I tried to connect a 3G modem in DragonBoard through a cable OTG in micro USB port but the port is not powered.
It is possible to use a modem 3g through a cable OTG in DragonBoard with Android OS?
Do you have anything (mouse or keyboard) connected to the other USB port? If yes, try removing those first.
https://www.qualcomm.com/products/snapdragon/processors/410 seems to indicate some kind of 3G support but there's not really much info on it.