ARUNACHAL PRADESH PUBLIC SERVICE COMMISSION ITANAGAR
SUBJECT: ELECTRICAL ENCINEERINC PAPER
Time: 3 hours Full Marks: 200
Note: Answer Question No.1 and any four from the rest. All questions carry equal marks.
1. Answer any ten: 10 x4 40

Define BIT and BYTE.


Compare a JFET and a BJT.


Why FEr's are: preferred over bipolar transistors at high frequencies?


Why do transformers have higher efficiencies than other electrical machines? Explain.


Why are the cores oftransformers laminated?


Why is the armature winding of a d.c. machine placed on rotor and the field Winding on the stator and not the other way?


What are the advantages of a digital voltmeter over an analog voltmeter?


What are 'base load' and 'peak load' plants?


How are relays different from circuit breakers?


Why is the overall efficiency of a steam power plant very low?


What are the advantages of HVDC transmission?


What is the advantage of corona effect in power system?


2. Attempt any 8 8 x 5 40

Discuss the significance of 'Flow-charting' in computer programming.


Distinguish between 'open loop' and 'closed loop' control system with a suitable example of each type.


Why the induction motors are named so? Can these motors run at synchronous speed? Justify your answer.


Explain how the back e.m.f. makes a d.c. motor adjust its input automatically to match the load on the shaft.


Why should a d.c. series motor not be started without some load on it? Explain.


Why does a 3-point starter trip when the speed control of d.c. motor is carried out by field control?


What are synchronous condensers? Discuss their uses.


What is a pumped storage scheme, and what are its advantages and disadvantages?


Explain why the terminal voltage of a d.c. shunt generator decreases with increasing


load.
Explain how corona loss is minimized in EHV A.c. systems?

3. Attempt any 5 5 x 8 40

Draw a flow chart and develop an algorithm to read n numbers and short them in ascending order.


Compare the merits and demerits of machine language and high level language.


Explain the mechanism of power transfer from primary to secondary when a transformer is loaded.


What are the advantages and disadvantages of using high transmission voltages?


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Explain how does the corona loss consideration limit the choice of conductors in high . voltage transmission line?


Describe Delta modulation systems. What are its limitations? How can they be overcome?


What is an FEr? What are the two types of FETs? Draw schematically the structure of an n-channel JFET and explain the terms source, drain, gate and channel.


4. Answer any four: 4 x 10 40

Write a computer program (in any high level language known to you) to read an array ofN S 100) integers, and then to find and print the following results:


Number of odd integers


Number of even integers


Sum of odd integers
Sum of even integers


Explain, with the help of appropriate circuit diagram, the working of a spiit-phase single-phase induction motor.


Draw a typical layout of a steam power plant, and explain the main features of the layout.


A 50 KW load operates from a 50-Hz, 10 KV line with a power factor of 0.5 lagging. Compute the capacitance that must be placed in parallel with the load to achieve a

p.f. of 0.9 lagging.


What do you mean by ALFC? Derive the block diagram of primary ALFC loop.


S. Answer any 2 2 x 20 =40

A d.c. shunt machine connected to 250 V mains, has an armature resistance of 0.12 and the resistance of the field winding is 100 O. Calculate the ratio of the speed as a generator to the speed as a motor, the line current in each case being 80 A.


The closed loop transfer function of a system is given by



S(S2 K

Use Routh-Hurwitz stability criterion to determine the range of Kfor which the system remains stable.
Incremental fuel costs in rupees per MWh for a plant consisting of two units are: IC1=O.lPGl 8.0 Rs./MWh IC2 0.15PG2 3.0 Rs./MWh
Find the optimum sharing of load by the two units when the total load is 100 MW.
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6. Answer any four: 4 x 10 40

What is an Op-Amp? Draw its symbol and state what each terminal represents. State

the characteristics of an ideal OP-Amp. What are the different applications of an OP­AMP?


The rotor resistance and standstill reactance per phase of a 3-phase, 6-pole, 50 Hz induction motor are 0.05 0 and 0.20 per phase respectively. Find the value of external resistance per phase to be inserted in the rotor circuit to give maximum torque at starting.


Using truth table, prove that A AB A B and illustrate the equivalence with the help of a switching circuit.


What is armature reaction? Describe the effects of armature reaction on the operation of d.c. machines. Explain how these effects are neutralized.


Discuss the operating principle of SF6 circuit breakers? What are their advantages? For what voltage range they are recommended?


7. Answer any 2 2 x 20 =40
For the system with the open loop transfer function
0 a

Determine if the following points are in the root locus
s -0.5 s=0.5 (iii)s =j1.732

A 100 6600/330 50 Hz, single-phase transformer took 10 A and 436 watts at 100 V in a short-circuit test, the figures referring to the high voltage side. Calculate the voltage to be applied to the high voltage side on full load at power factor 0.8 lagging, when the secondary terminal voltage is 330V.


Draw a typical daily load demand curve of an interconnected power system, and explain the strategy adopted for meeting the load. 10


A consumer is supplied energy at a rate of Rs. 90.00 per KVA of maximum demand and 30 paisa per KWh of energy consumed. Calculate the annual electricity charges to be paid by the consumer having a maximum demand of 150 KW at an average power factor of 0.85 lagging. Assume the annual load factor to be 0.65. 10
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