz	-2%	----
Class–I	112.75 V	+2.5%	50 msec.	-	-	----
110 V AC	97.25 V	-2.5%	50 msec.	-	-	----

Above transient conditions are experienced during situations like (a) load throw-off or loading, (b) motor starting.

4.5.4 The short circuit fault level at various buses i.e. 33 KV, 415V class-IV, 415V class-III, 240V class-II and 110 V DC class-I is indicated below:

			Required rating for SWGR.		Switchgear Rating
Sl. No.	System	Fault Level for the bus	Making level	Symmetrical Interrupting Level/withstand capacity	Making level	Symmetrical Interrupting Level/withstand capacity for 1 sec.
1.	33 KV AC Class-IV system	17.5 KA (rms)	36.75 kA	17.5 KA (rms)	52.75 kA	25 KA (rms)
2.	415 Volt AC Cl-III, Cl-II & Cl-IV with Cl-III to Cl-II tie CB closed	52.5KA (rms)	110.77 KA peak	52.5 KA (rms)	137KA peak	65 KA (rms)

			Required rating for SWGR.		Switchgear Rating
Sl. No	System	Fault Level for the bus	Making level	Symmetrical Interrupting Level/withstand capacity	Making level	Symmetrical Interrupting Level/withstand capacity for 1 sec.
3.	Power DC battery	9.4 KA	----	9.4 KA	----	20 kA

The above table indicates the interrupting ratings of switchgear provided at various voltage level.

From this data it can be seen that the ratings are adequate with adequate margins.

4.5.5 33 KV/433 Volt transformers are provided with off circuit tap links having ±5% range. The table below gives the terminal voltage for various load conditions for constant input voltage.

Sr.No.	Grid Voltage	Load as % of full load	Secondary voltage at rated tap	Required tap position	Expected secondary voltage
1.	33 KV
1.1		0%	433 V	Rated tap	433 V
1.2		50%	415.6 V	Rated tap	415.6 V
1.3		100%	398.3 V	-2.5%	444V
2.	33 KV+12%
2.1		0%	484.96V	+5%	461.8V
2.2		50%	465.56V	+5%	443.3V
2.3		100%	446.16V	+5%	424.8V
3.	33 KV-9%
3.1		0%	394V	-5%	414.7V
3.2		50%	378V	-5%	398.1V
3.3		100%	362.5V	-5%	381.5V

From the above table, it can be observed that steady state 433V bus voltage is maintained for the expected voltage variation on 33 KV side and various load conditions.

4.5.6 The class-III power supply should automatically come on stream when the class-IV power supply fails due to any reason. All the essential base loads like lighting, health and safety instruments, plant communication equipment etc., should be energized within time duration of 30 –100 seconds. Power supply for all other bulk loads like exhaust and off-gas fans should be made available within a time span commensurate with the health and safety requirement.

4.5.7 Rating of the two DG sets shall be so chosen that the entire class-III loads of the plant can be continuously fed even if one of the sets is not available.

4.5.8 Bulk-oil storage facility for DG Room shall be common for ROP, PREFRE & IP-1, which shall be suitably located between PREFRE and IP-1 and shall be about 15m away from any adjacent structure. Day tanks for ROP DG sets are to be near ROP substation adjacent to the furnace oil storage bldg.

4.5.9 In most of the plant areas, 30-40% of the lights installed shall be provided with class-III power supply whereas in control room, 50% of the lights installed shall be provided with class-III power supply & rest from class-II. Some of the plant facilities shall have special lighting provisions such as 250 W HPSV/ 500 W halogen lamp fixtures for fuel pond lighting, 150/250W high pressure sodium vapour lamps in the dissolver cell, 250 W HPSV for process cells, 35W/55 W SOX/ 18 W CFL for Hot cell & Blister (cubicles) lighting Flame proof fixtures with ML lamps for inflammable material stores. All the distribution boards have been provided with a 25% diversity factor.

