SWYD Fundamental

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24 May 2012 PMI Revision 00 1


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Presentation outline

Understanding basics of switchyard Switchyard equipments and schemes

Components of switchyard:

Breakers, Isolators, Earth switch, CT, CVT, Wavetrap etc

Brief Description of modes of transmission

Conclusion


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Power

plantTransformer Transformer

Local

distribution

net work

Transmission

line

Switch

Yards

Sub

Station/

Switchyard

Power Transmission system


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What is a Switchyard ?

It is a switching station which has the following credits :(i) Main link between Generating plant and Transmission

system,

which has a large influence on the security of the

supply.

(ii) Step-up and/or Step-down the voltage levels

depending upon the Network Node.

(iii) Switching ON/OFF Reactive Power Control devices,

which has effect on Quality of power.


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SWITCHYARD EQUIPMENTS

Equipments commonly found in switchyard :

1. Lightening arrestor

2. Current transformer

3. Voltage transformer

4. Power transformers / I.C.T.5. Bus bar and clamp fittings

6. Support structure

7. Isolators

8. Circuit Breaker9. Wave traps

10. Earthing switch


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Functions of various equipment :

* Transformers :

- Transforms the voltage levels from higher to lower level

or vice versa, keeping the power constant.

* Circuit breakers :

- Makes or automatically breaks the electrical circuits underLoaded condition.

* Isolators :- Opens or closes the electrical circuits under No-load

conditions.

* Instrument transformers :

- For stepping-down the electrical parameter (Voltage or

Current) to a lower and safe value for Metering andProtection logics.

* Earth switch :

- Used to connect the charged body to ground to dischargethe trapped charge to have a safe maintenance zone.


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* Lightning arrestors :

- Safe guards the equipment by discharging the high

currents due to Lightning.* Overhead earth wire :

- Protects the O/H transmission line from Lightningstrokes.

* Bus bar :

- Conductors to which a number of circuits are connected.* Wave Traps/Line traps :

- Used in PLCC circuits for Communication andtelemetering.

* Reactive Power control devices :

- Controls the reactive power imbalance in the grid byswitching ON/OFF the Shunt Reactors, Shunt Capacitors etc.,

* Current Limiting Reactors :

- Limits the Short circuit currents in case of faulty

conditions.


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Switchyard Single line DiagramTransfer Bus 400 KV

Main Bus II

Main Bus I

CB CB

CB

GT

20.5/400KV

Gen Bay Feeder Bay

Bus

Isolator

Transfer BusBay


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Bus Switching Schemes

Bus Bar Schemes

* Single Sectionalized bus

* Main & Transfer bus

* Sectionalized Main bus with Transfer bus

* Sectionalized Double Main & Transfer bus

Breaker Schemes

* Ring bus* One and Half breaker

* Double bus Double breaker


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Factors effecting the selection of

Switching Scheme

* Operational Flexibility

* Simplicity of Protection arrangements

* Ability to limit the Short Circuit levels

* Maintenance

* Ease of extension* Total land area

* Cost


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Single Sectionalized

Bus-bar system

I/C Feeders

O/G Feeders

Bus-bar

CB

Isolators


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Main & Transfer Bus-bar system

I/C Feeders

Transfer Bus

CB

Isolators

Main Bus

Bus Coupler


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Ring Bus system :

I/C Supply

O/G feeder

Bus

CB

O d H lf B k h


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One and Half Breaker scheme :

Tie CB

Main 1

Main 2

Feeder 1Feeder 2


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A circuit breaker is defined as a mechanical device capable of making,carrying and breaking currents under normal circuit conditions and alsomaking, carrying for a specific time and breaking currents under specificabnormal circuit conditions such as those of short circuit.

The circuit breaker serves two basic purposes

Switching during normal operating conditions for the purpose of operation andmaintenance.

Switching during abnormal conditions such as short circuit and interrupting fault currents.


