Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Parameter related to the reproduction or fidelity of a...
Reexamination Certificate
1995-05-25
2001-05-08
Arana, Louis (Department: 2862)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Parameter related to the reproduction or fidelity of a...
Reexamination Certificate
active
06229315
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a hand-held electrical measuring device and particularly to a harmonics detector for detecting the presents of harmonic currents on electrical power lines in industrial and residential facilities.
BACKGROUND OF THE INVENTION
Electrical distribution system components are designed to operate at the standard 60 Hz frequency. However, many loads found in industrial and residential facilities demand currents that are non-sinusoidal and may be mathematically represented as a Fourier series summation of a fundamental plus higher order harmonics. For example, switch mode power supplies found in computers and other office equipment draw highly non-sinusoidal currents rich in harmonics. Similarly, usage of adjustable speed drives (ASD) with rectifier and invertor circuits for induction motor speed control has contributed to much greater line current harmonic levels.
The presence of harmonic currents on electrical power lines is becoming a major problem for electrical power engineers. These currents are responsible for overheating transformers, circuit breakers, filters, and neutrals and other sometimes strange occurrences. Harmonic problems are, by their nature, non-local; the equipment or system damaged by harmonics may be some distance from the source of harmonics.
Detection, diagnosis, and mitigation of harmonic problems require specialized instrumentation to accurately assess the level of harmonics present in the system. Instrumentation available to field engineers is generally inadequate to perform any detection or assessment of harmonics. While harmonic analysis equipment is available commercially, it is expensive, bulky, and overly complex, which makes it inappropriate and frequently unavailable for the field engineer who is called upon to diagnose equipment failures. This lack of instrumentation leads to improper diagnosis of problems and failure to correct harmonic problems as they occur.
Currently several commercial vendors manufacture equipment for performing this type of analysis. The primary drawback of the equipment is that they are not designed for ease of use. As a primary diagnostic instrument, the harmonics detector should be carried by field personnel whenever diagnostic measurements are made on electrical power lines. Even if no specific problems are present, the instrument should be used in a preventive role, to determine if harmonic currents are present in excessive amounts in the system. However, the various instruments currently available share the following characteristics, which render their use unlikely:
These units have retail prices in the range of $1,000 to $10,000 and up. Instrumentation in this price range is not generally available to field personnel.
These instruments are relatively larger (some are suitcase size and weigh 30 lbs) and inconvenient to transport; this renders it unlikely that they will be carried to the trouble site.
While some allow for battery operation, many of them require AC power for operation, severely limiting their usefulness in the field, where 120 V outlets are seldom available at the trouble site.
They are complex instruments and a significant investment of time is required to learn their operation and few personnel are knowledgeable in their use. In particular, field personnel generally lack the training to use the equipment effectively.
Some require the use of a PC (personal computer) to analyze dafa.
For these reasons, the existing equipment is not carried by field personnel, and hence is not generally used for problem diagnosis and is seldom, if ever, used in a preventive maintenance manner.
There is therefore a need for a hand-held harmonics detector that solves the above problems.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide a low cost, easy to use, light-weight (typically 8 oz.), hand-held harmonics detector that will allow service engineers and technicians to diagnose harmonics probl
It is another object of the present invention to provide a hand-held harmonics detector completely based on commercial off-the-shelf components, including low-power CMOS circuitry and a low-cost microcontroller.
It is still another object of the present invention to provide a hand-held harmonics detector which can be produced at relatively low cost.
It is yet another object of the present invention to provide a hand-held harmonics detector that operates from a relatively small battery, such as a 9 volt battery.
It is another object of the present invention to provide a hand-held harmonics detector that has auto sensing for power on/off operation, sensing the presence of current to turn the detector on and switching off when the current is not present, thereby conserving battery life and providing convenience of use.
It is still another object of the present invention to provide a hand-held harmonics detector that has the capability to measure 3rd, 5th, 7th, 9th and 11th harmonics.
It is still another object of the present invention to provide a hand-held harmonics detector that measures current, since current harmonics are almost always present in higher levels and are a better indicator of potential harmonics problems than voltage harmonics. This advantage allows the use of a current probe to minimize safety hazards, since voltage inputs and dangerous voltages are avoided.
It is yet another object of present invention to provide a hand-held harmonics detector with auto-sensing for 60 Hz of 50 Hz (European) operation.
It is another object of present invention to provide a hand-held harmonics detector with a simple, easy to understand light emitting diode (LED) display for output.
In summary, the present invention provides a hand-held harmonics detector comprising current probe for placing adjacent a current carrying conductor, the current probe generating an output signal in response to the current in the conductor; a circuit operably connected to the current probe for processing the output signal from the current probe; the circuit including a switching portion responsive to the output of the current probe for automatically turning on or off the circuit when the current probe senses current in the electrical conductor; and a display for the output of the circuit for indicating the presence of harmonics in the conductor. The display includes a plurality of various colored LEDs that are lit depending on the severity of the harmonics of interest that are detected. The circuit also includes a microcontroller for computing the Fourier coefficients of the harmonics of interest and an automatic gain control feature for auto-ranging for various current inputs from the current probe.
REFERENCES:
patent: 5170114 (1992-12-01), Lowenstein et al.
patent: 5365164 (1994-11-01), Lowenstein et al.
patent: 5473255 (1995-12-01), Kunihiro et al.
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