Traction motor

As traction motors, traction motors and the motors are referred to with which a wheel of a locomotive is directly driven. This applies especially to the electric motor for driving rail vehicles and locomotives and railcars. Since the establishment of electronic frequency converter (Traction ) in the late 20th century to come, regardless of the configuration of the traction power system as traction motors predominantly three-phase induction motors are used.

Designs distinctions

When initially low speeds and simple claims significant differences in the traction motors were first in the electric mode. This reflects distinctions after the supply current system used can make, which can be differentiated according to particular DC, single phase with 16 2/3 or 50 Hz, three-phase or three-phase alternating current.

These distinctions are for modern railways rarely used, since in many cases nationwide uniform power system is, must be designed for the all engines of the respective web anyway. Concise therefore are within a rail system or on a particular vehicle, the mechanical differences according to the type of engine mounting between locomotive body and wheel set on the one hand and the type of power transmission from the motor to the wheel ( see below).

Distinction according to the current system

In the early days of electric railways electric traction power system had to orient to the requirements of the traction motors. The availability of power electronics are these requirements no longer and driving motors can be designed independent of the specific traction power system to meet the requirements of the vehicle by electronic frequency converter. The following sections and illustrations are at the historical background.

DC motor

The DC series-wound motor has a high starting torque, making it ideally suited for use in vehicles. The relatively low required wheel speeds also encourage the use of Kommutierungsproblemen respect of which tend at higher speeds. With DC motors is usually a " direct drive " with the supernatant removed from the catenary voltage carried out, possibly with interposition of controls. Unproblematic This was shown in trams and subways, which could be operated well with a few hundred volts at the limited length of the route. For long-distance trains, a high voltage was for the transmission of a low hand, on the other hand, however, unfavorable for the engine. The current systems used here broadly stable at 1.5 kV and 3 kV. At 3 kV in each case two engines are usually connected in series in order to halve the voltage for each motor. Nevertheless, the DC transmission over long distances showed as economically costly.

AC motor

Like the DC series motor of single phase series-wound motor has a high torque. The use of the specially developed for railway companies the AC motor can it be to reduce the financial burden on the current transfer through conduction of high voltages. This, however, under the condition that on the locomotive (as opposed to direct current " direct drive " ), a correspondingly large transformer and high-voltage tap changers were included to herunterzuspannen ultimately 15 kV to 25 kV amount tensions and currents onto the motor - acceptable sizes.

Be problematic initially showed to use the widespread industrial frequency of 50 Hz. With the large motors undesirably high induction voltages generated by this frequency in each case currently " dead zone " contained in the winding coil, which led to sparking, and high wear on the commutator and brushes. Experiments showed that the problem could dominate better at low frequencies. This led in 1912 to an agreement of the German-speaking countries on an AC catenary voltage of 15 kV at a frequency of one third of the 50 Hz - measure, ie from 16 2/3 Hz Later, other countries such as Sweden and Norway took this quite successful operating system. However, systems with higher voltages and frequencies could in addition also be applied worldwide, notably the 25 kV 50 Hz system.

Since about 1990, losing traction motors Single phase motors as important as for the ground- fixed by the availability of electronic power converters and control technology, the operational favorable phase motors can be used.

Three-phase motor

The three-phase asynchronous motor offers by its very simple structure in which primarily a power transmission is attributable to the rotating armature, some advantages. Therefore, the first ac traction drives were conducted in 1900 with AC motors. The disadvantage here were two main points: on the one hand allows the three-phase motor operate only with certain speeds, which are determined by the frequency of the phase current and the number of poles of the motor winding. Reversible motors can be only a rough speed control in a maximum of six steps. The other point was historically the costly overhead line which had to be carried out either three-pole or double pole (when adding the rails as the third pole). Technically and operationally especially the wiring on switches and crossings is complicated.

Nevertheless, the three-phase system has been used for example in the Italian State Railways from 1904 to 1976 in a large extent.

Since the 1990s, however, can be generated for motor drive with any frequency from DC or single phase of the contact line with modern power converters and control systems on the locomotive itself -phase current. This allows the use of simple, robust and powerful AC motors with variable speed control.

Distinction according to the Mounting

• Hollow shaft drive
• Nose-suspended drive

Distinction according to the power transmission

• Westinghouse spring drive
• Buchli drive
• Spring cup drive
• Rubber ring segment drive
• Cardan rubber ring spring drive
• Cone ring drive gear

Mechanical assembly variants

The heat generated during operation of the drive motor waste heat must be dissipated. This is done either directly plugged onto the motor shaft impellers ( self-cooled ) or with special traction motor fans which are located outside of the traction motor and have its own drive. Self-ventilated motors come in lightweight railcars for use, externally ventilated motors are used in locomotives and other vehicles with high power ratings.

The drive motor forms, together with the power transmission to the driving wheel. This results in different types of traction motors:

• Axis motor - The motor is located entirely on the axle shaft - formerly used in the United States
• Levitation motor - The rotor is arranged on the axle shaft, the stator is accommodated in the suspension chassis - formerly used in the United States
• Tatzlagermotor - traction motor based partly on the axis from high wheel / rail forces
• Frame motor - drive motor is housed entirely in the sprung chassis and transfers the force with rods, hollow shafts or cardan shafts on the wheel / wheel sets.

Previously also traction motors were used in which two electric motors were housed in the same housing:

• Twin engine - the shafts of the two rotors are adjacent
• Twin motor - the two rotors are on a common shaft, used in Italian DC locomotives and for 50Hz Einphasenreihenschlussmotoren.

The traction motors can be distinguished in the vehicle after the installation:

• Transverse engine - the most common arrangement in locomotives and railcars
• Longitudinal engine - in tramcars and high-speed trains
• Vertical engine - also used in some Locomotives

Most electric locomotives have Rekuperationsbremsen, the motors then function as a generator, similar to a hybrid car, and thus provide an additional braking effect available. The electric power thus generated can be fed back again into the overhead line with modern electric locomotives or is converted in older electric locomotives via braking resistors heat emitted through air vents on the roof of the locomotive to the environment.

• Schienenfahrzeugtechnik
• Electric locomotive technology
• Electric motor