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# PSU’s

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__ELECTRICAL ENGINEERING__

- A single phase transformer is connected to a supply of voltage V and frequency f and is supplying a load, connected across its secondary winding. If the supply voltage is reduced from V to V/2, the flux established in the core will
- decrease by nearly 50%
- increase by nearly 50%
- remain unchanged
- be affected by amount of load and not by the applied voltage
- Under magnetic saturation of the core of a transformer, the reactance parameters of its equivalent circuit are affected such that
- X1 and X2 increase while Xm does not change
- X1 and X2 do not change while Xm decreases
- X1 and X2 do not change while Xm increases
- X1 and X2 decreases while Xm does not change
- A single phase 2000/200 V, 10 kVA, two winding transformer is reconnected as a step-up autotransformer with 2000 V winding as primary. The kVA rating of the autotransformer shall be
- 10 kVA
- 11 kVA
- 110 kVA
- 220 kVA
- The power factor at which power is drawn by a transformer is
- very low under O.C. test but high under S.C. test
- high under O.C. test but low under S.C. test
- low both under O.C. and S.C. tests
- high both under O.C. and S.C. tests
- The O.C.C. of a shunt d.c. generator is represented by E = 12+66I. If the field resistance is 70 ohms, the no-load voltage of the generator will be
- 144 V
- 210 V
- 220 V
- 288 V
- In d.c. shunt motors, the developed torque is proportional to
- induced e.m.f.
- armature current
- output power
- line current
- The speed of a separately excited d.c. motor can be controlled below base speed by (a) armature resistance control and (b) supply voltage control. What happens to the slope of modified speed-torque characteristics under the two methods?
- It changes in both types of control
- It remains unchanged in both types of control
- It remains unchanged in armature resistance control while changes in supply voltage control
- It remains unchanged in supply voltage control while changes in armature resistance control
- The polarity of interpoles used in d.c. machines is
- same as the main pole ahead in generators while opposite of the main pole ahead in motors
- same as the main pole ahead ion motors while opposite of the main pole ahead in generators
- same as the main pole ahead in both motors and generators
- opposite of the main pole ahead in both motors and generators
- In synchronous generators, examine the following statements about voltage regulation:
- Synchronous impedance method gives pessimistic results
- MMF method gives optimistic results
- In unsaturated machine both methods (synchronous impedance and MMF) give same result
Which of the statements are correct?

- 1, 2 and 3
- Only 1 and 2
- Only 3
- Only 2 and 3

- Under symmetrical short circuit of a synchronous generator, the armature reaction is
- magnetizing
- demagnetizing
- cross-magnetising
- mainly magnetising
- In synchronous generators, the fifth harmonic in induced emf can be eliminated by using coils show chorded by an angle
- 9o
- 18o
- 27 o
- 36o
- In induction motor operation, a slip greater than 1 refers to
- regenerative braking
- motoring in reverse direction
- plugging
- dynamic braking
- As the applied voltage to an induction motor, operating under no-load, is reduced to half
- its speed reduced and stator current increases
- its speed reduced and stator current also reduces
- its speed reduces but there is not change in stator current
- there is no change in speed but stator current reduces
- A 3-phase induction motor is delivering a load of 10 kW at a lagging p.f. of 0.5. If a 3-phase capacitor bank of 7.3 kVAR is connected at its input, the resulting kVA drawn from supply shall be (approximately)
- 26.5
- 24.5
- 20.0
- 14.0
- An electric motor developing a starting torque of 10 Nm starts with a load of 6 Nm at its shaft. If the acceleration at start is 2 rad/sec2 , the moment of inertia of the system must be
- 2 kg-m2
- 2 N-m2
- 0.5 kg-m2
- 0.5 N-m2
- A synchronous motor works as a synchronous condenser if
- underexcited
- overexcited
- excited with 100% excitation
- unexcited
- In relation to damper bar winding in a synchronous motor, examine the following statements:
- Damper bars are provided in slots on poles
- Damper bars improve excitation
- Damper bars help the motor self start
- Damper bars minimize hunting.
- 1, 2, 3
- 2, 3
- 1, 4
- 1, 3, 4
- In large power ratings, synchronous motor is considered superior to induction motor, since
- it is less expensive
- its efficiency is better
- it can be operated at better power factor
- its speed regulation is superior.
- An induction motor drive is designed for two speed operation. For this purpose, the motor is provided with two windings on its stator corresponding to 4 poles and 8 poles. While the motor was running on 4 pole winding, a changeover to 8 pole winding is made. The motor will
- experience dynamic braking
- experience regenerative braking
- experience no braking but will slow down due to its inertia
- draw dangerously high current

Which of the statements are correct?

