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POWER DISTRIBUTION OF VSP Done at VISAKHAPATNAM STEEL PLANT
Document By SANTOSH BHARADWAJ REDDY Email:
[email protected]
Engineeringpapers.blogspot.com More Papers and Presentations available on above site
TABLE OF CONTENTS
#
Chapter name
1)
ABSTRACT
2)
OVERVIEW OF VSP
3)
INTRODUCTION
4)
SWITCH YARD EQUIPMENT
5)
MAIN RECEIVING STATION
6)
LOAD BLOCK STEP DOWN SUB-STATIONS
7)
CONCLUSION
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------: ABSTRACT: ------
Visakh Visakhapa apatna tnam m Steel Steel Plant Plant (V.S.P (V.S.P.) .) being being a major major proces processs indust industry ry requires uninterrupted power source. To meet this V.S.P. is having a unique power distribution system with 220 KV supply taken from AP TRANSCO and synchronized with the V.S.P. own captive generation stepped up to 220 KV at MRS. This synchronized 220 KV will be stepped down to 11 KV, 6.6 KV at load block sub stations-1,2,3,4 from where Voltage at this level will go to different shop flows of the Plant viz., sinter plant, blast furnace, steel melting shop, etc., there it is further stepped down to 415 V to fed the different loads of the plant by load center sub stations (LCSS) major loads like 11 KV and 6.6 KV motors are directly fed to HVLC transformers from LBSS. To have reliable power supply V.S.P. has adopted auto bus transfer system (ABT) to its various switch boards. Where the bus coupler closes automatically in case of failure of any one source of the switch board. This automatic clousure of the bus coupler ensures reliable power supply to the various units of V.S.P.
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-----: OVERVIEW OF V.S.P: ------
Visakhapatnam Steel Plant, the first coastal based steel plant of India is located 16 Kms. south west of Visakhapatnam. It It has an installed capacity of 3 million tones per annum of liquid steel and 2.656 million tones of saleable steel. At VSP VSP ther theree is emph emphas asis is on tota totall auto automa mati tion on,, seam seamle less ss inte integr grat atio ion n and and efficient up gradation, which result in a wide range of long and structural product meet stringent demands of customers within India and abroad. VSP is the first integrated Steel Plant in the country to be certified to all the the 3 Inte Interna rnati tion onal al Stan Standa dard rdss for for qual qualit ity y (ISO (ISO – 9001 9001), ), for for envi environ ronme ment nt management (ISO – 14001) and for occupational health and safety (OHSAS – 18001) VSP exports quality pig iron and steel products to Srilanka, Myanmar, Nepal, Middle East, USA and South East Asia. Having a total manpower of about 16,613 VSP has envisaged a labour productivity of 265 tones per manyear of liquid steel, which is the best in the country and comparable with international levels. The construction of the plant started on 1 st Feb. 1982. Government of India on 18 th Feb. 1982 formed a new company called Rashtriya Ispat Nigam Limited (RINL)
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and transferred the responsibility of constructing, commissioning and operating the plant plant at VISAKH VISAKHAPT APTNA NAM M from from author authority ity of India India Limite Limited d to RINL. RINL. Finally all the units were constructed and dedicated to the nation by then Prime Minister of India late Shri P.V. Narasimha Rao. MODERN TECHNOLOGY USED IN THE PLANT:
Modern Technology has been adopted in many areas of production, some of them for the first time in the country. They are as follows:
Selective crushing of coal.
7 maters tall coke ovens.
Dry quenching of coke.
On ground blending of sinter base mix.
Conveyor charging and bell less top for blast furnace.
Cast house slag granulates for blast furnace.
100% continuous casting of
Gas expansion turbines for power generation utilizing blast furnace top gas pressure.
Hot metal de-sulpherization.
Extensive Extensive treatment treatment facilities facilities of effluents effluents for ensuring ensuring proper proper environmental protection.
Computerization for process control.
Sophisticated high speed high production mills.
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RAW MATERIALS:
Iron ore lumps and fines
BF Limestone
SMS limestone.
BF dolomite.
