UFC 3-570-06
JANUARY 31 2003
Figure 7-12. Rectifier Efficiency
RECTIFIER EFFICIENCIES
160
AT FULL RATED VOLTAGE
140
120
AT FULL RATED CURRENT
100
80
60
EXAMPLE: 10% Voltage at Full Rated Current = 40% Efficiency
40
20
0
PERCENT OF RATED VOLTAGE OR CURRENT
7-6.3
Expected Efficiency. The expected efficiency of a rectifier depends on the
type of AC power (single or three-phase), Type of rectifying elements (selenium or
silicon), type of rectifier (bridge or center tap), and the percent of load of the unit. The
selenium bridge rectifier is the most common unit. The selenium inherently is less
efficient due to the voltage drop of the rectifier elements (and resultant heat). Selenium
ages with time and becomes less efficient as time passes.
7-7
DIELECTRIC TESTING PROCEDURES. Shorted dielectrics adversely
affect the operation of cathodic protection systems. If a cathodic protection system is
designed to protect an isolated structure, shorted dielectrics will normally result in loss
of adequate protection to that structure. Shorts may also result in poor current
distribution or shielding which will result in the loss of adequate protection to areas of
the structure. Testing an installed dielectric presents several problems. Since typical
installations normally include many dielectrics, all of which are in a parallel circuit, failure
of one dielectric can effectively short the entire system. There are indications of the
shorted condition of one dielectric at many, or all, other dielectrics installed. Usually,
the further the distance is between the dielectric being tested and the dielectric that is
shorted, the easier it is to test that dielectric. Most methods of testing a dielectric give a
reliable indication of only one condition of the dielectric (either shorted or not shorted
condition) and further testing may be required for the other condition. Only one method
gives a totally reliable indication of an installed dielectric. The radio frequency tester
(insulated flange tester), because of its wavelength and the strength of the signal, gives
a true indication of the condition of that specific dielectric. This method will not read
through other parallel paths, even when these paths are in the immediate vicinity. In
fact, this method can pinpoint the fault to a particular flange bolt or the flange gasket.
Therefore, this method should be used for testing when any other method is not
7-22
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