Patent Description:
A post insulator functions as a mechanical support between a transmission line and an electrical pole or tower while electrically insulating the transmission line from the pole or tower. For example, the post insulator may be mountable on a crossarm of an electrical pole and may be made of a ceramic or other suitable electrically insulative material. The transmission line, or conductor, may be supported on the post insulator by any of various devices, such as via bus bars, clamps, a tube-type support (e.g., the conductor may run through a tube in the post insulator), or a channel in the post insulator.

For various reasons, it may be desirable to obtain measurements of voltage and/or current of a conductor supported by a post insulator. In such instances, it may also be desirable that the voltage and/or current measurements have high accuracy and that the information may be easily transmitted. It is also desirable that voltage and/or current sensors for providing such measurements be reliable.

Related technologies are known from <CIT>,
<CIT>, <CIT>, <CIT>, <CIT>, <CIT> and <CIT>.

The present invention relates to a current monitor showing the technical characteristics of the independent claim. Embodiments of the current monitor according to the present invention are disclosed in the dependent claims.

According to the present invention, a current monitor is disclosed. The current monitor includes a housing configured to be coupled to an electric power line; an inductive current sensor in the housing configured to measure a value of a current on the electric power line to generate a sensor signal; a power source which is the electric power line; a power resistor in the housing coupled to the electric power line configured to generate a power voltage from an electric power line voltage; a sensing resistor in the housing coupled to the electric power line configured to generate a voltage sensor signal; and a sensor signal conversion circuit in the housing configured to receive power from the power source and to generate a current output signal based on the sensor signal, to receive the power voltage, and to generate a voltage output signal based on the voltage sensor signal. The power resistor shields the sensing resistor from noise or environmental temperature variation, and/or the sensor signal conversion circuit is configured to utilize the power voltage to generate the voltage output signal when little or no current is present on the electric power line.

In some embodiments, the sensor signal conversion circuit utilizes the received power to generate the current output signal such that the current output signal has a natively useful form.

In some embodiments, the sensor signal includes a gain change and a phase shift, and the sensor signal conversion circuit compensates the gain change and the phase shift to generate the current output signal such that the current output signal represents the value of the current on the electric power line with a constant gain and zero phase shift.

In some embodiments, the inductive current sensor does not fully surround the electric power line.

In some embodiments, the sensor signal conversion circuit comprises at least one active circuit element powered by the power from the power source, and the sensor signal conversion circuit utilizes the active circuit element for generating the current output signal.

In some embodiments, the current monitor includes a voltage sensor in the housing configured to measure a value of a voltage on the electric power line to generate a voltage sensor signal, the sensor signal conversion circuit being further configured to generate a voltage output signal based on the voltage sensor signal.

In some embodiments, the sensor signal conversion circuit comprises at least one active circuit element powered by the power from the power source, and the sensor signal conversion circuit utilizes the active circuit element for generating the voltage output signal.

In some embodiments, the sensor signal conversion circuit comprises a temperature conversion circuit powered by the power from the power source, and the sensor signal conversion circuit utilizes the temperature conversion circuit to generate the current output signal.

In some embodiments, the sensor signal conversion circuit is configured to utilize the power voltage to generate the current output signal when little or no current is present on the electric power line.

In some embodiments, the current monitor includes a second sensing resistor in the housing, wherein the power resistor shields the second sensing resistor from noise or environmental temperature variation, the sensing resistor is connected between the electric power line and the second sensing resistor, the second sensing resistor is connected between the sensing resistor and a common voltage, and a voltage across the second sensing resistor is utilized to generate the voltage sensor signal.

In some embodiments, the current on the electric power line has a power transmission frequency, and the current output signal comprises the value of the current on the electric power line at frequencies other than the power transmission frequency.

In some embodiments, the current output signal comprises a harmonic component of the current on the electric power line.

In some embodiments, the current output signal represents the current on the electric power line with an error of less than.

In some embodiments, the housing is an insulator body configured to electrically isolate the electric power line from an electric power line support.

