Alpha Technologies APX Series Manual del operador descargar pdf (Pagina 8)

1. INTRODUCTION

1.2 Operating Principle

The Modular Transformer Assembly (MTA) contains a ferroresonant transformer,

resonant circuit capacitor, and control panel with line input circuit breaker and output

fuse assembly.

Alpha APC (APL) Series non-standby power supplies utilize 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 significantly 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;

60dB transverse mode.

An oil-filled 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 fluctuations.

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.

Alpha’s non-standby power supplies are extremely efficient, having a typical

efficiency rating of 90% or better.

The output waveform from the ferroresonant transformer is not a true sine or square

wave, but is instead a quasi-square wave. NOTE: A true RMS voltmeter must be

used to correctly measure the output voltages.

Ferroresonant ‘Tank’ circuit and resulting output waveform

Ferroresonant

transformer and AC

capacitor

Noisy input waveform

Clean output waveform

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Alpha Technologies APX Series Manual del operador Pagina 8