ABB

ABB VADODRA PAPER 2 MAY,2004

TECHNICAL PAPER-40 QUESTION, 45- MINUTES 

(1)in a ckt. We r giving voltage of 50 Hz as well as 60. then what will be  the resultant frequency. 
(a)less than 50 (b)more than 60(c)in between 50 & 60 
(d)none..........according to our conclusion answer will be none because if  we apply two frequency component resultatnt frequency we can not say with  such an ease.U should confirm the answer 

2.In a ckt a single resistor is connected across a d.c. source, what will be  the effect on current in first resistor if we connect one more resistance in  parallel with earlier one.... 
Answer.. no change since it is a parallel combination. 

3.why we don,t like flashover in transmission line (t-line)-  (a ) it may create earth fault(b )it reduces the life of insulator..... 
Read something about flashover & puncture. 

4.total no of strands in a acsr conductor is 81, then what is the no. of  conductor in its outer layer....(a)36 (b)18 (c)24.......Also read some more  on acsr. 

5.Two questions based on p.u. calculation like , p.u. calculation is given  with respect to some old base and u have to calculate it with reference to  new base.  (new resistance/old)=(mva new /mva old)*(old voltage/new voltage)2. 

Other question is based upon transfer of p.u calculation in transformer i.e.  how base changes when we we move from primary to secondary or like wise.read  some more on p.u calculation. 

6.which table is referred for sag calculation- 
(a)stringing chart......answer 

7.in a R-L ckt a ac voltage is applied , such that instantaneous power is  negative for 2ms, then what will be the power factor. 
(a) 9 deg, (b) 18 deg, (c) 36 Deg...........(I don't know the correct ans) 

8. In an incandescent lamp 
(a) luminous intensity is more than non-luminous intensity 
(b) ,, ,, ,, less ,, ,, ,, 

Ans: Since efficiency is less than 100%, hence ans is (b), u should confirm 
it further. 

9. In which motor no-load to full-load diff. is lowest 
(a) series motor, (b) shunt motor, (c) Compound motor 
Ans: (b) 

10. In a 60Hz induction motor full load speed is 850 rpm then what is the  Synchronous speed. (a) 900 rpm, (b) 950 rpm, (c) 1600 
rpm....................Ans: (a) 

11. A sync. Motor is running at synch. Speed, if al of sudden D.C.  excitation is removed, then 
(a) it will rotate at slip speed, (b) it will stop, (c) it will continue to  rotate at sync. Speed 
Ans: (a), because actually it will acts as Induction motor. 

12. A transmission line is designed for 50Hz, 440KV. If we want to transfer  power at 60Hz, 440 KV, then the power transfer capability will 
(a) decrease, (b) Increase, (c)None 
Ans: (a) ...as P=( |Vt| |Ef| sin (delta) ) / X, where (delta) is torque 
angle. 

13. Increased rotor resistance in rotor ckt of induction motor is related  with 
(a) high starting torque, (b) more speed variation,.....................Ans: 
(a) 

14. In the formulae E = 4.44 f N Ô, Ô is 
(a) Avg value, (b) Rms value, (c) Maximum value.....................Ans: 
(a)...[confirm it] 

15. Voltage & current in a ckt is given by V= V1+j V2 and I= I1 +j I2, then rms power is 
.......(refer book by Edministrator on NETWORK ..) 

16. Input impedence of MOSFET is 
(a) more than BJT........(Ans) 

17, 18. Remember truth table of AND, NOR, NAND, OR, EX-OR ETC... 

19. Conversion of Binary number into Equivalent decimal No. 

20. Megger is used for the measurement of (a) Insulation resistance, (b) 
Conductor resistance.............Ans: (a) 

21. Form factor for sinusoidal as well as DC 

22. Formulae of Regulation (Vs- Vr)* 100/ Vr, then transmission line is 
(a) short transmission line, (b) long, (c) medium...................Ans: (a) 

23. Improvement in power factor reduces 
(a) power consumed by consumer, (b) power generation, (c) both a & 
b...........Ans: (c) 
[Confirm it] 

24. Read about field test of Series Motor... 

25. No-load test for Synchronous motor, the graph is drawn 
(a) stator open ckt emf Vs field 
current.......................................(Ans: a) 

26. An AC voltage of 50Hz is impressed in a resistive ckt, the oscillating  power has a frequency (a) 50 Hz, (b) 100, (c) no oscillating power is there  in resistive ckt......Ans: (a) 
27. Insulation used in transformer ___________leakage flux. 
(a) increases, (b) decreases............Ans: (b) 

28.After rain what happens to Insulator (a) break-down strength of Insulator  decreases, (b)Arch length reduces, ..........Ans: (b).....[Confirm it] 

29.Diversity factor helps to ............(what ?)  [Read diversity factor, load factor, Reserve capacity factor in depth, with 
calculation] 

30. Why capacitance is shown as a Shunt element in analysis of transmission  line 
(a) it is between Conductor & earth, (b) because Admittance is used for  calculation of capacitive reactance........................Ans: (a) 

31. B-R-Y sequence is followed in three phase system, if phase voltage in  B-phase is Vm sin 100, then the phase voltage in R-phase would be (a) Vm  sin (-20)
Ans:(a) 
32. In a particular ckt I = Im Sin (wt -270) and V = Vm Sin wt, then type of  ckt is (a) pure resistive ckt
[Ans] 
33. In a L-R ckt energy lost = 2000 W, energy conserved = 500W, then what is  the time constant...........Ans: time constant = L/R = 0.5 

34. In electro-dynamometer A'meter & wattmeter the type of scale is 
Ans:Non-uniform 
35. For the same current carrying capacity corona loss of ACSR will be  ________than copper conductor.
  (a) more, (b) less, (c) equal.
Ans:(b) 
36. A R-C ckt , supplied with DC, a bulb is connected across the Capacitor,  then what happens to the illumination, if we change the capacitance. 
Ans: No change at all 

37. Read about surge impendence of over-head and under-ground cable, Surge  impedence formula = sqrt(L/C) 

[N.B] We are not mentioning the options in sequence, and do not think  that ans for the most questions is option (a). Read all options very  carefully as all are very close to each other. 

QUANTITATIVE PAPER + PCM paper 

45 Questions ---------45 minutes 
1. About 10 quanti questions ( based on Mixture, Work etc. of very easy  type) 
2. What is GDP ? 
3. Vector algebra, codition for Co-planer vector etc. 
4. Gravitation, geo-synchronous satellite( it's hight, orbit , radius 
etc.), escape velocity, how g (gravitational accln) varies, about  gravitational potential. 
5. Basic electricity and Magnetism----Biot-savart law, current carrying  conductor properties. 
6. Nuclear physics, Bohr's constant, and Other theories related . 
7. Problem based on VIBGYOR , how wave length and frequency is varying. 
8. Questions based on Plank's Theory, E =hv 
9. V=u + at , V2=u2 + 2as and W = mgh  questions based on above theory 
10. Faraday's laws of electrolysis, m = Zit 
11. Heat conduction problem. 
12. Co lour-coding of resistor (BBROYGBVGW) 
13. How velocity of light changes in different medium while frequency remain  unchanged. 
14. statistics , calculation of mode, co-efficient regression (3-4  Questions) 
15. f(x) = Sin x + Cos x, find the maximum value of the function.......Ans:  sqrt (2) 
16. Formulae for parallel plate capacitor and force between plates.