BRAIN BRUSH-UP ACADEMY,PUNE
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BRAIN BRUSH-UP ACADEMY
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ANALOG & DIGITAL ELECTRONICS FOR AE (MAHADISCOM)
TOTAL QUESTIONS: 25 TOTAL MARKES: 55
Note : A) Each question carry 2.2 marks
B) ¼ th negative marks for each wrong answer
Power system for portal full length test for portal students
Test no-1
Question no -1
In a thermal power plant, ash is collected in
(A) mills
(B) hoppers
(c) bunkers
(D) boiler
Ans -b
Question no -2
The average life of neutrons after they decay is
(A) 1 sec
(B) 10 sec
(C) 100 sec
(D) 1000 sec
Ans -d
BRAIN BRUSH-UP ACADEMY,PUNE
Question no -03
The operating time of instantaneous relay is
(A) 0.001 sec
(B) 0.01 sec
(C) 0.1 sec
(D) 1 sec
Ans-b
Question no-04
Stringing chart is useful for
(A) the design of tower
(B) the design of insulator string
(C) finding the sag in the conductor
(D) finding the distance between the towers
Ans -C
Ans explaination
Question no-05
BRAIN BRUSH-UP ACADEMY,PUNE
The self GMD method is used to evaluate
(A) inductance
(B) capacitance
(C) inductance and capacitance
(D) resistance
Ans -a )Self gmd only in case of the inductor
Question no-06
The velocity of travelling wave through a cable of relative permitivity 36 is
(A) 3 x 108 m/sec
(B) 2 x 108 m/sec
(C) 0.5 x 108 m/sec
(D) 108 m/sec
Ans - C
3×108 m/sec 3×108
v= = = 0.5 × 108 m/sec
√μr 6
Question no-07
The coefficient of reflection for current wave is
(A) 1
(B) 2
(C) -1
(D) 0
Ans -c
BRAIN BRUSH-UP ACADEMY,PUNE
Question no-08
A relay has a rating of 5 A, 2.2 sec IDMT and a relay setting of 125% TMS = 0.6. It is connected to a
supply circuit through a C.T. 400/5 ratio. The fault current is 4000 A. The operating current of the relay is
(A) 6.25 A
(B) 5 A
(C) 8 A
(D) 2.2 A
Ans -a
Operating current of relay = relay setting × C T secondary
12.5
= × 5 = 6.25 A
100
Question no-09
Load flow studies involve solving simultaneous
(A) linear algebraic equations
(B) non linear algebraic equations
(C) linear differential equations
(D) non linear differential equations
Ans - b
Question no-10
A 12 bus power system has 3 voltage controlled buses. The dimensions of the Jacobian matrix will be
(A) 21 x 21
(B) 21 x 19
(C) 19 x 19
(D) 19 x 21
Ans-c
BRAIN BRUSH-UP ACADEMY,PUNE
Question no-11
The cost function of a 50 MW generator is given by (pi is the generator loading)
F(pi) = 225 + 53pi +0.02pi2
When 100% loading is applied, the Incremental Fuel Cost (IFC) will be
(A) Rs. 55 per MWh
(B) Rs. 55 per MWh
(C) Rs. 33 per MWh
(D) Rs. 35 per MWh
Ans -c
δfi δ
λ= = (225 + 53pi + 0.02p2i )
δpi δpi
= 0 + 53 + 0.04 pi
Fuel cost – Rs/hr
IFC ⇒ Rs/MWh
⇒ λ = 53 + 0.04 × 50 = 55 Rs/MWh
Question no-12
The ABCD constants of a 3 phase transmission line are
A =D=0.8L10
B=170 L850 Ω
C = 0.002L 90.40 mho
The sending end voltage is 400 KV. The receiving end voltage under no load condition is
(A) 400 KV
(B) 500 KV
BRAIN BRUSH-UP ACADEMY,PUNE
(C) 320 KV
(D) 117 KV
Ans-b
Vs = AVR + BIR Nc IR = 0
Vs 400 kv
Vc = AVR ⇒ VR = A
= 0.8L1
= 500 kvLi
Question no- 13
Bundled conductors are used for EHV transmission lines primarily for reducing the
(A) Surge impedance of the line
(B) I2R losses
(C) Voltage drop across the line
(D) Corona loss
Ans-d
𝑉𝑑 = 𝑐𝑟𝑖𝑡𝑖𝑐𝑎𝑙 𝑑𝑖𝑠𝑟𝑢𝑝𝑡𝑖𝑣𝑒 𝑣𝑜𝑙𝑡𝑎𝑔𝑒 = 𝑟. 𝑔.
