Protection of Telecom Sites in Countries with Unstable AC Mains
Developing countries often have weak power generation and distribution systems, frequently resulting in mains voltage fluctuations beyond the 184 Vac to 264 Vac input range mandated by the European Norm. The underlying International Electrotechnical Commission (IEC) standards assume that power generation and distribution are fairly stable and that voltage excursions will not be outside the specified input window of 184 Vac to 264 Vac. Unfortunately, that is not the case in many developing countries throughout the world. Even industrialized nations have their share of problems with ac mains availability. Mains voltages frequently fluctuate beyond the assumed 184 Vac to 264 Vac input range.
In the US State of California for example, a failed deregulation scheme coupled with the lack of corrective political will led to rolling blackouts that cut power to millions in early 2001. The desired expansion of generation and distribution capacity in developing countries is also constrained by a shortage of capital and, in some cases, political factors as well. Thus, it appears that the quality of ac mains, for developing countries, is at best uncertain into the foreseeable future.
The expansion of communications networks, such as cellular radio, direct radio access telephony (wireless in the local loop), paging networks, land mobile radio and satellite telephony stations, has led to a rapid increase of installed sites to support these networks. The proliferation of sites sometimes makes it difficult to place a particular site in an ideal location. The site might then be installed in a remote or difficult-to-access location.
The Problem
The power converters used in modern ac-dc rectifiers, uninterruptible power supplies and ac-dc switch-mode power supplies, are typically based on the IEC input range of 184 Vac to 264 Vac. Ac induction motors are sensitive to both high and low mains voltage, where low voltage can cause rotor lockup following a dip in mains voltage; and to saturation causing tripping of circuit breakers, as a result of high mains voltage. Transformers and other 50 Hz/60 Hz magnetics can easily get saturated when exposed to high input voltage, particularly at 50 Hz, when the magnetization curve of steel becomes non-linear much quicker than for 60 Hz.
