Principle of Operation
During braking, the motor fields are connected across either the main traction generator (diesel-electric locomotive, hybrid electric vehicle) or the supply (electric locomotive, electric vehicle) and the motor armatures are connected across braking grids (rheostatic) or the supply (regenerative). The rolling wheels turn the motor armatures and when the motor fields are excited, the motors act as generators.
During dynamic braking, the traction motors, which are now acting as generators, are connected to the braking grids of large resistors which put a large load on the electrical circuit. When a generator circuit is loaded down with resistance, it causes the generators to resist rotation, thus slowing the train. By varying the amount of excitation in the traction motor fields and the amount of resistance imposed on the circuit by the resistor grids, the traction motors can slow the train to about 5 mph (8 km/h).
For permanent magnet motors, dynamic braking is easily achieved by shorting the motor terminals, thus bringing the motor to a fast abrupt stop. This method, however, dissipates all the energy as heat in the motor itself, and so cannot be used in anything other than low-power intermittent applications due to cooling limitations. It is not suitable for traction applications.
Read more about this topic: Dynamic Braking
Famous quotes containing the words principle of, principle and/or operation:
“I often wish for the end of the wretched remnant of my life; and that wish is a rational one; but then the innate principle of self-preservation, wisely implanted in our natures, for obvious purposes, opposes that wish, and makes us endeavour to spin out our thread as long as we can, however decayed and rotten it may be.”
—Philip Dormer Stanhope, 4th Earl Chesterfield (1694–1773)
“The monk in hiding himself from the world becomes not less than himself, not less of a person, but more of a person, more truly and perfectly himself: for his personality and individuality are perfected in their true order, the spiritual, interior order, of union with God, the principle of all perfection.”
—Thomas Merton (1915–1968)
“An absolute can only be given in an intuition, while all the rest has to do with analysis. We call intuition here the sympathy by which one is transported into the interior of an object in order to coincide with what there is unique and consequently inexpressible in it. Analysis, on the contrary, is the operation which reduces the object to elements already known.”
—Henri Bergson (1859–1941)