4.5.10 The instrument power distribution board (IPDB) providing control power supplies to various instruments in control room, shall be fed with two feeders of Class II power. Each feeder shall be capable of meeting the entire instrumentation load. Duplication of feeders is to enhance the reliability and availability of power supply for the instrumentation system.

4.5.11 Class-I DC power supply to critical control relays, instruments & sub-station auxiliary loads shall be fed continuously through DC switchboard receiving power normally from the ACVRs and backed up with storage batteries.

4.5.12 Battery banks shall be adequately designed to supply the entire class-I power requirement for a period of 30 minutes at high discharge rates without affecting the life of batteries.

4.5.13 In the event of non availability of Class IV or Class III power supply to ACVRs, or during failure of ACVRs, the batteries take over the function of feeding DC power to plant's critical loads like switch gear controls, indications, communication system and also to the DC `EXIT’ lighting along the evacuation routes in active areas.

4.5.14 The system design should ensure the safety of plant equipment and that of the operating /maintenance personnel not only during normal operation but also during emergency conditions like outbreak of fire.

4.5.15 The design should be such that all important process loads can be controlled from the main control room. Indication of the availability of power supplies and ON/OFF status of major loads should also be available at the control room.

4.5.16 The layout of the power distribution centers should be such as to avoid lengthy cabling so that voltage drops can be minimized with consequent improved performance of plant equipment.

4.5.17 All major load centres should be segregated from each other so that planned or non- planned power interruption in one area does not affect the operation in other areas.

4.5.18 All electrical motors shall be connected through DOL type starter but for E2 fan motors

which will have VVVF drives.

4.5.19 Design shall facilitate control of all important process loads from main control room.

4.6 Safety requirements

4.6.1 There should be total segregation of class-IV, class-III and class-I power supply system.

4.6.2 D.G. rooms shall be partitioned with 3 hour fire rating wall.

4.6.3 The design should facilitate frequent in-service inspections and preventive maintenance for ensuring the uninterrupted availability of power for plant.

4.6.4 Separate cable trenches shall be provided for laying of power and control/ instrumentation cables.

4.6.5 Diverse cable routes shall be followed for group-A and group-B cables of safety related systems.

4.6.6 The enhancement of electrical system’s safety shall be maintained by using requisite quality materials and equipments.

4.6.7 Fire and Smoke detectors shall be provided in cable allies and at the top of electrical cables and panels (details given in Fire protection system DBR of ROP).

4.7 Site specific requirements

The system design shall be suitable for the following ambient conditions and the site environment:

1 1.1	Elevation above sea level Distance from sea coast	Near sea level About 1500 mtrs.
2	Ambient air temperature
2.1	Maximum	45°C
2.2	Average daily (max.)	35°C
2.3	Design temperature for electrical equipments	45°C
3	Relative Humidity
3.1	Maximum	98%
3.2	Design RH for electrical equipments	98%
4	Maximum RH and temperature occurring simultaneously	80% and 40°C resp.
5	Air Quality	Clean
6	Seismic data	Zone 2 on seismic scale
7	Soil resistivity	100 ohm-m
8	Available off-site power source	2 nos. of adequately rated 33 KV, 1500 MVA feeders

4.8 Standardization of design

4.9 4.8.1 The system engineering should adopt reliable, easy-to-maintain type of equipment so that maintenance work can be carried out safely and quickly. The equipments/ components/ materials used should be of tested and of proven performance, supplied by manufacturers of established reputation.

4.8.2 The system components and the equipments shall be of proven design and duly qualified for the application involved.

4.8.3 The equipment and the materials shall be so standardized that stock of inventory for O&M can be minimized to the extent possible.

4.10 Design changes/ improvements over previous plants

Following changes and improvements are envisaged in design of electrical systems as per ASPRC recommendations, various plants’s feedbacks and site constraints.

4.9.1 Dry type Cast Resin/ resin impregnated power and Distribution transformers shall be used in place of oil filled transformers for enhancement of system safety and the reliability.

