Power System-I (EX-404) - Important Questions

Explain the advantages and disadvantages of interconnecting power stations and the methods of controlling active (kW) and reactive (kVAR) power transfer between two interconnected stations.

Explain the meaning and types of renewable / non-conventional energy sources for power generation.

Write short note on any two including effect of transmission voltage on power system economy, skin and proximity effect, sag template, sectionalized double bus bar and ring mains.

Given individual peak loads, diversity factor and annual load factor, calculate maximum demand on station, annual energy supplied, and suggest installed capacity and number of units.

Explain how high load factor and high diversity factor reduce overall cost of generation.

For a straight-line yearly load duration curve with given maximum/minimum load and plant capacity, calculate load factor, plant capacity factor / plant size factor, utilization factor, maximum demand, installed capacity and reserve capacity.

From a given daily chronological load table, plot the chronological load curve and load duration curve and determine load factor, plant capacity factor and energy supplied.

Write short note on conventional, non-conventional and distributed generation, bundle conductors, tuned power lines, and voltage distribution of suspension insulator.

Derive the expression for power developed by wind and discuss advantages and disadvantages of horizontal and vertical axis wind mills.

Classify the types of electrical loads and draw and explain their characteristics in detail.

Calculate the demand factor and load factor given connected load, maximum demand, and annual energy generated.

Draw and explain the structure and components of modern power systems with typical voltage levels.

Calculate the loop inductance per km of a single-phase line of two parallel conductors for given spacing, diameter and permeability.

Distinguish between a bundled-conductor 3-phase line with two conductors per bundle and a double-circuit 3-phase line and compare their electrical characteristics.

Explain GMD and self GMD for single-phase lines with composite conductors and find the self GMD of a 7-strand conductor of strand radius $r$.

Explain the concepts of GMR (self GMD) and GMD (mutual GMD) in transmission line inductance calculation.

Compare the advantages and disadvantages of underground cables versus overhead lines.

Determine the inductance per phase per km of a double circuit 3-phase line. The radius of each conductor is 20 mm and the conductors are placed on the circumference of an imaginary circle of radius 7 m forming a regular hexagonal figure.

Derive the expression for per-phase inductance of a 3-phase overhead line with symmetrical and unsymmetrical spacing.

Explain what transposition in overhead lines means and why it is done.

Calculate the inductance and capacitance of a 3-phase equilateral-triangle overhead line of given length.

Calculate the inductive reactance of a 3-phase bundled-conductor line and compare it with that of an equivalent single-conductor line.

Given maximum and minimum dielectric stresses and conductor diameter of a single-core cable, find insulation thickness and operating voltage.

Derive an expression for capacitances of a single phase transmission system and discuss the effect of earth on capacitance with suitable equation.

For a short 3-phase line delivering given MW at given receiving voltage and pf with line loss as % of delivered power and given inductance per km, find sending-end voltage and voltage regulation.

Using nominal-T method, determine sending-end voltage/current, ABCD constants, regulation/efficiency for a medium transmission line supplying a given load.

Explain the Ferranti effect and derive an expression for power loss in an open-circuited line.

Show diagrammatic representation of medium line nominal-\(\Pi\) model with series impedance and shunt admittance in terms of per-unit-length R, L, C.

Explain the concept of the power circle diagram of a transmission line and the procedure for its construction.

Explain the various methods of voltage control in transmission lines.

Derive the A, B, C, D constants of a medium-length transmission line using the nominal-$\Pi$ configuration, including the phasor diagram.

For a single-phase line with given load, receiving voltage, pf, resistance and loop reactance, determine sending-end voltage, percentage regulation and transmission efficiency.

Derive expressions for voltage regulation and transmission efficiency of a medium transmission line.

For a 3-phase line with given load, pf, resistance per km and receiving voltage, determine maximum line length so that line loss does not exceed a given percentage.

Calculate the additional load transmissible when converting a single-phase AC system to a 3-phase, 3-wire system with same conductor size, line voltage and percentage losses.

Compare copper efficiency / volume for 3-phase 3-wire versus 3-phase 4-wire system for the same maximum voltage to earth.

Explain the different types of insulators used for overhead lines with neat sketches, including constructional features and comparison / advantages of suspension type over pin type for high voltage transmission

For a 3-unit suspension insulator string with given ratio of shunt (pin-to-earth) capacitance to self-capacitance, find the voltage distribution across the three units and the string efficiency.

Derive the parabolic shape and expression for sag (and tension) of a conductor strung between two supports at the same level.

Explain grading of insulators and the methods (grading of units and guard ring) to equalize voltage distribution and improve string efficiency.

Calculate the maximum sag of a transmission line conductor given conductor diameter and weight, span length, wind pressure, ice coating thickness and density, ultimate strength and factor of safety.

Numerical on sag for level span to determine required support height given ground clearance, conductor weight, span and safety factor.

Define string efficiency of suspension insulators and explain methods to improve it.

Explain string efficiency and methods to improve it for insulators, and how they are tested to determine flash-over voltage.

For a 3-unit suspension insulator string with given voltages across top and middle units, find the ratio of pin-to-earth capacitance to self-capacitance, the line voltage, and the string efficiency.

Numerical on sag with wind loading to determine factor of safety given span, conductor weight, breaking stress and sag.

Derive the expression for voltage distribution in an insulator string and string efficiency.

Explain the different types of overhead line supports and towers and their suitability with reference to system voltage and span.

Explain why power transmission uses a 3-phase 3-wire system whereas distribution uses a 3-phase 4-wire system.

Explain/state Kelvin's law for the most economical size of conductors for transmission, including limitations

Draw the layout / single-line diagram of a (indoor) substation showing the location of all equipment and accessories.

Explain:

Draw the single-line diagram of a typical A.C. distribution system arrangement and state the requirements of an ideal distribution system.

Describe the limitation of Kelvin's law and calculate the most economical current density for a given line cost, interest/depreciation, energy cost and loss factor

Explain the single bus-bar system with sectionalization along with its merits and demerits.

List the main equipment in a substation and explain each in brief.