Patent Application
20090154046
1. Field of the Invention
This invention pertains generally to electrical switching apparatus and, more particularly, to electrical switching apparatus, such as circuit breakers, including a trip unit. The invention also relates to trip units for circuit interrupters.
2. Background Information
Electrical switching apparatus such as circuit interrupters and, in particular, circuit breakers of the molded case variety, are well known in the art. See, for example, U.S. Pat. No. 5,341,191.
Circuit breakers are used to protect electrical circuitry from damage due to an overcurrent condition, such as an overload condition or a relatively high level short circuit or fault condition. Molded case circuit breakers typically include a pair of separable contacts per phase. The separable contacts may be operated either manually by way of a handle disposed on the outside of the case or automatically in response to an overcurrent condition. Typically, such circuit breakers include an operating mechanism, which is designed to rapidly open and close the separable contacts, and a trip unit, which senses overcurrent conditions in an automatic mode of operation. Upon sensing an overcurrent condition, the trip unit trips the operating mechanism to a trip state, which moves the separable contacts to their open position.
Industrial circuit breakers often use a circuit breaker frame, which houses a trip unit. See, for example, U.S. Pat. Nos. 5,910,760; and 6,144,271. The trip unit may be modular and may be replaced, in order to alter the electrical properties of the circuit breaker.
It is well known to employ trip units which utilize a microprocessor to detect various types of overcurrent trip conditions and to provide various protection functions, such as, for example, a long delay trip, a short delay trip, an instantaneous trip, and/or a ground fault trip. The long delay trip function protects the load served by the protected electrical system from overloads and/or overcurrents. The short delay trip function can be used to coordinate tripping of downstream circuit breakers in a hierarchy of circuit breakers. The instantaneous trip function protects the electrical conductors to which the circuit breaker is connected from damaging overcurrent conditions, such as short circuits. As implied, the ground fault trip function protects the electrical system from faults to ground.
The earliest electronic trip unit circuit designs utilized discrete components such as transistors, resistors and capacitors.
More recently, designs, such as disclosed in U.S. Pat. Nos. 4,428,022; and 5,525,985, have included microprocessors, which provide improved performance and flexibility. These digital systems sample the current waveforms periodically to generate a digital representation of the current. The microprocessor uses the samples to execute algorithms, which implement one or more current protection curves.
Each circuit breaker is designed for a specific maximum continuous current. This current rating may be set by a suitable selection mechanism, such as by a rotary switch or by selection of a resistor (e.g., a “rating plug”) which converts a current to a voltage for use by the trip unit. In some instances, a single circuit breaker frame may be easily adapted for installations which call for a range of maximum continuous currents, up to the design limits of the frame, through use of the selection mechanism by which the current rating of the device can be established. Typically, the pick-up currents for the various protection functions have been selectable multiples or fractions of this current rating. Thus, instantaneous protection trips the device any time the current reaches a selected multiple of the rated current, such as, for example, ten times the rated current. Pick-up for short delay protection is a lesser multiple of the rated current, while pick-up current for long delay protection may be a fraction of the rated current. Typically, the short delay trip is only generated when the short delay pick-up current is exceeded for a short delay time interval, although, in some applications, an inverse time function is also used for short delay protection.
Maintenance personnel often need to work on low voltage electric power circuits that are energized, for instance, when testing circuit breakers. Maintenance and test personnel can be exposed to live terminals when working or making measurements on energized switch gear. The potential for arc flash resulting from an accidental fault requires that such personnel wear protective clothing.
U.S. Pat. No. 7,203,040 discloses a circuit breaker and trip unit including an arc reduction maintenance switch for reduction of arc flash energy and the severity of arc flash exposure. Specific trip functions are manually overridden with a maintenance trip function that reduces arc energy should a fault occur. The manually enabled and disabled maintenance trip function reduces the pickup currents of the specified trip functions and/or reduces or eliminates the time delays of the specified trip functions. For example, instantaneous trip is reduced from 10 times to 2 times rated current, short delay pickup is reduced from 8 times to 1.5 times rated current, the short time delay of 0.5 second is reduced to 0.050 second (essentially no time delay), the (equipment protection) ground fault pickup current is reduced from 0.5 times to 0.25 times rated current, and the ground fault time delay is reduced from 0.5 second to 0.050 second (essentially no time delay). As another example, instantaneous trip is reduced from 10 times to 4 times rated current, short delay pickup is reduced from 8 times to 3 times rated current, the short time delay of 0.5 second is reduced to 0.050 second (essentially no time delay), the (equipment protection) ground fault pickup current is reduced from 0.5 times to 0.25 times rated current, and the ground fault time delay is reduced from 0.5 second to 0.050 second (essentially no time delay). A light emitting diode (LED) is energized with the maintenance switch in the maintenance position to alert personnel of the change in the trip function. Other means for signaling the implementation of the maintenance trip functions can be provided such as a text message where the trip unit has a visual display.