4.9.2 It is proposed to provide a remote control centre through SCADA system for substations, MCCs/ PCCs etc. preferably to be extended to the main control room for better co-ordination amongst the operating staff and also to reduce manpower. State of the art protective devices viz. Numerical relays shall be used for sub-station equipments. Qualification verification and reliability analysis have been carried out for the numerical relays for its suitability under Indian conditions.

4.9.3 Variable Voltage Variable Frequency (VVVF) drives shall be provided for all the ACVE system, Utilities & Services system equipments and also for some major motor pump sets for speed/flow control and the resultant energy conservation.

4.9.4 A PLC based Emergency Transfer system is envisaged for automatic sequential starting of all class III loads during power outage of Mains power supply.

4.9.5 Lighting transformer shall be provided for isolation purpose for high block as well as sub-station & low block. Power supply for lighting can be made available from the dedicated 415/415 V, 3 phase AN type isolating transformer of adequate rating.

4.9.6 A separate common utility control room shall be provided for the remote control of all the utilities and services of the plant.

4.9.7 Process cells shall be equipped with ‘SON’ lights through shielding plugs (with drawable type). ‘Gold plated’ 230V plug receptacles with local switch shall be provided in cells for maintenance. The shielding plug light shall be designed to withstand total cumulative dose of 100 MR.

4.9.8 16 kA SPN MCBs shall be provided for lighting & plug-circuits with separate neutral for each circuit . Also, HFFR wires shall be used for building electrification.

4.9.9 All major load centers shall have independent Motor Control Centres (MCC) for the group-A and group-B motors in equal number, for enhancement of reliability and redundancy.

4.9.10 Power Factor Improvement (PFI) capacitor banks are planned in ROP sub-station, distributed on both the buses of 415 V Class IV switchgear, and also at the major load centres.

4.9.11 All the important emergency power systems including DG sets, DG control panels & auxiliaries, Class III switchgears, redundant Motor Control Centres, UPS systems, DC battery Banks, ACVRs etc. shall be physically separated to avoid common mode failures.

4.9.12 Stainless Steel fixtures shall be used for areas likely to have acid fumes such as Tank Space, Make-up Area etc.

4.9.13 XLPE insulated, FRLS inner and outer sheathed cables shall be used in 415 V AC and 110 V/ 48 V DC systems.

4.9.14 HFFR wires shall be used for the building electrification of low and high block building.

4.9.15 Armored cables are to be used for all the outdoor applications and in-door applications, as applicable. All single core AC circuit cables will have aluminum armoring, otherwise round galvanized steel wire armoring shall be used for other systems’ cables.

4.9.16 Energy conservation in lighting shall be achieved through the use of CFLs, low loss/ electronic ballasts/ inverters. Also, ‘PID’ control shall be used for 50% ‘Normal’ lights in sampling gallery/ isolating corridor for energy saving.

4.9.17 Suitable Tie- lines are provided for 415V ROP class-IV switchgear with the class-IV switchgear of PREFRE substation to facilitate sharing of power between ROP & PREFRE, during system failures under administrative controls.

4.10 DESIGN SAFETY FEATURES

4.10.1 Necessary interlocking between breakers and auto load transfer facility shall be provided.

4.10.2 All the components and panels of the emergency control room (located in high block building of R.O.P.) including class-II UPS systems, shall be seismically qualified for SSE (Safe

Shutdown Earthquake) level of earthquake as per IEEE-344 standards. Electrical system shall

otherwise conform to IS-1893 for seismic requirements.

4.10.3 In view of low smoke densities and high radiation resistance, Chloro Sulphonated

polyethylene (CSPE) has been provided as sheathing material for power and control cables installed

in process cells and other highly radioactive areas. Flame Retardant Low Smoke Polly Vinyl

Chloride (FRLS-PVC) sheathed cables have been used in control room and other critical areas.

4.10.4 Earth mat network having stranded copper conductor with spacing of 11 meters between the

parallel conductors forming grid has been provided for grounding system of the plant.

4.10.5 All the structures under ROP Project, including the stack, have been covered under the

lightning protection system adopted for the plant.

4.10.6 All the major load centers shall be segregated from each other so that planned or non-planned

power interruption in one area does not affect the operation in other areas.