- A d.c. shunt motor drive of 100 h.p. is run (a) at half the rated speed by armature voltage control and (b) at 1.5 times the rated speed by field control. Its power rating in the two cases shall be modified as
- 100 h.p. in both cases
- 50 h.p. in case (a) and 150 h.p. in case (b)
- 50 h.p. in case (a) and 100 h.p. in case (b)
- 100 h.p. in case (a) and 150 h.p. in case (b)
- A single phase full controlled rectifier can work as inverter, if the firing angle is between
- 0o and 90o
- 60o and 90o
- 90o and 180o
- 0o and 60o
- When d.c. voltage is converted to a.c. by an inverter, PWM technique is used to
- control only the output voltage from within the inverter
- control both the output voltage and frequency from within the inverter
- control the output current
- reduce losses in the inverter
- A thyristor which is in ON state is to be switched OFF. For this purpose a reverse bias is applied across it. Examine the following statements regarding flow of current from anode to cathode (forward current):
- Forward current can continue to flow if the circuit is purely resistive
- Forward current can continue to flow if the circuit is dominantly inductive
- Forward current can continue to flow if the circuit is dominantly capacitive
- Forward current will immediately stop flowing.
- Only 4
- Only 1
- Only 2 and 3
- Only 2
- In a 3-phase full controlled thyristor bridge rectifier operating under continuous conduction mode, each thyristor conducts for
- 180o and two thyristors conduct at a time
- 120o and three thyristors conduct at a time
- 180o and three thyristors conduct at a time
- 120o and two thyristors conduct at a time
- A single phase fully controlled rectifier is feeding a d.c. motor. At a = 0o, the armature voltage is 200 V and motor speed is 1000 rpm. Neglecting armature resistance and considering continuous conduction, the armature voltage and speed at a = 60o will be
- 100 V and 500 rpm
- 100 V and 1000 rpm
- 200 V and 500 rpm
- 100 V and speed will depend upon load
- The grading capacitors are provided across the series connected interrupters in EHV circuit breakers for
- reducing short circuit current
- improving power factor
- equalizing distribution of recovery voltage across the interrupters
- preventing inductive current chopping.
- The minimum cost operating condition for a thermal plant is that
- the larger units should generate more power as compared to smaller units
- the smaller units should generate more power as compared to larger units
- the incremental cost rate of the units be proportional to their rating
- the incremental cost rate of all the units be equal
- The effect of earth on a three-phase transmission line is to
- increase its capacitance and decrease inductance
- decrease its capacitance and increase inductance
- increase its capacitance without affecting inductance
- increase its inductance without affecting capacitance.

Which of the above statements are correct?

- In case of a transmission line if the voltage regulation is negative, then the load power factor is
- zero
- lagging
- unity
- leading
- The voltage gradient at the surface of a cable, having a conductor of radius r and a sheath of radius R, is minimum when
- R = r/e
- R = r
- R =er
- R = er
- In an N-bus power system with M-PV buses, the size of the Jacobian matrix for load flow calculation is
- N×N
- (N-M) ×(N-M)
- (N-1) × (N-1)
- (N-M-1) × (N-M-1)
- The zero-sequence equivalent circuit of a delta-star transformer, with solidly grounded neutral, is
- The plug setting multiplier of a 5 Amp. IDMT relay for a fault current of 4000 Amp. and a relay setting of 125%, with a C.T. ratio of 80 will be
- 1
- 2
- 4
- 8
- If the cost of electricity generation is to be reduced then
- the diversity factor and load factor both should be low
- the diversity factor and load factor both should be high
- the diversity factor should be high while the load factor should be low
- the diversity factor should be low and the load factor should be high
- The coefficients of reflection for voltage and current for an open ended line are respectively
- -1.0 and -1.0
- -1.0 and 1.0
- 1.0 and 1.0
- 1.0 and -1.0
- If G is the MVA rating of a synchronous machine with inertia constant H sec. and operating frequency f, then the angular momentum M of the machine, in MJ-sec/electrical degree, is
- Circular grooves are provided underneath the insulator disc for
- reducing the weight of the disc
- improving disc strength
- increasing cooling of the disc
- increasing the creepage distance
- The arc formation in vacuum circuit breaker is initiated by
- field emission
- thermal emission
- photo emission
- secondary emission
- The series reactors are used to
- limit over voltages
- control Ferranti effect
- limit fault current
- improve stability

