Interview Questions regarding to OHE(Overhead Equipment) Part 1

OHE or Overhead Equipment, interview questions refer to queries commonly asked during job interviews related to the field of railway electrification and overhead power systems. These questions aim to assess a candidate’s knowledge, expertise, and suitability for roles involving the design, maintenance, or operation of electrification infrastructure for trains/railways.  I believe that after reading these question, you can easily crack any challenging OHE interview. This is the first part of the interview question series.

PART – 1

1. ACTM – AC Traction Manual
2. CORE- Central Organization for Railway Electrification
3. RITES- Railway India Technical & Economical Services

4 SCADA- Supervisor Control & Data Acquisition

5. Purpose of neutral section in OHE between two 25 kV, single phase , 50 Htz. Traction

Substation.

To separate the zones, which are fed by the adjacent substation of different phase

6. Normally, power generation & transmission system of the supply authorities are of

Three phase

7. 25 kV traction system needs the supply of

 Single phase

8. Normally, two adjacent 25 kV AC traction sub stations works as in

 Independent

9. The shortest section of OHE, which can be isolated through remote control by TPC is

called.

Sub sector

10. Distance between two consecutive OHE structures is called

Span length

11. In AC traction, span length varies in steps of

4.5 meters

12. Maximum span length in AC traction on tangent track is

72 meter

13. What is the diameter of Register arm dropper

7mm

14. Distance between first dropper and Suspension bracket (Mast)

2.25m

15. Maximum tension length in AC traction is

1500 m

16. In AC traction, maximum permissible tension length in yard :-

2000 m

17. Maximum tension length is restricted upto 1500 m due to

Maintain uniform tension in OHE conductors.

18. At the end of tension length, an overlap is formed due to

To provide smooth passage for pantograph

19. Maximum wind pressure is considered to design OHE structures for Red zone

 150 kgf /sq. m.

20. If OHE structures erected on more than 150 m long bridge, the wind load is considered

according to wind pressure zone for OHE structures

25 % more

21. Maximum wind pressure is considered to design OHE structures for Yellow zone

 112.5 kgf /sq. m.

22. Maximum wind pressure is considered to design OHE structures for Green zone

75 kgf /sq. m.

23. What will be the sag (s) in the conductor? Where, L= span length, T= tension in the

conductor & w = per meter weight of the conductor

s = wL*L /8T

24.Wind load on conductor is calculated by

2/3 (Projected area of conductor x wind pressure)

25. Maximum deflection of mast at contact wire level due to wind pressure, is allowed

60 mm

26. Maximum deflection of mast at top due to load is allowed

80 mm

27. Axial distance between catenary & contact wire at the OHE support, in vertical plane is

called

Encumbrance

28. In AC traction, normal encumbrance at support is

1.4 m

29. At obligatory structure of turnout, It is general practice to give encumbrance

1.4 m. turnout OHE & 0.9 m main line OHE

30. Maximum permissible relative gradient of contact wire in two adjacent span shall not be

greater than on main lines

  1.5 mm /m.

31. Maximum permissible relative gradient of contact wire in two adjacent span shall not be

greater than on sidings

5 mm/m.

32. Change of the height of the contact wire to be achieved very gradually, to avoid

(a) Loose contact between contact wire & pantograph.

(b) Exert excessive pressure on the contact wire by pantograph.

(c) Poor current collection.

33. Maximum permissible gradient of contact wire, when maximum permissible train speed is

more than 100 kmph on main lines

 3 mm/m

34. In AC traction, what will be encumbrance tolerance at support is ( As per RDSO latter

no.TI/OHE/GA/3013 dated 14.05.13

± 50 mm

35. In AC traction, minimum height of contact wire under ROB/FOB from rail level to permit

“C” class ODC

4.92 m

36. In AC traction, height of contact wire at support from rail level (regulated OHE) with 100

mm pre sag in contact wire is

5.60 m

37. At level crossing gate, maximum height of rail height gauge from the road surface is

4.67 m

38. The fittings, which is used to transfer the weight of contact wire to the catenary wire is

called

Droppers

39. Droppers are used for

Leveling the contact wire

40.Droppers are made out of

Hard drawn copper

41.Diameter of in-span dropper in AC traction is

5 mm

42. In AC traction , how many droppers in 72 m span length

9 Droppers

43. In AC traction , how many droppers in 58.5 m span length

 7 droppers

183. All supporting structures of crossing span have to be properly earthed & their

earth resistance should not be more than

         10 ohm

45. In AC traction , distance of 2nd dropper from 1st dropper in 60 m non standard span length

5.25 m

46. Chain droppers are used for smooth adjustment of section insulator, both the pieces of

chain droppers are connected together by P.G. clamp, what is the length of piece of

dropper ?

350 mm

47. Material of AC catenary wire is

 Cadmium copper

48. No. of layers & strands of AC catenary wire is

2 layers & 19 strands

49. Diameter of each strand of AC catenary wire is

2.11 mm

50. Cross section area of AC catenary wire is

65 sq mm

51. Per meter weight of catenary wire is

603 gm

52. Material of 107sq mm wire is

Hard drawn copper

53. Current density of copper (continuous) is

4 amps/sq. Mm

54. Conductivity of cadmium copper in terms of equivalent copper will be

80 %

55. Tensile strength of hard drawn copper is

42 kg /sq mm

56. Tensile strength of cadmium copper is

 63 kg /sq mm

57. Cadmium copper is used in place of hard drawn copper for AC catenary wire, why?

To increase tensile strength of catenary

58. In AC traction, maximum stagger of contact wire on curved track is

300 mm

59. In AC traction, maximum stagger of contact wire on tangent track is

200 mm

60. Maximum stagger is allowed at mid span is

100 mm

61. Contact wire is placed in zig- zag manner in entire span length , why ?

(a) To avoid formation of groove on pantopan strip

 (b) Uniform rubbing of pantopan strip within current collection zone

(c) To avoid breakdown due to formation of groove in pantopan strip

62. The offset of the track centre from the chord joining the two adjacent points at the track

centre is called

Versine

63. Versine “V” is calculated by the formula

Where, L = span length R= radius of curvature of track

 V= L*L / 8R

64. For odd no’s of tracks, versine is measured from

Individually measured for each track

65. Displacement of panto axis (D) , due to super elevation (d) is calculated by –

Where, G= Track gauge (for B.G. 1.676 m.)

H= Height of contact wire from rail level

D= d.H /G