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

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

A power station is to supply four regions of loads whose peak loads are 15000 kW, 10000 kW, 9000 kW and 11000 kW respectively. The diversity factor of the loads at the station is 1.5 and the average annual load factor is 60%. Calculate the maximum demand on the station, annual energy supplied and suggest the installed capacity and number of units.

Define load curve, load duration curve, load factor, plant capacity factor and utilization factor. Explain how a good load factor and good diversity factor help to keep the overall cost of generation low.

A generating station has a connected load of 45 MW and a maximum demand of 20 MW; the units generated being 61.5 x 10^6 kWh per annum. Calculate the demand factor, load factor and the cost of electricity per kWh if the fixed cost is Rs. 200 per kW of maximum demand and running cost is 10 paise per kWh.

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

Calculate the loop inductance per km of a single-phase line comprising of two parallel conductors 1 m apart and 1 cm in diameter, when the material of conductor is (i) copper and (ii) steel of relative permeability 50.

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

A 15 km long 3-phase overhead line delivers 5 MW at 11 kV at 0.8 lagging p.f. Line loss is 12% of power delivered. Line inductance is 1.1 mH per km per phase. Find the sending-end voltage and voltage regulation.

A 3-phase, 50 Hz, 100 km long medium transmission line has resistance 0.1 ohm/km/phase, inductive reactance 0.2 ohm/km/phase and capacitive susceptance 0.04 x 10^-4 S/km/phase. Using nominal-T method, determine the sending-end voltage and current, ABCD constants, voltage regulation and transmission efficiency for a load of 20 MW at 66 kV, 0.8 p.f. lagging.

Derive the A, B, C, D constants of a medium-length transmission line using the nominal-Pi configuration and draw its phasor diagram.

Derive the expressions for voltage regulation and transmission efficiency of short, medium and long transmission lines. Explain the mathematical solution to estimate regulation and efficiency for all types of lines.

Explain with neat sketches the different types of insulators used for overhead lines. Describe constructional features of pin type and suspension type insulators and list the advantages of suspension type over pin type for high voltage transmission.

In a string of three identical suspension insulator units, if the self-capacitance of each unit is C and the capacitance of each connector pin to earth is 11% of self-capacitance, find the voltage distribution across the three units and the string efficiency for a 33 kV line.

Show that an overhead line conductor strung between two level supports takes up the shape of a parabola. Obtain the expressions for sag and maximum tension when the supports are at the same level.

Write short notes on any two: (i) AC single-phase, 3-phase 3-wire and 3-phase 4-wire distribution systems - why transmission is 3-phase 3-wire and distribution is 3-phase 4-wire, (ii) Kelvin's law for most economical size of conductor, (iii) Substation layout showing location of all equipment.