Patent Application
20150130566
The following disclosure relates in general to electric motor branch circuits and more particularly to means for providing improved operation for electrically operated circuit breakers, disconnect switches, and contactors.
The electric motor is at the core of most industrial processes. They are controlled and protected by a combination of circuit breakers and contactors with a protective relay. The technology has remained unchanged for the last 50 years.
An example of motor control using conventional circuit breakers and contactors can be found in Motor Control Centers (MCCs). These MCCs comprise columns of starters often 6 high in individually isolated units called ‘buckets’. The size of low kW starters is dominated by the conventional circuit breaker used for isolation and short circuit protection. Such conventional circuit breakers are expensive and too slow to provide damage free protection. The construction is complicated by the need for a flange to mount an interlocked operating handle. Conventional circuit breakers also generate heat and their construction complicates electrical interconnects particularly on high kW ratings. The emphasis is on the ability to withstand fault currents rather than minimize damage. Remote operation needs the addition of a secondary motor driven actuator.
Efficient design of electromagnets inherently limit the magnetic gap and with it the amount of contact gap between line and load in the open position.
A straight pull electrically operated circuit breaker may be deficient in magnet pull to accommodate a contact gap sufficient for arc interruption and isolation.
Existing designs of circuit breakers and disconnect switches are mechanical and require add-on motor drives for remote operation.
When contactors are used in safety applications, two contactors connected in series are commonly used for safe isolation reasons.
In addition, current practice is to have expensive and space consuming mechanical mechanisms that operate on a circuit breaker and the enclosure door such as:
Electromagnetic circuit breakers, disconnect switches, and contactors have gaps between line and load contacts that may have insufficient dielectric strength for safe isolation. This invention provides such a means by using a secondary actuator to allow movement of the circuit breaker contact assembly from a ‘cannot operate’ position with inherently larger contact gaps to a ‘can operate’ position when closure is required.
The present disclosure provides solutions to most of the problems mentioned above. Electrical operation enables motor branch circuit protection motors to move into the digital world. This in turn enables a prevention based approach to protection and the flexibility that goes with digital controls, remote operation, and communications.
In addition, further safety measures include a means of providing electrical/electronic/digital safety interlocking between an electrically operated circuit breaker, solenoid operated door latches, and the doors of electrical enclosures.
For a more complete understanding of the present disclosure and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings, wherein like reference numerals represent like parts, in which:
A first key element is the use of a pulse width modulated (PWM) DC magnet to replace the mechanical spring/lever system in conventional circuit breakers. A second key element is secondary actuator 200 that facilitates a large contact gap 104 in circuit breaker 100 and provides the means to move armature 111 of circuit breaker 100 from a position where it cannot close to a position whereby it can close.
In addition, conventional mechanical means of providing safe operation and maintenance of electrical enclosures are replaced by electrical/electronic/digital means to improve safety. Thus, one major advantage of this new approach is to provide safety interlocking of electrical enclosures enabled by the electrically operated circuit breaker, whose operation is by means of a straight pull electromagnet rather than a mechanical mechanism. A second major advantage is the secondary actuator 200 whose actuating rod 223 provides a direct mechanical connection between the optional external locking means and the moving contact assembly of the circuit breaker 100. Thus, if a lock is attached to aperture 222 at the external end of actuator rod 223, circuit breaker 100 is positively locked into an OFF position. The significance of this is that there is no interposing mechanism between the moving contact assembly and the means of positively locking in the OFF position.
Electromagnetics may not have sufficient pull to allow for safe circuit breaker contact gaps for isolation or fault interruption. Thus, secondary actuator 200 provides the additional ability to move armature 111 of circuit breaker 100 to an appropriate position. Once in the energized position, actuator rod 223 then moves with armature 111 of circuit breaker 100 when circuit breaker 100 moves to its closed ON position.
The next safety level is provided by the interaction between circuit breaker 100 and secondary actuator 200 and the design of circuit breaker 100. When in its OFF position, circuit breaker 100 cannot by itself completely close as the size of magnet 110, return spring 109, and contact spring 108 do not permit the entire elimination of contact gap 104. Circuit breaker 100 can only operate when actuator rod 223 moves armature 111 of circuit breaker 100 to its ‘can operate’ position. When sensor 112 detects that armature 111 of circuit breaker 100 has moved from its ‘can operate’ position, secondary actuator 200 is de-energized and returns to its OFF position. Circuit breaker 100 coil control is precisely controlled such that it can hold armature 111 in a stalled position. Thus, when secondary actuator 200 starts to return to its OFF position, armature 111 of circuit breaker 100 momentarily stalls prior to increasing coil current to fully close circuit breaker 100. This allows the use of both return spring 109 and contact spring 108 with high forces that enable magnet 110 to release very quickly for fault current interruption.