In some embodiments, the current monitor includes an output circuit configured to communicate the current output signal to an external transceiver.

In some embodiments, the output circuit comprises a surface acoustic wave device.

The above and other features, aspects, and advantages of the present invention will become better understood with regard to the following description and accompanying drawings where:.

In the following detailed description, certain exemplary embodiments of the present invention are shown and described, by way of illustration. As those skilled in the art would recognize, the described exemplary embodiments may be modified in various ways without departing from the scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, rather than restrictive.

<FIG> is a current and voltage monitor <NUM> according to embodiments of the present disclosure. While the term "current and voltage monitor" will be used throughout the specification, it is noted that in some embodiments, the current and voltage monitor may include current monitoring capabilities without voltage monitoring capabilities, or may include both current and voltage monitoring capabilities. The current and voltage monitor <NUM> includes a housing <NUM> which encloses a current sensor. The current and voltage monitor <NUM> may be installed on or near an electric power line used for distribution or transmission (hereinafter "a transmission line") <NUM> in order to measure the current present on the transmission line <NUM>. In some embodiments, the current and voltage monitor <NUM> is mounted on the transmission line and supported by the transmission line (i.e., hanging from or wrapped around the transmission line). In some embodiments, the current and voltage monitor <NUM> is mounted on a transmission line support such as a transmission line pole or a crossarm in proximity to the transmission line <NUM>, and the housing <NUM> may contact the transmission line or may have one or more lead extending from the housing <NUM> to the transmission line <NUM>. In some embodiments, the housing of the current and voltage monitor <NUM> supports the transmission line <NUM>.

In the embodiment shown in <FIG>, the current and voltage monitor <NUM> includes a housing <NUM>, a recess <NUM>, and a keeper <NUM>. The housing <NUM> is an insulator body made of an insulating material. The insulator body may be utilized as a post insulator to be mounted on a crossarm of a transmission line pole or tower. The housing <NUM>, according to an embodiment, may have a recess <NUM> into which the conductor <NUM> may be received. That is, an upper region of the housing <NUM> may be U-shaped when viewed from a first side to define the recess <NUM> that extends from the first side to an opposite side. As such, the conductor <NUM> may be lifted into the recess <NUM> and supported by the current and voltage monitor <NUM> without being cut or requiring a jumper. However, the present invention is not limited thereto, and aspects of the present invention may also be applied to another type of post insulator, such as one having bus bars or clamps, for example.

The housing <NUM>, in an exemplary embodiment, may be made of Polysil, a high dielectric strength polymer known and available to those skilled in the art. However, the present invention is not limited thereto, and, in other embodiments, the insulator <NUM> may be made of a hydrophobic cycloaliphatic epoxy (HCEP) or other suitable epoxy, for example.

The current and voltage monitor <NUM> may include a keeper <NUM> and, in an embodiment, may include a pair of keepers <NUM> at opposite sides of the recess <NUM>. The keeper or keepers <NUM> may be configured to be removably coupled to housing <NUM> to retain the transmission line <NUM> in the recess <NUM>.

In some embodiments, the keeper <NUM> is configured to provide a contact for electrically connecting to the transmission line from inside the housing <NUM>. For example, the keeper <NUM> may be made of or may include a conductive material, and may attach to the housing <NUM> by bolts configured to be threadedly engaged in a respective pair of the threaded inserts. The keeper <NUM>, the bolts, and the threaded inserts may all include conductive materials providing an electrical path between the transmission line in contact with the keeper and the inside of the housing <NUM>.

The current sensor contained in the housing <NUM> is an inductive current sensor. In particular, the current sensor may be an inductive sensor that does not fully encircle the transmission line <NUM> in order to facilitate depositing the transmission line <NUM> in the recess <NUM> without cutting the transmission line <NUM> or requiring a jumper.

