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full load rediirrs thr lifr of 
the insulat,ion. 
Principal Effects of High Voltage on Induction Motors. The most, 
significant efferts of too high voltage are inrreased tnr(lue, inr,rrasrd 
starting rurrent, and decreased porer factor. 
The increased torque may muse rouplings to shear off or damage t o 
driven equipment. Increased starting curretit raiiscs greater voltage 
drop in the power system, henre increases light, flirker. Uecreased po~vzr 
factor is particularly disadvantageous where power-fartor peualty rlanses 
Effect on Induction Motors. 
Principal Effects of l ow Voltage on Induction Motors. 
206 VOLTAGE-STANDARD RATiNGS, VARIATIONS, CALCULATION OF DROPS 
TABLE 4.6 General Effect of Voltage Variation on 
Induction-motor Characteristics 
Starting and maximum running 
torque... ................. 
Synchronous speed.. .......... 
Per cent dip. . ............... 
Full-load speed. .............. 
Efficiency: 
Full load.. ................ 
9% load. .................. 
)i load . . ................. 
Full land.. ................ 
I( load.. ................. 
36 load. .................. 
Full-load ~urrent . ............. 
Starting wrrenl . . ............. 
Temperature rise, full load. ..... 
Maximum torque capocity.. .... 
Magnetic n0ire.m load in parlicu- 
lor.. ..................... 
Power faclor; 
I Voltage Variotion 
Decrease 19% 
No change 
Increase 23% 
Decreore 136% 
Decrease 2 points 
Proclicolly no change 
Increase 1 to 2 point$ 
Increase 1 point 
Increase 2 lo 3 point! 
Incrcoie 4 lo 5 points 
Increase I1 Yo 
Decrease 10 to 12% 
Increose 6 to 7 C 
Decrease 19% 
Decrease slightly 
90% voltage Functionof voltage 110% voltage 
(Voltage)’ 
Cons1.nt 
1 (voltagel~ 
ISyn. speod--.llpl 
InCreOle 21 
No change 
Decrease 17% 
Increase 1 % 
.............. .............. 
.............. 
.............. .............. 
.............. 
.............. 
Voitoge 
IV0l togeJ~ 
.............. 
.............. 
Small increo*e 
Decrease 1 to 2 points 
Procticdiy no change 
Decrease 3 points 
Decrease 4 points 
Decrease 5 lo 6 points 
Decrease7% 
Inc,eo.e 10 to 12% 
Decrease I lo 2 C 
Increa3e 21 % 
Increase slightly 
This table s h o w gencral effcets, which will vary somewhat for specific ratings. 
are applied by the utilities. The higher the motor voltage rises, the lower 
the power fartor mill become. This may result in a greater penalty and 
hence a higher power bill. 
While the temperature rise at full load on standard motors decreases 
slightly for moderate overvoltages, the temperature rise may increase on 
certain types of sperial motors a t even very small overvoltages. Over- 
voltages of 10 to 1.5 per cent have caused numerous burnouts on special 
four-speed grinder motors. Motors rated for intermittent load are also 
materially affected by overvoltagcs. 
While marry drive applications are not seriously affected by voltage 
deviations as much as plus or minus 10 per cent from rated voltage, there 
are import,ant applications that are. 
Effect on Synchronous Motors. The effect of voltage variation on the 
performance of synchronous motors is similar to that on induction motors. 
However, while t,he starting torque varies as the square of the voltage, 
the maximum or pull-out torque varies directly with the voltage. 
From the above discussions it will be noted that, in general, voltages 
slightly in excess of motor name-plate rating have less detrimental effect 
VOLTAGkSTANDARD RATINGS, VARIATIONS, CALCULATION OF DROPS 207 
on motor performance than voltage helow the name-plate rating. This 
is one of the bases on which the voltage spreads in Table 4.9 mere deter- 
mined. A s an example, the figures show a recommended spread of 420 
to 180 volts for the 480-volt nominal system voltage, which is approxi- 
mately 4 per cent below and 9 per cent above the 440-volt motor rating. 
The light output and life of incan- 
descent filament lamps are critically affected by the impressed voltage. 
In Table 4.7 is shown the relationship of lamp life arid output to voltage 
for a vokage range from 80 to 120 per cent of rated voltage. 
