Apparatus for the detection of leakage current in a system includes a power supply and conductors from the supply for supplying power to a load connected to the system. There is an interrupter connected in the system and to a ground point such that a ground leakage current in the system has a closed circuit. Activation of the interrupter about every 12 seconds effectively generates a pulse interrupted ground fault signal. Such signal is detected by a magnetic sensor located relative to a multi-feeder system with high capacitive reactance. The sensor is immune to random electromagnetic and electrostatic conditions in the distribution system. The sensor is synchronized to operate with the interrupter so that sensing is effected at a steady level of a square wave interrupted pulse.
CROSS-REFERENENCE TO RELATED APPLICATIONS
This is a continuation-in-part of applications Ser. Nos. 773,333, filed Sept. 6,1985, now U.S. Pat. No. 4,739,274, and Ser. No. 899,927, filed Aug. 25,1986. Now U.S. Pat. 4,739,27 4. The contents thereof are incorporated by reference herein.
To locate ground faults in a normally ungrounded DC circuit a centertapped voltage divider is connected across the positive and negative buses. An oscillator controlled switch is connected between the centertap and ground which when operating modulates the ground fault currents with a square wave having a repetition rate no greater than 3 hertz. A Hall probe including a field nulling coil is clamped successively along the conductors under test. A capacitive storage circuit maintains the energization of the nulling coil at the level that provided a null indication immediately prior to actuation of a test button. The Hall probe is connected to a read-out oscilloscope which indicates the presence or absence of the square wave modulation. Fault currents as small as 1 ma can be detected.
Disclosed is a ground fault detection apparatus for an operating, normally ungrounded supply system, the apparatus having a periodically grounded center tap of a test impedance that is connected across conductors of the system, and detector circuitry including a charge balance circuit having low gain and wide dynamic range that measures the amplified voltage output of a Hall effect current sensor. A preferred implementation of the circuit has a charge transfer variable oscillator. A pair of microprocessor-controlled counters that are responsive to the oscillator precisely measure the average frequency of the oscillator over intervals that are automatically maintained at approximately one second in duration, the microprocessor calculating the fault current as the difference between current measurements taken with and without the center tap grounded. The apparatus has sufficient dynamic range for directly measuring system currents on the order of 100 A, while reliably detecting leakage currents in the milliampere range.
A device is provided for inspecting an installed electrical system including a power panel and branch circuits with respective circuit breakers. The device includes a power interface unit with a Ground Fault Circuit Interrupter (GFCI) for connection with the power panel. Further, the device includes a power source for temporarily powering the electrical system through the GFCI. For safety purposes, the device allows the energized GFCI to be closed only when the device and the power panel are connected. Moreover, the device provides for selective closing of the circuit breaker of an individual branch circuit to test a power response thereof to indicate whether the individual branch circuit has a fault therein.
The present invention is implemented by deploying an enhanced ground fault detection and location apparatus and by using the apparatus in conjunction with specific circuit analysis methods, using the information generated by the ground fault detection and location apparatus. The ground fault detection and location apparatus comprises the functionality of a voltmeter, an ammeter, a frequency generator, and a variable power supply, thereby providing for a variety of signals and analyses to be performed on a unintentionally grounded circuit in an ungrounded AC or DC power distribution system. The apparatus includes a main unit and a remote unit, which may be a portable hand-held unit. In a first mode, the apparatus of the present invention can be used to detect ground faults. By switching to a second mode, the apparatus of the present invention can be used to locate ground faults. The methods of the present invention involve the generation of various signals by the main ground fault detection and location unit. The generated signals are introduced into the electrical distribution system and monitored by various means, including one or more remote units. By analyzing the system-level response to the generated signals, the specific location of the ground fault or faults can be more readily ascertained, thereby promoting rapid and efficient repair and recovery practices. The apparatus of the present invention may be implemented as a dedicated, permanent installation or as a temporary portable system. Additionally, the system may be implemented as an automatic computer-controlled ground fault location and detection system.
Each circuit breaker in an electrical distribution system is paired with an electronic device which includes a computer processor and an electrical sensor. The processor of each device receives sensory current signals from the sensor contained in the same device, converts the signals from analog to digital data, and processes this digital data into information indicative of the direction of current in the vicinity of the circuit breaker with which the device is paired. The devices are networked (e.g., via Ethernet) so that each device's processor receives the current direction information which is produced by every other device, and processes the entirety of the current direction information which is both locally and remotely produced, thereby identifying the suspected fault in the system and deciding whether to send an activation signal to the circuit breaker with which the device is paired in order to isolate the fault.