A problem with these electrically driven alerts and signals is that they are not provided to maintenance personnel during the time when the power circuit is de-energized, such as when the circuit breaker de-energizes the power circuit.
There is room for improvement in electrical switching apparatus, which enable selection of an arc reduction maintenance system.
There is also room for improvement in trip units, which enable selection of an arc reduction maintenance system.
These needs and others are met by embodiments of the invention, which provide a movable indicator to indicate whether one of a number of predetermined instantaneous current conditions or one of a number of predetermined arc reduction maintenance system current conditions is selected by a selector switch.
In accordance with one aspect of the invention, an electrical switching apparatus comprises: separable contacts; an operating mechanism structured to open and close the separable contacts; a trip mechanism cooperating with the operating mechanism to trip open the separable contacts, the trip mechanism comprising: a housing comprising a first opening and a second opening, a sensor structured to sense a current flowing through the separable contacts and to provide a signal representative of the current, a selector switch disposed proximate the first opening of the housing, the selector switch being structured to select one of a number of predetermined instantaneous current conditions and a number of predetermined arc reduction maintenance system current conditions, a movable indicator cooperating with the selector switch, the movable indicator being disposed proximate the second opening of the housing, the movable indicator being structured to indicate whether one of the number of predetermined instantaneous current conditions or one of the number of predetermined arc reduction maintenance system current conditions is selected by the selector switch, and a trip circuit cooperating with the sensor and the selector switch to evaluate the signal representative of the current with respect to the selected one of the number of predetermined instantaneous current conditions and the number of predetermined arc reduction maintenance system current conditions, and responsively cause the operating mechanism to trip open the separable contacts.
The selector switch may be a rotary selector switch including a pivot member pivotally disposed with respect to the housing and a selector member coupled to the pivot member, the selector member being disposed at the first opening of the housing; and the movable indicator may be a peripheral member peripherally disposed about the selector member and movable therewith, the peripheral member being disposed at the second opening of the housing.
The peripheral member may include a first portion with a first indicia corresponding to the number of predetermined instantaneous current conditions and a different second portion with a different second indicia corresponding to the number of predetermined arc reduction maintenance system current conditions.
The housing may include a faceplate having the first opening and the second opening; the trip circuit may include a printed circuit board coupled to the faceplate; the selector switch may be pivotally coupled to the printed circuit board; and the movable indicator may be peripherally coupled to the selector switch, the movable indicator being structured to pivot with the selector switch.
The selector switch may be a rotary selector switch including a pivot member pivotally disposed with respect to the housing and a selector member coupled to the pivot member, the selector member may be disposed at the first opening of the housing; and the movable indicator may comprise a peripheral member peripherally disposed about the selector member and an indicator member coupled to the peripheral member, the indicator member being disposed at the second opening of the housing.
As another aspect of the invention, a trip unit is for a circuit interrupter for an electrical circuit. The trip unit comprises: a housing comprising a first opening and a second opening; a sensor structured to sense a current flowing in the electrical circuit and to provide a signal representative of the current; a selector switch disposed proximate the first opening of the housing, the selector switch being structured to select one of a number of predetermined instantaneous current conditions and a number of predetermined arc reduction maintenance system current conditions; a movable indicator cooperating with the selector switch, the movable indicator being disposed proximate the second opening of the housing, the movable indicator being structured to indicate whether one of the number of predetermined instantaneous current conditions or one of the number of predetermined arc reduction maintenance system current conditions is selected by the selector switch; and a trip mechanism cooperating with the sensor and the selector switch to evaluate the signal representative of the current with respect to the selected one of the number of predetermined instantaneous current conditions and the number of predetermined arc reduction maintenance system current conditions, and responsively generate a trip signal.
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:
As employed herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality).
As employed herein, the term “processor” means a programmable analog and/or digital device that can store, retrieve, and process data; a computer; a workstation; a personal computer; a microprocessor; a microcontroller; a microcomputer; a central processing unit; a mainframe computer; a mini-computer; a server; a networked processor; or any suitable processing device or apparatus.
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 “indicia” means a distinctive marking or something that serves to indicate. Non-limiting examples of indicia include colors, distinctive patterns, a number of characters, distinctive symbols, distinctive labels and other human discernable indications.
