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9/18/2014mydocumentsNTPI_excitationControl1E.M.F.-RelationNSEMF, E [volts] = B * l * v.

B = webers / meter Sq.L = length in MetersV = Velocity in Meters/SecondcurrentcurrentARMATURELOADRotating Armature Generator

Rotating Field Generator

Typical Supply System

The Power System - It ComprisesGeneration Units that produce electricityHigh Voltage Transmission Lines that transport electricity over long distancesLow Voltage Transmission Lines That delivers electricity to ConsumersSubstations, which are the part of the electricity transmission and distribution system where the voltages are transformed to lower levels for distributing power to end user.

Major PlayersCentral Utilities such as NTPC, NHPC, Nuclear Power Corporation, Damodar Valley Corporation andNEEPCO.State Electricity Boards which are state-owned utilities like Orissa, Haryana, AP, Uttar Pradesh, Karnataka etc.Licensees such as BSES and CESC.Independent Power Projects (IPPs)Four basic energy sources Electric Power GenerationFossil fuel such - coal, oil and natural gas

Hydro electricity

Nuclear Power and

Renewable Energy bio-fuels, solar, biomass, wind and tidal.

TransmissionIn India, the power plants typically produce 50 cycle/second (Hertz) alternating current (AC) with voltages between 11 kV and 25 kV. Higher voltage means lower current but the insulation thickness and size increases.Hence an optimum voltage is selected.Electric power is brought from the power plant to the consumer through an extensive transmission and distribution (T&D) system. comprising distribution networks, state grids and regional grid.

Stages of TransmissionAt the plant, the 3-phase voltage is generated and stepped up to a higher voltage for transmission on conductors strung on cross country towers.High voltage(HV) and Extra High Voltage (EHV) transmission in the next stage to transport A.C. power from the power plant over long distances at voltages like 220kV, 400kV and 760 kV. For longer distances and higher powers, higher voltages are economical.In special cases HVDC (High voltage direct current transmission + 500 kV DC) is preferred.Example 1500 MW Chandrapur Padghe HVDC in Maharashtra.Stages of Transmission .Sub- Transmission network at 132 kV. 110kV, 66 kV or 33 kV constitutes the next link towards the end user.Network planning concept >(n-1)Major Players: Most of the states restructured their State Electricity Boards and have unbundled them in three entities- Generation, Transmission and Distribution.

DistributionDistribution at 11KV (6.6 KV in US) constitutes the last link to the consumers which is connected directly or through step-down transformers.11/0.4 KV or 6.6/0.110 KV Transformers. These transformers bring the voltage levels down to 400 V / 110 V. for 3 phase, 4 wire secondary distributions.The single phase residential lighting load is connected between any phase and neutral (230 V/110 V) and 3-phase load is connected across 3-phase lines directly.

Power Distribution SystemElectricity is carried through a transmission network of high voltage lines. Usually, these lines run into hundreds of kilometres and deliver the power into a common power pool called the grid.The grid is connected to load centres (cities) through a sub-transmission network of usually 33 kV (or sometimes 66 kV) lines. These lines terminate into a 33 kV (or 66 kV) substation, where the voltage is stepped-down to 11 kV for power distribution to load points through a distribution network of lines at 11 kV and lower.

The power network concern to the end-user is the distribution network of 11 kV lines or feeders downstream of the 33 kV substations. Each 11 kV feeder which emanates from the 33 kV substation branches further into several subsidiary 11 kV feeders to carry power close to the load points (localities, industrial areas, villages, etc.). At these load points, a transformer(DTC), further reduces the voltage from 11 kV to 415 V to provide the last-mile connection through 415 V feeders (also called LT feeders) to individual customers, either at 240 V (as single-phase supply) or at 415 V (as three-phase supply). The utility voltage of 415 V, 3-phase is used for running the motors for industry and agricultural pump sets and 240 V, single phase is used for lighting in houses, schools, hospitals and for running industries, commercial establishments, etc.

Components of T&D SystemTransformers.Circuit Breakers .Isolators.Surge Diverters. (L.A.) Horn Gaps.Drop Out Fuses (D.O.)Current Transformers (C.T.)Potential transformers (P.T.)Reactors.Capacitors.Cables .Conductors.CCGT-UTRAN-SWITCHGEAR DISTRIBUTION - 18/09/2014 - P 17Current Transformer.Measurement of current is the essence in all transducers.

