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
- ACTM – AC Traction Manual
- CORE- Central Organization for Railway Electrification
- RITES- Railway India Technical & Economical Services
4 SCADA- Supervisor Control & Data Acquisition
- 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
- Normally, power generation & transmission system of the supply authorities are of
Three phase
- 25 kV traction system needs the supply of
Single phase
- Normally, two adjacent 25 kV AC traction sub stations works as in
Independent
- The shortest section of OHE, which can be isolated through remote control by TPC is
called.
Sub sector
- Distance between two consecutive OHE structures is called
Span length
- In AC traction, span length varies in steps of
4.5 meters
- Maximum span length in AC traction on tangent track is
72 meter
- What is the diameter of Register arm dropper
7mm
- Distance between first dropper and Suspension bracket (Mast)
2.25m
- Maximum tension length in AC traction is
1500 m
- In AC traction, maximum permissible tension length in yard :-
2000 m
- Maximum tension length is restricted upto 1500 m due to
Maintain uniform tension in OHE conductors.
- At the end of tension length, an overlap is formed due to
To provide smooth passage for pantograph
- Maximum wind pressure is considered to design OHE structures for Red zone
150 kgf /sq. m.
- 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
- Maximum wind pressure is considered to design OHE structures for Yellow zone
112.5 kgf /sq. m.
- Maximum wind pressure is considered to design OHE structures for Green zone
75 kgf /sq. m.
- 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)
- Maximum deflection of mast at contact wire level due to wind pressure, is allowed
60 mm
- Maximum deflection of mast at top due to load is allowed
80 mm
- Axial distance between catenary & contact wire at the OHE support, in vertical plane is
called
Encumbrance
- In AC traction, normal encumbrance at support is
1.4 m
- At obligatory structure of turnout, It is general practice to give encumbrance
1.4 m. turnout OHE & 0.9 m main line OHE
- Maximum permissible relative gradient of contact wire in two adjacent span shall not be
greater than on main lines
1.5 mm /m.
- 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.
- Maximum permissible gradient of contact wire, when maximum permissible train speed is
more than 100 kmph on main lines
3 mm/m
- 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
- In AC traction, minimum height of contact wire under ROB/FOB from rail level to permit
“C” class ODC
4.92 m
- 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
- At level crossing gate, maximum height of rail height gauge from the road surface is
4.67 m
- The fittings, which is used to transfer the weight of contact wire to the catenary wire is
called
Droppers
- 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
- In AC traction , how many droppers in 72 m span length
9 Droppers
- In AC traction , how many droppers in 58.5 m span length
7 droppers
- All supporting structures of crossing span have to be properly earthed & their
earth resistance should not be more than
10 ohm
- In AC traction , distance of 2nd dropper from 1st dropper in 60 m non standard span length
5.25 m
- 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
- Material of AC catenary wire is
Cadmium copper
- No. of layers & strands of AC catenary wire is
2 layers & 19 strands
- Diameter of each strand of AC catenary wire is
2.11 mm
- Cross section area of AC catenary wire is
65 sq mm
- Per meter weight of catenary wire is
603 gm
- Material of 107sq mm wire is
Hard drawn copper
- Current density of copper (continuous) is
4 amps/sq. Mm
- Conductivity of cadmium copper in terms of equivalent copper will be
80 %
- Tensile strength of hard drawn copper is
42 kg /sq mm
- Tensile strength of cadmium copper is
63 kg /sq mm
- Cadmium copper is used in place of hard drawn copper for AC catenary wire, why?
To increase tensile strength of catenary
- In AC traction, maximum stagger of contact wire on curved track is
300 mm
- In AC traction, maximum stagger of contact wire on tangent track is
200 mm
- Maximum stagger is allowed at mid span is
100 mm
- 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
- The offset of the track centre from the chord joining the two adjacent points at the track
centre is called
Versine
- Versine “V” is calculated by the formula
Where, L = span length R= radius of curvature of track
V= L*L / 8R
- For odd no’s of tracks, versine is measured from
Individually measured for each track
- 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