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Based on Voltage

Low- less than 1kV

Medium - 1kV to 52kV High/Extra High- 66kV to 765kV

Ultra High -above 765kV

Based on location Indoor

Outdoor

Based on External design

dead tank

Live tank Based on Interrupting media

Air break

Air blast Bulk oil

Minimum oil

SF6 gas insulated

vacuum

Ai Bl t CB


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Air Blast CB :


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24 May 2012 22

ABCB- Principle of arc quenching


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FEATURES OF ISOLATORS

OPERATES UNDER NO LOAD CONDITION

INTERLOCKED WITH BREAKERS AND EARTHSWITCHES

SHOULD WITHSTAND EXTREME WIND PRESSURES

MOTOR DRIVEN AND HAND DRIVEN

LOCAL AS WELL AS REMOTE OPERATION POSSIBLE

ISOLATES SECTIONS FOR MAINTENANCE

USED TO SELECT BUS BARS


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FEATURES OF EARTH SWITCHES

USED TO GROUND SECTIONS REQUIRED FOR MAINTENANCE

GROUND INDUCTION VOLTAGES

INTERLOCKED WITH BREAKERS AND ISOLATORS

CAN OPERATE FROM LOCAL ONLY

MOTOR DRIVEN AS WELL AS HAND DRIVEN

SAFETY DEVICE


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Current transformers

Purpose :

- To step-down the high magnitude of current to a safevalue to incorporate Measuring and Protection logics

Current transformers are used for the instrumentation,protection or metering of power systems.


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Voltage transformers

Purpose :- To step-down the high magnitude of voltage to a safe

value to incorporate Measuring and Protection logics.

Voltage transformers serve a number of functions in apower system. They are required for the operation of many

types of instrumentation and relay protective systems.They measure voltage and in conjunction with CT , theymeasure power. They feed synchronizing equipment. Theycan be used as coupling capacitors in power line carriernetwork.


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INDUCED

ALTERNATING E.M.F

PRIMARY

WINDING

SECONDARYWINDING

IRONCORE

AC EXCITATIONSOURCE

FLUX LINKING

BOTH COILS


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Primary voltage is applied to a series of

capacitors group. The voltage across one of thecapacitor is taken to aux PT. The secondary ofthe aux PT is taken for measurement andprotection.

SECONDARY VOLTAGES(110 VOLTS AC) FORMETERS AND ENERGY METERS

VOLTAGES FOR PROTECTIVE RELAYS

VOLTAGES FOR SYNCHRONIZING

DISTURBANCE RECORDERS AND EVENT LOGS OVERFLUX RELAYS

PLCC

CVT internals :


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CVT internals :

Insulators which

acts as Capacitors

Intermediate PT

P S

Bus


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Lightning Arrestors


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Purpose :

- To discharge the high voltage surges in the power

system due to lightning to the ground.

Apparatus to be protected :* Overhead linesEarth/Ground wires (PA=30 deg)

* HV equipmentLAs

* Substation...Lightning Masts, Earth wires

T pes :


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Types :

Rod gap LA :

Insulator

Equipment

body

Rod gap

* Gap length is suchthat the break-downoccurs at 80% of thespark voltage

* After the surge, thearc in the gap ismaintained by the

normal supplyvoltage. So, only usedas a back-up.


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Isolator


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Earth Switches


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CB

Earth S/W

IsolatorIsolator LoadSource


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Wave Trap

Transmission Line


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WaveTrap

WaveTrap

Transmission Line

* Wave trap is used for Protection of the transmission line and

communication between the Substations.

* VHF signal is transmitted from one end to the another through thesame power line.

* Sends inter-trip signal to the other end CBs so that fault can be isolated

at the earliest time.

To control room

of S/S-2To control roomof S/S-1

S/S-1 S/S-2


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Power line communication (PLC), also known aspower line carrier communication, power linetelecom (PLT), or power line networking (PLN),is a system for carrying data on a conductor also

used for electric power transmission. Broadbandover Power Lines (BPL) uses PLC by sending andreceiving radio signals over power lines to provideaccess to the Internet.

