standards and guidelines for communication sites - Radio And ...

STANDARDS AND GUIDELINES FOR COMMUNICATION SITES RECTIFIER/DC POWER SYSTEMS
6.3.9 POWER QUALITY TESTING DURATION
The monitoring period is a direct function of the monitoring objective. Usually the monitoring period
attempts to capture a complete power period, an interval in which the power usage pattern begins to
repeat itself. For example, an industrial plant may repeat its power usage pattern each day, or each shift.
Depending on the monitoring objective, it may be necessary to monitor as little as one shift. (IEEE STD
1159-R2001, section 7.5.1)
It is generally recommended that the minimum monitoring period include at least one full work cycle,
normally seven or eight days. Longer monitoring periods are often needed to record disturbances that
occur on a random or seasonal basis. (IEEE STD 1100-1999, section 6.4.2.5.)
6.4 RECTIFIER/DC POWER SYSTEMS
This section provides guidelines and specifies requirements for selecting and installing site rectifier/DC
power system systems and components. Note that although specific recommendations are stated here,
actual equipment specifications are largely determined by factors peculiar to the installation being
performed. These stipulations are noted throughout the section.
6.4.1 RECTIFIER SYSTEM REQUIREMENTS
6.4.1.1 ACCEPTABLE RECTIFIER TYPES
Two general types of rectifiers are acceptable for powering communications equipment. The types are:
• Controlled Ferroresonant Rectifier
A controlled ferroresonant rectifier exhibits an exceptionally good Mean Time
Between Failure (MTBF), and typically provides an output exceeding 110% - 120%
of its rating for the life of the rectifier. Forced load sharing is an essential feature of
these rectifiers. In a multiple rectifier system, it prevents a single rectifier's output
from drifting down and becoming inefficient.
Both a potential drawback as well as benefit of this rectifier is its transformer. In an
area prone to excessive AC transients, a controlled ferroresonant rectifier will
continue to function satisfactorily. However, the transformer is large and heavy.
Suitability of this rectifier type will be based on balancing these criteria.
Although a ferroresonant supply is simple, low cost, and handles high current, it
cannot handle AC line frequency shifts, particularly on the low side. An applied low
line frequency (even 59 Hz) causes the ferroresonant supply to draw high current over
excessive ON cycles. This overheats the transformer and causes close to short-circuit
conditions within the tuned reactive circuit. A backup generator with a defective
speed governor is a typical source of this trouble.
68P81089E50-B 9/1/05 6-19