How does a Pantograph Work on a Train

How does a Pantograph Work on a Train
Image Credit: Pixabay

You have probably seen the overhead cable on the rain lines and wondered, how does a pantograph work on a train?

The pantograph transmits the electricity that powers some of our electric trains. Read on to learn the working principles of this innovative system.

The electric train was a welcome replacement for the cost-intensive steam trains. This new technology delivered higher thermal efficiencies to the steam and internal combustion engines.

Hence, it was not surprising to witness the gradual adoption of railway transport.

With a rising demand for maintenance and regular downtime, railway corporations began embracing the pantograph’s ingenuity and offered the third rail system.

Subsequently, we will learn everything about how the pantograph works on a train.

Table of Contents

How the Pantograph became a Modern Rail System Technology

The modern electric train gets power from overhead lines, a third rail, or onboard battery packs. This system does not cover the diesel-electric or gas turbine electric that has onboard fueled prime movers like gas turbines or diesel engines.

Electric trains run on electric generators or motors. This equipment requires electricity to gain the energy needed to move the train.

Several innovations sprung up to supply electric power to these motors, including the overhead lines and the third-rail system.

The modern railway systems adopted electric trains to switch to cleaner energy and eliminate the high operating cost of steam and internal combustion engines.

As a result, they turned to the more efficient electric motors, which often have efficiencies above 90%.

Also, it allowed for greater efficiency with regenerative braking, putting back the kinetic energy during braking on the line. The electric trains can use more power than diesel locomotives because they tap from bigger power plants.

These trains need equipment to tap the energy from the overhead lines. Hence, they can either use pantographs or a third rail to tap electrical power.

Sometimes, they can have rechargeable energy storage systems like batteries and ultracapacitors.

The pantograph stays on the train’s roof and clings onto the overhead wire to receive electrical energy. The train uses the energy to power the electric motors, propelling itself forward.

With the information so far, I believe you now have a fair knowledge of how a pantograph works on a train. Next, let’s look at what components make up a typical pantograph.

Primary Function of the Pantograph

Powering electric trains with batteries will require substantial battery packs. This system will be costly, but it will also limit the maximum distance.

As a result, the modern rail required a plan to provide a constant electricity supply at the proper voltage.

Engineers developed the overhead system that involved running a wire throughout the length of the rail line. This wire, supported by a catenary, would provide for the train’s current needs. Nonetheless, the train had to tap this energy from the overhead line.

The pantograph is the device that taps current from the overhead line to power the electric train. It stays in constant contact with the line throughout the journey.

Subsequently, you will know how it adjusts to vertical differences between the line and the train.

Components of a Pantograph

Components of a pantograph (source: electricalforall.co.in)

The pantograph collects an electric current to power electric multiple units or an electric train. It has a design that enables it to contact an electrified overhead wire called, and this connection allows it to transmit the energy to the needed components seamlessly.

Pantographs come in diverse shapes and sizes, depending on the power requirements or the train speed.

Other factors that influence the type of pantograph used include the train set and the power supply systems. Notwithstanding, they have the same essential components.

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Before answering the question clearly, we need to understand the components; how does a pantograph work on a train? The key components are the lower and the upper arms, and in essence, they form the most crucial connections on the pantograph.

All other parts link up through the lower and upper arms. The lower arm pivots vertically against the carriage roof and links up to the upper arm. As a result, it forms a connection to transmit the electric energy from the overhead line.

The upper arm connects to the collector head or pan, which is the only part that touches the wire pickup. You will find metalized carbon strips on the head that collect the electrical energy and transmit it down the pantograph.

Other pantograph components include the base frame, the mainspring with yoke, the contact strip, and the balance rod. At the very base is the lifting device that regulates the upward and downward motion of the system.

Furthermore, insulators at the base prevent leakage of electric current to the train’s body. They also support the entire structure, providing a solid foundation.

How does the Pantograph work on a Train?

How a pantograph works on a train (Source: railpictures.net)

Pantographs work as movable rods to collect power from the overhead wire. Compressed air from the braking system controls the movement of this mechanism.

