Candiilotes slwuJd attempt questions 1 and 5 which arecompulsory andanythree ojtheremaining questions selection oJ least one question selecting at leastone questionjrom e(f£h Section.
SECTION A
Answer any three of the following
The figure shows an equivalent clrcuit of a small two winding transformer in terms of the
primary

If the se1 finductance L3 of the secondary is 16 estimate the following
The actual winding resistance 0f the secondary
The secondary open Circuit voltage with primary supplied with 220 V ac
The mutual induclance M. between the primary and the secondary 6 6 8

Write the integral form of Maxwell's equations and ldentify each equation with the proper experimental law

A synchronous motor is runrung ldle on an infinite bus at its rated voltage and frequency ItlS excited to have an inducted voltage of 125% and its synchronous lmpedance is J Calculate the stator current, and its phase with resp ectto the bus voltage Where would such ldle runs be useful? 15 5

A super heterodyne reCelver uses an IF frequency of 455 kHz The recelver is tuned to a transmitter havmg a camer frequency of 1350 kHz Give two pemussible frequencles of the 10 cal 0scill ator and the lmage frequency for each

A filter has transfer function recl(£'2B) Whee


An input xCI) 2 W SIne is applied to !his filler, wheresinc(x)=sin piex/piex Find the output for W B Find the output for W B In which case does the output suffer distortion? Justify your answer 6

A d.c. shunt generalor supplies the £Ullload current of 50 A at 500 V Assume its field is drawmg 2A, and the armature voltage drop is 5%. The generalor is bemg driven at the rOlled speed 0 f 150 0 rpm, and1sworking at an effiClency of80% Estimate the speed at which 11 will run and the efficiency when the machine is working as a molor, drawmg 50 A from a 500 V d.c. source Assume the rolationa11osses (the lron, friction and wmdage losses) Vary as the square of the speed 10 10

Gennall1um and Silicon are both semi-conducting malenals and we have b alh diodes and triodes with gennaruum as well as Silicon. However, in respect of controlled rectifiers we have only sil1con-controlled rectifiers hut no gennanium-controlled rectifiers. Explain why

Use the two transistor equivalent Circuit of the SCR and show that when reverse blased the SCR cannot contact even 1f ltlS triggered 10 10

3. A locker can be opened by A and B when they are both there, as the locker has 2 keys one of which lS with A and the other Wlth B. C has both the keys, but he is pennitled to open the locker only when B lS not there. Show that the locker can be opened always lfboth A and C are there. Give the Boolean ldentity that symbolisms this situation

With respect to full load current why does an mduction motor take higher no-load current than a transfonner? A 3-phase inducti on motor draws 25 A from 460 V 3-phase line at a p f of 085 lagging. The stator copper loss lS 1 kW, and the rotor copper loss lS 500 W. The rotational losses due to windage and fri cti on are 250 core loss lS 800 and stray load 10 ss 1S200W. Calculate the air gap power Pg, the developed mechanical power,(iii) the output horse power, and the efficlency 5 15

Explain the pnnClpIe of pulse with rna dulated inverters for induction motor control What lS the purpose of using pulse Width modulation in this context?

4. Obtain the conditi ons under which the Clrcuit below produced oscillations



Whatl s the frequency 0f oscillations?

Define directive gain and directivity of an antenna. The radiation intensity of a certain antenna lS

Determine the directivity 0f the antenna 5 15

An AM modulator has output
30 cos 2pie(200)t 6 cos 2pie(180)t+ 6 cos 2pie(220)t
Detemine the mo du1ation mdex and efficlency
An upper Sideband SSB modulator has the message Signal Am cos amt. The urunodulated carrier is glven by Ac sin teta t. Sketch the modulator output 10 10

SECTION B

5 Answer any three of the folloWlng
Consider the op-amp Clfcuit shown


In the clrcuit make the usual assumption that the inverting and non-inverting ternunals are virtually at the same potential and the op amp does not take any mput current at its teminals. You would amve at the nonnal conclusiOn that v0=-v1/p1 r2 Is this conclusion valid? If yes giVe reasons why operational amplifiers are never used m this manner Wlth mverting mput grounded and mputto be amplified giVen to the non-mverting terminal

Use the properties 0f the unitlmpu1se function to evaluate the following lntegrals 10 10


Describe any brushless exatation system for large alter nators Exp1ain the working

What lS a Hertzian dipole? Find the radiation reSiStance of a Hertsian dipole

6. A standard air-filled rectangular waveguide with dimenslOns 8 6 cm and b 4.3 cm lS fed by 4 GHz camer from a coaxtal cable. Determine If a TE IO mode will be propagated If so, calculate the phase velocity and the group velocity

An FM modulator has mput met) 4 cos 10 ill. The peak frequency deviation lS 25 Hz The modulator lS followed by an Ideal band pass filter with a center frequency giVen by the camer frequency and a bandWldth of 54 Hz. Determine the power at the filter output assuming that the modulator output power lS 100 W. Express the answer in tenns of appropnate Bessel function values

In a certain region Wlth sigma= mew mewo and sigma= 6.25 the magnetic field 0f an EM WeNe lS


Find the phase constant beta and the corresponding E (electric field) using Maxwell's equations

7.(a)DeVise a 4-bit 0dd parity generator function using 3-level NOT-NOR-NOR log1c

A delta modulator has the message Signal 6 sin 2pie(I O)t 4 Sin 2pie t Determine the minimum sampling frequency reqUired to prevent slope overload, assuming thestep Sizetobe o.Im

In a non-magnetic medium Find relative permittivity and intrinsic Impedance 10
the time average power carried by the wave I0

Nl and N2 are two 2-port networks connected m parallel on both Input port Side as well as output port Side, to fonn a composite 2 -port network N as indicated

8 N1 and N2 are defined by the Z-parameters as below

Obtain the Z-parameters for the composite 2-port network N

WhatlS all day efficiency of a transformer? Why lS it necessary to calculate such efficiency? 5

A 300 KVA transfonner has a core loss of 1 5 kW and a fUll load copper loss of 45 kW Calculate the efficiency at 75% of fUll load output at a p.f of 0.8 lag. Calculate the max1mum effia ency and the load at which it occurs 15

Explain the main advantage of power MOSPETs over SCRs 5
A fully controlled bridge rectifier has a voltage of 200 V d.c applied to its input terminals as shown

Identify the forwarded and reverse bi ased SCRs in the CircUl t Assume the forward biased SCRs have aleakage reSiStance of 100 MO and the reverse biased SCRs have 200 MO. Show that each of the devices lS blocking a voltage of approXimately 100 V m the arcuit, irrespective of whether itlS forward biased or reverse biased 15