Starting resistors are in electrical machines (for example, electric railway locomotives with DC - traction motors ) electric resistors that are switched on to protect the traction motor during the start to the current limit in the engine to the permissible level. They are switched on or off with a drive switch . As a rule, they also serve as a braking resistor . As soon as the electric machine works as a generator ( electric motor brake ), they protect the machine from excessive voltage caused by induction . At the same time, the current leads to a reduction in the speed of the machine and thus to the braking of the vehicle.
Another type of starting resistor is the starting resistor for starting stationary electric motors.
In order to dissipate the resulting heat, the starting / braking resistors are usually placed on the roof. In railcars there is often an identical group of resistors in the passenger compartment in order to serve as heating in winter. In modern vehicles, they are located in a heat exchanger so that the room temperature can be regulated independently of the brake.
To get a better efficiency to achieve, now mostly be power controller or frequency converter used. The current is limited by only drawing short pulses from the supply network. When braking, energy is fed back into the supply network ( recuperation ) . However, braking resistors are present when using electromotive brakes. They are necessary in order to be able to brake safely even if the connection to the network is interrupted or the network is not capable of receiving for other reasons.
- Definitions of the mechanical engineering department at Bielefeld University of Applied Sciences ( Memento from November 9, 2007 in the Internet Archive )