Pantograph noises on class 379

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futureA

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I was on a class 379 the other day sat under the pantograph well. During the journey whist traveling at speed there where two occasions where it sounded like the pantograph dropped (a loud thud was heard coming from the roof above).

Is this what I heard? Why and how does this happen?
 
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scott118

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I was on a class 379 the other day sat under the pantograph well. During the journey whist traveling at speed there where two occasions where it sounded like the pantograph dropped (a loud thud was heard coming from the roof above).

Is this what I heard? Why and how does this happen?

Neutral sections.
 

Domh245

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What you heard is the Vacuum Circuit Breaker (VCB), which is used for Neutral sections. This is heard on all AC OLE EMUs, although it is louder on some trains than others
 

ainsworth74

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Is this what I heard? Why and how does this happen?

All AC EMUs and locomotive have a Vacuum Circuit Breaker (VCB) which is located nearby the pantograph. When the train is about to enter a neutral section of the overhead line the VCB opens (which creates a loud bang) isolating the train (well apart from the pantograph which remains in contact with the wire throughout) from the overhead wire whilst it passes through the neutral section and then the VCB closes again on the other side (causing another loud bang) linking the train back to the juice.

It helps to protect both the train and the infrastructure from any short circuiting or power surges whilst transiting through neutral sections.
 

samuelmorris

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and for whatever reason is extremely loud on modern units, when it was a barely perceptible 'clunk' on older ones (321s, 315s etc.) - it only seems loud enough to actually scare people on Electrostars, but really, I don't see why it has to be so loud inside the passenger area of the train.
 

Trog

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Triggered by magnets originally similar to the fixed magnet of an AWS ramp mounted on both sleeper ends, either side of the neutral section. Although there is now a smaller version of the magnets that mounts onto the rail foot so avoiding the need to fit special sleepers.
 

al.currie93

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I see now! That sound really made me jump when I first heard it! Again I've only heard it so loud on the 379s - no idea why they're so loud compared to other classes!
 
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