5.0 METHODS & TECHNIQUES:

5.1 Two 33 kV(E), 400 sq. mm. 3 core under ground cable feeders from MSEB/ TAPS-1 & 2 switchyard, taken from two different bus sections shall feed 33 KV switchgears of ROP sub-station for distribution of 33 KV power supply for PREFRE substation, ROP substation and proposed UNCF substation.

5.2 Substation shall be provided with ventilation air through supply air duct. Sub station control room shall have split air conditioner or split chilled water- fan coil unit sets for ensuring smooth functioning of sophisticated softwares and hardwares.

5.3 Transformers room shall be provided with roof at top at about 5.5 m height. Transformer rooms

shall be partitioned with each other.

5.4 The layout of the power distribution centres should be such as to avoid lengthy cabling so that

voltage drops can be minimized with consequent improved performance of plant equipment.

5.5 Monorails with chain pulley blocks are required in electrical workshop, DG room, lift rooms.

5.6 Installation of electrical PCC/MCCs/PDBs, Distribution panels and control panels shall be

made in separate and readily accessible areas, rooms/ enclosures attached to the plant areas such as tank space, access galleries, off gas rooms, FHA, labs, so as to avoid their exposure to the corrosive & radio-active environment.

5.7 All electrical motors shall be connected through DOL type starter but for E2 fan motors, which

will have VVVF drives. Running hour meter shall be provided for all the utility & services system motors.

5.8 There should be provision of fire and smoke sensors in cable allies and top of electrical cables/

panels.

5.9 Fire breaks/ barriers shall be provided wherever the cable crosses the floor/ ceiling.

5.10 There should be sealing on hume pipe sleeves meant for cable entry(s) into the plant buildings

(as anti-flood measures).

5.11 Separate cable routes/ trays shall be provided for laying of power and control/ instrumentation

cables.

6.0 SYSTEM CONFIGURATION

6.1 CLASS-IV POWER SUPPLY SYSTEM

Reliable ‘mains’ class-IV power supply is required for normal operation and maintenance of the plant.

Two 33 kV under ground cable feeders from MSEB/ TAPS-1 & 2 switchyard,, taken from two different bus sections shall feed the ROP sub-station through 33 kV switchgear to be housed in new indoor substation as per single line diagram/ drawing no.1. The ROP sub-station will provide 415 V, 3 phase, 4 wire A.C. power supply to all the plant loads. These two 33 KV HT incoming feeders to ROP HT switchgear will be used for ROP site, ensuring practically two independent sources of power supply to the plant.

The following equipments are planned in an indoor ROP sub-station for the class IV power system :

(1) 33 kV Vacuum circuit breakers .

(2) SCADA based switchgear system for 33 kV and 415 Volt power system.

(3) 33/ 0.433 kV, 2.5 MVA Dry type transformers.

6.2 CLASS-III POWER SYSTEM

Some of the equipment of the plant such as the exhaust & off-gas fans; part of the lighting in the active areas of the plant; installed health physics instruments and some of the vital in-process control/measurement instruments have to be available all the time on considerations of plant and personnel safety. For this purpose, class-III power system has been provided.

‘Emergency’ DG sets backed up class-III power supply is required for operation of such safety

related and important loads of plant during outage of class-IV power supply.

Two numbers of diesel generator sets of approximately 1010 kVA capacity each, shall provide 415 V, 50 HZ grounded AC power supply to safety related loads during class-IV power failure/outage conditions through a network independent of the class-IV power distribution. The total emergency power requirement of the ROP Project/AWTF is estimated at about 850 kVA.

The class-IV and class-III load particulars are given in Table-II & III respectively.

6.3 CLASS-II POWER SYSTEM

Two independent 230 V, 50 kVA, AC single phase class-II uninterruptible power supply (UPS) set shall be provided for critical control systems viz. SCADA system, Public Address System, criticality monitors, control instruments, turnstile gates etc. Two class-III power feeders shall be dedicated for the UPS system for continuous availability of power supply to these critical systems. Class-II load list is tabulated in Table-IV.

