because train has heavy mass & due to heavy mass inertia is also very high so more effort is required getting motion in train.
it is also known that any type of motor required more initial torque for come in speed.
becoz of high starting torqe to move train
Ac motor has a low starting torque so that DC series motor used in railways cause DC motor has high starting torque
capacitor start motor
to obtain high starting torque
In dc motors Speed is directly proportional to back emf and inversely proportional to flux i.e N∝(Eb/φ) In series motor back emf is practically constant. So if we start motor without any load Flux will be small and so speed will be very high. if we start motor without any load it will gain very high speed and may get damaged due to centrifugal forces. Series motor have very high starting torque and used where high starting torque is required.
Torque is the the force required to move a body about its fulcrum. The starting Torque is the force required to move the body from 0 rpm to the stipulated rpm, the Running torque is the force required to maintain the rpm. The Starting torque is often higher than the running force. Imagine peddling a push bike with one gear (say the one gear is a high gear), the force required to set off will be relatively high in comparison to the force you exert in order to maintain a velocity.
load is heavier so starting torque is requiredAnswerBecause the same current is passing through both the armature and field windings, the torque is proportional to the squareof the current. Since the starting current is alway high (no back emf), the torque will be very high indeed.
Series motors have the highest starting torque. The torque is proportional to the square of the current, and the starting current is so high it has to be limited by a resistor called a rheostat. Series motos are used mainly on trams and trolley buses.
becoz of high starting torqe to move train
it is kept at minimum position to produce more torque which is required for starting a motor
Ac motor has a low starting torque so that DC series motor used in railways cause DC motor has high starting torque
to obtain high starting torque
capacitor start motor
due to high starting torque and droping charactristics
1. Induction motor has high starting torque, therefore use for operate pump which need high starting torque. 2. Induction motor operate on variable speed. 3. It can be used as generator when speed of motor is higher than synchronous speed.
In dc motors Speed is directly proportional to back emf and inversely proportional to flux i.e N∝(Eb/φ) In series motor back emf is practically constant. So if we start motor without any load Flux will be small and so speed will be very high. if we start motor without any load it will gain very high speed and may get damaged due to centrifugal forces. Series motor have very high starting torque and used where high starting torque is required.
3 Phase induction motor because it produce high torque at starting