Transcript Mini Project Switchyardx

ABSTRACT:
• Electricity is a form a energy and is playing vital role in the world.
Electricity has become a part of human life. Electricity is developed at
one place and transmitted to other places, where the demand exists and
resources are not available. So as to achieve balanced regional
development of the country.
• The main aim of the project is
1.To study the operation of switchyard are to facilitate switching
operations in transmitting electrical energy from generating station to
substation.
2.To acknowledge the protection methods facilitated by the
switchyard.
3.And to know switchyard equipment and their operation in detail.
• The main functions of switchyard are to facilitate switching operations,
and to protect the generating station from the faults. Switching
operations includes stepping up the generated voltage levels to value
which is equal to the substation voltage, and monitoring electrical
parameters continuously.
INTRODUCTION TO PROTECTION:
 Protection is the electrical equipment from faulty section the main
objection of protection is to quickly isolate a fault from the ends
Faults can occur on any power system components like generator,
transformer, and motors etc. faults are generally falling in to two
categories short circuit faults. Open circuit faults, short circuit faults
are resulting in very abnormal high current if they followed to persist
even for short period of time, it can lead to extensive damage to
equipment.
SWITCHYARDLAYOUT:
After the bus bar arrangement has been decided upon and
key diagram are prepare to show the actual Position of the each
equipment
First prepared on the land plan, space is marked for civil and electrical
workers and also The roads and path for movement of men and material On the land
plan marked for electrical workers detailed layout which indicates the placing of
various equipments In the switchyard is prepared.
Switch yard is a place where the entire primary protecting
equipment of the power system is arranged in a systematic manner
from generator transformer to feeders by connecting the
transmission lines.
The switch yard mainly works on the purpose of
stepping the grid voltage down to a certain value. The
switchyard under study works on 132/11kv i.e., the input
of the transformers 132kv and It steps down to 11kv.the
substation receives the 132kv from 220kv substation. The
received voltage is stepped down to the required value by
using a three phase auto transformer .the auto
transformer is economically efficient compared the
ordinary there phase transformer. To step down the 132kv
voltage to 11kv, auto transformer having 15mva capacity
is employed.
TRANSFORMER:
Ratings of the Transformers:
The ratings of power transformers
that are used in A.P system
132/11 KV 15 MVA Transformers
11/0.44 KV 2MVA Transformers.
Most of the power transformers of
132/11 KV and above are of stardelta vector grouping with the
neutral solidly earthed. There are a
few transformers with delta-star
(delta on HV side). The 33/11 KV
and 11KV/415v transformers are of
delta-star (delta on HV side).
GENERATOR TRANSFORMER:
The generator takes power that is fed to it by the alternator. Here the voltage at
a lower level is transformed into a higher level as the higher level transmission
is very economical. A transformer is a static device by means of which of which
electric power in one circuit is transformed into electric power of the same
frequency in another circuit. it can rise or lower the voltage in a circuit, but with
a corresponding increase in current basically transformer will work on mutual
induction principle between two circuits linked by a common magnetic flux.
It is a star-delta power transformer the transformer is connected to the bus by a
thin laminated sheet conductors there by constant losses present in the bus can
be eliminated to a maximum extent. Thus the generator transformer connects the
electromechanical alternator to the static bus bar. The transformer protection is
carried out by the buchholz relay. Differential relay, distance relay, and lightning
arrester, thus the important part of the switchyard.
AUXILIARY TRANSFORMER:
This is the one used for the
maintaining the power
supply to the auxiliaries and
accessories present in the
power plant when the entire
generating unit of the
station is ruined. The
transformer takes power
from the grid to it is
connected and the power is
supplied. It is star delta
connected.
LIGHTNING ARRESTER:
Lightning arrester is also known as
surge diverter or surge arrester. They
are connected between the line and
ground at the substation and always
parallel with the equipment to be
protected and perform their function by
providing a low impedance path surge
currents, the surge arresters protective
level is less, than surge voltage
withstanding capacity of the insulation
equipment being protected.
The lightening arresters protective level is that the voltage appearing across the
terminals of the arrester at spark over or during the flow of current through the
arrester after spark gap over. The purpose of lightening arrester is to divert or
discharge the surge to the ground.
CURRENT TRANSFORMER:
 The current transformer is basically a step up
transformer.teh primary winding of the current
transformer is wound in series with the point
where the current is to be sensed small portion
of the current flows in the secondary depending
upon the turn`s ratio of the transformer.
To reduce the burden on the current
transformers banks of capacitors are connected
in parallel so that the voltage burden is
eliminated thus the efficient operation of the
system can be obtained.
Current transformers are the instrumentation transformers which are
used for the metering and protection purposes. The CT ratio is about
600/300:5 through the CT the high magnitude current is stepped down to
a corresponding lower current. This current is used for the metering
purpose.
CAPACITOR VOLTAGE TRANSFORMER (CVT):
•Voltage transformers are used for measurement
and protection.VT`S are necessary for voltage,
Directional distances protection. the primary of
VT`S is connected to power circuit between phase
and ground. The volt ampere rating of VT is smaller
as compared with that potential transformer.
•CVT`S are used for line voltmeters,synchroscope,protective relays,
traffic meter etc. The performance of CVT is inferior to that
electromagnetic voltage transformer. Its performance is affected by the
supply frequency, switching transients, magnitude of burden connected
etc. T he CVT is more economical than an electromagnetic VT,when the
system voltage normally increases above 66kv.the carrier current
equipment can be connected to the capacitor of the CVT`S thereby there
is no need of separate coupling capacitors.
BUS BAR:
 Bus
Bar means conductors to which a number of circuits are
connected. The power that is trapped from the station alternator by
the station transformer will be fed to the bus bars all the bus bars
must be cable of handling very high power ratings.
 Their mechanical strength is such that they are capable of
carrying thousands of amperes of current though them.
 Aluminum is used from the manufacturing bus bars. The bus bars
should have low resistance, higher softening temperature and good
mechanical properties the currents having an angle of 500 amps the
size of the conductor should be around 190mm.
 Generally a pair of buses, main bus and the stand by bus or
reverse bus connected with the help of bus coupler.
ISOLATORS:
o Isolators are used for making breaking the
circuits. Isolators operate under no load
condition only. It does not have any speccific
current breaking capacity or current making
isolator is not used even for breaking load
currents.
oCurrent is passed through the primary winding of standard C.T and C.T
under test. The ratio of the C.T can be determined by comparing the
currents in ammeters A1 and A2.
1) Isolators are used in addition to CB`s and are used while closing a
circuit. The isolator is closed first the CB.
2) Isolators are necessary on supply side of CB`s in order to ensure
isolation of the CB from live parts for the purpose of maintenance.
Automatic switching of isolators is preferred.
CIRCUIT BREAKER:
The circuit breaker we use in this 132/11kv
switchyard is sf6 circuit breaker .for high voltages
such as 132kv and above voltages, we use this
circuit breaker.
 The sf6 circuit breaker will operate mainly on the
principle of PUFFER principle in extra high voltage
operation.
As the puffer cylinder moves downwards for the
opening stroke, the pressure ratio p1/p2 raises.