<FIG> show different embodiments of a current sensor according to embodiments of the present disclosure. <FIG> is a cross section of a current monitor illustrating a dual-core inductive current sensor 210a according to embodiments of the present disclosure. The dual-core inductive current sensor 210a includes first and second inductive coils placed on opposite sides of the recess <NUM>. Because the transmission line <NUM> is seated in the recess <NUM>, the first and second inductive coils can be placed directly on either side of the transmission line <NUM>. The current flowing in the transmission line <NUM> generates a magnetic field which in turn induces current in the dual-core inductive current sensor <NUM>0a, and the induced current is used as a current sensor signal or utilized to generate the current sensor signal.

<FIG> is a cross section of a current monitor illustrating a single-core inductive current sensor 210b according to embodiments of the present disclosure. The single-core inductive current sensor 210b includes a single inductive coil. The inductive coil may be placed at any point adjacent to the conductor <NUM>. In some embodiments, the recess <NUM> is shallow, such that the sides of the recess are shorter than the circumference of the transmission line <NUM>, and the single-core inductive current sensor 210b is placed directly beneath the recess <NUM>. The current flowing in the transmission line <NUM> generates a magnetic field which in turn induces current in the single-core inductive current sensor <NUM>0a, and the induced current is used as a current sensor signal or utilized to generate the current sensor signal.

<FIG> is a cross section of a current monitor illustrating a Rogowski coil current sensor 210c according to embodiments of the present disclosure. The Rogowski coil 210c may be a single-turn, open-loop lead and a wire connected to one end of the open-loop lead and coiled around the lead along the length of the lead toward the other end. The single-turn, open-loop lead of the Rogowski coil 210c may have a U-shape and be oriented along the U-shape of the recess <NUM>. The current flowing in a transmission line <NUM> in the recess <NUM> may induce a current in the Rogowski coil 210c which may be used as the current sensor signal or may be utilized to generate the current sensor signal. The current sensor signal generated by the Rogowski coil 210c may be a derivative of the current on the transmission line <NUM>, and may therefore not be natively useful to other components of the current and voltage monitor <NUM>.

Some portion of the current sensor signal, or the entire current sensor signal, generated by the current sensor may not be natively useful to other components of the current and voltage monitor <NUM> (e.g., for determining the current on the transmission line, communicating the determined current, or performing an action based on the determined current) without further processing. For example, the current sensor signal from the dual-core inductive current sensor 210a may have a linear gain, but may exhibit non-linear phase shift at different frequencies. The characteristics of the current sensor signal from the single-core inductive current sensor 210b may vary based on the diameter of the conductor (i.e., the larger the conductor, the further the center of the conductor from the current sensor). The current sensor signal from the Rogowski coil 210c may be a derivative of the current on the transmission line <NUM>.

<FIG> is a block diagram of a current monitor according to embodiments of the present disclosure. The current monitor includes a current sensor <NUM>, a power source <NUM>, a power supply <NUM>, a sensor signal conversion circuit <NUM>, and an output circuit <NUM>.

The sensor signal conversion circuit <NUM> and/or the output circuit may include active components. The power supply <NUM> utilizes power from the power source <NUM> to generate one or more supply voltage for the active components of sensor signal conversion circuit and/or output circuit. The power source <NUM> comprises a power resistor outputting a power voltage from the transmission line voltage, as discussed below in more detail. In other embodiments beyond the scope of the present invention, the power source <NUM> may additionally or alternatively be a battery, a solar panel, an inductive energy harvesting circuit, or a combination thereof.

The current sensor <NUM> is an inductive current sensor which generates a current sensor signal based on the magnetic field generated by the current on the transmission line <NUM>, such as the dual-core inductive current sensor 210a, the single-core inductive current sensor 210b, or the Rogowski coil 210c discussed above. The current sensor <NUM> does not completely enclose the transmission line <NUM>. Accordingly, the current sensor signal generated by the current sensor <NUM> may not be natively useful (e.g., useful to the output circuit <NUM>) without further processing.

