[PRCo] Re: Polarity

[Jim Holland]

Clarifying Words added in  [CAPS]  in  Brackets!!!!!!!

Jim Holland wrote:
.

> 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 -- [SIMPLY]  reversing  [OVERHEAD]  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!
> .
> 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.
> .
> 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.
> .
> ETI's Do Operate through polarity reverse sections -- must be 
> something common to Trolley Coaches so the ETI's are protected against 
> this.
> .
> 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:::
> .
> 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.
> .
> Overview image (attached):
> .
> http://www.sfmuni.net/overhead/070105-120517-Union-Fillmore-fr5491-ReversedPolarityOverhead-E-lg.jpg
> .
> Leading switch:
> .
> http://www.sfmuni.net/overhead/070105-120529-Union-Fillmore-fr5491-ReversedPolarityOverhead-E-lg.jpg 
>
>
> .
> Trailing switch:
> .
> http://www.sfmuni.net/overhead/070105-120544-Union-Fillmore-fr5491-ReversedPolarityOverhead-SE-lg.jpg 
>
>
> .
> Robert Parks
> .
> .
> .
> Jim___Holland
> .
> .
> .
> Boris Cefer wrote:
> .
>
>> 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>
>>
>> ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
>>
>>> .
>>> 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
>>