6.4 CLASS-I POWER SYSTEM

Critical control instruments and auxiliary loads of the plant need class-I DC power supply. These will be fed continuously with DC power through the ACVR backed up by storage batteries.

The exit lighting provided in the main control room/other control centres and at all the escape/exit routes of the plant shall be connected to this power system. During emergency situations and class-IV power failure conditions, these lights come on automatically before the Diesel Emergency Power system takes over. This power system is categorized as class-I. Two battery banks, each of 110 V (nominal), 425 AH, 56 Cell YKP 35 plante type, shall provide Class-I, 110 V DC power supply to DC loads, in the event of non-availability of Class IV or Class III power supply on DC switchboard /ACVR terminals. Battery banks of 24V DC shall be provided for DG controls. Class-I DC load list is tabulated in Table-V.

7.0 SYSTEM DESCRIPTION

7.1 INCOMING POWER SUPPLY TO ROP SUBSTATION

Two 33 kV overhead MSEB lines are terminated in MSEB/NPC tapyard behind PREFRE complex. 2 nos. underground 400 sq. mm 3 core XLPE armoured cables are laid from the new switch yard to ROP HT switchgear. These two 33 KV HT incoming feeders to ROP HT switchgear will be used for ROP site, ensuring practically two independent sources of power supply to the plant.

These two 33 kV feeder lines from MSEB/NPC switchyard, taken from two different bus sections shall feed the ROP sub-station through 33 kV switchgear to be housed in new indoor substation as per single line diagram/ drawing no. 1. The ROP sub-station will provide 415 V, 3 phase, 4 wire ac

power supply to all the plant loads. Thus the plant shall have practically two independent sources of power assuring a reliable power supply.

7.2 SUB-STATION

The existing 33 kV outdoor switchyard provided in PREFRE plant for receiving and distributing ‘Mains Class–IV’ power supply for plant’s regular O&M needs, has 2 Bulk-oil circuit breaker and gang-operated switches with drop-out type fuses for protecting the complete Mains power system, which were installed during early 70’s. These designs are outdated, unreliable and inadequate to provide protections as per safety codes. Also, some of these devices have become unsafe and inoperable due to heavy corrosion, wear & tear under salt-laden atmosphere. Due to above reasons and because of their inadequate capacity to meet the enhanced load requirements of PREFRE plant and ROP project, it has been decided to renovate the complete power system of the plant by providing the following equipments of state-of-art technologies in an indoor ROP sub-station :

(1) 33 kV Vacuum circuit breaker.

(2) SCADA based switchgear system for 33 kV and 415 Volt power system.

(4) 33/ 0.433 kV, 2.5 MVA Dry type transformers.

(5) 2 nos., 1010 KVA, 3 phase, 433V D.G. sets.

(6) A static, high efficiency class-II UPS system for plant’s critical requirements.

(7) Class-I power system for managing total blackout condition in the plant.

The layout of the sub-station shall be such that the load centres are close to the sub-stations thereby avoiding lengthy cabling. Consequently, voltage drops are expected to be minimal with improved equipment performance. The sub-station is indoor, non-exposed type. XLPE cables shall be laid through accessible cable trenches for interconnection of transformers and HT switchgears

ROP sub-station building is planned behind PREFRE Low Block building by demolishing the existing outdoor 33 kV PREFRE switchyard. The low block building accommodates most of the utilities/services systems of PREFRE and ROP. This substation will thus feed major electrical loads like V2- fans, refrigeration compressors etc. HT switch gears and the storage batteries for the DC power supply shall also be located in this sub-station. This sub-station shall also cater to the process loads and the exhaust fans. The two diesel generators that supply emergency power to the plant shall also be installed in this sub-station.

