Thermal measuring and testing – Temperature measurement – In spaced noncontact relationship to specimen
Reexamination Certificate
2002-10-09
2004-08-17
Verbitsky, Gail (Department: 2859)
Thermal measuring and testing
Temperature measurement
In spaced noncontact relationship to specimen
C374S120000
Reexamination Certificate
active
06776522
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to apparatus and systems for thermal measurement of high voltage electrical power transmission and distribution lines and related high voltage components and equipment such as occur in substations, and more particularly, to apparatus and systems that make use of contact thermal sensors for determining the temperature of the power lines and associated high voltage components and equipment.
Demand for electric power has grown faster than the capability of the existing distributed power delivery assets to deliver it reliably. Since the mid-1990's, sales of power loaded onto the U.S. power transmission and distribution grids has increased 100-fold. Despite this unprecedented and growing demand for electrical power, erection of new transmission lines in the North America has not kept pace. New construction costs are high and lead times are long. Costs for the construction of new high voltage transmission capacity can range from $1,100,000 to $3,300,000 per circuit-mile. If land acquisition and/or establishment/extension of rights-of-way are involved, lead times can be as long as 4 years or more. Recent industry literature is replete with phrases such as, “construction of new transmission capacity is grinding to a halt.” On Jan. 1, 1992, 191,690 circuit-miles of transmission existed in North America. Ten-year plans ending 2002 called for 8.3% additions to transmission capacity through new construction. As of the end of 1998, approximately 30% of these additions had been built; the 207,586 circuit miles seen as required by 2002 had been whittled down to 202,196 circuit-miles, and completion of the additions had been pushed out 5 years to 2007. In 1998, the North American Electric Reliability Council (“NREC”), listed planned transmission additions (230 kV transmission systems and above) through 2007 of 6,588 circuit-miles.
As a result, the electrical power distribution industry is faced with squeezing more current delivery out of existing infrastructure. Utilities are being tasked to operate existing power lines at previously unexplored operating levels for extended periods of time. Transmission systems are being operated in a manner for which control of them was not designed. Blackouts, equipment damage, and system disturbances are becoming widespread, with ever increasing frequency and effect.
Electrical current flowing through a metallic conductor causes I
2
R losses in the conductor, that is, heat generation in the conductor changes exponentially with changes in current load. The current/temperature relationship affects not only the high voltage lines but also system equipment, conductors, and components in the power line circuit. This includes buses, switches, cables, transformers, etc. in high voltage transmission and distribution substations. This relationship of conductor temperature to current impacts two factors that limit how much current a given high voltage transmission line can safely and reliably transmit or carry on a continuous basis: firstly, the clearance between the mid-point of the line (at a span between two transmission towers) and the ground beneath the mid-point (or a grounded object, e.g., a tree); secondly, the temperature at which the transmission line begins to undergo irreversible physical (mechanical and/or electrical) changes.
Firstly, metals expand on heating. If too much current passes through a power line, the line may sag so close to the ground that it violates the mandated clearance for such lines. These clearances are regarded as ‘deadly serious’ by utilities. In some cases, the line may sag far enough to make contact with a grounded object. In such events, blackouts can and do result, and with these come losses: loss of equipment and property, loss of electric service to customers, lost utility revenues, customer manufacturing and product losses, productivity losses, and even loss life. Thus high line temperatures are a limiting factor of how much current a line can safely transfer.
Secondly, if too much current passes through the line, the resulting temperature of the line will cause the aluminum conductor material to anneal. When aluminum anneals, its mechanical and electrical properties change irreversibly; annealed aluminum has higher resistivity and lower mechanical strength than ordinary aluminum. After annealing, electrical transmission losses increase via heat generation, and the amount of sag increases for any given amount of current passing through the conductor. Once a line is annealed, electric power companies generally cut back or limit power flow. The damaged line can bottleneck the entire circuit in which it resides. In some cases, it is necessary to replace the annealed transmission line.
“Ampacity” is current carrying capability expressed in amperes. As a result of the effect of current on temperature and the effect of temperature on metal, manufacturers of high voltage lines, system equipment, conductors, and other components in the power line circuit thermally rate their products according to limiting ampacities. These name plate ratings are based on the characteristics of the materials used in the product and, at least in the case of transmission lines, on limited assumptions of environmental conditions (e.g., 90° C. and a crosswind of 2 feet per second for transmission lines). Power distribution companies may “de-rate” the nameplate value based on the intended use of the product, for example, because of predicted heating of the product by the environment in which it will operate. Environmentally caused heating is founded on historical information and assumptions of conditions such as wind speed and direction, ambient temperature, humidity, barometric pressure and incident solar radiation. Conservative safety factors (e.g., hottest day, little or no wind, etc.) are applied to reach the rating. Power distribution companies operate their equipment within the name plate ampacity ratings of the manufacturers to prevent the annealing and line sag problems mentioned. To do this, power companies measure current to indirectly gain a reading of percentage of name plate ampacity that a given power load represents.
The ampacity of a power line varies according to the temperature component of the line imposed by actual environmental conditions under which a power line circuit is operating. More current can be transferred through a circuit when the lines are colder than when they are hotter. In order to transfer more current through existing lines without blackouts or system disturbances, power companies need to know in real time as conditions change, moment to moment, at any time, day or night, the dynamic actual ampacity of its equipment, not the static name plate ampacity predictively rated by the manufacturer. Knowing the dynamic actual ampacities, power loads can be safely, accurately, and reliably increased and adjusted within the real time current carrying capabilities of the power distribution system. As a result, the true capacity of the system at the moment can be utilized to safely and reliably deliver more power to customers than present static ratings and operational control methods allow.
Dynamic actual ampacity can be determined by knowledge of actual moment to moment temperatures of the power line. In addition, by knowing actual equipment operating temperatures, substations can be operated and protected optimally based on the thermal state and history of equipment. Substation equipment is routinely tripped (i.e., taken off line in order to protect it) based on information from current sensors, without regard to actual equipment operating temperature. In many instances, such equipment is operating safely, from a thermal standpoint, and is not in danger of undergoing thermal damage. Continuous temperature monitoring allows such equipment to continue operating safely.
In earlier years, in order to monitor power line sag, a number of diverse technologies were developed to monitor line temperatures directly or indirectly. Early methods provided electrical devices mounted o
Clark Roy
Syracuse Steven J.
Burgess Tim L.
Verbitsky Gail
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