of

hunting of synchronous machines, etc. In the phenomenon of

frequency,

hunting, frequently two periods are superimposed, forcedresulting from the speed of generator, etc., and the natural

frequency of the machine. Counting the number of impulses,

/, per minute, and the number of nodes, n, gives the two

frequencies :/+- and/ ; and as one of these frequencies 2i 2i

is

the impressed engine frequency, this affords a check. Not

infrequently wave-shape distortions are met, which are

but

not due to higher harmonics of the fundamental wave,are incommensurable therewith. In this case there are two

entirely unrelated frequencies. This, for instance, occurs in

the secondary circuit of the single-phase induction motor; two

sets of currents, of the frequencies / and (2ffs) exist (where

/ is the primary frequency and / the frequency of slip).

Of this nature, frequently, is the distortion produced by surges,

oscillations, arcing grounds, etc., in electric circuits; it is

a combination of the natural frequency of the circuit with the impressed

frequency. Telephonic currents commonly show

such multiple frequencies, which are not harmonics ofeach Engineering

work leads to more or less extensive numerical

investigation

calculations, when applying the general theoreticalto the specific cases which are under consideration. Of importance

in such engineering calculations are; (a)

The method of calculation. (6)

The degree of exactness required in the calculation. (c)

(d) a.

Method of Calculation. Before

carefully

beginning a more extensive calculation, it is desirableto scrutinize and to investigate the method, to find the simplest

system

way, since frequently by a suitable method andof calculation the work can be reduced to a small fraction of

what it would otherwise be, and what appear to be hopelessly

complex calculations may thus be carried out quickly

and expeditiously by a proper arrangement of the work.

The most convenient way usually is the arrangement in

tabular form. As

example, consider the problem of calculating the regulation of

a 60,000-volt transmission line, of r=60 ohms resistance, x

= 135 ohms inductive reactance, and fe 0.0012 condensive susceptance,

for various values of non-inductive, inductive, and

condensive load. Starting

transmission

with the complete equations of the long-distanceline, as given in "Theory and Calculation of Transient

Electric Phenomena and Oscillations," Section III, paragraph

power-factors, 2.

90 PER CENT POWER-FACTOR, LAG. cos

0=09; sin0=Vl-0.92 =0.436;

j

sin 0) =

i (0 9+0.436j); Si

= (0.919- 0.03Gj> + (56.8- 131.8/K0.9 +0.436j>o =

(0.919- 0.036j>o + (108.5 -

93.8/H

=

4 + ' :

/i

= (0.919-0.036j)(0.9

+0.436j)io- (0.0144 +U '

=

(0.843

+0.366j> -

(0.0144

+1.168j> 10-3 =C/ -D, and

now the table is calculated in the same manner as under 1. Then

manner,

corresponding tables are calculated, in the samefor power-factor, =0.8 and =0.7, respectively, lag, and

for power-factor -0.9, 0.8, 0,7, lead; that is, for cos

0+] sin 0=0.8 +0.6]'; 0.7+0.714]';

0.9-0.436]';

0.8-0.6]';

0.7-0.714].

Then

curves are plotted for all seven values of power-factor, from

0.7 lag to 0.7 lead. From

these curves, for a number of values of i ,

for instance, to

taken,

=20, 40, 60, 80, 100, numerical values of ii, e^ cos Q, aroand plotted as curves, which, for the same voltage ei

= 60 at the step-up end, give i\ } eo, and cos 6, for the same value

IQ, that is, give the regulation of the line at constantcurrent output for varying power-factor.9; and considering that for every one of the variouslag, and lead, a sufficient number of valuesThe intelligibility of the results,The reliability of the calculation.other. frequently

Hy, Good afternoon,

ReplyDeleteVery atentif and instructor of knowledge for people o can absorve the areas of techicnician work,

tanks for the invite, i hope we can stant as friends and share cience, techonologie and nature,

atently,

AkuaCelta