LECTURE 19

 Current collection systems

CUURENT COLLECTION SYSTEMS

1. OVERHEAD EQUIPMENT:

The primary requirement of a collector is that it should maintain a continuous contact with trolley – wire at all speeds. The three types of commonly used are:

 Trolley collector  collector

TROLLEY COLLECTOR:

 A trolley collector is used on tramways and trolley- and is mounted on the roof of the vehicle.  A contact with the overhead wire is made by means of either a grooved wheel or a sliding shoe carried at the end of a light attached to the top of the vehicle and held in contact with overhead wire by means of a spring.  The pole is hinged to a swivelling base so that it may be reversed for reverse running thereby making it unnecessary for the trolley wire to be accurately maintained above the centre of the track.  Trolley collectors always operate in the trailing position.  The trolley collector is employed upto speeds of about 32km/h as beyond this speed there is every possibility of the wheel jumping off the trolley wire.

BOW COLLECTOR

 It consists of a light metal strip or bow (about 1 m long) pressing against the trolley wire for collection of current and the framework is mounted on the roof of the car.  The strip is purposely made of soft material in order that most of the wear may occur on it rather than on the trolley wire.  There is no possibility of the strip jumping off the trolley wire.  A bow collector also operates in trailing position; hence it requires provision of either duplicate bows or an arrangement for reversing the bow for running in the reverse direction.  It can be employed for higher speeds.  It is not suitable for railway work where speeds upto 120 km/h and current upto 3000 A are encountered.

PANTOGRAPH COLLECTOR:

 It maintain link between overhead contact wire and power circuit of the electric at different speeds under all wind conditions and stiffness of overhead equipment.  This necessitates that positive pressure must be maintained at all times to avoid loss of contact and sparking but the pressure must be as low as possible so that wear of overhead contact wire is minimum.  It is mounted on a pentagonal framework which can be raised or lowered by compressed air or springs. Compressed air for raising is normally used.  It is used where the vehicles run at high speeds, i.e., in railways and where currents to be collected are large (2000 to 3000 A)

2. CONDUCTOR – RAIL EQUIPMENT:  Depending on the position of the contact surface, the conductor rails may be divided into three classes: top, bottom and side.  The following figure shows a conductor rail system when electric supply is collected from the top of an insulated conductor rail running parallel to the track at a distance of 0.3 to 0.4 m from the running rail which forms the return path.  For collecting the current, a shoe is used as shown in figure below.  The shoe presses on to the rail with a force of about 150 N with a current collection ranging from 300 to 500 A per shoe.  Since the conductor rail is not always laid on the same side of the track shoes are attached to the motor – coach or locomotive on both sides.

Wiener khinchine theorem