Arc fault circuit interrupter without DC supply

Details Arc fault circuit interrupter without DC supply Arc fault circuit interrupter without DC supply

1999-05-19

2001-03-06

Leja, Ronald W. (Department: 2836)

Electricity: electrical systems and devices

Safety and protection of systems and devices

Ground fault protection

Reexamination Certificate

active

06198611

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an apparatus for arc faults in electrical power lines, and more particularly to apparatus that does not include a DC power supply.
2. Description of the Prior Art
A number of devices and methods have been used in the past to detect arc faults. Some of the prior art devices and techniques have involved the use of E and B field arc sensors, the detection of the amplitude of arc fault rate of change of current signals, the use of non-overlapping band-pass filters to detect white noise of arcs, and devices which detect the disappearance of arc faults near current zero crosses. Most of the prior art of arc detection occurs in circuit breakers where it acts as an enhancement to thermal-magnetic detection elements, which alone may fail to detect arc faults.
There is a need for an economical arc fault detector which may be mounted into a wiring device which offers the same down stream protection as an arc fault detecting circuit breaker but at the similar cost advantage that currently exist between ground fault interrupting receptacles and ground fault interrupting circuit breakers. This invention provides that cost advantage.
SUMMARY OF THE INVENTION
It is an object of this invention to provide an arc fault circuit interrupter that is simpler and less expensive to manufacture than those previously known. Briefly stated, and in accordance with a presently preferred embodiment of the invention, an arc fault detecting circuit includes a saturating current transformer coupled to the electric power circuit to be protected that senses di/dt arc fault steps in current. A rectifier is preferably connected to the sensor, and an integrator is connected to the rectifier. The integrator voltage is used to activate a trigger device. The trigger device activates circuit interrupting means. The device does not require a DC power supply as found in the prior art.
The saturating current transformer produces a constant output voltage at a pre determined level of arc fault current. This eliminates the effect of brief high current pulses of short duration from having the same effect on the detector as a series of smaller amplitude arc faults steps.
In accordance with a further embodiment of the invention, a second integrator and trigger device is used instead of a saturating transformer to mitigate the effect of normal switching arcs and also the brief high current arc pulses.
In accordance with another embodiment of the invention, an inhibit switch is placed between the integrator and trigger device, where it acts to inhibit the di/dt charging integrator from activating the trigger device unless the associated peak 60 Hz component of arc current exceeds a predetermined value.


REFERENCES:
patent: 5185686 (1993-02-01), Hansen et al.
patent: 5459630 (1995-10-01), MacKenzie et al.

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