Armature 224 of secondary actuator 200 is given a non-magnetic coating to allow a fast opening when de-energized. This is important as secondary actuator 200 must not impede any opening of circuit breaker 100 to its fully open OFF position.
In the OFF position, return spring 109 of circuit breaker 100 moves the contact assembly to the fully open position. Contact gap 104 is then able to be 3 to 5 mm greater as compared to an assembly without secondary actuator 200. In the OFF position, magnet 110 of circuit breaker 100 is unable to close armature 111, placing circuit breaker 100 in the ‘cannot operate’ position.
Thus, when circuit breaker 100 is required to close, magnet 225 of secondary actuator 200 acts to move armature 111 of circuit breaker 100 to a ‘can operate’ position. With contact gap 104 now shortened, circuit breaker 100 is then able to operate when its control coil is energized. Energizing coil 107 of circuit breaker 100 has a current source, pulse width modulated (PWM), control that is able to move armature 111 1 mm and then stall momentarily. When sensor 112 detects movement of armature 111, secondary magnet 225 is de-energized and armature 111 moves rapidly to closure. This is important because secondary actuator 200 must be in the OFF position, so when circuit breaker 100 is called on to interrupt a fault current, it will have sufficient contact gap 104 to permit the arc to be extinguished.
The requirements for contactors and disconnect switches, while different in function, share the same principle design benefits.
The use of secondary actuator 200 allows return spring 109 to be profiled so as to permit high contact pressures and initial moving contact return springs so as to give maximum contact opening force. Lower rate springs 108 and 109 return the moving contact assembly to the fully OFF position. This is critical in ensuring that circuit breaker 100 can quickly respond to high fault currents and to keep the force needed by secondary actuator 200 to remain low.
Both single pole and multiple pole arrangements are possible. It may be advantageous for the coils 107 and 221 of circuit breaker 100 and secondary actuator 200 to have control circuitry that reverses coil current for the fastest possible opening.
Being digital, all major components are given unique product data for displaying through the controller and via the communication network.
Circuit breaker 100 provides certain safety measures. Two actions are needed before the device can be operated—first, energizing the secondary magnet coil 221 of secondary actuator 200 and second, followed by energizing the operating coil 107 of circuit breaker 100. Supply failure will result in the device opening to its fully open ‘cannot operate’ position. Contact gap 104 in circuit breaker 100 and dielectric strength in the open position allows for safe maintenance of electrical equipment and its load. Secondary actuator 200 can itself be integrated with circuit breaker 100 into an electrically based enclosure safety interlocking system with additional levels of safety. Safety applications with contactors can use a single device instead of two.
This system provides multiple levels of safety interlocking as follows:
One or more electrically operated door latches, 334, 335, and 336 of
A controller, whose function may reside in an associated product, provides for a means of logically coordinating the safe operation of the circuit breaker, secondary actuator, motor switching contactor, and the associated safety interlocking. It also contains the 24 volt DC power supply and PWM control for both circuit breaker and motor starting contactor. The electrical controls operate on 24 volt DC to facilitate safe maintenance. The user interface has an access code for controlling both access and controller functions.
The local display is configurable, dispensing with the need for custom door controls and indicator lights.
The circuit breaker/secondary actuator assembly discussed herein provides a solution to the problems encountered by conventional circuit breakers. Improved circuit breaker operation and enhanced safety measures can be achieved using the techniques provided above.
It may be advantageous for the secondary actuator function to be integrated into a single assembly with the straight pull circuit breaker.
Although the present disclosure has been described in detail with reference to particular embodiments, it should be understood that various other changes, substitutions, variations, alterations, and modifications may be ascertained by those skilled in the art and it is intended that the present disclosure encompass all such changes, substitutions, variations, alterations, and modifications as falling within the spirit and scope of the appended claims. Moreover, the present disclosure is not intended to be limited in any way by any statement in the specification that is not otherwise reflected in the appended claims.