It depends upon the throat diameter of the nozzle and speed of
puffer cylinder the pressure ratio increases to about S times during
opening condition. The compressed gas is released through the
convergent-divergent nozzle. The arc is quenched at a current zero,
for higher interrupting ability, the flow pattern is optimized.
PROPERTIES OF SF6 CIRCUIT BREAKER:
High dielectric strength.
Thermal and chemical stability.
Non- inflammability.
Pure sf6 gas is inter and thermally stable.
Sf6 gas is an electro negative gas.
When arcing takes place through the gas some y-products are
produced due to break down of the gas .these by products are hazard to
the health of the maintenance of the personal and therefore proper fare
should be taken.
PROTECTIVE RELAYS:
Protective relays are the devices that detect abnormal conditions in
electrical circuits by constantly measuring the electrical quantities,
which are different normal and fault conditions.
The Functional Requirements of the Relay:
Reliability: The most important requisite of protective relay is
reliability since they supervise the circuit for long time before a fault
occurs, if a fault then occurs, the relays must respond instantly and
correctly.
Sensitivity: The relaying equipments must be sufficiently sensitive
so that is operates reliably when required under the actual condition
that produces least operation tendency.
Speed: the relay must operates at thee required speed it should
neither be slow which may result in damage to equipment nor should
it be fast which may result in undesired operation.
CONCLUSION:
With advancement of power systems, line and other equipments
operates at high voltage and carry large current when a short circuit
occurs on the system heavy current flowing through the equipment may
cause damage.

 Switchyard is a place where the entire primary protecting equipment
of the power system is arranged in a systematic manner from generator
transformer to feeders by connecting the transmission lines.
 Switch gear covers wide range of equipment concerned with switching
& interrupting current under normal & abnormal conditions it includes
CT`s, CB`s, relays and other equipment.
Switchyard protects the generating station from the faults. It suppress
the faults by making them not to reach the generating unit. Thus, a
switchyard plays a vital role in the protection