power distribution of vsp done at vizag steel

8/7/2019 Power Distribution of Vsp Done at Vizag Steel

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POWER DISTRIBUTION OF VSPDone 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: ------

Visakhapatnam Steel Plant (V.S.P.) being a major process industry

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 has an installed capacity of 3

million tones per annum of liquid steel and 2.656 million tones of saleable steel.

At VSP there is emphasis on total automation, seamless integration 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 3 International Standards for quality (ISO 9001), for environment

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 man-

year of liquid steel, which is the best in the country and comparable with

international levels.

The construction of the plant started on 1st Feb. 1982. Government of

India on 18th 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 at VISAKHAPTNAM from authority of India Limited to 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 area

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 treatment facilities of effluents for ensuring p

environmental protection.

Computerization for process control.

Sophisticated high speed high production mills.Bharadwaj


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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 (i) By-Products (ii) By-Products

Angles Nut coke Granulated slag

Billets Coke Dust Lime fines

Channels Coal Tar Ammonium soleplateBeams Anthracene oil

Squares HP Naphthalene

Flats Benzene

Rounds Toluene

Re-bars Zylene

Wire rods Wash Oil

MAJOR DEPARTMETS IN VSP:

Raw material handling plant (RMHP)

Coke ovens and coal chemical plant (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)

Wire rod mill (WRM)

Medium merchant and structural mill (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

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 of zigzag type and its star point is connected to Neutral Grounded

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 gear

2. Auxiliary switch gear

Main switchgear comprises of circuit breakers, isolators, bus bars, current

transformers, potential transformers, etc. In the main circuit of generator-

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 installed near the transformer terminals. Isolator is also called 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 over-

voltage will cause burning of the insulation. It is absolutely, necessary to

provide protection against the traveling surges caused by lighting. 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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lightning arrestor or surge diverter must posses the following conditions

(characteristics)

a) It should not absorb any current during the normal operation. At over

voltage surges it must provide an easy path to earth.

b) After the first discharge of the current has taken place through them they

must be capable of carrying the discharge current for some interval of

time without any damage to themselves.

c) After the over voltage discharge it must be capable of interrupting 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

2) Sphere gap lightning arrester.

3) Horn gap lightning arrester.

4) Expulsion type arrester.

5) Impulse protective gap with electrolyte lightning arrester.

6) Electrolytic type.

7) Lead Oxide type.

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8) Pellet type lead per-oxide type.

9) Thyrite lightning arrester

10) Valve type.

CIRCUIT BREAKERS:

For low voltage 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 w

replacement for low capacities a fuse combined with circuit

arrangement is quite useful and economical. The following

requirements for a circuit breaker or a switch gear;

1) It must safely interrupt the normal working current as well as short circuit

current.

2) After occurrence of fault the switch gear must isolate the faulty circuit as

quickly as possible.

3) It must have high sense of discrimination i.e., in systems where 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 an over current flows under healthy condition.

There are different types of circuit breakers among those air blast circuit

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 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 motorburns out a 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 happensto 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 sayvery 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 current transformers of 5A secondaries. Current Transformers of 1A

Secondaries are normally used in the protection of 220 KV 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. CTs 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. CTs 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 reasons for choosing proper CTs for extra high voltage net work

protection are;

1. The time constants of DC components in the short circuit currents of

EHV net works are large.

2. The ratio of the short circuit current to the rated current is very high, due

to increased energy concentration.

3. High Speed relaying is essential to protect electrical 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. CTs 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 = Vp / Vs. The difficulty in maintaining the

accurate turns 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

minimized by keeping the primary, secondary windings as 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 / m2.

4) Minimum Voltage Drop: 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 current increases with corresponding increase in primary 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

divided into main relays and auxiliary relays. The main relays are 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 and voltage)

Thus protective relaying is one of several features of the system design

connected with minimising damage to the equipment and interrupts power

supply when fault occurs. It is therefore necessary a 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 and it is closed to discharge the voltage trapped on the isolated 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. This voltage is significant in hv systems. Before commencement 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-Station-

5 (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 A

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 transformers. Duplicate Type with a Transfer bus arrangement has

been provided in LBSS-5. Totally there are 11 Circuit breaker bays viz., Four

Transformer Bays, three bays for double circuit connection to 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 connections are so arranged that clearance and access

facilities required for safe maintenance of any section are maintained when the

remaining sections are alive. The following maximum clearanc

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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transformer feeder in LBSS-5. MRS and LBSS-5 are provided 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 as number of cores, burden, and accuracy classes of each core are

indicated in the single line diagrams for MRS and LBSS-5 respectively.

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 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 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 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 the permissible limits. The earth connection from the equipment

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

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 sub-

station 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. of 630 KVA, 11 KV / 433V Transformers. One number 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. of outgoing feeders from the load centre ACDB has been decided

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

conditioned and ventilating boxes are provided for battery room and 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 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 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

CIRCUIT BREAKER WHEN CIRCUIT BREAKER IS TAKEN OUT

FROM THE LINE FOR MAINTENANCE PURPOSE:

1) Ensure earth switch 57C is in open position.

2) Ensure earth switch 57A-PT is in open position for charging main Bus-I.

3) Ensure earth switch 57B-PT is in open position for charging main Bus-II.

4) Ensure transfer bus isolator of other feeders are in open position,

5) Close the transfer bus isolator 29D of the required feeder.

6) Ensure breaker 52 BP is in 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 in which breaker is taken out maintenance purpose to transfer

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 52-BC.

5) Open Isolator 29A BC and 29B BC.

6) From remote point operate discrepancies switch and open isolator

29B and close isolator 29A to transfer charge from 29B to 29A.

7) Close breaker 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 29A 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 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 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

Receiving Station and the voltage is further step down to 0.4 KV 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-1 receives power from LBSS-5 through 2 number of 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 through 2 numbers of 220 KV Lines named

L2 & L2 and L2, L1 (B Bay and A-Bay) This 220 KV is stepped dow

11 KV and 6.6 KV by 3 number of 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. 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, BH

BHS 2. There is one more transformer of 220 / 33 KV, 31.5 MVA

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

Switch Board. From the switch board the power has been feeded to 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 dire

connected to Thermal Power 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 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.

power distribution of vsp done at vizag steel

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