Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Plural inputs
Reexamination Certificate
1998-03-25
2001-05-08
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Plural inputs
C324S141000
Reexamination Certificate
active
06229295
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the field of electric utility meters. More particularly, the present invention relates to electronic utility watthour meters or meters utilized to meter real and reactive energy in both the forward and reverse directions.
BACKGROUND OF THE INVENTION
Electric utility companies and power consuming industries have in the past employed a variety of approaches to metering electrical energy. Typically, a metering system monitors power lines through isolation and scaling components to derive polyphase input representations of voltage and current. These basic inputs are then selectively treated to determine the particular type of electrical energy being metered. Because electrical uses can vary significantly, electric utility companies have requirements for meters configured to analyze several different nominal primary voltages. The most common of these voltages are 120, 208, 240, 277 and 480 volts RMS. Presently, available meters have a different style for each of these applications, both electro-mechanical and electronic. This forces the electric utility companies to inventory, test and maintain many different styles of meters. Consequently, a need exists for reducing the number of meter types a utility need inventory by providing a meter capable of operation over a wide dynamic range.
The problem of wide amperage dynamic range was addressed in U.S. Pat. No. 3,976,941—Milkovic. It was there recognized that solid state electronic meters were becoming more desirable in metering applications, however, such solid state meters had a critical drawback in their amperage dynamic range. An effort was described to improve the amperage dynamic range of solid state meters so that such meters would be operationally equivalent to prior electromechanical meters. The problem with such meters, however, was their failure to address the multiple voltage situation. Utility companies utilizing such meters would still be forced to inventory, test and maintain many different styles of meters in order to service the various voltages provided to customers.
It has been recognized in various meter proposals that the use of a microprocessor would make metering operations more accurate. It will be understood, however, that the use of a microprocessor requires the provision of one or more supply voltages. Power supplies capable of generating a direct current voltage from the line voltage have been used for this purpose. Since electric utility companies have requirements for various nominal primary voltages, it has been necessary to provide power supplies having individualized components in order to generate the microprocessor supply voltages from the nominal primary voltage.
Consequently, a need exists for a single meter which is capable of metering electrical energy associated with nominal primary voltages in the range from 96 to 528 volts RMS. Applicants resolve the above problems through the use of a switching power supply and voltage dividers. It will be recognized that switching power supplies are known. However, the use of such a power supply in an electrical energy meter is new. Moreover, the manner of the present invention, the particular power supply construction and its use in an electrical energy meter is novel.
It will also be noted, in order to solve the inventory problem, designing a wide voltage range meter in the past involved the use of voltage transformers to sense line voltage. A significant problem associated with the use of such transformers was the change in phase shift and the introduction of non-linearities that would occur over a wide voltage range. It was not easy to remove such a widely changing phase shift or to compensate for the non-linearities.
Consequently, a need still exists for a single meter which is capable of metering electrical energy associated with nominal primary voltages that also minimizes phase shift in the voltage sensors over a wide voltage range.
SUMMARY OF THE INVENTION
The previously described problem is resolved and other advantages are achieved in an apparatus for metering at least one type of electrical power over a predetermined range of service voltages which comprises a voltage input circuit which divides a voltage component to a divided voltage, a current input circuit which produces an induced current proportional to the current component, a processing unit which processes the divided voltage and the induced current to determine the at least one type of electrical power, and a power supply which receives a voltage component within a predetermined range of power supplies and generates a supply voltage from the voltage component.
In accordance with a feature of the present invention, the power supply further comprises a transformer having first and second windings, a switching device connected to the first winding for permitting and preventing the flow of current through the first winding, and a controller connected to the switching device for generating the control signal in response to the output of the power supply. An input voltage is provided to the first winding so that current flows through the first winding and the second winding defines the output of the power supply, and the switching device is operable in response to a control signal. The transformer may further comprise a third winding that is substantially similar to the second winding so that the voltage across the third winding is similar to the voltage across the second winding. In accordance with this feature, the controller generates the control signal based on the voltage across the third winding, and the control signal operates to disable the switching member.
In accordance with another feature, the power supply may further comprising a bridge rectifier and protection circuit connected to receive the input voltage where the bridge rectifier rectifies the input voltage to produce an unregulated voltage, and the protection circuit directs the input voltage away from the first winding and disables the switching device when the input voltage exceeds a desired level. The protection circuit may comprise first and second transistors and a biasing device connected to the first and second transistors. The biasing device biases the first and second transistors so that the voltage provided by the protection circuit does not exceed a desired level. In addition, the protection circuit may be connected in series with the transformer and the switching member.
In accordance with still another feature, the apparatus may further comprise a non-volatile power source, such as a battery or a capacitor, and a reference voltage generator which generates a reference voltage. The voltage input circuit may be connected to the reference voltage generator such that the voltage input circuit references the divided voltage to the reference voltage.
In accordance with yet another feature, the apparatus may further comprising a charge storage device, connected to the second winding, which stores an electrical charge when current is flowing through the first winding and discharges stored electrical charge when the switching member interrupts current flowing through the first winding.
In accordance with another feature of the present invention, the electrical power may comprise polyphase power comprising a plurality of phases of voltage and current components, and wherein the power supply is connected to receive one phase of the plurality of phases of voltage as the input voltage. The voltage input circuit may comprise a plurality of resistive divider networks, each of the plurality of resistive divider networks receiving a different one of the plurality of phases of the voltage component, and the current input circuit may comprise a plurality of current transformers, each of the plurality of current transformers receiving a different one of the plurality of phases of the current component.
In accordance with yet another feature, the controller may comprise a current-mode regulator, wherein a current reference signal is generated by the current-mode regul
Hemminger Rodney C.
Munday Mark L.
Schleifer Fred F.
ABB Power T&D Company Inc.
Kobert Russell M.
Metjahic Safet
Woodcock Washburn Kurtz Mackiewicz & Norris
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