7.2.1 SALIENT FEATURES OF R.O.P. SUB-STATION

7.2.1.1 Physical separation of class-IV, class-III, class-II and class-I power supply systems.

7.2.1.2 Risk of fire hazards is avoided by using cast resin power transformers and vacuum circuit breakers.

7.2.1.3 Physical separation of class-III emergency bus sections.

7.2.1.5 Separate cable routings for class-IV, class-III, class-II and class-I power and control cables.

7.2.1.6 All cables have FRLS (Fire resistance low smoke) inner and outer sheaths.

7.2.1.8 PLC based auto sequential starting of loads.

7.2.1.9 .Improvement of power factor by using APFC (Automatic power factor correction) panels.

7.2.1.10 Substation control room shall have SCADA based data management and control.

7.3 CLASS-IV POWER SUPPLY SYSTEM

7.3.1 TRANSFORMERS (GENERAL FEATURES)

The power transformers for ROP electrical system shall be of in-door, cast resin encapsulated, epoxy impregnated, dry type and air cooled type. The transformers shall have essential protective devices for safe and reliable operation.

Two number of transformers (33 kV/0.433 kV, 2500 kVA rating) shall be installed in sub-station. The transformers can withstand the maximum rated current at -2.5% tap on HV side and they can also withstand 110% continuous overflowing. They shall be capable of withstanding 3 starts per hour (under hot conditions) at DOL starting of highest rating motors with maximum base load. Maximum noise level of the 2500 kVA transformer is 65 dB. The neutral point of star connection can withstand highest over current. They are equipped with winding temperature controllers. Core, windings, terminals, tap changers, auxiliaries shall be designed for continuous and short time overload capacity. It gives maintenance free operation. It has highest level of safety measures. The transformers are class-H insulated cast resin system. Cast resin offers high mechanical strength, improved earth tracking resistance, high dielectric, moisture repellent and flame retardant qualities. The transformers shall have ‘Over current’, ‘Earth fault’, REF (Restricted Earth Fault) and winding temperature protection using RTDs. Technical particulars of Dry type transformers are listed in Table VI.

The transformer rooms shall be provided with roof at the top. They are isolated from each other by the partitioning walls so that in the event of fire, it’s spread can be avoided. Provision of exhaust fans may also be available for better ventilation of the room.

1.0 INTRODUCTION:

2.0 SCOPE OF THE DESIGN BASIS REPORT

This Design Basis Report covers mainly design criteria, system description, salient features of

components electrical system of ROP sub-station, criteria for selection of safety and non-safety

related electrical equipments, postulated initiating events and their consequences on safety related

systems to meet their intended functions. Separate DBR has been prepared for ROP facility.

3.0 DESIGN OBJECTIVES

3.1 Class-IV Mains Power Supply System (33 KV)

33KV `Mains’ HT power system shall be designed to provide 33 KV mains power to ROP, PREFRE and proposed UNCF.

3.2 Class-IV Mains Power Supply System (415 V)

415V `Mains’ LT power system shall be designed to meet the needs of class-IV power supply of projects ROP, AWTF and SFSF.

3.3 Class-III power for ROP, AWTF & SFSF

The system design shall ensure availability of class-III power supplies for ROP, AWTF and SFSF projects.

3.4 Class-II Power Supply System (230 V)

The system shall be designed to meet the needs of 230V, class-II power supplies (UPS) for C&I loads of ROP project.

3.5 Class-I DC Power Supply System (110 V)

The system shall be designed to meet the needs of 110V, DC class-I power supplies for switchgear controls and exit lights of ROP project.

3.6 To ensure safety of plant and the O&M personnel

System design shall ensure the safety of plant equipment and that of operating/ maintenance personnel during normal as well as emergency conditions like power outages, flooding and outbreak of fire.

3.7 To provide adequate illumination levels

The design shall ensure adequate illumination levels in the plant areas for ease of operation and maintenance.

3.8 To ensure Continuous availability of Power

Electrical design facilitates periodic in-service inspections and preventive maintenance for ensuring availability of power to the important plant systems.

3.9 To reduce man-rem expenditures.

The design shall facilitate remote maintenance for the electrical equipments planned to be installed in the radioactive areas, so as to reduce man-rem expenditures.

3.10 To enhance system safety

Enhancement of system safety by using requisite quality materials/ equipments.

