Re: XPT HEP power - was: Very smoky XPT

[matthew@mail.usyd.edu.au (Matthew Geier)]

In article <mauried.204.36942122@commslab.gov.au>,
Maurie Daly <mauried@commslab.gov.au> wrote:
>In article <770uh8$bpu$1@metro.ucc.usyd.edu.au> matthew@mail.usyd.edu.au (Matthew Geier) writes:
>>From: matthew@mail.usyd.edu.au (Matthew Geier)
>>Subject: Re: Very smoky XPT
>>Date: 7 Jan 1999 00:18:48 GMT
>
>>In article <mauried.203.3693DEC6@commslab.gov.au>,
>>Maurie Daly <mauried@commslab.gov.au> wrote:
>>>
>>>>>
>> The main difference is that the XPT has a real neutral in the train line,
>>the traditional railway HEP supply doesnt.
>
>
>Its not absolutely necesssary to have a neutral if the majority of the load is 
>a 3 phase load, which would be the case if the air con uses 3 phase 
>compressors or 3 phase motors driving conventional compressors.
>You would need it though for 240 V single phase applications , if there wasnt 
>an isolation transformer on the train somewhere.

>Do the HEP sets in normal power vans provide 3 phase with neutral?


 Now I know how the 'standard' power vans work, having gone over the drawings
of the RTM's underfloor alternator powered buffet car.

 The 3 phase train line has NO neutral as such. The train line has 3 phases
and a sense wire. The sense pin is shorter than the power pins, so that if
a connector works loose the power trips before any live pins are exposed.
 The are two HEP trainlines, on opposite sides. These are often feed by
different alternator sets, although for redundancy any alternator can feed
either train line, or both.

 The neutral is the car bodies, which is also the earth. Ive not checked for
certain but I think the jumper cable sheath makes the earth/neutral connection
as the couplers would not make effective contact.

 The big loads on the train line are the air-conditioning which are 3 phase
loads. The lighting is spread across the 3 phases of both trainlines. Any
neutral required is the car body. Some effort was made to balance the
240v loads in each car. This needs to be done anyway - an unbalanced load
would be hell on the alternator set.

 All this doesn't comply with the current electrical standards and if one
was starting from scratch a neutral wire would be needed - like the XPT has.
Its just the wieght of history that preserve the system - it would cost a
fortune to rewire every HEP equiped car in the country.

 The RTM's buffet car actually has a quite complicated set of contactors
to cope with all this. The car can run independant, from the train line
or feed the trainline. However as it was built recently, it had to comply
with the current electrical code so it does have seperate neutral and earth
when running standalone or on shore supply. The internal wiring is seperate
earth and neutral with RCD protection, however if the car is feeding or being
feed from a trainline the earth and neutral are connected together in the
switching cabinet at the point the trainline connects to the system.

 Earth and neutral are connected together in normal use anyway. Every main
switchboard in the country as the 'MEN' link between the neutral line and
the installation main earth.