The simple functions of the pantograph include:

  • Provide continuous contact that collects the electric current from the overhead lines
  • Transfer the electrical power from the contact wire to the electric generators or motors

The pantograph goes by the current collector or receiver in some cases.

The electric transmission system for modern electric trains consists of an upper, weight-carrying cable (the catenary). The contact wire precisely suspends from the catenary with the clever use of droppers.

Efficient operation demands that the contact wire stays horizontal as much as possible. To achieve this, engineers have to determine the correct length of the droppers at different locations in the rail line.

The pantograph pushes a contact shoe against the underside of the contact wire to tap the electricity needed by the train.

A spring-loaded mechanism controls the entire movement of the pantograph. Also, the steel rails of the tracks act as the return to complete the circuit.

As the train pushes forward, the contact show slides along the cable. Care must be taken because this motion can set up acoustic standing waves in the wires, breaking the contact and degrading the current. Essentially, using adjacent pantographs is harmful and prohibited.

The compressed air from the train’s braking system raises the pantograph and holds it against the contact wire.

In some cases, springs work with the air to raise and lower the arms. However, the system needs a catch to hold down the arm when lowered.

High-voltage systems use the same air supply to blow out the electric arc in cases that involve roof-mounted circuit breakers.

Which Pantograph works best on a Train?

The usage environment of pantographs keeps changing as the train passes through different environments. This change happens due to the speed of the train and weather conditions.

As a result, they need to maintain constant contact throughout the journey. Pantographs must collect a stable amount of electricity without damaging the catenary.

Experts developed different types of this device to accommodate various scenarios in railway transport. Below are the different kinds of pantographs:

Based on the arm construction

  • Single-arm Pantograph

A single-arm pantograph takes low power from the overhead line, and it makes a connection with an overhead single-phase AC system. In addition, the Z shape arm commonly defines this type of pantograph, and today, it is the most popular type used on trains.

  • Double-arm pantograph

The double-arm pantographs cannot function without the three-phase AC power system, and they consume high power to propel the train forward at high speeds. Also, you will find this type of pantograph with a diamond shape, unlike the z-shape of the single arm.

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The double-arm pantographs have more weight and require more power to raise and lower the arms. However, they are more fault-tolerant than the single-arm.

Based on operating speed

  • High-speed pantograph
  • Normal-speed pantograph

Based on the frame layers

  • Double-layer pantograph
  • Single-layer pantograph

Based on the operation of the spring

  • Non-spring operated pantograph
  • Spring operated pantograph

The Special Case of Inclined Pantographs

Answering the question, how does a pantograph work on a train? It will not be complete if we don’t learn about these exceptional inclined cases.

There are tons of passenger trains worldwide, but others carry freight rather than passengers. We have exceptional cases where an excavator loads products onto the coach beds.

This type is common in mining environments where trains move the raw materials from the mining site to the processing facilities.

It could even occur within the mines if the mining carts use pantographs. Operating a piece of overhead loading equipment in the presence of catenaries is dangerous.

As a result, there is the risk of electrocution if the machine contacts the overhead electric lines. The construction of pantographs and the catenary could be offset rather than in the middle.

This system will allow the free movement of the loading equipment while operating safely from the overhead lines.

We can see that trains in this scenario or operations can still benefit from using pantographs while allowing for a safe working environment.

These overhead lines carry large amounts of current and must stay safe from a reachable distance.

When the Pantograph is Preferred over the Third Rail System

Pantographs are more fragile than the third-rail system, but they allow the use of higher voltages. As a result, they are the dominant form of electricity collection for modern electric trains, which doesn’t wholly write off the third-rail technology.

Some rapid transit systems, especially above-ground running, use pantographs. Nevertheless, the third rail is still the preferred system. The main limitation of the third-rail system shows up in public areas.

Most pre-metro or metro-tram lines use the pantographs when their route includes tracks on city roads and publicly accessible areas. These lines include line 51 of the Amsterdam Metro, Frankfurt U-Bahn, San Francisco’s Muni Metro, and MBTA Green Line in Cleveland.

The Switch from Third Rail to Overhead Lines

The rail lines switch to the overhead wires to avoid the risk of electrocution. It will be dangerous to run electricity on the ground in built-up areas.

