DC Power in Network environments

Is this the year that DC power can finally enter the mainstream for equipment analysis and decision-making?

Although the structure of telephony has been changing rapidly, senior management has traditionally left decisions about powering telephony equipment to an equipment engineer or an engineering standards group, with one very knowledgeable individual usually controlling the decision-making process for that company.

The practice started many years ago, when telephony centered around POTS. This telephone service was expected to never fail in spite of any catastrophes or any equipment limitations that existed before the days of solid-state electronics, distributed networks with redundant paths, and alternate networks and services. The original local exchange carriers—primarily the Bell regional holding companies and large Independent telephone companies—ensured that the basic telephony network was impregnable. LECs established iron-clad specifications that detailed every known variant, including electromagnetic interference (EMI), voltage regulation, load-sharing characteristics and transient load response, among a host of other things.

Batteries were also subject to intense scrutiny and a rigorous maintenance schedule that ensured they were always properly charged in case of an AC outage. Bellcore added equipment stipulations that all Bell companies also followed. It was often said that it took an inordinate amount of time to become qualified as an approved LEC supplier, but once approved, the supplier enjoyed a privileged relationship simply because of the strict standards approval process.

Then came divestiture and with it, cellular service, competitive access providers and interexchange carriers. Within the last year, personal communication services providers have entered the picture, along with new telecom reform legislation, global telephony services and products, as well as the Internet and combined cable/telephony (broadband) services.

Today, telecommunications accounts for approximately 6% of the world's gross national product. So where does that leave DC power and batteries? DC power is one of the most important elements in the networking infrastructure equation. Without it, most telecom equipment simply does not operate. Plus, if the power system is not truly reliable, it will shorten the life of the sealed valve regulated batteries while causing high service and maintenance costs for all the equipment acquired.

Yet increasingly, the decision of what to do about power is left to an engineer who often sees it as a necessary evil, a less important item to manage. Because the initial hardware cost for DC power usually equals no more than 10% to 12% of the total equipment outlay, it is relegated to a "B" or "C" priority for the typical engineer, who is responsible for a variety of competing equipment and services. The choice of power supply could be assigned to the switch or radio equipment vendor, who throws it in with the other equipment. It's easy, it's simple—and it's one less worry in the initial infrastructure decision.

The problem with this approach is the potential effect on installation, maintenance and upgrade costs. Corporate downsizing inside the old, established telephone companies has eliminated or greatly reduced the level of technical expertise available to install, maintain and service the equipment and specify revisions. For newer companies, the name of the game is to get it installed now and worry about the consequences later.

Now, suppose you have a network of several hundred or several thousand equipment sites to service. There are significant advantages to ensuring that the battery and power plant are just as advanced as the new switching platforms and miniaturized cell sites being employed.

To do this there are a number of questions that potential DC power equipment users need to ask regarding the equipment and its supplier.

Key Questions The first important question is: Does the equipment offer state-of-the-art features that simplify installation and serviceability, thus reducing installation time and costs substantially?

A power system that permits setting of all voltage, current and alarm thresholds via a simple upload from a laptop eliminates a lot of installation time (and cost) while ensuring consistent integrity of all settings across all sites. Alarm thresholds can be predetermined and set automatically.

Voltage drift conditions among rectifiers have caused havoc with false rectifier failures that result in "no fault found" situations. This would require on-site tweaking of the rectifiers to effect proper load sharing. This situation can be prevented by using intelligent, solid-state control of the rectifiers.

In addition, an ideal power system would offer complete modular expandability based on increased load demand over time. It would not require equipping the power plant with unused shelves, rectifiers or AC connections at the outset. (Table 1 provides feature/benefit statements for state-of-the-art power systems.)

The second question is: Does it provide enhanced operating features that will optimize performance in the new network's demanding environments?

Because many new applications require equipment to be housed in outdoor-type enclosures, the equipment must operate at full capacity across a temperature range from at least -20 C to at least 50 C. Even though the enclosures have heating and air conditioning systems, the environmental conditions during an extended AC outage can still be extreme.

Monitoring the condition and measuring the internal resistance of individual cells in the battery string —while adjusting the battery's charging voltage in terms of temperature—provide a considerable advantage when multiplying the battery strings by the number of installation sites by the cost of each string. A 50% enhancement in extended battery life could save thousands, if not millions, of dollars over several hundred sites during an eight- to 10-year period.

Active power factor correction, now a standard in Europe, is also a clear advantage in today's environment. If an equipment site is located near sensitive electronic equipment such as a 911 emergency center or a financial services telemarketing center, active power factor correction eliminates nasty AC harmonic distortions that could cripple computer equipment operating in close proximity to the power site. (Table 2 provides a feature/benefit comparison for evaluating operating performance in today's environments.)

A third important consideration is to find out how simple it is to follow the documentation when installing a power plant.

Installing power and batteries is different from installing benign equipment that operates only after the "hot" current is applied to a terminal connection. Documentation must be clear, intuitive and concise. Checking and comparing the documentation packages of DC suppliers is a step that will ensure ease and consistency of installation in the long run.

Fourth, what type of service, maintenance and support factors are provided by the equipment supplier? If power system management includes the use of a centralized controller with a built-in modem, monitoring and diagnostic analysis of the power plant can be done anytime, anywhere, without additional cost. For example, an up-to-date control system permits electronic labeling of circuit breaker or fuse positions so that a technician can identify an actual breaker trip even before going to the site.

Let's examine another situation. A major alarm condition is received at the network management center at 2 a.m., and an on-duty technician is called at home. Before going anywhere, the technician can interrogate the site with a laptop PC over a regular home telephone line.

The technician reads a rectifier "fail" condition and notices an over-voltage shutdown in the events log. After monitoring the site for a few minutes the technician sees the failed rectifier restart, go back on-line and clear the alarm. The technician knows that the alarm condition was caused by an abnormal surge from the AC line and that the site is now normal. A time-consuming trip to the site is avoided.

Remote diagnostic capability also permits a partnership with the equipment supplier and its 24-hour technical support center. For example, assume an unusual condition exists and the local technician wants the supplier's support engineer to help analyze it. By calling the 24-hour support center, the local technician can authorize the supplier's on-duty engineer to contact the site and provide diagnostic assistance—before the technician is dispatched.

The final question to ask is: What kind of warranty is provided by the supplier for its equipment?

It's not uncommon for a one- or two-year warranty to be provided on the DC power equipment. Batteries are typically guaranteed for one year with a pro rata warranty for up to 20 years. Yuasa-Exide, for example, offers a five-year, unconditional warranty if proper power and battery management procedures are used with its system.

While there are many other benefits to using a dedicated power and battery systems provider, the thing to remember is whether you are a wireline provider supplying basic and enhanced network services or a wireless cellular or PCS carrier. The efficiency and reliability of your network can be significantly enhanced by asking these key questions before deciding how to address your DC power and battery needs.

Chris Searles is Product and Marketing Manager of the Energy Products Group of Yuasa-Exide Inc., Reading, Pa.