Types Of Current Collector
In order to collect the current sparkless, and even pressure should be maintained against the trolley wire at all speeds. Three types of collectors are mainly used which are as follows.
(i) The trolley type
(ii) The bow type
(iii) The pantograph type.
A trolley collector is used on tramways and trolleybuses and mounted on the roof of the vehicle. Contact the overhead wire is made by means of either a grooved^wheel or a sliding shoe carried at the end of a light trolley pole attached to the top of the vehicle and Held in contact with overhead wire by means of a spring. Trolley collectors always operate in trailing position. It is employed up to speeds of about 32 km/h as beyond this speed there’s every possibility of wheel jumping off the trolley wire.
The trolley collector is adopted on tramways and trolleybuses. Current is collected by means of a grooved wheel or a sliding shoe, supported at the end of a long trolley pole attached to the top of the car and held in contact with the wire by a spring. The pole is made to swivel about its support so that it can be reversed for reverse running and rendering it unnecessary for the trolley wire to be accurately maintained above the center of the track. It enables the bus to manage in traffic up to a distance of 3.5 to 4.5m on either side of the contact wire. Although the wheel has a deep groove there is a danger of its jumping off the wire, at points and crossings, at speeds of more than 30 km/hr.
It can be employed for a higher speed. It consists of a light metal strip or bow (about 1m long) pressing against trolley wire and the framework is mounted on the roof of the car. The strip is made up of soft material (e.g. Copper, Aluminum or Carbon). A bow collector also operates in a trailing position. Hence it requires the provision of either duplicate bows or an arrangement for reversing the bow for running in the reverse direction. It is not suitable for railway work where speed up to 120 km/h and currents up to 3000A.
The current may be collected by means of a light metal strip of bow 0.5 or 1 meter wide, attached to a framework mounted on the roóf of the car. This type of collector is commonly used for tramways in Europe. It enables higher speeds to be run without danger of jumping.
Pantograph collector maintains the link between overhead contact wire and power circuit of the electric locomotive at different speeds under all wind conditions and stiffness of overhead equipment. This necessities that positive pressure must be maintained in the least times to avoid loss of contact ad sparking but the pressure must be as low as possible in order that wears of overhead contact wire is minimum. It is mounted on a pentagonal framework which may be raised or lowered by compressed gas or springs. Compressed air for raising is normally used. It is used where vehicles nin at high speeds i.e. in railways and where currents to be collected are large (2000 to 3000A).
For railway work for speeds up to 150km/h or 130 km/h and currents up to 3000 A and a light pantograph construction, as shown on the locomotive is used. The tubing of high-tensile alloy steel is generally employed to ensure lightness as well as adequate strength.