The sensor signal conversion circuit <NUM>, utilizing active components powered by the supply voltage from the power supply <NUM>, receives the current sensor signal from the current sensor <NUM> and processes the current sensor signal into a current output signal which can be utilized by the output circuit <NUM>, and passes the current output signal to the output circuit <NUM>.

In one embodiment, the sensor signal conversion circuit <NUM> includes a gain circuit <NUM> and a phase adjust circuit <NUM>. The gain circuit <NUM> receives the current sensor signal from the current sensor <NUM>. <FIG> shows the gain at different frequencies of a related art sensor device which does not include a gain circuit <NUM>. As can be seen, the gain may be different at different frequencies, and the device may be configured to have peak gain at the power transmission frequency (e.g., <NUM>). A current sensor signal generated from such a configuration may include information about the power at the power transmission frequency, but may lose information related to the harmonic components located at higher and lower frequencies which may reduce the accuracy of the reading or may lose specific information provided by the harmonic components. In embodiments of the present disclosure where the gain circuit <NUM> utilizes active components, powered with the supply voltages generated by the power supply <NUM>, the gain circuit <NUM> can provide unity gain across the relevant frequency spectrum as shown in <FIG>. As a result, harmonic components of the current on the transmission line containing information which may be desirable to monitor may be preserved and included in the current output signal. Passive gain components may provide gain at the frequency of the transmission line current, but may not provide the same gain to the harmonics, and this information may be lost.

The phase adjust circuit <NUM> may receive the output of the gain circuit <NUM>. <FIG> shows the phase shift at different frequencies of a related art sensor device which does not include a phase adjust circuit <NUM>. As can be seen, the phase shift may be different at different frequencies, and the device may be configured to have zero phase shift at the power transmission frequency (e.g., <NUM>). Components of the current on the transmission line at frequencies other than the power transmission frequency such as the harmonic components may be subject to phase shift, and therefore may not be captured or may not be actionable or otherwise useful without further processing. In embodiments of the present disclosure where the phase adjust circuit <NUM> utilizes active components, powered with the supply voltages generated by the power supply <NUM>, the phase adjust circuit <NUM> may process the current sensor signal to provide zero phase shift across the entire frequency spectrum of interest as shown in <FIG>. As a result, harmonic components of the current on the transmission line may be recovered and/or actionable or useful.

The sensor signal conversion circuit <NUM> may additionally or alternatively include other active components for converting the current sensor signal into a natively useful current output signal, including but not limited to an integrator, a differentiator, a temperature compensation circuit, and/or an equation-based non-linear transform circuit. In one embodiment, the current sensor <NUM> is a Rogowski coil and the sensor signal conversion circuit <NUM> includes an active integration circuit to compensate for the transfer function of the Rogowski coil. In some embodiments, such as embodiments utilizing the single-core inductive current sensor 210b, the sensor signal conversion circuit <NUM> generates the current output signal by compensating the current sensor signal based on the distance from the center of the transmission line (e.g., based on the diameter of the conductor).

In some embodiments, the sensor signal conversion circuit <NUM> generates the current output signal such that it represents the current on the transmission line with an error of less than <NUM>%. In some embodiments, the sensor signal conversion circuit <NUM> generates the current output signal such that it represents the current on the transmission line with an error of less than. <NUM>% and the voltage and current monitor is used for revenue metering applications. In some embodiments, the sensor signal conversion circuit <NUM> is able to generate the current output signal such that it represents the current on the transmission line with an error of less than. <NUM>%, e.g., by accounting for the harmonic components of the current on the transmission line in the current output signal utilizing an active gain circuit and/or an active phase shift circuit. In some embodiments, the sensor signal conversion circuit <NUM> generates the current output signal such that it represents the current on the transmission line with an error of less than. <NUM>% by utilizing an active gain circuit and/or an active phase shift circuit to recover the harmonic components of the line current and by utilizing a temperature compensation circuit to correct for temperature variations.

