Automatic Dropper Device and the VCB

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387star

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Why does the Vacuum Circuit Breaker (VCB) not trip (ie light come on in drivers cab/ VCB turned off) if the Automatic Dropper Device (ADD) operates?

The VCB light comes on if the pantograph is dropped normally to prevent arcing as the pantograph lowers however interestingly this isn't the case with ADD operation.

Also how effective is the ADD at lowering a damaged pantograph? I believe there may be circumstances when it will be down to the Driver to lower the pantograph and therefore it is advisable to do this anyway in case the ADD has not operated quick enough

Sorry for getting technical
 
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westcoaster

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Why does the Vacuum Circuit Breaker (VCB) not trip (ie light come on in drivers cab/ VCB turned off) if the Automatic Dropper Device (ADD) operates?

The VCB light comes on if the pantograph is dropped normally to prevent arcing as the pantograph lowers however interestingly this isn't the case with ADD operation.

Also how effective is the ADD at lowering a damaged pantograph? I believe there may be circumstances when it will be down to the Driver to lower the pantograph and therefore it is advisable to do this anyway in case the ADD has not operated quick enough

Sorry for getting technical

could you be more specific with a class type. some stock 377/387 have a seperate ADD light that flashes.

the ADD normally operates when the carbon strips get damaged/chipped and allows air out of the air gallery. or the pan goes over height
 
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westcoaster

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because the ADD is to stop pan damage, the vcb is for power to the transformer, it opens to stop current being drawn, and closes to dram power.
 

387star

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because the ADD is to stop pan damage, the vcb is for power to the transformer, it opens to stop current being drawn, and closes to dram power.

indeed but the vcb opens when the pantograph is lowered manually (to prevent arcing) but not when it is lowered automatically by the ADD?
 

westcoaster

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indeed but the vcb opens when the pantograph is lowered manually (to prevent arcing) but not when it is lowered automatically by the ADD?

the ADD and VCB are two seperate things, and are not linked.

is this in relation to a scinario.
--- old post above --- --- new post below ---
easy way to thinkof it, the ADD protects the pan, and the VCB protects the transformer.
 

387star

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the ADD and VCB are two seperate things, and are not linked.

is this in relation to a scinario.
--- old post above --- --- new post below ---
easy way to thinkof it, the ADD protects the pan, and the VCB protects the transformer.

ok thanks

presumably the risk of arcing is a risk worth taking (supposing the ADD has operated) because the pantograph is damaged and perhaps the ADD lowers the pantograph so quickly arcing is unlikely
 
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westcoaster

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ok thanks

presumably the risk of arcing is a risk worth taking given the ADD has operated because the pantograph is damaged or the ADD lowers the pantograph so quickly arcing is unlikely
if the ADD operates the pan willl drop quickly, to be honest ive never seen arcing droping the pan ever.

even when you drop the pan normally, they sometimes (stones faiverly ones) are still up with the vcb open.
 
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387star

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if the ADD operates the pan willl drop quickly, to be honest ive never seen arcing dropping the pan ever.

ok thanks


anyway guess I was overthinking it

and that might just apply to one type of pantograph fair point
 
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westcoaster

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ok thanks

like I say when lowering the pantograph eg when switcing to DC mode the VCB light comes on to prevent arcing apparently

anyway guess I was overthinking it

and that might just apply to one type of pantograph fair point

vcb does not come on when dropping the pan, it comes on when raising the pan.
 

ComUtoR

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Pan Up, Juice off (AC). Would you get a VCB ? The line light would be out but I'm not sure if you would get a VCB.

I've not yet been in a situation (other than flying through a neutral section) where the AC has been isolated for some reason and my pan is up.
 

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Pan Up, Juice off (AC). Would you get a VCB ? The line light would be out but I'm not sure if you would get a VCB.

I've not yet been in a situation (other than flying through a neutral section) where the AC has been isolated for some reason and my pan is up.

as I understand it indication is the same as for a ADD operation ie no vcb light will come on only line light goes out
 

westcoaster

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ah i think we are, i thought as in post 1 you were talking about cab indications.
--- old post above --- --- new post below ---
Pan Up, Juice off (AC). Would you get a VCB ? The line light would be out but I'm not sure if you would get a VCB.

I've not yet been in a situation (other than flying through a neutral section) where the AC has been isolated for some reason and my pan is up.

no it would not open or the light come on. i have when prepping at cricklewood and the power had not been switched back on yet, and during a power blip/outage.
--- old post above --- --- new post below ---
may be pantograph type dependent but my understanding is when dropping the pan manually the vcb light goes ON meaning the vcb is OFF (which happens automatically)

not sure if you are confusing the light ON.OFF with the vcb ON.OFF

vcb ON ie energised= vcb light in cab OFF
vcb OFF ie deenergised= vcb light in cab ON (vcb has tripped)

dont get confussed, because you cant drop the pan on a 319 without going into dc mode, where the vcb light will not come on.
 
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ComUtoR

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no it would not open or the light come on. i have when prepping at cricklewood and the power had not been switched back on yet, and during a power blip/outage.

Cheers. All my 319 preps are DC side.
 

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ah i think we are, i thought as in post 1 you were talking about cab indications.
--- old post above --- --- new post below ---


no it would not open or the light come on. i have when prepping at cricklewood and the power had not been switched back on yet, and during a power blip/outage.
--- old post above --- --- new post below ---


dont get confussed, because you cant drop the pan on a 319 without going into dc mode, where the vcb light will not come on.

true I was wrong once in dc mode it won't be on even if the vcb Opens . I presumed it came on briefly as the pantograph lowered
--- old post above --- --- new post below ---
pressing the dc mode button to drop the pan won't lighten up the vcb light even though the vcb has tripped as no longer ac mode

so would make sense if the vcb does in effect trip but doesn't light in the cab when the ADD is operated
 
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