Solid state inverse overcurrent relay

A relay for tripping a power system circuit breaker, said relay comprising:

• means connected to the power system for providing a radiation signal proportional to line current flow in the power system with the same time-current characteristic as a fuse,
• a trip coil connected to the circuit breaker, and radiation sensing means connected to energize said trip coil in response to a predetermined radiation signal whereby the circuit breaker is opened when the predetermined signal is sensed.

The relay according to claim 6 wherein said sensing means includes a silicon controlled rectifier connected in series with said trip coil and a DC power source, said sensing means being connected to fire and silicon controlled rectifier upon sensing the predetermined radiation signal.

The relay according to claim 7 wherein said sensing means includes a phototransistor.

The circuit according to claim 9 wherein said shunt circuit includes a transistor having a base circuit connected across said trip coil and a zener diode connected in series with said heater wire and transistor.

A solid state inverse overcurrent relay for tripping a power system circuit breaker, said relay comprising:

• an infrared radiation signal means connected to provide a heat radiation signal in proportion to the current flow in a power system which is time dependent upon the thermal time constant of the radiation source,
• an infrared detector positioned to respond to the infrared radiation signal means and trip means connected to said detector to respond to a predetermined radiation signal to trip and circuit breaker.

The relay according to claim 11 wherein said detector is responsive to the total energy radiation from the signal means.

An inverse overcurrent circuit for tripping a power system circuit breaker under overcurrent conditions, said circuit comprising:

• a source of infrared radiation connected to respond to current flow in the power system circuit, said source having a thermal response inversely proportional to the second power of current,
• a trip coil connected to the circuit breaker and means responsive to the infrared radiation from said source for energizing said trip coil to open said circuit breaker.

A solid state inverse overcurrent relay for a power system, said relay comprising:

• means connected to respond to current flow through the power system for providing an infrared radiation signal which is time dependent upon the thermal time constant of the radiation source and the magnitude of current flow,
• an infrared radiation detector positioned to sense the radiation signal from said providing means,
• and a tripping circuit including a circuit breaker in said power system and connected to respond to a predetermined infrared radiation signal sensed by said detector to open said circuit breaker.

The relay according to claim 14 wherein said detector comprises a phototransistor.