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Modern, Z-shaped pantographs are marvels of engineering. You can see how seamlessly they unfold and collect power from the overhead lines. Watch what happens if the collector head is not horizontal during the folding and unfolding of the pantograph. To better understand this important quality of modern pantographs, let’s examine this scaled-down demonstration.
The current collector is connected with this upper arm. You can notice, when I push the pantograph up, the angle of the upper arm changes, it changes a lot. Surprisingly the angle of the current collector doesn’t change, it just remains horizontal. In short, the pantograph acts like a gimbal. How did the engineers achieve this? How did they manage the horizontal orientation of the current collector without using electronic control?
Before we dive deeper into the details of a modern pantograph, let’s first explore why trains use one. Consider this underbridge case: due to such constructions or hill slope of ground sometimes it is difficult to maintain a fixed distance between the train and the OH line.
This is why we need a pantograph. This mechanism can adjust to these height changes,
not only does it touch the cable, but it also makes sure that a sufficient contact force is present between the current collector and the OH line.
The simplest pantograph would look like this: a copper conductor with a compressed spring arrangement. When allowed to rise, it starts collecting the current. The current is then supplied to the motors. In a pantograph, the circuit can easily be completed by connecting it to the ground through the wheels. However, this simple collector will easily fail due to the lack of lateral stability!
To improve its stability, let’s lean the rod in this direction. Rearranging the spring allows this collector to stay in contact with the line. However, too much force on the spring can break the tensioned OHL. To counterbalance this spring force, let’s use rope to tie the collector in the other direction. This method balances the collector perfectly. For precise alignment, we can attach a grooved copper head. This current collector design idea, called a trolley pole collector, was first invented by Frank J. Sprague.
This collector will inevitably undergo wear and tear due to continuous running of the train. The regular friction can break this groove head after only two to three weeks. To overcome this problem, railway engineers increased the length of the head and kept it perpendicular. Now, consider the ingenious innovation in the overhead lines: the zig-zag pattern of cables. The line is arranged to slide over the entire length of this collector head. Therefore, the collector head’s contact area changes continuously, greatly slowing down wear and tear on the head.
However, now the overhead line can undergo wear and tear. This can be managed by introducing a carbon strip as shown. This modified design can run smoothly at increased speeds of up to 35 to 100 kilometres per hour. This design, along with additional side horns, is called a bow collector. We’ll explore these horns’ purpose towards the end of this video.
As the speed increases, this design’s one major drawback becomes apparent: the air resistance and vibrations! You can see the complicated path the bottom air particles must take in this design. This will lead to a net downward force and a loose contact. The vortices you see in this visual also cause vibration. To overcome these issues, in 1903, John Q. Brown patented a current-collector design called the pantograph.
The springs you see in the middle of the mechanism are compressed. When released, the spring will try to reduce the pantograph’s height. The output motion of the pneumatic pistons is connected to the mechanism in such a way that when the driver increases the air pressure, the height of the mechanism increases.
The driver makes the decision to increase or decrease the air pressure by observing the tension in the line. This way, the driver can ensure the pantograph is always in close contact with the OHL. Here, you can see the current path through the body of the pantograph. This symmetrical teardrop design solves the vibration issue and reduces the air drag considerably. This symmetrical design also makes sure that the collector head is always horizontal.
However, because the two-armed pantograph is bulky and heavy, it requires significant power to raise and lower. To address this problem, Mr. Louis Faiveley introduced a new technology—the single-armed pantograph. The main parts of this pantograph are marked here. You can see the upper arm changes its angle during the operation, and the most important part of this device—the collector head—is connected to this upper arm.
The current collector is connected with this upper arm. You can notice, when I push the pantograph up, the angle of the upper arm changes, it changes a lot. Surprisingly the angle of the current collector doesn’t change, it just remains horizontal. In short, the pantograph acts like a gimbal. How did the engineers achieve this? How did they manage the horizontal orientation of the current collector without using electronic control?
Before we dive deeper into the details of a modern pantograph, let’s first explore why trains use one. Consider this underbridge case: due to such constructions or hill slope of ground sometimes it is difficult to maintain a fixed distance between the train and the OH line.