SMS dolomite
Manganese ore
Medium coking coal (MCC)
PRODUCTS OF VSP:
Steel Products Angles Billets Channels Beams Squares Flats Rounds Re-bars Wire rods
(i) By-Products Nut coke Coke Dust Coal Tar Anthracene oil HP Naphthalene Benzene Toluene Zylene Wash Oil
(ii) By-Products Granulated slag Lime fines Ammonium soleplate
MAJOR DEPARTMETS IN VSP:
Raw material handling plant (RMHP)
Coke ovens and coal chemical plant (CO ( CO and CCP)
Sinter Plant (SP)
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Blast Furnace (BF)
Steel melting shop (SMS)
Continuous Casting Shop (CCD)
Rolling Mills
Light and Medium Merchant Mills (LMMM) (LMMM)
Wire rod mill (WRM)
Medium merchant and structural mill (MMSM) (MMSM)
------: INTRODUCTION: ------
The estimated power requirement of V.S.P. is 280 MW at 0.3 MT stage the peak load being 292 MW and the essential load being 49 MW present average plant load is about 200 MW. The installed inplant generating capacity is 286.5 MW comprising of 247.5 MW captive thermal power generations, 24 MW from gas expansion turbo generators utilizing blast furnace high top pressure and 15
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MW from back pressure turbo generators is utilizing the waste heat recovered at coke dry cooling plant with the help of waste heat boilers. VSP receives power from AP TRANSCO at 220 KV level in two lines. These two lines are terminated at MRS. Also VSP generating its own power at TPP at 11 KV level and is stepped up to 220 KV Level. This 220 KV supply at LBSS-5 is transmitted through tie-lines to MRS. Both 220 KV supplies of AP TRANSCO and VSP are fed to two different buses. There is one more bus at 220 KV level named as transfer bus or auxiliary bus has been provided at MRS to facilitate bus coupling operations. Normally 220 KV at MRS is in synchronized condition with APTRANSCO power and this synchronized power is supplied to different load block sub-station-2, 3, 4 and LBSS-1 from LBSS-5.
Each of the LBSS receives 220 KV level supplies with two lines. There are two lines will feed to three transformers (except at LBSS-2) of 80 MVA capacity, 220/11 KV 3-winding voltage level. In LBSS-2 there are two 220 KV sources will feed to three 80 MVA Transformers of 220/11/6.6 KV and one 31.5 MVA 220/33 KV Transformer. At LBSS-1 also three 220 KV sources will feed to three 80 MVA 220/11/6.6 KV level 3-winding transformers.
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All these 220 KV Transformers are of Star/delta connections. To facilitate earth fault protection of these transformers and also for local supplies at LBSS, each transformer is provided with two earthing transformers. So there are Earthing-cum-Stationery Transformers (EST) existing in each LBSS from where 415 Volts power supply is available for LBSS own loads. These ESTs are are of zigz zigzag ag type type and and its its star star poin pointt is conn connec ecte ted d to Neut Neutra rall Groun rounde ded d Resistance (NGR) of very less value. From MRS to LBSS the 220 KV power is transmitted through overhead lines of ACSR/AAA Conductor. At LBSS this 220 KV power is transmitted through IPS Tubes. Of course this 220 KV Power Transmission is equipped with isolators, current transformers, potential transformers, lightening arrestors and earth switches to facilitate protection as well as operation.
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------: SWITCH YARD EQUIPMENT: ------
Switchyard as a main connecting link between the generating plant and transmission systems has a large influence on the security of supply. As the switchyard handles large amount of power, it is considered essential that it remains secure and serviceable to supply the out going transmission system even under conditions of major equipment or bus bar failure. The choice of bus switching scheme is governed by various factors which ultimately aim and achieving the objective of the security. In all these regions, there are switchgears. The switchgear in generating stations can be classified as 1. Main switch switch gear gear 2. Auxiliary switch gear Main switchgear comprises of circuit breakers, isolators, bus bars, current transfo transforme rmers, rs, potent potential ial transf transform ormers, ers, etc. etc. In the main main circui circuitt of genera generator tor-associated transformers of transmission lines. It is generally of Extra High Voltage and outdoor type. Auxiliary switchgear is generally indoor type and controls the various auxiliaries of the generator, turbine, boiler and the station auxiliary.
