Patent Application
20240145186
The disclosed concept relates generally to circuit interrupters, and in particular, to mechanisms for opening separable contacts of circuit interrupters at high speeds.
Circuit interrupters, such as for example and without limitation, circuit breakers, are typically used to protect electrical circuitry from damage due to an overcurrent condition, such as an overload condition, a short circuit, or another fault condition, such as an arc fault or a ground fault. Circuit interrupters typically include mechanically operated separable electrical contacts, which operate as a switch. When the separable contacts are in contact with one another in a closed state, current is able to flow through any circuits connected to the circuit interrupter. When the separable contacts are not in contact with one another in an open state, current is prevented from flowing through any circuits connected to the circuit interrupter. The separable contacts may be operated either manually by way of an operator handle, remotely by way of an electrical signal, or automatically in response to a detected fault condition. Typically, such circuit interrupters include an actuator designed to rapidly close or open the separable contacts, and a trip mechanism, such as a trip unit, which senses a number of fault conditions to trip the separable contacts open automatically using the actuator. Upon sensing a fault condition, the trip unit trips the actuator to move the separable contacts to their open position.
Hybrid circuit interrupters employ a power electronic interrupter in addition to the mechanical separable contacts, which are often components of a vacuum switch. The electronic interrupter comprises electronics structured to commutate current after a fault is detected. Once current is commutated from the mechanical vacuum switch to the electronic interrupter, the mechanical separable contacts are able to separate with a reduced risk of arcing. It is advantageous to open the mechanical separable contacts at fast speeds in order to limit the let-through current and commutate as much current as possible to the electronic branch as quickly as possible.
Thomson coil actuators are noted for their ability to open mechanical separable contacts very high speeds, and are often employed in hybrid circuit interrupters. However, because it is preferable to minimize the time that it takes to separate the mechanical separable contacts, there is always room for improvement in increasing the speed at which an actuator opens mechanical separable contacts in order to minimize the time that elapses between detection of a fault condition and interruption of a fault current. Because the elapse of any time between the occurrence of a fault condition and the opening of the mechanical separable contacts leads to at least some let-through current passing through the mechanical separable contacts, there is always a need for actuators that can open mechanical separable contacts at higher speeds than available actuators can.
There is thus room for improvement within actuators used to open mechanical separable contacts of hybrid circuit interrupters.
These needs, and others, are met by a dual conductor Thomson coil actuator that comprises two nested conductors wound to form a single coil, rather than one single conductor wound to form a coil of the same size. Each of the two nested coils is structured to be excited by a capacitor bank with half the capacitance of a capacitor bank that would be used to excite the single larger coil, with the two capacitor banks used to charge the dual conductor coil being charged to the same voltage as the one capacitor bank used to excite the single conductor coil. Thus, when the same charging voltage that would be used to charge the capacitor bank for the single larger coil is used to instead charge the two capacitor banks for the two nested conductors of the dual conductor coil, the initial pulse of aggregate current through the dual conductor coil is greater than the initial pulse of current through the single conductor coil, which results in the aggregate magnetic force exerted by the two nested conductors of the dual conductor coil being greater than the magnetic force that would be exerted by the single conductor coil.
In accordance with one aspect of the disclosed concept, an actuator for use with a circuit interrupter comprises: a conductive plate structured to be coupled to a drive assembly of the circuit interrupter, and a conductive coil. The coil comprises: a plurality of turns, a first conductor wound into a first number of turns, a second conductor wound into a second number of turns, a first power source electrically connected to the first conductor, a second power source electrically connected to the second conductor, and an opening structured to receive the drive assembly and to enable the drive assembly to move freely during an opening stroke. The plurality of turns is the sum of the first number of turns and the second number of turns, and the first conductor and the second conductor are nested such that the first number of turns forms alternating turns of the coil relative to the second number of turns. The first power source and the second power source are configured to simultaneously supply a first time-varying current signal and a second time-varying current signal, respectively, to the first conductor and the second conductor. The actuator is structured to cause the coil to repel the conductive plate when the first and second time-varying current signals are supplied to the first and second conductors.
In accordance with another aspect of the disclosed concept, a hybrid circuit interrupter comprises: a line conductor structured to connect a load to a power source; a hybrid switch assembly disposed between the power source and the load, the hybrid switch assembly comprising a fixed mechanical separable contact and a movable mechanical separable contact and an electronic interrupter, the movable separable contact being structured to move between a closed state and an open state, the electronic interrupter being structured to commutate current when a fault is detected on the line conductor; a drive assembly operably coupled to the movable separable contact; an electronic trip unit structured to monitor the line conductor for fault conditions; and an actuator structured to open and close the movable separable contact. The actuator comprises a conductive plate coupled to the drive assembly, and a conductive coil. The coil comprises: a plurality of turns, a first conductor wound into a first number of turns, a second conductor wound into a second number of turns, a first power source electrically connected to the first conductor, a second power source electrically connected to the second conductor, and an opening structured to receive the drive assembly and to enable the drive assembly to move freely during an opening stroke. The plurality of turns is the sum of the first number of turns and the second number of turns. The first conductor and the second conductor are nested such that the first number of turns forms alternating turns of the coil relative to the second number of turns. The first power source and second power source are configured to simultaneously supply a first time-varying current signal and a second time-varying current signal, respectively, to the first conductor and the second conductor, and the actuator is structured to cause the coil to repel the conductive plate when the first and second time-varying current signals are supplied to the first and second conductors.
