Test: Power Systems- 2 - Electrical Engineering (EE) MCQ

If various types of power plants are operated in combination, the system will become more flexible i.e Steam and Nuclear power plants will supply base loads, Hydroelectric power plants will supply base or peak loads depending upon the availability of water, Gas turbine power plant will meet peak load demand and existing Diesel power plant will operate in emergency only.

At θ=45°, ZVR and maximum VR coincide.

Number of non zero elements = 50*50*20/100 = 500 non zero
Number of TL = (500-50)/2 = 225 transmission lines.

For the complete protection of the power system, one can use 3 phase fault relays and two earth fault relays so that to cover the entire zone of operation.

Load curve is obtained by plotting fluctuating load be keeping load on y axis and time in x axis. The area under the load curve represents the total number of units generated in a particular time.

For maximum power transfer, X=√3 R
3=√3 R
R=√3.

Reactance diagram is drawn by the help of symmetrical network of various power system components by neglecting resistance of various components, static loads like induction motors and shunt component of Transformers.

Output of such plants is never constant. This is because of their dependency over flow rate of water in river which is seasonal. No fuel requirement low running cost and no standby losses are advantages of hydroelectric power plants.

About 54% of energy losses occurs in condenser. Losses in boiler and alternator are about 1% and 16% because of such high losses overall efficiency of thermal power plant reduces to 29% for normal old thermal power plant and 50% for modern super critical pressure steam power plant which employs many heat saving devices.

Peat and lignite coals have low calorific value and high ash content. Anthracite coals are found in small quantities and are therefore costlier for power generation. Bituminous coals have enough calorific value, low moisture and ash content so most suitable for power generation.

Open and contact type haters are in small power plants. Such heaters recives steam from back pressure turbine. In large modern power plants heaters bleed steam from the main turbine and use it for heating of feed water.

Out of all the corona losses are less in HVDC system.

The overall efficiency of gas turbine is low, because a greater part of power developed by the turbine (about 65%) is used in driving the compressor.

The power plants to be employed as peak load plant should only have the capability of quick start, synchronization and taking up of system load and quick response to load variations.

Only balanced power system can be represented by a single line diagram. Single line diagram is drawn on per phase basis. A power system with LLG, LG and LL faults becomes unbalanced and can not be represented in per phase basis.

Single line diagram is a representation of balanced power system on per phase basis with neutral eliminated. Neutral wire is not shown in single line diagram. Winding connections (star or neutral) is represented beside the symbol of transformer with its Impidance and rating.

Total buses = 200
PQ buses = 160
PV buses = 200-160 = 40
Slack bus = 1
Total number of equation = (40-1)*1 + (160*2) = 359.

A LG fault will create a sudden dip in the voltage profile and it will be recovered.

LF = (Average Demand)/(Maximum Demand)=0.5
Plant capacity factor =(Average Load)/(Plant Capacity)= 0.5/0.4
Plant capacity= (0.5/0.4)*15 = 18.75 MW
Reserve Capacity = 18.75-15 = 3.75 MW.

VR is rise in voltage at receiving end for a transmission line.