The current carrying conductor is threaded through a donut shaped device.

A C.T. produces an alternating current or

alternating voltage proportional to the current being measured.

CCGT-UTRAN-SWITCHGEAR DISTRIBUTION - 18/09/2014 - P 18

3-phase C.T.sCCGT-UTRAN-SWITCHGEAR DISTRIBUTION - 18/09/2014 - P 19LIVE TANK C.T.

CCGT-UTRAN-SWITCHGEAR DISTRIBUTION - 18/09/2014 - P 20DEAD TANK C.T.

CCGT-UTRAN-SWITCHGEAR DISTRIBUTION - 18/09/2014 - P 21

E.H.V.-C.T.

DRYSHIELD

TYPE

CCGT-UTRAN-SWITCHGEAR DISTRIBUTION - 18/09/2014 - P 22C.V.T.E.H.V.BUS / LINECapacitorswindingsWhen a C.T.is to be changed, proper matching is MUST

LIGHTNING ARRESTERS

The earthing screen and ground wires can well protect the electrical system against direct lightning strokes but they fail to provide protection against travelling waves, which may reach the terminal apparatus. The lightning arresters or surge diverters provide protection against such surges. A lightning arrester or a surge diverter is a protective device, which conducts the high voltage surges on the power system to the ground

EHV LIGHTNING ARRESTERSystem Voltage : 0.5 ~ 245kVRated Voltage (kV) : 0.5 ~ 216kVNominal discharge current (kA) : 5 ~ 10 kVHigh current capability (4/10us) kA : 65 ~ 100Energy Class : D, 1, 2 & 3Energy absorption Capability kJ/kV : 2 ~ 8Short Circuit (Pressure relief) kA : 40Standard in accordance with : IEC 60099-4 & IS 3070 Part III

Working Principle of L.A. Surge Arrester consists of highly non-linear varistor elements housed in a non porous electrical porcelain housing . When an electric surge due to natural lightning or switching action appears across the arrester, the block stack allows the entire energy to earth by posing a very low resistance and instantaneously recovers to its original insulation property after the passage of surge, getting ready for next operation.Lightening Arrester / Surge Diverter

L.A. FunctioningIt consists of a spark gap in series with a non-linear resistor. One end of the diverter is connected to the terminal of the equipment to be protected and the other end is effectively grounded. The length of the gap is so set that normal voltage is not enough to cause an arc, but a dangerously high voltage will break down the air insulation and form an arc. The property of the non-linear resistance is that its resistance decreases as the voltage (or current) increases and vice-versa. This is clear from the volt/amp characteristic of the resistor shown in Fig.The action of the lightning arrester or surge diverter is as under:(i) Under normal operation, the lightning arrester is off the line i.e. it conducts no current to earth or the gap is non-conducting(ii) On the occurrence of over voltage, the air insulation across the gap breaks down and an arc is formed providing a low resistance path for the surge to the ground. In this way, the excess charge on the line due to the surge is harmlessly conducted through the arrester to the ground instead of being sent over the line.

(iii) It is worthwhile to mention the function of non-linear resistor in the operation of arrester. As the gap sparks over due to over voltage, the arc would be a short-circuit on the power system and may cause power-follow current in the arrester. Since the characteristic of the resistor is to offer low resistance to high voltage (or current), it gives the effect of short-circuit. After the surge is over, the resistor offers high resistance to make the gap non-conducting.Horn Gap Protection

