On the Indian Railways, the coveted Rajdhani tag ensures that the train gets top priority over other trains over the entire route. All efforts are made to ensure the train’s punctuality. Less important trains have to make way for the Rajdhani to go ahead. Rajdhanis also get high speed coaches and the most powerful high-speed locomotives available.
However, once in a while, even a Rajdhani has to slow down and stop for halts, speed restrictions, and an occasional train running ahead.
An average train has considerably more mass compared to road vehicles. To illustrate, an average car weighs around 1 ton. A loaded coal rake weighs around 5,500 tonnes. Therefore, the train needs higher distances to not only stop, but also to accelerate back to normal speeds. Significant time is also lost in the process of deceleration and acceleration back to maximum permissible speed.
Challenges at High Speeds
To partly remedy this issue, in the case of the CR Rajdhani, IR has outdone themselves. Ordinarily, there is only one locomotive in charge of a passenger service. This time, IR is experimenting with a relatively new concept in passenger train operations.
The CR Rajdhani will initially run with two locomotives attached to the front. These locomotives belong to the WAP-5 class, with a total of 11,000 HP on tap. This arrangement, with twice the power to weight ratio, will result in faster acceleration, and improve average speeds.
While hauling trains with two or even more locomotives is nothing new for IR, twin locos are only used for hauling heavy and slow goods trains. The longest passenger rake in use today rarely exceeds 1,500 tonnes. A standard coal wagon rake weighs around 5,500 tonnes. Goods trains rarely run at speeds above 75 kph. The necessity of ensuring higher speeds for Rajdhanis, routinely operating at maximum speeds of 120-130 kmph, presented a new challenge.
Electric locomotives get their power supply from the wires overhead. A device called the Pantograph is used to maintain contact with the wire. Constant contact with the wire is the only way to ensure that the locomotive gets power to operate.
A New Approach
As the speed of the train increases,wind and other dynamic forces acting on the pantograph create turbulence in the overhead wires. This can cause the pantograph to lose contact with the wire and cause the locomotive to shut down. Pantographs require clever engineering to ensure they maintain stable contact with the wire despite high speeds and turbulence.
When multiple locomotives are attached together to increase hauling power, this problem of turbulence is compounded. At high speeds, the pantograph of the rear loco can repeatedly lose contact with the turbulent wire, resulting in frequent power supply interruptions.
To address this, IR chose to use one pantograph for both locomotives. In such an arrangement, a sturdy, heavily insulated cable is used to connect both locomotives. This cable feeds power supply from the active pantograph to the rear unit. Both locomotives are controlled from the leading locomotive and work in perfect synchronism.
Such an arrangement is popularly called the ‘Twin-WAP5’, or simply ‘The Twins’, by the railfan community.
Hopefully, IR will introduce this system of haulage on more trains. The measure can go a long way in not only improving punctuality, but also increase average speeds on the network.