This is why we need a pantograph. This mechanism can adjust to these height changes,
not only does it touch the cable, but it also makes sure that a sufficient contact force is present between the current collector and the OH line.
The simplest pantograph would look like this: a copper conductor with a compressed spring arrangement. When allowed to rise, it starts collecting the current. The current is then supplied to the motors. In a pantograph, the circuit can easily be completed by connecting it to the ground through the wheels. However, this simple collector will easily fail due to the lack of lateral stability!
To improve its stability, let’s lean the rod in this direction. Rearranging the spring allows this collector to stay in contact with the line. However, too much force on the spring can break the tensioned OHL. To counterbalance this spring force, let’s use rope to tie the collector in the other direction. This method balances the collector perfectly. For precise alignment, we can attach a grooved copper head. This current collector design idea, called a trolley pole collector, was first invented by Frank J. Sprague.
This collector will inevitably undergo wear and tear due to continuous running of the train. The regular friction can break this groove head after only two to three weeks. To overcome this problem, railway engineers increased the length of the head and kept it perpendicular. Now, consider the ingenious innovation in the overhead lines: the zig-zag pattern of cables. The line is arranged to slide over the entire length of this collector head. Therefore, the collector head’s contact area changes continuously, greatly slowing down wear and tear on the head.
However, now the overhead line can undergo wear and tear. This can be managed by introducing a carbon strip as shown. This modified design can run smoothly at increased speeds of up to 35 to 100 kilometres per hour. This design, along with additional side horns, is called a bow collector. We’ll explore these horns’ purpose towards the end of this video.
As the speed increases, this design’s one major drawback becomes apparent: the air resistance and vibrations! You can see the complicated path the bottom air particles must take in this design. This will lead to a net downward force and a loose contact. The vortices you see in this visual also cause vibration. To overcome these issues, in 1903, John Q. Brown patented a current-collector design called the pantograph.
The springs you see in the middle of the mechanism are compressed. When released, the spring will try to reduce the pantograph’s height. The output motion of the pneumatic pistons is connected to the mechanism in such a way that when the driver increases the air pressure, the height of the mechanism increases.
The driver makes the decision to increase or decrease the air pressure by observing the tension in the line. This way, the driver can ensure the pantograph is always in close contact with the OHL. Here, you can see the current path through the body of the pantograph. This symmetrical teardrop design solves the vibration issue and reduces the air drag considerably. This symmetrical design also makes sure that the collector head is always horizontal.
However, because the two-armed pantograph is bulky and heavy, it requires significant power to raise and lower. To address this problem, Mr. Louis Faiveley introduced a new technology—the single-armed pantograph. The main parts of this pantograph are marked here. You can see the upper arm changes its angle during the operation, and the most important part of this device—the collector head—is connected to this upper arm.
As we saw in the demonstration, the collector head remains perfectly horizontal even though it’s connected to the upper arm. Let’s now explore the secrets of this amazing invention.
Does the lower portion of this pantograph seem familiar to you? This is a four-bar arrangement. If we rotate this green bar clockwise, observe what happens to the small, yellow bar—it’s going for a good angular variation. Let’s extend this yellow bar and attach the collector head at its tip. You can see that this mechanism gives a good height variation to the collector head. However, the angle of the collector head changes since it is connected to the upper arm. This is a big issue. Such rotation will make the contact between collector head and overhead line quite ineffective. Can you identify a potential solution? To resist this rotation of the collector head, let's introduce a balancing rod, which is hinged with the lower arm and a small extension of the collector head. You can see that when the mechanism moves, the distance between the collector head and lower arm hinge point decreases. Because the balancing rod cannot decrease its length, it must push the collector head in the opposite direction. In a pantograph, this opposite rotation exactly cancels the collector head’s tilt before introducing the balancing rod. Hooray! The collector head has now achieved a perfect horizontal position throughout its height. This demonstrates how the pantograph uses a beautiful combination of two four-bar mechanisms. In short, we have developed a technology that consistently keeps the collector head horizontal without any sensors or electronic controls.
The lower arm rotates using the same pneumatic piston arrangement.
In cases if the pantograph has to be lowered or disconnected, the train will continue its free run for a few kilometers due to its high momentum.
