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Principles of Energy Conversion
Published in Hamid A. Toliyat, Gerald B. Kliman, Handbook of Electric Motors, 2018
Hamid A. Toliyat, Gerald B. Kliman
In dynamic braking, traction motors are used as generators to retard vehicles. This limits wheel and brake shoe heat and wear while holding heavy loads on favorable grades or while slowing vehicles that stop frequently. Rheostatic braking is dynamic braking in which the absorbed energy is dissipated as heat in resistors. It is widely used on mass-transit, light rail vehicles, and internally powered vehicles. For the mass-transit application (short time and intermittent) air flow over the vehicle suffices to cool the resistor grids. On internal powered vehicles such as locomotives or OHVs, which can have sustained periods of retarding, the grids are typically cooled using blowers driven by dc series wound motors. This is one application where the dc motor has a unique niche, unlikely to be replaced by ac. The dc blower motor unit is self loading and designed to reach its maximum blower speed at maximum grid amps and is tapped across (put in parallel with) some portion of the grid resistor such that it will obtain the correct voltage. The beauty of this arrangement is that no control system is required since the blower motor unit operates automatically whenever power is applied to the grids—and it also uses waste power. In regenerative braking, power is returned to the line. While transit cars in principle can return energy to the line when stopping, the process has many limitations depending on the line's ability to receive power. Therefore, a full rheostatic braking system is also needed, for the foreseeable incidents when the line will be unreceptive.
dc Motor Speed Control Employing dc/dc Converters
Published in K Sundareswaran, Elementary Concepts of Power Electronic Drives, 2019
When the existing power source is a dc grid or battery, a dc chopper or dc/dc converter can be used for either armature voltage control or field excitation control of a dc motor drive for variable-speed operation. Chopper circuits with a dc motor drive system are conveniently developed and analyzed for either first-, second-, or four-quadrant operation. In addition to regenerative braking, dynamic braking can also performed with dc motors using chopper circuits.
A fast simulation approach to assess draft gear loads for heavy haul trains during braking
Published in Mechanics Based Design of Structures and Machines, 2023
Jony J. Eckert, Ícaro P. Teodoro, Luis H. Teixeira, Thiago S. Martins, Paulo R. G. Kurka, Auteliano A. Santos
The locomotives traction force Ft1 and Ft2 are defined among the eight available notch points, P1 to P8, as shown in Figure 2a. In braking situations, the locomotive electric motors act in the dynamic braking mode, which allows the absorption of a portion of kinetic energy that is converted into heat to be dissipated. For the selected locomotive, there are four stages for the dynamic brake forces which are expressed by the D1 to D4 curves shown in Figure 2b.
Analysis of the energy and safety critical traction parameters for elevators
Published in EPE Journal, 2018
Anand Raghavendra Rao, Matada Mahesh
The sample elevator data for torque, energy consumption is measured. While the empty cabin is travelling up and down for both the sample machines that are specified, when the elevator car travels in the down direction, the machine is working in the motoring regime. When the elevator is travelling up, the machine works in the generator regime, and the maximum out of balance torque is achieved when the full load car travels up or the empty car travels down from the top landing. The machine, when in the generator regime, generates power that is generally dissipated in the form of heat through dynamic braking resistors, as the capacity and speed is very low.