[PRCo] Polarity

[Jim Holland]

The  'Principle'  behind reversing the motor on a PCC is what Fred 
described  --  dassn't work like models where we simply reverse the 
polarity because models use permag motors while prototype have field 
wound motors  --  reversing polarity on the prototype reverses both 
commutator and field without a change in direction!!       But I am 
preaching to the Choir here  --  you know that.       Think this is the 
point where the two wires were minus an insulator and you and Fred 
shorted out!
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But for the Average TrolleyCar there wouldn't be the need to switch 
polarity  --  Don't Want Positive In The Rails!!!  --  so there 
shouldn't be a need to protect against polarity reverse in the overhead 
wire - singular!       But where TrolleyCars share overhead with TCs  
o-r  where TrolleyCars are equipped with dual poles, the  'possibility'  
of polarity reverse in the overhead wires does exist.
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SF-Muni TrolleyCars share some TC overhead but nothing complicated and 
nothing where polarity reverse would be any problem  --  only have 2 or 
3 such locations in the TC overhead where polarity is reversed and these 
are far from TrolleyCar tracks.
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ETI's  Do  Operate through polarity reverse sections  --  must be 
something common to Trolley Coaches so the ETI's are protected against this.
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I-F   Sparky  (Robert__"S"__Parks!)  hasn't changed his website, here is 
a photo of polarity reverse in TC overhead at Union and Fillmore in SF:::
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Interesting, if you care to follow the current paths. The third image 
shows the interesting jumper arrangement used to get 600V to the 
curbside wire.
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Overview image (attached):
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http://www.sfmuni.net/overhead/070105-120517-Union-Fillmore-fr5491-ReversedPolarityOverhead-E-lg.jpg 

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Leading switch:
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http://www.sfmuni.net/overhead/070105-120529-Union-Fillmore-fr5491-ReversedPolarityOverhead-E-lg.jpg 

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Trailing switch:
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http://www.sfmuni.net/overhead/070105-120544-Union-Fillmore-fr5491-ReversedPolarityOverhead-SE-lg.jpg 

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Robert Parks
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Jim___Holland
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Boris Cefer wrote:
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> I am aware some PCC equipment with "variable polarity". I have to look 
> whether my books contain any such diagrams and what that "variable 
> polarity" means in the term of function.
>
> Semiconductor propulsion is far more sensitive on polarity. Unless 
> there is a sophisticated system that allows automatical polarity 
> conversion, it can't work. If there are experts on electrical 
> engineering in relation to transit, each comment is welcome!
>
> B
>
> ----- Original Message -----
> From: "Jim Holland" <prcopcc at p-r-co.com>
>
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>> .
>> VERY___Interesting your comments about polarity and the PCC -- the 
>> Muni older Flyer TCs were simple beasts but the electronic ETI's are 
>> more PCC-esque and I wonder about polarity reverse in relationship to 
>> them. We do still have some overhead like that here in SF; we just 
>> had a discussion about same on the SFMuniHistory list!!!
>> .
>> Now, Lettuce see if this goes through -- And When -- If-Ever!!!
>> .
>> .
>> .
>> Jim___Holland
>