The flux produced by a DC series motor is proportional to the load current I. So at light loads flux is less and the speed will be tending to infinity i.e. very high. Hence a DC series motor should never be run on no load.
Why DC series motor should never be started on no load?
Thus from equation (2), it is clear that speed of DC Series Motor is inversely proportional to Armature Current Ia. … Therefore if the DC Series Motor is started at No Load then the speed of DC Series Motor will become dangerously high which will definitely damage the DC Series Motor.
Why is a DC series motor used to start heavy loads?
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.
Can we operate DC series motor at no load condition?
At no load condition, load on the motor is zero hence armature current(Ia) is also zero. … Hence based on above discussion it is advised that DC Series motor should not operate at no load condition. We can also understand above by knowing characteristics of DC series motor.What will happen when DC series generator is started without load?
If there is no load is connected to series generator the current in the field winding would be absent and there by no flux is available for voltage to be generated.
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 be started at no load?
This can be seen from the speed-armature current and the speed-torque characteristics that on low armature current and low torque condition motor shows a tendency to rotate with dangerously high speed. This is the reason why DC series motor should never be started or Operated on light loads or No load conditions.
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.What is the main disadvantage of a series motor?
The series motor has poor speed regulation. When the load speed of the machine increases, the DC shunt motor keeps its constant speed from no load to full load. The dc series motor’s Torque drops sharply when the speed increases.
What happens when the load from a series motor is suddenly taken off?What occurs if the load is removed from an operating series DC motor? It will stop running. Speed will increase slightly.
Article first time published onWhy the series field windings have less no of turns?
The field winding of a DC series motor always have a small number of turns and made by thick wire . Our intention is to reduce the starting current of the DC series generator . This less number of turns and thick wire of coil makes the effective flux small.
What is the importance of no load characteristics?
(E0/If) Open circuit characteristic is also known as magnetic characteristic or no-load saturation characteristic. This characteristic shows the relation between generated emf at no load (E0) and the field current (If) at a given fixed speed. The O.C.C.
When a DC motor has no load what will happen to the back EMF?
At no load condition,( i.e when there is no mechanical load connected to armature end) small torque is required to overcome the friction and windage losses. Since torque is directly proportional to armature current Ia ,therefore the armature current Ia is small so the back emf is nearly equal to the applied voltage.
Which can be started on no load Unlike DC series motor?
Unlike DC series motor, DC compound motor can be started on no-load. Explanation: Cumulative motor takes best from shunt motor and series motor as well. Due to shunt field flux component, DC cumulative motor can be started on no load.
Why DC shunt motor should be started with load?
When the motor is connected across the supply mains without load, it draws small current from the supply mains. … The increase in back emf weakens the armature current and hence the field current. This cause again increases the speed so the back emf.
Why DC shunt motor is never started with field open?
Fractional-Horsepower Motors The shunt field must never be opened while the motor is running. If the shunt field suddenly opens while the motor is being operated under full-load conditions, only a small voltage due to the residual magnetism of the pole pieces will be induced into the armature.
What is the one disadvantage of Series DC motor?
Disadvantages of DC Series Motor: Speed regulation in the series motor is quite poor. With the increase in the load speed of the machine decreases, DC shunt motor maintains almost constant speed from no load to full load.
What are the advantages and disadvantages of a DC series motor?
- It is an easy assembly and simple design.
- Vast starting torque.
- Protection is very easy.
- It is cost-effective.
- Series wound motors can use for AC or DC supply so it is also known as universal motors.
- Compare with shunt motor DC series motor develop power for the same construction size.
What are the disadvantages of DC motor?
- High initial cost.
- Increased operation and maintenance cost due to the presence of commutator and brush gear.
- Cannot operate in explosive and hazard conditions due to sparking occur at brush (risk in commutation failure)
What happens if DC series motor connected to a load suddenly gets un loaded?
The DC motor will continue its rotation if it is at NO LOAD. If the load is more than the no load ( torque required to overcome friction and windage losses) condition the motor stops and a chance of high current flow may damage the winding if the voltage applied is high (Close to rated voltage if it is there).
What happens when a DC motor loses power to its Series field?
In case of DC series motor. If we cut the series motor field winding , motor stops rotating. If we cut shunt motor, it will rotate with dangerous speeds. Because of the residual magnetic flux emf will be generated which helps in rotating of motor.
What happens when the motor runs on no load?
When the motor is connected across the supply mains without load, it draws small current from the supply mains. This current will flow through the series field and armature, the speed tends to increase so that back emf may approach the applied voltage in magnitude. … This cause again increases the speed so the back emf.
How does DC motor differ from DC generator in construction?
The most significant difference between DC motor and DC generator lies in the conversion mechanism. DC motor converts electrical energy into mechanical energy whereas DC generator converts mechanical energy into an electrical energy.
What is the difference between a DC shunt and a series motor?
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 will happen if DC shunt motor running on no load has shunt field winding opened accidently?
Ans: if a shunt motor, running at no load has its shunt field opened or burnt out, the back emf will fall to nearly zero . the armature current will continuously increase the speed of the motor until its parts fly apart.
Why Series generator is not suitable for General Electric Supply?
Applications of Series Wound DC Generators These types of generators are restricted for the use of power supply because of their increasing terminal oltage characteristic with the increase in load current from no load to full load. … They give constant current in the dropping portion of the characteristic curve.
Why is there always some no load voltage in a separately excited DC generator?
Let us consider a separately excited DC generator giving its no load voltage E0 for a constant field current. If there is no armature reaction and armature voltage drop in the machine then the voltage will remain constant. … Due to armature reaction, Due to ohmic drop (IaRa).
What will happen to a DC motor if its back emf is equal to the supply voltage?
The maximum power is developed in the motor when the back emf is equal to half of the supply voltage.
What is the advantage of back emf?
The presence of back emf makes the d.c. motor a self-regulating machine i.e., it makes the motor to draw as much armature current as is just sufficient to develop the torque required by the load. When the motor is running on no load, small torque is required to overcome the friction and windage losses.