3.11 Provisions for Future Expansions

The system design shall have provisions for expansion and up gradations in future.

4.0 DESIGN CRITERIA

The ROP electrical system shall be designed to meet the following criteria :-

4.1 Load requirements: HV systems

4.2 Load requirements: LV systems

4.3 References/ Guidelines

The compliance of following codes shall be ensured :

-Indian Electricity Rules

-NEC-85

-AERB Codes (SGD-11) & guides

-Latest applicable IS & IEEE standards.

The detailed reference list is given in Annexure-1.

4.4 Classification of power supplies

The following power supply systems have been envisaged at ROP substation to meet operational & safety requirements:

The break-up of individual maximum demand of above mentioned power supply systems of ROP project is as under:

HIGH BLOCK BUILDING

Class-IV Class-III Class-II Class-I

1000 KVA 495KVA 40KVA 10 KW

LOW BLOCK BUILDING

Class-IV Class-III Class-II Class-I

40 KVA 5 KVA 1 KVA (16 KW) 1 KW

SERVICE BUILDINGS

Class-IV Class-III Class-II Class-I

600 KVA 100KVA - 1 KW

The load list of class-IV, class-III, class-II and class-I power systems of ROP project are given in Table-II, Table-III,

Table-IV and Table-V respectively.

4.5 Functional requirements

4.5.1 The design shall ensure quality power for the electrical drives and devices through two independent mains power

supply and by using safe, reliable, energy efficient and easy to maintain type system components and the associated

distribution network.

4.5.2 The permissible steady state voltage and frequency limits (in terms of maximum, minimum & percentage) for

continuous operation of equipments connected to various voltage levels are indicated below:

System Voltage	Permissible values			System Frequency	Permissible values
System Voltage	Maximum	Minimum	Range in %	System Frequency	Maximum	Minimum	Range in %
Class IV & class III
415 V(AC)	439.9 V	390.1 V	± 6 %	50Hz	51.5Hz	48.5Hz	± 3%
230V AC	243.8 V	216.2 V	± 6 %	50Hz	51.5Hz	48.5Hz	± 3%
Class II
230V AC	235.75V	224.25V	± 2.5%	50Hz	50.5 Hz	49.5 Hz	± 1%
Class I
110V DC	112.75 V	97.25 V	± 2.5%

4.5.3 The permissible transient state voltage and frequency limits ( in terms of maximum,

minimum & percentage) for continuous operation of equipments connected to various voltage levels

are indicated below:

System Voltage	Expected Transient Voltage Variation			Expected Transient Frequency Variation
System Voltage	Magnitude	Percentage	Recovery Time	Magnitude	Percentage	Recovery Time
Class-IV	556 V	+34%	50 msec.	54.25Hz	+8.5%	15 sec. To
415 V AC	290.5 V	-30%	200 ms.			52.5 Hz

Class-III	556.1 V	+34%	50 msec.	54.25Hz	+8.5%	15 sec. to
415 V AC	498 V	+20%	2.4 sec	52.5Hz	+5%	52.5 Hz
	332 V	-20%	2.4 sec.	47.5Hz	-5%	2.4 sec.

Class–II	253 V	+10%	50 msec.	51Hz	+2%	----
230 V AC	207 V	-10%	50 msec.	49Hz	-2%	----
Class–I	112.75 V	+2.5%	50 msec.	-	-	----
110 V AC	97.25 V	-2.5%	50 msec.	-	-	----

Above transient conditions are experienced during situations like (a) load throw-off or loading, (b) motor starting.

