Alpha Technologies APX Series - Manual (Page 8)

8 016-030-B0-005, Rev. C
1.0 Introduction
The Alpha APX Series Non-standby Power Supply provides conditioned power to signal amplifi ers in
cable television and broadband distribution systems. The modular design, consisting of a baseplate,
transformer assembly and enclosure cover, supplies the load with current-limited, regulated AC
power, that is free from spikes, surges and other forms of power line transients. The design supports
easy upgrades simply by replacing the transformer assembly, saving time and money.
Alpha’s non-standby power supplies are extremely effi cient, with a typical effi ciency rating of 90% or
better.
The versatile APX Series includes an AC input circuit breaker, output fuse, *output receptacle,
VSF fi tting, and external grounding clamp and can be mounted on poles, walls, racks, shelves, or
pedestals. Operator controls are inside the enclosure on the main transformer assembly.
You can equip the APX with various options, including a *Time Delay Relay (TDR-M), Plug-in
Lightning Arrestor (LA-M), Status Indicator LED (SIL-C), plug-in *Amp-Clamp (ACAT-3P), *Ammeter
(AMM-C), and Enclosure Security Lock (GLK). See Section 1.3 for a complete description of all
available options
1.1 Operating Principle
The Alpha Modular Transformer Assembly (MTA) contains the ferroresonant transformer,
resonant circuit capacitor, and control panel with line input circuit breaker and output fuse
assembly.
The Ferroresonant Transformer
Alpha APX Series uses ferroresonant transformer technology to provide line conditioning and
voltage regulation. The primary and secondary windings of the transformer are physically
isolated from each other by a large steel core which signifi cantly reduces the capacitive
coupling of spikes and noise to the secondary winding. This provides a regulated, current-
limited output with excellent isolation and noise attenuation, (120dB common mode and 60dB
transverse mode).
Another unique feature of the ferroresonant transformer is its ability to provide current limiting
in the event of a short circuit. This effect is called foldback. The transformer’s output current
can typically reach 150% of the nameplate output current rating for a short period of time
without damage to the transformer. When the transformer reaches the saturation point, the
output current will decrease (foldback on itself) to a minimum value, and thereby provide
current limiting. Designs based on ferroresonant transformer are extremely rugged and
reliable offering many years of trouble-free operation.
The Resonant Circuit Capacitor
An oil-fi lled resonant AC capacitor is connected to the resonant (secondary) winding of
the transformer forming a tank circuit. This provides the resonant circuit function which
contributes to the voltage regulation of the supply. The advantage of this type of transformer/
capacitor design is the ability of the ferroresonant transformer to regulate its output voltage
over a wide range of input voltages and output loading. Typical output voltages may vary
+/- 3% to 5%, with input voltages variations of +/- 15% of nominal line voltage, and output
loading of 20% to 100%. This tight regulation is advantageous in cable television applications
as the active devices are protected from dangerous voltages fl uctuations.