*where e = natural exponent*

- If the spacings Dab, Dbc and Dca between the phases a, b, and c of a three phase transmission line are not equal, then the equivalent spacing Deq can be calculated as
- (Dab + Dbc + Dca)/3
- (Dab * Dbc * Dca)/3
- (Dab + Dbc + Dca)1/3
- (Dab * Dbc * Dca)1/3
- For calculating fault current for a double line to ground fault in an ungrounded system
- positive, negative and zero sequence networks are connected in series
- positive, negative and zero sequence networks are connected in parallel
- positive and negative sequence networks are connected in parallel
- positive and negative sequence networks are connected in series
- The unit of R, the regulation constant of turbine speed governor, is
- Hz/MW
- MW/sec
- MW/Hz
- MW-Hz
- If in a power system the line to line base voltage is VB kV and the 3-phase base MVA is SB, then the base impedance of the system is
- The pumped storage hydro plants are used as
- Base load plants
- Peak load plants
- Mid-range plants
- both (A) and (B)
- The specified operating criteria for the proper operation of interconnected power system is , that Area Control Error (ACE) must be zero at least once in a
- 1 sec period
- 1 min period
- 10 min period
- 1 hr period
- If a network has b branches and n nodes, then the number of independent KVL equations for the network are
- b-n
- n-b+1
- b-n-1
- b-n+1
- What will be the value of ZL for maximum power transfer condition in the circuit shown in Fig. Q.47?
- (2-j2)W
- (2+j2)W
- (3-j2)W
- (3+j2)W
- Which of the following statements does not apply to series RLC circuit?
- The current and the admittance are maximum at resonance
- The phase angle of the impedance changes from +90o to –90o as the frequency is varied from 0 to ¥
- The total stored energy in the circuit is constant at resonance
- The power factor is unity at resonance
- The average value of a sine wave over a full cycle is
- zero

- A two port network is reciprocal and symmetrical, if ABCD parameters satisfy the conditions:
- AB-CD = 1 and A = D
- AD-BC = 1 and A = D
- AC-BD = 1 and A = D
- AD-BC = 1 and B = C
- Tellegen’s theorem is applicable to
- linear time invariant networks only
- non-linear time invariant network only
- any network satisfying Kirchoff’s current and voltage laws
- linear time variant network only
- The circuit element having identical properties for forward and reverse direction of current flow through it, is called a
- linear element
- irreversible element
- bilateral element
- unilateral element
- A fundamental cut set contains
- only one tree branch and minimum number of links
- only one link and minimum number of tree branches
- only tree branches
- only links
- In the circuit shown in Fig. Q. 54 if the switch is opened at t = 0 and the initial current through the switch and L1 is 10 A, then the current i(t) and the voltage v(t) of t > 0 are
- 0 A, 0 V
- 0 A, ¥ V
- 6 A, 12 V
- 10 A, 20 V
- The Thevenin and Norton equivalents of network A at points X, Y (Fig. Q.55) can not be found if
- Networks A and B are coupled
- A is an active network
- B is a passive network
- B is a non-linear network
- If X×Y= 0 then XÅY is equal to
- X+Y
- 1
- The value of base x will be
- 2
- 7
- 8
- 10
- Consider the counter circuit shown in Fig. Q.58.
- QA = 1, QB = 1
- QA = 1, QB = 0
- QA = 0, QB = 1
- QA = 0, QB = 0
- In 8085 A mp, stack pointer is a 16 bit register which is
- Incremented by 2 whenever data is pushed on to stack
- Incremented by 2 whenever data is popped from stack
- Incremented by 1 whenever data is pushed on the stack
- Neither incremented nor decremented a result of PUSH and POP operation

