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ABC OF ELECTRICITY
BASIC FORMULAS
F
(force)= m (mass) * a (acceleration)
Work
done = Force * distance
Q
(coulomb)=I (current) * t (time)
V
(voltage)= I (current) * R (resistance)
Power
( in watts ) = Volts * Ampears
Watt-hour
= Watt * Hour
Volume
Resistivity =(r)*( l / a)=(r)*(V/a2)=(r)*( l 2/V)
Conductance
( G ) =
( l / r)
* (a / l ) = ( g
a / l )
Where, r = Resistivity
l a =
Uniform Cross-section area
V = Volume of
the Conductor
g
= Conductivity
Alternators
KVA
=1.73* Line current * Voltage
D.C.
Motors and Generators
E.m.f.
equation of a D.C. generator
E = (fZN/60)(P/A) *10 - 8 V
Armature
torque of a D.C. motor
Ta = ( 0.118*10 – 8 *
f * ZIa
(P/A) ) Ib.- ft.
= 7.04 ((Eb * Ia) / (N)) Ib.-ft.
Shaft
torque of a D.C. motor
Tsh
=
(33000*B.H.P.) /(746) Ib.-ft.
Relationship
between motor speeds At different loads
(N2 / N1) = (Eb2 / Eb1)*(f1
/ f2)
KW
Output of Motors = ( 2 * PI * N(Speed in RPM ) * T ( Torque in KGM)) / 4500
In
Electromagnetism
Flux
from a pole of strength m units f = 4pm
maxwells
Field
strength from a point Pole of strength m
H = (m) / (m d 2)
e.m.u.
Flux
density from a pole of strength m units
B = (m) / (r 2) e.m.u.
Inverse
square law F =(m1
m2) / (m d2) dynes
Force
on a current-carrying Conductor F =(Bil) / (10) dynes
Field
strength due to an Infinitely long current-carrying Conductor at a distance of r
H = ( 2i ) / (10r ) maxwells/cm2
M.M.F.
= (4pni ) / (10) gilberts
Field
intensity at the center of a Long solenoid
H =(4pni ) /(10l
) lines/cm2
Electromagnetic
force between two parallel current-carrying conductors
F = (2 i1 i2 l
) / (100d) dynes
Basic
magnetic field relationship
B = mH
The
ohm’s Law for a magnetic Circuit f = (1.257 Ni) /( l / am
) lines
Ampere-turns
required AT = 0.8Hl
E.m.f.
induced by change of flux Linkages
e =-n (df /
dt) *10 –
8V
E.m.f.
induced by ‘flux cutting’
e = Bln
* 10 – 8
V
Inductance
of a long solenoid
L = (nf)
/ ( i ) *10 – 8
H
= (4pn2)
/( l / am)
* 10 – 9
H
Mutual
inductance M = (4 p n1 n2) / (l
/ am)
*10 – 9
H
Magnetic
energy density
(BH) /(8p)
=(mH2) /(8p)
Hysterics
loss
Wn
= xy(Area of B/H loop) ergs/c.c.cycle
Steinmetz
relation for hysterics Loss
Wn
= h Bmax.1..6 ¦ V ergs/sec.
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