The output circuit <NUM> performs an output action based on the current output signal. In some embodiments, the output circuit <NUM> stores the value of the current on the transmission line in a database, where the value of the current on the transmission line is determined based on the value of the current output signal. In some embodiments, the output circuit <NUM> includes a radio and the radio transmits the current output signal or the value of the current on the transmission line (derived from the current output signal) to an external receiver. In some embodiments, the output circuit <NUM> includes a line driver powered by the supply voltage from the power supply <NUM>, and the line driver is used to transmit the current output signal or the value of the current on the transmission line. In some embodiments, the output circuit <NUM> includes a fiber optic communication circuit powered by the supply voltage from the power supply <NUM>, and the fiber optic communication circuit is used to transmit the current output signal or the value of the current on the transmission line.

In some embodiments, the output circuit <NUM> includes an RFID circuit configured to communicate the value of the current on the transmission line, the value of the current output signal, or another measurement to an external transceiver. In some embodiments, the RFID circuit communicates an identifier (e.g., a unique identifier) for the current and voltage monitor <NUM> with the value or measurement. In some embodiments, the RFID circuit utilizes a surface acoustic wave ("SAW") device to perform signal processing and/or to take measurements to be communicated to the external transceiver. For example, this can be accomplished using SAW devices available from SenSanna.

<FIG> is a block diagram of a current and voltage monitor according to embodiments of the present disclosure.

The current and voltage monitor of <FIG> includes a current sensor <NUM> sensing the current on a transmission line <NUM>, a transmission line voltage interface <NUM>, a power supply <NUM>, a voltage sensor signal conversion circuit <NUM>, a current sensor signal conversion circuit <NUM>, and an output circuit <NUM>.

The transmission line <NUM> and the transmission line voltage interface <NUM> act as a power source. The transmission line voltage interface <NUM> generates a power voltage and a scaled voltage from the transmission line voltage. The power supply <NUM> utilizes the power voltage to generate one or more supply voltages which it provides to the voltage sensor signal conversion circuit <NUM> and the current sensor signal conversion circuit <NUM>. When no power is delivered through a transmission line, the transmission line may still have its normal operating voltage level, but may have no current or a low level of current passing through the transmission line. In such circumstances, systems which generate power from the current on a transmission line (e.g., by inductively harvesting power) may not be able to generate power and may therefore be inoperative. Generating the power voltage from the transmission line voltage may allow the current and voltage monitor to generate the power voltage, and thereby remain operative, even when no power is being delivered through the transmission line.

The voltage sensor signal conversion circuit <NUM> utilizes the scaled voltage as a voltage sensor signal and generates a voltage output signal. In some embodiments, the voltage sensor signal conversion circuit <NUM> utilizes active components powered with a supply voltage from the power supply <NUM> to generate the voltage output signal. The current sensor signal conversion circuit <NUM> receives a current sensor signal from the current sensor <NUM>, and utilizes active components powered with a supply voltage from the power supply <NUM> to generate a current sensor output signal. The sensor signal conversion circuits <NUM> and <NUM> pass the voltage output signal and the current output signal to the output circuit <NUM>.

<FIG> is an isometric cross section view of a current and voltage monitor <NUM> according to embodiments of the present disclosure, and <FIG> is a side cross section view of the current and voltage monitor <NUM>. With reference to <FIG> and <FIG>, the current and voltage monitor may include one or more contacts <NUM>, a current sensor <NUM>, a transmission line voltage interface <NUM>, an electronics package <NUM>, and the housing <NUM>. Shielded wires may be used to electrically connect elements inside the housing <NUM> in order to prevent or reduce noise (e.g., from the transmission line <NUM> or neighboring transmission lines). The housing <NUM> houses (e.g., encapsulates) the transmission line voltage interface <NUM>, the electronics package <NUM>, and/or the current sensor <NUM>.