As employed herein, the term “selector switch” means a rotary selector switch, a pivotally coupled selector switch, or any suitable selection apparatus structured to select one current condition from a plurality of different current conditions.
As employed herein, the term “movable indicator” means a movable indication apparatus.
The invention is described in association with a three-phase circuit breaker, although the invention is applicable to electrical switching apparatus having any number of phases or poles, and to trip units for such electrical switching apparatus.
A trip mechanism, such as a trip circuit as shown by the example electronic trip unit 9, monitors the currents sensed by these CTs 7A,7B,7C,7N and generates a trip signal 10 in response to predetermined current and/or predetermined current/time conditions. The electronic trip unit 9 incorporates a suitable processor, such as the example microprocessor (μP) 11. The microprocessor-based electronic trip unit 9 may be similar to the type disclosed in U.S. Pat. Nos. 4,752,853; and 6,167,329, which are hereby incorporated herein by reference. The electronic trip unit 9 preferably incorporates a resistor (not shown) or other suitable mechanism that sets the frame rating (e.g., the maximum continuous current) that will be permitted by the circuit breaker 1.
The electronic trip unit 9 generates the trip signal 10 in response to the specified overcurrent conditions. As is conventional, an operating mechanism 15 is structured to open and close sets of separable contacts 17A, 17B and 17C. The trip signal 10 actuates (through a suitable trip device (e.g., without limitation, trip coil; trip solenoid (not shown)) the operating mechanism 15, which responsively opens the sets of separable contacts 17A, 17B and 17C, in order to interrupt current through the corresponding phase conductors 3A, 3B and 3C of the electrical system 2. Hence, the trip unit 9 cooperates with the operating mechanism 15 to trip open the separable contacts 17A,17B,17C.
The circuit breaker 1 and, in particular, the electronic trip unit 9, provides several conventional modes of protection. In particular, an instantaneous protection mode and an Arc Reduction Maintenance System (ARMS) protection mode are provided. Long delay, short delay and/or ground fault protection may also be provided.
The trip unit 9 includes a routine 20 executed by the μP 11. The routine 20 is structured to evaluate the signals 8 with respect to a selected one of a number of predetermined instantaneous current conditions 22 and a number of predetermined arc reduction maintenance system current conditions 24, and responsively generate the trip signal 10.
As best shown in
The trip unit 9 cooperates with the CTs 7A, 7B, 7C using the routine 20 to evaluate the signals 8 with respect to the selected one of the current conditions 22,24, and responsively cause the operating mechanism 15 to trip open the separable contacts 17A,17B,17C. For example, with reference to
Referring to
The selector switch 32 is pivotally coupled to the printed circuit board 35. The movable indicator 34 is peripherally coupled to the selector switch 32 and is structured to pivot with the selector switch 32. In particular, the selector switch 32 is a rotary selector switch including a pivot member 40 pivotally disposed with respect to the trip unit housing 26 and a selector member 42 coupled to the pivot member 40. The selector member 42 is disposed at the first housing opening 28. The movable indicator 34 includes a peripheral member 44 peripherally disposed about the selector member 42 and movable therewith. The peripheral member 44 is disposed at the second housing opening 30. The pivot member 40 includes an opening 48 that receives a pivot post 50 that is coupled to the printed circuit board 35. The movable indicator 34 also includes an indicator member 46 coupled to the peripheral member 44. The indicator member 46 is disposed at the second housing opening 30.
The example trip unit 9 (
The disclosed trip unit 9 allows for fine adjustment of the interruption current on the ARMS current conditions 24 of about 2.5 per unit (p.u.) and about 4 p.u. for the ARMS mode of operation of the circuit breaker 1. The trip unit 9 employs the example rotary selector switch 32, the peripheral member 44 and the indicator member 46 to provide a movable indication for the lowest two ARMS current conditions 24. For example and without limitation, an example blue (although any suitable color or other suitable indicia may be employed) flag provides visual indication and distinguishes the two ARMS current conditions 24 from the other relatively higher instantaneous current conditions 22, which correspond to a different white (although any suitable different color or other suitable different indicia may be employed) flag that provides a different visual indication. This advantageously provides an indication to the operator of, or maintenance person for, the circuit breaker 1 and/or the electrical system 2 even when the circuit breaker 1 and/or electrical system 2 are momentarily de-energized. Hence, the operator or maintenance person knows whether a relatively lower ARMS current condition setting or a relatively higher instantaneous current condition setting has been selected by the selector switch 32.
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 the invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.
