During the Dynamic or rheostatic braking the kinetic energy of the motor is converted into electrical energy. This energy is dissipated in resistive elements. 17 Aug Rheostatic or dynamic brakes use traction motors of a vehicle as generators for sustained slowing without the use of frictional brakes. braking resistor wirewound The property of resistors to dissipate heat can be used to slow down a mechanical system. This process is called dynamic braking .
|Published (Last):||13 July 2009|
|PDF File Size:||13.39 Mb|
|ePub File Size:||1.20 Mb|
|Price:||Free* [*Free Regsitration Required]|
In Dynamic Brakinga braking resistor Rb is connected across the armature as soon as the DC motor is disconnected from the supply mains. As this condition results in flow of high current into the armature winding an additional resistance is inserted simultaneously with the operation of reversing the connections of the fheostatic.
It should also consider that value of the the external resistance connected should be less than the critical value, otherwise there will be no excitation of the generator.
The generated energy can be dissipated by connecting a power resistor as load. During the Dynamic or rheostatic braking the kinetic energy of the motor is converted into electrical energy. In order to reverse the torque developed, either magnetic field or armature current has to be reversed.
From Wikipedia, the free encyclopedia. Whenever a supply is given to the electric motor, the motor rotates, as the moter rotates, a kinetic energy is stored in its rotating mass. To decelerate an electric motor, kinetic energy is transformed back into electrical energy. Firstly the separately excited or shunt motor can be connected either as a separately excited generator, where the flux is kept constant.
This method of braking is most inefficient as not only the kinetic energy of the moving mass is wasted but it requires additional energy from supply for the development of the counter torque. Braking resistors are used for applications where the motor speed exceeds the speed that is set by the variable frequency drive VFD or when fast deceleration is required.
DC Motor Braking Methods
For the braking graking in Dynamic Braking, the motor is connected in two ways. Regenerative braking is most efficient. Stopping a train requires the dissipation of a lot of energy. This energy is dissipated in resistive elements. From the figure beside we can see that the torque is not zero at zero speed. Plugging braking of induction motor is done by interchanging connections of any two phases of stator with respect of supply terminals.
This article needs attention from an expert in Trains. When a machine is connected to terminal B, it dissipates the stored kinetic energy in the form as heat via braking resistance R B. This page was last edited on 26 Octoberat Braking torque of rheostaic decreases linearly with the speed of the dc motor. The faster the dissipation of the kinetic energy, the move rapid is the braking.
In case of shunt motor armature is disconnected from the supply and reconnected across the resistance. Dynamic braking may also be used on railcars with multiple unitslight rail vehicleselectric tramstrolleybuses and electric and hybrid electric automobiles.
Li-ion batteries have also been used to store energy for use in bringing trains to a complete halt. Since field winding will have large time constant because of the heavy inductance, it is usual practice to reverse the armature current.
As the rate of electrical power generation, and conversely braking power, are proportional to the rate at which the power shaft is spinning, a stronger magnetic field is required to maintain braking power as speed decreases and there is a lower limit at which dynamic braking can be effectve.
Dynamic or Rheostatic Braking of Electric Motors
But when induction motor drives were invented and implemented, they were given preference because of many advantages over DC motors. During an electric braking, the kinetic energy stored in the rotating parts of the machine and the connected load is converted into electric energy, when the bra,ing is working as a generator.
While the motor rotating, a kinetic energy is stored in its rotating mass.
Views Read Edit View history. Brake resistors for variable frequency drives Braklng DC motors will behave as generators as soon as they are removed from the power supply.
When the speed of the motor is more than the synchronous speed, relative speed between the motor conductors and air gap rotating field reverses, as a result the phase angle because greater than 90 o and the power flow reverse and thus regenerative braking takes place.
The braking operation can be understood easily.
We to update you. We may make mistakes spelling, program bug, typing mistake and etc. Hence, when a quick braking is required, the machine is connected in self-excitation mode. DC Dynamic Braking To obtain this reostatic of braking the stator of a running induction motor is connected to a DC supply.