The starting torque of the DC series motor is proportional to the square of the armature current. … That is why DC series motor is capable to produce high starting torque, and it is preferred for driving heavy loads.
Why should DC series motor started with load?
At the starting of the motor there is no back emf, so large current current flows cause high starting torque. This starting torque leads to very fast acceleration of motor if shaft is not connected to any load. This fast acceleration cause motor to damage. So series motor are always started with load.
Which motor is best suited for heavy traction loads?
Explanation: DC motors are used for traction as, according to the characteristics of DC motors speed is inversely proportional to torque and square of armature current as well, if linear magnetization is concerned. Thus, DC motors are perfectly suitable for traction. 2.
Why do we use DC series motor?
A series motor has very high starting torque and is commonly used for starting high inertia loads, such as trains, elevators or hoists. This speed/torque characteristic is useful in applications such as dragline excavators, where the digging tool moves rapidly when unloaded but slowly when carrying a heavy load.
Why a DC series motor has a higher starting torque?
Series motors have the characteristic of developing very high starting torques. The reason for this is the same current that passes through the armature also passes through the field windings.
Can we start the DC series motor without load?
A series motor should never be started at no load. With no mechanical load on the series motor, the current is low, the counter-EMF produced by the field winding is weak, and so the armature must turn faster to produce sufficient counter-EMF to balance the supply voltage. The motor can be damaged by overspeed.
Why Series motor produces high torque and speed initially without load?
Explanation: At no load, armature current tends to zero, flux φ tends to zero, where speed is inversely proportional to the flux, speed will tend to infinity. Thus, no load speed of DC series motor is highest.
Which DC motor is usually preferred for heavy loads?
The starting torque of the DC series motor is proportional to the square of the armature current. The armature current-Torque characteristics of the DC series motor is as given below. That is why DC series motor is capable to produce high starting torque, and it is preferred for driving heavy loads.
What is the principle of DC series motor?
The DC motor is the motor which converts the direct current into the mechanical work. It works on the principle of Lorentz Law, which states that “the current carrying conductor placed in a magnetic and electric field experience a force”. And that force is the Lorentz force.
Which type of DC motor is used for sudden application of heavy load?
Since a series motor develops high starting torques at low speeds and low torque at high speeds, therefore, speed – torque characteristics of a DC series motor is a hyperbola. High starting torque enables, even a small series motor to start a heavy load.
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Which motor is usually used in DC traction?
MotorApplicationDC series motorTraction system, Cranes, air compressorsDC shunt motorLathe Machines, Centrifugal Pumps, Blowers, Conveyors, Weaving Machine, Spinning machinesDC compounded motorPresses, Shears, Elevators, Rolling Mills
Why is the starting torque of a series DC motor more than that of a DC shunt motor of the same rating?
Thus we observe from the above equation that, torque in DC Series Motor is directly proportional to the square of armature current and torque is directly proportional to armature current in DC shunt motor. This is the reason why DC series motor have high starting torque than DC shunt motor.
Which DC motor produces the greatest starting torque?
DC Series motor has highest starting torque. 3-phase Induction motors have highest staring current, 5 to 7 times full-load current and develop about 2 times the full-load torque.
What is the starting torque of a DC motor?
Starting torque is the torque transferred by the shaft coupling during run-up (see Start-up process). It is calculated based on the ratio of power (P) to angular velocity (ω) and is represented as a rotational speed function.
Can we start DC shunt and DC series motor without load?
You can start a DC shunt motor without a load, but never start a DC shunt motor with heavy load because, The change in field flux is very less due to the load, so we can assume the flux to be constant. So flux ɸ is constant, and the speed, N ∝ Eb where Eb is the back emf.
Which motor should not start without load?
If it is started without load the field current will be less, hence flux will be less and due to this motor speed will go infinite and damages itself. This is the reason why series motor should not be started without load and shunt motor can be started without load. , Made my first DC motor at age of 7.
What would happen if you try to start a DC motor without applying field supply?
The motor will try to speed up to develop a back-emf and with no field it requires a very large armature current. … Normally the armature fuses just blow as the current drawn can be very high depending upon the applied armature voltage. In this case the motor will accelerate and run away until the fuses blow.
How do you use a series motor?
⇒ DC series motors are used where high starting torque required. These motors are only used where the variation of speed is possible. series motors are not suitable for constant speed applications. ⇒ DC series motor is used in a vacuum cleaner, traction systems, sewing machines, cranes, air compressors etc.
How does a DC series motor start?
A series DC motor converts electric energy to mechanic energy based on the electromagnetic principle. In this type of DC motor, a power supply terminal sits at one end of the armature and field coils. By applying the voltage, power starts in these terminals and passes through armature and field windings.
Where are DC series motors used?
Series DC motors are generally used where high starting torque is required, and speed variations are possible. These types of direct connection motors are, for instance, used in the traction system, cranes, air compressors, vacuum cleaners, sewing machines, etc.
What happens when a DC series motor is connected to AC supply?
Detailed Solution. When AC supply is given to DC series motor: An AC supply will exert unidirectional torque because the direction of armature current and field current reverses at the same time and the direction of rotation will as it is.
Which type of motor is used for traction purpose?
Many single phase ac motors have been developed for traction purposes but only compensated series type commutator motor is found to be best suited for traction. Single phase induction motors have been abandoned as they are not capable of developing high starting torque.
Which method is best for series traction motor?
Explanation: Series-parallel control method is superior to the rheostatic control insofar as efficiency is concerned. However, it is limited to two speed steps. The method is commonly employed for speed control of series traction motors.
What is the speed of DC motor?
DC controls adjust speed by varying the voltage sent to the motor (this differs from AC motor controls which adjust the line frequency to the motor). Typical no load or synchronous speeds for an AC fractional horsepower motor are 1800 or 3600 rpm, and 1000-5000 rpm for DC fractional hp motors.
Why the starting torque is low in DC shunt motor?
The high number of turns allows a strong magnetic field to be generated, but the smaller gauge wires provide a high resistance and limit the current flowing through the shunt coil. Therefore, the starting torque of a DC shunt motor is low, meaning that the shaft load must be small at startup.
How do you increase the starting torque of a DC motor?
Any DC motor will experience a decrease in speed when a load is applied, which causes the back EMF to decrease. The reduction in back EMF increases the net voltage, since the supply voltage remains constant. The net voltage increase causes the armature current to increase, which increases the motor torque.
What is the difference between series and shunt motors?
A series motor respond by decreasing its speed with small increase in current for a given load torque. A shunt motor holds its speed nearly constant with large increase in input current for same amount of load torque.
What would be the starting torque of a motor?
The start-up torque of a mechanical system is the minimum torque required to get it moving from a standstill. the start-up torque of a motor is the maximum torque which it is capable of producing from a standstill.
Why is stall torque important?
You should care because stall torque is the highest point of failure on a drive unit or a motor. The device is going to draw a lot of current at stall. In fact, it’s going to draw the highest amount of current you’ll ever see while under normal operating conditions. The keyword there being normal operating conditions.
What creates torque in a motor?
That torque is created by the pistons within an engine as they reciprocate up and down on the engine’s crankshaft, causing it to rotate (or twist), continuously. This torque is then transferred to the vehicle’s wheels through the transmission and drivetrain.
