In any DC motor the speed depends inversely on the flux. … If u start the motor without load the speed will increase. as speed increases the back emf increases. this decreases the current through the series winding and hence flux decreases and the speed further increases.
Why dc series motor should be started with no load?
The d.C. Series motor should always be started with load because 1. At no load, it will rotate at dangerously high speed 2. It will fail to start 3. It will not develop high starting torque 4.
Why do DC series motors start heavy loads?
The DC series motor provides high starting torque because the field and armature winding are connected in the series and carry the same current. … That is why DC series motor is capable to produce high starting torque, and it is preferred for driving heavy loads.
Why does Series motor tend to race at no load and light loads?
According to speed equation, N α 1/Φ as Eb is almost constant. So on very light load or no load as flux is very small, the motor tries to run at dangerously high speed which may damage the motor mechanically. … This is the reason why series motor should never be started on light loads or no load conditions.
What are the advantages of DC series motor?
Advantages of DC Series Motor
- Dc series motor have good accelerating torque.
- Dc series motor have a relatively huge starting torques.
- Dc series motor delivers high torque during an overload.
- The dc series motor draws less current and power from the source compared to a shunt or compound motor.
What is no load current in dc motor?
The no-load current is the current required just to turn the motor shaft with nothing connected. It is the current required to overcome the bearing and brush friction plus the aerodynamic drag caused by the rotor moving in the air and moving air through the motor for cooling purposes.
Which type of DC motor can start with 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.
Which DC motor is preferred for heavy loads?
4. Which DC motor is used with flywheel for intermittent light and heavy loads? Explanation: Cumulative compound DC motor is used with flywheel carrying peaks and so to smooth out the load on the motor as well as to reduce peaks on power system. Without flywheel the motor construction will be much larger.
Which type of DC motor is used for sudden application of heavy loads?
Like dc series motor, a dc cumulatively compounded dc motor has also variable speed, adjustable variable speed, and high starting torque. We use cumulatively compounded dc motors for intermittent high torque loads, shears, punches, elevators, conveyors, heavy planers and rolling mills, etc.
Which type of load is connected to the DC series motor?
A series DC motor connects the armature and field windings in series with a common D.C. power source. The motor speed varies as a non-linear function of load torque and armature current; current is common to both the stator and rotor yielding current squared (I^2) behavior.
When load is removed motor will run at the highest speed?
1 Answer. When load is removed, series motor will run at the highest speed.
Why starter is used in DC shunt motor?
Starters are used to protect DC motors from damage that can be caused by very high current and torque during startup. They do this by providing external resistance to the motor, which is connected in series to the motor’s armature winding and restricts the current to an acceptable level.
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 disadvantages of DC motor?
Disadvantages of DC motors
- 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 are the disadvantages of DC?
Disadvantages of DC Transmission:
- Due to commutation problem, electric power can’t be produced at High (DC) Voltage.
- In High Voltage transmission, we cant step-up the level of DC Voltage (As Transformer won’t work on DC).
- There is a limitation of DC switches and circuit breakers (and they are costly too).