However, rail lines that pass-through tunnels made by tunnel boring machines have no trouble using the third-rail system.

The only exception to these technologies is the lines that use the tram system. They include rail lines in Bordeaux, Angers, Reims and Dubai, where Alston developed the Alternative Power Supply.

Furthermore, this technology is a proprietary underground system that applies power to segments of the track with a tram.

The core reason for developing these alternative systems was to avoid visual intrusion. An example is a line in Bordeaux.

Other developers of the tram system include Bombardier, AnsaldoBreda, and CAF. In some cases, they use battery packs for short distances and physical ground infrastructure for others.

Another reason for using the pantograph over the third-rail system is to avoid freezing in certain winter conditions. The MBTA Blue Line uses a pantograph for all surface sections of its route and a third rail for the underground passages.

Notwithstanding, numerous rail lines combine the overhead and third-rail systems. This way, they eliminate the weaknesses of each technology while enjoying the benefits of both.

Now, you can see that it is not enough to answer the question; how does a pantograph work on a train? It is equally important to inform you of alternative technologies and the one that works best in certain conditions.

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Single and three-phase power supply

Trains that use the three-phase power supply have two pantographs, and the running rails provide the third phase circuit. However, Walter Reichel at Siemens & Halske designed an experimental high-speed installation in 1901.

They use three vertically mounted overhead wires while horizontally extending pantographs carry the collectors. On the other hand, a single-phase power supply requires only one pantograph.

Advantages of a Pantograph

Pantographs maintain constant contact with the overhead lines, ensuring a stable electricity supply. This way, the train can travel as far as the line goes without a drop in power supply.

It is safer to use overhead lines in public and built-up areas. This system eliminates the risk of electrocution that the third-rail system might bring. The electricity is at a safe distance away from human commute and interaction.

Pantographs allow for higher travel speeds because they can collect higher voltages than other systems. Trains can sustain their speeds because of the constant contact the pantographs create.

In many ways, we have seen that answering the question (how does a pantograph work on a train?) falls back to transportation.

The Limitations of the Pantograph on a Train

Let’s take an alternative look at the question, how does a pantograph work on a train? Pantographs are indeed efficient, replacing the third rail in many cases. However, there are some downsides to this technology.

A block of graphite maintains the contact between the pantograph and the overhead line. This material lubricates the line while conducting electricity. However, as it gets brittle, it can break off during operation.

Another downside is that a bad pantograph can grab the wire and tear it down. On the other hand, a line can break away or damage the pantograph.

Rail lines use a pantograph monitoring station to avoid this. Also, sustained high (above 300km) can generate too much friction.

This friction will cause the contact strip to become red hot and excessive arcing. Inevitably, failure occurs. Nevertheless, engineers are developing clever solutions to work around these limitations.

In the UK, air pressure raised the pantographs, creating an air gallery between the graphite contact carbons in the head.

This way, air comes out if s graphite strip breaks away. As a result, the pantograph lowers through the automatic drop device to prevent damage.

More sophisticated systems can detect disturbances caused by arcing at the contact point when the graphite strips break away. This solution can help in preventing total failure.

Some rail lines like the British Rail Class 390 have used two pantographs if one fails during transit. The rear pantograph prevents damage to both when there are entanglements. Notwithstanding, both can experience damage if the front one is in operation.

This unfortunate scenario occurs when debris from an entanglement damages the rear, rendering both inoperable. As we look forward to the future, we should see immense progress in this technology. Rail transport remains a crucial means of commuting.

Conclusion

Modern electric trains and streetcars continue to use the pantographs to draw the needed power. They use this power to operate the electric generators or motors that propel the locomotive forward.

In answering your question, how does a pantograph work on a train? We have seen the components and operating principles of this innovative piece of technology.

Also, we should expect more developments in this technology though battery packs are becoming more advanced.

A close competitor to the pantograph is the third-rail system, and it equally gives power to the electric train but falls short in terms of the total voltage it can carry. The pantograph is safer in public areas and inside cities than the third-rail system.

Notwithstanding, the third-rail system rules when the train passes through tunnels or super-high bridges. Pantographs are essential components of electric trains and will continue to support the transport system in years to come.

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