DC MACHINES
The direct current (dc) machine can be used as a motor
or as a generator.
DC Machine is most often used for a motor.
The major advantages of dc machines are the easy
speed and torque regul
Magnetic Circuits
Lorentz Force
The force on a moving charge in a magnetic field is
proportional to the charge, velocity, and magnetic field
strength.
Faradays Law
Currents can be induced in wires b
Resonance
Resonant circuits (series or parallel) are useful for
constructing filters, as their transfer functions can be highly
frequency selective.
They are used in many applications such as selecti
FindEb
10 A
0.8
400
Eb
Ia
200V
Onecurrenttworeadings!
Alternating currents and voltages vary with
time and periodically change their direction
Sine Waves
Sine waves
by far the most important form o
Find the wattmeter reading. CC is the current coil. PC is the pressure coil.
The coil polarities are suitably selected to ensure a positive deflection.
a
3-PHASE
BALANCED
SUPPLY
400V
50Hz
100 + j0 O
1
Impedance
Resistor:
V=IR
The impedance is ZR = R
Inductor:
V = I jL
The impedance is ZL = jwL
Capacitor:
The impedance is ZC = 1/jC
CircuitAnalysisUsingPhasorsandImpedances
1.Replace the time desc
Complex Numbers
j = (- 1)
z
y
imaginary
axis
real
axis
x
Rectangular Coordinates
Z = x + jy
Polar Coordinates:
Z = z
Exponential Form:
Z = Z e j = ze j
x is the real part
y is the imaginary part
z
No power losses are associated with capacitors and pure inductors in
an AC circuit
In a capacitor, during one-half of a cycle energy is stored and
during the other half the energy is returned to the c
Capacitance
Capacitance occurs when two conductors
(plates) are separated by a dielectric
(insulator)
Charge on the two conductors creates an
electric field that stores energy
+
Capacitance
The vol
ThreephaseCircuits
An AC generator designed to develop a single sinusoidal voltage for each rotation
of the shaft (rotor) is referred to as a single-phase AC generator.
If the number of coils on the r
Three phase Connections
Both the three phase source and the three phase load can be
connected either Wye or DELTA.
We have 4 possible connection types.
Y-Y connection
Y- connection
- connection
1. Mesh analysis
Step 1: Name the meshes/loops in the circuit by assuming currents in the same
direction, preferably in the clockwise direction.
Step 2: Write the KVL equations for each mesh/loop.
o
o
Losses, efficiency and
characteristics of DC Machines
Open Circuit Characteristics
The O.C.C curve for self-excited generators whether shunt or series wound is
shown in above figure.Due to the residal
N1 = No. of turns in primary
N2 = No. of turns in secondary
m = Maximum flux in core in webers = Bm x A
f = Frequency of a.c. input in Hz.
The flux increases from it's zero value to maximum value m in
Direct Current Motors
Principle of Operation
When a current carrying conductor is placed in a
magnetic field, it experiences a mechanical force
whose direction is given by Flemings left hand rule.
Con
SteadyStateSinusoidalAnalysis
1.Identify the frequency, angular frequency, peak
value, rms value, and phase of a sinusoidal signal.
2.Solve steady-state ac circuits using phasors and
complex impedance
Magnetic Circuits
H
Amperes law: dl I
C
Lorentz force: F q B
v
Necessary to solve magnetic circuit
equations
Materials
Permeability m.
Vacuum has m0 = 4p x 10-7 H/m.
Materials:
Diamagnetic m < m
Phasor Diagram of a Transformer
Equivalent Circuit
Equivalent circuit referred to primary
Equivalent circuit phasor diagram
Approximate Equivalent Circuit
Equivalent Circuit referred to Secondary
Tran
Regulation and Efficiency
Vno-load Vload
percent regulation
100%
Vload
Pload
Ploss
100%
power efficiency
100% 1
Pin
Pin
Normally the OC test is done in LV side.
Why?
SC test is done in HV side
Energy Storage Elements
Capacitors store energy in an electric field.
Inductors store energy in a magnetic field.
Capacitors and inductors are passive
elements:
Can store energy supplied by circuit
Ca
Example-1
The switch in the circuit of figure 1 has been closed for a long time
and it is opened at t = 0. Calculate:
The initial value of iL and, the final value of . iL
The time constant for t 0.
An
Review of Last Lecture
Power at Receiving End
At Receiving End
Approximate formulae
Short line
Large X/R ratio
Power-angle characteristics
Circle diagram
At Sending End
Usage of the formulae while sol
Review of Last Lecture
Design parameters and materials of power system Components.
Mechanical design of transmission line
Parameters affecting
Various types of towers
Sag, Span, and Ground clearanc
Voltage Distribution Along The Insulator String
Methods of Equalizing the Potential
Methods to improve string efficiency
Selection of m
Grading of units
Static shielding or guard rings
Semiconducting
Review of Last Class
Compensation in Power System
Series compensation
Shunt compensation
Line Parameters
29/05/17 06:20
Line Parameters
Electrical Parameters
Resistance
Inductance
Capacitance
Cond
Line Parameters
Review of Last Lecture
Resistance
Type of conductors (ACSR, AAC, AAAC, ACAR, Expanded
ACSR)
It depend on
Temperature
Dimensions
Frequency
Inductance
Internal inductance
External induct
Review of Last Lecture
Inductance of three-phase line
Symmetrical spacing
Unsymmetrical spacing without transposition
Unsymmetrical spacing with transposition
Inductance of Composite Conductor
Inducta
Review of Last Lecture
Lumped and Distributed Parameters
ABCD parameters of the transmission line
Transmission line models
Short transmission line
Medium transmission line
Long transmission line
29/05
Review of Last Lecture
Inductance of Composite Conductor
Bundled conductors
Inductance of double circuit line
Bundled Conductors
http:/en.wikipedia.org/
Bundled Conductors
Corona loss
Surface voltage