SWITCHYARD & ITS
SWITCHYARD & ITS
EQUIPMENTS & HVDC
EQUIPMENTS & HVDC
BY-ELITE GROUPAmit joshi UPES Dehradun
INTRODUCTION
INTRODUCTION
The switchyard is a junctionconnecting the
Transmission &Distribution system to the power plant.
Switchyard consists of the air insulated aluminium bus
type and of high voltage SF6 –insulated dead tank
circuit breakers arranged in a ring bus
configuration.
Each circuit breaker are equipped with a no-load
breaker, air insulated, disconnect switch on each side.
An isolating disconnect switch are installed in each
generator transformer connection to the bus.
In switchyard, a power transformer is used to step
up or step down the voltage.
Current and Voltage transformers are located
at points within the switchyard to provide for metering and relaying.
Control, protection and monitoring for the
switchyard will be located in the switchyard relay room of the electrical building.
All protection and circuit breaker control will be
powered from the station battery-backed 220V DC system.
A grounding grid are provided to control step
and touch potentials .
Lightning protection are provided by shield wires
for any overhead lines- Lightning arrestors.
Interface with SCADAsystem are provided. The
communication between the facility switchyard and the control building is facilitated.
Revenue metering are provided on the outgoing
lines, recording net power to or from the switchyard.
OVERVIEW
OVERVIEW
11 kV Bus –Bar Lightning Arrestor Isolator 11 kV Circuit Breaker Current Transformer Power Transformer 11 kV/ 400 kV 1)Bus Bar 2)Insulators 3)Lightening Arrestor 4)Earthing System 5)Control Panel 6)Transformer 7)Circuit Breaker 8)Arching horns 9)SCADA Nodes 10)ROW 11) 12) 13) 14) 15) 16)
Equipments used in
Equipments used in
Switchyard
Switchyard
Used to interconnect the loads and sources
of electrical power
It connects incoming and outgoing
transmission lines
Also connect generator and main
transformer in power plant
Material used: Copper or Aluminium
Size of bus bar to determine max. amount of
BUS BAR
Rigid bus-bars:used for low,md. And high
voltages
Strain bus bars:used for high voltages
Insulated phase bus bars:used for mdium
voltages
Sulphur hexaflouride bus bar:used for
medium and high voltage system
TYPES OF BUS BAR
Supported the poles and towers in such a
way that currents from conductors do not flow to earth through these supports
Insulator
Pin type
Suspension type:design for 11 kv
Types of Insulators
Used on power system to protect the system
from damaging effect of lightning
Lightning Arrestor
•It Does not Absorb the Lightning
•It Does not Stop the Lightning
•It Does Divert the Lightning to Ground
•It Does Clamp (limit) the Voltage produced by
the Lightning
•It Only protects equipment electrically in
parallel with it.
What exactly does a Lightning
What exactly does a Lightning
Arrestor Do?
Control panel mostly consists of meters and
protective relays. The meters include
ammeter, voltmeter, wattmeter, energy meter etc. The relays include fuse failure relay, auto reclose relay, check synchronizing relay,
auxiliary relay and transformer relays like
OLTC out of step, winding temperature alarm, oil temperature alarm. The trip indicators
included are CB SF6 gas density low, CB Air pressure low, VT fuse fail alarm, CB pole disc trip, carrier signal received, back up
protection, auto reclose lock out, control DC supply fails, distance protection inoperative, carrier out of service, distance protection trip etc.
Control Panel
Earthing is to be provided in substations
due to following
reasons:- To provide a means to carry electric current
into the earth under normal and fault conditions , without exceeding any
operating and equipment limits or
adversely affecting continuity of service .
To assure that a person in the vicinity of
grounded facilities is not exposed to the danger of electric shock.
Earthing Systems
Circuit Breaker
Circuit Breaker
A circuit breaker is an
automatically-operated electrical switch designed to
protect an electrical circuit from damage caused by overload or short circuit. Its function is to interrupt continuity, to
immediately discontinue electrical flow.
In switchyard High Capacity Circuit Breakers
are used.
In 400/220KV substation Power Grid there is
SF6 circuit breaker system.
SulphurHexafluoride Circuit
SulphurHexafluoride Circuit
Breakers
Breakers
The SF6 is an electro-negative gas and has a
strong tendency to absorb free electrons.
The contacts of the breaker are opened in a
high pressure flow of SF6 gas and an arc is struck between them.
The conducting free electrons in the arc are
rapidly captured by the gas to form relatively immobile negative ions.
This loss of conducting electrons in the arc
quickly builds up enough insulation strength to extinguish the arc.
Advantages of using SF6
Advantages of using SF6
Circuit breaker
Circuit breaker
Very short arcing time.
Can interrupt much larger currents.
Noiseless operation due to its closed gas
circuit.
No moisture problem.
No risk of fire since SF6 gas is
non-inflammable
Low maintenance cost.
No carbon deposits so that tracking
Disadvantages of using SF6
Disadvantages of using SF6
SF6 breakers are costly due to high cost of
SF6.
SF6 gas has to be reconditioned after every
operation of the breaker, so additional equipments are required.
Instrument Transformers
Instrument Transformers
Current transformers, together with
potential transformers (PT), are known
as instrument transformers.