Working of Horn Gap ProtectionHorn shaped metal rods A and B separated by a small air gap. The distance between horns gradually increases towards the top as shown. The horns are mounted on porcelain insulators. One end of horn is connected to the line through a resistance and choke coil L while the other end is effectively grounded. The resistance R restricts the follow current to a small value. The choke coil offers small reactance at normal power frequency but a very high reactance at transient frequency. Thus the choke does not allow the transients to enter the apparatus to be protected. The gap between the horns is so adjusted that normal supply voltage is not enough to cause an arc across the gap.Under normal conditions, the gap is non-conducting i.e. normal supply voltage is insufficient to initiate the arc between the gap. On the occurrence of an over voltage, spark-over takes place across the small gap G. The heated air around the arc and the magnetic effect of the arc cause the arc to travel up the gap. The arc moves progressively into positions 1,2 and 3. At some position of the arc (position 3), the distance may be too great for the voltage to maintain the arc; consequently, the arc is extinguished. The excess charge on the line is thus conducted through the arrester to the ground.Kingston/load dispatch/20Aug0933Integration of WR-ER-NR-NER NRWRSRNERERHVDC Back to Back400/220 kV AC linesHVDC Bi Pole400 kV AC linesPower system in India

Power ratings of lines Normally for continuous operation the transmission lines on various voltage are designed to carry maximum power loads at the designed maximum conductor temperature of 65 deg. C. as followsAt 132 kv with 'Panther' ACSR = 75 MVAAt 220 kv with 'Zebra' ACSR = 200 MVAAt 400 kv with 'Moose' ACST = 500 MVACurrent ratings of EHV Conductors.Sl. No.Size of Conductor (Code Name)Current carrying Capacity in AmperesAt maxim. designed Temperature of 650 CAt maxim. designed temperature of 750 CNew Conductor (Up to one year)Old Conductor (Beyond 10 years)New Conductor (Up to one year)Old Conductor (Beyond 10 years)1.'Dog' ACSR141.12150.20229.65245.062.'Panther' ACSR179.89200.60340.83371.423.'Zebra' ACSR201.26249.51496.46553.704.'Moose' ACSR133.60218.89530.51603.78Surge Impedance LoadingThe characteristic impedance of a transmission line is expressed in terms of the surge impedance loading (SIL), or natural loading, being the power loading at which reactive power is neither produced nor absorbed:

in which V is the phase voltage in volts.Loaded below its SIL, a line supplies reactive power to the system, tending to raise system voltages. Above it, the line absorbs reactive power, tending to depress the voltage. The Ferranti effect describes the voltage gain towards the remote end of a very lightly loaded (or open ended) transmission line. Underground cables have a very low characteristic impedance, resulting in an SIL that is typically in excess of the thermal limit of the cable. Hence a cable is almost always a source of reactive power.

Ferranti EffectFerranti effect is an increase in voltage at the receiving end of a long transmission line. This occurs when the line is energized but is a very lightly loaded or the load is disconnected. The capacitive line charging current produces a voltage drop across the line inductance that is in-phase with the sending end voltages. Therefore both line inductance and capacitance are responsible for this phenomenon.The Ferranti Effect will be more pronounced the longer the line and the higher the voltage applied. The relative voltage rise is proportional to the square of the line length.The Ferranti effect is much more pronounced in underground cables, even in short lengths, because of their high capacitance.

ACSR CONDUCTORS

ALL ALUMINIUM CONDUCTORS (AAC)

This conductor is manufactured from electrolytically refined (E.C.GRADE) aluminium, having purity of minimum 99.5% of aluminium. This conductor is used mainly in urban areas

The spacing is short and the supports are close. All aluminium conductors are made up of one or more strands of aluminium wire depending on the end usage. These conductors are also used extensively in costal because it has a very high degree of corrosion resistance.AAA CONDUCTOR

ALL ALUMINIUM ALLOY CONDUCTORS (AAAC)

This conductor is made from aluminium-magnesium-silicon alloy of high electrical conductivity.It contains enough magnesium silicide to give it better mechanical properties after treatment. These conductors are generally made out of aluminium alloy 6201. AAAC CONDUCTOR has a better corrosion resistance and better strength to weight ratio and improved electrical conductivity than ACSR CONDUCTOR on equal diameter basis.

TYPICAL S/S SCHEMESIMILAR WILL BE FOR LOWER VOLTAGES

Single Bus System

Single Bus System is simplest and cheapest one. In this scheme all the feeders and transformer bay are connected to only one single bus as shown. Advantages of single bus systemThis is very simple in design.This is very cost effective schemeThis is very simple to operateDisadvantages of single bus systemOne major difficulty of these type of arrangement is that, maintenance of equipment of any bay is not possible without interrupting the feeder or transformer connected to that bay.

