Ohm’s Law for A-C Circuits

Geplaatst op door colani Reactie
The fundamental Ohm’s law formulas for
a-c circuits are given by:
I = E / Z Z = E / I
E = I*Z P = E*I*cos Ø
Where: I = current in amperes,
Z = impedance in Ohms,
E = volts across,
P = power in watts,
Ø = phase angle in degrees.
Phase Angle
The phase angle is defined as the difference
in degrees by which current leads voltage in a
capacitive circuit, or lags voltage in an inductive
circuit, and in series circuits is equal to the
angle whose tangent is given by the ratio X/R and
is expressed by:
arc tan (X/R)
Where:
X = the inductive or capacitive reactance in ohms,
R = the non-reactive resistance in ohms,
of the combined resistive and reactive components
of the circuit under consideration.
Therefore:
in a purely resistive circuit, Ø = 0°
in a purely reactive circuit, Ø = 90°
and in a resonant. circuit, Ø = 0°
also when:
Ø = 0°, cos Ø = l and P = E*I,
Ø = 90°, cos Ø = 0 and P = 0.
————–
Degrees x 0.0175 = radians.
1 radian = 57.3°
Power Factor
The power-factor of any a-c circuit is equal to
the true power in watts divided by the apparent
power in volt-amperes which is equal to the
cosine of the phase angle, and is expressed by
E*I*cos Ø
p . f . = —————- = cos Ø
E*I
Where:
p.f. = the circuit load power factor,
E*I*cos Ø = the true power in watts,
E*I* = the apparent power in voltamperes,
E = the applied potential in volts
I = load current in amperes.
Therefore:
in a purely resistive circuit.
Ø = 0° and p.f. = 1
and in a reactive circuit,
Ø = 90° and p.f. = 0
and in a resonant circuit,
Ø = 0° and p.f. = 1
Ohm’s Law for D-C Circuits
The fundamental Ohm’s law formulas for
d-c circuits are given by,
E



R		 E



I
E = I*R P = I*E
where:
I = current in Amperes,
R = resistance in ohms,
E = potential across R in volts,
P = power in watts.

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