Reversing switch
The reversing switch , mostly as due to the main function of driving reversing switch or ride Wender called, is part of electromechanical or electronic assembly recently an electric locomotive that can be used where the direction of rotation of the traction motors switched. It is thus possible to drive forwards and backwards with a tram or locomotive.
functionality
The direction of the current to the magnetic fields of the motors is switched with the reversing switches. This changes the direction of rotation of the motor. By switching over while driving, the traction motors of the locomotive can be used as generators (electric brakes). This requires a controlled feed back into the contact line and / or a device to convert the electrical energy into thermal energy via a resistance device. Reversing switches can be switched manually when the power is off, but this is only possible when the locomotive is at a standstill.
Construction
In order to keep the size small and thus the weight low, reversing switches are not designed as load switches. They are only operated when there is no load and are often coupled with the tap changer. This ensures that they can only be operated in the so-called zero position (no drive power) of the tap changer.
If the reversing switch is only responsible for a single motor (normal case), it often has a mechanical zero position, which means that a drive motor can be disconnected individually in the event of a defect. The actuation in modern electric locomotives is usually done pneumatically .
Installation location
The reversing switches are usually present several times, either a reversing switch for each bogie (usually designed as a drive unit), or individually for each traction motor. On the locomotive, they are usually the last switching element before the traction motor and in this case are located between the step switch and the traction motor.
History of origin
At the beginning of electric locomotive construction, only the reversing switch was known . With the introduction of electrical resistance braking systems , a second switch of similar construction was used, the so-called brake reversing switch , which switched the drive motor from driving to braking. Since the two switches actually perform the same circuit, these circuits are now performed by one component, the reversing switch . However, this presupposes that the step switch has braking positions, because the combination of both functions, unlike in the past, transfers the braking energy to the braking resistors via the step switch.
The first combined drive and brake step switches were used in single-phase AC machines with a so-called recuperation brake , since there the load and braking energy are conducted via the transformer and step switch and the same cables and busbars can therefore always be used. For generator operation, only a contact wire-independent external excitation of the traction motors must be possible.
Reversing switch in AC technology
In three-phase AC technology, the term reversing switch refers to switches and contactors that are used to change the direction of rotation of the AC network.
Advancement of technology, electronics
In recent times, the formerly electromechanical assemblies in drives are increasingly being made fully electronic with power semiconductors . These assemblies are less prone to wear and tear and are easier to use, and some can be controlled electronically. The electronic control makes it possible not to use braking resistors to convert the energy generated during braking into heat, but to feed it back into the alternating current network.
Individual evidence
- ↑ Brockhaus der Naturwissenschaften und Technik, Wiesbaden 1952, V. No. W 118, page 543
- ↑ Karl Sachs: Elektro Vollbahnlokomotiven , Verlag J. Springer, 1928, page 246f