The document discusses transmission line parameters and modeling. Unit I covers the structure of power systems and parameters of transmission lines including resistance, inductance, capacitance, symmetrical and unsymmetrical spacing, and effects of skin and proximity. Transmission line performance is modeled as short, medium and long lines with equivalent circuits in Unit II. Unit III covers mechanical design of overhead lines including tower types and insulator types. Underground cable types and parameters like capacitance and heating are covered in Unit IV. Unit V discusses distribution systems including voltage control techniques and types of substations.
2. UNIT I
TRANSMISSION LINE PARAMETERS
• Structure of Power System - Parameters of
single and three phase transmission lines with
single and double circuits -Resistance,
inductance and capacitance of solid, stranded
inductance and capacitance of solid, stranded
and bundled conductors, Symmetrical and
unsymmetrical spacing and transposition –
application of self and mutual GMD; skin and
proximity effects -Typical configurations,
conductor types and electrical parameters of
EHV lines.
3. UNIT II
MODELLING AND PERFORMANCE OF
TRANSMISSION LINES
• Performance of Transmission lines - short line,
medium line and long line – equivalent
circuits, phasor diagram, attenuation constant,
phase constant, surge impedance -
phase constant, surge impedance -
transmission efficiency and voltage regulation,
real and reactive power flow in lines – Power
Circle diagrams - Formation of Corona –
Critical Voltages – Effect on Line
Performance.
4. UNIT III
MECHANICAL DESIGN OF LINES
• Mechanical design of OH lines – Line
Supports –Types of towers – Stress and Sag
Calculation – Effects of Wind and Ice loading.
Insulators: Types, voltage distribution in
Insulators: Types, voltage distribution in
insulator string, improvement of string
efficiency, testing of insulators.
5. UNIT IV UNDER GROUND CABILITYS
• Underground cabilitys - Types of cabilitys –
Construction of single core and 3 core
Cabilitys - Insulation Resistance – Potential
Gradient - Capacitance of Single-core and 3
Gradient - Capacitance of Single-core and 3
core cabilitys -Grading of cabilitys - Power
factor and heating of cabilitys– DC cabilitys.
6. UNIT V DISTRIBUTION SYSTEMS
• Distribution Systems – General Aspects –
Kelvin’s Law – AC and DC distributions –
Techniques of Voltage Control and Power
factor improvement – Distribution Loss –
factor improvement – Distribution Loss –
Types of Substations -Methods of Grounding –
Trends in Transmission and Distribution:
EHVAC, HVDC and FACTS (Qualitative
treatment only).
11. Magnetic field intensity inside the conductor
• Since, the current density (Ix/a’ = I/a) is same throughout the
conductor,
a’ : area of the conductor at radius x
a : area of the conductor at radius R
• Using Ampere’s law,
a : area of the conductor at radius R
27. Transposed Lines
• Transposing of power conductors means changing the position of
phase conductors at regular interval along the line so that each
conductor occupy others positions over an equal distance, as in
Figure.
• If transmission lines are not transposed, the voltage drop in the
transmission line will not be the same due to unequal inductances.
Transposition of lines
36. • For the voltage rating more than 230 kV, it is not possible to use the
round conductors due to excessive corona loss.
• It is preferred to have the hollow conductor, normally in substations,
and bundled conductors in transmission lines.
The main advantages of using bundled conductors are:
• Reduced corona loss
• Reduced corona loss
• Reduced voltage gradient at the surface of the conductor
• Low reactance due to increase in the self-GMD
• Reduced radio interference
• Increase in capacitance
• Larger loading capability and
• Increase surge impedance loading.
37. Resistance of Transmission lines
• The transmission capacity of a line mainly depends on the
inductance and the capacitance, as resistance and conductance are
very small.
• The resistance used for analysis of transmission line performance is
the effective (or ac) resistance. The direct current resistance (Rdc) of
a conductor is defined as,
a conductor is defined as,
• The ac resistance is more than dc resistance due to skin effect.
38. SKIN EFFECT
• The alternating current distribution in a wire is not uniform. The
current density near the surface is more than near to the centre. It is
affected by the frequency of the current. If the frequency of current is
more, the current distribution is more non-uniform. This effect is
known as skin effect.
• Due to this effect the effective resistance (or ac resistance of the
• Due to this effect the effective resistance (or ac resistance of the
conductors) becomes more than the direct current (dc), where the
current distribution is uniform.
39. PROXIMITY EFFECT
• Like skin effect, the proximity effect also increases the resistance of
the conductor.
• The alternating flux in a conductor caused by the current flowing in
neighbouring conductors gives rise to circulating currents, which
cause the non-uniformity of the current and thus increases resistance.
• This effect is more pronounced in cable where the phase conductors
are nearer to each other. The proximity effect is negligible in
overhead transmission line.
• Both skin effect and proximity effect depend on the conductor size,
frequency of the supply, resistivity and permeability of the conductor
material.
