Patent Grant
7340311
This invention relates generally to electrical panels and, in particular to an improved electrical panel configuration providing genuine emergency-stop, power buss lock-out, and other capabilities.
Various standards exist in relation to electrical panels and control functions, including the ANSI Control Reliability Standard, ANSI-B11.10. This standard has been in place for many years, and has yet to be truly modernized. One reason is that, since traditional systems function adequately in most circumstances, there is little incentive to introduce the latest technologies, particularly in view of that fact that these systems involve safety-related functions.
One area in need of updating, for example, is the “Lock-Out” function, which simply refers to the right of one individual to lockout others from reinstating power to equipment while they work on that equipment. This is a safety measure, similar to “pulling a meter” on a residence or business. The switches associated with this function are lockable, typically with a padlock, thereby informing maintenance personnel that the panel is now dead. There are times when the reverse is required; that is, where as a trades-person needs to work on a live panel. This is achieved by turning the power back on once the door is open. Switching power on with the door open can, and has, caused personnel injuries.
The disconnect switch is mechanically coupled to a pull-down handle used to interrupt power to the entire panel. A mechanical lock, such as a padlock is installed on the disconnect handle when the handle is pulled down. Although this arrangement now meets consensus standards, but is often not followed and is very inconvenient.
Another area in need of improvement is the emergency stop or “E-Stop” used to interrupt power provided by such panels to certain pieces of equipment, as might be found on the factory floor. For many years, such emergency stopping was accomplished with a master relay wired to interrupt power, much like a switch controlling a saw. One problem with such an arrangement is that if someone running a saw presses the E-Stop button, the starter contacts are welded closed due to a short circuit. This would be considered a system failure and the E-Stop button will not work as intended. The button itself. may be defective, thus, the very purpose of having an E-Stop is defeated. The inability of the E-button to perform as anticipated can result in a very dangerous situation, including the possible loss of life.
Most E-Stop configurations today follow a consensus standard of control reliability requiring redundant switches that are self-checking, adding a very high level of reliability to the control side of the circuit. This is accomplished through the use of safety relays. However, even using the most recent technology, known as safety PLCs, the potential power remains. Also in many situations the emergency stop button is used to halt the flow of electricity for non-emergency reasons, such as operator break periods.
A further need of improvement is panel access in general. Currently anyone can obtain access to a control panel; all that is needed is a screwdriver to open the panel door. Many mechanical door interlocks are broken and require no tools to open panel doors. In many factories people use these private areas to put their lunches, radios, and other personnel items in live control panels containing typical 480-volt, 3-phase power. Nevertheless, traditional panel door hardware techniques are employed.
Accordingly, the need remains for an improved electrical panel access and control technology, preferably one which includes true emergency stop, automated power buss lockout, and other advanced functions.
This invention improves upon existing electrical panel designs by providing a modular, power-reliable, buss-lockout and emergency-stop device. In broad and general terms, the approach moves control reliability to the power side of machinery and opposed to the control side.
The invention provides safety for skilled tradespersons required to work on machines or in electrical control panels while, at the same time, providing a true emergency or E-stop function, in the sense that externally derived control or electronic signals, such as single or multiple channel coded wave-forms, are used to disconnect the line from the load through an operator interface, thereby preventing power from being routed to the machinery where a problem might exist.
In contrast to existing systems, the inventive approach strives to interrupt power altogether by disconnecting the potential, so that power cannot be routed to devices such as motors, solenoids, drives, power-supplies etc. It is further recommended that machines or systems using the invention support two levels of stop buttons, one for ordinary “controls stop” as stated in the Background, and in the event of a true emergency, those labeled “E-Stop” according to this invention. Through the use of an electronic or electro-mechanical interface, the approach eliminates numerous outdated, if not antiquated, parts, including safety locks, mechanical disconnect switches, E-stop safety relays, and safety PLCs.
In addition, a modular panel design saves interior panel space, permitting the use of single-door access, in some cases. In the preferred embodiment, control panel doors cannot be opened with live electricity without some form of electronic authorization. The preferred embodiment further includes a records access capability if the panel is left unattended. The power may not then be reactivated with the doors opened, thereby virtually eliminating disconnect related accidents. In addition to the remote E-stop capability, automatic shut down will occur with a plant network emergency, ground-fault interruption, or panel door violation.
Other benefits of the approach include the capability of local programming through an RS-232 or other plant network, visual (color) display of system status and diagnostic display in conjunction with card/code lock-out access. This approach presumes a remote interface may be used in conjunction with a primary interface unit. The invention may be deployed in any number of environments, including a wide variety of industrial applications, such as factory lines, loading docks, and so forth.
Reference will now be made to
The preferred embodiment of the invention incorporates a modular power bus, is a simplified block diagram of which is depicted generally at 200 in
When the last authorized person swipes at 350 or manually enters with ID pad 302, and presses reset button 344, the powered disconnect will be reinstated, and the HOT/NOT display will switch to HOT. If the authorized person must work in the cabinet with the power on, they will first swipe or manually input their password and press the BYPASS button 312. This will allow the person to open the doors of the cabinet with the power on. When such personnel has completed working in the panel, they will close the door(s) which removes their I.D. from the display 322.
Note that, with the display keeping track of all personnel access (preferably stored in a nonvolatile memory), it will be clear to management who has gained access to the panel, and when such access occurred. Moreover, in the event that someone fails to reset the panel as required, such information will be clearly evident to permit appropriate reprimand. Depressing the OFF pushbutton 352 will open switch 226, and the HOT/NOT display will switch to NOT.
In the preferred embodiment, the higher-voltage switches and control functions are segregated, such as in the upper right hand comer of the unit, with lower-voltage signals being routed to and through the control interface unit relative to the power buss (L1, L2, L3). In this way, certain devices such as motor starters and other components, may interlock onto (and cover up) the high-voltage lines, thereby preferably creating a finger-safe environment for maintenance personnel.
Power will be removed and reinstated through the use of switches P1 and P2400, which may take the form of any control switch according to the invention, including solid-state devices. In fact, the main switches 400 may be implemented in a number of forms, namely, electromechanical, which includes coil-switched contacts, signal pulses or wave forms, electronic form solid-state gated devices, as may be derived through silicon-controlled rectifiers (SCR), tiracs, power FETs and the like, contactors, and double molded circuit-breakers with a shunt trip. It is the intention of this claim to provide redundant and self checking signals to comply with ANSI requirements for control reliability.
It should be noted that regardless of implementation, switches P1 and P2400 will be “force guided,” in the sense that neither will open without all opening, so that there can never be a failure in one leg of the line. This is in accordance with ANSI standards, which does not allow for a single component failure in an integrated safety device, to interfere with full shut down.
Also in accordance with the ANSI standard, the door of the panel cannot be opened without turning off power in much the same way as E-stops switches 402 interrupt the line. Note, however, that in contrast to previous designs, the emergency stop or E-stop function in this case is a true E-stop function, since power is turned off as early as possible up the line, rather than through some mechanism between the panel and the operator. With such a configuration, workers and operators on the line will be forced to use the E-stop control only for an emergency stop condition, since recreational use will shut down more than their own equipment, which is the way emergency stop functionality was originally intended to operate. Programming will be derived through the RS232 port or plant network, as described previously.
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| Number | Date | Country | |
|---|---|---|---|
| 20030178893 A1 | Sep 2003 | US |