Advantages of single bus system with bus sectionalizerIf any of the sources is out of system, still all loads can be fed by switching on the sectional circuit breaker or bus coupler breaker.If one section of the bus bar system is under maintenance, part load of the substation can be fed by energizing the other section of bus bar.Disadvantages of single bus system with bus sectionalizerAs in the case of single bus system, maintenance of equipment of any bay is not be possible without interrupting the feeder or transformer connected to that bay.The use of isolator for bus sectionalizing does not fulfill the purpose. The isolators have to be operated off circuit and which is not possible without total interruption of bus bar. So investment for bus-coupler breaker is required.

Double Bus SystemIn double bus bar system two identical bus bars are used in such a way that any outgoing or incoming feeder can be connected to any of the bus.By closing any of the isolators one can put the feeder to associated bus. Both buses are energized and total feeders are divided into two groups, one group is fed from one bus and other from other bus. But any feeder at any time can be transferred from one bus to other. Advantages of Double Bus SystemDouble Bus Bar Arrangement increases the flexibility of system.The arrangement permits breaker maintenance without interruption.

One & Half Breaker SystemThis is an improvement on the double breaker scheme to effect saving in the number of circuit breakers. For every two circuits only one spare breaker is provided. The protection is however complicated . As shown in the figure that it is a simple design, two feeders are fed from two different buses through their associated breakers and These two feeders are coupled by a third breaker which is called tie breaker. During failure of any feeder breaker, the power is fed through the breaker of the second feeder and tie breaker.Therefore each feeder breaker has to be rated to feed both the feeders, coupled by tie breaker.

Main & Transfer Bus This is an alternative of double bus system. The main conception of Main and Transfer Bus System is, here every feeder line is directly connected through an isolator to a second bus called transfer bus. The isolator in between transfer bus and feeder line is generally called bypass isolator. The main bus is as usual connected to each feeder. There is one bus coupler which couples transfer bus and main bus .through a circuit breaker. If necessary the transfer bus can be energized by main bus power by closing the bus coupler breaker. Then the power in transfer bus can directly be fed to the feeder line by closing the bypass isolator. If the main circuit breaker associated with feeder is switched off or isolated from system, the feeder can still be fed in this way by transferring it to transfer bus.

Ring Bus It provides a double feed to each feeder circuit. One breaker under maintenance or otherwise does not affect supply to any feeder. But this system has two major disadvantages. One as it is closed circuit system it is impossible to extend in future and hence it is unsuitable for developing system. Secondly, during maintenance or any other reason if any one of the circuit breaker in ring loop is switch off, reliability of system becomes very poor as the closed loop becomes opened. Since, at that moment for any tripping of any breaker in the open loop causes interruption in all the feeders between tripped breaker and open end of the loop.

760 / 400 KV Lines 760 / 400 KV Sub Stations.220/132 KV Lines.220/132 KV S/S 33/22 KV Lines 33/ KV S/S 11 KV Lines 11 KV 11/ 0.440 KV DTCs

Supply SchemesRadial Feeders.Ring Mains.Major cities have 220/132 KV ring mains.220/132/33 KV s/s can be fed from two sides.Even 11/0.440 KV DTCs can be fed from two ends.DTCs ideal connected load is 70% of its capacity.When one DTC fails, the loads can be shifted to adjoining DTCs. Special ComponentsReactors- For long +400 KV lines, reactors are used to limit switching surge voltages.Capacitor Banks EHV Capacitor banks are used to improve power factor and voltage.H.V.D.S.- This system eliminates 440 Volts , L.T. lines which prevents theft.Consumers are directly fed from the smaller DTCs (25 KVA) . Losses in LT line are 625 times of HT line as the current is 25 times more in L.T.line.Power FactorThe System load consists of active KW component and reactive KVAR component.Vector sum of these two is the KVA load.

