UPRVUNL 2021, UPRVUNL ELECTRICAL

UPRVUNL JE Recruitment 2021:

A total of 196 vacancies were released by the UPRVUNL Recruitment 2021. The selection process will be based on the written examination which will be divided into two parts – Part I and Part II. Part I will have 150 objective-type questions from the syllabus for the Diploma Engineering in the relevant branch. While Part II will have 50 objective-type questions comprising General Knowledge, General Hindi, and Reasoning.

UPRVUNL’21 EE: Daily Practices Quiz 03-Sep-2021

Each question carries 1 mark.

Negative marking: 1/4 mark

Total Questions: 06

Time: 08 min.

Q1. In a torque(T)-slip(s) characteristics of 3-phase squirrel cage induction motor, at maximum torque:
(a) dT/ds is maximum
(b) dT/ds is zero
(c) ds/dT is zero
(d) slip is maximum

Q2. At a full-load of a transformer, the iron loss and copper loss are 3000 W and 4000 W respectively. Then total loss at maximum efficiency is:
(a) 7000 W
(b) 8000 W
(c) 6000 W
(d) 4000 W

Q3. Two 3-phase transformers cannot be operated in parallel, if their:
(a) KVAs are different
(b) % Impedances are different
(c) Voltage ratios are different
(d) Phase sequence are different

Q4. …………. opposes the change in circuit voltage.
(a) Resistance
(b) Inductance
(c) Capacitance
(d) Inductive reactance

Q5. Which one of the following is the best method of measurement of temperature of hot bodies radiating energy in visible spectrum?
(a) Thermocouple
(b) Barometer
(c) Thermopile
(d) Optical pyrometer

Q6. The brake test for the determination of efficiency of a DC machine is………….
(a) A regenerative method
(b) A direct method
(c) An indirect method
(d) None of the above

SOLUTIONS
S1. Ans.(b)
Sol. The values of maximum torque and the slip at that torque, can be obtained by using dT/ds=0.
So, when slip s = R2 / X2, the torque will be maximum and this slip is called maximum slip S_m and it is defined as the ratio of rotor resistance to that of rotor reactance.

S2. Ans.(c)
Sol. For maximum efficiency; copper loss=iron loss
Or, total loss= 2×iron loss=2×3000=6000 W.

S3. Ans.(d)
Sol. Condition for Parallel Operation of Transformer:
Some of these conditions are convenient and some are mandatory.
Convenient conditions:
Same voltage ratio and turns ratio (both primary and secondary voltage rating is same)
Same percentage impedance and X/R ratio.
Identical position of tap changer
Same KVA ratings
Mandatory conditions
Same phase angle shift (vector group are same)
Same frequency rating
Same polarity
Same phase sequence.
NOTE: When the convenient conditions are not met, paralleled operation is possible but not optimal.

S4. Ans.(c)
Sol. Capacitor resists a sudden change in the voltage.

S5. Ans.(d)
Sol. When temperature being measured is high and there is no physical contact with the process to be measured, the thermal radiation methods like optical pyrometer are used.

S6. Ans.(b)
Sol.
Brake test is also known as direct method of testing of dc machines.
It is suitable for small dc machines.