A full understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:
Directional phrases used herein, such as, for example, left, right, front, back, top, bottom and derivatives thereof, relate to the orientation of the elements shown in the drawings and are not limiting upon the claims unless expressly recited therein.
As used herein, the singular form of “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise.
As employed herein, the statement that two or more parts are “coupled” together shall mean that the parts are joined together either directly or joined through one or more intermediate parts.
As employed herein, when ordinal terms such as “first” and “second” are used to modify a noun, such use is simply intended to distinguish one item from another, and is not intended to require a sequential order unless specifically stated.
As employed herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality).
As employed herein, the term “processing unit” or “processor” shall mean a programmable analog and/or digital device that can store, retrieve, and process data; a microprocessor; a microcontroller; a microcomputer; a central processing unit; or any suitable processing device or apparatus.
The circuit interrupter 1 further includes a hybrid switch assembly 6, an operating mechanism 8, and an electronic trip unit 10. The hybrid switch assembly 6 in
Under normal operating conditions, the mechanical contacts 12 are in a closed state such that they are in contact with one another, enabling current to flow through the line conductor 2 and the mechanical contacts 12 to the load 4. In addition, the electronic interrupter 14 is powered off under normal operating conditions, such that current cannot flow through the electronic interrupter 14. In response to detecting a fault condition, the electronic trip unit 10 is configured to output a first signal to the electronic interrupter 14, in order to power on the electronic interrupter 14, and to output a second signal to the operating mechanism 8, to initiate actuation of the operating mechanism 8 in order to open the mechanical contacts 12. Powering on the electronic interrupter 14 with the first signal enables the electronic interrupter 14 to commutate fault current from the mechanical contacts 12 to the electronic interrupter 14. The transmission of the second signal from the trip unit 10 to the operating mechanism 8 is timed to ensure that the operating mechanism 8 does not open the mechanical contacts 12 until after the current has been commutated to the electronic interrupter 14, in order to minimize let-through current and the effects of arcing.
Referring now to
Referring now to
The coil 34 comprises a first lead 38 and a second lead 39 that are used to electrically connect the coil 34 to a power source, such as a capacitor bank 40. The capacitor bank 40 is kept fully charged, and when the mechanical contacts 12 are closed and a fault condition is detected, the signal transmitted by the trip unit 10 to the operating mechanism 8 causes the capacitor bank 40 to discharge so that a time-varying current is supplied to the coil 34 via the first lead 38, generating a magnetic field. The magnetic field repels the conductive plate 32 away from the coil 34, causing the drive shaft 26 and movable conductor 24 to separate the movable contact 23 from the stationary contact 21.
The prior art coil 34 shown in
The first conductor 104 comprises a first lead 111 and a second lead 112, and the second conductor 105 comprises a first lead 113 and a second lead 114, with the leads being used to electrically connect each conductor 104, 105 to a power source, such as a capacitor bank. As shown in
As can be seen by comparing
Table 1 below shows the results of the FEA wherein each modeled winding Lwinding104 or Lwinding105 of the dual conductor coil 102 is excited by its corresponding capacitor bank 116 or 118 with 3.3 mF at 700V, with an external resistance (R1, R2) of 5 mohm and an external inductance (L1, L2) of 1.25 uH. Table 1 also includes the results of an FEA for a modeled winding corresponding to the prior art single conductor coil 34 excited by the same total capacitance and voltage as the disclosed dual conductor coil 102, and with the same total number of turns as the dual conductor coil 102:
As shown in Table 1, when the disclosed dual conductor coil 102 is excited by the same total stored energy (6.6 mF at 700V) as the prior art single conductor coil 34, the dual conductor coil 102 outperforms the single conductor coil in the output parameters of peak force, force rise time, peak current, and time elapsed during the first 1 mm of travel of the movable mechanical contact 23 during an opening stroke.
It is noted that maximizing the speed of the initial 0.1 mm of travel of the movable contact 23 is considered especially significant for reducing let-through current. As the position vs. time curves in
While specific embodiments of the invention 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 disclosed concept which is to be given the full breadth of the claims appended and any and all equivalents thereof.