In general i t may be said that for incandescent filament lamps a 1 per 
cent deviation from rated voltage causes a change of 3 to 335 per cent in 
light output. It can be seen from Table 4.7 that a 10 per cent reduction 
in lamp voltage results in a 30 per cent reduction in light output. In 
other words, when the voltage is 10 per cent low, the investment in the 
lighting system is working at only 70 per cent efficiency-thus, 30 per 
Effect on Incandescent lamps. 
!i! 
2 
3 
a 
0 
c PER CENT NORMAL VOLTS 3 
9 a 
FIG. 4.10 
average of many lampr. 
Characteristics of large gar-filled incandescent type C lampr. There are the 
208 VOLTAGbSTANDARD RATINGS, VARIATIONS, CALCULATION OF DROPS 
cent of the investment is lost. With an overvoltage of 10 per cent the 
lamp-life is reduced to less than oue-third~-t,hus lamp-replacement costs 
are three times as great as a t normal voltage. Other dat,a arc shown in 
Fig. 4.10, from which it, should be noted that the lumens per watt., or lamp 
efficieilcy, rises sharply at voltages above 100 per cent. In some cases, 
operating eronnmies result from hurriing lamps at higher efficiency and 
short life, or vice versa. 
TABLE 4.7 Effect of Voltage Variations on Gar-filled 
Incandescent-lamp Choracteristics 
80 
85 
90 
92 
94 
96 
98 
100 
102 
104 
106 
108 
110 
115 
I20 
Socket 
voltage 
~ 
96.0 
102.0 
108.0 
110.4 
112.8 
115.2 
117.6 
120.0 
122.4 
124.8 
127.2 
129.6 
132.0 
138.0 
144.0 
~- 
47 
58 
70 
75 
81 
87 
93 
I00 
105 
115 
I20 
I30 
I40 
I60 
185 
Per cent Per cent 
rated rated 
voltage lighl output 
Per <en1 
heoretical* 
life 
1900 
850 
400 
300 
225 
170 
130 
100 
75 
60 
45 
35 
30 
15 
10 
* Throrrticnl l i fv in thc nhsrrrcc of any mcrhanicnl hrcakagc.. In onlinary sprvire, 
mcchanird hrrakage r cdn r r s t h p l i ip expectanrc a t tlrr lo\ver roltagrs. 
The changes in lamp characteristics 
iI-ith rariatioii in cirruit, voltage arc given in Fig. 4.1 1. III general, 1 per 
cent variatiim i n line voltage n-ill changc t,he lumeir oudput only about 
1 per cent. Toltage is a factor in starting reliahility, and voltages l o w r 
than recommeiided may result in unsatisfactory starting. It will be 
noted that the ores-all efficiency (if the fluoresrerrt, lamp decreases if the 
line volt,age is raised above normal. The increased line volt,age causes 
the choke t,o pass more current to the lamp. This loivers the resistance 
of the arc. column, rcsulting in a lower voltage drop i n the lamp itself. 
The input, Ti-atts t o the lamp are slightly increased, and t,herefore the 
lumen output increases over a cert,aiii range. In this condition, however, 
the higher currcnt density priiduces the short ultraviolet radiation less 
effirieutly; wilserpently t,he luminous efficiency of the lamp decreases. 
Effect on Fluorescent lamps. 
VOLTAGGSTANDARD RATINGS, VARIATIONS, CALCULATION OF DROPS 209 
Fluorcsreiit lamps are fa r less af'ectrd hy circuit voltage variatioli tllan 
filament lamps, from t,he standpoint of life. 
The life of preheat-type lamps should he quite satisfartmy throrlghollt, 
the range of published voltage fur the various I ial lasts; tlicsr volt:tg(. 
ranges, iii general, are 110 ti] 125, 100 t o 2l(i, 220 to 250. :ind 240 t o 280. 
There may be some derrease i n life performalire \\-3ir11 opwitcd a t maxi- 
mum vokage as compared with that, a t miiiimiim vdt:igr. I I ~ i ~ e v t ~ r , 
there are a numher of other fartors, SWIM: of whidi arc i ~ i r p r ~ ~ d i r ~ t a l ~ l ~ ~ , tlr;lt,