And this will boost your bottom line long term. Get in touch with us to learn more about how our DC motor brakes can help you to get the job done efficiently and effectively from one task to the next. View Larger Image. What Is Dynamic Braking? Alex Rouse T October 7th, General. Related Posts. A Simple Guide to Lathe Brakes. The value of R is selected so maximum braking speed is obtained when all resistance is cut out by the speed regulator.
Because of the similarity in the construction of a synchronous motor and an alternator AC generator , a synchronous motor can be reconnected as an alternator to provide faster stopping. The kinetic energy of the rotor and the driven machine is converted to electrical energy by generator action and then to heat by the dissipating resistors.
A method developed by the author for the dynamic braking of a synchronous motor is illustrated in the elementary diagram of Ill. When the start button is pressed, contactor A is energized and opens the resistor circuits connected to the motor leads in the control panel. Contactor A energizes coil M to maintain the circuit and start the motor across the line. Time-delay relay coil TR is energized and its timing cycle begins.
After the motor is brought up to speed by the windings in the rotor, the normally open, delay-in-closing con tact TR energizes the DC contactor B to sup ply current to the field. The field discharge resistor circuit's opened as well.
When the stop button is pressed, the AC supply is removed from the stator. The timer coil, however, remains energized so that its contact remains closed. As a result, direct current continues to flow through the rotor. As the rotation continues, the magnetic lines of force of the rotor cut across the stator windings to generate a cur rent. This current keeps the timing relay con tact TD closed.
The contact remains closed as long as the rotor maintains a voltage drop across the braking resistor R2. Direct current is removed automatically from the rotor when it's almost at a standstill. This timed, semiautomatic method of synchronizing was selected to illustrate this method of braking for reasons of simplicity.
With a simple modification, it's readily adaptable to any completely automatic, synchronizing control system. What becomes of the energy used to brake the motor dynamically for the two methods described?
Referring to Ill. Why is it necessary to open the disconnect switch when the machine isn't in operation Ill. Why may it be necessary to reverse the polarity of the series field of a compound motor if it's used in the dynamic braking circuit?
Draw a schematic diagram of a circuit to reverse the polarity of the series field of a compound motor used in the automatic braking circuit when the stop button is pressed see Ill. Home Articles Forum Glossary Books. Describe the general series of controller connections that can be made to obtain hoisting, lowering, and braking operations at different speeds. List several advantages of dynamic and regenerative braking. During electric braking, the kinetic energy stored in the rotating parts of the machine and the connected load is converted into electric energy, when the motor is working as a generator.
The energy is dissipated as heat in the braking resistance R b and armature circuit resistance R a. The connection diagram of shunt motor braking with self and separate excitation is shown in the figure below:. For Dynamic Braking, the series motor is disconnected from the supply. A variable resistance R b as shown in the figure below is connected in series, and the connections of the field windings are reversed.
The field connections are reversed so that the current through the field winding flows in the same direction as before i. Forward Starting. When the forward button is pressed, the normally open forward contacts close and the normally closed forward contacts open.
The control circuit's illustrated in 2. The forward contactor coil is energized from L1 through the over load contacts, stop button, forward pushbutton contacts 1—2 when closed , and reverse button contacts through the forward contactor coil to L2. The forward contacts F seal in the forward pushbutton. In the power circuit the F contacts of the forward energized contactor close, and thus complete the armature circuit through the starting resistance. The normal counter emf starter sequence of operations then continues to completion.
Reverse Operation. If the reverse pushbutton is pressed, contacts 3—4 of the reverse button open, and thus deenergize the forward contactor coil F. In addition, the F contacts are opened as well as the sealing contacts F. Pressing the reverse button also completes the circuit of the reverse contactor coil R which closes the R contacts.
The motor armature circuit's now complete from L1 to A2 and A1 to L2 2. The armature connections are reversed and the armature rotates in the opposite direction. It is impossible for the reverse contacts to close until the forward contacts are open, due to the electrical and mechanical interlocking system used in this type of control circuit. The mechanical inter locks are shown by the broken lines between the R and F coils.
The purpose of dynamic braking is to bring a motor to a quicker stop. To do this there must be a method to quickly use the mechanical energy stored in the momentum of the armature after the main switch is opened.
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