The connection diagram is shown below when braking with self-excitation is performed. Therefore, the supply voltage V and the induced voltage E b i. It is a form of braking in which the kinetic energy of the motor is returned to the power supply system. Whether mechanical or electrical, the braking of the drive should be such as to stop the motor at the specified point of time and location, for reasons of safety. Counter current braking is accomplished by reconnecting the supply to the armature of the motor so that the motor draws a current to develop a torque to oppose its already existing rotation. A running motor may be brought to rest quickly by either mechanical braking or electrical braking.
When applied voltage to the motor is reduced to less than back emf Eb, obviously armature current Ia will get reversed, and hence armature torque is reversed. The torque developed is T b , which maintains the speed constant. The nature of the speed-torque curve of a dc series motor is such that it does not extend to the second quadrant As no-load is approached, the speed increases asymptotically to the speed axis. It passes through the no-load speed point with the same slope as in the first quadrant motoring. This type of braking is possible in the case of drive motors where the speed can go beyond no-load speed or the terminal voltage can be momentarily decreased, e. Function Generation and Linearisation. The induced voltage becomes greater than the supply voltage to which the motor is connected and the current flows from the machine to the supply. The torque developed retards the load being lowered and runs it at constant speed.
Short Time Intermittent Duty. Alternatively, the field may be separately excited during braking. The machine is then able to self excite in this case.
Why not share it? The Dynamic or Rheostatic Braking is an insufficient method of braking because all the energy which is generated is dissipated in the form of heat in the resistance.
The torque developed is T bwhich maintains the speed constant. This type of braking is possible in the case of drive motors where the speed can go beyond no-load speed or the terminal voltage can be momentarily decreased, e.
This type of braking is possible when the driven load forces the motor to run at a speed higher than its no-load speed with a constant motof. The armature current reverses and flows in a direction opposite to the current during motoring Fig. The armature current is also constant.
Dynamic or Rheostatic Braking of Electric Motors
This is similar for both series and shunt wound methods. It develops a torque to oppose the motion and hence hreostatic control the acceleration.
The field remains connected to the supply with full excitation, and the induced voltage in the armature has the same polarity. C Programming C Programming Data structures. Rhekstatic the friction torque is greater than the load torque the motor is stationary. When a machine is connected to terminal A, it runs as a motor. A running motor nraking be brought to rest quickly by either mechanical braking or electrical braking.
Your email address rhesotatic not be published. We to update you Update me. Consequently, a current flows in a direction opposite to the one existing during normal motoring. When bbraking supply to the armature of a de series motor is reversed, care must be taken to see that the field current retains its direction, for effective braking.
However, in hoists a stand by mechanical brake system is also provided, to avoid accidents in case of power failure. In the case of dc motors this is achieved by reversing the polarity of the supply voltage to the armature, while for ac motors the phase sequence is altered. Basically, there are three types of electrical braking done in a DC Motor: Leave a Reply Cancel reply Seris email address will not be published.
It is very interesting to note that regenerative braking cannot be used to stop rheostaitc motor but to control its speed above the no-load speed of the motor driving the descending loads. The braking is effective and the motor stops very fast if the field is available at its full value, for which reason it is separately excited. Classification of Electric Drive. The mechanical energy is converted to heat; there is additional power input from the supply.
The machine now starts working as a self-excited series generator. Interview C Interview Aptitude. The counter current braking in a shunt motor is accomplished by reversing the supply to the armature, while the connection to the field winding remains unchanged. Cranes and Hoist Drives. Plugging gives greater braking torque as compared to rheostatic braking.
Types of Braking in a DC Motor
The second way is that it can be connected to a self-excited shunt generator, with the field winding in parallel with the armature. The braking characteristics in this case are obviously similar to those of a separately excited motor. Thus the machine will now feed the current to the connected rheostat and heat will dissipate at the rate of I 2 R. As generated emf is greater than applied voltage machine is acting as a DC generatorpower will be returned to the line, this action is called as regeneration.
Due to reversal of the armature terminals, applied voltage V and back emf Eb starts acting in the same direction and hence the total armature current exceeds. Commutation in DC Motor.
In other words, the motor is stopped by the voltage and current action in the circuit rather than the mechanical friction brakes on the rotor. This is achieved by suitably changing the electrical connections of the motor. Feedback Control in Drive System. The load forces the motor in some applications to accelerate beyond no-load speed. 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 energy can be returned to the mains or dissipated seriies an external resistance.
The connection diagram of shunt motor Braking with self and separate excitation is shown in the figure below. It is a form bra,ing braking in which the kinetic energy of the motor is returned to the power supply system. In this method, armature connections are reversed and hence motor tends to run in opposite direction. The nature of the speed-torque curve of a dc series motor is such that ij does not extend to the second quadrant As no-load is approached, the speed increases asymptotically to the speed axis.
Dynamic Braking is an inefficient method of braking as all the generated energy is dissipated as heat in resistances. The induced emf cannot be greater than the terminal voltage. Simply, a circuit consist of a motor Mpower supply Sbraking resistance R B and a two pole switch. It passes through the no-load speed point with the same slope as in the first quadrant motoring.
This implies that an increase in speed of a dc series motor is followed by a decrease in the armature current and field flux.