TRANSMISSION CONDUCTORSHigh-voltage overhead conductors are not covered by insulation. The conductor material is an aluminium alloy, made into several strands and possibly reinforced with steel strands. Improved conductor material and shapes are regularly used to allow increased capacity and modernize transmission circuits. Conductor sizes range from 12mm2 to 750mm2, with varying resistance and current-carrying capacity. Thicker wires would lead to a relatively small increase in capacity due to the skin effect, that causes most of the current to flow close to the surface of the wire. Because of this current limitation, multiple parallel cables (called bundle conductors) are used when higher capacity is needed. Bundle conductors are also used at high voltages to reduce energy loss caused by corona discharge.EHV SUB TRANSMISSION DISTRIBUTION VOLTAGESLower voltages such as 66kV and 33kV are usually considered subtransmission voltages but are occasionally used on long lines with light loads. Voltages less than 33kV are usually used for distribution. Voltages above 230kV are considered extra high voltage. Since overhead transmission wires depend on air for insulation, minimum clearances to be observed to maintain safety. Adverse weather conditions of high wind and low temperatures can lead to power outages. Wind speeds as low as 43km/h can permit conductors to encroach operating clearances, resulting in a flashover and loss of supply.Oscillatory motion of the physical line can be termed gallop or flutter depending on the frequency and amplitude of oscillation.

Double Circuit Tower & Typical ACSR

Underground transmissionElectric power can also be transmitted by underground power cables instead of overhead power lines. Underground cables take up less right-of-way than overhead lines, have lower visibility, and are less affected by bad weather. However, costs of insulated cable and excavation are much higher than overhead construction. Faults in buried transmission lines take longer to locate and repair. Underground lines are strictly limited by their thermal capacity, which permits less overload or re-rating than overhead lines. Long underground cables have significant capacitance, which may reduce their ability to provide useful power to loads.

High-voltage direct current

High-voltage direct current (HVDC) is used to transmit large amounts of power over long distances or for interconnections between asynchronous grids. over very long distances, it is more economical to transmit using direct current instead of alternating current. For a long transmission line, the lower losses and reduced construction cost of a DC line can offset the additional cost of converter stations at each end. Also, at high AC voltages, significant (although economically acceptable) amounts of energy are lost due to corona discharge, the capacitance between phases or, in the case of buried cables, between phases and the soil or water in which the cable is buried.HVDC is also used for long submarine cables because over about 30 kilometres AC can no longer be applied. In that case special high voltage cables for DC are built. Submarine connections up to 600 kilometres are currently in use.CONTROL ON POWER FLOW HVDC links are sometimes used to stabilize against control problems with the AC electricity flow. The power transmitted by an AC line increases as the phase angle between source end voltage and destination end increases, But too great a phase angle will allow the generators at either end of the line to fall out of step. Since the power flow in a DC link is controlled independently of the phases of the AC networks at either end of the link, this stability limit does not apply to a DC line, and it can transfer its full thermal rating. A DC link stabilizes the AC grids at either end, since power flow and phase angle can be controlled independently.

Capacity

The amount of power that can be transmitted is limited. The limits vary depending on the length of the line. For a short line, the heating of conductors due to line losses sets a thermal limit. If too much current is drawn, conductors may sag too close to the ground, or conductors and equipment may be damaged by overheating. For intermediate-length lines about 100 km , the limit is set by the voltage drop in the line. For longer AC lines, system stability sets the limit to the power that can be transferred. Capacity of very long lines.The power flowing over an AC line is proportional to the cosine of the phase angle of the voltage and current at the receiving and transmitting ends. Since this angle varies depending on system loading and generation, it is undesirable for the angle to approach 90 degrees. Very approximately, the allowable product of line length and maximum load is proportional to the square of the system voltage. Series capacitors or phase-shifting transformers are used on long lines to improve stability. High-voltage direct current lines are restricted only by thermal and voltage drop limits, since the phase angle is not material to their operation.

Power Line Carrier CommunicationSpecial coupling capacitors are used to connect radio transmitters to the power-frequency AC conductors. Frequencies used are in the range of 24 to 500 kHz, with transmitter power levels up to hundreds of watts. Several PLC channels may be coupled onto one HV line. Filtering devices at substations prevent the carrier frequency current from being bypassed through the station apparatus and to ensure that distant faults do not affect the isolated segments of the PLC system. These circuits are used for control of switchgear, and for protection of transmission lines. For example, a protective relay can use a PLC channel to trip a line if a fault is detected between its two terminals, but to leave the line in operation if the fault is elsewhere on the system.While utility companies use microwave and fiber optic cables for their primary system communication needs, the power-line carrier apparatus is useful as a backup channel or for very simple low-cost installations that do not warrant installing fiber optic lines.