** **

** **

(101)x + (110)7 = (101)8 + (29)16

If the present state QA QB of the counter is QA = 1 & QB = 0, the next state of the counter will be

- The instruction LDA 0805H is used to input a data from an I/O device. Choose the correct statement
- It is possible only if device is interfaced using memory mapped I/O
- It is possible only if device is interfaced using I/O mapped I/O
- Instead of LDA 0805H, the instruction STA 0805H should be used
- only IN PORT instruction can be used in 8085 A mp.
- The macro RTL implemented by INR M in 8085 A microprocessor is
- (M)¬ (M) +1
- (H,L)¬(H,L) + 1
- M(H,L) ¬M(H,L) +1
- (H) ¬ (H) + 1, (L) ¬ (L) +1
- In an 8085 A microprocessor when INTR interrupt, becomes active, the control will be transferred to
- 0024 H memory location
- 003C H memory location
- anywhere in the memory decided by the interrupting device
- 0034 H memory location
- In an 8255 programmable peripheral interface both the groups are programmed in made ‘0’. The possible number of combination in which the ports can be programmed is
- 16
- 4
- 3
- 2
- The meaning of direct addressing mode is
- The address of operand is available in register pair
- The address of operand is available in PC
- The data is directly available in the instruction itself
- The address of the operand is available in the instruction itself.
- The schematic symbol shown in following Fig. Q. 65 is that of
- Zener diode
- Esaki diode
- Varistor
- Varactor
- The V-I characteristic shown in Fig. Q. 66 is that of
- PN junction diode
- Tunnel diode
- Zener diode
- Varactor
- In a four variable V-K Map shown in Fig. simplified expression for X is
- In following circuit assuming voltage drop of LED as 2 V, the LED current when transistor is saturated will be
- 12 mA
- 9.7 mA
- 6 mA
- 5.8 mA

** **

** **

** **

- In the following circuit the collector voltage VC is (assume VBE = 0.7 V)
- -17.4 V
- 5.6 V
- 12.3 V
- 17.4 V
- From the following V-K map the simplified expression for Z is
- The method of absolute measurement of resistance is
- Ohm method
- Potentiometer method
- Lorenz method
- Rayleigh method
- The instrument which gives the value of the quantity to be measured in terms of instrument constants and its deflection is called the
- absolute instrument
- secondary instrument
- recording instrument
- integrating instrument
- The current passing through a resistor of (50±0.2)W is (4.0±0.02)A. The limiting error in the computed value of power will be
- 0.2 %
- 0.4 %
- 0.9 %
- 1.4 %
- The coil of an instrument has 40 turns. The mean length of the coil is 25 mm and the axial length of the coil is 20 mm. If the flux density is 0.1 T and the coil current is 20 mA, the torque on the moving coil will be
- 40×10–6 N-m
- 20×10–6 N-m
- 40×10–3 N-m
- 20×10–3 N-m
- In thermocouple element, heat energy transferred to the hot junction is converted to electrical energy by
- Johnson’s effect
- Seebeck effect
- Hall effect
- Faraday’s effect
- The scale of dynamometer type instrument marked in terms of RMS value would be
- uniform throughout
- non-uniform, crowded near full scale
- non-uniform, crowded at the beginning
- non-uniform, crowded around mid-scale
- The harmonic distortion percentage is accurately measure with
- V.T.V.M.
- An oscilloscope
- Harmonic distortion meter
- Square wave generator
- A thermometer has a time constant of 3.5 s. It is quickly taken from a temperature 0oC to water bath at 100oC. What temperature will be indicated after 1.5 s?
- 100oC
- 50oC
- 35oC
- 15oC
- A digital voltmeter employees an ADC which requires a start pulse, uses an analog comparator and has a relatively fixed conversion time independent of applied voltage. The ADC is
- digital ramp converter
- dual slope converter
- successive approximation converter
- flash type

