Overload detecting scheme for an electric propulsion system for traction vehicles

DETAILED DESCRIPTION A general objective of this invention is to provide an improved overload detecting scheme for the electric propulsion system of a traction vehicle.
It is another object of the invention to provide an electrical overload detecting scheme which discernably responds to any one of a variety of different abnormal conditions in such a propulsion system, including a shorted field switch, a malfunction in the field switch control, and an excessive demand for power.
A further object is the provision of such a scheme capable of detecting a potentially harmful overload condition while riding through short-term disturbances.
In carrying out this invention in one form, an intermittently conductive switch is connected in series with a shunt field winding of an exciter for a prime mover-driven generator which supplies electric power to the traction motors of a self-propelled vehicle, and the proportion of time that the switch is conductive is suitably controlled so as to vary the level of generator excitation as desired between predetermined normal maximum and minimum limits.
If the field switch were conductive continuously instead of intermittently, the generator would be overexcited and the power components of the vehicle propulsion system would be electrically overloaded.
To detect this unsafe condition, monitoring means is connected across the field switch for producing an output signal in response to the field switch being continuously conductive for an abnormally long period of time.
In a preferred embodiment, the detecting scheme also includes means responsive to the production of the aforesaid output signal for automatically reducing the level of field excitation.
The invention will be better understood and its various objects and advantages will be more fully appreciated from the following description taken in conjunction with the accompanying drawings.