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Bus bars are conducting bars to which a number of local feeders are connected. They operate at constant voltage and are insulated from earth and from each other. Isolator is a no-load switch designed to operate under no-load conditions. Therefore, the isolator opens only after the opening of the circuit breaker. While closing, isolator closes first and then circuit breaker. Lighting arrestors connecting between conductor and earth, divert the high voltage surges. It is also also inst instal alle led d near near the the tran transf sfor orme merr termi termina nals ls.. Isola Isolato torr is also also call called ed as disconnecting switch or simply disconnected. Lightning Arrestors:
Lightning is one of the most serious causes of over voltages. If the power equipment especially at the outdoor sub-station is not protected the overvoltage will cause burning of the insulation. It is absolutely, necessary to provid providee protec protectio tion n agains againstt the the travel traveling ing surges surges caused caused by light lighting ing.. Such Such protective device is called lightning arrestors or surge diverters. They are connected between the line and earth at the sub station when the traveling surge reach the diverter and attain the prefixed voltage a spark is formed across the gap. The diverter then provides a low impedance path to earth. The surge diverter should provide a path of low impedance only when the traveling surge reaches, the surge diverter neither before it nor offer it. A good
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lightn lightning ing arrest arrestor or or surge surge divert diverter er must must posses posses the follow following ing condit condition ionss (characteristics) a) It should should not absorb absorb any curren currentt during during the normal normal operat operation ion.. At over voltage surges it must provide an easy path to earth. b) After the first discharge discharge of the current current has taken place place through them them they must be capable of carrying the discharge current for some interval of time without any damage to themselves. c) After the over over voltage discharge discharge it must be capable of interruptin interrupting g the normal frequency current from flowing to the ground as soon as the voltage reaches below the break down value. There are different types of lightning arrestors or surge diverters which are used in practice. 1) Rod gap arrester arrester 2) Sphere gap lightning arrester. 3) Horn gap lightning lightning arrester. 4) Expulsion type arrester. 5) Impulse protective gap with electrolyte lightning lightning arrester. 6) Electrolyt Electrolytic ic type. type. 7) Lead Oxide Oxide type. type.
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8) Pellet type type lead per-oxide type. 9) Thyrite lightning arrester
10) Valve type.
CIRCUIT BREAKERS:
For low voltage voltage circuits, circuits, fuses are used to isolate the faulty circuit. But for high voltage circuits isolation is achieved by the Circuit Breaker. The circuit
breaker can close the circuit as well as break the circuit without replacement for low capacities a fuse combined with circuit breaking
arrangement is quite useful and economical. economical. The following are th requirements for a circuit breaker or a switch gear; 1) It must safely interrupt the normal working working current as well as short circuit circuit current. 2) After occurrence of fault the switch gear must isolate the faulty circuit as quickly as possible. 3) It must must have have high high sens sensee of disc discrim rimin inat atio ion n i.e. i.e.,, in syst systems ems wher wheree in alternate arrangements have been made for continuity of supply it should isolate the only faulty circuit without effecting the healthy one. 4) It should not operate when when an over current flows under under healthy condition. There There are differ different ent types types of circui circuitt breake breakers rs among among those those air air blast blast circui circuitt breaker, magnetic blast circuit brakes and oil circuit breaker are there.
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In the air blast circuit breaker a blast of air is utilized to blow out the arc. The breakers for about 5,000 Volts and coil are provided. In the oil circuit breakers the arc is extinguished by an oil blast. Inside the circuit breaker panel (right) you can see the two primary wires from the transformer entering the main circuit breaker at the top. The main breaker lets you cut power to the entire panel when necessary. Within this overall setup, all of the wires for the different outlets and lights in the house each have a separate circuit breaker or fuse:
If the circuit breaker is on, then power flows through the wire in the wall and makes its way eventually to its final f inal destination, the outlet.
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What an unbelievable story! It took all of that equipment to get power from the power plant to the light in your bedroom. The next time you drive down the road and look at the power lines, or the next time you flip on a light, you'll hopefully have a much better understanding of what is going on. The power distribution grid is truly an incredible system.
Safety Devices: Fuses Fuses and circuit breakers are safety devices. Let's say that you did not have fuses or circuit breakers in your house and something "went wrong." What could possibly go wrong? Here are some examples: A fan motor burns out a bearing bearing,, seizes, overheats and melts, causing a direct connection between power and ground. A wire comes loose in a lamp and directly connects power to ground. A mouse chews through the insulation in a wire and directly connects power to ground. Someone accidentally vacuums up a lamp wire with the vacuum cleaner , cutting it in the process and directly connecting power to ground. A person is hanging a picture in the living room and the nail used for said picture happens to puncture a power line in the wall, directly connecting power to ground. When a 120-volt power line connects directly to ground, its goal in life is to pump as much electricity as possible through the connection. Either the device or the wire in the wall will burst into flames in such a situation. (The wire in the wall will get hot like the element in an electric oven gets hot, which is to say very hot!). A fuse is a simple device designed to overheat and burn out extremely rapidly in such a situation. In a fuse, a thin piece of foil or wire quickly vaporizes when an overload of current runs through it. This kills the power to the wire immediately, protecting it from overheating. Fuses must be replaced each time they burn out. A circuit breaker •
•
•
•
•
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uses the heat from an overload to trip a switch, and circuit breakers are therefore resettable. The power then enters the home through a typical circuit breaker panel like the one above.