- In measurements made using Q-meter, impedance elements should be connected in
- star
- delta
- series
- parallel
- The measured values of iron losses of a magnetic specimen are 15 W and 25 W at, 40 Hz and 60 Hz respectively at constant flux density. The respective hysteresis and eddy current losses at 50 Hz are
- 14.584 W and 5.208 W
- 7.5 W and 12.5 W
- 5.208 W and 14.548 W
- 5 W and 10 W
- The most common and best bridge method for precise measurement of inductance over a wise range is
- Maxwell’s
- Hay’s
- Wien
- Anderson
- The AC bridge that can be used for accurate determination of excitation frequency is
- Wien bridge
- Schering bridge
- Anderson bridge
- De Sauty bridge
- A thermo-couple arrangement is to be used to measure temperature in the range of 700-800oC. Point out the pair that would be most suitable for this application
- Copper-constantan
- Chromel-alumel
- Platinum-platinum rhodium
- Iron-constantan
- Rotameter is employed for measuring
- flow
- rotation
- specific gravity
- viscosity
- Consider the following statements regarding the stability of a control system
- Gain margin and phase margin are negative
- Gain margin and phase margin are positive
- All roots of characteristic equation must lie in left half of s-plane
- Gain margin is positive and phase margin is negative
- 1 and 3 are correct
- 1 and 2 correct
- 2 and 3 are correct
- 3 and 4 are correct
- In the feedback system shown below, if the steady state error for a step input is 0.05, then the value of K is
- 0.05
- 0.95
- 1.9
- 19
- Match List I with List II and select the correct answer using the codes given below the lists:
- 4 1 2 3
- 3 4 2 1
- 1 3 2 4
- 1 3 4 2

Out of these statements

** **

**List I (Location of poles on s-plane)**

**List II (Impulse Response)**

__Codes:__

A B C D

- The Nyquist plot for a control system is shown in Fig. Q.89. The Bode plot of |G| for the same system will be
- A unity feedback second order control system is characterized by
- peak overshoot
- damped frequency of oscillations
- setting time
- rise time
- The second order system X = AX has . The value of its damping factor x and natural frequency wn are respectively
- 0.5 and 1
- 1 and 1
- 0.707 and 2
- 1 and 2
- A negative unit feedback system has forward path transfer function as Ks/(s2+2s+25). The break in point(s) of root locus occur at
- s=5
- s=-5
- both A & B
- s = 25
- In an electrical analog of mechanical system of rotational motion, using torque-voltage analogy, inertial and viscous damper are respectively analogous to
- Inductance and capacitance
- Capacitance and resistance
- Inductance and resistance
- Capacitance and inductance
- The characteristic equation of a feedback system is given by
- 0 £ K £ 40
- 0 £ K £ 10
- 0 £ K £ ¥
- 0 £ K £ 20
- The eigen values of the matrix are
- (a+1), 0
- a, 0
- (a-1), (a-1)
- 0, 0
- A first order linear system is initially relaxed. For a unit step signal u(t), the response of the system is
- 3(1-e-3t) .u(t)+ e-3t. d(t)
- (1-3e-3t) .u(t)
- 3(1+e-3t) .u(t)
- 3.u(t)
- Consider the following statements regarding the non linear system
- dead zone can be classified as single valued non-linearity
- hysteresis and backlash can be classified as double valued non-linearity
- Coulomb friction can be classified as double valued non-linearity
- 1 and 3 are correct
- all three are correct
- 1 and 2 are correct
- 2 and 3 are correct
- Consider the system
- d1 > 0, b2 > 0, b1 and d2 can be anything
- d1 > 0, d2 > 0, b1 and b2 can be anything
- b1 > 0, b2 > 0, d1 and d2 can be anything
- b1 > 0, b2 > 0, d1 < 0 and d2 can be anything
- The semilog plot of gain characteristic (BODE plot) of a network is shown in the Fig. Q.99.
- 20 rad/sec
- 30 rad/sec
- 40 rad/sec
- 25 rad/sec
- The pole-zero configuration of a phase lead compensating network is given by

** **

where

J = moment of inertia

B = viscous damping coefficient

K = system gain

The transient response specification which is not affected by variation of system gain is the

For this system, stable closed loop behavior can be ensured when gain K is such that

(1-e-3t), t > 0

If a signal 3. u(t) + d(t) is applied to the same initially relaxed system, the response will be

Out of these statements

.

The condition for complete state controllability and complete observability is

The gain cross over frequency wc is

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