Jegadesh sankar

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Comprehension Q&A(Updated)

Posted by jakku on November 5, 2006

hi !

After a long long time here is a post that is useful for Electrical and Electronics engineers.I have comp exam on 9th of this month. Got some question bank from class groups. It is really intresting to solve. Now i have worked some MCV sir questions and here it is….

NOTE: The answers given here are only up to my knowledge. There may be some wrong answers. So please reply if there is any wrong entry.

UPDATE : I have created a new page for this comprehension questionjs and answers which contains more Q&A. Check here.


1. Which type of indicating instrument MI,PMMC,Rectifier,Electrodynamometer) would you choose to measure the average value of a voltage having periodic sawtooth waveform? Give reason for your choice.

2. Why polarity of connection is not important while measuring dc currents and
voltages using a MI instrument?

The deflecting torque is directly proportional to the square of the RMS value of the operational current. So the deflecting torque is unidirectional whatever may be the direction of operational current.

3. A 20A dc current is suddenly passed through a PMMC ammeter with a wrong
polarity of connection. What will be the consequence if the range of the meter is (i) 5A and (ii) 25A?

4 It is required to measure the rms value of the square wave output voltage of an .astable multivibrator . Can you use a rectifier type voltmeter? Give reason.

No. Rectifier type of instruments are calibrarated in terms of RMS values of sin current and voltage.

5. What is the most important restriction is using rectifier type instruments in measuring currents and voltages?

It can be used only to measure sinusoidal current and voltage. Effect of rectifier resistance and capacitance

6. Can you use a MI voltmeter to measure the rms value of a sinusoidal voltage having a frequency of 5000Hz? Give reason.

No. MI instruments are suitable for measuring upto 125 hz. Change in frequency may cause error due to changes in reactance of the working coil.

7. Can you use a rectifier type ammeter to measure the rms value of a sinusoidal current having a frequency of 1Hz? Give reason.

8. Repeat Question No.7 with a MI ammeter.

Not suitable. Reason same as given in question no 6. operation range in 25-125hz

9. Repeat Question No.6 with a rectifier voltmeter.

10. It is required to measure accurately the rms value of a voltage having non-sinusoidal periodic waveform. Which type of meter is to be recommended?


11. What is a True RMS meter? Why a rectifier type meter is not a TRMS meter?

RMS meter are used to measure the complex waveforms most accurately. Rectifier type meter is not a true RMS meter because it is calibrated only for pure sin wave.

12. What is a transfer instrument? Why it is needed?

A transfer instrument is one that can be calibrated with a D.C source and then used to measure A.C without any modification

13. What are the advantages of a DMM compared with an analog multimeter? What is the purpose of providing a bar graph on DMMs?

Advantages of DMM

– High accuracy

– High input impedance

– Smaller in size

14. What is a 3 ½ digit display DMM? What is a 3 ¾ digit display DMM?

What is a 4 ¾ digit display DMM with a 50000 count?

15. What is an intelligent instrument?

16. Why one has to pay due attention in choosing a dynamometer type wattmeter for measuring power in a low-power factor circuit?

The wattmeter will read high value at lagging pf loads and low in leading pf loads.

This is due to pressure coil inductance.

17. What is the A/D conversion technique which can be made immune to power supply hum? How it can be accomplished?

Dual slope

18. What is the A/D conversion technique, which is fastest?

Flash type A/D

19. Mention an A/D conversion technique, which has a constant conversion time.Is there any advantage with constant conversion time? Explain.

20. What is the A/D conversion technique more often used in DMMs?

Dual slope method is used.

23. Ammeters should have as low resistance as possible and voltmeters as high resistance as possible. Explain this statement by means of examples using necessary circuit diagrams.

Ammeters are connected in series in the circuit. The power lossin the circuit is I square R. Therefore ammeter should have low resistance.

Voltmeter are connected in parallel with circuit. Power loss in the circuit is Vsquare/R. So voltmeter should have high resistance

32. What is an ELCB? What purpose does it serve?

Earth leakage circuit breaker. This primarily used in household premises to protect the personnel handling the power equipments. When the current through the person is more than a specific value say 40ma or so the circuit breaker trips isolating the power supply and saving the life of the person. It trips instantaneously.

40. Which is the fastest A/D conversion technique? Which is the slowest one?

Fast : Flash type

Slow : Dual slope

41. What is the A/D conversion technique which can be made immune to power supply hum? Explain your answer.

Dual slope


Posted in 6.11.06 NEW
Tom i have Lab. So caunt spend much time in comp. Here are some questions and answers. Will keep posting Tom also

<!–[if !supportLists]–>100. <!–[endif]–>What is the single purpose of transmitting power at high voltages?

Due to lot of advantage. Reduced conductor dia and volume due to less current in HV lines. I square loss is reduced because of less current.

101. A power system is operated as an interconnected system rather than isolated

blocks. Why?

Power system are operated in interconnected grid system due to the following advantages.

<!–[if !supportLists]–> <!–[endif]–>Exchange of peak loads.

<!–[if !supportLists]–> <!–[endif]–>Continuity of supply can be maintained in case of maintenance and failure of any generating stations

<!–[if !supportLists]–> <!–[endif]–>More reliable

102. Industrial consumers who operate their loads at low power factor have to

pay additional charge. Why is the additional charge?

103. Three-phase power is transformed by use of three-phase transformers. However, in large EHV systems, a bank of three single-phase transformers is connected in three-phase arrangement. Why?

For Transformers used In EHV lines, providing insulation is the major problem. If all the three phase windings are kept is a same casing as in the case of three phase transformer, electrical stress is high. So three single phase transformers are use.

104. What are the three pointers to assess the quality of a power system from the consumers’ point of view?

Constant Voltage (No voltage fluctuation )

Continuity of power supply

105. What is a relay? How is this different from a circuit breaker?

Relay is the operating element of the circuit breaker. A C.B responds when relay is operated. For example when there is a over current in the circuit the relay operates and opens the circuit breaker. CB has relays, switches and arc quenching mechanism etc..

106. What are the typical protections employed in transformers used in power system?

Over current protection, Differential protection, Lightning arresters etc. Bucholz relay, Translay relay, overcurrent relay are used.


4 Responses to “Comprehension Q&A(Updated)”

  1. jakku said

    you can also post the questions and answers that you know.
    Just type it and submit.

  2. sharmistha said


  3. […] Top Posts Comprehension Q&A(Updated)Treat for the success of Eupraxia 06Gazzag steals your password?University practicalsHow I started this blog? […]

  4. ethext said

    100$ per click

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