Resistor protection systems

Abstract

A system for protecting an electrical resistor, such as, for example, the dynamic braking resistor of a D.C. traction motor used in a diesel-electric locomotive, from burn-out in the event of a malfunction such as a cooling fan failure or air blockage, over-load, high ambient temperature, etc. Such protection is afforded by a noise-immune system that continuously monitors the resistor temperature and provides an output signal when the resistor temperature reaches a predetermined level above its normal operating temperatures short of an unsafe level. This is done by sensing the change in resistivity of the resistor with change in temperature thereof to provide a first control signal. A second control signal proportional to the current in the resistor is obtained and compared with the first control signal to obtain the aforesaid output signal proportional to the resistor temperature above ambient temperature. This output signal is used to trip the system at the predetermined temperature level thereby to reduce or interrupt the current or perform some other function to protect the resistor from damage. A modified system provides both an output trip signal and temperature readout.