Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Electrical signal parameter measurement system
Reexamination Certificate
2000-03-27
2001-12-11
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Electrical signal parameter measurement system
C702S057000, C702S062000, C702S064000, C702S122000
Reexamination Certificate
active
06330516
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to power distribution systems, and more particularly to apparatus for monitoring power usage by a plurality of loads connected to a panel board or circuit breaker. The invention utilizes non-contact current sensors wired to the panel board or breaker and a digital signal processor module connected to receive inptus from the current sensor and from each voltage source so as to avoid having to attach a separate meter to each branch circuit to be monitored. The digital signal processor also enables monitoring of power quality as well as energy consumption for each branch circuit.
2. Description of Related Art
In order to audit or monitor energy usage in a more efficient manner, it is often desirable to monitor not only the overall energy usage by a facility, but also power consumption by individual branch circuits, as well as the effect on power quality of loads in the branch circuits. Such individual branch circuit monitoring not only permits billing for energy used, but also can provide an indication of conditions in the branch circuit, and trigger alerts in case individual limits on such parameters as RMS voltage or current, power factors, or harmonic distortion are exceeded. Furthermore, individual branch circuit monitoring permits billing to be extended to take into account low power factors and/or high total harmonic distortion, promoting efficiency by allowing the operator of a facility to determine whether and where capital investment for power quality enhancement equipment would provide the best return on investment.
Presently, monitoring of individual branch circuits in order to measure branch power parameters such as energy usage by a load, and the effects of the load on power factor and total harmonic distortion (THD), requires the installation of individual current sensors encircling and tied to the wire conductors of the branch circuits that the installer connects from the load to the branch circuit breakers. In order to record energy used, a conventional kilowatt-hour meter needs to be attached to each branch circuit. The costs involved in monitoring branch circuit energy usage can be significant for a typical manufacturing facility, in which multiple discrete circuit breakers or power distribution panels each typically service up to 84 branch circuits. When power quality or other parameters are to be taken into account, the costs rapidly become prohibitive due to the need for installation of additional meters.
SUMMARY OF THE INVENTION
It is accordingly a first objective of the invention to overcome the deficiencies of the prior art by providing a branch circuit monitor that can be wired directly to the panel board or circuit breaker without having to attach sensors to every branch circuit wire, and without requiring multiple kilowatt-hour meters for each circuit.
It is a second objective of the invention to provide a branch circuit monitor which is not limited to monitoring kilowatt-hours, but rather is capable of measuring, for each of a plurality of branch circuits, any or all of the following parameters: power factor, root-mean-square (RMS) current, RMS voltage, apparent power(kw)or real power (kv), total energy usage (kwhours), percent loading, and voltage and current THD.
It is a third objective of the invention to provide a branch circuit monitor capable of issuing, for each of a plurality of branch circuits, alarms on any or all of the following parameters: over/under voltage, over current and/or excess power or voltage consumption, high power factor and/or THD, and overall energy usage in multiple kwhr increments.
It is a fourth objective of the invention to provide a branch circuit monitor capable of generating, for each of plurality of individual branch circuits, real time data that can be used for billing of energy used, for calculating credits for energy that is out-of-tolerance, for levying surcharges for low power factors and/or high total harmonic distortion, and for determining whether the capital investment for power quality enhancement equipment would result in a positive return on investment.
It is a fifth objective of the invention to provide a branch circuit monitor that can be customized to provide any type of indication required by a particular application or facility, and which is scalable to allow for monitoring not only of any number of local branch circuits, but also remote sites in any number of cities or countries.
These objectives are achieved, in accordance with the principles of a preferred embodiment of the invention, by replacing the conventional individual current sensors tied to the wire conductors of the branch circuits with a plurality of non-contact current sensors, one for each branch circuit, and by utilizing a digital signal processor (DSP) module connected not only to the current sensors but also to voltage inputs from each voltage source to process the inputs from the current sensors.
In an especially preferred embodiment of the invention, the digital signal processor module monitors not only overall energy usage, but also RMS voltage, RMS current, power factor, real power, apparent power, and frequency for each branch circuit.
While not limited to a particular type of non-contact or induction transducer, the non-contact current sensors of the illustrated embodiment are in the form of miniature non-contact Rogowski coils that can easily be fitted on printed circuit boards arranged to fit within the dimensions of a typical panel board.
The inclusion of a digital signal processor module allows the branch circuit monitor to make data available, via communications protocols such as Modbus RTU or RS232/RS485/422, to any number of remote sites. The individual branch circuit monitors can be wired in a daisy chain or star network configuration and even connected to the Internet via an appropriate interface device so as to enable centralized billing or auditing of power usage, and remote monitoring of branch circuit conditions.
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Wahl, Frank P.,Select Current Sensor Performance to Match the Application's Requirements, PCIM Magazine, pp. 1-11, 1998.
POWERLOGIC® Power Monitoring and Control Systems, Energy and Enercept Meters, Class 3020, 3050, pp. 1-2.
Bacon & Thomas
Hoff Marc S.
Power Distribution Inc.
Tsai Carol S.
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