Signals and indicators – Indicators – Temperature responsive or compensating means
Reexamination Certificate
1999-07-27
2001-02-20
Gutierrez, Diego (Department: 2859)
Signals and indicators
Indicators
Temperature responsive or compensating means
C116S216000, C116S218000, C374S160000, C374S026000
Reexamination Certificate
active
06189479
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a method and an apparatus for detecting an insulation failure in an electrical insulator through a ground fault and, more particularly, to such method and apparatus which provides visual indicia of a temperature increase in the electrical insulator, which may indicate the flow of potentially harmful leakage electrical current through the electrical insulator. The apparatus and method of this invention are especially useful in underground mining operations.
2. Background and Related Art
Electrical insulators prevent the passage of electricity out of the electrical insulators to some other device or area, such as to a wooden pole which holds electrical power lines off of the ground, so that the electricity does not cause harm or death to those who touch areas or devices which are adjacent to the electrical insulators.
High-voltage insulators are generally large-sized components produced from porcelain which isolate high voltage electrical power lines at electrical power generation stations, and within the transmission and distribution networks of the major utilities. Low-voltage insulators are typically used as feed-through insulators or stand-offs. High-strength porcelain is generally used in the manufacture of insulators for transformers, switch gears, terminators and low voltage distribution applications.
The advantages of providing electrical service to underground mines is well known. Many of the operations performed in underground mines today could not otherwise be performed were it not for the availability of electrical power underground at the mine face. Typically, electrical service is provided underground via a series of electrical conductors extending from an above-ground power distribution center and down the mine shaft. The electrical conductors, which are normally suspended from the mine shaft roof by electrical insulators, provide electrical power for much of the underground equipment, such as mining machines, conveyor belt systems and trolley systems which dislodge, transfer and carry mined coal or other materials from the mine face to above-ground storage facilities.
The electrical insulators used to suspend electrical conductors from the mine shaft roof must be capable of withstanding the rigors of an extremely harsh working environment. Moisture, exposure to mining chemicals and minerals (including mining dusts), and the almost constant vibration caused by operating machinery and moving vehicles in the mine tend to cause the electrical insulators used to suspend electrical conductors from the mine roof to begin to fail over time. As an electrical insulator begins to fail, it allows a “leakage” electrical current to flow through the electrical insulator from the electrical conductor to the earth ground to which the electrical insulator is anchored. As the magnitude of the leakage current flowing through the electrical insulator increases, the temperature of the electrical insulator begins to rise. When the temperature on the outer surface of the electrical insulator reaches a certain critical temperature equal to the autoignition temperature of coal, coal dust or other dust, a fire can occur due to the faulty electrical insulator. The occurrence of a fire in an underground mine can not only result in the destruction of mining equipment and closure of the mine, but more importantly can result in the injury or death of mining personnel.
In an effort to detect faulty electrical insulators used in underground mining operations, a system has heretofore been employed which includes an electric lamp mounted on a wooden pole. The lamp is wired to a pair of electrical contacts, one at each end of the pole. The wooden pole is positioned relative to an electrical insulator so that one of the electrical contacts is in contact with the electrical insulator and the other electrical contact is in contact with the electrical conductor suspended from the electrical insulator. Illumination of the electric lamp provides an indication that the electrical insulator under test is faulty.
The electric lamp/wooden pole assembly has shortcomings. For example, testing each and every electrical insulator in an underground mining system with such an assembly would be extremely time consuming, and would result in the possible delay in mine operations. In addition, the condition of a particular electrical insulator could not be determined visually without actually using the electric lamp/wooden pole assembly. Thus, failures of insulators will not be detected until the next scheduled test or evaluation. Consequently, a need exists for improved warning methods and devices for providing visual indicia of a faulty electrical insulator which overcomes the difficulties of the prior art.
SUMMARY OF THE INVENTION
The present invention relates to a method and a heat-sensitive warning device designed to satisfy the aforementioned needs, and to provide a visual indication of a temperature increase on the outer surface of an electrical insulator, which is indicative of the flow of potentially harmful leakage electrical current through the electrical insulator, prior to the development of a significant risk of a dangerous situation such as a fire or explosion. This device may be used in any electrical power-conducting system in which an electrical insulator is in a path to ground (e.g., mines, refineries, off shore oil platforms, chemical and other plants, etc.). The heat-sensitive warning device of the invention provides visual indicia of a heat rise in an electrical insulator (indicating an electrical insulator short and potential safety hazard) without mine or other personnel assistance. The presence of a faulty electrical insulator anywhere in an electrical power-conducting system may be detected visually or otherwise without personal assistance. Once detected, the faulty electrical insulator may be replaced well in advance of the electrical insulator reaching an unsafe temperature, such as the autoignition temperature of coal, coal dust or other dust.
The present invention also provides a heat-sensitive warning device which may be fitted on the outside of any electrical insulator utilized in any electrical power-conducting system in which an electrical insulator is in a path to ground. This device also detects an increase in the temperature of an outer surface of an electrical insulator, which may indicate the flow of potentially harmful leakage electrical current therethrough, and also provides visual or other indicia of this increase in temperature.
One preferred heat-sensitive warning device of the invention comprises: (a) a hollow housing in thermal contact with the outside of an electrical insulator, and having an open first end and a partially open second end; (b) a spool positioned within the hollow housing; (c) an indicator element (e.g., a Telfon™ ribbon) wound around the spool and having a first end secured to the spool and a second end secured to an outer wall of the housing; (d) a first thermosensitive end plug which seals the open first end of the housing, which encloses the spool and the indicator element within the housing, the first thermosensitive end plug being made from a material which melts at a first preselected temperature which is above ambient temperature and which is below a second preselected temperature; (e) a second thermosensitive end plug which seals the partially open second end of the housing, which also encloses the spool and the indicator element within the housing, both prior to and after the melting of the first thermosenstitive end plug, the second thermosensitive end plug being made from a material which melts at a second preselected temperature, the second preselected temperature being the same as, or above, the first preselected temperature and below an unsafe temperature for the particular electrical insulator being used under the particular conditions of use; and (f) ejection means positioned within the hollow housing for ejecting the spool and the indicator e
Francis Faye
Gutierrez Diego
Klarquist Sparkman Campbell & Leigh & Whinston, LLP
The United States of America as represented by the Department of
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