One or more contacts <NUM> may provide a conductive pathway for electrically connecting objects inside the housing <NUM> with the transmission line <NUM>. In some embodiments, the contact <NUM> is a threaded insert which threadedly engages a conductive bolt. The conductive bolt may be used to couple the current and voltage monitor <NUM> to the transmission line <NUM>, such as described above with respect to the keeper, bolt, and threaded inserts of <FIG>. In some embodiments, all of the contacts <NUM> may be tied together at a common potential.

The power source of <FIG> and <FIG> is the transmission line <NUM> and the transmission line voltage interface <NUM>. The transmission line voltage interface <NUM> electrically connects components of the current and voltage monitor <NUM> to the voltage on the transmission line <NUM> without causing the components to be damaged by the potentially high power present. The transmission line voltage interface <NUM> includes a power resistor <NUM>. The power resistor is electrically coupled to the transmission line <NUM>, for example by being electrically coupled to the contact <NUM>, and configured to output a power voltage. The power voltage may be used to power components in the current and voltage monitor <NUM>, which will be described in more detail below. The transmission line voltage interface <NUM> includes a sensing resistor <NUM>. The sensing resistor <NUM> is electrically coupled to the transmission line <NUM>, for example by being electrically coupled to a contact <NUM> or by being connected to the power voltage output from a power resistor <NUM>. The sensing resistor <NUM> is configured to output a voltage sensor signal corresponding to the voltage level on the transmission line <NUM>.

The current sensor 210c depicted in <FIG> and <FIG> is a Rogowski coil (e.g., a coil with an open-loop lead and a wire connected to one end of the open-loop lead and coiled around the lead along the length of the lead toward the other end). The open-loop lead of the Rogowski coil may be oriented along the U-shape of the recess <NUM>. <FIG> shows an isometric cross section view of another embodiment of a current and voltage monitor according to the present disclosure, where the current sensor 210a includes first and second inductor coils in a dual-core current sensor arrangement. The first and second inductor coils 210a are positioned on opposite sides of the recess <NUM>.

Referring again to <FIG> and <FIG>, the electronics package <NUM> may be located at an end of the housing <NUM> opposite the end which is in contact with the transmission line <NUM>. A ground port may be coupled to an external ground and may connect the electronics package <NUM> to the external ground. The electronics package <NUM> may receive a voltage sensor signal and/or a power voltage from the transmission line voltage interface <NUM>, and a current sensor signal from the current sensor <NUM>.

The electronics package <NUM> may include the sensor signal conversion circuit, including a current sensor signal conversion circuit and/or a voltage sensor signal conversion circuit. The electronics may also include an output circuit, e.g., a communication circuit. Any of the circuits in the electronics package <NUM> may be powered by the power voltage generated from the voltage on the transmission line by the transmission line voltage interface <NUM>. The sensor signal conversion circuit receives the current sensor signal from the current sensor <NUM> and generates a current output signal based on the current sensor signal. Similarly, the sensor signal conversion circuit receives the voltage sensor signal from the sensing resistor <NUM> and generates a voltage output signal based on the voltage sensor signal. In some embodiments, the voltage sensor signal from the sensing resistor <NUM> can be used directly as the voltage output signal. In other embodiments, the voltage sensing circuit only includes a gain step for converting the voltage sensor signal to the voltage output signal. The communication circuit may be connected to an antenna, and may utilize the antenna to transmit the current output signal and/or the voltage output signal to a receiver. The antenna may be near to an outer surface of the housing <NUM> such that a signal may be transmitted easily to the receiver.

