Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Plural ranges – scales or registration rates
Reexamination Certificate
2002-04-05
2004-05-11
Karlsen, Ernest (Department: 2829)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Plural ranges, scales or registration rates
C324S076550, C324S086000, C324S107000
Reexamination Certificate
active
06734658
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
REFERENCE TO A SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISK APPENDIX
Not Applicable.
BACKGROUND OF THE INVENTION
Generally, the present invention relates to multimeters, and, more specifically, to multimeters having functions that may be especially useful to those involved in servicing, maintaining, and/or operating electrical power transmission and distribution systems.
Three-phase electrical power is delivered to commercial, industrial, and residential users through a system known as the power distribution grid, which generally includes such components as generating plants, transformers, and electrical power lines. These lines generally consist of both transmission lines, which typically have AC voltages in the range of about 69,000 to 765,000 volts, and distribution lines, which typically have AC voltages in the range of about 2,300 to 50,000 volts. Inevitably, there is an element of danger in measuring and working with these high voltages, yet there are many instances in which utility workers have to either service or repair, or install or interconnect high voltage power lines in the performance of their duties. These duties have been further expanded over the past few years due to the increase of electrical power co-generation by entities that are not part of, or owned by, the electrical power utility that owns and operates the primary power distribution grid. These co-generation entities, however, still connect to the electrical power utility in most cases, and generally do so at the aforementioned high voltage levels.
Generally, therefore, those individuals working with electrical power lines often find it necessary to be able to determine or measure the following parameters: phase-to-phase, phase-to-ground, ground-to-phase, and zero reference test, voltages associated with those lines, which can range from zero volts to full transmission line voltages; the phase rotation or the phase sequence of the three-phase AC lines; and the number of degrees of separation between any two phases. Currently, many different pieces of equipment are used for determining the above-mentioned parameters. As examples, the absolute voltage carried by a line may be measured by a “high line resistive voltmeter” or a “phasing voltmeter,” and the phase sequence (or phase rotation) may be determined by using a phase sequence indicator (or a phase rotation meter) prior to connecting individual lines of multi-phase networks together.
Presently, high-voltage phasing voltmeters use a series connected meter, two test probes, which are basically high-voltage dropping resistors that are housed in an insulated holder, and a connection cable, which is used for connecting the second test probe to the other components. The test probes generally have metal hooks or other fittings on their ends for making good electrical contact with the power lines, and often the meter is mounted to one of the two test probes and oriented so that the electric utility worker can read the voltage displayed on the meter while taking a measurement. Additionally, insulated extension poles, commonly referred to as “hot sticks” may be used to hold and elevate the entire assembly, and in many situations may be required in order to protect the worker from the hazards associated with high-voltage power lines. Generally, the above-mentioned meter may be designed to measure either voltage or current, but, generally, its display will only indicate voltage. One issue when taking AC voltage measurements, however, is the concern that the indicated voltage is not always the true voltage for the four types of voltage measurements listed above. This is especially a concern when taking high-voltage measurements.
High-voltage measurements are plagued with inaccuracies including those stemming from stray capacitive charging currents. At high-voltages, these stray currents emanate from the surface of every component of the measuring device including the connection cable, and other, i.e., additional, currents may be induced by the electromagnetic fields associated with the power lines. The capacitive current is related to the capacitive reactance, Xc, and, depending on the position of the meter and the connection cable with respect to the ground, the magnitude of this impedance can widely range from a very low to a very high value. Under extreme conditions, such as when the connection cable is lying directly on the ground between two pad-mounted transformers, the value of the capacitive reactance can be very low, which can result in the capacitive current equalling or exceeding the measured current and in highly inaccurate meter readings. In other words, it is often the case that the voltage measured by the meter will vary depending on the location of the meter and the cable.
These AC phasing voltmeter inaccuracies, which are generally attributable to capacitive currents, are eliminated in analog and digital devices using an earth ground lead or cable by the design disclosed and described in the commonly owned U.S. patent application Ser. No. 09/766,254, filed on Jan. 18, 2001, which will be referred to herein as “Companion Specification 1,” and are eliminated in digital devices that do not require the use of an earth ground lead or cable in the commonly owned U.S. patent application, Ser. No. 60/327,481, filed on Oct. 5, 2001, which is attached hereto and incorporated in its entirety herein by reference, and which will be referred to herein as “Companion Specification 2.”
Regardless of the above, there are still other problems with standard phasing voltmeters. On occasion, the electrical power transmission lines are separated by a considerable distance and, even though the alternating current phasing voltmeter disclosed in Companion Specification 1 practically eliminates capacitive currents regardless of the length of the cable, it does not effectively address the problem of the logistics involved in dealing with a long cable, or the problem of having a cable that is not long enough. This problem, however, was addressed and eliminated by the design disclosed and described in a commonly owned U.S. patent application Ser. No. 09/814,993, filed Mar. 22, 2001, which will be referred to herein as “Companion Specification 3.”
Other related problems, however, still exist. For example, when measuring very high-voltages there is a difficulty associated with having to use an unwieldy or cumbersome length of dropping resistors and extension pole segments in order to take the high-voltage measurements and/or to determine other electrical parameters. Secondly, due to the hazards associated with the high-voltages being measured, the meter oftentimes has to be kept a considerable distance away from the user. Thirdly, the meter is generally used out of doors during all types of weather and at all times of the day. Because of these constraints, even though accuracy in making the measurements may be accomplished through use of the inventions described in the Companion Specifications, this does not always translate to a user being able to accurately read the meter. In other words, being able to extract the indicated voltage or parameter information is not always easy to do, or can it be done accurately and/or efficiently when using a standard prior art meter.
Thus there remains a need for an alternating current phasing multimeter that can be used without an earth ground lead or cable, can be used over a large range of voltages, can provide other useful information to the user, can be easily and efficiently read, and can be easily used when the power lines are separated by more than a few feet.
SUMMARY OF THE INVENTION
According to its major aspects and briefly recited, the present invention is a wireless AC phasing multimeter, which is comprised of an AC phasing voltmeter, preferably having improved accuracy, and may also include a phase sequence or phase rotation indicator, along with a phase comparison indicator. Furthermore, the present invention can be view
Karlsen Ernest
Mann Michael A.
Nexsen Pruet , LLC
Slabouz Timothy J.
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