Download Module 1_Basic Electrical Concepts

USE OF ICT IN EDUCATION FOR ONLINE AND BLENDED LEARNING-IIT BOMBAY
BIRLA INSTITUTE OF TECHNOLOGY
MESRA, RANCHI
ASSIGNMENT( MODULE BASIC ELECRICAL)
Submitted by:
Dr. Deepak Kumar(Group Leader)
Dr. Vikash Kumar Gupta
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INTRODUCTION & HISTORY
•
Electrical engineering is the study of generation, transmission and
distribution of power.
• Earlier it included electronic engineering, which has obtained an identity of
its own only in the recent years. In most cases, both of these disciplines are
offered through a combined course of study.
•
Electrical engineering gained recognition in the 19th century . Many
contributed in its growth, notable among them are Nikola Tesla , Thomas
Alva Edison etc.
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Applications of Electrical
Engineering
• The primary objective of electrical engineering is to supply electricity
safely to consumers. This includes both, the design of electrical appliances
as well as suitable wiring system.
• Industrial automation and automobile control system design are also a part
of electrical engineering.
• In Signal processing, principles of electrical engineering is used to modify
signals to obtain the required output .
• Principles of electrical engineering are also used in Telecommunication
engineering, which deals with the transmission of information through
different channels to enable communication.
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Resistance
• The electrical resistance of an electrical element is the opposition to the
passage of an electric current through that element.
• The SI unit of electrical resistance is the ohm (Ω).
• The resistance (R) of an object is defined as the ratio of voltage across it to
current through it, while the conductance (G) is the inverse.
i.e. R=V/I, G=I/V
• A resistor limits current flow.
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Inductance
• An electric current I flowing around a circuit produces a magnetic field and
hence a magnetic flux Φ through the circuit.
• The ratio of the magnetic flux to the current is called the inductance of the
circuit. Inductance is measured in Henry (H)
L = Ø/I
1H = 1Wb/A
• An inductor stores energy in a magnetic field. When the magnetic field
collapses in the coil, it liberates its energy.
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Capacitor
• Capacitance is the ability of a body to store an electrical charge.
• If the charges on the plates are +q and −q, and V gives the voltage between
the plates, then the capacitance is given by
C= q / V
• Capacitance is measured in farads, symbol F. However 1F is very large, so
prefixes (multipliers) are used to show the smaller values.
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Basic Elements & Introductory
Concepts
• Electrical Network is a combination of various electric elements (Resistor,
Inductor, Capacitor, Voltage source, Current source) connected in any
manner what so ever.
• Passive Elements are the elements which receives energy (or absorbs
energy) and then either converts it into heat (R) or stored it in an electric
(C) or magnetic (L ) field.
• Active Elements are the elements that supply energy to the circuit is called
active element. Examples: voltage and current sources, generators, and
electronic devices that require power supplies.
• Bilateral Elements conducts current in both directions with same
magnitude . Example: Resistors, Inductors, Capacitors.
• Unilateral Element allow conduction of current in one direction. Example:
Diode, Transistor etc.
• The behaviour of output signal on the application of input signal to a
system is called response of the system.
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Resistor , Diode
Fig1.1 Ex. Of Bilateral & Unilateral Element
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Linear and Nonlinear Circuits
• Linear Circuit: A linear circuit is one whose parameters do not change with
voltage or current. More specifically, a linear system is one that satisfies (i)
homogeneity property (ii) additive property (See Fig. 1.2 )
• Non-Linear Circuit: A non-linear system is that whose parameters change
with voltage or current. Non-linear circuit does not obey the homogeneity
and additive properties.
• A circuit is linear if and only if its input and output can be related by a
straight line passing through the origin Otherwise, it is a nonlinear
system. (See Fig. 1.2)
• Potential Energy Difference: The voltage or potential energy difference
between two points in an electric circuit is the amount of energy required
to move a unit charge between the two points.
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V-I Characteristics of Linear and
Non-Linear Elements
Fig1.2 V-I Characteristics
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Basic Definitions
• Node- A node is a point where two or more components are connected
together. This point is usually marked with dark circle or dot. Generally, a
point, or a node in an circuit specifies a certain voltage level with respect
to a reference point or node.
• Branch- A branch is a conducting path between two nodes in a circuit
containing the electric elements. These elements could be sources,
resistances, or other elements.
• Loop- A loop is any closed path in an electric circuit i.e., a closed path or
loop in a circuit is a contiguous sequence of branches which starting and
end points for tracing the path are, in effect, the same node and touches
no other node more than once.
• Mesh- A mesh is a special case of loop that does not have any other loops
within it or in its interior.
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Kirchhoff’s Laws
•
Kirchhoff's laws are analytical tools to obtain the currents and voltages in
both, direct-current and alternating current system.
• Kirchhoff’s Current Law (KCL): KCL states that at any node (junction)
in a circuit the algebraic sum of currents entering and leaving a node at any
instant of time must be equal to zero. Here currents entering and currents
leaving the node must be assigned opposite algebraic signs .
• Kirchhoff’s Voltage Law (KVL): It states that in a closed circuit, the
algebraic sum of all source voltages must be equal to the algebraic sum of
all the voltage drops.
• Voltage drop is encountered when current flows in an element (resistance
or load) from the higher-potential terminal toward the lower potential
terminal. Voltage rise is encountered when current flows in an element
(voltage source) from lower potential terminal (or negative terminal of
voltage source) toward the higher potential terminal (or positive terminal of
voltage source). Kirchhoff’s voltage law is explained with the help of fig
1.4(b) .
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Illustration of Kirchhoff's Current
Law
Fig. 1.4(a) Illustrate the KCL
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Illustration of Kirchhoff’s Voltage
Laws
Fig 1.4(b) Illustrate the KVL
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Independent & Dependent Sources
• Independent Sources are those where the generated voltage (Vs) or the
generated current (Is) are not affected by the load connected across the
source terminals or across any other element that exists elsewhere in the
circuit or external to the source.
• Dependent Sources are those source voltage or current depends on a
voltage across or a current through some other element elsewhere in the
circuit. In general, dependent source is represented by a diamond shaped
symbol as not to confuse it with an independent source.
•
Classification of dependent sources:
(i) Voltage-controlled voltage source (VCVS)
(ii) Current-controlled voltage source (ICVS)
(iii) Voltage-controlled current source(VCIS)
(iv) Current-controlled current source(ICIS)
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Dependent Sources
Fig. 1.5 Ideal Dependent (Controlled) Sources
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Dependent Sources
• When the value of the source (either voltage or current) is controlled by a
voltage somewhere else in the circuit, the source is said to be voltagecontrolled source.
• When the value of the source (either voltage or current) is controlled by a
current somewhere else in the circuit, the source is said to be currentcontrolled source.
• KVL and KCL laws can be applied to networks containing dependent
sources. Source conversions, from dependent voltage source models to
dependent current source models, or visa-versa, can be employed as needed
to simplify the network.
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Mesh Current Method
Fig. 1.6 Circuit for Mesh Current Method
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Mesh analysis
• The analysis of a dc network by writing a set of simultaneous algebraic
equations (based on KVL only) in which the variables are currents, known
as mesh analysis or loop analysis.
• Step-1: Draw the circuit on a flat surface with no conductor crossovers.
• Step-2: Label the mesh currents (I) carefully in a clockwise direction.
• Step-3: Write the mesh equations by inspecting the circuit (No. of
independent mesh (loop) equations=no. of branches (b) - no. of principle
nodes (n) + 1).
Note:
• If possible, convert current source to voltage source.
• Otherwise, define the voltage across the current source and write the mesh
equations as if these source voltages were known. Augment the set of
equations with one equation for each current source expressing a known
mesh current or difference between two mesh currents.
• Mesh analysis is valid only for circuits that can be drawn in a twodimensional plane in such a way that no element crosses over another.
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Node voltage analysis
• The Node voltage analysis can be used to solve any linear circuit. In Nodal
analysis, KCL equations are used to form equations.
• Step-1: Identify all nodes in the circuit. Select one node as the reference
node (assign as ground potential or zero potential) and label the remaining
nodes as unknown node voltages with respect to the reference node.
• Step-2: Assign branch currents in each branch. (The choice of direction is
arbitrary).
• Step-3: Express the branch currents in terms of node assigned voltages.
• Step-4: Write the standard form of node equations by inspecting the circuit.
(No of node equations = No of nodes (N) – 1).
• Step-5: Solve a set of simultaneous algebraic equation for node voltages
and ultimately the branch currents.
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Node voltage analysis
Remarks:
• Sometimes it is convenient to select the reference node at the bottom of a
circuit or the node that has the largest number of branches connected to it.
• One usually makes a choice between a mesh and a node equations based on
the least number of required equations.
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Node voltage analysis
Fig. 1.7 Circuit for Node Voltage Analysis
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Node voltage analysis
• KCL equation at node 1
 V 1 V 2   V 1 V 3 
Is1  Is 3  