All power line communications systems operate byimpressing a modulated carrier signal on the wiringsystem.

BASIC ARRANGEMENT OF WAVE TRAP AND
http://en.wikipedia.org/wiki/Electric_power_transmissionhttp://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/Communications_systemhttp://en.wikipedia.org/wiki/Communications_systemhttp://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/Electric_power_transmission


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C=1/2FC

30KHZ TO 500KHZ

IMPEDENCE 75 OHMS

WAVE TRAP

2FL

LMU

PLCC

POWER FREQ -50 KHZ

STATION BUS

LINE

BASIC ARRANGEMENT OF WAVE TRAP AND

COUPLING CAPACITOR

>500KHZ NOISE PICKUP


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Modes

ofTransmission

AC transmission


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AC transmission

Advantages- Power can be generated at high voltages.

- Step-up/Step-down is possible.

Disadvantages- Requires more copper.

- Due to Skin effect, the effective resistance is increased

- Continuous loss of power due to charging current even

when the line is open.

- Requirement of Transposition of conductors.

DC transmission


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DC transmissionAdvantages- Low cost due to less copper requirement

- No Stability and synchronising problems.- Asynchronous lines (Interregional ties)

- No increase in Fault level if interconnected.

- Less Corona and RI.

- Better Voltage regulation due to absence of Inductance.

- Requires less insulation as the potential stress is less

Disadvantages- Higher generation is not possible due to commutation

- Step-up/Step-down is not possible.

- Limitations in HVDC CBs, Switches etc.

HVDC transmission Vs EHV AC transmission


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HVDC transmission Vs EHV AC transmission

km

Cost

100 300 1100500 700 900

Break Even distance

HVDC Preferred

EHVAC Preferred

Cost of Substation


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Power line communication (PLC), also known as power line carrier, mains communication, powerline telecom (PLT), or power line networking (PLN), is a system for carrying data on a conductor alsoused for electric power transmission. Broadband over Power Lines (BPL) uses PLC by sending andreceiving radio signals over power lines to provide access to the Internet.

Electrical power is transmitted over high voltage transmission lines, distributed over medium voltage,and used inside buildings at lower voltages. Powerline communications can be applied at each stage.Most PLC technologies limit themselves to one set of wires (for example, premises wiring), but somecan cross between two levels (for example, both the distribution network and premises wiring).

All power line communications systems operate by impressing a modulated carrier signal on the wiringsystem. Different types of powerline communications use different frequency bands, depending on thesignal transmission characteristics of the power wiring used. Since the power wiring system wasoriginally intended for transmission of AC power, the power wire circuits have only a limited ability tocarry higher frequencies. The propagation problem is a limiting factor for each type of power linecommunications.

Data rates over a power line communication system vary widely. Low-frequency (about 100-200 kHz)carriers impressed on high-voltage transmission lines may carry one or two analog voice circuits, ortelemetry and control circuits with an equivalent data rate of a few hundred bits per second; however,

these circuits may be many miles (kilometres) long. Higher data rates generally imply shorter ranges; alocal area network operating at millions of bits per second may only cover one floor of an office building,but eliminates installation of dedicated network cabling.
http://en.wikipedia.org/wiki/Electric_power_transmissionhttp://en.wikipedia.org/wiki/Electric_power_transmissionhttp://en.wikipedia.org/wiki/Electric_power_transmissionhttp://en.wikipedia.org/wiki/Electric_power_transmissionhttp://en.wikipedia.org/wiki/Electric_power_transmissionhttp://en.wikipedia.org/wiki/Electric_power_transmissionhttp://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/Communications_systemhttp://en.wikipedia.org/wiki/AC_powerhttp://en.wikipedia.org/wiki/Local_area_networkhttp://en.wikipedia.org/wiki/Local_area_networkhttp://en.wikipedia.org/wiki/AC_powerhttp://en.wikipedia.org/wiki/Communications_systemhttp://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/Electric_power_transmission

SWYD Fundamental

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