Dynamic brake limiting system

Claim 2

A dynamic brake control system comprising: at least one electrical machine including a variably driven armature and a field winding; a dynamic braking grid resistance connected across the armature; energizing means for variably energizing the field winding; a first current sensor responsive to current through the field winding for generating a first signal having a magnitude defined by the expression K1 I1 where K1 is a constant and I1 is the magnitude of the current through the field winding; a second current sensor responsive to current through the dynamic braking grid resistance for generating a second signal having a magnitude K2 I2 where K2 is a constant and I2 is the magnitude of the current through the dynamic braking grid resistance; means connected to the first and second current sensors for generating a limit signal when the magnitude of the sum K1 I1 + K2 I2 is Equal to a specified value; and regulating means coupled between the last mentioned means and the energizing means for controlling the energizing means in response to the limit signal to limit the magnitude of the sum K1 I1 + K2 I2 to the specified value to thereby limit the braking effort of the electrical machine.

Claim 3

A locomotive dynamic brake system comprising: at least one locomotive traction motor operating as a generator and having a field winding and an armature driven by the wheels of the locomotive; a dynamic braking grid resistance connected across the armature; energizing means for variably energizing the field winding; manually operable means for controlling the energizing means to establish a pre-selected magnitude of current through the field winding representing a locomotive braking demand; a first current sensor for generating a first signal having a magnitude related to the magnitude of current through the field winding; a second current sensor for generating a second signal having a magnitude related to the magnitude of current through the dynamic braking grid resistance; means connected to the first and second current sensors for generating a first limit signal when the magnitude of the sum of the first and second signals is equal to a specified maximum sum; means responsive to the magnitude of current through the dynamic braking grid resistance for generating a second limit signal when the magnitude of said current exceeds a specified maximum grid current; and regulating means coupled to the energizing means for overriding the manually operable means in response to the first limit signal to control the energizing means so as to limit the magnitude of the sum of the first and second signals at the specified maximum sum and overriding the manually operable means in response to the second limit signal so as to limit the magnitude of the current through the dynamic braking grid resistance at the specified maximum grid current to thereby control the braking effort of the locomotive traction motor.

Claim 4

A locomotive dynamic brake system comprising: at least one locomotive traction motor operating as a generator and having a field winding and an armature driven by the wheels of the locomotive; a dynamic braking grid resistance connected across the armature; energizing means for variably energizing the field winding; manually operable means for controlling the energizing means to establish a pre-selected magnitude of current through the field winding representing a locomotive braking demand; a first current sensor for generating a first signal having a magnitude related to the magnitude of current through the field winding; a second current sensor for generating a second signal having a magnitude related to the magnitude of current through the dynamic braking grid resistance; means connected to the first and second current sensors for generating a first limit signal when the magnitude of the sum of the first and second signals is equal to a specified maximum sum; means responsive to the magnitude of current through the dynamic braking grid resistance for generating a second limit signal when the magnitude of said current exceeds a specified maximum grid current; and regulating means coupled to the energizing means for overriding the manually operable means in response to the first limit signal to control the energizing means so as to limit the magnitude of the sum of the first and second signals at the specified maximum sum and overriding the manually operable means in response to the second limit signal so as to limit the magnitude of the current through the dynamic braking grid resistance at the specified maximum grid current to thereby control the braking effort of the locomotive traction motor.

Claim 5

A locomotive dynamic brake system comprising: at least one locomotive traction motor operating as a generator and having a field winding and an armature driven by the wheels of the locomotive; a dynamic braking grid resistance connected across the armature; energizing means for variably energizing the field winding; manually operable means for controlling the energizing means to establish a pre-selected magnitude of current through the field winding representing a locomotive braking demand; a first current sensor for generating a first signal having a magnitude related to the magnitude I1 of current through the field winding; a second current sensor for generating a signal having a magnitude related to the magnitude I2 of current through the dynamic braking grid resistance; summing means coupled to the first and second current sensors for generating a control voltage having a magnitude equal to the sum K1 I1 + K2 I2, where K1 and K2 are constants; means coupled to the manually operable means for generating a reference voltage having a magnitude related to the locomotive braking demand, the magnitude of the reference voltage representing a specified maximum magnitude of the sum K1 I1 + K2 I2; an NPN transistor; means for coupling the control voltage to the base electrode of the transistor; means for coupling the reference voltage to the emitter electrode of the transistor, the transistor being biased into conduction when the magnitude of the control voltage exceeds the magnitude of the reference voltage to generate a first limit signal; grid current limiting means responsive to the magnitude of current through the dynamic braking grid resistance for generating a second limit signal when the magnitude of said current exceeds a specified maximum grid current; and regulating means coupled to the energizing means, the transistor And the grid current limiting means for overriding the manually operable means in response to the first limit signal to control the energizing means so as to limit the magnitude of the sum K1 I1 + K2 I2 at the specified maximum sum and overriding the manually operable means in response to the second limit signal so as to limit the magnitude of the current through the dynamic braking grid resistance at the specified maximum grid current to thereby control the braking effort of the locomotive traction motor.

Claim 6

A locomotive dynamic brake system comprising: at least one locomotive traction motor operating as a generator and having a field winding and an armature driven by the wheels of the locomotive; a dynamic braking grid resistance connected across the armature; energizing means for variably energizing the field winding; manually operable means for controlling the energizing means to establish a pre-selected magnitude of current through the field winding representing a locomotive braking demand; a first current sensor for generating a first signal having a magnitude related to the magnitude I1 of current through the field winding; a second current sensor for generating a signal having a magnitude related to the magnitude I2 of current through the dynamic braking grid resistance; summing means coupled to the first and second current sensors for generating a control voltage having a magnitude equal to the sum K1 I1 + K2 I2, where K1 and K2 are constants; means coupled to the manually operable means for generating a reference voltage having a magnitude related to the locomotive braking demand, the magnitude of the reference voltage representing a specified maximum magnitude of the sum K1 I1 + K2 I2; an NPN transistor; means for coupling the control voltage to the base electrode of the transistor; means for coupling the reference voltage to the emitter electrode of the transistor, the transistor being biased into conduction when the magnitude of the control voltage exceeds the magnitude of the reference voltage to generate a first limit signal; grid current limiting means responsive to the magnitude of current through the dynamic braking grid resistance for generating a second limit signal when the magnitude of said current exceeds a specified maximum grid current; and regulating means coupled to the energizing means, the transistor And the grid current limiting means for overriding the manually operable means in response to the first limit signal to control the energizing means so as to limit the magnitude of the sum K1 I1 + K2 I2 at the specified maximum sum and overriding the manually operable means in response to the second limit signal so as to limit the magnitude of the current through the dynamic braking grid resistance at the specified maximum grid current to thereby control the braking effort of the locomotive traction motor.