UPPSC-LECTURER’21 EE: Daily Practices Quiz 10-Dec-2021

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Exam Date: 22/12/2021

UPPSC polytechnic lecturer QUIZ: EE

UPPSC-LECTURER’21 EE: Daily Practices Quiz 10-Dec-2021

Each question carries 3 marks.
Negative marking: 1 mark each or 1/3rd
Total Questions: 06
Time: 08 min.

Q1. Which of the following happens in Kando system?
(a) Three-phase A.C. is converted into D.C.
(b) Single phase A.C. is converted into D.C.
(c) Single phase supply is converted into three phase system
(d) None of the above

Q2. Generally short circuit fault in a transformer is protected by:
(a) MHO relay
(b) Impedance relay
(c) Reactance relay
(d) Merz price protection

Q3. If holding current of a thyristor is 2 mA then latching current should be
(a) 0.01 A
(b) 0.002 A
(c) 0.004 A
(d) 0.009 A

Q4. For the equation, s^3-4s^2+s+6=0 the number of roots in the left half of s-plane will be
(a) Zero
(b) One
(c) Two
(d) Three

Q5. Schering bridge is used to measure
(a) Dielectric loss
(b) The inductance
(c) Low resistance
(d) Mutual Inductance

Q6. The maximum efficiency of a Full-wave rectifier is …………………
(a) 40.6 %
(b) 81.2 %
(c) 50 %
(d) 25 %

SOLUTIONS

S1. Ans.(c)
Sol. Kando System:
In this system, single-phase 16-kV, 50 Hz supply from the sub-station is picked up by the locomotive through the single overhead contact wire. It is then converted into 3-phase ac supply at the same frequency by means of phase converter equipment carried on the locomotives. This 3-phase supply is then fed to the 3-phase induction motors.

S2. Ans.(d)
Sol. Merz price differential protection is used to protect the transformer from internal short circuit, Internal ground faults and inter turn shorts. Transformer is a static device. Merz price differential protection is nothing but a percentage differential protection Which works under the principle of circulating current scheme.

S3. Ans.(c)
Sol. given that holding current= 2 mA=0.002 A
And we know that, the value of latching current is approximately 2 to 3 times to that of holding current.

S4. Ans.(b)
Sol. s^3-4s^2+s+6=0

by R-H criterion:

s^0 6
Here there is two sign changes( s^3 to s^2 and s^2 to s^1).
So, number of roots in RHS=2
∴Number of roots in LHS=3-2=1.

S5. Ans.(a)
Sol. Schering bridge is used to measure dielectric loss. It is an AC bridge circuit that is used for measuring the insulating properties of electrical cables and equipment. It has the advantage that the balance equation is independent of frequency.
Maxwell bridge is used to measure the value of unknown inductance.
Heaviside bridge is used to measured mutual inductance in terms of a known self-inductance.
Kelvin bridge is used to measure the value of low resistance.

S6. Ans.(b)
Sol.

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