type of dc motors used by electric train/subway,crane & fan.give a brief explanation to your answer?
I believe that electric trains and subways use series motors when DC motors are used because the series motor has a torque vs. speed curve that provides high torque at low speed and low torque at high speed. Since power is equal to torque times speed, that is essentially a constant power mode of operation. I believe that mode is selected because it results in a smaller and less expensive complement of power delivery equipment and more efficient operation. Although it has been many years since DC motors were used extensively for cranes, I believe that series motors were used more than other types for the same reasons stated above. However, compound or separately excited motors may have been used for better speed and torque control at low speeds. Except for heater fans in vehicles, I don't believe DC motors have ever been used much for fans. Today, permanent magnet DC motors are used for all of the little motors in vehicles including the radiator fan that was formerly belt driven by the engine. A permanent magnet motor is like a separately excited motor or a shunt motor. The optimum DC motor for a fan would probably be a shunt motor because a fan requires increasing torque as speed increases. Today, computers are cooled by brushless DC motors.
