Tài liệu Secret of power ppt

power Powering a home appliance is simple. There are no choices to make. Power for your network, on the other hand, never has been more complicated. And in today’s competitive environment, the issues are not only technical; there are business considerations as well: • Obviously, power distribution systems must be effective. But this means more than delivering the required amperage. They also must be easy to configure, install and maintain. • Power distribution systems have to be reliable. They should deliver power continuously with a minimum of trouble over the longest possible life. • Equipment must be safe—safe for the network and facilities and safe for the installers and technicians who work with them. • Installations should be economical. This is not just a matter of comparing purchase prices. Cost can increase by the need for excess “real estate” or maintenance or by the loss of revenue because of fail- ure. • Finally, there are time considerations. In fast-moving markets, decisions must be made and implemented quickly. Service providers must be able to balance the previously mentioned criteria with little time for deliberation or experimentation. And once choices have TELEPHONY • www.internettelephony.com • April 24, 2000 POWER C heck the troubleshooting guide for any electri- cal appliance, and the first question will prob- ably be, “Is it plugged in?” Go ahead and laugh (unless you’re the red-faced guy reaching for the plug), but the point is plain: Electrical devices need power. And if the device is part of a critical communications system, problems with power definitely can be serious. Secrets of Secrets of With all the variables to consider when installing a power system for your network, at least one thing is clear: It ain’t as easy as plugging in a toaster by D AVID S CHOMAKER With all the variables to consider when installing a power system for your network, at least one thing is clear: It ain’t as easy as plugging in a toaster been made, equipment must be available when needed. It doesn’t take much delay for customers to exercise their newfound freedom of choice by going elsewhere for service. Complicated networks, complicated power Consumer appliances are simple. You can take your dig- ital clock radio anywhere: home or office, Boston or San Diego. Plug it in, set it and it runs. You also can plug a different home appliance into the same socket, and it still will work. All the complicated work already is done. From the wall-socket in, credit the power company (for providing standardized 110 V, 60 Hz service) and the electrician (for using standard outlets and wiring to code). From the plug out, the appliance manufacturer is responsible for equipping the device with circuitry that adjusts the current up or down as needed to power var- ious appliances. Powering telecom devices is far more complex. The power company delivers AC voltage. The equipment supplier provides DC devices. The transition is up to you, and that’s where things get complicated. You could be installing any type of equipment, from wired—or wireless—transmitters to multiplexers or routers. It could be located in a central office (CO) or at a remote location—a controlled environmental vault, hut or out- side plant cabinet. Mountings vary, as do requirements, for -48 or -24 VDC (Figure 1). Playing it safe All doctors must take the Hippocratic Oath, the point of which is to do no harm. The same rule might be applied to power systems—and for good reason. Electricity is the genie in the bottle. Properly managed, it does our chores, but when it goes where it doesn’t belong, it can injure or destroy. None of this would be a problem if all installations were alike (they aren’t); the professionals working with them had all the time in the world (they don’t); and systems were installed in unchallenging en- vironments (they’re not). In the real world, power distribution systems have to be custom configured to their applications. They are installed and maintained by busy technicians with schedules to keep. They are located in COs and in remote locations. And despite our best efforts, they can be subject to every kind of shock and insult, from water leakage to earthquakes. Considering the risks, there’s only one sensible solution: constructive paranoia. Research may suggest that optimists live longer, happier lives, but to ensure long happy lives for net- works and the people who maintain them, it pays to ask, “What could go wrong?” History is full of “impossible” occurrences. If Hannibal could drive elephants over the Alps, you can assume that someone, someday, will fail to close the water-resistant door of your hut or cabinet, expos- ing your powering equipment to the elements. Someone will drill a hole into your wall. And your best- trained technician will, someday, reach in someplace he shouldn’t. The question is not whether things will go wrong. Rather, the question is how soon—and how often. Several steps can be taken to pre- pare for the inevitable: • Choose a single power distribu- tion platform for your entire net- work. Don’t make your technicians learn two or three different ones. Even if individual installations are customized, the same basic struc- ture will simplify training proce- dures, allowing technicians to develop and follow safe routines. Purchasing and inventory management also will become simpler. • If wiring and electronic elements shouldn’t be touched, make sure that they are adequately covered and labeled. • If single-post grounding is good, two-post ground- ing is better. • Don’t cut corners. Fire, injury and loss of service can be disruptive and expensive enough to offset any savings you may have realized. Something for the optimists With all this talk of things that could go wrong, it may seem impossible to choose the right product. That’s why there are standards. Standards bodies collect the experi- ence of experts and apply them to products. Power sys- tems for telecom are, in fact, some of the most