UPRVUNL'21 EE: Daily Practices Quiz 11-Sep-2021

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 11-Sep-2021

Each question carries 1 mark.
Negative marking: 1/4 mark
Total Questions: 06
Time: 06 min.

Q1. Spacers are provided between adjacent coils…
(a) To provide free passage to the cooling oil
(b) To insulate the coils from each other
(c) Both a and b
(d) None of the above

Q2. The following protection is not used in power transformer…
(a) Earth fault protection
(b) Inter-turn protection
(c) Reverse power flow protection
(d) Over fluxing protection

Q3. A current transformer must at all times have….
(a) A secondary load
(b) Short circuited secondary
(c) Either a or b
(d) None of these

Q4. Under heavy loads, transformer efficiency is comparatively low because
(a) Secondary output is much less as compared to primary input
(b) Voltage drops both in primary and secondary become large
(c) Iron loss is increased considerably
(d) Copper loss becomes high in proportion to the output

Q5. The short circuit test in a transformer is used to determine……
(a) Eddy current
(b) Hysteresis loss
(c) Copper loss at any load
(d) Iron loss at any load

Q6. Ferranti effect happens in a transmission line when line is
(a) short and unloaded
(b) long and unloaded
(c) short and loaded
(d) none of the above

SOLUTIONS
S1. Ans.(a)
Sol. Spacers are provided between adjacent coils to provide free passage to the cooling oil.
In Power transformers, the coils shall be supported between adjacent sections by insulating spacers and bracers. Bracings and other insulation used in the assembly of the windings shall be arranged to ensure a free circulation of the oil and to reduce hot
spots in the windings.

S2. Ans.(c)
Sol. The reverse power relay is a directional protective relay that prevents power from flowing in the reverse direction. The relay is used in installations where a generator runs in parallel with the utility or another generator so as to prevent power from the bus bar or another generator from flowing back to the active generator when its output fails.
Restricted earth fault protection is provided in electrical power transformer for sensing internal earth fault of the transformer.
Over fluxing protection is recommended for generator transformers in power stations.
Transformers which may be exposed to over voltage, Overexcitation protection should also be included.

S3. Ans.(c)
Sol. As we know that Current Transformers (CTs) are always used with secondary winding connected with Ammeter, Relays or Wattmeter Coils. A precaution which shall always be taken is that Never open the secondary winding circuit of a Current Transformer while its Primary Winding is energized.

S4. Ans.(d)
Sol.
At high load, copper loss increases as P_c α I^2 (Where; I=load current)
Due to increased copper loss, efficiency decreases.

S5. Ans.(c)
Sol. SC test of transformer:
Used to determine copper loss or ohmic loss
LV side short circuited
Instruments kept on HV side
Also determines equivalent resistance and leakage reactance

S6. Ans.(b)
Sol.
Ferranti effect occurs for medium and long transmission line.
Due to Ferranti effect, receiving end voltage is more than sending end voltage.
It occurs at light loaded or no-load condition.