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INTRODUCTIONINTRODUCTION
TOTOELECTRICALELECTRICAL
POWERPOWER
DISTRIBUTIONDISTRIBUTION
byby
N.Ramchander,N.Ramchander,Asst Professor,Asst Professor,
EEEDEEED--BVRIT.BVRIT.
byby
N.Ramchander,N.Ramchander,Asst Professor,Asst Professor,
EEEDEEED--BVRIT.BVRIT.
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IntroductionIntroduction
HistoryHistory ofof ElectricityElectricity (General(General Concept)Concept)
CharacteristicsCharacteristics ofof PresentPresent DistributionDistribution SystemSystemDistributionDistribution SystemSystem LossesLosses
DistributionDistribution SystemSystem PlanningPlanning
FactorsFactors AffectingAffecting DistributionDistribution SystemSystem PlanningPlanning
LoadLoad ModelingModeling andand theirtheir CharacteristicsCharacteristics
ClassificationClassification ofof loadsloads andand theirtheir CharacteristicsCharacteristics
CONTENTS
CONTENTS
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INTRODUCTION
INTRODUCTION
Classical Structure of Power System
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Modern View of Power System
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Present Power Scenario in INDIA
Present Power Scenario in INDIA
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In INDIA, phenomenal expansion has taken place in the
in the area of power systems since last FIVE DECADES.
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For example generation capacity has grown at an
average rate of 12% and reached a level of more than1,57,000MW(Approx) as on today.
Similarly the development of transmission network
followed the growth, starting with a meager Tr.network,
with 132KV as the highest Tr. Voltage at the time of
Independence, today beside HVDE lines, we have
765KV as the highest Tr.voltage.
And five regional grids under operation and formation
of a National Grid inter connecting all the regional grids
in under progress (like National Highways) In our country out of total 5,87,258 villages as per 1991
survey more than 86% villages have been electrified, 13
states are 100% electrified.
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Distribution SystemDistribution SystemDistribution SystemDistribution System
The distribution system is particularly important to anelectrical utility for two reasons
1. its close proximity to the customers
2. its high cost of investment
Mainly distribution systems are two types
1. Primary Distribution (33KV/11KV)
2. Secondary Distribution (11KV/440V)
Household electricity is alternating current (AC)
Household voltages are typically 120V or 240V
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Distribution System Considerations
In determining the design of distribution systems, three
broad classifications of choices need to be considered:
1. The type of electric system: dc or ac, and if ac,
single- phase or poly phase.
2. The type of delivery system: radial, loop, or network.
Radial systems include duplicate and throwover systems.
3. The type of construction: overhead or underground.
DESIRED FEATURES
1. Safety
2. Smooth and Even Flow of Power
3. Economy
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Direct Current Systems
Alternating Current Single-Phase Systems1. Two-wire Systems2. Three-wire Systems
3. Series system
Alternating Current Two-phase Systems1. Four-wire Systems
2. Three-wire Systems
3. Five-wire Systems
Alternating Current Three-phase Systems1. Four-wire Systems
2. Three-wire Systems
Alternating Current Six-phase Systems
1. Six-wire Systems
2. Seven-wire Systems
Types of Electric Systems
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Direct Current Systems
Alternating Current Single-Phase Systems
1. Two-wire Systems
AC single-phase two wire system.
2. Three-wire Systems
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3. Series system
Alternating Current Two-phase Systems
1. Four-wire Systems
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2.Three-wire Systems
3.Five-wire Systems
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Alternating Current Three-phase Systems
1. Four-wire Systems
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2.Three-wire Systems
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Alternating Current Six-phase Systems
1. Six-wire Systems
2.Seven-wire Systems
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Types of Delivery Systems:
1. Primary distribution, which carries the load at higher
than utilization voltages from the substation (or other source)to the point where the voltage is stepped down to the value at
which the energy is utilized by the consumer.
Primary distribution systems include three basic types:
1. Radial systems, including duplicate and throwover systems 2. Loop systems, including both open and closed loops
3. Primary network systems
2. Secondary distribution, which includes that part of thesystem operating at utilization voltages, up to the meter at the
consumers premises.
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FKEE, UMP
30
Principle of Operation
Torque producing mechanismTorque producing mechanismWhen a 3 phase statorwinding is connectedconnected to a 3
phase voltage supply, 3 phase current will flowflow inin thethe
windingswindings, hence the stator is energized.A rotating flux is produced in the air gap. The flux
induces a voltage Ea in the rotor winding (like atransformer).
The induced voltage produces rotor current, if rotor
circuit is closed.The rotor current interacts with the flux , producing
torque. The rotor rotates in the direction of the rotatingflux.
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FKEE, UMP
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Direction of Rotor Rotates
Q: How to change the direction of
rotation?
A: Change the phase sequence of the power supply.
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Induction motor speed
At what speed will the IM run?
Can the IM run at the synchronous speed, why?
If rotor runs at the synchronous speed, which is the
same speed of the rotating magnetic field, then therotor will appear stationary to the rotating magnetic field
and the rotating magnetic field will not cut the rotor. So,
no induced current will flow in the rotor and no rotor
magnetic flux will be produced so no torque isgenerated and the rotor speed will fall below the
synchronous speed
When the speed falls, the rotating magnetic field will cut
the rotor windings and a torque is produced
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Induction motor speed
So, the IM will always run at a speed lowerthan
the synchronous speed
The difference between the motor speed and the
synchronous speed is called the Slip
Where nslip= slip speed
nsync= speed of the magnetic field
nm = mechanical shaft speed of the motor
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The Slip
sync m
sync
n ns
n
!
Wheres is theslip
Notice that : if the rotor runs at synchronous speed
s = 0
if the rotor is stationary
s = 1
Slip may be expressed as apercentageby multiplying the above
eq. by 100, notice that the slip is a ratio and doesnt have units
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Problem(1)
(p)A 208-V, 10hp, four pole, 60 Hz, Y-connected
induction motor has a full-load slip of 5 percent
1. What is the synchronous speed of this motor?
2. What is the rotor speed of this motor at rated load?
3. What is the rotor frequency of this motor at rated
load?
4. What is the shaft torque of this motor at rated load?
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Solution
1.
2.
3.
4.
120 120(60)1800
4
e
sync
fn rp
P! ! !
(1 )
(1 0.05) 1800 1710
m sn s n
rpm
!
! v !
0.05 60 3r ef sf Hz! ! v !
260
10 746 /41.7 .
1710 2 (1/ 60)
out out
loadmm
P P
n
hp watt hpNm
X
[T
T
! !
v
! !
v v
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Problem(2)
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Example 1
1. A 4 poles, 3J Induction Motor operates from a supplywhich frequency is 50Hz. Calculate:
a. The speed at which the magnetic field is rotating
b. The speed of the rotor when slip is 0.04
c. The frequency of the rotor when slip is 3%.
d. The frequency of the rotor at standstill
SolutionSolution
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Previous Questions from IM
1. Explain the working principle of three phase
induction motor. 2. Explain with the help of suitable diagrams how
rotating magnetic field is produced
in a three phase induction motor.
3. Explain with neat sketches the construction of asynchronous machine.
4. A 6 pole induction motor is fed by three phase 50
HZ supply and running with a full load slip of 3%. Find the full load speed ofinduction motor and also
the frequency of rotor emf.
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