Electrical Braking is usually employed in applications to stop a unit driven by motors in an exact position or to have the speed of the driven unit suitably controlled during its deceleration. Electrical braking is used in applications where frequent, quick, accurate or emergency stops are required.
DC injection braking works just as its name implies — by injecting DC voltage into the motor windings. When DC current is applied to the motor windings, it creates a fixed (rather than rotating) magnetic field. Braking action is produced by the rotor working to align to this stationary field.
In single stage electric braking method, the braking and energy regeneration are achieved by the use of single stage bidirectional DC/AC converter which is used to drive the BLDC motor. The BLDC motor driven by a single stage bidirectional converter is shown in Fig. 1.
Brake Requirements:The brake must be strong enough to stop the vehicle within minimum distance. It is inversely proportional to brake efficiency and proportional to square of speed. Provide good control over vehicle during emergency braking and vehicle must not skid.
The electric motor in your hybrid or electric car runs in two directions - one to drive the wheels and move the car, and the other to recharge the battery. When you lift your foot off the accelerator pedal and onto the brake, the motor swaps directions and starts to put energy back into the battery.
1. Which of the following is the best braking method? Explanation: Braking methods based on friction, electromechanical action, eddy-currents, etc. are independent of the motor but sometimes electric braking is better justified owing to its greater economy and absence of brake wear.
Regenerative braking is used in vehicles that make use of electric motors, primarily fully electric vehicles and hybrid electric vehicles.
The Drive reported that it's the first fully electric car to include this technology, which engages a electrohydraulic system. The car's computer controls the system, and it still doesn't involve traditional brake pads. But it responds based on how much pressure the driver applies to the brake pedal.
Electric cars and trainsA typical modern electric train can save around 15–20 percent of its energy using regenerative brakes in this way. Some vehicles use banks of supercapacitors for storing energy instead of batteries.
The technique of regenerative braking is most effective in full stop passenger trains and subway trains (metro), because they stop often enough to make recovery worthwhile. Conventional freight trains only have a limited potential to recover power with the help of regenerative braking.
In a battery-powered electric vehicle, regenerative braking (also called regen) is the conversion of the vehicle's kinetic energy into chemical energy stored in the battery, where it can be used later to drive the vehicle. It is braking because it also serves to slow the vehicle.
The advantages of the regenerative system are the reduced energy consumption and the reduced wear of brake shoes and wheel tyres, and the consequent lowering of maintenance costs.
Also, danger can arise if regenerative braking is applied to two-wheel-drive brake systems. However, regenerative braking does have various benefits. A proper implementation of regenerative braking system extends driving range, improves braking efficiency, reduces brake wear, and improves energy conservation.
both instances it employs the use of magnetic ?elds to slow the rotation of a motor. The advantage of dynamic braking is that there are no mechanical brake shoes to wear out. The disadvantage is that dynamic brakes cannot hold a suspended load.
The electric braking of a DC motor is of three types, (i) Rheostatic or dynamic braking, (ii) Plugging or reverse current braking and (iii) Regenerative beaking.
The material used for braking is normally in the form of a block or pad. The vast majority of the world's trains are equipped with braking systems which use compressed air as the force to push blocks on to wheels or pads on to discs. These systems are known as "air brakes" or "pneumatic brakes".
With dynamic braking, an IGBT (transistor) allows power to flow to a resistor, where it's dissipated as heat. Regenerative braking takes the energy generated by the motor and feeds it back to the AC power source or to a common bus, where it can be used again.
Dynamic braking is the use of the electric motors as generators when slowing the machine speed. It is termed rheostatic if the generated electrical power is dissipated as heat in brake grid resistors, and regenerative if the power is returned to the supply line.
The generated CEMF decreases as the speed of the motor decreases. As the motor speed approaches zero, the generated voltage also approaches zero. This means that the braking action lessens as the speed of the motor decreases. As a result, a motor cannot be braked to a complete stop using dynamic braking.
When, in an emergency, you apply the brake pedal quickly and with force but without really further increasing brake pressure, Dynamic Brake Control (DBC) instantly builds up maximum brake pressure, bringing your BMW more quickly to a halt.
Dynamic braking resistors are used on AC variable frequency drives (VFD's) to dissipate energy that is produced in the motor as the drive provides braking torque to stop the motor. The dynamic braking resistor is connected to the DC bus and will see voltages as high as 800 volts during braking conditions.
In Dynamic Braking, a braking resistor Rb is connected across the armature as soon as the DC motor is disconnected from the supply mains. This method is also known as Rheostatic Braking because an external braking resistance Rb is connected across the armature terminals for electric braking.
3. What is the relationship between torque and speed in constant type loads? Explanation: Speed hoist is a perfect example of constant type loads in which torque variation is independent of speed. The speed-torque characteristics of this type of load are given by T=K where K is a constant.
Explanation: For armature voltage control, armature current is increased so as to reduce speed below base speed. In field control flux is reduced so the speed would be above base speed. Explanation: The torque limit of the shunt motor remains constant till the base speed.
Conventional AC operated crane drives use slip ring induction motor whose rotor windings are connected to power resistance in 4 to 5 steps by power contactors. Reversing is done by changing the phase sequence of the stator supply through line contactors. Braking is achieved by plugging.
7. Which type of force phenomenon is used in Sugar mills? Explanation: In sugar mills, a centrifugal is used to separate out sugar crystals from the syrup by the action of centrifugal forces. Centrifugal force acts away from the center.
What will happen if DC motor is used without starter? Explanation: It would cause intolerably heavy sparking at the brushes which may destroy the commutator and brush-gear. Sudden development of large torque will cause mechanical shock to the shaft, reducing its life.
1. Which of the following type of brakes can bring the member to an absolute rest? Explanation: The electric and hydraulic brakes cannot bring the member to rest and are mostly used where large amounts of energy are to be transformed. 2.