It controls excess and low current
It also helps in steping up or down the
potential.
Since the measuring instruments and
protective devices are designed for low voltages (generally 110V) and currents (about 5A). Therefore, they will not work properly if mounted directly on power
Current Transformer
Current Transformer
The current transformer is used to measure
the very high current passing through the bus.
It step downs the current and
measurements are taken in the control room the ratings of CT is based on the ampere
These CTs are connected to the control room
Voltage Transformer
Voltage Transformer
There is a step down transformer, which
step down the high voltage to a value that can be measured using the measuring
instruments in the control room.
This has an additional core for the carrier
communication.
Arcing Horns
Arcing Horns
Arcing horns are for the protection of the
insulators in case of high voltage, which it cannot stand.
They are two metal rods fitted at the top
most and bottommost parts of the insulator.
During high voltage insulators can't resist
this and cracks may be developed. In order to avoid these arcing horns are provided. They conduct the high voltage to the
ground and protect the insulator.
SCADA nodes
SCADA nodes
SCADA stands for supervisory control and
data acquisition
It basically stores data for current and give
alarm to Power Line Communication
Carrier(PLCC) which further is transmitted to National Load Despatch Centre(NLDC)
ROW(Right of Way)
ROW(Right of Way)
It is the path to access devices of a
switchyard
Physical path IT equipments
HVDC
Aim of Electric power
Aim of Electric power
supply
supply
Supply of required amount of power to all
consumers over the entire geographical area at all the time continuously.
Supply energy at lowest cost.
Maximum possible coverage of geographical
area.
Maximum Security of supply and minimum
fault duration.
Supply of power within the targeted limit of
frequency. (in case of AC supply)
Why DC over AC?
Why DC over AC?
Power Transfer through an AC transmission
link is given by:
Pac= ( |V1|.|V2|.sinδ)/X
Reactive power comes in play.
Power Transfer through the AC line can’t be
controlled easily, quickly and accurately.
Losses are high as the reactive power is
high.
Voltage drop will be more.
HVDC
HVDC
High-voltage, direct current (HVDC)
:bulk transmission of electrical power.
For long-distance distribution, HVDC
systems are less expensive and suffer lower electrical losses.
For shorter distances, the higher cost of DC
conversion equipment compared to an AC system may be warranted where other
AC DC
Ac
Synchronization of stations, as per
frequency as well as voltage.
Interconnecting two same frequency line. Asynchronous DC linkage between the AC
Economic Consideration
Economic Consideration
+Ve for HVDC:
Lesser conductors are used as compare to
AC.
Lesser losses so better quality. Long distances covered.
Simpler design of towers. HV so more security.
Economic Consideration
Economic Consideration
-Ve for HVDC:
Not for Short distance. Higher Initial cost.
Economic Consideration
Economic Consideration
(for overhead lines)
HVDC
HVDC
AC DC AC
Equipments used in Converter stations:
1.Shunt Capacitors.
2.Converters.(silicon controlled rectifiers, Thyristors)
Transmission Models
Transmission Models
Monopolar: The line has one energized
conductor with the return path through the earth.
Bipolar: A bipolar transmission gives two
circuits which are almost independent of each other. Bipolar mode has one conductor at a positive potential with respect to ground and a second conductor operating at negative potential of the same magnitude.
Back-to-back station is a plant in which both
static inverters and rectifiers are in the same area, usually in the same building. The length of the direct current line is kept as short as possible.
coupling of electricity mains of different
frequency.
coupling two networks of the same nominal
Advantages Of HVDC
Advantages Of HVDC
Economical for long distance bulk
transmission.
Greater power per conductor and simpler
line construction.
Ground return is possible.
No charging current and skin effect.
Less voltage regulation problem because
Advantages cont.
Advantages cont.
Easy reversibility and controllability of power
at DC link.
DC line is an asynchronous or flexible link it
can interconnect two rigid systems operating at different frequencies.
For a single DC line b/w 2 converter stations,
circuit breakers are unnecessary since control of the converters can be used to block current flow during faulty conditions.
Disadvantages
Disadvantages
Installation of complicated converters and DC
switchgear is expensive.
Converters require considerable reactive
power.
Harmonics are generated which requires
filters.
Converters do not have overload capacity.
Disadvantages Cont.
Disadvantages Cont.
There is nothing like DC transformer which
can change the voltage level in a simple way.
Reactive power required by the load is to be
supplied locally as no reactive power can be transmitted over a DC link.
Contamination of the insulators in polluted
areas or along the sea coast. Pollution affects DC more then AC.
Present Scenario
Present Scenario
India has been a pioneer developer of HVDC
since 1990 when the 1000 MW Rihand-Dadri line was commissioned in UP.
Since then many 500 MW lines have come
up.
The 2000 MW Talchar-Kolar link is the
Future Trends
Future Trends
R & D work is under way to provide a better
understanding of the performance of HVDC links to achieve more efficient and
economical designs of the thyristor valves and related equipments .
Controllers would be more & more
microprocessor based which can be
modified or upgraded without requiring hardware changes.
Future Trends
Future Trends
In the near future, it is expected that fibre
optics system would be used to generate firing signals & direct light fired thyristors would be employed for HVDC converters.
THANK YOU !!
