Figure 1-41.-No-break "uninterrupted" power supply system components.

NO-BREAK POWER SUPPLIES

PRINCIPLES OF OPERATION

A no-break power supply is designed to provide

The input 440-volt, 60-cycle, 3-phase power is

uninterrupted electrical power by automatic takeover

stepped down by transformers and applied to an SCR

should the normal supply fail or momentarily deteriorate

(diode) 3-phase bridge. The output voltage of the bridge

beyond the system demands. No-break power supplies

can be controlled by varying the phase that the SCRs are

are provided for communication systems, computers,

triggered. The output is then filtered and sent to the load.

navigational equipment, automated propulsion systems,

and related equipment where a momentary loss of power

The voltage across the load is compared with an

would cause a permanent loss of information resulting

internally generated, temperature-compensated,

in the need to recycle or reprogram the equipment. Since

reference voltage. Any difference between the actual

equipment requiring no-break power normally requires

load voltage and the desired load voltage, indicated by

closely regulated power, no-break power supplies are

the reference voltage, is amplified by the voltage control

designed not only to provide uninterrupted power, but

circuit. This amplified voltage is combined with a

also to provide power that is regulated to meet the needs

properly phased ac signal and applied to the trigger

of the equipment it serves.

circuit of the SCRs. The ac signal controls the time of

firing of the SCRs. By controlling the time of firing of

COMPONENTS

the SCRs, the output voltage is also controlled.

The SCRs are fired earlier if the output voltage is

The no-break "uninterrupted" power supply system

too low. They are fired later if the output is too high.

consists of two major assemblies plus the storage bat-

Special frequency-shaping circuits are used to ensure

teries. The control cabinet and motor-generator set are

shown in figure 1-41.

stability and prevent oscillations or hunting.

Figure 1-41.-No-break "uninterrupted" power supply system components.

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