Negative booster

A negative booster is employed to conform to the regulation that the potential difference between any two points of the rail return shall not exceed 7 V.

Two boosters, positive and negative, are used which are mechanically coupled together and driven by a DC motor. The positive booster is connected to the trolley wire (near the generating station) and the negative booster (separately excited) is connected to the track rail. 

The 'positive booster' adds voltage to the line while the 'negative booster lowers the potential of the point it is connected to.

As we go along the trolley wire away from the generating station/sub-station, the potential drop increases, and the voltage of the trolley wire falls. Since the current returns via the track rail points away from the generating station acquire high potentials.

This potential is brought down by the negative boost provided by the negative booster. When the load is sufficiently far away from the generating station, the trolley wire is fed by the positive booster. 

The current in the positive booster provides the excitation for the negative booster. The feeder current as it flows through the booster maintains the voltage of the trolley wire within 1imits. 

The potential at the corresponding point on the tack is reduced by the negative booster since its voltage is regulated by the same feeder current. Thus the track is maintained nearly at earth potential.

The negative booster is separately excited. As we go along the trolley wire away from the sub-station, the potential drop increases and the voltage of the trolley wire falls. 

Since the current returns via the track rail, the points away from the sub-station acquire higher potentials. This potential is brought down by the negative boost provided by the negative booster.

The trolley wire is fed by the positive booster PB when the load is sufficiently far away from the generating station. The current in the positive booster provides the excitation for the negative booster. 

The voltage of the trolley wire is maintained within certain limits by the feeder current as it flows through the booster.

The potential at the corresponding point on the track is reduced by the negative booster since its voltage is regulated by the same feeder current. Thus, the track can be maintained at nearly earth potential.