Electricity: electrical systems and devices – Safety and protection of systems and devices – Ground fault protection
Reexamination Certificate
2001-09-14
2003-09-09
Jackson, Stephen W. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Ground fault protection
C361S045000, C361S048000
Reexamination Certificate
active
06618229
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to electrical control systems, and more specifically to an aircraft electrical control system which disconnects power to a load when a current imbalance is sensed.
In the electro-mechanical arts, current imbalances are indicative of serious problems that can lead to disastrous results, such as arcing within fuel pumps. Since fuel pumps are often housed within a fuel vessel to directly pump fuel out of the vessel, arcing within a fuel pump can lead to an explosion of fuel-air mixture and a subsequent breach of the fuel vessel, which can be catastrophic. In light of the seriousness of such an event, a device or methodology is needed which can suppress this type of arcing, as well as other associated problems. Presently, a common type of circuit protection device being utilized in aircraft is a thermal circuit breaker. However, arcing typically does not cause thermal circuit breakers to activate. Thus, there has been a long-felt need for the function of current imbalance detection in an aircraft. One very important form of current imbalance is a ground fault in which current is flowing between a circuit or electrical device to ground, when such current flow is not desired. In the prior art, ground fault detection has been addressed by a separate ground fault interruption unit. However, such prior art systems have had limitations, including the necessity of rewiring the aircraft. In addition to the requirement to rewire the aircraft, additional space had to be found to accommodate the ground fault interruption system.
One currently available ground fault interruption unit made by Autronics (model 2326-1) has been used in large commercial aircraft for the purpose of ground fault protection for fuel pumps. The Autronics unit detects a ground fault and outputs a signal indicative of a fault by use of a current transformer and acts by removing power to the fuel pump control relay.
There exists a need for an improved circuit protection device for aircraft. It would further be desirable for the circuit protection device to be included within an existing device in the aircraft, or to be packaged with an existing device, sharing the same connections to existing electrical circuits, since space for avionics is limited in any aircraft and adding wiring to accommodate a new device is very difficult. The present invention addresses these and other concerns.
SUMMARY OF THE INVENTION
Prior art systems for ground fault detection are helpful to reduce arcing in aircraft electrical systems, including aircraft fuel pumps. This issue has become a major concern of the Federal Aviation Administration and recent studies have promulgated a variety of studies and regulations in an attempt to prevent fuel tank ignition. One recent conference on fuel tank ignition prevention hosted by the FAA on the 20
th
and 21
st
of June 2001 at the SEATAC Airport Hilton was given in order to better understand the provisions SFAR No. 88 and related certification procedures and airworthiness standards for transport category aircraft. A copy of the materials handed out and discussed at that meeting is attached hereto as Appendix A and incorporated herein by reference. Also attached as Appendix B is a copy of the Federal Register of Monday, May 7, 2001 relating to SFAR No. 88, “Fuel Tank System Fault Tolerance Evaluation Requirements and Related Airworthiness and Certification Standard”. These materials and this conference emphasized the importance of detecting ground faults and operating on the circuit to prevent, to the largest extent possible, arcing within fuel pumps and the like that may be exposed to flammable materials.
In addition to the Autronics Corporation Model No. 2326-1 series ground fault current detector previously discussed (and attached hereto as Appendix C), there also exists a ground fault detection system sold by PRIMEX Aerospace Company as Part No. 437, 437. A brochure for the PRIMEX system is attached as Appendix D. The PRIMEX system uses a current transformer to detect ground fault currents in three phase 400 Hertz motors. However, these prior art systems has serious limitations if they are to be broadly applied to aircraft, either as original equipment or retrofit, and they require separate wiring and space in addition to the currently existing equipment. The present invention offers many operational and functional advantages, in that it fits into the space available on the panel for the existing relays, utilizes the power of the system it is monitoring to operate, and is functionally faster and more efficient in detecting a ground fault and removing power from the system being monitored.
The present invention is a current imbalance detection and circuit interrupter particularly attractive for use in aircraft, for protecting a circuit having a line side and a load side. In a currently preferred embodiment, the present invention incorporates the current imbalance detection and circuit interrupter within the existing aircraft power control relay package. For example, in a fuel system application, the current imbalance detection and circuit interrupter is incorporated within the fuel pump control relay package. Therefore, the invention can be retrofit to existing aircraft, or can be utilized in newly constructed aircraft and new aircraft designs already incorporating the relay system. The current imbalance detection and fault circuit interrupter includes a housing, a power supply, a circuit to be monitored, a sensor, a logic controller, and a power controller (for example: relay, contactor, solid state relay, etc.). In a presently preferred embodiment, the invention can also include a fault indicator, a press to test switch and a reset switch. The power supply is configured to provide power to the sensor, logic controller and the power controller. The sensor is configured to sense a current imbalance in the circuit being monitored. In one presently preferred embodiment, the sensor to monitor current imbalance is a Hall effect sensor. The logic controller is configured to monitor a relay control input signal and to process inputs from the sensor.
In a presently preferred embodiment, the logic controller compares the sensor signal with predetermined limits representing acceptable operation and outputs a signal representing a circuit current imbalance when the sensor signal is outside the acceptable limits. The power controller is configured to receive input from the logic controller and remove power to the load side of the circuit when a current imbalance is sensed. In a presently preferred embodiment, the power removal from the load side of the circuit due to a sensed current imbalance is maintained until the power source to the current imbalance detection and circuit interrupter is cycled. In another presently preferred embodiment, power removal is maintained until a reset switch is activated. In a presently preferred embodiment, the fault indicator provides an indication of whether a current imbalance condition has occurred. A press to test switch may be included to check the operation of the unit during maintenance. In a presently preferred embodiment, the fault reset switch is used to reset the fault indicator.
The present invention also provides for a method for interrupting an electrical circuit for an electrical load, the electrical circuit having a line side and a load side with a ground fault. In summary, the method comprises providing a supply of power, continually monitoring and sensing the line side of the circuit for a current imbalance, continually monitoring the relay control input, receiving input from a logic controller and interrupting the relay control input signal when a current imbalance is sensed, and enabling the fault indicator. In one presently preferred aspect of the method, interrupting of the circuit when a current imbalance is sensed is maintained until the power source is cycled. Typically, the load being supplied with the current being monitored is a motor. In another preferred aspect, the current imbalance de
LandOfFree
Aircraft applicable current imbalance detection and circuit... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Aircraft applicable current imbalance detection and circuit..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Aircraft applicable current imbalance detection and circuit... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3056823