Electric locomotive gets power from overhead contact wire through pantograph. For smooth operation of locomotive, the movement of pantograph should be unobstructed on the contact wire. When any broken part of pantograph comes in between overhead wires or vice versa, panto entanglement takes place.
The OHE is meant for supply of power where as the pantograph is for collecting power for the locomotive. The parameters of designs of OHE and pantograph are such that the pantograph remains in contact with contact wire with sufficient pressure to collect current.
Pantograph normally used on AC locomotives are Faively types AM-12. The whole assembly of pantograph is mounted on the insulated base of locomotive roof. It is operated for its raising/ lowering positions with compressed air through servomotor.
OHE is also designed in such a way that the contact wire always remains on the top of pantograph. At turn outs the contact wire of main line and secondary line are adjusted in such a way that main line contact wire always remains below the secondary line contact wire. This permits smooth working of loco on high speed on main line.
Panto entanglement causes damage to pantograph and overhead equipment resulting in dislocation of electric traction traffic.
1.2CONSTRUCTION OF PANTOGRAPH AM – 12
Pantograph is an essential fitting of electric locomotives. There are two pantographs mounted on the roof of an electric locomotive, each one on four insulators as shown in figure 1.1 and 1.2. At a time one is raised and connects the locomotive with the OHE contact wire. Normally the pantograph rear to cab used for driving is raised i.e. rear to the direction of movement of the locomotive (if rear is defective or damaged, front can be used to work).
The pantograph consists of a base on which a horizontal spindle is fitted. One end of lower arm is integrally jointed in the middle of this spindle and the other end of this lower arm is jointed with a frame called upper frame. This joining end is known as “YOKE”. A thrust rod ensures positioning of this upper frame. This thrust rod is pivoted on one end at the yoke and the other end is fixed at a point on the base.
Details of Figure 1.1 and 1.2
10.Joint of Upper Tube
15.Tie Rod Insulator Horn
The suspension for the collector is composed of a transverse tube with a turning at the end of the upper frame assembly as shown in figure 1.3 and 1.4. The tube has two spring boxes on its both ends. In each spring box there is a sliding plunger with a fork on the top as shown in figure 1.5. The yoke of the collector is mounted on these two forks of the plunger. Positioning link is pivoted on a pin at the yoke side end of the thrust rod. This link maintains the contact plane in horizontal position during the vertical movement of the collector. Collector frame carries two bolted current collecting strips and uninstalled horns. There are two working springs whose tension always balances the mass of the articulated system and at the same time raises the pantograph and provides the contact force. These springs are fixed between the ends of a balancing member and arm on the horizontal spindle.
The articulated system is designed to allow an extension of 2.460 meters. There is a pneumatic control mechanism. The piston is held at the bottom against the spring for lowering the pantograph and for holding it in down position. Force is transmitted by a piston inside the cylinder and...