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The starting current is high because when the motor is not rotating no back-emf is generated, leaving the starting current to be determined by the armature resistance, which should be low.
What else can I help you with?
What are components of a DC motor starter that can be affected by a high starting current if it is not limited?
armature
Is torque and current proportional?
Sometimes, for example in a separately excited dc motor. But in a series-wound dc motor the torque is proportional to current-squared, which gives the motor a very high starting torque and this makes series motors very popular for traction.
Why the armature rheostat of dc is motor kept at maximum resistance position?
It isn't. It is only kept at maximum resistance when the motor is not running. That is done to limit the starting current.
Which of the following Dc motor is suitable for high starting torque?
capacitor start motor
Why ac motors are not used in railways?
Ac motor has a low starting torque so that DC series motor used in railways cause DC motor has high starting torque
Why the starting torque of a dc series motor is high?
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.
What motors is used in railway engines for traction?
dc series motor :A series-wound DC motor has a low resistance field and armature circuit. Because of this, when voltage is applied to it, the current is high. (Ohms Law: current = voltage/resistance). The advantage of high current is that the magnetic fields inside the motor are strong, producing high torque (turning force), so it is ideal for starting a train. The disadvantage is that the current flowing into the motor has to be limited, otherwise the supply could be overloaded and/or the motor and its cabling could be damaged.
Why dc series motor cannot be start without any load?
If a DC series motor is started without load, the armature winding (winding that doesn't spin) current will be at a minimum, resulting in the motor going to maximum speed / runaway, which can cause things to fly apart. As Armature current increases, the speed of the motor will decrease. The armature current will be forced to increase / speed of the motor will be forced to decrease as more and more load is applied.
Why a dc series motor should never run at no load condition?
if you run the unloaded motor at max rpm the centrifugal forces will cause the motor to be totally destroyed so it is advisable to not to run it at max rpm it should be okay to run it till 50% of max rpm without loading it
Why is a starter required for a DC motor?
Large DC motors with field windings instead of permanent magnets present a very heavy load when starting. To prevent fuses blowing, a series of ever smaller resistors are sequentially switched in series with the motor. As the motor picks up speed, a back EMF in opposition to the applied voltage limits the maximum current. When the motor reaches it's running speed the 'starter' is out of circuit.
Why is it necessary to insert resistance in series with the motor armature when starting a dc motor?
Inserting resistance in series with the motor armature when starting a DC motor is necessary to limit the inrush current. At startup, the motor has low back electromotive force (EMF) due to its initial stationary state, leading to a potentially very high current that could damage the motor windings or the power supply. The resistance helps to gradually increase the current as the motor accelerates, allowing it to reach its operational speed safely. Once the motor is up to speed, the resistance can be removed or reduced to improve efficiency.
Why dc series motor should start with load?
In DC Series Motors the field is in series with Armature. When the motor starts at no load, the armature current is very low and so is the field current. As the speed of DC Motor is inversely proportional to field current, the motor will try to shoot up to very high speed at no load and it can be dangerous for the motor itself and for this reason, any DC Motor should always be started on load.