<FIG> is a cross section view of a transmission line voltage interface <NUM> according to embodiments of the present disclosure. The transmission line voltage interface <NUM> comprises a power resistor <NUM>, and a first sensing resistor <NUM>, and a second sensing resistor <NUM>. The power resistor <NUM> may have a cylindrical or substantially cylindrical shape with an inner cavity defined through the middle of the power resistor <NUM> and openings at both ends (e.g., a tube shape). The ends of the power resistor <NUM> are used as the terminals, and one terminal is electrically connected to the transmission line to receive a transmission line voltage VTRANSMISSION LINE and the other outputs a power voltage VPOWER, for example to the electronics package <NUM>. The first sensing resistor <NUM> and the second sensing resistor <NUM> are positioned inside the inner cavity of the power resistor <NUM>. For example, the first sensing resistor <NUM> and/or the second sensing resistor <NUM> may have a rod shape which runs coaxially or substantially coaxially with the length of the cavity and the ends of the rod shape may be used as the terminals. One terminal of the first sensing resistor <NUM> is electrically connected to the transmission line to receive a transmission line voltage VTRANSMISSION LINE and the other may be electrically connected to a terminal of the second sensing resistor <NUM>. The other terminal of the second sensing resistor <NUM> may be electrically connected to ground. A scaled voltage VSCALED can be measured across the second sensing resistor <NUM>, for example by the electronics package <NUM>.

The voltage drop across a resistor such as the second sensing resistor <NUM> may be influenced by noise (e.g., electrical fields) from outside sources, capacitive coupling with external objects, and/or the temperature of the surrounding environment. The transmission line voltage interface <NUM> of <FIG> may utilize the first sensing resistor <NUM> and the second sensing resistor <NUM> to generate a very accurate scaled voltage VSOALED to determine the voltage on the transmission line. As the power resistor <NUM> surrounds the first sensing resistor <NUM> and the second sensing resistor <NUM>, it shields the first sensing resistor <NUM> and the second sensing resistor <NUM> from noise, such as noise from the transmission line <NUM> or from neighboring transmission lines, preventing that noise from impacting the scaled voltage VSCALED. Capacitive coupling may be present between the transmission line voltage interface <NUM> and the housing <NUM>, especially where the housing <NUM> is wet, such as when it rains. Where there is capacitive coupling between the transmission line voltage interface <NUM> and outside elements such as the housing <NUM>, the capacitive coupling is with the power resistor <NUM>, and thereby has a reduced or a nonexistent impact on the scaled voltage VSCALED. The power resistor <NUM> heats up during operation, and thereby heat its inner cavity. The heated inner cavity provides a temperature environment for the first sensing resistor <NUM> and the second sensing resistor <NUM> which has a smaller range of possible temperatures than the environmental temperature where the current and voltage monitor <NUM> is installed. Accordingly, the transmission line voltage interface <NUM> reduces or eliminate variations in the scaled voltage VSOALED caused by environmental temperature changes. As a result, the current and voltage monitor <NUM> utilizing the transmission line voltage interface <NUM> may measure the voltage on the transmission line with an error of less than.

It will be understood that, although the terms "first," "second," "third," etc., may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. Thus, a first element, component, region, layer or section described below could be termed a second element, component, region, layer or section, without departing from the scope of the present invention.

Claim 1:
A current monitor (<NUM>) comprising:
a housing (<NUM>) configured to be coupled to an electric power line (<NUM>);
an inductive current sensor (<NUM>, 210a, 210b, 210c) in the housing (<NUM>) configured to measure a value of a current on the electric power line (<NUM>) to generate a sensor signal;
a power source (<NUM>), wherein the power source (<NUM>) is the electric power line (<NUM>);
a power resistor (<NUM>) in the housing (<NUM>) coupled to the electric power line (<NUM>) configured to generate a power voltage from an electric power line voltage;
a sensing resistor (<NUM>) in the housing (<NUM>) coupled to the electric power line (<NUM>) configured to generate a voltage sensor signal;
a sensor signal conversion circuit (<NUM>, <NUM>, <NUM>) in the housing (<NUM>) configured to receive power from the power source (<NUM>) and to generate a current output signal based on the sensor signal, to receive the power voltage, and to generate a voltage output signal based on the voltage sensor signal,
characterized in that:
the power resistor (<NUM>) shields the sensing resistor (<NUM>) from noise or environmental temperature variation; and/or
the sensor signal conversion circuit (<NUM>, <NUM>, <NUM>) is configured to utilize the power voltage to generate the voltage output signal when little or no current is present on the electric power line (<NUM>).