Pantograph Entanglement — Traction Distribution Notes

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Panto entanglement happens when any part of the pantograph gets caught between overhead wires (or vice versa) — causing damage to both the pantograph and the OHE, and disrupting electric traction traffic. The three root-cause categories are OHE defects, pantograph defects, and external defects.

OHE Defects — Turnout & Crossover

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Exam Focus — The 43% Statistic

About 43% of ALL OHE failures are caused by improper adjustment at turnouts and crossovers — a real, frequently-tested statistic. The core fix: turnout/crossover contact wire height must be kept 5 cm above the main line contact wire at obligatory locations.

'G' Jumpers should be provided at 5.6 distance from the obligatory mast, for cross-over and turnout points respectively towards the parallel run side.
10 m towards turnout side from the obligatory mast, hogging on main line contact wire is removed by increasing dropper length.
At 10 m towards turnout side, loop line contact wire height is adjusted +3 cm compared to main line height.
At the obligatory mast itself, contact wire height difference between main line and loop line should never be less than 5 cm.
While tower-wagon running on main line, the panto should take in/take off from the turnout track at about 65 ± 2 cm from the centre of the tower wagon's panto.
On cross-type turnout, height difference should be +1.5 cm at the obligatory point, and at 5 m and 10 m from the mast.

Auto Tensioning Device (ATD)

ATD keeps the OHE at correct tension. If the ATD drum doesn't move freely, tension won't remain correct — causing sag at higher temperatures, and sag is directly prone to panto entanglement at high speed. Ensuring free ATD movement and providing a 100mm sleeve on the anti-falling device rods (in short tension lengths) prevents this sagging.

Pantograph Defects

Spring box failures — a large share of pantograph defects. Check for cracks in the cylinder, steady-link welding, cylinder support, and sub-mounting assembly via Liquid Penetrant Testing (LPT); ensure free plunger movement.
Static force: the pantograph must exert 7 kg static force on the contact wire — if less, large oscillation causes the pan to leave contact, sparking and locally heating the wire.
Static adjustment: a 7 kg weight on the panto pan should balance it at 2.25 m height — done in the maintenance shed during every IA schedule.
Split pins at articulation points should be opened out to 60 degrees so they don't work loose during running.
Panto pan wearing strips are replaced once worn beyond 2mm; sharp edges must be filed off.

Checks After Panto Entanglement

The Real Post-Entanglement Checklist

Measurements — height/stagger of contact wire (main line & turnout/crossover), vertical height of steady arm clamp from register arm; must match structure erection drawing.
Locations of hit marks — search steady arm, registration arm tube, PG clamps, droppers, contact wire, splices, and jumpers.
Condition of cracked OHE fittings — record whether cracks in clamps/brackets/clips are fresh or old.
Pantograph wearing strips — properly fastened, no bent strip or deep grooves, smooth joints.
Mechanical movement of panto pan — should be horizontal, freely vertically movable, bow plunger sliding freely.

Standard measurement reference (if panto pan is found intact): A=520, B=1800, C=300, D=380 — real reference figures used to confirm a pantograph hasn't been structurally deformed by an entanglement.