Aircraft D-C Circuit Breakers for 28 and 120 Volts

The electric systems of many modern airplanes, particularly the generator circuits of multiengined airplanes, are being operated without adequate electrical operation. This practice is quite different from that usually followed in other electric systems. To provide the necessary protection, new aircraft circuit breakers have been developed with ratings of 300 and 600 amperes at 28 volts and 250 amperes at 120 volts. The interrupting ratings, over a range of altitude from sea level to 50,000 feet, are 12,000 amperes and 5,000 amperes for the 28-and 120-volt circuit breakers respectively. A compact and efficient interrupter makes the 120-volt rating possible. For generator circuit applications, an inverse time-delay reverse-current trip device has been designed for the circuit breakers. For other applications, nondirectional time delay and directional and nondirectional instantaneous trip devices have been designed. Trip-free mechanisms for both the manually and electrically closed circuit breakers and antipump control for the closing solenoid add to the protection provided by these circuit breakers. The operation of these circuit breakers is satisfactory under conditions of vibration, shock, sand and dust, and extremes of temperature and humidity, incident to aircraft.