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 by a changing
magnetic fields.
Lenzs Law
The induced cu
Type of Electric Motors
Electric Motors
Alternating Current
(AC) Motors
Synchronous
Induction
Single-Phase
Three-Phase
Direct Current (DC)
Motors
Separately
Excited
Series
Self Excited
Compound
Shunt
Induction Motors
Most common motors in industry
Advan
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 rotor is increased in a specified manner, the result is
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
-Y connection
Balanced Wye-wye Connection
Line current
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
The eqvt. circuit for no load test
The eqvt. circuit
Phasor Diagram of a Transformer
Equivalent Circuit
Equivalent circuit referred to primary
Equivalent circuit phasor diagram
Approximate Equivalent Circuit
Equivalent Circuit referred to Secondary
Transformer Parameters Determination
Open circuit test
Shor
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 < m0
Paramagnetic m > m0
Ferromagnetic m > m0
Superconduct
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 impedances.
3.Compute power for steady-state ac circuits.
4.Find
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.
Constructionally, D.C. Generator and D.C. motor have no
ba
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 one
quarter of the cycle i.e. in 1/4 f second.
Therefo
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 magnetism in the poles, some e.m.f
(=OA) is gnerated e
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
If a branch is a resistive branch, use Ohms law to exp
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 regulation.
However, their application is limited to mills,