CURRENT TRANSFORMERS:
Current Transformers are used in current circuits in protection systems employing secondary relays. This transformer is to measure large currents. The primary which is usually of few turns or even a single turn or thick copper or brass bar is inserted into the core of the transformer is connected in series with the load. The secondary current is normally rated for 5A or 1A and the number of turns in the secondary will be high. When the current transformer has two secondary windings then one winding is connected to the protective relay system and the other is to indicating / metering circuit. Current transformer windings are polar in nature. The current transformers with 1A rating secondaries can handle 25 times more burden than the curren currentt transfo transformer rmerss of 5A second secondari aries. es. Curren Currentt Transf Transforme ormers rs of 1A Seco Second ndar arie iess are are norm normal ally ly used used in the the prot protec ecti tion on of 220 220 KV – 440 440 KV Transmission lines where the substation apparatus is located at a considerable distance from the control room, where the relays are situated. The magnitude of the current which flows through the secondary winding of a CT is a function of the primary current, the transformation ratio and also the impedance of the secondary circuit. CT’s normally operate under
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conditions close to short circuit conditions. The Secondary winding burden further depends upon the method of connection of the CT secondary, the relay windings and the kind of short circuit experienced. CT’s used for extra high voltage net work protection must be capable of accurately transmitting currents both during steady state process and under transient conditions in order to permit operation of the protective devices correctly.
The The reas reason onss for for choo choosi sing ng prop proper er CT’s CT’s for for extr extraa high high volt voltag agee net net work work protection are; 1. The time constan constants ts of DC compon component entss in the short short circuit circuit currents currents of EHV net works are large. 2. The ratio of of the short circuit circuit current to the rated current current is very high, due to increased energy concentration. 3. High Speed relaying relaying is essential essential to protect electrical electrical equipment equipment during fault and to increase system stability. For any type of protection the most important requirement is that the current transformer should not get saturated before the pick up level of the relays. CT’s must transform exactly the primary current, both in phase and amplitude. In the case of differential type of protection, the two currents are compared.
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POTENTIAL TRANSFORMERS:
Instrument Transformers are of means of extending the range of A.C. instruments like ammeters, voltmeters, V.A.R. meters, Walt-meters. They are two types of potential transformers. The primary of the potential transformers is connected across the transmission line whose voltage may range from 2.4 KV to 220 KV. The secondary voltage is standardized at 110 KV. The load connected to the secondary is referred to as burden. The requirements of the good potential transformers are: 1) Accurate turns ration, n = V p / Vs. The difficulty in maintaining the
accurate turn’s ratio is due to resistance and reactance of the windings and the value of the exciting current of the transformer. 2) Small leakage reactance. The leakage reactance is due to the leakage of the magnetic fluxes of the primary and secondary voltages. They can be minimi minimized zed by keepin keeping g the primar primary, y, second secondary ary windin windings gs as close close as possible subject to insulation problem as the primary is at high voltage. 3) Small magnetic current. This can be achieved by making the reluctance
of the core as small as possible and flux density in the core is also low, and it is very less than 1 wb / m 2. 4) Minimum Voltage Drop: The The resistance of the windings is made as small as possible.
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The Primary as it carries high voltage should be heavily insulated. Hence it is immersed in oil and the terminals are brought out to porcelain bushing. Now-a-days synthetic rubber insulation like styrene is used avoiding oil and porcelain. When the load or burden on the secondary is increased. The secondary secondary current increases increases with corresponding corresponding increase in primary primary current current so that transformation ratio remains the same.
RELAYS:
Protective relays are devices which close and open electrical circuits for control of circuit breakers, when the quantity they are designed to respond to, reaches a pre-determined value (Current, Voltage, Power, Impedance etc.) According to their functions in the relay protection scheme relays are divi divide ded d into into main main rela relays ys and and auxi auxili liary ary rela relays ys.. The The main main rela relays ys are are the the protective elements, which respond to any change in the actuating quantity e.g. Current, voltage, power. The auxiliary relays are those which are controlled by other relays to perform some supplementary functions such as time delay, multiplying the number of contacts, passing a command pulse from one relay to another relay, acting upon circuit breaker closing (or) opening, energizing a signal or alarm etc.
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Relays are classified to how they are connected. “Primary Relays” are those whose measuring elements are directly connected in the circuit. The secondary relays are those whose measuring elements are connected to the circuit, they protect through instrument transformers (Current ( Current and voltage)
Thus protective protective relaying relaying is one of several features of the system design connected with minimising damage to the equipment and interrupts power supply supply when fault occurs. occurs. It is therefore therefore necessary necessary a second second line of defence is provided to protect the electrical equipment when the main protective system fails. The main one is called as Primary and the other is called as Back up Protection.