Power line carrier communication (PLCC) is mainly used for telecommunication, tele-protection and tele-monitoring between electrical substations through power lines at high voltages, such as 110 kV, 220 kV, 400 kV. The major benefit is the union of two applications in a single system, which is particularly useful for monitoring electric equipment and advanced energy management techniques.The modulation generally used in these system is amplitude modulation. The carrier frequency range is used for audio signals, protection and a pilot frequency. The pilot frequency is a signal in the audio range that is transmitted continuously for failure detection.

The voice signal is compressed and filtered into the 300 Hz to 4000 Hz range, and this audio frequency is mixed with the carrier frequency. The carrier frequency is again filtered, amplified and transmitted. The transmission power of these HF carrier frequencies will be in the range of 0 to +32 dbW. This range is set according to the distance between substations. PLCC can be used for interconnecting private branch exchanges (PBXs).

Wave TrapTo sectionalize the transmission network and protect against failures, a "wave trap" is connected in series with the power (transmission) line. It consist of a resonant circuit, which blocks the high frequency carrier waves (24 kHz to 500 kHz) and permits the power frequency current (50 Hz - 60 Hz) to pass through. Wave traps are used in switchyard of most power stations to prevent carrier from entering the station equipment. Each wave trap has a lightning arrester to protect it from surge voltages.A coupling capacitor is used to connect the transmitters and receivers to the high voltage line. This provides low impedance path for carrier energy to HV line but blocks the power frequency circuit by being a high impedance path. The coupling capacitor may be part of a capacitor voltage transformer used for voltage measurement.Wave Trap details

A Line enters the sub station

Symbols

Distribution Details Feeders route the power from the substation throughout the service area. They are either overhead distribution lines mounted on wooden poles, orUnderground cable sets. Feeders operate at the primary distribution voltage in primary distribution system and secondary distribution voltage in the secondary distribution systemPrimary Voltage 11KV, 22kv , 33 kvSecondary Voltage 440 VoltsFeederA feeder consists of all primary or secondary voltage level segments of distribution lines between two substations orBetween a substation and an open point . The most common primary distribution voltages in use are 11 kV, 22 kV and 33 kV. The main feeder, may branch into several main routes.

Configuration of Feeders

Feeders are connected in a configuration, which depends on the type of network required in the distribution system. Three types of network are normally available in the electrical distribution system: Radial Loop Cross-loop network.Layout of FeedersRadial feeder emanates from one point and ends at the other.In radial network, load transfer in the case of breakdown is not possible.A radial feeder can be loaded to its maximum capacity, but, in the case of breakdown, quite a large area may remain in dark until the fault is detected and repaired.In loop arrangement, two feeders are connected to each other so that in thecase of breakdown, the faulty section can be isolated and the rest of theportion can be switched on. In loop system, the feeder is normally loaded to 70% of its capacity so that in the event of breakdown it can share the load of other feeders also.A cross-loop network provides multiple paths and the flexibility further increases. In case of breakdown in any line, the faulty system can be isolated and supply can be resumed very quickly. In this type of network, feeders should normally be loaded to 70% of their current carrying capacity. This system is highly reliable, but more expensive.Various Feeder Layouts

Comparison of Feeder Layouts

Ring mainsIn big cities, the concept of 33 kV ring main is very popular and two ring mains are laid: one outer and one inner. The outer ring main is laid using the panther conductor and the inner ring main is laid using the dog conductor.The use of these two types of ring mains provides excellent flexibility to the system and at the time of breakdown, supply can be immediately switched on from another 132 kV substation. While making any distribution planning for metros, the aspect of outer and inner 33 kV ring mains is extremely essential and should be included for providing uninterrupted supply.OUTER & INNER RING MAIN FOR REDUNDANCY

