ABB Placement Paper

Company: Abb Technologies

Paper: ABB Placement Paper Held On 2 May 2004 At Vadodara (Technical)

(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 resultant 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.

Ans:- 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…..

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.

6.which table is referred for sag calculation-

Ans:- stringing

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

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.

(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)

15. Voltage & current in a ckt is given by V= V1+j V2 and I= I1 +j I2, then rms power is

16. Input impedence of MOSFET is

Ans:- more than BJT

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

18. What is Truth Table Explain?

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)

25. No-load test for Synchronous motor, the graph is drawn

Ans:- stator open ckt emf Vs field current

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)

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

Ans:- Vm sin (-20)

32. In a particular ckt I = Im Sin (wt -270) and V = Vm Sin wt, then type of ckt is

Ans:- pure resistive ckt

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