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1945 Theatre Catalog, 4th Edition, Page 313 (289)

1945 Theatre Catalog, 4th Edition
1945 Theatre Catalog
1945 Theatre Catalog, 4th Edition, Page 313
Page 313


1945 Theatre Catalog, 4th Edition, Page 313

connection between the motor and the generator and partially because of the flywheel effect of the rotating armature. From the first set of curves in Figure 2, which are for the flat compound motor generator, it can be seen that sudden normal changes in a.c. power supply have no effect on the d.c. arc circuit.

The second and third set of curves in Figure 2 show the amount of disturbance transmitted to the d.c. arc circuit by two other common types of rectifying equipment. Notice that the direct current supplied to the arc follows the changes in a.c. line voltage very faithfully, and that the amount of change in direct current due to varied nominal changes in a.c. supply voltage are much greater than can be tolerated for quiet and stable arc operation.

Because there is no electrical connection between the alternating current input voltage and the direct current output to the arc where a motor generator set is used, no ripple or harmonics in the d.c. power are reflected whatsoever into the a.c. line to affect the speaker systems.

In Figure 2 are presented graphic curves showing the amount of ripple transmitted by various types of converting equipment from the alternating current line to the direct current arc circuit. Notice that the d.c. current supplied to the arc follows the changes in a.c. line'voltage very faithfully be FIGURE 2.v-Graphic curves showing the amount of disturbance transmitted by various types of voltage-converting equipment (flat compound motor generator, copper oxide rectifier, and hot cathode tube rectifier) from the a.c. line to the d.c. arc circuit of low-voltage, highdntensity, non-rotating arcs due to a.c. line

"do 52c.

Z20 ZIO ZOO

50.

D.C.AMP5. A.C.Vous

FLAT COMPOUND Moron GENERATOR

7.30

ZIO 7.00

D.C. Amps. A.C.Vorrs

L30 ZZO ZIO

At. You:



D.C.AMP5. p I,

l945-THEAYRE

5 SEC.

i'i

CATALOG

cause of the fiywheel effect of the rotating armature, and that the amount of change in the current due to varied nominal changes in a.c. supply voltage are much more than can be tolerated for quiet and stable arc operation. In a motor-generator set, there is no electrical connection between the alternating current input voltage and the direct current output. This means that any ripple or harmonics in the d.c. power are not reflected whatsoever into the a.c. Rectifiers of the type usually supplied for motion picture arc service are connected electrically between the a.c. input and the d.c. output. This allows harmonics from the rectifier to be refiected into the a.c. line and these harmonics are of the order Gabi 1, where a is any positive integer. Also, on the direct-current output side, harmonics are superimposed on the nominal d.c. ripple and the order of their frequency is na, where n is the number of phases in the rectifier and BL is any positive integer. The magnitude of these harmonics is proportional to the reactance of the load circuit.

The direct current generator designed for are service does not pass on harmonics t0 the arc circuit, but only a small amount of inherent ripple due to the commutator. The magnitude of this ripple is only a small percentage of that normally found in the output of a threephase rectifier.

armature.

l0 SEC.



COPPER Cm: RECTIFlEE



HOT CATHODE TUBE RECTIFIER

I5 Sac.

' y A.(. Luna VOLTAGE . D.(.. ARC Amazes

MAINTENANCE

The motor-generator set, while it contains a rotating member, still requires only an extremely small amount of maintenance. Practically all sets are equipped with high grade ball bearings which do not require lubrication more often than every three to six months, and the only other preventive maintenance suggested is the occasional blowing out of dust and dirt which normally accumulates on any type of equipment.

The only part of rotating equipment which can be said to be normally consumed in service are the carbon brushes used on the commutator. Brushes, as now manufactured and applied, should run for a period of at least five years without replacing. This item is relatively inexpensive at such time as replacement is required.

Arguments can be advanced pro and con regarding the proper location of rectifying equipment including motor generator sets for projection service. The motor-generator set is usually installed in a very small, well-ventilated room adjacent to the projection booth. It can be installed in a room so as to be entirely unobserved practically all the time due to the low maintenance and faithful service inherent with this type of equipment.

It is generally desirable to locate other types of rectifying equipment very close

fluctuations. The tests were made with Suprex 7-mm. by 12-inch positives and 6-mm. by 9-inch negatives. Notice that the d.c. current supplied to the arc follows the changes in the a.c. line very faithfully because of the flywheel effect of the (Hertner Electric Company graph, prepared for this publication.)

10 SEC.

AC. LINE VOLTMaE

0.6. ARC AMPEKES

ALLINE VGLTAGE

D.C. AEL AMPEEES
1945 Theatre Catalog, 4th Edition, Page 313