All the London railway stations :
Carpenders Park is on the London Overground line, and is accessible to wheelchair users via a 90 metre ramp with a moderate gradient to platforms. See pictures and further accessible transport in London detail from links below.
Underground lines : London Overground (Watford DC Line)
Accessibility friendly : Yes (TFL)
General description : See wiki
More comment : National Rail Map & Guide, 90 metre ramp, and shorter train boarding ramps also available.