def METHOD_NAME(power_plants, cfg):
    # Define bus_id for power plants without it
    power_plants_no_busId = power_plants[power_plants.bus_id.isna()]
    power_plants = power_plants[~power_plants.bus_id.isna()]
    power_plants_no_busId = power_plants_no_busId.drop(columns="bus_id")
    if len(power_plants_no_busId) > 0:
        power_plants_no_busId = init_pp.assign_bus_id(
            power_plants_no_busId, cfg
        )
    power_plants = power_plants.append(power_plants_no_busId)
    return power_plants