Hybrid power for remote communications networks – Part Two

By Peter Spiteri*
Modern mining facilities are faced with the dilemma of how to power a variety of telecommunications and networking equipment as reliably and economically as possible.
However, with the convergence of information technology and telecommunications networks, equipment input power requirements are no longer standardised around -48VDC. Alternative approaches have been devised to power modern telecommunications facilities having both AC and DC-powered equipment.
It’s useful to consider the advantages and disadvantages of the various design approaches along with application-specific guidelines considered best-practice for Australia’s mining industries.

Developing a power protection solution
Today’s converging communications networks often requires facilities managers to accommodate equipment that requires an AC power source. The AC power can be derived by way of inverters powered from the –48 VDC power system. An alternative is the use of an AC UPS, which is often more straightforward, efficient, and lower cost. In comparison to DC systems, AC UPS uses higher voltage batteries, provides regulated voltage output, is available in higher power capacities, and allows for longer power distribution distances.
But it isn’t as simple as placing any AC UPS into your existing set up. As networks grow with stunning speed and unpredictability, power quality and environmental factors become much more complex issues. It is important that the AC UPS provide power as reliably as the associated DC power system. In many systems, the DC powered equipment is not fully operational without the AC powered  equipment and vice versa. It is, therefore, important to take a total systems approach.

A System Approach - today's best solutions
To avoid compromising the availability of load equipment, the power system needs to be about 10 times more reliable than the load equipment. Therefore, redundancy in the power system is required.
To facilitate implementation of the power system redundancy, a number of critical telecommunications and information technology equipment is available with dual input power connections.
In its basic form, distributed redundancy involves creating two (redundant) power protection system busses and redundant power distribution systems. This eliminates as many single points of failure as possible, all the way up to the load equipment’s input terminals. In order to provide “fault tolerance,” some method of allowing the load equipment to receive power from both power protection busses must be provided.
To protect against fast power system failures, such as circuit breaker trips or a power system fault, either dual input load equipment or very fast transfer switches need to be applied between the two independent power sources to eliminate any common failures.
A number of distributed redundant power distribution configurations have been devised. For today’s large convergent telecommunications facilities, that is, those with large, high-availability information technology equipment, dual redundant UPS system with redundant AC power distribution have been deployed.

The Importance of Support
Specifying and maintaining a high level of power availability absolutely require access to a number of support services. Preventative maintenance is critical to long-term effectiveness of a power protection program. This includes regular testing, checking the battery plant, verifying that the UPS and rectifiers are operating properly, and a thermographic survey of selected equipment and connections to prevent failures in the electrical systems.
Telecommunications sites, particularly if they are unmanned or remote, need thorough periodic reviews. These reviews should be included in an effective power protection program, to prevent problems or recommend corrective actions.

Summary
Different applications require different solutions. Applications involving almost exclusively – 48VDC powered equipment, like central office applications, need to follow the traditional telecom DC power system model.
Applications involving almost exclusively AC – powered information technology need to follow the traditional AC UPS power system Model. In applications where there is a significant mixture of co-dependant AC - and DC – powered equipment, hybrid power systems are required. A systems approach borrowing the “best practices” of both AC and DC power systems need to be employed to achieve a cost effective and reliable hybrid power system.

* Peter Spiteri joined Emerson Network Power in 2003, bringing with him over 20 years of experience in marketing management, IT and engineering. He started his career as a software engineer with Honeywell in Boston, designing the EFTPOS network for Australia and New Zealand. He then held various product marketing and channel development roles for 3COM, Cisco, Tech Pacific and Nortel.

To read the first part of this story, click here.