ISOLATORS AND EARTH SWITCHES:
Isolator is a no-load switch designed to operate under no-load conditions therefore the isolator opens only after the opening after the circuit breaker. While closing, isolator closes first and then circuit breaker. Isolator is also called as disconnecting switch or simply disconnector. It is interlock with circuit breaker such that wrong operation is avoided.
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Earth Switch is connected between the line conductor and earth. Normally it is open open and and it is clos closed ed to disc discha harg rgee the the volt voltag agee trap trappe ped d on the the isol isolat ated ed or disconnected line. When the line is disconnected from the supply end, there is some voltage on the line to which the capacitance between the line and earth is charged. charged. This voltage voltage is significant significant in hv systems. Before commencemen commencementt of maintenance work it is necessary that these voltages are discharged to earth by closing the earthing switch. Normally the earthing switches are mounted on the frame of the isolator.
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------: MAIN RECEIVING STATION (M.R.S): ------
The power for the Steel Plant is supplied from AP TRANSCO or as well as from inplant generation. The 220 KV incoming power supply from AP TRANSCO is brought to main receiving station (MRS) over one double circuit 220 KV Transmission Lines. These lines are terminated at the 220 KV bus of MRS the MRS is interconnected with load block step down Sub-Station5 (LBSS-5) with one set of double circuit 220 KV over head tie lines. From MRS 220 KV power has been taken to each of LBSS-2, 3, 4 over a set of double circuit 220 KV overhead lines. Also a set of 220 KV double circuit lines have been taken to LBSS-1 from LBSS-5.
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Duplicate type 220 KV bus bar arrangement with a transfer bus has been provided in M.R.S. Totally there are 14 bays viz., two incoming AP TRANSCO feeder bays, three power plant and blower house (PP & BH) tie feeder bays, seven outgoing feeder bays, one bus couples bay and one bypass bay. The power generated at power plant and blower house coke oven and by product (CO – BP) and Blast Furnish (BF) has been paralleled in three groups at 11 KV over three separate 11 KV buses located at PP & BH. These 11 KV buses are interconnected with the 220 KV bus at LBSS-5 over three numbers 220 / 11 KV, 50/63 MVA and 220/11/11 KV. 31.5 / 40 / 50 MVA split secondary secondary transformers. transformers. Duplicate Duplicate Type with a Transfer Transfer bus arrangement arrangement has been provided in LBSS-5. Totally there are 11 Circuit breaker bays viz., Four Transfo Transformer rmer Bays, Bays, three three bays bays for double double circui circuitt connec connectio tion n to MRS, MRS, two outgoing feeders to LBSS-1 one bus coupler and one bypass bay. The 220 KV Power is stepped down over three 220 / 11 / 6.6 KV three winding transformers at each of LBSS-1 and LBSS-2 and over three 220 / 11.5 / 11.5 KV split secondary transformer at LBSS-4. The basic parameters for the 220 KV System is as follows: Normal System Voltage
220 KV
Highest System Voltage
245 KV
Number of Phases
3
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Rated Frequency
50 HZ
System Earthing
Solidly earthed
Fault level
15,000 MVA (40 KA)
Short time current rating
40 KA / Sec.
Power frequency withstand voltage
395 KV RMS
Impulse withstand Voltage
950 KV Peak
The 220 KV base connection connectionss are so arranged arranged that clearance clearance and access facilities required for safe maintenance of any section are maintained when the remaining sections sections are alive. alive. The following maximum maximum clearances are are maintained in MRS and LBSS-5.
Phase to Phase
2160 mm
Phase to Earth
1880 mm
Sectional Clearance
4400 mm
Ground Clearance
5300 mm
SUB-STATION LAYOUT:
The Sub-Station Layout and single line diagram for Main Receiving Station and load Block Sub-station –5 are shown in the following figures. Broadly the layout for MRS and LBSS-5 are similar for number of feeders and
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transfo transforme rmerr feeder feeder in LBSS-5. LBSS-5. MRS and LBSS-5 LBSS-5 are provid provided ed with the duplicate type bus (main bus-1 and 2) with a transfer bus. Each incoming and outgoing feeder bay is provided with a line isolator, a circuit breaker, a transfer bus isolator and two bus isolators. Bus coupler connects main bus-1 and 2 through a circuit breaker and 2 bus isolators. All feeders are provided with 3 single phase current transformers. However, bus coupler is provided with 6 single phase current transformers. The details such such as numb number er of core cores, s, burd burden en,, and and accu accura racy cy clas classe sess of each each core core are are indi indica cate ted d in the the sing single le line line diag diagra rams ms for for MRS MRS and and LBSS LBSS-5 -5 resp respec ecti tive vely ly.. Incoming feeders at MRS, LBSS-5 Tie-Feeders. At MRS and LBSS-5 are provided with 3 single phase potential transformers. Also three single phase potential transformers are provided in bypass bay for main bus-1 and in bus coupler bay for main bus-2 for potential measurements. Each 50/63 MVA, 220 / 11 KV Transformer is provided in three transformer bays of LBSS-5 and one 31.5 / 40 / 50 MVA, 220 / 11 / 11 KV Transformer is provided in the fourth Transformer bay. All feeders for bus coupler and bypass feeders f eeders in MRS and LBSS-5 are provided with lightening arresters. Each bay is provided with a marshalling kiosk in which the auxiliary contacts of Isolators and Breakers are brought for interlocking purpose. Also secondary terminals of Current Transformers and Potential Transformers of the bay are taken to control panels through marshalling mar shalling kiosk.
