Traction motor
Traction motorrefers to a type ofelectric motor.A traction motor is used to make rotationtorqueon amachine.It is usually changed into a straight line motion.
Traction motors are used inelectricallypowered rail vehicles such aselectric multiple unitsand electriclocomotives.They are also used in electric vehicles, such aselectric milk floats,elevators,andconveyors.Vehicleswith electrical transmission systems such asDiesel-electriclocomotives, electrichybrid vehiclesandbatterypoweredelectric vehicles.
Transportation applications
[change|change source]Railroad
[change|change source]Railroads first usedDCmotors. These motors usually ran on about 600 volts. High-poweredsemiconductorswere developed to control the switching of AC motors. They have madeACinduction motors a better choice.[1]An induction motor does not require contacts inside the motor. These AC motors are simpler, and more reliable than the old DC motors. AC induction motors known asasynchronous traction motors.
Before the mid-20th century, a single large motor was often used to drive multiple wheels through connecting rods. This was the same way thatsteam locomotiveswould turn their drive wheels. Now, the normal practice is to use one traction motor to drive each axle through a gear drive.
Usually, the traction motor is mounted between the wheel frame and the driven axle. This is called a "nose-suspended traction motor". The problem with this mounting is that some of the motor's weight is on the axle. This causes the track and frame to wear out faster.[1]The "Bi-Polar" electric locomotives built byGeneral Electricfor the Milwaukee Road had direct drive motors. The rotating shaft of the motor was also the axle for the wheels.
The DC motor is made in two parts; therotating armatureand thefixed field windings.The field windings, also called thestator,surrounds the armature. The field windings are made of tightly wound coils ofwireinside the motor case. The armature, also called therotor,is another set of coils of wire wound round the centralshaft.The armature is connected to the field windings throughbrushes.The brushes are spring loaded contacts pressing against thecommutator.The commutator sends the electricity in a circular pattern to armature windings. Aseries-woundmotor has the armature and the field windings connected in series. A series-wound DC motor has a low electrical resistance. Whenvoltageis applied to the motor, it makes a strongmagnetic fieldinside the motor.[1]This produces a high amount oftorque,so it is good for starting a train. If morecurrentthan needed is sent to the motor, there would be too much torque and the wheels would spin. If too much current is sent to the motor, it could damage the motor.Resistorsare used to limit the current when the motor starts.
As the DC motor starts to turn, the magnetic fields inside start to join together. They create an internal voltage. Thiselectromagnetic force(EMF) works against the voltage sent to the motor. The EMF controls the current flow in the motor. As the motor speeds up, the EMF falls. Less current flows into the motor, and it makes less torque. The motor will stop increasing its speed when the torque matches (is the same as) thedragon the train. To accelerate the train, more voltage must be sent to the motor. One or more resistors are removed to increase the voltage. This will increase the current. The torque will increase, and so will the speed of the train. When no resistors are left in thecircuit,full line voltage is applied directly to the motor.
On an electric train, the train driver originally had to control the speed by changing the resistance manually. By 1914, automatic acceleration was being used. This was achieved by an accelerating relay in the motor circuit. This was often called anotching relay.The relay would watch the fall of current and control the resistance. All the driver had to do was select low, medium or full speed. These speeds are calledshunt,seriesandparallelfrom the way the motors were wired.
Road vehicles
[change|change source]Traditionally road vehicles (cars,busesandtrucks) have useddieselorgasolineengines with atransmission.In the latter part of the 20th century, vehicles with electrical transmission systems began to be developed. These vehicles have a source of electricity frombatteriesorfuel cells.They may also be powered by aninternal combustion engines.
A benefit from using electric motors is that some types can generate energy. They act as adynamoduring braking. This helps improve the efficiency of the vehicle.
Cooling
[change|change source]Because of the high power levels used by traction motors, they create a lot of heat. They usually require cooling, often with forced air.[2]
References
[change|change source]- ↑1.01.11.2"Electric Traction Drives".railway-technical.Railway Technical Web Pages. Archived fromthe originalon 2012-08-31.Retrieved2010-09-17.
- ↑"Evaporative Air Conditioning".snowman.au. Archived fromthe originalon 16 May 2016.Retrieved28 April2016.
Other websites
[change|change source]- "Deconstructing a traction motor - Associated Rewinds (Ireland) Limited"
- Image of a nose mounted traction motor onanR46New York City Subway car. The motor can be clearly seen behind the axle with the gear box with the writing on it in the center.
- Another nose mounted traction motor on a wreckedR38Subway car.
- Coney Island Truck Repair shop; many pictures regarding traction motors
- Detached truck with Traction Motors.
- Information About Electric Vehicles