Arial Bunched cables 1. Elimination of cable trenching work in grounds having high water table making trenching difficult andAlong narrow streets which causes serious public inconvenience.2. Utilization of existing assets such as poles and structures for supporting the cable, which reduces cost of installation.3. Elimination of cable faults due to dig in damages caused by other agencies.4. Speedy service connections in LT distribution.H.V.D.S.Significantly high losses take place in the secondary distribution system. (440 Volts)This is due to higher current densities and ease of pilferage at low voltages.. One of the latest innovations in efforts to reduce technical and commercial losses is the use of High Voltage Distribution System(HVDS) or LT-less system.For 100 KVA load; HT =6 Amps; LT = 150 Amps.Typical HVDS No L.T. Line

HVDS - Advantagesuse of small size ACSR or aluminium alloy conductor Better voltage profile; reduced line losses; and reduced commercial losses.Improved Reliability and Security of SupplyThe use of HT distribution leads to improved reliability and security of supply for the following reasons:The faults on HT lines are far less compared to those of LT lines.Number of small distribution transformers is high in HVDS.The failure of one transformer does not affect supply to other consumers connected to other transformers. In the event of failure of distribution transformers, only a small number of consumers (2 to 3 power consumers or 10 to 15 domestic consumers) would be affected. On the other hand, a large distribution transformer supplies power through LV distribution lines to even remotely located consumers in LVDS. Hence, the failure of an existing large size distribution transformer would affect a group of 40 to 50 powe consumers and/or 100 to 200 domestic consumers.THANK YOUELEMENTSELEMENTS OF SUPPLY SYSTEMSr.No.IN A POWER STATION1SWITCHGEARSIN-DOOROUT-DOOREHVHTLT2TRANSFORMERSSTEP-UPSTATIONUATAUXILLARYLIGHTING3CABLESSINGLE-Ph3-Ph.ArmouredPVCPILCX.L.P.E.H.T.L.T.4TERMINATION5CIRCUIT BREAKERSO.C.B.M.O.C.B.A.B.C.B.S.F.-6V.C.B.M.C.B.6ISOLATORS7SWITCHES8BUS-BARS-INSULATORS-GANTRIESE.H.V.H.T.L.T.PORCELAINPVC9EARTHING ARRANGEMENTSOLIDRESISTANCEREACTANCE10EARTHING TRANSFORMERS11NEUTRAL GROUNDING TRANSFORMER12PANELS13D.C. SUPPLY SYSTEM.---D.C.D.B.14STATION BATTERIES AND CHARGERS

TRANSFORMERSTRANSFORMERSPROTECTIONSOVER-CURRENTEARTH-FAULTR.E.F. [RESTRICTED EARTH FAULT]FOR INTERNAL FAULTSBUCHHOLZ RELAYFOR INCIPIENT INTERNAL FAULTSDIFFERENTIAL PROTECTION

CTPRIMARYTANKSECONDARIESBASE

INSULATOR

Sheet3

ELEMENTSELEMENTS OF SUPPLY SYSTEMSr.No.IN A POWER STATION1SWITCHGEARSIN-DOOROUT-DOOREHVHTLT2TRANSFORMERSSTEP-UPSTATIONUATAUXILLARYLIGHTING3CABLESSINGLE-Ph3-Ph.ArmouredPVCPILCX.L.P.E.H.T.L.T.4TERMINATION5CIRCUIT BREAKERSO.C.B.M.O.C.B.A.B.C.B.S.F.-6V.C.B.M.C.B.6ISOLATORS7SWITCHES8BUS-BARS-INSULATORS-GANTRIESE.H.V.H.T.L.T.PORCELAINPVC9EARTHING ARRANGEMENTSOLIDRESISTANCEREACTANCE10EARTHING TRANSFORMERS11NEUTRAL GROUNDING TRANSFORMER12PANELS13D.C. SUPPLY SYSTEM.---D.C.D.B.14STATION BATTERIES AND CHARGERS

TRANSFORMERSTRANSFORMERSPROTECTIONSOVER-CURRENTEARTH-FAULTR.E.F. [RESTRICTED EARTH FAULT]FOR INTERNAL FAULTSBUCHHOLZ RELAYFOR INCIPIENT INTERNAL FAULTSDIFFERENTIAL PROTECTION

CTPRIMARYTANKSECONDARIESBASE

INSULATORINSULATOR

Sheet3