Resistance brake

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Braking resistors of a resistance brake on the roof of a type E tram car in Vienna (behind the pantograph)

In drive technology, a resistance brake is a braking method in which electric motors are braked using special braking resistors .

Layout and function

There are mains-dependent and mains-independent drag brakes. Like any electromotive brake , both variants take advantage of the fact that an electric motor can be operated as a generator by simply reversing the polarity ; the kinetic energy of the work machine is thus converted into electrical energy. The difference between the two variants lies in the generation of the excitation voltage . With the mains-dependent resistor brake, the excitation voltage is provided by a transformer . Since the excitation voltage in electrically powered rail vehicles comes from the auxiliary winding of the transformer, this excitation only works when the main switch is switched on . With the mains-independent resistor brake, the excitation field is initially generated by a current surge. The voltage for this is taken from a battery . The exciter field is then supplied with energy from the braking current generated.

The braking energy converted into electrical current is not used, but converted into heat via special braking resistors. In electrically powered vehicles, the braking resistors can either be mounted on the roof, in the passenger compartment or under the vehicle. For cooling, these resistors are either provided with their own fans or they are self-ventilated. In order to make the brake effective, the motor is disconnected from the mains and switched to the braking resistor. The speed of the motor drops quickly. The motor is braked almost to zero.

application

The (electric) resistance brake is used in electric and diesel-electric locomotives and railcars . The name resistance brake comes from the fact that the electricity generated is converted into heat in resistors directly on the locomotive . Depending on the network conditions, there is now an increasing possibility of feeding the electricity back into the contact line. This regenerative brake (recuperation brake) has largely replaced the pure resistance brake; Mixed forms occur. They also enable low-wear braking when the catenary network is not receptive because there are neither consumers in their own feed area, nor is the supplying substation capable of energy recovery. Resistance brakes are also often used on trams . The resulting heat is also used to heat the vehicle. Another use of the resistance brake is in hoists as lowering braking.

Advantages and disadvantages

The advantage of the resistance brake lies in its freedom from wear . For this reason, it was initially installed in particular in locomotives that were mainly used on mountain routes, as the resistance brake can be used to keep the speed constant on slopes in a simple manner. Its main advantage, however, is that it remains fully functional even if the contact line cannot be removed. Regenerative braking is dependent on the network, into which it is supposed to feed back the braking energy, that it is also capable of receiving it. With the appropriate design of a resistance brake, it is even possible to travel downhill without contact line voltage and it can also be used in diesel-electric vehicles. In the case of direct current vehicles with classic controls, in particular, the same resistances can be used as when starting off.

The disadvantage of the dynamic brake compared to regenerative brakes is the energy loss, since there is no energy recovery. Since the kinetic and potential energy is converted into heat via the braking resistors and dissipated, this energy component can be used poorly and is therefore practically useless. The braking current can only be used for heating the car. However, this braking energy is also lost in the case of friction brakes, and these also do not work without wear. The resistance brake, like any regenerative brake, does not work until it comes to a standstill; a mechanical brake is always required for holding braking and for holding the vehicles stationary.

literature

  • Zarko Filipovic: Electric Railways . 4th revised edition, Springer Verlag, Berlin Heidelberg New York 2005, ISBN 3-540-21310-4

Individual evidence

  1. ↑ a b c Ernst Hörnemann, Heinrich Hübscher: Electrical engineering specialist training in industrial electronics. 1st edition. Westermann Schulbuchverlag GmbH, Braunschweig, 1998, ISBN 3-14-221730-4 .
  2. ^ A b c Jürgen Janicki, Horst Reinhard: Rail Vehicle Technology. 2nd revised and expanded edition, Bahn Fachverlag GmbH, Heidelberg Mainz 2008, ISBN 978-3-9808002-5-9 .
  3. ↑ a b Detlev Roseburg: Electrical machines and drives. Fachbuchverlag Leipzig in Carl Hanser Verlag, 1999, ISBN 3-446-21004-0 .
  4. ↑ European patent specification: Self-ventilated braking resistor No. EP 1 074 026 B1 ( Memento from March 4, 2016 in the Internet Archive ) (accessed on March 13, 2012; PDF; 47 kB).
  5. ↑ Heinz M. Hiersig (Ed.): VDI-Lexikon Maschinenbau. VDI-Verlag GmbH, Düsseldorf 1995, ISBN 9783540621331 .
  6. ↑ a b Hans Streiff: Recovery of braking energy in rail transport (Part I) ( Memento from August 31, 2011 in the Internet Archive ) (accessed via the web archive on May 30, 2016).

See also

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