𝑑
𝑉𝑑 = 𝑟. 𝑔. ln ( )
𝑟
𝑟 𝑓+25 2
𝑟 ↑ 𝑣𝑑 ↑: 𝑃𝐿 = 242.5 × √𝛼 . ( 𝛿
)× (𝑣𝑝 − 𝑣𝑑 ) 𝐾𝑣/𝑘𝑚/𝑝ℎ
𝑟 ↑→ 𝑣𝑑 ↑→ 𝑝𝑙 ↓
Question no-14
If all the sequence voltages at the fault point in a power system are equal, then the fault is
(A) three phase fault
(B) line to ground fault
(C) line to line fault
(D) double line to ground fault
Ans-d
BRAIN BRUSH-UP ACADEMY,PUNE
Question no-15
Severe over voltages are produced during arcing faults in a power system with the neutral
(A) isolated
(B) solidly earthed
(C) earthed through a low resistance
(D) earthed through an inductive coil
Ans-a
Question no-16
Auto reclosing is used in case of
(A) lightning arrester (C) air blast C.B
(B) bulk oil C.B (D) minimum oil C.B
Ans -C
Question no-17
A transmission line has 1 P.U impedance on a base of 11 KV, 100 MVA. On a 55 KV, it will have a P.U
impedance of
(A) 1 P.U
(B) 0.2 P.U
(C) 0.04 U
(D) 0.1 P.U
Ans-c 0.04u
Question no-18
A 50 Hz, 4 pole turbo alternator rated at 20 MVA, 13.2 KV has an inertia constant H = 4 KW sec/KVA. The
K.E. stored in the rotor at synchronous speed is
BRAIN BRUSH-UP ACADEMY,PUNE
(A) 80 KJ (B) 80 MJ (C) 40 MJ (D) 20 MJ
Ans-b
Question no-19
Under no load conditions, the current in a transmission line is because of
(A) capacitance effect
(B) corona effect
(C) proximity effect
(D) back flow from earth
Ans -a
Explanation
Under no load condition, current flows due to capacitance of transmission line. This effect is known as
ferranti effect.
Hence (A) is correct option.
Question no-20
Equivalent r model is quite suitable for analyzing the performance of transmission line of
(A) 50 km length
(B) 150 KM length
(C) 250 KM length
(D) All of the above
Ans -c explanation
For long transmission line(length 250 km or more than that) nominal -π method is more accurate and
efficient. Hence (C) is correct option.
Question no-21
BRAIN BRUSH-UP ACADEMY,PUNE
Guard ring in transmission lines is used to
(A) reduce the earth capacitance of the lowest unit.
(B) increase the earth capacitance of the lowest unit.
(C) reduce the transmission line losses.
(D) none of the above
Ans-a explanation
Guard ring in transmission lines is used to minimize the earth capacitance of the lowest unit. Hence (A)
is correct option
Question no-22
Consider the following statements :
Addition of lumped capacitances in parallel to a loss-free transmission line increases
1. characteristic impedance
2. propagation constant
3. system stability
4. charging current
Which of these statements are correct?
(A) 1 and 3
(B) 2 and 4
(C) 2, 3 and 4
(D) 1, 2 and 4
Ans -b
explanation
Let the inductance is L and capacitance is C. then
L 1
Characteristic impedance Zc = √C ⇒ Zc α
√C
so addition of lumped capacitance in parallel does not increase the characteristic impedance.
Propagation constant γ = jω√LC ⇒ γα√C
BRAIN BRUSH-UP ACADEMY,PUNE
Increase in capacitance also increases propagation constant
Charging current Ic = jωCV ⇒ Ic α √C
Therefore addition of lumped capacitance increases charging current.
Hence (B) is correct option.
Question no-23
Zero-sequence currents shall flow
(A) when SLG and LG fault occurs
(B) all transformer are star-star type
(C) when return path is available
(D) when the neutral is only reactance grounded
Ans -C
Question no-24
How many relays are used to detect inter phase fault of a three-line system?
(A) One
(B) Two
(C) Three
(D) Six
Ans -C
We need three over-current relays as phase-fault relays to detect phase fault error of a three-line
system.
Hence (C) is correct option.
Question no-25
Which of the following statement is true ?
BRAIN BRUSH-UP ACADEMY,PUNE
A fuse is
(A) always connected in series with the circuit.
(B) always connected in parallel with the circuit.
(C) normally connected in series with the circuit.
(D) normally connected in parallel with the circuit.
Ans-a
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