rigor- ously tested and standardized of all products. By April 24, 2000 • www.internettelephony.com • TELEPHONY POWER POWER DISTRIBUTION SCENARIOS Primary power distribution Power equipment Incoming AC power AC power distribution Batteries Rectifiers Fuse panel DC-powered equipment DC-powered equipment Source: ADC Secondary power distribution (power distribution panel) FIGURE 1 demanding the highest levels of standards-compliance in the products you use, you avoid unnecessary prob- lems. The approvals you should look for include: • UL (Underwriter’s Laboratories). This is a safety standard for electrical products • NEBS (network equipment building standards) Level 3. NEBS Level 3 is the highest of three levels of safety and operability under worst-case conditions, including Zone 4 earthquake protection. NEBS Level 3 is required of most power products purchased by incumbent carriers, and it is being embraced by other North American carriers. Look for 100% independent testing (as opposed to vendor self-testing) to this stan- dard. • NEC (national electrical code). NEC is written by the National Fire Protection Agency and must be car- ried by any product connected to a U.S. telecom net- work. NEC 1999 is the most recent version of this standard. • CE (Conformité Européenne) and IEC (International Electro-technical Committee). CE is a requirement for all telecom equipment sold in the European Union. Stan- dards cover person- al safety, protection of public networks, interoperation with pub- lic network equipment and electromagnetic compatibility. IEC writes global standards of a similar nature. Look for approvals from both bodies. One final thought on the subject: There is no excuse for failure to fully comply with applicable standards. Ease of use Power systems don’t exist in a vac- uum. They are installed by real peo- ple in real places. Product design can make that process easier, safer and more economical. As already mentioned, standards compliance is a good start, but there’s more that can be done. A single, configurable system of components provides the consisten- cy that installers need to work quickly, effectively and safely. Flexibility in configuration lets them tailor each installation to the application and environment in which it is installed. A system that automatically adjusts for voltage and polarity requirements further simplifies the process. And the ability to “one-stop- shop” eases purchasing. Telecom applications can present unique problems, such as tight fits in crowded locations. Seemingly small features such as high-visibility fuses and LEDs, flexible mounting options and field-replaceable parts can speed and simplify field work, while reducing danger and dis- comfort for personnel. Clear plastic covers provide an extra margin of safety without reducing visibility of input/output power connections (see sidebar). Reliable, safe power is critical to the network. Absolute compliance with applicable standards is the least you should expect. Also, look for a system that is comprehensive, easy to configure and deploy and reli- able. Especially in today’s competitive telecom market, be aware that seemingly small matters can impact oper- ations, performance and, ultimately, revenue. When it comes to safety, flexibility, simplicity and reliability, don’t hesitate to make the necessary investment. You’ll profit over the life of the network. David Schomaker is the Senior Product Manager of PowerWorx products for the Broadband Connectivity Group at ADC Telecommunications in Minneapolis. His e-mail address is david_schomaker@adc.com POWER Power rules P owering telecommunications networks never will be easy, but the process can be simplified by following some practical rules: ❍ Absolute standards compliance, including indepen- dent NEBS (network equipment building system) Level 3 testing. This can be especially critical for competitive local exchange carriers co-locating equipment with incumbent carri- ers. Incumbents tend to be strict about standards compliance. ❍ High input power per bus. This allows flexibility in the deployment and helps hold down the cost of systems, labor and real estate. ❍ Flexibility of voltage and polarity. The ability to handle -48 or -24 VDC applications on the same type of panel provides the consistency that makes a technician’s work easier and safer. ❍ Flexibility of mounting. Panels that can fit either 19- or 23-inch racks can reduce inventory and cost. Choice of front/rear or all-front access simplifies deployment. ❍ Density. As in all installations, density reduces the need for expen- sive real estate, especially in remote locations. In power distribution, for example, the ability to install GMT fuses without spacing can make a big difference. ❍ Ease of ordering. Systems that can be “configured-to-order” in terms of power input/output, fuse management, mounting, etc., are faster and simpler to tailor to applications throughout the network. Better fit means better operation and lower cost. ❍ Speed of delivery. The best equipment is useless if it isn’t where you need it, when you need it. Choose a vendor with proven delivery capability. ❍ Choose a vendor with proven telecom experience. An experienced vendor will understand your network, and you’ll be able to leverage this experience to your benefit. ❍ Expect more than just a product. Look for a vendor to provide techni- cal support, information, documentation and, if desired, engineer, furnish and install services. ❍ Look for a solid warranty—the longer the better. Reprinted with permission from the April 24, 2000, issue of Telephony . ® Copyright 2000, Intertec Publishing, A PRIMEDIA Company, Overland Park, KS. All rights reserved. . devices need power. And if the device is part of a critical communications system, problems with power definitely can be serious. Secrets of Secrets of With. www.internettelephony.com • TELEPHONY POWER POWER DISTRIBUTION SCENARIOS Primary power distribution Power equipment Incoming AC power AC power distribution Batteries