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Power Grid Corporation Of India Ltd. Technical Question Paper- Electrical Engineering
1.(a)Identify the correctness of the following statements. Justify your answers :
(i)The root locus gives idea about system's transient behaviour.
(ii)For an inherently stable second-order system, all the coefficients of characteristic equation are of the same sign.
(iii)A critically damped system has sustained oscillations.
(b)(i)In 8085 microprocessor, what is the advantage of multiplexing the address bus with a data bus?
(ii)Write an assembly level program of 8085 microprocessor to exchange the contents of DE register pair with that of HL register pair, using only PUSH-POP instructions.
(c) (i) What is the impedance of the ideal load connected to an HVAC transmission line?
(ii) What is the nature of the load of an HVAC transmission line by itself, capacitive or inductive?
(iii) Which electrical quantity measures the magnitude of electrical load in a system? What is generally the nature of the load current, capacitive or inductive, in the power system?
(iv) Under which condition is the receiving-end voltage higher than the sending-end voltage in a transmission line? Explain with the help of a phasor diagram.
(d)Describe the essential features of protective relay.
(i) A binary PCM system uses a uniform quantizer and an 8-bit binary encoder. If the bit rate is 100 Mb/s, what is the maximum bandwidth for which the system operates satisfactorily? Determine the output signal to quantization ratio when full-load sinusoidal modulating wave of frequency 1MHz is applied to the input.
2.(a)(i) Draw power triangles showing the three types of power and their units for-
(1)inductive loads;
(2) capacitive loads.
(ii) A single-phase,240 V a.c. voltage is applied to a series circuit whose impedance is 1OL60° Q. Find R, X, P and Q, and also the power factor of the circuit.
(b) (i) Explain ASK, FSK and PSK modulation schemes used for transmitting the data. Draw clearly the block diagram for coherent detection and non-coherent detection of FSK modulation scheme.
3.(a)(i)Under which different conditions agenerator or a number of generators together may lose synchronism or fall out of step in an inter-connected power system? Explain in brief.
(ii)Relating the torque angle and the rotor angular displacement (electrical) of a synchronous generator,derive the`swing equation' taking into consideration the inertia constant of the machine.Make suitable assumptions.
(b)For an 8085 microprocessor, write an assembly level program to transfer the contents of the stack pointer register to the output ports AO and A1. Write comments with selected instructions.
(c)(i)Some control systems have more than one inputs applied at different points in the system. How do we find the response of such systems, using block diagram algebra? Illustrate your answer with the help of a simple example.
4.(a)(i) What are the limitations of Routh,Hurwitz and continued fraction stability criteria when used for determining system stability? What is Nyquist analysis? Where is this technique used?
(ii) Why are integral and derivative controllers not used in practice?
(b) Can the 8085 microprocessor be interrupted before completion of existing Interrupt Service Subroutine (ISS)? Justify your answer.
(c)(i)Draw the basic circuit of an analog series ohmmeter to measure an unknown resistance R.
(ii) What would be the resistance value marked for 0.5 FSD (full-scale deflection)?
(iii) What component should be connected and in which way to take care of falling battery voltage?
(iv) When each time ohmmeter is used,what adjustment is recommended for accurate measurement?
(d)(i) Define an electrical power grid in one sentence. How is it achieved?
(ii) Write four main advantages of the electrical power grid system.
(iii) What is the purpose of installing a `reactor' at a suitable location on a long high-voltage a.c. transmission line?
(iv) Write the full form of FACTS.
(v) What are the advantages of `reactive power control' installed on the transmission lines?
(e) What is circuit breaker rating? Explain the rated making capacity of a circuit breaker.
5.(a)(i) What are the basic elements of a static relay? Describe the function of each element.
(ii) What are the advantages of static overcurrent relays over the electro-magnetic form?
(b) Draw a block schematic of an 8255-programmable parallel I/O device, showing all elements and control word format. For mode 0 (simple input and output),determine the addresses of its ports and of the control register. Write a control word in the control register, when port A = output, port C U = output, port B = input and port CL = input.
6.(a)(i) Draw the circuit diagram for a single line to ground fault on an unloaded Y-connected generator with its neutral grounded through reactance. Also draw the connection for three symmetrical component sequence networks for this case showing the currents and voltages.
(b)(i) Draw the neat sketch of OSI model. What is the significance of data link layer? Explain the flow-control and error-control mechanism.