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All Isolators installed in the out door yard can be operated controlled manually or electrically on electrical mode both local / remote operations is possible. All circuit breakers can be operated / controlled in electrical mode either local / remote position. The remote control / monitoring of all isolators and circuit breakers is done with the help of a set of control and metering panels. One number of doublex type panels with minimic diagram is provided for each bay. All metering requirements and protective relays of that bay are mounted on the same panel. All the control and relay panels along with the Metering Panel for MRS are install in the MRS Control Building. Control and Relay Panels for LBSS-5 are installed in the capacitive power plant control building.
EARTHING:
Earthing of the sub-station is provided by means of an earth mat. The earth mat is provided by means m eans of 75 X 10 mm G.I. Strips buried at a depth of 1 meter. The earth mat is designed keeping the touch and step potentials within within the permis permissib sible le limits limits.. The earth earth connec connectio tion n from the equipm equipment ent earthing terminals to the main earth mat is done by 65 x 8 mm GI strips. All equipment in the sub-station, rail track for transformers, cable rocks and trays and structures are properly earthed. The two earth conductors are joined by means of welding. One coat of red load, aluminum and lituminous point is
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applied on the welding portion. Details of earthing are indicated in diagrams for MRS and for LBSS-5. Totally 75 numbers of earth points are provided for MRS and 96 numbers of earth points are provided for LBSS-5. Lightening arresters and lightening mat are provided with separate earth points. Transformer neutrals are separately connected to 2 Earth Points. The auxiliary A.C. supply for the outdoor yard equipments for MRS as well as the equipments in MRS control room is obtained from a load centre substation in MRS. The double ended load substation LCSS No. – 41 LC3 comprises of 2 Nos. of 11 KV 630A Isolators, 2 Nos. of 630 KVA Isolators, 2 Nos. Nos. of 630 630 KVA, KVA, 11 KV / 433V 433V Trans Transfo form rmer ers. s. One One numb number er of AC distribution board and interconnecting HT and LT for ducts. The single line diagram for the load centre substation is shown in diagrams. No. No. of outg outgoi oing ng feed feeder erss from from the load load cent centre re ACDB ACDB has has been been deci decide ded d considering individual AC feeder taken for each 220 KV circuit breakers by add the equipments involved in the substation. A.C. auxiliary supply system for LBSS type equipment is not in MGEE scope of supply. The Auxiliary D.C. supply for MRS and LBSS-5 is taken from a set of 220 KV, 250 A Battery Charger 1 set of 220 V batteries. The DC output of charger / battery is fed to a DC Distribution Board. The single line diagram for DC DB is indicated in diagrams. The number of outgoing feeders of DC
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DB has been decided considering individual DC feeder taken for each 220 KV circuit breaker bay and other Equipment involved in the sub-station. All the equipments involved the AC / DC Auxiliary systems for MRS are installed in MRS control room. The layout of all the equipment in MRS control building is indicated in diagram. The control room in MRS is air condit condition ioned ed and ventil ventilati ating ng boxes boxes are provid provided ed for battery battery room room and store store rooms. Four numbers of packaged type standard air conditioners each of 10 Ton along with compressors and its drives are provided for this purpose and they are installed in MRS control building. One set of factory assembled totally enclosed, metal elude, dead front, and compartmentalized motor control centre is installed for building ventilation boxes and conditioners equipments.
SWITCHING SEQUENCES: For charging Main Bus-I and Bus-II: 1) Keep the breaker 52 in open position.
2) Ensure earth switches 57A, 57B 57B and 57C are in open position. 3) Ensure earth switch 57A, PT of the bus Isolator 29A PT in open position
for charging main Bus-I. 4) Ensure that switch 57B – PT of bus isolator 29B – PT is in open position for charging main bus-II.
