The operation and maintenance (O&M) of converter stations (also known as
valve halls) in high voltage DC (HVDC) grids is a key element in long-term, reliable and stable operation, especially in inherently adverse offshore environments. The use of robotic systems to conduct remote inspections of offshore wind farm HVDC converter stations has been proposed as a promising solution to reduce O&M down-time and costs. However, the nature of the electromagnetic field environment inside HVDC valve halls presents a challenge for the operation of traditional off-the-shelf inspection robots. In this paper, the impact of the external magnetic field on the operation of an inspection quadcopter's propulsion motors is assessed. An experimental method is proposed to identify the maximum magnetic field tolerable by off-
the-shelf quadcopter motors. The reported method can be used to test commercial off-the-shelf quadcopter motors to identify their suitability for use in HVDC valve halls inspection robots. The paper experimental results show the failure of direct torque control (DTC) algorithm, that is used in quadcopters speed controllers in mitigating the magnetic field impact on motor's speed and current consumption.