Download - SWYD Fundamental
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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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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
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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.
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