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5) Close isolator 29C. 6) Close isolator 29A if bus-I is required to be charged or close isolator 29B
if bus-II is required to be charged. 7) Both isolator 29A and 29B should not be closed closed simultaneously. 8) Close the breaker 52 (Breaker can not be closed unless synchronous condition is satisfied) II) FOR CHARGING MAIN BUS-I AND BUS-II THROUGH BY PASS CIRCUI CIR CUIT T BRE BREAKE AKER R WHE WHEN N CIR CIRCUI CUIT T BRE BREAKE AKER R IS TA TAKEN KEN OU OUT T FROM THE LINE FOR MAINTENANCE PURPOSE:
1) Ensure earth switch 57C is in open open position. 2) Ensure earth switch 57A-PT is in open open position for charging main Bus-I. 3) Ensure earth switch 57B-PT is in open open position for charging main Bus-II. 4) Ensure transfer bus isolator isolator of other feeders are in open position, 5) Close the transfer bus bus isolator 29D of the required feeder. 6) Ensure breaker 52 – BP is in open open position and close the isolator 29C-BP. 7) Ensure earth switch 57A-BP is in open position if Bus-I is required to be charged and close isolator 29A or close isolator 29B – BP if bus-II is required to be charged.
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8) Put the trip transfer switch provided on the panel corresponding to the bay bay in whic which h brea breake kerr is take taken n out out main mainte tena nanc ncee purp purpos osee to tran transfe sfer r position. 9) Close the breaker 52.
III) FOR TRANSFERING THE CHARGER FROM MAIN BUS-II TO BUS-1 THROUGH BUS COUPLER:
1) Ensure earth switches 57-B BC, 57A-BC, 57B-PT and breaker 52-BC is in open position. 2) Close the isolator 29A – BC and 29BBC. 1) Close the breaker 52-BC. 2) Operate OLBT Switch. 3) On operation of OLBT switch Bus-II isolator opens and Bus-I isolator
closes automatically. 4) Open breaker breaker 52-BC. 52-BC. 5) Open Isolator 29A – BC and 29B – BC.
6) From From remote remote point point operat operatee discre discrepan pancie ciess switch switch and open open isolat isolator or 29B and close isolator 29A to transfer charge from 29B to 29A. 7) Close breaker breaker 52. 52.
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IV) FOR TRANSFERING THE CHARGER FROM MAIN BUS-1 TO BUS-II THROUGH BUS COUPLER:
1) Ensure earth switch 57B-BC and 57A-BC and 57A-PT, 52-BC are in open position. 2) Close the isolator isolator 29A – BC, BC, and 29BBC. 3) Close the breaker 52-BC. 4) Operate OLBT Switch. 5) On operation of OLBT Switch bus-I isolator Opens and bus-II isolator closes simultaneously. 6) Open breaker 52-BC,. 7) Open isolator 29A-BC, and 29B-BC. 8) From remote point operate discrepancy switch and open isolator 29A and close isolator 29B. 9) Close Close breaker breaker 52.
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------: LOAD BLOCK STEP DOWN SUB-STATIONS:
------
All the Load Block Step Down Sub-Stations 2, 3, 4 receives power from MRS at 220 KV level and the LBSS-1 receives power from LBSS-5. At the LBSS-1, 2 the voltage is stepped down from 220 KV to 11 KV / 6.6 KV by 3 winding transformers Star/Delta/Delta. At LBSS-2, another transformer of 220 KV / 33 KV, 31.5 MVA is installed for feeding power to ladder furnace. At LBSS-3 and LBSS-4 the voltage is stepped down from 220 KV to 11 KV / 11 KV by 3 winding transformer (Star / Delta / Delta) At LBSS-5 three transformers of rating 50/63 MVA, 220/11 KV are connected to GSB-1 at Thermal Power Plant, to which 3 x 60 MW Turbo generators are also connected. Fourth Transformer at LBSS-5 is of 220 / 11 / 11 KV, 31.5 / 40 / 50 MVA is connected to the GSB-2 and 3 at TPP, to which 2 x 12 MW GETGS and 2 x 7.5 MW BPTGs are are connected. Fifth transformer is of 220 / 11 KV, 90 MVA at LBSS-5 is directly connected to 67.5 MW Turbo generators at TPP. The 11 KV and 6.6 KV switch boards located inside the LBSS Buildings are connected to the Transformers secondaries through totally enclosed bus ducts. High capacity 11 KV motors like feed air compressor in ASP, primary air compressors in compressor house-1 and exhausters of sinter plant are feed from LBSS itself.
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The power is feeded to CPRS through Transformers TF 1 and TF 2 of 220 / 33 KV, 125 MVA rating and this is further reduced by the transformers T1 and T2 of 33 / 11 KV and the 11 KV is distributed to Central Power Rece Receiv ivin ing g Stat Statio ion n and and the the volt voltag agee is furt furthe herr step step down down to 0.4 0.4 KV and and is distributed to house hold purposes.
