The teenager was pronounced dead at sidings in Wrenthorpe, near Wakefield in West Yorkshire.
A BTP spokesman said a 16-year-old boy and a woman aged 18 had been taken to hospital with non-life-threatening injuries after the incident at 6.40pm.
The spokesman said: “A 15-year old local boy has died after he appears to have come in to contact with overhead power lines.
“The boy was initially treated by paramedics but was pronounced dead at the scene.
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“Two others who are also local to the area and were with the boy at the time of the incident have been taken by ambulance to Pinderfields Hospital in Wakefield.
“The extent of their injuries is presently unknown although they are not thought to be life threatening.”
Describing the circumstances of the incident, the BTP spokesman added: “At this stage it would appear that the two boys and the female were on the railway line and the 15-year-old boy had climbed on to a freight train at the location.”
The death is not being treated as suspicious and a file will be prepared for the local coroner.
Transport police officers have also informed the Office of Rail Regulation of the death.