Electricity: electrical systems and devices – Safety and protection of systems and devices – Ground fault protection
Patent
1997-03-18
1998-06-16
Gaffin, Jeffrey A.
Electricity: electrical systems and devices
Safety and protection of systems and devices
Ground fault protection
361 78, H02H 300
Patent
active
057680779
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
A first aspect of the present invention relates to an earthing wire disconnection detection apparatus for detecting disconnection of an earthing wire between an electrical or electronic device and earth, and in particular to an earthing wire disconnection detection apparatus which can detect earthing wire disconnection even during operation of the electrical or electronic device. A second aspect of the present invention relates to a leakage detection apparatus for detecting leakage of an electrical or electronic device, and in particular to a leakage detection apparatus which can continuously monitor for the presence of a disconnection of an earthing wire and for leakage, even during operation of the electrical or electronic device, by using an earthing wire disconnection detection apparatus.
BACKGROUND ART
With electrical or electronic devices, there are cases in which circuit operation requires the device to be earthed, and cases where although circuit operation does not require them to be earthed, in order to prevent danger such as electrocution due to leakage, they must be earthed. With this type of electrical or electronic device, if the earthing wire is disconnected, then the intended circuit operation cannot be obtained, or there is the possibility of electrocution or the like due to leakage.
Heretofore, as an apparatus for monitoring the earthing condition of an earthing wire, there is the apparatus disclosed for example in Japanese Unexamined Patent Publication No. 7-83976.
With this apparatus, prior to starting a load machine, the electric power circuit for the machine is forcibly grounded to an earth terminal, and a detection device is used to detect if the circuit is properly earthed.
With this apparatus however, the earth condition of the earthing wire is only checked prior to starting the machine, and monitoring of the earthing wire during operation of the machine is not carried out. Therefore, if the earthing wire becomes disconnected during operation of the machine, then of normal circuit operation being lost, machine use will continue without this being known, thus inviting an unexpected result.
For example, taking a known line filter circuit as an example, this has a normal mode noise absorbing capacitor connected between two lines, a common mode choke coil connected into the lines at a subsequent stage, and two common mode noise absorbing capacitors connected at a further subsequent stage between the lines and an earth terminal. The common mode noise absorbing capacitors are two terminal capacitors with a series connection point (central point) connected to earth.
With the above-mentioned line filter circuit, if a disconnection occurs in the earthing wire connecting the central point of the common mode noise absorbing capacitors, then the normal noise filtering function is lost. Since with the conventional apparatus, this disconnection fault the earthing wire cannot be detected, then in despite the earthing wire being disconnected, it is treated as if the normal filtering function is being obtained. Therefore, noise is propagated to the load, or the power source or signal supply side, connected to the line filter.
Moreover, with the circuit configuration of the above-mentioned earthing condition monitoring apparatus, the earthing wire for the load machine is connected between a ground relay contact point and earth. Therefore, even if the earthing wire is disconnected, a small current flows in a photocoupler of a detection device, with the problem that the controller for the unit is judged to be in a normal earthed condition.
Furthermore, as a conventional apparatus for detecting leakage of an electrical or electronic device, there is a type which detects an imbalance current in a power supply line to the electrical or electronic device.
With this leakage detection apparatus, for example with a load machine such as a motor, leakage is detected by monitoring for imbalance of a current flowing in the two power supply lines connected to the motor coil in the housing case.
REFERENCES:
patent: 4661880 (1987-04-01), Futsuhara
patent: 4757417 (1988-07-01), Futsuhara
patent: 5027114 (1991-06-01), Kawashima et al.
Asada Norihiro
Futsuhara Koichi
Gaffin Jeffrey A.
Medley Sally C.
The Nippon Signal Co. Ltd.
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