Patent Application
20140022085
1. Field
The disclosed concept pertains generally to current transformers and, more particularly, to current transformers for sensing current flowing in a conductor. The disclosed concept also generally pertains to energy monitoring systems for sensing current flowing in a conductor. The disclosed concept also generally pertains to methods for sensing current flowing in a conductor.
2. Background Information
Energy monitoring systems can monitor energy passing through one or more electrical conductors. A typical energy monitoring system includes one or more current transformers electrically connected to a base unit.
Current transformers of various types are generally known. Typically, a current transformer includes an annular iron core about which a plurality of turns of a number of windings are wrapped. In use, an electrical conductor is situated in the hole of the annular iron core, and when an alternating current is passed through the conductor, the conductor serves as a single turn primary winding to induce a current in the secondary winding. Depending upon the application, the secondary winding is electrically connected with a burden resistor of a base unit. The base unit senses a voltage across the burden resistor and responsively provides an output which may be, for instance, a measurement of the current. While current transformers and energy monitoring systems have been generally effective for their intended purposes, they have not been without limitation.
A dangerous or undesirable condition can arise when the secondary winding of the current transformer on an active primary load becomes open circuited. The open circuited condition may be caused by, for example, broken sensor wires between the current transformer and the base unit or unterminated sensor wires. The open circuited condition can cause the current transformer to output dangerous or undesirable voltage levels. Additionally, the open circuited condition prevents monitoring of the current of the active primary load.
In order to prevent the dangerous or undesirable voltage levels at the current transformer, a clamping circuit has been included in current transformers in order to limit the voltages levels at the current transformer. Although the clamping circuit prevents dangerous voltage levels at the current transformer, the open circuited condition will still prevent monitoring of the current of the active primary load.
The identification of the type and location of the error in the energy monitoring system requires the use of resources such as the time of a technician and/or the use of troubleshooting equipment. Moreover, in the case that the energy monitoring system includes a plurality of current transformers, troubleshooting resources are needed to even identify which one of the current transformers is not operating properly.
It thus would be desirable to provide an improved current transformer or energy monitoring system that overcome these and other shortcomings associated with the relevant art.
These needs and others are met by embodiments of the disclosed concept in which a current transformer is electrically connected with a base unit via a sensor cable. The current transformer includes a clamping circuit to clamp a voltage of a secondary winding and an indicator circuit electrically connected in series with the clamping circuit to indicate when the clamping circuit is active.
In accordance with one aspect of the disclosed concept, an energy monitoring system for a power conductor comprises: a base unit; a sensor cable; and a current transformer electrically connected to the base unit by the sensor cable, the current transformer comprising: a secondary winding inductively coupled to the power conductor; a clamping circuit electrically connected in parallel with the secondary winding, the clamping circuit being structured to clamp a voltage across the secondary winding when the voltage across the secondary winding is greater than a predetermined value; and an indicator circuit electrically connected in series with the clamping circuit to indicate when the clamping circuit is actively clamping the voltage.
In accordance with another aspect of the disclosed concept, a current transformer for a power conductor comprises: a secondary winding structured to be inductively coupled to the power conductor; a clamping circuit electrically connected in parallel with the secondary winding, the clamping circuit being structured to clamp a voltage across the secondary winding when the voltage is greater than a predetermined value; and an indicator circuit electrically connected in series with the clamping circuit to indicate when the clamping circuit is clamping the voltage.
In accordance with another aspect of the disclosed concept, a method of detecting and indicating an open circuit between a burden resistor and a secondary winding of a current transformer comprises: inductively coupling the secondary winding of the current transformer with a conductor; clamping a voltage across the secondary winding with a clamping circuit when the voltage is greater than or equal to a predetermined voltage; and indicating that the voltage is being clamped by an indicator circuit electrically connected in series with the clamping circuit. The indicator circuit may include a light emitting diode.
A full understanding of the disclosed concept can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:
As employed herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality).
As employed herein, the term “electrical conductor” shall mean a wire (e.g., without limitation, solid; stranded; insulated; non-insulated), a copper conductor, an aluminum conductor, a suitable metal conductor, or other suitable material or object that permits an electric current to flow easily.
As employed herein, the statement that two or more parts are “connected” or “coupled” together shall mean that the parts are joined together either directly or joined through one or more intermediate parts. Further, as employed herein, the statement that two or more parts are “attached” shall mean that the parts are joined together directly.
As employed herein, the term “clamping” shall mean limiting maximum and minimum values of a signal. For example, and without limitation, if an alternating current (AC) signal normally has a peak voltage of +/−10V and the AC signal is clamped at +/−5V, the clamped AC signal will not increase above +5V and will not decrease below −5V.
Referring to
The first, second, and third current transformers 130, 130′, 130″ are inductively coupled to first, second, and third power conductors 140, 140′, 140″, respectively. The current flowing through the first, second, and third power conductors 140, 140′, 140″ induces currents in the respective first, second, and third current transformers 130, 130′, 130″. As such, the energy monitoring system 100, which is electrically connected to each of the current transformers 130, 130′, 130″, can monitor the current flowing through each of the first, second, and third power conductors 140, 140′, 140″, respectively.
The base unit 110 includes a burden resistance (Rb) 111. The current transformer 130 includes a secondary winding 131 inductively coupled to the power conductor 140. The current transformer 130 also includes a clamping circuit 132. The clamping circuit 132 is electrically connected in parallel with the secondary winding 131 and clamps the voltage across the secondary winding 131 when the voltage is greater than a predetermined value. The clamped voltage can be greater than a maximum normal operating voltage of the secondary winding 131. The clamping circuit 132 includes an indicator circuit 133 that is configured to indicate when the clamping circuit 132 is actively clamping the voltage across the secondary winding 131.
Referring to
Referring to
The current transformer 230 includes a clamping circuit which includes a first zener diode 232 and a second zener diode 233 (e.g., without limitation, transient voltage suppression diodes) connected to terminals (not numbered) of the secondary winding 231. The current transformer 230 also includes an indicator circuit, which is a part of the clamping circuit, and includes a third zener diode 234 and a light emitting diode 235. The first zener diode 232 and the second zener diode 233 are electrically connected in series with the parallel combination of the light emitting diode 235 and the third zener diode 234. When the voltage across the secondary winding 231 becomes greater than a predetermined value, the clamping circuit clamps the voltage and the light emitting diode 235 turns on to indicate that the clamping circuit is active.
Continuing to refer to
Referring to
While specific embodiments of the disclosed concept have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the disclosed concept which is to be given the full breadth of the claims appended and any and all equivalents thereof.
