Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1996-10-22
1998-08-04
Mullen, Jr., Thomas J.
Communications: electrical
Condition responsive indicating system
Specific condition
340660, 340664, 324510, 324691, 324714, B60Q 100
Patent
active
057900388
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention generally relates to a system for the remote measuring of the protection ground associated to any kind of electric system, for civil or industrial use, and in particular it refers to a remote detecting system of the protection ground which employs a telephone line as support for the transmission of the control signals and of the quantities associated to this measurement.
BACKGROUND ART
The protection ground electric system is used in order to bring part of a metallic structure of an electric/electronic device as much as possible to a value corresponding to the ground potential, when for some unusual reasons (anomalous contacts, failure, atmospheric discharges, etc.), a potential is applied to the metallic structure that can cause damage to the safety of a person.
The lower the value of the ground resistance, the safer is the protection.
Since often it may be very difficult and expensive to obtain low values of the resistance, the law requires values of the ground resistance depending on the use and the possible discharge currents.
Since the ground resistance is used only during certain periods and since its value may vary also considerably due to the aging of the electric system or to changes in environmental conditions, a periodic control of the ground resistance is necessary in order to guarantee, in every condition, a value which is always lower than that established by the law.
The measurement of the ground resistance is performed by means of portable instruments, using stakes driven into the ground, in different ways, but usually relying on the volt-ammeter method.
In order to perform this operation, one has to reach the region of measure and drive the stakes into the ground by following appropriate rules.
The above described practice often implies also noticeable difficulties which render problematic a measurement which is already expensive, and which must be carried out anyway respecting terms provided by the law.
Moreover, the ground measurements performed according to the conventional technique using the volt-ammeter method employ detection stakes located at a distance of 20/40 m from each other. In this manner, the electric current which is involved in the measurement in part flows through the surface layer of the ground and does not involve the equipotential region which lies in the deeper layers.
Therefore, the measurement is influenced by the detection of a ground surface resistance which apparently is very low and does not correspond to the actual one, and since said apparent ground resistance is lower than the actual ground resistance, a safety coefficient will be deduced, according to the ground resistance, which is fictitious and overestimated; but this is extremely dangerous.
DISCLOSURE OF INVENTION
The object of the present invention is that of providing a system which allows the remote measuring of the ground resistance without forcing an operator to move and in extremely short times.
A further object of the present invention is that of providing a remote measuring system of the protection ground, which allows to operate at very deep soil layers, thereby increasing the precision of the measurement.
Finally, an object of the present invention is to provide a remote measuring system of the protection ground, which is easy to use and which has a limited cost.
These objects and other ones which will become apparent as the description proceeds, are achieved through a remote measuring system of the protection ground comprising a centralized ground measuring device, remote controlled actuators which comprise ground terminals connected to the soil and a line selector which connects the centralized ground measuring device with the remote controlled actuators by means of two wires.
This remote controlled actuator is provided with contacts to connect the wires of the line to the ground terminals for closing the measurement circuit and is located near the region where said ground measurement is required, whereby said ground resistance measurement is done
REFERENCES:
patent: 3913010 (1975-10-01), Scarpino
patent: 4529929 (1985-07-01), Berggren
patent: 4947469 (1990-08-01), Vokey et al.
patent: 5365179 (1994-11-01), Rogers
084166, 8 Nov. 1982.
Mullen Jr. Thomas J.
Wu Daniel J.
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