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All the step down actions are taken place with necessary precautions. And all the lines are connected by the well tested protective equipment in order to prevent damage to the system in case of any faults. From MRS the power is distributed to all the LBSS through 2 lines and at Bus-1 the AP TRANSCO incoming lines are connected. At bus 2 all the outgoing feeders are connected during normal operating conditions. There is another bus called as auxiliary bus. Under fault conditions if any one of the buses one or two is damaged then the power is transferred from that bus to auxiliary bus and then the service is continued until the bus is repaired. This auxiliary bus is operated by operating the by pass. From Bus 1 the power is transferred to the Bus 2, by closing the bus coupler. Each line is named as 1 Bay. There are 14 Bays at MRS. Each bay is named with a certain alphabet and it consists of a line isolator and a circuit breaker, a transfer bus isolator and 2 Bus isolators. From MRS the power has been distributed to the CPRS and then to household consumers through A Bay. Through B bay and C bay the power has been feeded to LBSS-2 from MRS at 220 KV Level. By means of H Bay, and G Bay, the power has been feeded to the LBSS-4 from MRS at 220 KV Level. Similarly to LBSS-3 the power has been feeded through M Bay and L Bay and to LBSS-5 the power has been feeded through N-Bay, P Bay and R-Bay.
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LBSS LBSS-1 -1 rece receiv ives es powe powerr from from LBSS LBSS-5 -5 thro throug ugh h 2 numb number er of 220 220 KV Transmission lines. This 220 KV is further stepped down to 11 KV and 6.6 KV by using 3 numbers of 3 winding transformers of 80 MVA of star/delta/delta. Each having secondaries of 11 KV and 6.6 KV. LV1 of each transformer is connected to 11 KV Switch Board and LV2 of each transformer is connected to 6.6 KV Switch Board from the Switch Board the power has been feeded to different loads viz., Coke Oven, CP, RMHP.
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LBSS-2 receives power from MRS MRS through 2 numbers of 220 KV Lines L ines named L2 & L2 and L2, L1 (B Bay and A-Bay) This 220 KV is stepped down to 11 KV and 6.6 KV by 3 number of transformers of 80 MVA of star / delta / delt delta. a. Each Each havi having ng seco second ndar arie iess of 11 KV and and 6.6 6.6 KV. KV. LV1 LV1 of each each transformer is connected to 11 KV Switch Board and LV2 of each transformer is connected to 6.6 KV Switch Board. Each secondary is connected to Earthing cum Stationery Transformer (EST) and from the switch boards the power is feeded to different loads namely, BF1, BF2, SMS, CRMP, ASP, BHS1, BHS 2. There is one more transformer of 220 / 33 KV, 31.5 MVA is installed to Feed the power to Ladder furnace.
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LBSS-3 receives power from MRS through 2 numbers of 220 KV Transmission Lines named L3 and L2 and L2 and L1. This 220 KV is stepped down to 11 KV through 3 number of transformers of 80 MVA of Star/delta/delta is having secondaries of 11 KV. LV1 of each transformer is connected to 11 KV Switch Board and LV 2 of each Transformer is connected to 11 KV Switch Board. From the switch boards the power has been feeded to different loads viz., MMS. (Medium Merchant Stationery Mill)
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LBSS-4 receives power from MRS through 2 number of 220 KV Transmission line named L4 and L1 and L4 and L2. This 220 KV is further stepped down to 11 KV by using three numbers of 3 winding transformers of star/delta/delta. Each having secondaries of 11 KV, LV1 of each transformer is connected to 11 KV Switch Board and LV2 of each transformer is connected to another 11 KV Swit Switch ch Boar Board. d. From From the the swit switch ch board board the powe powerr has has been been feed feeded ed to the the different loads like LMMM, WRM, Stores, and Pump House.
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------: CONCLUSION : ------
LBSS area of DNW Department is very critical as far as HT Supply system is concerned. The GSB feeders of this area switchboards plays a vital role in Steel Plant Units viz., SMS, BF, ASP, WMD, etc. Which are directly connected connected to Thermal Power Plant. Plant. This can not be afforded to fail for a Bus Fault which may affect the plant generation.
Hence, all the LBSS and GSB Switch Boards were provided with new over current instantaneous relays to trip the feeders and also prevents the Bus Coupler to close in auto in case of Bus faults the reliability of the system has become very high. Thus Thus the reliability of the system has become very high.
The above said modification has achieved the desired requirement of reliable power supply to LBSS area units of VSP.
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