Selecting ac Voltage

MIL-HDBK-1004/10

Selecting ac Voltage. Select alternating current voltages of

6.5.3.3

almost any commercial power supply voltage. Units with either 115 V, 230-V or

440-V single-phase or 208-, 230-, or 440-V three-phase inputs are the most

common. Some units are supplied with dual input voltage selected by wiring

arrangements during installation. Choices between single-phase and

three-phase units should be based upon a balance between first cost and

efficiency as discussed in para. 6.4.2. The following table can be used to

select the combinations of rectifier capacity and input voltages which are

commonly most economical if a selection of supply voltages is available:

RECTIFIER dc

SINGLE-PHASE

THREE-PHASE

RATING (W)

VOLTAGE

Up to 2,700

115

208

2,700 to 5,400

230

5,400 to 7,500

440

230

Over 7,500

440

dc Voltage and Current Output. Direct current voltage outputs from

6.5.3.4

8 to 120 V and current outputs from 4 A to 100 A are common. Almost any

current can be provided but it is generally best to select a smaller standard

size rectifier unit such as 20 A and use multiple units if very large amounts

of current are required. Many small units cause far less interference and

provide more uniform current distribution along the protected structure than

few large units.

Filters. Electrical filters are used to both increase the

6.5.3.5

efficiency of the rectifier by reducing alternating current ripple and to

reduce interference with communications equipment. Efficiency filters can

increase the efficiency of single-phase bridge type rectifiers by 10 to 14

percent and their use should be based upon a first cost versus operating

(power) cost basis. Efficiency filters are not commonly used with three-phase

rectifiers as the alternating current ripple in these units is inherently low.

Noise interference filters should be used when a large unit is to be installed

in the vicinity of communications lines or can be retrofitted when noise

problems are encountered and are significantly affected by turning the unit on

and off.

Explosion Proof Rectifiers. Rectifiers and other system components

6.5.3.6

such as switch and circuit breakers are available in explosion proof

enclosures conforming to Electrical Safety Standards for Class I Group D

hazardous conditions that may be encountered in fuel or natural gas storage or

distribution systems. Such enclosures should be specified whenever explosive

hazards may exist.

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