4.5.4 The short circuit fault level at various buses i.e. 33 KV, 415V class-IV, 415V class-III, 240V class-II and 110 V DC class-I is indicated below:

			Required rating for SWGR.		Switchgear Rating
Sl. No.	System	Fault Level for the bus	Making level	Symmetrical Interrupting Level/withstand capacity	Making level	Symmetrical Interrupting Level/withstand capacity for 1 sec.
1.	33 KV AC Class-IV system	17.5 KA (rms)	36.75 kA	17.5 KA (rms)	52.75 kA	25 KA (rms)
2.	415 Volt AC Cl-III, Cl-II & Cl-IV with Cl-III to Cl-II tie CB closed	52.5KA (rms)	110.77 KA peak	52.5 KA (rms)	137KA peak	65 KA (rms)

			Required rating for SWGR.		Switchgear Rating
Sl. No	System	Fault Level for the bus	Making level	Symmetrical Interrupting Level/withstand capacity	Making level	Symmetrical Interrupting Level/withstand capacity for 1 sec.
3.	Power DC battery	9.4 KA	----	9.4 KA	----	20 kA

The above table indicates the interrupting ratings of switchgear provided at various voltage level.

From this data it can be seen that the ratings are adequate with adequate margins.

4.5.5 33 KV/433 Volt transformers are provided with off circuit tap links having ±5% range. The table below gives the terminal voltage for various load conditions for constant input voltage.

Sr.No.	Grid Voltage	Load as % of full load	Secondary voltage at rated tap	Required tap position	Expected secondary voltage
1.	33 KV
1.1		0%	433 V	Rated tap	433 V
1.2		50%	415.6 V	Rated tap	415.6 V
1.3		100%	398.3 V	-2.5%	444V
2.	33 KV+12%
2.1		0%	484.96V	+5%	461.8V
2.2		50%	465.56V	+5%	443.3V
2.3		100%	446.16V	+5%	424.8V
3.	33 KV-9%
3.1		0%	394V	-5%	414.7V
3.2		50%	378V	-5%	398.1V
3.3		100%	362.5V	-5%	381.5V

From the above table, it can be observed that steady state 433V bus voltage is maintained for the expected voltage variation on 33 KV side and various load conditions.

4.5.7 Rating of the two DG sets shall be so chosen that the entire class-III loads of the plant can be continuously fed even if one of the sets is not available.

4.5.12 Battery banks shall be adequately designed to supply the entire class-I power requirement for a period of 30 minutes at high discharge rates without affecting the life of batteries.

4.5.16 The layout of the power distribution centers should be such as to avoid lengthy cabling so that voltage drops can be minimized with consequent improved performance of plant equipment.

4.5.17 All major load centres should be segregated from each other so that planned or non- planned power interruption in one area does not affect the operation in other areas.

4.5.18 All electrical motors shall be connected through DOL type starter but for E2 fan motors

which will have VVVF drives.

4.5.19 Design shall facilitate control of all important process loads from main control room.

4.6 Safety requirements

4.6.1 There should be total segregation of class-IV, class-III and class-I power supply system.

4.6.2 D.G. rooms shall be partitioned with 3 hour fire rating wall.

4.6.3 The design should facilitate frequent in-service inspections and preventive maintenance for ensuring the uninterrupted availability of power for plant.

4.6.4 Separate cable trenches shall be provided for laying of power and control/ instrumentation cables.

4.6.5 Diverse cable routes shall be followed for group-A and group-B cables of safety related systems.

4.6.6 The enhancement of electrical system’s safety shall be maintained by using requisite quality materials and equipments.

4.6.7 Fire and Smoke detectors shall be provided in cable allies and at the top of electrical cables and panels (details given in Fire protection system DBR of ROP).

4.7 Site specific requirements

The system design shall be suitable for the following ambient conditions and the site environment:

1 1.1	Elevation above sea level Distance from sea coast	Near sea level About 1500 mtrs.
2	Ambient air temperature
2.1	Maximum	45°C
2.2	Average daily (max.)	35°C
2.3	Design temperature for electrical equipments	45°C
3	Relative Humidity
3.1	Maximum	98%
3.2	Design RH for electrical equipments	98%
4	Maximum RH and temperature occurring simultaneously	80% and 40°C resp.
5	Air Quality	Clean
6	Seismic data	Zone 2 on seismic scale
7	Soil resistivity	100 ohm-m
8	Available off-site power source	2 nos. of adequately rated 33 KV, 1500 MVA feeders