0
R
4
R
2

 

1 
 1
 1 
 1 
Is1  Is 3    V 1   V 2   V 3  0
 R2 R4 
 R4 
 R2 
• KCL equation at node 2
 V1 V 2   V 2 V 3 


  Is 2  0
 R 4   R3 
1 
 1 
 1
 1 
 Is 2  

V 1  
V 2   V 3
 R4 
 R3 R 4 
 R3 
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•
KCL equation at node 3
 V 2 V 3   V1 V 3   V 3 
Is 3  

   0
 R3   R 2   R1 
1
1 
 1 
 1 
 1
Is 3  
V 1   V 2    R 2 
V 3  0
R
2
R
3
R
1
R
3


 


•
In general, for the ith node the KCL equations can be written as
 Iii  Gi1V 1  Gi 2V 2  .......  GiiVi  .....  GiNVN
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Delta – Wye Connection
• Delta and Wye connections are one of the basic connections.
• They are named depending on their shapes.
• These three terminal networks can be redrawn as four-terminal networks .
• We can convert delta connection to wye connection and vice versa.
Fig. 1.8 Resistances connected in (a) Delta and (b) Star
configurations
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Delta(Δ)-Star(Y) conversion
and Star-Delta conversion
• The formulas for star-delta conversion
Ra 
R 2 * R3
R1  R 2  R3
Rb 
R1 * R 2
R1  R 2  R3
R1 * R3
Rc 
R1  R 2  R3
• The formulas for delta-star conversion
R1 
Ra * Rb  Rb * Rc  Rc * Ra
Ra * Rb  Rb * Rc  Rc * Ra
R2 
Ra
Rc
R3 
Ra * Rb  Rb * Rc  Rc * Ra
Rb
•The formulas here are given in terms of resistances but the same can be
applied for complex circuits also by replacing resistances by impedances.
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Delta(Δ)-Star(Y) conversion and
Star-Delta conversion
•
The equivalent star (Wye) resistance connected to a given terminal is equal
to the product of the two Delta (Δ) resistances connected to the same
terminal divided by the sum of the Delta (Δ) resistances (see fig. 1.8).
• The equivalent Delta (Δ) resistance between two-terminals is the sum of the
two star (Wye) resistances connected to those terminals plus the product of
the same two star (Wye) resistances divided by the third star (Wye (Y))
resistance (see fig. 1.8 ).
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Thank You
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