Now, back to the curious question we posed previously in this video. The horns are quite useful for when the train switches tracks. During track switching, the pantograph also needs to switch the overhead line. In this animation, you can see how the horns help in the smooth switching between overhead lines, otherwise the line could have stuck below the collector head.
The voltage across the pantograph is approximately 25000 Volts.
So to isolate the metallic body of the train from this high voltage, these insulators with high electrical resistance are used. They also provide good mechanical support to the pantograph.
Fantastic! We have now designed the pantograph completely.
You might have seen that most of the time the pantograph is connected at the rear of the engine. This simple change will reduce the aerodynamic drag considerably.
The reason is the boundary layer effect, please have a look at the velocity distribution around the train body.
If the pantograph is connected to the front of the engine, it has to move against high speed air. However, you can see the pantograph at the rear of the engine faces much lower air velocity, since it is immersed inside the boundary layer; this definitely reduces drag.
Have you ever thought about why two pantographs are installed on top of a train engine?
At low speed the train can operate with a single pantograph, however at speeds more than 150 kilometers per hour, the single pantograph trains will have a major issue.
Suppose there is only one pantograph installed and the train is travelling in reverse direction at high speed. Here again, aerodynamics is the villain, causing vortices and increasing the drag force on the train.
This is why for the train's reverse motion, we need another pantograph with the exact opposite orientation.
We hope you enjoyed this video! Thanks for watching. See you next time!
Does the lower portion of this pantograph seem familiar to you? This is a four-bar arrangement. If we rotate this green bar clockwise, observe what happens to the small, yellow bar—it’s going for a good angular variation. Let’s extend this yellow bar and attach the collector head at its tip. You can see that this mechanism gives a good height variation to the collector head. However, the angle of the collector head changes since it is connected to the upper arm. This is a big issue. Such rotation will make the contact between collector head and overhead line quite ineffective. Can you identify a potential solution? To resist this rotation of the collector head, let's introduce a balancing rod, which is hinged with the lower arm and a small extension of the collector head. You can see that when the mechanism moves, the distance between the collector head and lower arm hinge point decreases. Because the balancing rod cannot decrease its length, it must push the collector head in the opposite direction. In a pantograph, this opposite rotation exactly cancels the collector head’s tilt before introducing the balancing rod. Hooray! The collector head has now achieved a perfect horizontal position throughout its height. This demonstrates how the pantograph uses a beautiful combination of two four-bar mechanisms. In short, we have developed a technology that consistently keeps the collector head horizontal without any sensors or electronic controls.
The lower arm rotates using the same pneumatic piston arrangement.
In cases if the pantograph has to be lowered or disconnected, the train will continue its free run for a few kilometers due to its high momentum.
Now, back to the curious question we posed previously in this video. The horns are quite useful for when the train switches tracks. During track switching, the pantograph also needs to switch the overhead line. In this animation, you can see how the horns help in the smooth switching between overhead lines, otherwise the line could have stuck below the collector head.
The voltage across the pantograph is approximately 25000 Volts.
So to isolate the metallic body of the train from this high voltage, these insulators with high electrical resistance are used. They also provide good mechanical support to the pantograph.
Fantastic! We have now designed the pantograph completely.
You might have seen that most of the time the pantograph is connected at the rear of the engine. This simple change will reduce the aerodynamic drag considerably.
The reason is the boundary layer effect, please have a look at the velocity distribution around the train body.
If the pantograph is connected to the front of the engine, it has to move against high speed air. However, you can see the pantograph at the rear of the engine faces much lower air velocity, since it is immersed inside the boundary layer; this definitely reduces drag.
Have you ever thought about why two pantographs are installed on top of a train engine?
At low speed the train can operate with a single pantograph, however at speeds more than 150 kilometers per hour, the single pantograph trains will have a major issue.
Suppose there is only one pantograph installed and the train is travelling in reverse direction at high speed. Here again, aerodynamics is the villain, causing vortices and increasing the drag force on the train.
This is why for the train's reverse motion, we need another pantograph with the exact opposite orientation.
We hope you enjoyed this video! Thanks for watching. See you next time!